Chevron AC Motors' Manual Dri200

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200 AC Motors and Generators

AbstractThis section discusses three-phase alternating-current (AC) induction and synchro-

nous motors and AC generators. Direct-current (DC) motors are also mentionedbriefly, but given little coverage. In addition, motor types, performance characteris-tics, enclosures, mechanical features, maintenance considerations, and proceduresfor selecting, specifying, and applying motors are covered.

Contents Page

210 Engineering Principles 200-3

211 Basic Principles

212 Power

213 Service Factor

214 Speed

215 Voltage and System Frequency

216 Environmental Factors

217 Electrical Current

218 Torque

220 Application Considerations 200-29

221 Horsepower and Speed

222 Efficiency

223 Noise

224 Vibration Limits

230 Selection Criteria 200-36



200 AC Motors and Generators Driver Manual

236 Options and Modifications

237 Pulsating Torque Loads238 Cyclic Loads In Walking Beam Pumping Units

239 High Inertia Loads

240 Special Applications 200-60

241 Electrical Submersible Motors

242 Multi-Speed, Squirrel-Cage Motors

250 Mechanical Analysis 200-64

251 Magnetic Influence on Vibration

252 Torsional and Lateral Critical Speeds

260 Bearings and Lubrication 200-69

261 Sleeve Bearings versus Anti-Friction Bearings

262 Thrust Bearings on Vertical Motors

263 Grease and Oil as Lubricants

264 Greasing the Bearing

270 Instrumentation 200-74

271 Temperature Indicators and Detectors

272 Oil Level Indicators

273 Pressure Indicator274 Alarms and Shutdown

275 Driver Auto Start System

280 Generators 200-78

281 Generation of Alternating Current

282 Excitation Control of Motors and Generators

290 Maintenance Considerations 200-87

291 Replace Induction Motors With High Efficiency Motors Versus Rewind



Driver Manual 200 AC Motors and Generators

210 Engineering Principles

211 Basic Principles

An induction motor uses the principle of induction, with “primary” windings onthe stator or stationary portion of the motor and “secondary” windings on therotating element or rotor. There is a small space, or air gap, between the stator androtor. Alternating current is supplied to the stator (primary winding) from an elec-tric power system. This current induces an opposing current in the secondary

winding on the rotor. (Induction is creation of an electric current or voltage in onecomponent caused by the magnetic field from a second component.)

The interaction of the induced rotor-current field with the stator-current fieldproduces the motor torque. The induced secondary current distinguishes the induc-tion motor from the synchronous motor. Unlike an induction motor, a synchronousmotor or direct-current (DC) motor has the secondary current and magnetic field inthe rotor supplied by a DC exciter or some other external power source.

Induction motors produce continuous rotation due to a revolving magnetic field.

The alternating current flowing in the winding of each phase, produces a rotatingmagnetic field within the stator. The fields of all three phases together create aconstant-magnitude revolving field which drives the rotor.

See Figure 200-1 for a comparison of induction versus synchronous motors.Typical applications for induction and synchronous motors are covered inSub-section 230.

Fig. 200-1 Induction vs. Synchronous Motor Comparison Chart

Induction Motors Synchronous Motors

Less efficient for the same output rating. More complicated in structure; therefore,more expensive.

Operation depends on relative motion, or“slip” between the magnetic field induced

in the rotor winding and that of the stator.The motor will slow down, usually 1–2%,

as load is applied.

More rotor weight (and, therefore, inertia)for equal output rating making it possible

to drive pulsating torque loads withsmaller flywheels.

Stator windings are energized by an alter-

nating- current power supply. The rotorrotates due to the interaction of the

current induced in the rotor winding andthe current in the stator winding.

Maintains a constant speed, regardless of

shaft load, because the magnetic fields of the rotor and stator interact in a constant

manner.




Induction Motor Construction

See Figure 200-2 for typical construction of an induction motor.

The main elements of the induction motor are the stator and the rotor. The statorconsists of a frame which serves as an enclosure and as a support for the core. The

core is comprised of primary windings and a laminated steel core. The rotor is the

rotating element of the motor and includes the shaft, the rotor core, and thesecondary windings. End brackets added to the stator frame complete the motorenclosure and contain the bearings which position the rotor within the stator, andallow the rotor to spin.

Depending on the motor size, the stator frame may be cast iron, steel, or fabricatedfrom steel plate. The core consists of thin laminations (0.010 to 0.020 inch thick) or

segments made from electrical sheet steel having good magnetic characteristics.Insulated windings are placed in slots near the air gap in the stator core. The wind-ings are designed and connected in accordance with the number of phases, thepower-supply frequency and voltage, and the desired speed of the motor. The rotoris comprised of a laminated core assembly mounted on the shaft. The copper,copper alloy, or aluminum alloy secondary windings are located in slots in the corenear the air gap and are short-circuited through “end rings” at each end of the rotorcore The resulting structure looks like a “squirrel cage ” hence the name squirrel-

Fig. 200-2 Typical Small Induction




Power has two basic components, real power and reactive power.

Real power (watts) is the energy used in producing work or dissipated in heat. It isdefined by:

P (watts) = V (volts) × A (amperes) × cos θ(Eq. 200-1)

where:

θ is the angle between the voltage (V) and the line current (A). (This angle, θ, is acharacteristic of AC circuits.) This is the quantity measured by the wattmeter on the

electrical circuit and is the energy used to provide horsepower output in a motor. Inlarge power systems the watts are usually expressed in units of 1000 called a kilo-watt (kW).

Reactive power [volt-amperes-reactive or (VAR)] is the power absorbed by aninductive or capacitive circuit. This component does not perform measurable work.Reactive power is defined by:

VAR = V (volts) × A (amperes) × sin θ (Eq. 200-2)

where:

θ is the angle between the voltage (V) and the line current (A).

In large power systems the VAR is usually expressed in units of 1000 called akVAR.

There are two types of reactive power, lagging and leading.

Lagging reactive power [volt-amperes-reactive or (VAR)] is the power absorbedby an inductive circuit, such as an induction motor or a reactor, which does not domeasurable work. It is the power component associated with the magnetizingcurrent in the induction motor; whereas watts are associated with the workperformed by the motor or horsepower output. In this case, the current is laggingthe voltage as shown by Figure 200-3 part A.

Leading reactive power (volt-amperes-reactive or VAR) is the power absorbed bya capacitive circuit, such as a capacitor. Synchronous motors also draw leadingVAR unlike induction motors which draw lagging VAR. Similar to lagging-VAR,leading-VAR represents reactive power which does not perform measurable work.

In this case, the current is leading the voltage as shown in Figure 200-3B.

Apparent power (volt-amperes) is the total power used by a load (or delivered by) i l di b h l ( ) d i ( A )




For a three-phase system, the V term in Equations 200-1, 200-2, and 200-3 is theline-to-neutral voltage and the equations give the P, VAR, or VA per phase.

(Multiply by three to give the total for all three phases.)

Power factor is defined by the following relationship:

Power Factor = = cos θ

(Eq. 200-4)

where:

θ is the angle between the voltage (line-to-neutral for a three-phase system) and theline current. This angle is also called the power factor angle. The power factor canbe viewed as representing the relative efficiency at which a given kilowatt load can

be supplied by the system. The closer the power factor is to 1.0, or unity, the moreefficiently the electrical system will be operated.

Figure 200-3 illustrates the power factor angle (θ) between the voltage and thecurrent. In Figure 200-3 part A, the current sine wave reaches its crest after the

voltage sine wave; hence, the current is lagging the voltage. This is characteristic ofan inductive load, such as an induction motor, where the load is absorbing reactivepower. The power factor of an inductive circuit is referred to as lagging.

Figure 200-3 part B shows a current sine wave which reaches its crest before thevoltage sine wave; hence, the current is leading the voltage. This is characteristic ofa capacitive load, such as a capacitor or 0.8 power factor synchronous motor, wherethe load is delivering reactive power into the system. The power factor of a capaci-

tive load is said to be leading.

Figure 200-3 part C shows a current sine wave which reaches its crest at the sametime as the voltage sine wave. The phase angle between the voltage and current iszero. The cosine of this angle is 1.0; hence the term unity power factor. This is char-

acteristic of a resistive load or a unity power factor synchronous motor. The load onthis circuit is neither absorbing nor delivering reactive power, only kilowatts arebeing consumed. Therefore, the current needed to supply a given kilowatt load inthis circuit is at a minimum. Since the current is minimized, the system losses are at

a minimum, the system voltage drop is minimized, and the efficiency is maximized.It is for these reasons that improving the power factor toward unity (usually toabout 0.95 lagging) is often desired.

Horsepower (HP) is a measure of the rate at which work is done and defines theoutput capability of motors.

kW

kVA------------




Fig. 200-3 Phase angle relationship of voltage and current for different power factors. Note: The lagging andleading power factor angles are shown at 90 degrees but may be anywhere between 0 and 90 degrees.

Example: 0.8 leading power factor is 36.9 degrees leading.

A. Lagging Power Factor, Current Lags Voltage

B. Leading Power Factor, Current Leads Voltage




ratings for DC motors range from a fraction up to approximately 10,000 HP. Thelargest size DC motors used by the Company are typically 3000-4000 HP.

The rating, according to National Electrical Manufacturers Association (NEMA)Standards, is usually expressed as the continuous horsepower available at the shaftat a specified speed, frequency (for AC), and voltage, with an ambient temperatureof 104 °F (40°C) at an elevation of 3300 feet or less.

The output of induction generators is defined in terms of horsepower or kilowatts.Typical sizes range up to a few hundred horsepower, but sizes up to a few thousandare sometimes used.

The output of synchronous generators, which are the most common type, is ratedin terms of (kW). In addition to real power (kW), the synchronous generator alsoproduces reactive power (kVAR). The combined kW and kVAR rating of thesynchronous generator is kilovolt-amperes (kVA). The relationship between kW,kVAR, and kVA is:

kVA = (kW2 + kVAR2)1/2

(Eq. 200-6)

Thus, the output capability of the synchronous generator is defined by kW, kVAR,

and kVA ratings. The generator nameplate usually will have a kVA rating andpower factor, where rated kW can be determined from Equation 200-7 and kVAR atrated kW can be determined from Equation 200-6. The typical power factor ratingfor generators is 0.8.

Rated kW = (Rated kVA) (Rated Power Factor)(Eq. 200-7)

At loads other than the rated kW of the generator, the kVAR capability must bedetermined from the generator reactive capability curve and the kVA rating fromEquation 200-6. Refer to Figure 200-4 for a typical generator reactive capability

curve.

Available synchronous generator ratings range from 1 to 1,200,000 kVA. Typically,the generators used by the Company are rated 75,000 kVA and below.

213 Service Factor

The concept of “service factor” originated to cover the intermediate horsepowerratings between the standard ratings, primarily for medium, AC motors smaller than

500 HP. The use of service factor ratings is not recommended. You should normally




Fig. 200-4 Typical Synchronous Generator Capability Curve (Courtesy of Westinghouse Canada Ltd.)




the service factor. Available service factors are given in NEMA MG 1, typically1.15 for 460-V “medium” AC motors, and 1.0 for “large” AC motors rated 2300 V

and greater.

The service factor rating is achieved by allowing the motor to operate at a higherwinding temperature than at rated (1.0 service factor) horsepower. Operation athigher temperatures will reduce the life of the insulation. For motors with grease-lubricated anti-friction bearings, high winding temperatures result in high frametemperatures and may also compromise the lubrication of the bearings and reducetheir life. Also, specifying a 1.15 service factor may cause the motor to havemarginal accelerating and breakdown torque if loaded to the service factor rating(see Sub-section 218). For these reasons, the motor should not be sized on the basisof utilizing the service factor for expected load or overload conditions. The motorshould normally be sized as necessary for the maximum load and specified with a1.0 service factor.

The medium, AC motors (primarily 460 V motors) designed and built to Companyspecifications and IEEE 841 have Class F insulation but are rated for the lowerClass B temperature rise. (See Sub-section 234 for a discussion on insulation types

and related temperatures.) This provides a motor which operates well below theinsulation thermal capability for a long service life. The motor also has an inherent

1.15 service factor if the Class F temperature rise is used even though the motornameplate may not have 1.15 service factor marked. This is essentially the samemotor that would be supplied by the manufacturer as standard if a 1.15 servicefactor were specified. However, it is not recommended that use of this inherentservice factor capability be planned since operation at the higher temperature mayreduce service life. If a 1.15 service factor is desired to account for future loading,the motor winding temperature rise should be limited to Class B (90°C by the resis-tance method) at the service factor load. This requirement is included in Companyspecifications when a 1.15 service factor is specified. Keeping the temperature rise

at this level will help ensure long insulation and bearing life if the service factorrating is used. However, this criterion will result in a larger, more expensive motor.

214 Speed

The synchronous speed of an AC motor or generator is determined from thefollowing relationship:

Synchronous Speed =

(Eq. 200-8)

120f

p-----------




Since the magnetic poles always occur in pairs, typical machine synchronousspeeds for a 60-Hz system are:

Synchronous machines operate at the synchronous speed determined byEquation 200-8.

In order for an induction motor to develop mechanical torque, there must be rela-tive motion between the rotor conductors and the rotating stator field. This relativemotion is known as slip. Consequently, a loaded induction machine will alwaysoperate at a speed slightly below synchronous speed.

Actual Speed = Synchronous Speed × (1.0 - Slip)

The slip of a specific motor may vary from one manufacturer to another, dependingon the design requirements. It will usually be within the following limits:

Assuming a slip of 1.5% at 100% load, the actual speed of an 1800 RPM inductionmotor is:

Actual speed = 1800 (1.0 - 0.015)= 1773 RPM

As the load decreases, the speed will increase to approach synchronous speed at noload.

NEMA Design B, AC motors are used for loads in which the torque varies as the

Poles Synchronous Speed

2 3600 RPM

4 1800 RPM

8 900 RPM

10 720 RPM

12 600 RPM

NEMA Design Slip

B 1.5% to 5%

C 3% to 5%

D 5% to 13%

Large induction motors, 250 HPand larger

1% to 1.5%




For DC motors, speed is varied by adjusting the field current and/or the armature(rotor) voltage. Typical base speeds range from 50 to 3500 RPM. Base speed is the

lowest rated speed obtained at rated load with rated armature voltage and fieldcurrent applied.

The single speed shown on the DC motor nameplate is usually the base speed. Iftwo speeds are shown, this indicates the speed range achieved by adjusting the fieldcurrent, unless a dual armature voltage rating is given. Speed control is most oftenachieved by adjusting the field current.

215 Voltage and System FrequencyMotor and generator voltage ratings are selected on the basis of:

• Machine size

• Available system voltage

• Space availability

• Cost (including related switchgear, cables, and transformers)

Figure 200-5 part A shows typical rated voltages and sizes for (AC) inductionmotors. The motor’s rated voltage is usually slightly lower than the nominal systemvoltage to compensate for voltage drops across the system.

Typical voltages and size ranges for (AC) synchronous motors are given inFigure 200-5 part B. Synchronous motors generally are not recommended for volt-ages 600 V and below, or with ratings less than 500 HP due to the high cost. As

with induction motors, the rated voltage of 1.0 power-factor rated synchronousmotors is usually less than the nominal system voltage to compensate for voltage

drop across the system. However, with leading (overexcited) power-factor synchro-nous motors, the rated voltage is usually the same as the nominal system voltagebecause this motor does not cause a system voltage drop. The overexcited motoractually operates at a voltage slightly above system nominal voltage so the motor

can deliver reactive power into the system.

Typical voltages and size ranges for (AC) generators are shown in Figure 200-5 part C. The rated voltage is usually the same as the system nominal voltage.

Typical armature voltage ratings and horsepower ranges for DC motors are shownin Figure 200-5 part D.

Electrical System Frequency

AC motors and generators for application in the United States are usually designed

for an electrical system frequency of 60 Hz (cycles/second) However in some loca




Deviations from Rated Voltage and Frequency

Three phase induction and synchronous motors are designed to operate satisfacto

(1) Higher voltage for 0.8 power factor (overexcited) motors

Fig. 200-5 Typical Rated Voltages of Three-Phase Motors and Generators

A. Typical Voltage and Horsepower of AC Induction Motors

Nominal System Voltage Rated Voltage of Motor Horsepower Range

120/240 V Single Phase 115/230 V to 1/2 HP

480 V 460 V 3/4—600 HP

2,400 V 2,300 V 200—4,000 HP

4,160 V 4,000 V 400—7,000 HP

13,800 V 13,200 V above 3,000 HP

B. Typical Voltage and Horsepower of AC Synchronous Motors

Nominal System Voltage Rated Voltage of Motor(1) Horsepower Range

2,400 V 2,300 V or 2,400 V 500—4000 HP

4,160 V 4,000 V or 4,160 V 500—7,000 HP

13,800 V 13,200 V or 13,800 V 3,500—25,000 HP

C. Typical Voltage, Output of AC Synchronous Generators

Rated Voltage Typical Size RangeKilowatt Output Rating

at 0.8 Power Factor

480 V Up to 1,500 kVA Up to 1200 kW

2,400 V 1,000 kVA—3,750 kVA 800—3000 kW

4,160 V 1,000 kVA—6,250 kVA 800—5000 kW

13,800 V Above 6,250 kVA Above 5,000 kW

D. Typical Voltage and Horsepower of DC Motors

Rated Armature Voltage Typical Horsepower Range

240 V Up to 250 HP

250 V 250 HP—1,000 HP

500 V Up to 3,000 HP

700 V 500 HP and above

Above 700 V Custom Made




• The sum of the voltage and frequency variation does not exceed 10% (providedthe frequency variation does not exceed 5%) above or below normal.

Figure 200-6 summarizes the effects of voltage and frequency variations for induc-tion motors.

Voltage Unbalance

The effects of unequal voltage between the phases include increased heating,

decreased torque, reduced full-load speed, and unbalanced currents. These effectsare most significant on a fully loaded motor.

Voltage unbalance as defined in NEMA MG 1-1993, is given by the relationship:

(Eq. 200-9)

where:

∆V

max= maximum voltage deviation from average voltage (V

avg)

Vavg = average of the three line-to-line voltage magnitudes

In general, the voltage unbalance between phases should not exceed 1%. Mostthree-phase systems operate within this value. If the voltage unbalance exceeds 1%,the motor must be derated in accordance with Figure 200-7, from NEMA MG 1-1993. With an unbalanced voltage of 5%, the motor must be derated to 75% ofnameplate horsepower.

Operation with a voltage unbalance greater than 2% is usually not recommended.Such an unbalance may occur on remote distribution systems or some producingapplications where so called “open-delta” transformers are employed to supplymotors.

When the voltages applied are not exactly equal in each phase, unbalanced currents

will flow in the stator winding with the magnitude depending on the amount ofunbalance. A small percentage voltage unbalance will cause a much largerpercentage running current unbalance. For example, a 1% voltage unbalance maytypically produce a 6% current unbalance.

Synchronous generators are designed to operate satisfactorily at rated kVA,frequency, and power factor at any voltage within plus or minus 5% of the rating,but not necessarily in accordance with the performance standards for rated voltage.

S h t h ld b t d ith b l d t b t bl

%Vunbal

∆Vmax

Vavg----------------- 100×=




Fig. 200-6 Effects of Voltage and Frequency Variation on Induction Motors




DC motors can operate satisfactorily at up to 110% of rated DC armature or fieldvoltage if the maximum speed is not exceeded. However, performance will notnecessarily be the same as established at rated voltage. For operation below base

speed (obtained by reducing the armature voltage), it may be necessary to reducethe load torque to avoid overheating the motor. This is due to reduced heat dissi-

pating capability of the motor fan at lower speeds. Refer to NEMA MG 1-1987 andconsult the motor manufacturer for further information.

216 Environmental Factors

Ambient Temperature

Ambient temperature is the temperature of the surrounding medium (usually air)

that contacts the heated parts of the motor or generator. Standard motors and genera-tors are rated for operation in an ambient temperature of 0° to 40°C (10° to 40°Cfor water cooled machines). Machines applied outside this ambient temperaturerange must be specially designed. Specifically, machines for application in higher

Fig. 200-7 Polyphase Squirrel-Cage Induction Motor Derating Factor Due to UnbalancedVoltage (Used by permission of the National Electrical Manufacturers Associa-

tion. From NEMA Standards. MG-1, 1993)




To ensure satisfactory temperature is maintained, proper ventilation must beprovided in accordance with the enclosure design, and fans and air filters must be

properly maintained (also see Sub-section 233).

Altitude

The standard machine rating, as given in NEMA MG 1, is based on operation at an

altitude of 3300 feet (1000 meters) or less, and at a maximum ambient temperatureof 104°F (40°C). Since the less dense air at higher altitudes has less mass, coolingfor the machine is reduced. At elevations above 3300 feet, a lower ambient tempera-ture may compensate for the increase in machine temperature rise. If the ambient

temperature remains at 104°F (40°C), the allowable temperature rise of the machineshould be reduced by 1% for each 330 feet above 3300-foot elevation.

For example, a motor is designed for 80°C internal temperature rise with anambient temperature of 40°C at the standard elevation of 3300-foot. If the motorwere installed at 6600-foot elevation, the allowable temperature rise if tested at sealevel up to 3300 feet elevation would be reduced by (6600-3300)/330 = 10%, from

80°C to 72°C.

Motors having a service factor of 1.15 will operate satisfactorily at 1.0 servicefactor at an ambient of 40°C at altitudes up to 9000 feet. However, this application

will use the higher temperature rise allowed by the 1.15 service factor rating.

For machines applied at elevations above 3300 feet, the manufacturer should beconsulted to obtain the applicable reduction in horsepower or kVA ratings.Machines can be specified and built for applications above 3300 feet.

217 Electrical Current

Full-load Current

Full-load current is drawn by an AC motor when it operates at rated voltage,frequency, and horsepower. Given the efficiency and power factor of a three-phasemotor, its full-load current may be calculated:

Full–load Amperes =

(Eq. 200-10)

where:

HP = horsepower

746( ) HP Rating( )3 EFF( ) PF( ) E( )⋅------------------------------------------------





(Eq. 200-11)

where:

kVA = three-phase kilovolt amperes

kV = rated line-to-line voltage (in kilovolts)

For a DC motor, the full-load current may include both the armature current and thefield current depending on the machine type and connection. The DC full-load

current may be calculated from the following equation:


(Eq. 200-12)

where:

HP Rating = rated horsepower

EFF = efficiency at rated horsepower

E = applied DC voltage (in volts)

The system conductors must be able to carry the machine full-load current continu-ously. This current is usually given on the machine nameplate.

Locked-rotor Current

Locked-rotor current is the current drawn by the motor during startup (refer toFigure 200-8). At startup, the increased current can cause significant voltage dropon the power supply. This current typically is six times the full-load current for asquirrel-cage induction machine and four or five times rated current for a synchro-nous motor. The system protective devices must be set to permit the temporary

starting current so the motor can be brought up to speed. Refer to the Electrical

Manual for information on motor protective devices.

For squirrel-cage induction and synchronous motors, the starting kVA is indicated

by a code letter stamped on the motor nameplate. Figure 200-9 lists the corre-sponding kVA per horsepower for each code letter. The locked-rotor current can bedetermined from:

Locked–rotor Current (Amperes) =

kVA

3 kV⋅-------------------

746( ) HP Rating( )EFF( ) E( )--------------------------------------------

Starting kVA per HP( ) HP( )




where:

P = 1 for single-phase

P = for two-phase

P = for three-phase

kV = line-to-line voltage (in kilovolts)

HP = horsepower

For DC motors, the starting current is usually limited to approximately two timesthe rated current by connecting resistance in series with armature. The resistance isusually switched out in steps to provide optimum accelerating torque.

No-load Current

N l d t f i d ti t i th i t d ith th

Fig. 200-8 Current/Torque vs. Speed

2

3




The current for a synchronous motor at no-load (with field excitation adjusted for

minimum stator current) is much smaller than with an induction motor. This repre-sents primarily the rotational losses (fan windage and bearing friction) and excita-tion power. Typical no-load current in synchronous motors is 1 to 2% of the rated-

Fig. 200-9 Locked Rotor Indicating Code Letters for Squirrel-Cage Induction and Synchro-nous Motors

CodeLetter

Kilovolt Amperes (kVA) perHorsepower with Locked Rotor

A 0.00—3.14

B 3.15—3.54

C 3.55—3.99

D 4.0—4.49

E 4.5—4.99F 5.0—5.59

G 5.6—6.29

H 6.3—7.09

E 4.5—4.99

F 5.0—5.59

G 5.6—6.29H 6.3—7.09

J 7.1—7.99

K 8.0—8.99

L 9.0—9.99

M 10.0—11.19

N 11.2—12.49P 12.5—13.99

R 14.0—15.99

S 16.0—17.99

T 18.0—19.99

U 20.0—22.39

V 22.4 and up




Power Factor and Capacitor Application

A low power factor load requires more current to deliver the same kilowatts. Highercurrents in turn cause greater losses in electrical lines and equipment. (Refer to

Sub-section 212 for additional discussion of power factor.) A low power factorcauses financial loss in two ways:

• The system efficiency is lowered by the higher losses due to higher current.

• Utilities often impose a penalty if the power factor is below a minimum value;a typical minimum value is 0.85. The power factor penalty expense is usuallymuch larger than the cost of distribution losses.

In addition to these direct costs, a low power factor also reduces the power deliverycapability of the system. All electrical conductors have limited current carryingcapacity. Once the maximum current is reached, no further load expansion ispossible without a revamp of the existing facility.

To optimize power system efficiency, voltage regulation, and operating costs, anelectrical system should be operated with a power factor between 90 to 95%

Fig. 200-10 No-Load to Full-Load Current vs. Induction Motor Horsepower

Exam ple:

To find the no-load currentof a 100 H P 1800 R PM (fourpole)m otor,read 0.25 N LA /FLAw here 100 H P and fourpole lines m eetatthe ordinate.The full-load currentof a 100 H P

m otoris about 120 A m ps.The no-load current = 0.25 x 120 = 30 A m ps.




The higher the power factor, the lower the kVA consumed by the motor. The lowerkVA results in lower reactive power consumption for a given kW load. It is desir-

able to operate at a high power factor because the lower kVA frees total powersystem capacity and reduces losses. The lower reactive power reduces voltage drop,and the high power factor may avoid penalties charged by some electric utilitycompanies. This refers to a “lagging” power factor where the motor is absorbing

reactive power from the system. Both induction motors and AC-to-DC convertersfor DC motors operate at lagging power factors.

Power Factors for Synchronous Motors

Synchronous motors usually operate at a power factor of 1.0, or a leading (overex-cited) power factor. At 1.0 power factor, the motor is absorbing only kW from the

system without reactive power (kVAR). At a leading power factor the motor isabsorbing kW from the system but generating kVAR into the system. In thismanner, the synchronous motor can be used to improve the overall system powerfactor. Synchronous motors usually are rated at either 1.0 power factor or 0.8leading power factor.

Note It is not desirable to operate a system at a leading power factor due to

possible excessive voltage rises, increased system losses, and energy costs for overcorrecting the power factor. The choice of the unity power factor or 0.8 power

factor synchronous motor will depend on the system’s need for power factor correc-

tion or voltage regulation.

Power Factor For Induction Motors

Depending on the motor design, induction motor power factor generally improvesas motor size increases (in the same RPM range). Lower speed motors generally

operate at lower power factors. Figure 200-11 plots the power factor versus thepercent load for a typical NEMA frame motor. Figure 200-12 plots the power factorversus motor horsepower ratings and may be used in determining motor demandsrelative to electrical power systems.

As load and real power decrease, reactive power stays at the same level, resulting inlow power factors for partially loaded motors. Typically, a 25- to 300- HP motorwith 50% load will exhibit a 58% power factor versus an 80% power factor at fullload. Therefore, it is recommended that motors be sized to run as fully loaded as

practical. (The motor efficiency may often peak at near 75% of rating. However, thelower power factor for the lightly loaded motor which reduces the system efficiencyand the higher equipment cost for the larger motor normally offset the benefits ofthe slightly improved motor efficiency.)

Capacitor Sizes




factor to 0.95 or 0.211 × 50 kW = 10.6 kVAR of capacitors to correct to 0.95 powerfactor. To avoid possible overvoltages when switching the motor and capacitor

together, the capacitor rated current should never exceed the motor no-load current.

Finally, if power factor correction capacitors are located at the motor terminals, thecurrent passing through the feeder cables and overload relay heaters will be

reduced. The size of the overload heaters must, therefore, be reduced to protectagainst motor overload. The new motor full-load current will be inversely propor-tional with the power factor increase or:

(Eq. 200-14)

where:In = new motor full-load current to be used for heater sizing

Io = motor full-load current (nameplate)

PFmc = combined motor/capacitor power factor

Fig. 200-11 Efficiency and Power Factor vs. PercentInduction Motor Load (Typical NEMA

Frame Motors). See Figure 200-20 for MoreSpecific Information.

Fig. 200-12 Induction Motor Power Factor Curve

In Io

PFm

PFmc-------------×=






218 Torque

Torque is the rotating force produced by a motor. The torque characteristic (speedvs. torque) of a motor is significant because it determines the ability of the motor toaccelerate and drive the load at its rated speed. The startup time to bring the load tooperating speed is a function of the inertia of both the driven load and the motor.The motor must be sized with sufficient torque to overcome this inertia, and toaccelerate the load to operating speed without exceeding the safe accelerating time

of the motor. The motor must also develop sufficient torque to drive the load atnormal running speed without overheating or experiencing large speed changes.

Torque is expressed in units of force and distance representing a turning moment.The units normally used are foot-pounds, inch-ounces, and meter-kilograms,

depending upon the magnitude of the torque and the units system used. A preferredmethod of expression is percent of rated full-load torque.

The output torque of an induction motor can be derived from:

(Eq. 200-15)

where:

T = torque (foot-pounds)

S = actual motor speed in RPM

HP = horsepower

1 HP = 550 ft-lb/sec

Torque Definitions of Induction Motors

The following terms are important for interpreting, and often specifying the charac-

teristics of motors (refer to Figure 200-14 for torque curve):

• Full-load torque is the torque necessary to produce rated horsepower at fullspeed. This is the torque available for driving the load continuously at

rated horsepower output. Full-load torque needs to be adequate to meet the

torque demand of the driven equipment.

• Locked-rotor torque of an induction motor is the minimum torque developedat rest for all angular positions of the rotor, with rated voltage applied at rated

frequency. This quantity is important to assure there is sufficient torque to

exceed the torque demanded by the load at zero speed (breakaway torque)

T5250 HP( )

S

-------------------------ft–lb=




the motor does not have sufficient acceleration torque, it will fail to accelerateand “hang up” at a speed which is less than full-load speed (until the protectiverelays disconnect the motor). This problem is more common with motorslarger than 500 HP.

• Breakdown torque for an induction motor, sometimes called “maximumtorque,” is the maximum torque developed at rated voltage and frequency inputwithout an abrupt change in speed. This is the maximum torque the motordevelops to drive the load and is typically 1.75 to 2.0 times full-load torque.This characteristic identifies the capability of the motor to handle sudden,

brief increases in load torque requirements above the full-load torque. Themotor will stall if sustained load torque requirements exceed the breakdowntorque.

• Pull-up torque for an induction motor is the minimum torque developed byan induction motor with rated voltage and frequency applied during the period

f l ti f t d till t th d t hi h b kd t

Fig. 200-14 Torque Terms for Induction Motors




Torque Definitions of Synchronous Motors

The synchronous motor is started as an induction motor with the DC field winding

shorted. During this starting period, the locked-rotor, pull-up, and acceleratingtorques are the same as for induction motors. The typical induction motor speedtorque characteristic shown in Figure 200-14 applies only during this startingperiod. Additional torque definitions are as follows:

• Pull-in torque is the torque developed during the transition from slip speed tosynchronous speed. For the synchronous motor it is the maximum constanttorque with which the motor will pull its connected load inertia into synchro-

nism, with rated voltage and frequency, when its field excitation is applied.This quantity is important to assure the motor can achieve synchronous

speed with its connected shaft load during the starting sequence.

• Pull-out torque is the maximum sustained torque a synchronous motor can

develop at synchronous speed with rated voltage and frequency applied andnormal excitation. This identifies the capability of the motor to handle brief

load torque requirements above the full-load value. Typical pull-out torquevalues are 150 to 200% of rated full-load torque. The motor will pull out of

synchronism if the sustained load torque exceeds the motor rated pull-outtorque.

• Synchronous torque is the steady state torque developed during synchronousspeed operation with rated voltage and frequency applied. It is the torque

available to drive the load. At rated power, it is analogous to full-load torque.

Torque Definitions of DC Motors

The torque characteristics are usually constant from standstill up to base speed,

instead of having torque characteristics similar to Figure 200-14. However, it maybe necessary to decrease the motor torque load when operated below base speed toavoid overheating the motor due to reduced cooling at the slower speed. Betweenbase speed and maximum speed, the torque characteristics decrease with increasingspeed to maintain a constant horsepower output.

NEMA Design Classifications: Induction Motors Less Than 600 Volts

NEMA defines polyphase, squirrel-cage induction motors by classification

according to design, starting inrush current, and torque-versus-speed from zero tosynchronous speed of the machine. Designs A, B, C and/or D are used only for“NEMA frame” medium, AC motors with voltages of 600 V and less. Large motorsare individually designed and considered case by case. Brief definitions of thesedesigns are provided with references to sections of NEMA MG 1. Figure 200-15 illustrates the torque versus speed curve for each design

200 AC M d G D i M l




Design D motors are purchased for cyclic loads such as rod pumps due to their highslip, but they have lower efficiency than Design B and C types.

Inertia and AccelerationA motor must be capable of accelerating the inertia of the motor and the drivenequipment to normal running speed without exceeding the allowable temperaturerise of the rotor or stator. Since the motor draws locked rotor current for most of theacceleration period, the motor starting time is compared with the “locked-rotor

withstand time” of the motor Motors designed to Company model specifications

Fig. 200-15 Classification by Design Torque vs. Speed Curves: Polyphase Squirrel-CageInduction

D i M l 200 AC M t d G t




220 Application Considerations

221 Horsepower and Speed

Horsepower

An electric motor will attempt to provide the horsepower demanded by the drivenmachine. If undersized, the motor will be overloaded, experience reduced life, and

performance of the driven equipment may be affected. The motor controls includeoverload relays which may operate to protect the motor by shutting it down unex-

pectedly. A motor sized too large will cost more and generally operate with lowerefficiency and power factor. Therefore, the motor horsepower should be matched asclosely as possible to the requirements of the load.

Preliminary horsepower estimates for motor-driven pumps, compressors, and fanscan be made by using the motor application equations shown in Figure 200-16.

The following example uses Equation 200-17, shown in Figure 200-16, to size amotor for a centrifugal pump:

Fig. 200-16 Motor Application Equations

Horsepower RequiredTo calculate motor horsepower if torque and speed

required by the driven machine are known:

(Eq. 200-16)

Positive Displacement and Centrifugal Pumps

(Eq. 200-17)

Fans and Blowers

(Eq. 200-18)

HPTorque (ft–lb) RPM( )

5250-------------------------------------------------=

HP GPM (head in feet)3960 pump efficiency( )------------------------------------------------------=

HPCFM (Pressure in lb/sq.ft)

33,000 efficiency( )------------------------------------------------------------=

HPGPM head in feet( )

--------------------------------------------------------=





efficiency. Refer to the Pump Manual and Compressor Manual for more informa-tion on sizing driven equipment and calculating horsepower.

Speed

In cases where there is a choice in driven equipment speed, the operating speedshould be matched to the standard speeds available from induction motors to avoid

the use of gears, belts, or chain drives.

Figures 200-17 and 200-18 provide typical relative cost versus horsepower as afunction of speed for induction and synchronous motors. These charts may be used,with discretion, for preliminary information, but they should not be used as a design

basis, nor as criteria for final selection. Instead, compare actual vendor quotes.

222 Efficiency

Efficiency is defined as the ratio between the machine output power and the inputpower and directly affects the cost of operating the machine. Selecting a motor size

appropriate for the driven load is very important to attaining high motor efficiency.For example, oversizing may cause a typical motor operating at 50% load tooperate five percentage points below peak efficiency (refer to Figure 200-11).Figure 200-19 shows a curve for motor efficiency versus motor horsepower ratings

Fig. 200-17 Relative Cost Factor Based on Speed for

Squirrel-Cage Induction Motors: For prelim-inary information only. Do not use foractual design or selection. See “Speed”

under Sub-section 221.

Fig. 200-18 Relative Cost Factors Based on Speed for

Brushless Synchronous Motors, Three-phase, 60 Hz with Standard Open, Drip-proof or Open Enclosures: For preliminary

information only. Do not use for actualdesign or selection. See “Speed” under

Sub-section 221





and energy used for actual work are the same for each competing motor. The evalua-tion should normally be made at the motor nameplate rating.

When evaluating bids from various vendors, be consistent when making LCCcomparisons. These comparisons are made using the nominal efficiency for motors

rated 600 V and below and guaranteed efficiency for all large, AC motors rated2300 V and above. The nominal efficiency represents the average efficiency of a

large population of motors of the same design and is appropriate to use for low-voltage and medium, AC motors. A guaranteed efficiency (by test) is appropriate

for large, higher voltage motors. Refer to Figure 200-20 (located at the end of thischapter) for typical efficiency ratings. LCC of the differences may be defined asfollows:

LCC = P + EF [0.746 (BHP) (100/E –1)](Eq. 200-19)

where:

P = purchase price in dollars

BHP = horsepower at the driven equipment operating point

E = motor efficiency in percent at the driven equipment operatingpoint (if operating point is not known, normally use rated horse-

power)

Fig. 200-19 Typical Induction Motor Efficiency Curve (standard efficiency)

11 9 7 6 5 4 3 281 9 7 6 5 4 3 288 234567912345





The PWF (cumulative present worth factor) normally used in LCC analysis for elec-tric machines is four. You may need to adjust this factor if your project requires a

more specific PWF based on actual project life, discount rate, tax rate, and deprecia-tion. For assistance, contact the Corporate Planning and Analysis Staff in San Fran-cisco, CA.

LCC calculations and comparisons are recommended for all purchased motors.

For example, a 94% efficient, 100-HP motor (which may have a 1988 purchaseprice between $4000 and $6000) operating continuously at rated load with a powercost of $0.05/kW-hr, costs $34,760 a year to operate. A 1% improvement in effi-

ciency represents an operating cost savings of $366 a year. With the recommendedcumulative present worth factor of four applied to the LCC calculation it would be

worth spending $1464 (4 x $366) more for the 100- HP motor with 95% efficiencythan the motor with 94% efficiency for the conditions stated.

Note the preceding assumes installation and maintenance costs to be the same. Ifnot, these effects should be included where there are known differences.

Standard versus High Efficiency Motors

“High-efficiency” motors are available that typically include the following featuresto increase motor efficiency:

• Use of special grade or low-loss lamination steel

• Reduction of lamination thickness

• Increase in the stator and rotor core length

• Increase in the amount of copper used in the stator winding

• Optimized low-resistance rotor design

• Smallest practical air gap

• Optimized design of ventilation fan

• Computer optimized design

High-efficiency motor initial cost is greater than for a standard motor, but the initialexpenditure usually can be recovered in a reasonable length of time from lower

operating costs.

When obtaining quotations from a driven-equipment original equipment manufac-turer (OEM), you should obtain alternate quotes for higher efficiency. Request theprice difference and efficiency for each motor, and select the motor which has the

lowest LCC.

Figure 200-20 provides a comparison table of nominal standard versus high effi-

ciency for NEMA frame size motors (1 200 HP) Motors above 200 HP are usually




Fig. 200-20 Nominal Performance Data (Courtesy of Siemens Energy & Automation, Inc.) (1 of 2)




Fig. 200-20 Nominal Performance Data (Courtesy of Siemens Energy & Automation, Inc.) (2 of 2)




223 Noise

The noise levels associated with rotating machinery are evaluated using the “A”

weighted sound pressure level. The “A” weighting takes a reference frequency of1000 Hz and gives positive or negative adjustments to all other frequencies toapproximately simulate the response of the human ear. This scale is a convenientmethod for evaluating noise annoyance and potential hearing damage.

The “A” weighted sound pressure level at a reference distance of three feet isnormally used for evaluating machinery noise. The units of the sound power levelsare “A” weighted decibels—dBA. See the Noise Manual for additional information.

An average sound pressure level (SPL) of 85 dB(A) at rated voltage and no load isrecommended by IEEE Standard 85 and is commonly quoted by vendors. Themeasurement is made by microphone positions at 3 feet from the motor in variouslocations. The average of all these readings should not exceed 85 dB(A). OSHAlimits the noise levels taken three feet from the motor under operating conditions toa measured maximum of 85 dB(A) SPL. The operating limit at rated load is

included because the noise can increase from the no-load values if the motor ispoorly designed. Company specifications reflect the “maximum” SPL requirements

to meet OSHA requirements when the motor is installed.

If no-load sound levels are measured, the maximum value should be limited to 82dB(A) to allow a 3 dB(A) increase from no load to full load. Refer to the IEEE 85Standard for additional information on the defined positions for sound levelmeasurements.

224 Vibration Limits

The vibration of a machine is usually measured at two locations: the bearing hous-

ings or supports, and the shaft relative to the bearing housing. Acceptable vibrationlevels are largely the result of user experience and empirical equations which havebeen developed over the years. Refer to Volume 2, Specification DRI-MS-3547, Inspection and Testing of Large Motors and Generators for recommended accept-able vibration limits for various types of motors.

Machinery vibration is covered extensively in the CUSA Manufacturing IMI Candi-

dates Manual. Also, the General Machinery Manual covers continuous vibrationmonitoring and shutdown systems.

Bearing Housing Vibration

The vibration displacement measured in mils peak-to-peak (p-p) amplitude repre-sents how well the bearing housing or other bearing supports contain the unbal-




to use accelerometers in accordance with API 678 and a monitoring system withvelocity readouts and set points.

Shaft Vibration

Shaft-to-bearing-housing relative motion is usually measured with non-contactproximity probes.

Location of the probes along the shaft is very important. The probes must be within

3 inches of the bearing, but not near a node of the rotor mode shape. These nodes,or positions of zero lateral motion, may be determined from the lateral criticalspeed analysis. The best axial location for probes is usually inboard (towards the

rotor) of the bearings. While the probes may not be easily accessible in this posi-tion, this is better than locating a shaft probe where little or no shaft motion willoccur.

230 Selection Criteria

Motors are classified by: (1) electrical type (AC induction motor, AC synchronousmotor or DC motor), (2) frame size, (3) enclosure type (housing built around the

motor to protect it against the environment that it is subjected to during its lifetime),(4) insulation (in the windings that defines the allowable temperature rise the

motor can withstand without deteriorating), and (5) intended application (definite-purpose, general-purpose or a special-purpose motor).

231 Induction Versus Synchronous Motors

Figure 200-21 lists typical applications of synchronous and inductions motors. This

is the first decision in applying a specific motor.

232 Frame Size

Squirrel-cage induction motors are generally grouped by frame size as either:

• Fractional horsepower

• Integral horsepower

• NEMA frame size• Above NEMA frame size

The frame size determines the physical size and dimensions of the motor, whilerated horsepower specifies the shaft output horsepower and does not necessarilydictate a specific frame size. “NEMA frame” motors have standardized dimensions




Fig. 200-21 Induction vs. Synchronous Motor Application/Selection Guide (1 of 2)Note : For enclosure types see Figure 200-28.

2 M F



2 0 0 A C M o t o r s a n d G e n e r a t o r s

D r i v e r M a n u a l

M a r c h 1 9 9 6

2 0 0 - 3 8

C h e v r o n C o r p o r a t i o n

Fi g .2 0 0 -2 1

I n

d u c t i o n v s . S y n c h r o n o u s M

o t o r A p p l i c a t i o n / S e l e c t i o n

G u i d e ( 2 o f 2 )

N

o t e : F o r e n c l o s u r e t y p e s s e

e F i g u r e 2 0 0 -2 8 .




Fig. 200-22 Dimensions for Foot-Mounted Machines




233 Enclosure Types and Methods of Cooling

Enclosures are provided to protect motor internal components from environ-

mental contaminants such as water and dust. In addition, various enclosurescarry different electrical area ratings due to their construction. Selecting the appro-priate enclosure is an important decision that affects purchase price, reliability, andmaintenance expense.

In general, motors are classified by enclosure types under three major categories:

• Open—“open dripproof” is the most commonly used in indoor areas. (Refer toFigure 200-25.)

• Weather Protected—is used in outdoor areas. (Refer to Figure 200-26.)

• Totally Enclosed—“fan cooled” (TEFC) is the most common for severe envi-ronments. A modified form is also available as “explosionproof” for Division 1hazardous locations. (Refer to Figure 200-27.)

Figure 200-28 may be used as a guideline to select an enclosure. Figure 200-29 illustrates typical applications of enclosures. In addition to Figures 200-25 through

200-29, the following information applies to commonly used enclosures:

Open Dripproof and Splashproof Categories

Primarily, these are used when the driven equipment is located in an environmen-tally protected building or structure. The motors should not be subjected to rain orsleet during operation. (Refer to Figure 200-25 for an illustration.)

Weather Protected, Type-I

These are used where some protection from the environment is available such asprotected areas on offshore platforms and onshore plants having a roof, but no sidewalls. (Refer to Figure 200-26 for an illustration.)

Weather Protected, Type-II

These are used outdoors in electrical classification areas which are nonhazardous orClass I, Division 2. (Also refer to Figure 200-26 for an illustration.)

Totally-Enclosed, ExplosionproofPredominantly used in Class I, Division 1 locations. All types of enclosures areappropriate in Class I, Division 2 as long as there are no sparking contacts and thesurface temperature of the space heaters are limited to 80% of the ignition tempera-ture.




Fig. 200-23 Standardized Dimensions for T-Frame Alternating Current Foot-Mounted Machines with Single Straight-Shaft Extension

Frame Designation A Max B Max D(1) E(2) 2F(2) BA H(2) U N—W

143T 7.0 6.0 3.50 2.75 4.00 2.25 0.34 hole 0.875 2.25

145T 7.0 6.0 3.50 2.75 5.00 2.25 0.34 hole 0.875 2.25

182T 9.0 6.5 4.50 3.75 4.50 2.75 0.41 hole 1.125 2.75

184T 9.0 7.5 4.50 3.75 5.50 2.75 0.41 hole 1.125 2.75

213T 10.5 7.5 5.25 4.25 5.50 3.50 0.41 hole 1.375 3.38

215T 10.5 9.0 5.25 4.25 7.00 3.50 0.41 hole 1.375 3.38

254T 12.5 10.8 6.25 5.00 8.25 4.25 0.53 hole 1.625 4.00

256T 12.5 12.5 6.25 5.00 10.00 4.25 0.53 hole 1.625 4.00

284T 14.0 12.5 7.00 5.50 9.50 4.75 0.53 hole 1.875 4.62

284TS 14.0 12.5 7.00 5.50 9.50 4.75 0.53 hole 1.625 3.25

286T 14.0 14.0 7.00 5.50 11.00 4.75 0.53 hole 1.875 4.62

286TS 14.0 14.0 7.00 5.50 11.00 4.75 0.53 hole 1.625 3.25

324T 16.0 14.0 8.00 6.25 10.50 5.25 0.66 hole 2.125 5.25

324TS 16.0 14.0 8.00 6.25 10.50 5.25 0.66 hole 1.875 3.75

326T 16.0 15.5 8.00 6.25 12.00 5.25 0.66 hole 2.125 5.25

326TS 16.0 15.5 8.00 6.25 12.00 5.25 0.66 hole 1.875 3.75

364T 18.0 15.2 9.00 7.00 11.25 5.88 0.66 hole 2.375 5.88

364TS 18.0 15.2 9.00 7.00 11.25 5.88 0.66 hole 1.875 3.75

365T 18.0 16.2 9.00 7.00 12.25 5.88 0.66 hole 2.375 5.88

365TS 18.0 16.2 9.00 7.00 12.25 5.88 0.66 hole 1.875 3.75

404T 20.0 16.2 10.00 8.00 12.25 6.62 0.81 hole 2.875 7.25

404TS 20.0 16.2 10.00 8.00 12.25 6.62 0.81 hole 2.125 4.25

405T 20.0 17.8 10.00 8.00 13.75 6.62 0.81 hole 2.875 7.25

405TS 20.0 17.8 10.00 8.00 13.75 6.62 0.81 hole 2.125 4.25

444T 22.0 18.5 11.00 9.00 14.50 7.50 0.81 hole 3.375 8.50

444TS 22.0 18.5 11.00 9.00 14.50 7.50 0.81 hole 2.375 4.75

445T 22.0 20.5 11.00 9.00 16.50 7.50 0.81 hole 3.375 8.50

445TS 22.0 20.5 11.00 9.00 16.50 7.50 0.81 hole 2.375 4.75

447T (3) (3) 11.00 9.00 20.00 7.50 (3) (3) (3)

449T (3) (3) 11.00 9.00 25.00 7.50 (3) (3) (3)

Note All dimensions in inches




(1) Frames 143U to 326US, inclusive—The tolerance on the D dimension for rigid base motors shall be +0.00 inch, – 0.03 inch.Frames 364U to 500, inclusive—The tolerance on the D dimension for rigid base motors shall be +0.00 inch, – 0.06 inch.

No tolerance has been established for D dimension of resilient mounted motors.

(2) Frames 143U to 500, inclusive—The tolerance for the 2E and 2F dimensions shall be ±0.03 inch and for the H dimension shall be

+0.05 inch, – 0 inch.

Fig. 200-24 Standardized Dimensions for U-Frame Alternating-Current Foot-Mounted Machines with Single Straight-Shaft Extension

Frame Designation A Max B Max D(1) E(2) 2F(2) BA H(2) U N—W

182 9.0 6.5 4.50 3.75 4.50 2.75 0.41 hole .875 2.25

184 9.0 7.5 4.50 3.75 5.50 2.75 0.41 hole .875 2.25

213 10.5 7.5 5.25 4.25 5.50 3.50 0.41 hole 1.125 3.0

215 10.5 9.0 5.25 4.25 7.00 3.50 0.41 hole 1.125 3.0

254U 12.5 10.8 6.25 5.00 8.25 4.25 0.53 hole 1.375 3.75

256U 12.5 12.5 6.25 5.00 10.00 4.25 0.53 hole 1.375 3.75

284U 14.0 12.5 7.00 5.50 9.50 4.75 0.53 hole 1.625 4.875

286U 14.0 14.0 7.00 5.50 11.00 4.75 0.53 hole 1.625 4.875

324U 16.0 14.0 8.00 6.25 10.50 5.25 0.66 hole 1.875 5.625

324US 16.0 14.0 8.00 6.25 10.50 5.25 0.66 hole 1.625 3.25

326U 16.0 15.5 8.00 6.25 12.00 5.25 0.66 hole 1.875 5.625

326US 16.0 15.5 8.00 6.25 12.00 5.25 0.66 hole 1.625 3.25

364U 18.0 15.2 9.00 7.00 11.25 5.875 0.66 hole 2.125 6.375

364US 18.0 15.2 9.00 7.00 11.25 5.875 0.66 hole 1.875 3.75

365U 18.0 16.2 9.00 7.00 12.25 5.875 0.66 hole 2.125 6.375

365US 18.0 16.2 9.00 7.00 12.25 5.875 0.66 hole 1.875 3.75

404U 20.0 16.2 10.00 8.00 12.25 6.625 0.81 hole 2.375 7.125

404US 20.0 16.2 10.00 8.00 12.25 6.625 0.81 hole 2.125 4.25

405U 20.0 17.8 10.00 8.00 13.75 6.625 0.81 hole 2.375 7.125

405US 20.0 17.8 10.00 8.00 13.75 6.625 0.81 hole 2.125 4.25

444U 22.0 18.5 11.00 9.00 14.50 7.50 0.81 hole 2.875 8.625

444US 22.0 18.5 11.00 9.00 14.50 7.50 0.81 hole 2.125 4.25

445U 22.0 20.5 11.00 9.00 16.50 7.50 0.81 hole 2.875 8.625

445US 22.0 20.5 11.00 9.00 16.50 7.50 0.81 hole 2.125 4.25

447U 22.0 20.5 11.00 9.00 20.00 7.50 0.81 hole 2.875 8.625

Note All dimensions in inches




Fig. 200-25 Typical Drip-Proof and Splash-Proof Machines (Courtesy of Electric Machinery - Dresser Rand)

Fig. 200-26 Typical Weather Protected Machine I and Weather Protected Machine II (Courtesy of Electric

Machinery - Dresser Rand)

Fig. 200-27 Typical Totally Enclosed Fan-Cooled Machinery and Totally Enclosed Water-Air Cooled Machine(Courtesy of Electric Machinery - Dresser Rand)

2 0 0

M a Fig. 200-28 Guidelines for Selection of Motor Enclosures (1 of 2)



0A C M o t o r s a n d G e n e r a t o r s


ar c h 1 9 9 6

2 0 0 -4 4




D r i v e

r M a n u a l

2 0

0 A C M o t o r s a n d G e n e r a

t o r s


2 0 0 -4 5

M a r c h 1 9 9 6

Note See the appropriate figures for enclosure type illustrations.

Fig. 200-28 Guidelines for Selection of Motor Enclosures (2 of 2)

2 0 0

M a

Fig. 200-29 Additional Application Criteria for Motor Enclosures



A C M o t o r

s a n d G e n e r a t o r s


r c h 1 9 9 6

2 0 0 -4 6


(1) Usually least expensive motors are least efficient in energy savings. More expensive motors often pay out the incremental purchase cost.

(2) Relative cost numbers may vary with motor speed horsepower and material selected for heat exchangers.

(3) In offshore locations with condensing fog the space heaters provided by the manufacturer may not be large enough to keep the motor dry.

(4) Used in hp ratings where explosion proof motors are not available.

(5) No Arcing device is acceptable.

TYPES OF ENCLOSURE

DRIP-PROOF

DP

SPLASH-

PROOF SP

WEATHER

PROTECTED

TYPE-I WP-I

WEATHER

PROTECTED

TYPE-II WP-II

TOTALLY

ENCLOSED

FAN-COOLED

TEFC

TEFC

EXPLOSION

PROOF

TEFC-XP

TOTALLY

ENCLOSED

PIPE

VENTILATED

TEPV

TOTALLY

ENCLOSED

WATER AIR

COOLED

TEWAC

TOTALLY

ENCLOSED

AIR-TO-AIR

COOLED

TEAAC

RELATIVE MOTOR COST(1) (2) 1.0 1.1 1.25 1.4 1.8 2.2 1.7 2.0 2.0

ENVIRONMENTAL CONDITIONS

DUSTY (NON-ADHERING) N N N N P A A P P

OILY VAPORS AND ADHERING DUST (CATA-

LYST FINES COKE DUST)

N N N N A A A P A

OFFSHORE N N A(3) A(3) P A A(3) A P

SHELTERED, ONSHORE P P A A A A A A A

UNSHELTERED, ONSHORE N N N P P A A A A

CORROSIVE N N N N P A A P P

AREA CLASSIFICATION SUITABILITY

CLASS I DIVISION 1 N N N N N P P(4) N N

CLASS I DIVISION 2(5) A A A A A A A A A

CLASS II DIVISION 1 N N N N N P P N N

CLASS II DIVISION 2 N N N N A A A N N

UNCLASSIFIED A A A A A A A A A

Legend: P: PREFERRED A: ACCEPTABLE N: NOT RECOMMENDED

Notes CLASS I DIVISION 1 IGNITABLE CONCENTRATION OF FLAMMABLE GASES OR VAPOR EXIST UNDER NORMAL OPERATING CONDITIONS

CLASS I DIVISION 2 IGNITABLE CONCENTRATION DUE TO ABNORMAL OPERATION OF EQUIPMENT OR ACCIDENTAL RUPTURE OF CONTAINERS.

CLASS II DIVISION 1 COMBUSTIBLE DUST EXIST UNDER NORMAL OPERATING CONDITIONS.

CLASS II DIVISION 2 COMBUSTIBLE DUST NOT NORMALLY IN THE AIR IN QUANTITIES TO PRODUCE EXPLOSIVE OR IGNITABLE MIXTURE BUT DUE TO MALFUNC-

TIONING MAY GET IGNITED.




Totally-Enclosed, Water-Air-Cooled

This motor is provided with a water-cooled heat exchanger for cooling the internal

air and a fan(s), integral with the motor shaft, for circulating the internal air. (Referto Figure 200-27.)

Totally-Enclosed, Nonventilated

This motor is not equipped for cooling by external means.

Totally-Enclosed, Fan-Cooled

An enclosed motor equipped with a fan integral with the machine, but external to

the enclosed parts. (Refer to Figure 200-27.)

Area Classification for Motors and Generators

The following is a brief summary of typical area classifications at Company loca-

tions. Electrical area classifications are discussed in more detail in the Electrical

Manual.

Class I Division 1 Locations

Class I division Motors and generators for Class I Division 1 Locations must beapproved for such locations. They should be totally-enclosed, explosionproof or atype supplied with positive pressure ventilation from a clean air source.

Class I Division 2 Locations

Motors and generators of open, dripproof, TEFC, totally-enclosed nonventilated(TENV), and non-explosionproof construction are permitted, but these machinesmust have no brushes, switching mechanisms, or similar arc-making devices unless

they are either hermetically sealed or enclosed in a purged or pressurized enclosure.Most induction motors and brushless synchronous machines meet these criteria.

These machines need not be specifically approved for use in these locations. Single-phase motors are not appropriate unless certified as explosionproof. (This is due tosparks from a shaft mounted speed switch.)

Class II Division 1 Locations

Motors and generators selected must be totally-enclosed, pipe-ventilated, or

approved for Class II, Division 1 Locations.

Machines installed in Class II Locations must function at full rating without devel-oping surface temperatures high enough to cause excessive dehydration or gradualcarbonization of any organic dust deposits that may accumulate.




Motors and generators of any type of construction are used in non-hazardous loca-tions. No restriction applies to the enclosure with respect to hazardous locations asdefined by NEC 500. Environmental factors must be considered.

234 Insulation Systems

Insulation is the non-conducting material which separates the current-carrying partsfrom each other or from the core of the electric machine. Electrical insulationsystems are divided into classes according to the respective total temperature theycan withstand without deteriorating. Four classes of insulation systems (defined in

NEMA MG 1-1.66) are used in motors:

• Class B and F are readily available (Class F is more common)

• Class H, while available in low-voltage systems (600 volts), is seldom used

• Class A insulation is obsolete and not used

Class A motors run the coolest, Class H the hottest. A given motor frame woundwith Class H insulation can deliver a higher rated horsepower than the same framewound with Class A. However, the motor using Class H insulation and temperature

rise will subject the bearings to higher operating temperatures and is rarely used.Motors using Class F insulation and rated for Class B temperature rise are

commonly available and provide a cool running motor with an expected longservice life.

The allowable total winding temperature for the four classes are as follows:

Total allowable temperature is the sum of the ambient temperature and the windingtemperature rise. The latter consists of the rated rise of the winding copper, theservice factor allowance (if applicable), and the “hot spot” allowance.

The hot spot allowance is defined as the standardized temperature differencebetween the measured temperature and the total allowable temperature of the insula-tion. The difference between the total allowable temperature and the hot spot allow-ance gives the total observable temperature. The difference between theobservable temperature and the ambient temperature is the allowable motor temper-t i Th bi t t t i ll 40°C l th i ifi d

Class °C °F

Class A 105 221

Class B 130 266Class F 155 311

Class H 180 356




Total allowable temperature = 40 + 80 + 10 = 130°C

General Recommendations

Class F insulation is normally recommended for motor windings due to its bettermechanical performance and extended life, particularly when operated at Class Btemperature rise at rated full load.

A recommended approach is to specify the motor with a 1.0 service factor and

class F insulation, but rated for a class B insulation temperature rise.

The class F insulation system will not be subjected to temperatures above itsnormal rating when the motor is operated at loads up to approximately 10% greaterthan its 1.0 service factor rating. However, the motor rating should still be selected

on the basis of matching rated horsepower to the load. This will provide bettertorque characteristics for the load and longer service life.

For motors rated 2300 V and above, a vacuum pressure impregnated (VPI) insula-tion system is recommended for the stator. The VPI process effectively seals theinsulation system to provide protection from moisture and other contaminantscommonly found in a petrochemical environment. This process consists of placing

the pre-dried stator in a tank, drawing a vacuum to remove trapped air and othergases from the insulation, flooding with an epoxy resin material, applying a pres-sure to force the resin to penetrate the insulation, and baking to cure the resin.

Special insulation treatments, such as additional resin dips and bakes to protectagainst moisture infiltration, and special compounds to inhibit the formation offungus are recommended on all motors for offshore platform applications and oper-ations in tropical climates. Consideration of these treatments should also be given

to small intermittent-operation motors that cannot be protected by space heaters due

to size limitations.

In general, 460-V motor stators should be random wound copper. However, form

wound copper windings are desirable for large 460-V motors (250 HP and above)

where the manufacturer can offer these windings. Random wound machines haveinsulated wire wound directly into the stator slots to create the windings. Formwound machines have the coils formed and insulated outside the machine. The coilsare then inserted into the stator slots and interconnected to create the windings.Motors above 460 V should have form-wound copper stator coils. Motors withform-wound stators offer a better coil insulation system, more efficient use of slot

space, and a greater degree of mechanical strength.

In high corrosion levels, aluminum material should be avoided unless the alloy hasa copper content of less than 0.2%. Corrosion may be a problem with alloys having




Temperature rise of any motor can be measured by resistance, which means themotor winding’s direct-current (DC) resistance is measured by an instrument at aknown, typically ambient temperature and then measured again immediately after

operation at rated load. This method gives an average temperature of the wholewinding. Some parts will be hotter than others; usually, the end turns will be some-what cooler than parts of the winding in the middle of the iron core. There is a

direct proportionality between the resistance of copper and temperature, so thewinding temperature at rated load can be calculated knowing the ambient tempera-ture, ambient temperature resistance, and rated-load resistance. This gives a betterindication of the temperature in the hottest part of the winding than thermometermeasurement.

On machines equipped with temperature detectors embedded within the windingsthere will usually be a difference in the readings taken by an embedded detector andby winding resistance, with the detector usually reading slightly higher since it ispositioned where the highest winding temperature is expected.

235 General-, Definite-, Special-Purpose Motors

Definite-purpose motors as defined by NEMA, and general-purpose and special-

purpose motors as defined by API are the most common types of motors used bythe Company. A summary chart of the different types and application of motors inCompany plants is given in Figure 200-30.

Definite-Purpose Motors

Definite-purpose motors are designed in standard ratings, have standard operatingcharacteristics and construction, and are for use in unusual service conditions or aspecific type of application.

Special-Purpose Motors

Special-purpose motors typically drive unspared equipment in critical service, arerated over 1000 HP, drive high inertia loads, are part of a complete train requiring

vibration sensitivity criteria, or operate in abnormally hostile environments and/orvertical cmotors supporting high thrust loads. Two-pole (3600 RPM) inductionmotors rated 600 HP and larger should also be treated as special-purpose due to thecare needed to achieve adequate reliability.

General-Purpose Motors

General-purpose motors are those machines which do not fall in the special-purpose category. Some motors rated over 1000 HP and up to 3000 HP may beplaced in this category if none of the other special-purpose criteria apply




humidity, it may be protected from condensation by space heaters installed withinthe motor frame and energized when the motor is not running. Voltage available tooperate the space heaters should always be specified, usually 120 V or 240 V.

Anti-condensation space heaters are highly recommended for all offshore

motors. However, small motors (below 5 HP) may not be equipped with spaceheaters due to physical limitations. In these instances, the starter can be equippedwith a small power transformer to reduce voltage to a low level (24 V) for connec-tion between two phases of the motors while it is at rest. The reduced voltageapplied to the motor windings allows current to flow and keep the windings dry.This 24-V source is de-energized when the motor is energized.

Space heaters should be low-watt-density type for long life and to limit maximumsurface temperature allowed by the electrical area classification. The heater surfacetemperature should not exceed 80% of the ignition temperature of the gases whichcould be present in the area.

Elimination of moisture can be achieved by keeping the winding temperature about

9°F (5°C) above ambient. Where the machine is closed except for a small vent atthe top and bottom for circulation, the heat can be estimated by the following equa-

tion:

(Eq. 200-20)

where:

H = heat, kilowatts

D = machine end-bell diameter, feet (for round enclosures)

L = machine length between end-bell centers, feet

W = machine end width, feet

h = machine end height, feet

Tropical Protections

Motors operated in tropical areas require special treatment as follows:

• Derating of the motor for ambient temperatures greater than 40°C.

• Special insulation materials or a special winding coating for prevention offungus growth.

HDL

35--------

W h+( )55

------------------- L= =




Breathers and Drains

For TEFC and TEFC-explosionproof motors, combination breathers and drains arerecommended to keep air circulating through the motor and to allow any condensa-tion to drain from the motor.

Resistance Temperature Detectors (RTD)

Temperature monitoring of motor windings and bearings may protect the motorfrom extensive damage and could prevent extended down time. Depending on criti-

cality of the motor and types of enclosure, consider equipping motors over 200 HPwith winding RTDs.

Two RTDs per phase should be embedded in each stator winding and wired to aterminal box separate from all AC services.

Bearing RTDs should be applied on motors consistent with the protective system

philosophy of the driven equipment. Normally, only large motors in unattendedlocations should be equipped with bearing RTDs. Refer to the General Machinery

Manual for additional information.

Generally, the Company selects nickel-resistance type RTDs with 120 ohms at

32°F. Other options include copper-resistance type RTDs with 10 ohms at 32°F orplatinum resistance type RTDs with 100 ohms at 32°F. See the General Machinery

Manual for more information and protection recommendations.

Terminal Boxes

Electrical feeder systems for motors are covered in the Electrical Manual. In addi-tion, size the terminal box on motors rated 600 V or less in accordance with NEMAMG 1-11.06. If required, the box should be sized in accordance with the National

Electric Code for the next larger size THW type insulated conductors and forentrance provision of rigid steel conduit.

For motors rated 2300 V or greater, the minimum dimensions and usable volumesshould not be less than those given in Table 5 of ANSI C50.41. (See Volume 2,Specification DRI-MS-4814.) Sometimes larger boxes may be necessary to accom-modate special cable terminations or accessories. On special-purpose motors, theterminal box minimum internal length adjacent to termination should be 16 inchesto provide space for shielded terminations.

Large (1500 HP and larger) motor applications normally have all six stator leads(one from each end of the three windings) brought out to the terminal box. Themanufacturer may install three window-type current transformers in the terminal

box for self-balancing differential protection. A separate conduit hub should beid d f h f d i di i S h l




provided with low-surface-temperature, anti-condensation heaters, or guarded incan-descent fixtures. The surface temperature limitation is consistent with the auto-igni-tion temperatures of the gases or vapors which could be present.

Terminal boxes should meet the requirements of the area classification in whichthey are installed. TEFC motors should have cast, diagonally-split, rotatableterminal boxes. All explosionproof motors should have NEMA 7 terminal boxes.Totally enclosed motors with water-cooled heat exchangers (TEWAC) should haveNEMA 4 terminal boxes. Pipe ventilated or inert gas purged motors used in Class I,Division 1 areas should have their main terminal boxes equipped with ventilation orinert-gas purging systems.

Filters/Differential Pressure Switches

When forced ventilation and water cooling are required to remove heat generatedby the motor, use the following information as a guide (depending on the allowabletemperature rise and effectiveness of the cooling system):

40°C Rise: Motor requires 125 CFM/kW of losses



For example, a 95% efficient motor would have 5% of its rating to dissipate aslosses.

The rise in temperature of cooling air passing through a motor will be given by:

Degree C Rise = at 40°C

(Eq. 200-21)

Where the air is passed over a heat exchanger, approximately one GPM of coolingwater at 85°F is required to dissipate one kW of losses.

Filters. Air filters prevent airborne contamination from entering and depositing onmotor internal parts. In some of the Company operations, the air around the motorscarries dust such as catalyst fines, coke dust or sand. In such cases, the motor enclo-sure normally specified is TEWAC or TEAAC depending on the availability ofwater as a heat exchanging medium. Refer to Figures 200-28 and 200-29 for motorenclosure applications.

Air filters are rated in terms of efficiency (percent particles removed by size), resis-tance to air flow, and dust capacity. Filter resistance increases with air flow (face

1900 kW Loss( )

CFM

--------------------------------------


Diff i l P (DP) S i h



Differential—Pressure (DP) Switch

DP switch taps are used to monitor the pressure drop through the filter. The switchactivates a visual indicator on the system panel to alert maintenance that the filterneeds renewal or cleaning. It can also be used to supplement winding RTDs in themotor. When the filters are clogged, the RTDs will also indicate higher windingtemperatures than normal. For more information see Sub-section 270 on Instrumen-tation.

237 Pulsating Torque Loads

Induction Motors Driving Reciprocating CompressorsInduction motors for reciprocating compressor drives are often a different electricaldesign than a motor of the same rating intended for use with a smooth load. Thesemotors generally operate with a higher slip and may have a larger air gap with aresultant larger value of magnetizing current and lower power factor. A flywheel

may be applied to the motor to improve damping of torque pulsations.

The engineer need not specify this motor, but the OEM (original equipment manu-

facturer, typically the driven-equipment vendor) needs to let the motor manufac-turer know that the intended purpose of the motor is to drive a reciprocatingcompressor.

An oscilloscope can help evaluate a motor design by looking at the oscillations inthe current. This test can be done at the plant site by the motor manufacturer, ifrequested, for additional cost. To determine this pulsating stator current variation,use an oscillograph or similar instrument (not an ammeter ampere reading). A lineshould be drawn on the oscillogram through the consecutive peaks of the current

wave. This line is the envelope of the current wave. The variation is the differencebetween the maximum and minimum values of this envelope. Refer toFigure 200-31 for an example. This variation should not exceed 40% of themaximum value of the rated full-load current of the motor.

Synchronous Motors Applied to Drive Reciprocating Compressors

For a synchronous motor driving pulsating loads (requiring a variable torque duringeach revolution), the combined installation should have sufficient inertia in its

rotating parts to limit the variations in armature current to a value not exceeding66% of full-load current.


Fi 200 30 A li ti f M t



Fig. 200-30 Application of Motors

Fig. 200-31 Oscillogram Showing Variation of a Current to a Synchronous Motor Driving a Typical ReciprocatingCompressor. Line A is the Envelope of the Current Wave. Difference B-C Divided by Rated Full-LoadCurrent Multiplied by 100 is Percent Current Pulsation (Courtesy of Ingersoll-Rand)


238 Cyclic Loads In Walking Beam Pumping Units



238 Cyclic Loads In Walking Beam Pumping Units

Beam pumping comprises about 90% of the artificial lift systems used in the petro-

leum industry. Electric motors are operated with highly cyclical loading on beampumping units, as shown in the typical torque curve during a pumping cycle (referto Figure 200-32). The application of motors to these units can have a significantimpact on the power consumption, as explained below. This varying load impactsmotor efficiency and energy consumption. NEMA D motors are normally selected

for beam pumping units due to their high starting torque and high breakdowntorque characteristics. The high slip characteristic enables the motor speed toincrease or decrease with the cyclic load, which reduces the peak torques andthereby the mechanical stress on the pumping unit and motor.

The motor efficiency curve given by a manufacturer is for a constant load over anormal operating range of 25 to 125% of rating. However, because of the cyclicalnature of a pumping unit, the motor will operate over a much wider range. The

minimum energy consumption of a unit will come when the motor is generating (pumping unit operating at negative torque). The maximum energy consumption isnear locked rotor or peak torque.

From the IEEE paper (PCIC-87-35) Optimal Sizing of Motors for Beam Pumping

U i h f ll i l i d il bl Th id li h b

Fig. 200-32 Torque During a Pumping Cycle (Courtesy of American Petroleum Institute)


• Greater improvement in efficiency is realized when a larger frame motor is



• Greater improvement in efficiency is realized when a larger frame motor is

implemented. Typically the losses do not increase proportional to the motor

rating.

Example: A motor rated at 25 HP has a maximum efficiency of 90%, while one

rated at 10 HP has a maximum efficiency of 85%. A cyclic load of 8 HP represents

63% overall efficiency using a 10- HP motor and 84% overall efficiency using a 25-

HP motor. This is an improvement of over 21 points or a 33% improvement in

energy usage. (Refer to Figures 200-33 and 200-34).

The motors used in this study are NEMA Design D motors. They provide high

starting torque, (minimum of 275%), to overcome hard starting conditions. Their

typical slip characteristics at full load are 7 to 8%, permitting increased speed varia-tion for improved production, and reduced mechanical stress.

The conclusions are summarized as:

• The best efficiency for a walking-beam unit will be achieved when the motor is

operating at 40 to 50% of its rating.

• A motor provides adequate starting torque for a conventional unit only when

the motor rating is two times the average load or greater.

239 High Inertia Loads

The cage winding in an induction motor accelerating a connected load must absorb

heat energy equivalent to the kinetic energy of the rotating mass of the entire train at

full speed. In an attempt to prevent damage to the cage winding, NEMA has estab-

lished normal-load inertia (WK2) values for squirrel-cage motors per NEMA MG 1-

20.42.

If these normal inertia loads (WK2) are exceeded, or if the frequency of starts is

more severe, consider a squirrel-cage motor designed for extra heat absorption. In

rare cases, a wound-rotor induction motor might be considered.

High inertia loads are considered two to ten times the normal inertia as defined in

the following paragraph.

Normal Load Inertia For Polyphase Squirrel-Cage Induction Motors

The values of “NEMA Standard Connected Inertias” are calculated as follows:

Load WK2 AHP0.95

RPM 2 4------------------------ 0.0685

HP1.5

RPM 1 8------------------------–=


WK2 = Inertia in lb-ft2



WK = Inertia in lb ft

Fig. 200-33 10-HP Efficiency at Various Loads (From IEEE Paper No. PCIC87-35 by Dunham and Lockherd © 1987

IEEE)

Fig. 200-34 25-HP Motor Efficiency at Various Loads (From IEEE Paper No. PCIC87-35 by Dunham and Lockherd ©

1987 IEEE)


A motor can accelerate its load without injurious temperature rise under the



A motor can accelerate its load without injurious temperature rise under thefollowing conditions:

• Motors should have the starting capabilities summarized in Figure 200-35 ifpurchased to API Standard 541 for motors 250 HP and larger. Otherwise, theNEMA standard starting capabilities apply: two starts in succession with amotor coasting down to rest between starts with the motor initially at ambienttemperature, and one start for all other conditions.

(1) Where the total load inertia referred to the motor shaft does not exceed 66% of the value listed in Table 20-1 (NEMA MG 1-20.42), the

number of starts permitted is four.

• During the accelerating period, the torque developed by the motor should begreater than the torque required by the driven load by a margin of at least 20%of the rated motor’s torque.

The accelerating time can be calculated from a procedure discussed in the Elec-

trical Manual.

For motors driving inertias over the values given in Equation 200-22, the motormanufacturer should be consulted to determine whether total acceleration time iswithin the motor’s thermal capabilities. The rotor heating during acceleration must

be dissipated by the thermal mass of the rotor without damaging the rotor bars andend ring.

In general, induction motors accelerating heavy inertias need additional stator brac-ings and rotor bars and end rings that have a large mass of conductor material.

Rotors driving high-inertia loads are usually larger than normal rotors of the samehorsepower to provide extra thermal mass.

i b k i h d i i hi h i i l d

Fig. 200-35 Starting Capabilities for Induction Motors 250 HP and Larger Purchased to API Standard 541.

Capability Number of Starts at 1.0 Service Factor

Consecutive 2 Second Jogging Applications 10Seconds Apart. First Start Is a Cold Start.

3

Consecutive Starts With the Motor Coasting to Rest

Between Starts. First Start Is a Cold Start.

2

Consecutive Starts With the Motor Coasting to Rest

and Remain Idle for 20 Minutes. First Start Is A ColdStart.

3

Evenly Spaced Start in First Hour Prior to ContinuousRunning. First Start is a Cold Start.

3(1)


• A motor driving a high-inertia load should be disconnected until the motor



g gvoltage decays (typically a few seconds) and then energized to restart the load.This can be accomplished with a timer inserted in the motor start circuit.

Normal Load Inertia For Synchronous Motors

The inertia of the driven load has a significant effect on the design of a synchronous

motor. It largely determines the speed the motor must reach to effect successful pull-in when excitation is applied (see Sub-section 218). It is also the principal factor indetermining how much heat the rotor “damper” winding must accept during acceler-ation. Since load inertia is such an important factor, NEMA (21.6) has establishednormal load inertia values for each size synchronous motor as determined by the

following equation.

Normal WK2 of load =

(Eq. 200-23)

Synchronous motors generally have lower locked-rotor torques than an inductionmotor of the same horsepower rating and consequently have longer accelerating

time. At added cost, adjustments can be made during the design of the motor tohandle high-inertia load.

240 Special Applications

241 Electrical Submersible Motors

Electrical submersible motors are available in a broad range of voltages to give thegreatest versatility of switchboard and cable selection for various depths. Settingdepth is a determining factor in motor voltage selection due to voltage loss at aparticular amperage and cable. When the voltage drop becomes too great (morethan 20%), a higher voltage (lower amperage) motor is required. With a higher

voltage motor, economics becomes a factor. In deeper wells it is possible to use asmaller, less expensive cable. However, a higher voltage (more expensive) switch-board may have to be used.

The electrical submersible motor is a three-phase, two-pole squirrel cage induc-tion type (Figure 200-36). Owing to the diametric restrictions, the unit is extremelylong and slender and is oil filled. The oil, having low compressibility, makes itcompatible with the high external ambient pressures existing due to submergence.Furthermore, it provides lubrication and effective heat transfer for dissipation of the

0.375 HP Rating( )1.15

Speed in RPM/1000( )2--------------------------------------------------------


Fig. 200-36 Electric Submersible Pump (From IEEE Paper No. PCIC82-83 by Brinner © 1982



The thermal life of the motor is a function of the following:

• Ambient temperature of the produced field

• Composition of the produced field in terms of its capacity to carry the heat

away

• Velocity of the produced fluid past the motor

• Level of losses within the motor

These functions establish the ambient temperature, the temperature rise, and inreturn the total temperature experienced by the stator windings. The rate of deterio-ration for insulating materials commonly used in motors is an exponential functionof winding temperature. It is generally accepted that the useful life of the windingis reduced 50% for every 10°C increase in winding temperature.

The life of the motor is also related to the ability of the design to maintain the

internal oil in a clean and uncontaminated state. Internal oil contamination mayoccur via any or a combination of the following events:

IEEE)


• The unit is operating in a region of a well casing which results in its operation



in a bent mode leading to excessive bearing wear, vibration, and eventualprotector seal loss.

Because of the geometric restrictions of the design, the stator winding tends to bemore susceptible to transient dielectric stress than comparably rated surface motors(Figure 200-37). Most surface motors in the 25 to 1000-HP range are many timeslarger from a diametric standpoint. Thus more insulation and much larger radiusand turns can be employed at the ends of the motor. In other words, the end turngeometry of a typical submersible motor relates closely to that which might beexpected on a surface motor in the fractional horsepower range. However, fractionalhorsepower units are not rated at voltages up to 3300 V as submersibles may be.All manufacturers utilize sophisticated dielectric systems to control the voltagestress in the end turn area, but it remains an area of great susceptibility.

Fig. 200-37 ESP Motor Construction (From IEEE Paper No. PCIC82-83 by Brinner © 1982

IEEE)


242 Multi-Speed, Squirrel-Cage Motors



The two speed, two winding and pole amplitude modulation (PAM) motors are the

two most common types of multi-speed motors used by the Company. Some of thecommon applications for two speed motors (high and low speed), are in processpumping, positive pressure blowers, centrifugal compressors and rod pumps.

Squirrel cage motors are essentially constant speed devices, the speed varying onlyslightly from full load to no load. However, there are some applications where twoor more such fixed speeds are desirable. Since synchronous speed is a function ofthe number of stator poles, speed change necessitates a change in stator windings orstator winding connections.

It is relatively simple to obtain a 2:1 speed ratio (such as 1200 and 600 RPM). Toobtain other ratios necessitates a completely independent stator winding which mayalso have its own 2:1 speed combination.

The following table (Courtesy of Electric Machinery) gives some of the possiblespeed combinations on 60 Hz power systems using two windings:

1. 1800, 1200, 900, 600

2. 1200, 900, 600, 450

3. 1200, 720, 600, 360

4. 900, 600, 450, 300

Additional types of single winding, multi-speed motors to achieve speed ratios

other than 2:1 are also available. Some of the stator pole combinations available are4/6, 6/8, 8/10 and 10/12. These arrangements have been given the name Pole

Amplitude Modulation windings because they utilize a principle similar to ampli-tude modulation techniques used for AM radio transmission.

Multi-speed motors are designed as:

• Variable–torque motors

• Constant–torque motors

• Constant–horsepower motors

Variable-torque motors are used on loads such as in centrifugal pumps and fanswhose horsepower requirement decreases more rapidly than the square of the reduc-tion in speed.

Constant-torque motors have horsepower ratings at each speed directly propor-

tional to speed, (20/10 HP and 1200/600 RPM) and are used on conveyors, mixers,


250 Mechanical Analysis



This section discusses the influence of magnetic forces on the vibration of motors,

the source of vibration, and identification during testing. The importance oftorsional and lateral critical speeds for rotating electrical machines is also brieflycovered.

251 Magnetic Influence on Vibration

Most motor vibration problems are a combination of mechanical and magnetic

problems, often further complicated by motor-base problems. The two major

“magnetic” problems are related to air gap variations (eccentricity) and current vari-ations.

“Machinery” problems can be distinguished from “magnetic” by conducting a trip

check. For more details refer to the paper on Diagnosing Induction Motor Vibration included in Appendix A. Two-pole (3600 RPM) induction motors are particu-

larly prone to problems. In addition to the mechanical vibration, the rotatingmagnetic fields inside the motor generate magnetic vibration.

Large, two-pole motors are often mounted on common bases with the driven equip-ment on rails or steel beams. This situation often leads to resonance problems or

inadequate base stiffness.

Diagnostic Chart

The Electric Motor Diagnostic Chart, Figure 200-38, can assist you with a prelimi-nary motor diagnostic survey before the actual problem is confirmed with diag-nostic equipment.

Motor Frequencies

Rotation

• Operating speed in Hz (cycles per second), f n• Harmonics will exist normally up to 20 × f n• Predominate Harmonics—2-5 × f n

Line frequency: 60 Hz

Twice line frequency: 120 Hz

Stator slot frequencies

D r

C h Fig. 200-38 Electric Motor Diagnostic Chart (1 of 3) (Courtesy of the Louis Allis Company)

http://driappa_.pdf/

http://driappa_.pdf/



ri v e r

M a n u a l

2 0 0

A C M o t o r s a n d G e n e r a t o

r s

h e v r o n C o r p o r a t i o n

2 0 0 - 6

5

M a r c h 1 9

9 6

g g ( ) ( y p y)

Note: See Sub-section 250 under “Diagnostic Chart” for a legend of commonly used terms.

2 0 0 A C M o

M a r c h 1 9 9 6

Fig. 200-38 Electric Motor Diagnostic Chart (2 of 3) (Courtesy of the Louis Allis Company)




o t o r s

a n d G e n e r a t o r s


6

2 0 0 - 6 6

C

h e v r o n C o r p o r a t i o n

D r i

C h Fig. 200-38 Electric Motor Diagnostic Chart (3 of 3) (Courtesy of the Louis Allis Company)



iv e r

M a n u a l

2 0 0

A C M o t o r s a n d G e n e r a t o

r s

e v r o

n C o r p o r a t i o n

2 0 0 - 6

7

M a r c h 1 9

9 6



Multiples of these frequencies will exist, dependent upon condition, i.e., 2f ss, 2f ss1,2f ss2, 3f ss, etc.



ss2, ss,

Rotor slot frequencies

• (Number of rotor slots)⋅(f n) = f rs.

• Harmonics

f rs1 = f rs + 120 Hz

f vs2 = f rs - 120 Hz

Multiples will exist, dependent upon condition, i.e., 2 f rs, 2 f rs1, 2 f rs2, 3 f rs, etc.

252 Torsional and Lateral Critical Speeds

These subjects are covered further in the General Machinery Manual. You shouldcontact a Company specialist for assistance with these complex analyses.

Torsional Critical Speed Analysis

All rotating electrical machines experience torsional oscillations to some degree

during starting and continuous operation. The equipment engineer must determinethe severity of these torsional oscillations and evaluate the system reliability.Torsional vibrations (oscillations) can be just as destructive as lateral vibrations—shaft fracture can occur due to fatigue.

The torsional vibration response of rotating machinery is an important consider-ation in defining the operational reliability of a rotating equipment train. Accurateresponse prediction requires analysis techniques which include consideration of allforcing functions in the system in addition to the mass elastic properties in the

shafts and couplings.

Rapid acceleration during starting (particularly with synchronous motors) appliesan oscillating driving torque, typical from 120-Hz down to zero-Hz frequency,which is resisted by the inertia of the driven load and induces significant stresses inthe shafts and couplings.

The severity of the torsional oscillations and stresses depends upon the relationship

between the operating speed or frequency of unsteady torque and the torsional

natural frequencies of the shaft system. The difference between these frequenciesis referred to as the separation margin between the operating speed and the criticalspeed.

Torsional analysis should be performed on all gearbox driven trains 500 HP and


Lateral critical speed calculations are usually performed by the driver vendor. Thedriven equipment vendor may have to provide this data if he is responsible for the



entire train.

Unbalanced response tests are recommended for the following. See the General

Machinery Manual for additional guidance on motor dynamic tests.

• Two-pole (3600 RPM) induction machines larger than 600 kW (800 HP)

• Two-pole and four-pole (3600 RPM and 1800 RPM) synchronous machineslarger than 1000 kW (1340 HP)

These tests should demonstrate the operational reliability with rotor unbalance, and

verify compliance with separation margin requirements of Company specifications.No rotor resonances should occur within the separation margin limits of plus orminus 15% of any running speed multiple or 40% to 60% of running speed. Other-wise a “well damped” (attenuated) response must be demonstrated. For details seeVolume 2, Specification DRI-MS-3547, Inspection and Testing of Large Motors

and Generators.

260 Bearings and Lubrication

Bearings and lubrication are covered in more detail in the General Machinery

Manual. Note that vendors normally specify the type of bearing supplied in a givenmotor. The following is included as general information.

Bearings provide the mechanical link between the rotor and stator and must with-stand the forces between, and maintain alignment of, these parts. Forces actingbetween the stator and rotor are gravity, magnetic pull, reaction force when deliv-ering shaft torque, and certain dynamic forces such as those resulting from rotor

unbalance.

A properly specified and applied bearing will last for the life of the machine if keptproperly lubricated. Bearings used in motors up to 500 HP rated 600 V and below

are usually the anti-friction type. Journal bearings (also called sleeve bearings) arecommonly used where the motor is greater than 250 HP rated 2300 V and above.

261 Sleeve Bearings versus Anti-Friction Bearings

The type of bearing selected for horizontal motors depends primarily on the motorhorsepower, voltage, and shaft speed. Generally sleeve bearings are used withmotors rated above 600 V.

The dN factor is another determination in the use of sleeve bearings. Sleeve bear-


Fig. 200-39 Sleeve and Anti-Friction Bearing Comparison

Sleeve Bearing Advantages Anti-Friction Bearing Advantages



Where sleeve bearings are provided, motors should have rotor end-float and

coupling end-float limited in accordance with NEMA MG 1-14.38.2 and 20.81.

(Refer to Figures 200-40 and 200-41.)

Sleeve Bearing Advantages Anti Friction Bearing Advantages

Sleeve bearings have the following advantages over

anti-friction bearings:

With proper lubrication, sleeve bearings have infinite

life. Anti-friction bearings have a discrete design life.

For large shaft motors, sleeve bearings are more

commonly available than anti-friction bearings.

For high-speed motors (3600 RPM) sleeve bearings are

preferred for better performance and longer life.

In some special applications where the motor sleevebearings are in contact with the fluid pumped (whichalso acts as a coolant), antifriction bearings cannot beused.

Most integral horsepower motors (1 through 250 HP)

purchased by the Company have anti-friction bearings.The advantages of ball bearings are as follows:

Low friction especially at starting.

High load capacity, particularly thrust loading.

Standardization. Replacement bearings of many typesare available as off-the-shelf items and can be

secured all over the world.

Loss or deterioration of the lubricant will shorten thebearing life but does not usually result in immediatebearing failure.

Grease lubrication is simpler and can be used inmotors mounted in any position. Use of pre-lubricated

sealed bearings are recommended for small horse-power motors located in corrosive atmosphere. Forlarger motors, bearings with one end shield and not

pre-lubricated are used so that grease can be filled in

the bearing cavity.

Ball bearings may be locked in place to provide thevery small shaft axial movement for close coupled

drives or where component parts, such as pumps orimpellers are directly mounted on the shaft extension.

Fig. 200-40 Recommended Motor Rotor and Coupling Floats: NEMA MG 1-14.38.2 Table(Used by permission of the National Electrical Manufacturers Association. From

NEMA Standards. MG-1, 1993)

NEMA MG 1-14.38.2 TABLE

Motor Horsepower

SynchronousSpeed of Motor,

RPMMin. Motor Rotor

End Float, InchMax. Coupling End

Float, Inch

125 to 250, incl 3600 and 3000 0.25 0.09

300 to 500, incl 3600 and 3000 0.50 0.19

125 500 i l 1800 d b l 0 25 0 09


Fig. 200-41 End Play and Rotor Float for Coupled Sleeve Bearing Horizontal Induction Machines: NEMA 20.80.1.(Used by permission of the National Electrical Manufacturers Association. From NEMA Standards. MG-

1 1993)



(1) Couplings with elastic axial centering forces are usually satisfactory without these precautions.

Most motors with sleeve bearings are designed to run on magnetic center, with nothrust load. All thrust loads are carried by the driven machine. (Magnetic center isthe axial position where the rotor positions itself with no applied axial load.)

Motors with rolling element bearings are more capable of withstanding thrust loadsthan the sleeve type, but thrust bearings must still be set to accommodate thermalexpansion from internal heat.

Standard sleeve bearings sometimes have a babbitted thrust face which can mate

with a shoulder on the shaft. These bearings are capable of maintaining end playand of absorbing only limited momentary thrust. Machines can be supplied withspecial sleeve bearings where the thrust face of the sleeve bearing has beenincreased and steps have been taken to provide lubricating oil at this thrust face.This permits limited continuous thrust and increases momentary thrust capability.

262 Thrust Bearings on Vertical Motors

Electric motors are inherently low thrust producers. Therefore, thrust bearings areusually of low to moderate capacity. However, motor rotors are easily influenced bytransmitted thrusts from the driven machine, and special attention must be paid tokeep motor thrust bearings from being overloaded.

Vertical motors can usually take higher thrust loads, depending on configuration.Close-coupled and rigid-coupled vertical pumps have motors that take the thrust ofboth machines, including the weights of both rotors. This weight can be substantial

for long-shafted deepwell and vertical turbine pumps. For this reason, verticalmotors usually incorporate heavy duty ball or roller thrust bearings. Care must betaken to accurately set the axial rotor position for end performance without impellerrubs.

Sleeve bearings are not used in vertical motors because they depend on the weight

1, 1993)

MachineHp (kW)

Synchronous Speed,Rpm

Min. Motor Rotor EndFloat, Inches

Max. Coupling EndFloat,(1) Inches

500 (400) and below 1800 and below 0.25 0.09

300 (250) to 500 (400) incl. 3600 and 3000 0.50 0.19

600 (500) and higher all speeds 0.50 0.19


Figure 200-42 shows typical thrust capacities of various kinds of thrust bearingsused in electric motors.



Figure 200-43 shows the relative thrust capabilities of four different anti-frictionbearing types. Relative thrust capacity is governed by the geometry of the rollingelement and race contact angles.

Values in Figure 200-43 are for comparison purposes only. Actual catalog values

for load ratings, limiting speed, etc., should be used. Oil when used as a lubricantremoves heat and results in less heat accumulation than grease, so that catalog speci-fied speed limits are reduced by one-third to one-half when a bearing is grease lubri-cated.

Fig. 200-42 Typical Thrust Capabilities of Bearings

Type of Bearing Continuous Momentary

Standard ball bearing Low Low

Angular contact ball bearing Moderate downthrust/upthrust Moderate downthrust/upthrust

Spherical roller bearing High High

“Kingsbury” pad-type thrust

bearing

Very high Very high

Fig. 200-43 Relative Thrust Capabilities of Four Different Bearing Types


Hydrodynamic thrust bearings for vertical motors are babbitted multiple-segmenttype. Tilting pad-type bearings, if used, should incorporate a self-leveling featureassuring that each segment carries an equal share of thrust load The thrust collar



assuring that each segment carries an equal share of thrust load. The thrust collar

should be replaceable. Fretting and axial movement is prevented either by posi-tively locking the collar or by other methods. Split thrust collar should not be used.

Hydrodynamic thrust bearings for vertical motors are sized to continuously carry200% of the maximum thrust load. Anti-friction bearings are sized to carry 200%of maximum thrust load for an AFBMA L-10 life of 5000 hours. (L-10 life means90% of bearings are satisfactory after operating at the specified load for the speci-fied number of hours.) In addition to the thrust from the rotor, the maximum axialforce from the driven equipment transmitted through the coupling is considered a

part of the load of any type of thrust bearing. The proper thrust bearing to satisfythe above load and life criteria is selected by the motor manufacturer using thrustdata provided by the driven equipment manufacturer.

For further details on thrust bearings, refer to the General Machinery Manual.

263 Grease and Oil as Lubricants

See the General Machinery Manual for additional information on lubricants andlubrication systems. Refer to Figure 200-44 for a summary of factors regarding oil

and grease lubrication, specific to motors.

Essentially all anti-friction bearings are grease lubricated. Grease may be forcedinto a relatively small void around the anti-friction bearing and can provide lubrica-tion for prolonged periods of time.

264 Greasing the BearingGrease should be worked into the bearing from one side of the bearing to the otherside of the rolling elements, and repeated by adding grease to the other side of thebearing. Rotate the bearing a few times by hand during the charging operations toensure that the grease is worked into the ball pockets. Surplus grease can beremoved with a splinter free spatula or similar device.

Double-shielded bearings are generally prepacked at the factory but single-shieldedbearings may or may not be prepacked. In practice, motor manufacturers some-times flush out the “standard” grease from single-shielded bearings in order to use

another grease specified by the Company. The grease can only be added from oneside where there is no shield.

The end covers provided for the bearings are designed to hold sufficient grease in


Fig. 200-44 Summary of Grease and Oil Lubrication Applicable to Motors

Advantages of Grease: Advantages of Oil Lubrication:



The amount of grease added to the end covers range from approximately 25 to 30%of the volume of the cavity, but for vertically mounted motors the top end covershould contain less grease.

Less tendency to leak, less contamination.

Requires less maintenance.

Easier to mount motors containing grease-lubricated

bearings in various mounted positions.

Overgreasing:Prevents proper grease circulation.

Causes the bearing to heat up, and grease to flow out

of the seals.

Recommend filling only 1/3 of void spaces in thehousing.

Handling Grease:Avoid contamination in storing/dispensing.

Never leave packages open.

Never use wooden paddles or spatulas (may producewood slivers).

Clean tools, hands, containers, guns, etc.

Use a small dispenser instead of removing package lid

each time grease required.

Leave protective grease on new rolling bearings until

the proper facilities for cleaning and drying are avail-able.

Use solvents such as mineral spirits, avoiding lowerboiling range solvents or chlorinated solvents.

Drain motor bearings after interim storage prior tocharging with grease (10 to 15 minutes).

Protect the bearings from foreign particles in the air.

Regreasing Intervals:Do not over-lubricate.

Follow relubrication methods recommended by the

motor manufacturer.

Used on larger heavily loaded and high-speed ball and

roller bearings (due to additional cooling required).

Motor manufacturer selects proper oil viscosity.

See the General Machinery Manual for oil-deliverysystems.

Oil Operating Service Temperature:Temperature of oil over 180°F (82°C) results in prema-

ture bearing failure.

Cloudy oil may mean water present, a burned smellmay mean it is overheated.

For oil-ring lubricated bearings, routinely check if rings

are turning, or there is a coke buildup on their surface.


271 Temperature Indicators and Detectors

Bearing Temperature Detectors



Bearing Temperature Detectors

Bearing temperature detectors may be used to monitor the condition of the bear-ings. They provide a warning and may provide automatic protection against poten-tially catastrophic failures; however, they may not respond quickly enough tosudden problems to prevent considerable damage. Vibration monitoring is the onlygood method to detect and respond to sudden problems.

Bearing temperature detectors are applied on motors consistent with the protective

system philosophy of the driven equipment. Large or critical equipment trains

usually have thrust bearing temperature detectors. Critical motors on such trains arealso provided with thrust bearing temperature detectors.

Radial bearing temperatures may be monitored by Resistance Temperature Detec-

tors (RTDs) commonly using nickel-resistance type, 120 ohm at 32°F. On unat-tended motors, 500 HP and larger, each bearing should be provided with at leastone detector. Special-purpose motors, 500 HP and larger, in attended locationsshould also be equipped with at least one bearing temperature detector on eachbearing. Bearing RTDs are generally insulated from the bearing metal.

Vertical motors with hydrodynamic bearings are usually monitored for bearingtemperature with RTDs.

Where a pressure lubrication system is furnished for special-purpose motors andgenerators, the temperature of the oil is usually monitored with a 3-inch minimumindustrial or dial thermometer, mounted in individual wells in the oil piping of theoil cooler inlet and outlet.

Stator Winding Temperature DetectorsWinding (RTDs) are nickel-resistance type, commonly 120 ohms at 32°F. A totalof six detectors should be located in stator slots between coils, centered axially, anddistributed around the stator, and should comply with the requirements of NEMA.Winding detectors are recommended for all machines 1500 HP (1100 kW) andlarger and for all machines with weather protected enclosures normally down to500-HP (375 kW) rating.

272 Oil Level Indicators

All motors and generators using oil as a lubricant should be furnished with a sightlevel indicator on the bearing housing of motors and generators. The breakage ofthe level indicator should not permit drainage of the oil sump The level indicator


lent. The recommended oil level is marked on the outside of bearing housings by acast mark or stainless steel tag. This oiler serves as a reservoir and keeps dirt andwater out. All pressure lubricated systems should have a sight flow indication on



p y g

the drain line from each bearing.

273 Pressure Indicator

Where a pressure lubrication system is furnished for motors and generators, 3-inchminimum size stainless steel Bourdon tube pressure gages should be furnished atthe discharge of each oil pump upstream of the check valve. A separate pressure

gage is recommended downstream of the oil filters. Excessive pressure drop at the

oil filter necessitates a filter change or service.

274 Alarms and Shutdown

High Temperature of Stator Windings

Winding temperature detectors are recommended for all critical applications,regardless of motor size. They should be specified for all weather protected typemotors (WPI, WPII) normally down to 500-HP rating because air filters arecommonly used or retrofitted on these type of enclosures. Filter blockage can besensed by winding temperature detectors.

When the temperature approaches or exceeds the limitations of the bearing andstator winding specified by the machine vendor, the monitors purchased for sensing

bearing and stator winding temperature should have auxiliary relays for initiatingalarm and/or shutdown functions.

In the alarm condition, the electrical machine may run until the cause for over-heating is investigated.

Air Filter Flow

Large motors and generators with WPI or WPII enclosures normally use cleanableair filters sandwiched in a stainless steel frame. The filter condition should be moni-tored by a differential pressure switch across the filter. This switch operates avisible alarm (such as a red light) or sounds an audible alarm to alert operation that

the filter needs cleaning.

Coolant Flow

Large motors and generators with TEWAC enclosures use water as a coolant. Theflow of water is monitored with a differential pressure switch or a flow switch. On


additions to or deletions from this list. See the General Machinery Manual for moreinformation.



Refer to Volume 2, Specification DRI-MS-3903, and the related data sheet for otherfunctions. This data sheet also serves as a checklist.

Vibration

Vibration monitoring on the shaft or bearing housing and automatic shutdown has

Fig. 200-45 Typical Alarm and Shutdown Functions for General-Purpose Machines

Fig. 200-46 Alarm and Shutdown Function for Special-Purpose Machines


vibration monitoring and API 678 for bearing housing vibration monitoring. Referto the General Machinery Manual for additional information on these systems.Section 600 of the General Machinery Manual also contains more guidance and



background on what applications warrant the expense of these systems.

275 Driver Auto Start System

When a plant depends on continuous pumping, it is important that the spare pumpin the critical service be automatically activated when the main pump or motor fails.

In manufacturing process plants, (and many production facilities) pumps are auto-matically started on occasion. An example is a crude oil shipping pump from a tank

to a pipeline or refinery. When the pressure drops below a setpoint, it calls for morepumps to come on line.

Automatic pump start (APS) costs are usually negligible when compared to the lossof production due to a pump/motor failure. The engineer needs to evaluate the

requirement of the auto start based on plant productivity and profitability. This isdone case by case.

A typical design drawing, from the Richmond Refinery (D-254455 for automatic

start of a standby pump showing the control configuration) is included at the end ofthis section as Figure 200-62. This includes the following:

• Automatic pump start for either pump (operator selected). For systems with adedicated main and standby pump, an APS would be installed for the standbypump only.

• Control house alarm to indicate when the APS has activated.

This standard is recommended for all new APS systems and could be used as aguide for reviewing all existing installations.

280 Generators

281 Generation of Alternating Current

Direct-current systems have a voltage that remains at a constant value and thecurrent flows in one direction. In alternating-current systems, the voltage and

current reverse their direction regularly from up to a maximum value in one direc-tion to the same maximum value in the opposite direction, alternating continuously.

The alternating current generator is available with either a revolving armature or a


Fig. 200-47 Simplified Diagram of a Single-Phase Alternating-Current Electric Generator(From Electrical Drafting and Design Textbook by Charles Snow © 1976. Used by

permission from Simon & Shuster, Prentice Hall, Inc.)



Single-phase Generators

Figure 200-47 shows a simplified diagram of a two-pole, single-phase revolvingarmature, alternating current electrical generator. The horseshoe-type electricmagnet is used to illustrate the magnetic field. The conductor which must passacross the magnetic lines of flux is formed into the shape of a loop which can be

imagined to rotate on the axis X-X. The ends of the conductor are connected torings (called slip rings) mounted on the shaft and brushes (labeled B- B) ride onrings so that the flow of electrons can flow from rotating conductor into circuit “A”that is external to the machine. The brushes are usually made from blocks ofcarbon, which is a good conductor, and can be shaped to fit closely to the rings.They are held in place and pressed against the rings by spring devices mounted on

the brush holders.

The magnetic flux is developed through the winding on the magnet core and is

powered from an external direct-current source so that the flux in the gap remainssteady and constant. The current in this magnet is called the exciting current.

The magnetic field, the coils of wire around the iron core, and the coil itself are

called the field of the generator. The rotating loop is called the armature.


It is important to note the location of a particular spot on the conductor and followit through the diagrams because the value of the voltage generated relates to howmany lines of flux the conductor is crossing at any given time.



If the voltage completes 60 cycles in one second, it is called 60-Hz voltage. Thecurrent that this voltage will cause to flow is called 60-Hz current. This character-istic is called the frequency of the system.

Fig. 200-48 Diagram of a Loop of Wire Rotating in a Magnetic Field (From Electrical Drafting and Design Textbook by

Charles Snow © 1976. Used by permission from Simon & Shuster. Prentice Hall, Inc.)


The Three-phase Synchronous Generators

Today, most power systems produce and transmit three-phase power because it isbest adapted to motors and provides the least expensive power distribution.



Figure 200-49 illustrates the voltage over time of such a system. Figure 200-50 illustrates the principles of a three-phase AC generator.

The three-phase generator is a combination of three loops mounted on a single shaftequally spaced at 120 degrees around the axis and designed to rotate in the samemagnetic field. Figure 200-49 shows the voltage produced in a three-phase gener-ator.

This arrangement of coils is shown in simplified form in Figure 200-50. Both endsof the coils are wired out through the slip rings.

Fig. 200-49 Curve Showing Voltage Produced in a Three-Phase Generator (From Electrical Drafting and Design Text-

book by Charles Snow © 1976. Used by permission from Simon & Shuster, Prentice Hall, Inc.)

Fig. 200-50 Three-Phase Generator with Internal Connection (From Electrical Drafting and

Design Textbook by Charles Snow ©1976. Used by permission from Simon &

Schuster, Prentice Hall, Inc.)


Most actual generators have a stationary three-phase armature and a revolving field.The reason for this is that armature currents are usually much greater than fieldcurrents and the operating voltage level of the armature is usually much greater



than the field (for example, 13,800 V versus 250 V). It is much easier to construct areliable insulation system on a stationary structure. A further refinement of an exci-tation source for the field was made in the 1960’s which eliminated the brushes and

slip rings. This is called “brushless” excitation and is described in Sub-section 282.

Induction Generators

Most of the generators used by the Company are synchronous generators. An induc-tion machine may be used as a generator where emergency loads or loads that needto be run on loss of utility power are not saved. An induction motor can serve as an

induction generator if it is driven to a speed slightly above its synchronous speed.As a first approximation, if a motor develops its rated power at a slip of s below itssynchronous speed N, it will generate its rated power at a slip s above the synchro-nous speed N. The difference of N-s to N+s depends on the rotor type and the normal slip value. If s = 0.05, then N-s = 1.00-0.05 = 0.95, and N+s = 1.00 + 0.05 =1.05. A motor that has a normal loaded slip of 5% below the synchronous speedwill rise to 5% above synchronous speed when generating its rated power as induc-tion generator. The machine must be connected to a power system to function in

this manner. If its main contactor is opened, it cannot generate its own voltagebecause it derives its magnetic excitation from the power system to which it isconnected.

Advantages and Disadvantages of an Induction Over a SynchronousGenerator

Advantages of an Induction Generator:

• Controls are simple

• It is an induction motor which may be readily available

• It costs less than a synchronous generator

• No synchronization required

Disadvantages of an Induction Generator:

• On power-interconnect loss, the induction machine cannot generate power• May need power factor correction capacitors

• Short circuit current output decays very rapidly


The most commonly used excitation system today is the rotating brushless exciterwith a solid-state regulator (one type is shown in Figure 200-51). Today’s staticexciter/regulator system designs employ highly reliable solid-state components that



do not age or wear as compared with electro-mechanical systems.

Some advantages of the brushless exciter and solid-state voltage regulator over

previously used equipment are the following:

• Lower maintenance costs (no brushes or slip rings)

• Improved reliability (number of rotating parts is reduced)

• Better performance—(response time is improved in reaction to short circuits orthe starting of motors.)

• Higher efficiency (direct conversion of AC to DC and no brush losses)

• Less radio-frequency interference (RFI) (due to sparking at brushes)

Excitation Systems

The voltage regulator acts in conjunction with the exciter to automatically maintainthe voltage of the generator within a given operating range. The voltage regulatorreturns the voltage to this range when load changes cause the generator voltage tofluctuate.

Fig. 200-51 Brushless Excitation System


Fig. 200-52 Typical Shunt Excited, Brushless Rotating Excitation System



Voltage, Power Factor, and VAR Control of Synchronous Machines

All electrical equipment is designed to be operated at or near its rated voltage. For

l ll d i d i f il l i 10%

Fig. 200-53 Brushless Excitation System with Permanent Magnet Generator (PMG)


Power factor is directly related to voltage regulation. A lagging-power-factor load,which means the load is absorbing watts and VAR, causes a feeder voltage drop. Aleading-power-factor load, which means the load is absorbing watts and deliveringVAR, causes a feeder voltage rise. A unity (one) power factor load, which means



, g y ( ) p ,the load is absorbing watts but not absorbing or delivering VAR, causes only asmall voltage drop.

As the power factor of a load or generator approaches unity, the current flowapproaches a minimum. Thus, the watt losses in the system are reduced and the effi-ciency is maximized. Also, since the current magnitude is reduced, the systemcapacity for additional load is increased. Finally, many electric utility companiescharge a penalty to offset the higher costs associated with supplying a low power

factor load.

Therefore, it may be necessary to control power factor for improved voltage regula-tion, efficiency, and a utility power cost.

VAR flow is directly related to voltage regulation and power factor. By changing

the VAR absorbed by the load or produced by the synchronous machine, the voltageor power factor can be adjusted as desired.

By controlling the excitation-voltage of the synchronous motor or generator the

voltage, power factor, or generated VAR can be held constant. This is accomplishedby increasing or decreasing the machine excitation voltage as system load or othercondition change. If the excitation voltage is increased, the VAR flow from themachine increases. If the excitation voltage is decreased, the VAR flow from themachine decreases. Under normal conditions synchronous machines are alwaysoperated either “overexcited” to deliver VAR to the system, or at unity power factorto just deliver power and neither deliver nor absorb VAR. The machine operatesmost efficiently at unity power factor, since the current carried by the armature is

minimum, also minimizing losses. However, for motors the pullout torque may belower at unity power factor than at leading power factor conditions. For generators,steady-state stability (the ability of a generator to stay connected to the powersystem while generating power) may be of concern at near unity power factor. Inpractice, the machine operating power factor will be a compromise of concerns forefficiency, power factor correction, voltage regulation, and other system consider-ations.

The choice of power factor control, VAR control, or voltage regulation will depend

upon the operating conditions. Many modern controllers allow switching betweenthe three options as necessary.

Power factor control may be chosen when it is desired to select and maintain an effi-i t ti f t f th t t H th VAR t t


VAR control may be chosen when it is necessary to maintain a constant VARoutput as the machine kW load varies. For example, if the system load has a rela-tively stable VAR requirement for overall power system power factor correction butthe machine kW loading varies, VAR control is a good choice instead of power



factor control.

Voltage control may be selected when it is necessary to maintain a constant busvoltage. By regulating the voltage to the nominal value, the overall system powerfactor as seen by the electric utility may also be improved, although not to aspecific value. In the case of a generator running isolated from the utility system,voltage control must be used by at least one generator. Otherwise there is no way tocontrol the bus voltage to a specified value. VAR generation will be as necessary to

meet the load requirement. Most modern excitation voltage regulator systemsprovide for automatic change from power factor or VAR control to voltage controlwhen the generator becomes isolated from a utility system, (if a utility is used.) SeeNote 3 of Figure 200-54.

Fig. 200-54 Typical Interconnection Diagram for VAR/Power Factor Controller


Most synchronous machines use power factor or VAR control when operating inparallel with the utility. As previously mentioned, generators then switch to voltagecontrol when isolated from the utility system.

M h i i hi h i ll



Many synchronous motors use excitation systems which are not automaticallyadjusted. The excitation is manually adjusted to meet the necessary system-VARrequirementsandisfixed.TheVARproductionofthemotor’remains fairly constant,but does vary somewhat with kW load as shown by Figure 200-55.

A specific example of a synchronous motor being used for correcting the powerfactor is shown in Figure 200-56.

Figure 200-54 illustrates a typical power factor/VAR controller and voltage regu-

lator for a generator. The controller and regulator receive input signals from thecurrent transformer and voltage transformers. These voltage and current signals areinterpreted by the controller and regulator and the generator exciter voltage isadjusted appropriately to maintain the regulated power factor, VAR flow, or voltage.

290 Maintenance Considerations

291 Replace Induction Motors With High Efficiency Motors Versus Rewind

The rewind of a standard efficient induction motor is often not a good economic

choice when compared to replacement with an energy efficient motor. This isalmost always the case for a motor in need of a rewind that is unspared or spared bya steam driver. Deciding whether to replace or rewind involves many factors: costand availability of the new motor, energy and labor costs, motor efficiency, oper-ating hours, rewind cost, possible modification costs, and hurdle rate of return.

Replace/rewind decisions will differ from area to area due to regional differences inthese factors. Rebates may also be available from the local utility company.

Replacing a motor versus rewinding a motor should be based on favorableeconomics. To date, most motors are rewound, not because of favorable economics,but because a replacement motor is not readily available.

Developing guidelines to assist the user in making good business decisions onreplacement vs rewind involves two critical steps. The first is the upfront planning

including the economic analysis that defines when to replace. The second is to havea field implementation system in place to quickly purchase and install replacement

motors.

This section can assist you in developing the guidelines for making the replace vsi d d i i id if i i il bili d i f


Fig. 200-55 Lead kVAR Variation with Synchronous Motor Load Excitation Constant (Courtesy of Electric Machinery

Synchronizer)




Fig. 200-56 Correction Using a Synchronous Motor Power Factor




Fig. 200-57 Example of Site Specific Motor Replace vs Rewind Flowchart

Motor Needs a Rewind



Factors Influencing Economic AnalysisEarnings are derived from decreased energy consumed by the new high efficiencymotor and elimination of the maintenance cost to rewind the existing motor. Creditcan also be given for the reduction of future maintenance costs due to the improved

No No NoYes

YesYes

Is

Motor

Spared?

Is

Motor

Spared?

Motor

Previously

Rewound?

HP HP

Steam

Spare

Motor

Spare HP

Steam

Spare

Motor

Spare

HP

7.5 Rewind 7.5 Rewind Rewind 7.5 Replace Rewind 7.5 Replace

10 Rewind 10 Rewind Rewind 10 Replace Rewind 10 Replace

15 Replace 15 Replace Rewind 15 Replace Rewind 15 Replace







75 Replace 75 Replace Rewind 75 Replace Replace 75 Replace

100 Replace 100 Replace Rewind 100 Replace Replace 100 Replace

125 Replace 125 Replace Replace 125 Replace Replace 125 Replace




instead of the spare steam driver. When a motor spares another motor, commonpractice is to equally share the operating time between the two motors.

The operating factor has two components: The plant operating factor and the motor

operating factor Most facilities have an average plant operating factor of 0 9



operating factor. Most facilities have an average plant operating factor of 0.9.

The motor operating factor will depend upon its spare. If no operating preference

exists, assume the following: For an unspared motor, assume the motor operates90% of the time. For a steam spare, assume the motor operates 90% of the time, thesteam driver, 10%. For a motor spare, assume both motors operate 50%.

The overall operating factor is the product of the two:

Unspared = 0.9 × 0.9 = 0.81Steam-driven spare = 0.9 × 0.9 = 0.81

Motor-driven spare = 0.9 × 0.5 = 0.45

Motor Efficiencies: See Figure 200-58.

Average Motor Load. Most motors were originally designed to operate at 3/4 load.

If the facility has been debottlenecked and is operating above the original designrate, the average motor load should be increased accordingly.

Each Rewind May Result in a 1% Loss in Efficiency. If the motor has not beenrewound, assume a 1% loss in efficiency for the economic analysis. If the motor has

(1) Standard efficiency data is based on Reliance XT type, and high efficiency data on Reliance XT XE type

TEFC, 2 Pole motors operating at 3/4 load.

Fig. 200-58 Efficiencies of Standard And High Efficiency Motors

MotorHP(2 Pole)

StandardEfficiency(1)

(%)

HighEfficiency(1)

(%)

MotorHP(2 Pole)

StandardEfficiency(1)

(%)

HighEfficiency(1)

(%)

7.5 80.2 90.1 50 87.5 93.2

10 84.2 91.1 60 87.2 93.7

15 83.7 91.2 75 88.7 94.3

20 85.8 92.5 100 88.9 94.6

25 83.5 92.0 125 90.3 94.6

30 85.1 92.6 150 91.1 94.9

40 86.8 92.6 200 93.0 95.6


Developing A Replace vs Rewind Flowchart

The replace/rewind flowchart shown in Figure 200-57 can be created by collectingaverage data for your facility and making the economic analysis. Motor rewind

costs, including transportation, repair and installation can be obtained from themaintenance division or from a local repair shop New motor costs can be obtained



costs, including transportation, repair and installation can be obtained from themaintenance division or from a local repair shop. New motor costs can be obtainedfrom purchasing or a local supplier. The following example will illustrate themethod.

Fig. 200-59 Data for Evaluating Motor Replacement

MotorHP

Standard

Eff

(1)

(%)

High

Eff

(1)

(%)

New

MotorCost(2) InstallCost(3)

RewindCost(4) InitCost(5) OperFac(6) AnnualSavings(7)

Rateof

Return

(8)

(%)

50 88.2 93.2 $2,200 $800 $600 $2,400 0.81 $953 34

100 88.9 94.6 $4,600 $800 $1,200 $4,200 0.45 $1,343 20

Notes:

1. Efficiency values from Figure 200-58.

2. New motor cost is a budgetary estimate.

3. Includes motor installation and any modifications for overload heaters or relays, conduit, coupling, and transition baseplate. Since both

motors are T-Frame, there are no modifications.

4. Includes cost to transport to shop, rewind, and install.

5. Initial cost is the sum of new motor cost and installation less rewind cost and is the investment cost for the economic analysis.

6. Operating factor for a steam spare is 0.81 and for a motor spare is 0.45.

7. Annual Savings = KWH Saved × Annual Hours of Operation × Energy Cost

KW Saved = Original HP × (100/(old eff-1%) - (100/new eff)) × Motor Load × 0.746 KW/HP

(subtract 1% from old eff for each previous rewind)

Annual Hours of Operation = 8760 Hours × Operating Factor

Energy Cost = $0.065/KWH (cost for the next KWH purchased from the utility)For 50 HP Motor:

KW Saved = 50 HP × (100/(88.2 -1)

- (100/93.2)) × 0.75 × 0.746 KW/HP

= 2.07 KW

Hours of Operation = 8760 Hours × 0.81 = 7096 Hrs

Energy Cost = $0.065/KWH

Annual Savings = 2.07 KW × 7096 Hours × $0.065.KWH = $953

For 100 HP Motor:

KW Saved = 100 HP × (100/(88.9-2)- (100/94.6)) × 0.75 × 0.746 KW/HP

= 5.24 KW

Hours of Operation = 8760 Hours × 0.45 = 3942 Hrs

Energy Cost = $0.065/KWH


Example:

Two motors are in need of a rewind. The first is a 50 HP 2 pole, TEFC, T-Frame, standard efficiency, NEMA design B motor. It is spared by a steam

driver. The second is a 100 HP, 2 pole, TEFC, T-Frame, standard efficiency,A d i h i l d d i d b h



, p , , , y,NEMA design B motor, that was previously rewound and is spared by anothermotor. What is the rate-of-return to replace each motor with an energy efficientmotor.

Solution:

A table of data is presented in Figure 200-60 to assist in the analysis. With anacceptable hurdle rate of return of 15%, both motors in this example should be

replaced with a new high efficiency motor versus rewound.

Field Implementation

Implementing a replace versus motor rewind program hinges upon a well conceivedplan that effectively gets the replacement motor installed without unplanned field

rework or startup delays.

The following activities need to be fully developed ahead of time in order to havean effective and successful implemention plan:

• Maintain motor data and repair history cards.

• Stock new energy efficient replacement motors.

• Plan for field modifications and changes.

Maintain Motor Data And Repair History Cards

A motor data and repair history card is an important tool to assist in making good

decisions on the maintenance of motors. Up-to-date motor data cards should bekept for all motors and include basic motor specifications and repair history.Rewind data is especially important since there is a good chance that the efficiencyof a rewound motor may drop by about 1% with each rewind. Figure 200-60 is asample motor data and repair history card.

It is not unusual to find a motor that after being rewound once will become achronic maintenance problem. Poor rewind practices can permanently damage thestator core, resulting in hot spots that affect the life of the rewound coil. A hotter

running motor can also affect bearing lubrication and bearing life. When repairwork is done, it should meet minimum requirements. (See Specification DRI-MS-4927).

Stock New Energy Efficient Replacement Motors


Fig. 200-60 Sample of Motor Data and Repair History Card

INDENT NO.

H.P. MFGR. TYPE

VOLTS FL AMPS LR AMPS PHASE TEMP. RISE



SYNCHRONOUS INDUCTION TYPE NO.

EXCITATION AMPS. SYN. SPEED F.L. SPEED

MODEL NO. FORM NO. MFG. SHOP ORDER NO.

SERIAL FRAME NEMA DESIGN

INSULATION FAN ROTAT.

ENCLOSURE CLASS DIV. GROUP

BEARING TYPE COUP. END OPP. END LUB

DRIVEN EQUIP. SPARE DRIVER(1)

SPECIAL FEATURES

NO LOAD 1/4 LOAD 1/2 LOAD 3/4 LOAD 4/4 LOAD

EFF WHEN PURCHASED

PF WHEN PURCHASED

MOTOR SERVICE RECORD

DATE INSTALLED ON/REMOVED FROM WHAT EQUIPMENT COMMENTS AND NOTES


their stock of locally warehoused motors to match a customers predetermined needsand can deliver in less than 24 hours. Often the motor manufacturer will establishan arrangement with a local electrical supplier to stock additional frame motors tocover a wider spectrum of stocked motors.

A knowledge of the number of motors replaced in a typical month and the motor



A knowledge of the number of motors replaced in a typical month and the motorframe will be necessary information in setting up any arrangement with a supplier.

Plan for Field Modification and Change

Baseplate and coupling modifications will be rare except with the oldest motors(1969 and earlier). All NEMA T-Frame foot-mounted motors with single straightshaft whether standard efficiency or high efficiency type have the same shaft height

and diameter and the same mounting dimensions. Therefore, no baseplate orcoupling modifications are necessary for any T-Frame motor.

NEMA U-Frame motors are physically larger than similar horsepower T-Framemotors and will almost always require a baseplate modification and a new couplingwhen replaced by an energy efficient T-Frame motor. Many of the transition base-plates offered by manufacturers are fabricated of light-gage metal and are inade-

quate. Robust transition baseplates may be designed and fabricated and the costshould be included in the economic analysis. Figure 200-22 shows the standard T-

Frame and U-Frame dimensions. Figure 200-61 shows the significant differencesbetween T-Frame and U-Frame dimensions. There are only two important dimen-sional differences, (1) the shaft diameters on the T-Frame are from 0.25 to 0.50inches larger in diameter (except in a few cases when they are equal) and, (2) theshaft length from the shoulder to the shaft end differ by 0.25 to 0.50 inches.However, there is no consistency in one frame type always being longer.

High efficiency motors have slightly higher in-rush current than similar size stan-

dard efficient motors. This may result in the nuisance tripping of the magneticcircuit protector (MCP) that was set for the original motor. If so, the trip setting ofthe MCP should be set slightly higher to eliminate any nuisance tripping.

Heater strips for the thermal overload relays may have to be replaced due to thelower full load current of the energy efficient motor. Overload heaters are adjust-able, typically plus or minus 15%. If the new setting for the energy efficient motoris outside the adjustable range of the existing heater, a new heater will be necessary.


Fig. 200-61 Significant Dimension Differences for U-Frame and T-Frame Foot-Mounted Machines with SingleStraight Shaft Extensions

U-Frame

Designation U (1) N—W(1)T-Frame

Designation U (1) N—W(1)

143T 0.875 2.25



145T 0.875 2.25

182 0.875 2.25 182T 1.125 2.75

184 0.875 2.25 184T 1.125 2.75

213 1.125 3.0 213T 1.375 3.38

215 1.125 3.0 215T 1.375 3.38

254U 1.375 3.75 254T 1.625 4.00

256U 1.375 3.75 256T 1.625 4.00

284U 1.625 4.875 284T 1.875 4.62

284TS 1.625 3.25

286U 1.625 4.875 286T 1.875 4.62

286TS 1.625 3.25

324U 1.875 5.625 324T 2.125 5.25

324US 1.625 3.25 324TS 1.875 3.75

326U 1.875 5.625 326T 2.125 5.25

326US 1.625 3.25 326TS 1.875 3.75

364U 2.125 6.375 364T 2.375 5.88

364US 1.875 3.75 364TS 1.875 3.75

365U 2.125 6.375 365T 2.375 5.88

365US 1.875 3.75 365TS 1.875 3.75

404U 2.375 7.125 404T 2.875 7.25

404US 2.125 4.25 404TS 2.125 4.25

405U 2.375 7.125 405T 2.875 7.25

405US 2.125 4.25 405TS 2.125 4.25

444U 2.875 8.625 444T 3.375 8.50

444US 2.125 4.25 444TS 2.375 4.75

445U 2.875 8.625 445T 3.375 8.50

445US 2.125 4.25 445TS 2.375 4.75

447U 2.875 8.625 447T (2) (2)

Note All Dimensions in Inches

Driver Manual 200 AC Motors and

Fig. 200-62 Drawing D-254455-1



Chevron Corporation 2-97 M

Documents

Chevron AC Motors' Manual Dri200