WMEA Conference Papers/ac_induction_motors... · Enclosure, Stator Construction, ... passage of external cooling air over and around the windings of the ... WPII - Weather

Copyright © Siemens AG 2009 - All rights reserved No portion of this document may be reproduced either mechanically

or electronically without the prior consent of Siemens.

WMEA Conference ABC’s of AC Induction Motors

Presented By:

Jim Bender – Business Development Mgr, Siemens

Ben Flick – Product Eng Mgr, Siemens

May 29, 2014

Rapid City, South Dakota

Copyright © Siemens AG 2009 - All rights reserved No portion of this document may be reproduced either mechanically or electronically without the prior consent of Siemens.

Motor Standards

National Electrical Manufacturers Association

NEMA Standards Publication MG1 – Motors and Generators

www.nema.org

International Electrotechnical Commision

IEC 60034-1

www.iec.ch/

http://www.nema.org/

http://www.iec.ch/


What are considered “NEMA” motors…

Horsepower

1-500 HP

Speeds

3600, 1800, 1200, 900 RPM

Mounting

Horizontal

Flange Mounted

Vertical

Enclosures

ODP, TEFC, TENV, XP

Voltage (3-phase)

208, 230, 460, 575, 600V

Frequency

60 Hz

Frame sizes

143T-449T

Standards

NEMA, ANSI, IEEE, U.L.,

C.S.A., API and other applicable

US, Canadian and Mexican

Standards


Low Voltage TEFC Enclosure Frame Assignments


What is a “severe duty” motor??

A motor designed for use in a harsh, indoor or outdoor application. TEFC

enclosure all cast iron construction, NEMA ™ Premium efficient (IEEE-841

specification?).


Page 6

Specifications – Motors

General

Horsepower, Speed, Voltage, Frequency

Construction Specific

Enclosure, Stator Construction, Rotor Construction, Bearing Type, Lubrication

Performance Specific

Temperature Rise, Starting conditions, Vibration

Monitoring Accessories

RTDs, Vibration Probes, Switches, Surge Protection


Shaft

Core

Rotor bars

End connectors

Retaining rings

Internal fans

© Siemens 2014. All Rights Reserved.

Industry Sector, DT LD AP

Rotor | Design Basics | Open – Copper


Shaft

Core

Rotor bars / End connectors (ADC)

Air duct

Internal fan

External fan

© Siemens 2014. All Rights Reserved.

Industry Sector, DT LD AP

Rotor | Design Basics | TEFC – ADC


Page 9

Stator Construction

Major Classification

Random Wound (Less than 600 volts )

Form Wound (Greater than 600 volts )


Stator Construction

coil-sidecorona shielding

stress grading

mica tapes

strand insulation

overhang bracing

slot wedge

covering tape

main insulation


Page 11

Temperature Rise

Machines with a 1.0 Service Factor at Rated Load

Method of Class

HP V Determination A B F H

HP < V < RESistance 60 80 105 125

HP 1500 V < DETector 70 90 115 140

HP 1500 V 7000 DETector 65 85 110 135

HP > 1500 V > 7000 DETector 60 80 105 125

Machines with a 1.15 Service Factor at Service Factor Load

Method of Class

HP V Determination A B F H

HP < V < RESistance 70 90 115 135

HP 1500 V < DETector 80 100 125 150

HP 1500 V 7000 DETector 75 95 120 145

HP > 1500 V > 7000 DETector 70 90 115 135


Page 12

Temperature Rise – Hot Spot

Allowance for Hot Spots

More accurate temperature

measurements (Ex. RTDs) allow

higher limits (On-line Testing)


Page 13

Monitoring – Accessories - Stator

Location of the temperature

detector is important!

Ideally located in the hot spot,

especially if blind limits are

used.

Thermistors

RTDs

Stator Winding Temperature Protection

Thermocouples

Thermostats


Page 14

Monitoring – Accessories - Stator

Voltage Surge Protection

Surge Capacitors

Current Imbalance Monitoring

Current Differential Protection CTs

Sudden Overvoltage Protection

Lightning Arresters


Deep Groove: Good for

general purpose. Can take

moderate radial & axial loads

Cylindrical Roller: Good for

large radial loads. Cannot

support any axial loading.

Anti-friction (ball or rolling element) bearing basics

Deep Groove

Ball Bearing

Cylindrical

Roller Bearing


Each bearing serves a different function

► Lower: Guide bearing, Deep groove ball

► Upper: Thrust bearing High Thrust (HT)

Two-pole motors limited to 4000# - Deep groove ball

Angular Contact (ACB)

Tandem Angular Contact (TACB)

Spherical Roller (SRB)

Kingsbury (KTB) – plate-style

Speed and amount of thrust determine type of bearing

arrangement and cooling

Continuous design downthrust

Maximum momentary downthrust – 200% continuous

Maximum momentary upthrust – 30% of continuous

Higher thrusts/speeds can require water cooling

Anti-Friction Bearings – Types – Vertical


Page 17

Anti-friction bearing temperature limits

Alarm

Shut

Down API

A/F

Bearings 100 C 105 C N/A

Sleeve

Bearings 90 -

95 C

95 –

100 C 93 C

Cage – Pressed or

machined steel, brass

Rolling Element –

Case-hardened Steel

Inner/Outer Races –

Case-hardened Steel Typical Bearing

Material Limits -

150°C

Conservative

Limits

Larger Bearings, Faster

Speeds = More Heat

Generation

Temperature

Int. Clearance

Thermal

Runaway

Condition


Page 18

Sleeve bearing basics

Sleeve Bearing Types

Basic Sleeve

Bearing Design

Sleeve Bearing Design

500 Frame ODP

Plain Cylindrical Bore

Journal Tilting Pads

Four-Lobe Bore

Two-Lobe Bore

(Lemon Shape)


Page 19

Sleeve bearing temperature limits

TYPICAL BABBITT MATERIAL

ASTM B23, Alloy #2

Increased Sleeve Bearing Temperature =

Decreased Babbitt Yield Strength =

Decreased Bearing Load Capability

Melting Point =

241 °C

Typical

Conservative

Limit

Alarm

Shut

Down API

A/F

Bearings 100 C 105 C N/A

Sleeve

Bearings

90 -

95 C

95 –

100 C 93 C

Q. What are the

material limits of

a typical sleeve

bearing babbitt?

Larger Bearings, Faster Speeds = More Heat Generation

Q. Can my bearing run

hotter than the

manufacturer’s

recommended limits?


Page 20

Monitoring – Bearings - Temperature Detection

Rigid Stem Type

RTD

Embedded RTDs

(Sleeve Bearings

Only)

Dial Type

Thermometer

(Sleeve Bearings

Only)


Page 21

Motor Enclosures – Major Classification

Open Machines

An open motor is one having

ventilation openings which permit

passage of external cooling air over

and around the windings of the

machine

Open Drip Proof (ODP)

Weather Protected I (WPI)

Weather Protected II (WPII)

Totally Enclosed Machines

In a totally enclosed machine, the

external cooling medium is not permitted to

mix with the internal cooling air of the

motor.

Totally Enclosed Fan Cooled (TEFC)

Totally Enclosed Air Over (TEAO)

Totally Enclosed Air to Air Cooled (TEAAC)

Totally Enclosed Water to Air Cooled (TEWAC)

Totally Enclosed Pipe Ventilated (TEPV)

Totally Enclosed Explosion Proof (TEFC) (XP)

Totally Enclosed Force Ventilated (TEFV)


Page 22

Enclosures – Open

1

2 3

1

2

3

Air Inlet:

Three

90°

Bends

Air Outlet:

Three 90°

Bends

ODP/WPI

WPII


Page 23

Enclosures – Totally Enclosed

TEAAC

TEFC

TEWAC TEAO


Page 24

Enclosures – Degree of Protection

Environment dictates a minimum degree of protection.

Over-protection is as good as throwing money out the window.

FRAME

NEMA IEC/NEMA SIZE COST

ODP - Open Drip Proof IP12 SMALL LOW

WPI - Weather Protected Type I IP22 SMALL LOW

WPII - Weather Protected Type II IP24W SMALL MOD.

TEAAC - Totally Enclosed Air to Air Cooled IP 44-IP54 + 20% HIGHER

TEFC - Totally Enclosed Fin Cooled IP 44-IP54 + 30% HIGHER

TEWAC - Totally Enclosed Water-Air Cooled IP 44-IP54 SMALL HIGHER

TEFV - Totally Enclosed Forced Ventilated IP44 SMALL MOD.


Page 25

Monitoring – Accessories - Enclosures

Differential Pressure Switch

Gives indication of the condition of

air filters

Leak Detectors

Gives indication on the integrity

of water coolers


Page 26

Monitoring – Accessories - Enclosure

Strip Style Placed at lowest point of frame

Wraparound Style Placed directly on the end turns

Space Heaters Keeps windings warm to eliminate condensation Energized when motor is off


Page 27

Starting Conditions – Reduced Load Curves

Starting

Condition

Torque at Full

Speed

Pump (centrifugal) Valve Closed 25 - 40%

Fan Dampers Closed 40 - 90%

Compressor

(centrifugal)

Vanes Closed 25 - 60%

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 % Torque

% S

peed

100% 60% 40% 25%

On Screw

Compressors

High Torque Required

at Low Speed, Will

Cause Trouble for a

Standard Motor at

Reduced Voltage

NEMA & IEC

Load Curve

Reduced Load

Curves

Typical Reduced Load Torque Requirements

Load @ Full Speed

Pump Valves Closed 25-40%

(Centrifugal)

Fan Dampers Closed 40-90%

Compressor Vanes Closed 25-60%

(Centrifugal)


Page 28

Starting Conditions – Reduced Voltage Curves

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250

% Torque

% S

pe

ed

Load and Motor

Torque are too Close

(Recommended Margin

10% of Rated Torque)

65 % Voltage

100 % Voltage

50 % Voltage

25% Load Curve Acceleration Time (t)

t = WK2 x RPM

(308 x TA)

TA


Page 29

Starting Conditions

Successful Starting Requires The Following Information

Actual voltage at the motor terminals

Load torque starting curve

Load WK2

Method of Starting

Starting Duty

Note, Motor component heating is proportional

acceleration time (I2R x Time)

Rotor bar

Rotor end connector

Stator winding


Page 30

Starting Duty

Starting can be detrimental to motors!

Obey your starting duty start limits and cooling times!

Motors can be limited by:

Rotor Bars

End Connectors (Shorting Ring)

Stator


Page 31

Starting Duty - Number of starts and Cooling times

Number of starts, coasting to rest between starts:

2 starts with motor initially at ambient temperature (cold)

1 starts with motor at service factor operating temperature (hot)

Cooling period after either of above before making an additional

start:

100 minutes, motor running at service factor load

20 minutes, motor running, equipment unloaded

120 minutes, motor de-energized, coasted to rest and left idle


Page 32

0

50

100

150

200

250

300

350

400

0 2 4 6 8 10 12

Time (Min)

Tem

p (

C)

Starting Duty - Starting Cycle

When the thermal limit of a component is exceeded, damage is being done!

Bar Thermal Limit

Stator Thermal Limit

Ring Thermal Limit


Page 33

Mechanical Unbalance

Motor, Coupling Load

Magnetic Unbalance

(Rotating Magnetic Force

not opposed)

Stationary Magnetic Force

Vibration Stator/Rotor

Mechanical Problems

Looseness, Rubbing,

Bearing Problems

Sources of motor vibration


Vibration Switch Measures Perpendicular Vibration

Standard vendors are Robert Shaw and PMC Beta Accelerometer Measures Vibratory Acceleration

Standard vendor is Bently Nevada Velomitor Measures Vibratory Velocity

Standard vendor is Bently Nevada

Or we can offer Provisions Only

(only includes the Mounting Pad)

Vibration Switch Accelerometer

Velometer

Provisions for Vibration Monitoring “Golf Tee” style

Provisions for Vibration Monitoring “Cube” style

Monitoring – Accessories - Housing Vibration


Page 35

Monitoring – Accessories - Shaft Vibration

Typical shaft

vibration limit for

sleeve bearing

motors: ½ the

diametrical

clearance of the

sleeve bearing

Trip Limits May be

Increased by 10%

Over Alarm Limits

Industry Limits

(mils)


Page 36

Degradation of Bearings

Loosening of Rotor Bars

Coupling Degradation

Changes in Mounting Conditions (Deterioration of Grouted Base, Changes in

Alignment/Soft Foot, etc.)

Accumulation of Debris in the Oil Guards, between Rotor and Stator, etc.,

causing Rubs.

Accumulation of Debris in the Rotor Vents, End Rings or Fans causing

Unbalance.

Plugging up of Rotor Vents causing uneven Heating-Thermal Unbalance.

Vibration May Increase Over Time Due To:


Page 37

Monitoring

A good idea… but how far do you

go?

How critical is the application?

What is the cost of downtime?

How useful is the information?

What is the cost of monitoring?


Page 38

Monitoring

SETTING PROPER MOTOR LIMITS INVOLVES… • Good Motor Performance History • Knowledge of Application and Machine

Motor Limits

Well

-Balan

ced Li

mit Disadvantages

•Unwanted Nuisance Trips

•Unnecessary machine

down-time

•Unnecessary maintenance

Disadvantages

•Premature Equipment Failure

•Expensive Equipment Reworks

•Significant Lost Production

Time


Questions?

Documents

WMEA Conference Papers/ac_induction_motors... · Enclosure, Stator Construction, ... passage of external cooling air over and around the windings of the ... WPII - Weather