Alternator 240504 Ing

AKSA JENERATOR SAN.A.Ş.

Training Departmant

AKSA JENERATOR AKSA JENERATOR SAN.A.Ş.SAN.A.Ş.

Training DepartmantTraining Departmant

ALTERNATOR TRAINING

Prepared By:Mustafa KILIÇ

240505

Mustafa KILIÇ Training Dept.AKSA2

Magnetism And Magnetic InductionAlternating Current, ACFrequency Generator Voltage RegulationsElectric FormulasAlternator types which we useAlternator Parts And Internal Connection DiagramsOperation Principle Of PMG & AREPStarting UpParallel Operation Of AlternatorsMaintenanceDefects And RemediesHandling, Location, Transporting, Storage

Training Programme


What is the energy ?

Energy is the ability to ability to do do workwork.Energy comes in many different forms ; heatheat,,atomicatomic,,mechanical and electricalmechanical and electrical.One form of energy may be changed to another form.In a plant generating electricity, oil is burned to produce heat energyheat energy.The heat is

used to change water into steamchange water into steam.The steam, in turn is used to drive drive a a turbineturbinewhich produces produces a a mechanical energymechanical energy. This mechanical energy drives This mechanical energy drives a a generator generator which converts the mechanical energy to electricitywhich converts the mechanical energy to electricity..

The electricity then The electricity then can be can be transmitted and converted to other energy transmitted and converted to other energy formsforms..


MethodsElectricty can be produced by a variety of methods.

A A common method common method of of producing electricityproducing electricity is through a chemical reactionchemical reaction. A device that produces electricity through a chemical reaction is called a a BatteryBattery.A battery has a major disadvantagemajor disadvantage in that only a a small amountsmall amount of of electricity electricity can be can be producedproduced.Most industries require large amount of electricity. To provide the electricity needed for industries , an an electromagnetic generator electromagnetic generator is is usedused..


Now takeNow take a bara bar magnet and thrust the magnet and thrust the magnet into the coilmagnet into the coil.. The meter will The meter will deflectdeflect..

When a copper wire is moved through a magnetic fieldmagnetic field ormagnetmagnet barbar is movedthrough copper wire, an electric current will flow electric current will flow through the wirethrough the wire. A voltage is inducedinduced by “cutting the cutting the magnetic flux linesmagnetic flux lines””.

(Connect the ends of the coil to a DC milliammeter or galvanometer.)

Magnetism And Magnetic Induction-1


Magnetism And Magnetic Induction-2The Generator consider a magnetic field

that is constant in its intensity. In this fieldis a rotating coil. For simplicityFor simplicity, this diagram on the right shows it as a single-turn loop. The endsThe ends ofof the coil are brought the coil are brought out toout to a a metermeter.

Please note that this meter has red and blue scale sections to show the change inpolarity of the current as the coil rotates.

The coil is rotated in the constant magnetic field by mechanical means (inin practice by practice by water power or by diesel power etcwater power or by diesel power etc.)..).


Magnetism And Magnetic Induction-3When the plane of the loop is verticalvertical between the jaws of this magnet, the loop

elements are moving parallel with the direction of the magnetic field. The loop is notcutting any lines of force. So the meter will read zeroSo the meter will read zero.

When the plane of the loop is horizontalhorizontal, the loop elements will be moving vertical inthe jaws of this magnet, a maximum cutting of the magnetic field. So the meter will So the meter will read maximum currentread maximum current.


Magnetism And Magnetic Induction-4As the loop rotates, the meter will read a current first in one direction, pass through zero, and then

show a current in the other direction, then back to zero - one full cycle.((ItIt isis shownshown herehere by the red and blue readingsby the red and blue readings onon the meterthe meter .).)Consider the angle made by the plane of the loop with any vertical line on the diagram. This

angle is significant. When the plane of the loop is vertical in the diagram, the plane of the loop is at zero degrees with a vertical line. When the planeWhen the plane ofof the loopthe loop isis horizontalhorizontal,, this angle this angle is is 9090 degreesdegrees..

The output current indicatedThe output current indicated onon the meter follows this angle change the meter follows this angle change -- aa sinewavesinewave.


Magnetism And Magnetic Induction-5At 30 degrees, the current will be sin30 = 0.5 of

the maximum, at 45 degrees, the current willbe sin45 = 0.707 of the maximum, at 60degrees, 0.866, and so on.

The frequency of the wave is related to the revolutions, one revolution produces one cycle. One cycle in one second is a 1 Hzsignal.

The 50 Hz mains supply can be produced by mechanical means, and examples are inevery powerhouse supplying the national grid. Fifty cycles in one second (50 Hz) is 3000 revolutions in each minute.(2 pole)

Multi-polar machines are used in practice witha slower rotation speed.


Alternating Current, AC

Most generators produce voltages and current in the form of alternating current (AC). There are two reasons for this ;

AC is cheaper to produce and distributeAC is more versatile than DC

Alternating current, AC, which is used for mains supply in most countries,just as Turkey.(220V-50Hz)


Alternating Current, AC RMS - 1 In many countries, the ACmains is about 220V, but this this voltage cannotvoltage cannot bebemeasuredmeasured asas simplysimply as DCas DC.In fact, a '220V AC supply rises to approximately 310 V at the peak of its oscillation. Furthermore, since the voltage rises to apeak in the opposite direction alternately ( +310V and -310V ) its average value is 0V.The form of AC described right side is called single phase

RMS Voltage (220V)

Actual Voltage (310V)


Alternating Current, AC RMS – 2 The effective average voltage produced by a generator is that which would be produced by applying the same driving power to a DC generatorof the same size. It can be found by the simple mathematical procedure of squaring the peak value - since the square of anegative number is a positive number,this produces an all positive result (green linegreen line ). This valueThis value isis knownknown asas thethe RMSRMSvalue andvalue and isis whatwhat aa voltmeter readsvoltmeter readswhen measuring mains voltagewhen measuring mains voltage. . Don't get confused, the actual electricity is the sine wave purple line,the 220V AC RMS value is not a DCvalue!

RMS Voltage

Actual Voltage

∫=T

RMS tdtVT

V0

2 )()(1


Three Phase SupplyThe generators supply what is knownas three phase electricity. This is a way of supplying three timesthree timesasas muchmuch electricity along three wires as can be supplied through two, without having to increase the thickness of the wires. Three phase electricityThree phase electricity isis usually usually usedused inin industry to drive motors and industry to drive motors and other devicesother devices..Generators have three coilsthree coils equally spaced around the rotating EXTERNALmagnetic field, and each of theseproduces a 50 Hz Ac supply which istransmitted to a separate wire.

1 3

2


Advantages of AC over DCThe advantages of AC rather than DC power supply isthat the voltage can be stepped up or down using atransformer, which have no moving parts and hence are extremely efficient. This proves to be essential for power distribution systems....Also, AC electric motors are generally more efficient and more reliable than similar DC motors


Three Phase Alternator-1

The three-phase alternator, as the name implies, has three single-phase windings spaced such that the voltage inducedin any one phase is displaced by 120° from the other two.


Three Phase Alternator- 2The voltage waveforms generated

across each phase are drawn on agraph, phase-displaced 120° from each other.

The three-phase alternator asas shownshowninin this schematicthis schematic is made up ofthree single-phase alternators whose generated voltages are outof phase by 120°.

The three phases are independentof each other.

* The rotor is omitted for simplicity.


Three Phase AlternatorsWye (Y) Connected

Rather than having six leads coming outsix leads coming out ofof the threethe three--phase alternatorphase alternator, the same leads from each phase may be connected together to form a wye (Y)connection. It is called a wye connection because,without the neutral, the windings appear as the letterY, in this case sideways or upside down.

The neutral connection is brought out to a terminal when asingle-phase load must be supplied.

Single-phase voltage is available from neutral to A,neutral to B, and neutral to C.

In a three-phase, Y-connected alternator, the total voltage,or line voltage, across any two of the three line leads isthe vector sum of the individual phase voltages. Each line voltage is 1.73 times one of the phase voltages. Because the windings form only one path for current flow between phases, the line and phase currents are the same (equal).

Nfff VV −− ×= 3

2203 ×=− ffV

VV ff 380=−


Three Phase AlternatorsDelta ( ) ConnectedA three-phase stator can also be connected

so that the phases are connected end-to-end; it is now delta connected . (Deltabecause it looks like the Greek letterdelta)

In the delta connection, line voltages are equal to phase voltages, but each line current is equal to 1.73 times the phase current.

Both the wye and the delta connections are used in alternators.

Three phase alternators are much more efficient than either two-phase or single-phase alternators.

NLff II −− ×= 3


Rotating Armature-Alternators

The rotating armature-alternator is essentially aloop rotating through astationary magnetic stationary magnetic fieldfield cutting actionaction ofofthe loopthe loop through the magnetic field generates ac in the loop.

This ac is removed from the loop by means of slip rings and applied to an external load.

Old type alternatorsOld type alternators....


Rotating - Field Alternators*

The rotating-field alternator has astationary armature and arotating field. High voltagescan be generated in the armature and applied to the load directly, without the without the needneed ofof slip rings and slip rings and brushesbrushes.

The low dc voltage is applied to the rotor field by means of slip rings, but this does notintroduce any insulation problems.

Exciter Voltage Brushes


Brushless GeneratorsA A major major problem problem associated associated with generators that use slip with generators that use slip ring ring and brushes and brushes is is that the that the brushes wear outbrushes wear out.A brushless generator overcomes this problem by replacing the slip rings and brushes with a small generator on one end of the rotor shaft. This small This small generator generator is is called called ananEXCITEREXCITER.The exciter uses to produce The exciter uses to produce the the DC DC voltage necessary for voltage necessary for the the rotorrotor.

Exciter


The Importance Of SpeedFrequency and voltage depend directly on rotational speed.This must be kept as as constant constant asas possible on its nominal value no matter what the loadDrive-motor speed control system generally have a small drop in speed between no-load and loaded conditionsWe therefore recommend setting no-load speed 33--4% 4% aboveabove nominal speed (52 (52 HzHz)) at engines which has got mechanical govarnors systems.


Frequency-1The output frequency of alternator voltage

depends upon the speed of rotation of therotor and the number of poles.

• The faster the speed, the higher the frequency.

• The lower the speed, the lower the frequency.• The more poles there are on the rotor, the

higher the frequency is for a given speed.When a rotor has rotated through an angle such

that two adjacent rotor poles (a north and asouth pole) have passed one winding, the voltage induced in that winding will have varied through one complete cycle.

For a given frequency, the more pairs of poles there are, the lower the speed of rotation.


Frequency-2A A twotwo--pole generator must pole generator must

rotaterotate atat four times the speedfour times the speedof anof an eighteight--pole generator to pole generator to produce the same frequencyproduce the same frequencyofof generated voltagegenerated voltage. .

The frequencyThe frequency ofof any ac any ac generatorgenerator in hertz (in hertz (HzHz),),whichwhich isis the numberthe number ofof cycles cycles per secondper second, is, is related to the related to the numbernumber ofof poles and the poles and the speedspeed ofof rotationrotation, as, asexpressed by the equationexpressed by the equation

8 Pole 2 Pole


SINGLE-BEARING GENERATORSMost small generators are the single-bearing type.Single-bearing generators carry half of the generatorrotor weight, rotating unbalance, and electrical force onthe generator bearing and the other half is carried by the engine’s rear crankshaft bearing. A flex plate attaches to the engine flywheel and the generator rotorinput shaft. Single-bearing generators ;

are generally compact and lighter than two-bearing generatorsare well suited for portable generators or installations with asub-base.

A single bearing generator frame must be stiff enough to hold theengine and generator in alignment and carry the weight of therotor on the rear bearing.


TWO-BEARING GENERATORS

Two-bearing generators carry the full weight of therotor with the front and rear generator bearings. A torsional coupling is used to join the crankshaft to the rotor input shaft. Two-bearing generators are longer and more costlythan single-bearing generators and are typically used inlarge generator sets on solid foundations. In a two-bearing generator set, the engine can be removed without disturbing the generator.


Generator Voltage Regulation-1InIn anan alternatoralternator, an , an alternating voltagealternating voltage isis inducedinduced inin the the

armature windings when magnetic fieldsarmature windings when magnetic fields ofof alternating alternating polarity are passed across these windingspolarity are passed across these windings..

The amount of voltage induced in the windings depends mainly on three things:•• The numberThe number ofof conductorsconductors inin series per windingseries per winding, , •• The speedThe speed ((alternator rpmalternator rpm) at) at which the magnetic which the magnetic

field cuts the windingfield cuts the winding,,•• The strengthThe strength ofof the magnetic fieldthe magnetic field. .

Any of these three factors could be used to control the amount of voltage induced in the alternator windings.


Generator Voltage Regulation-21. The number of windings, of course, is fixed when the

alternator is manufactured.2.2. AlsoAlso,, if the output frequencyif the output frequency isis required torequired to be of abe of a constant constant

valuevalue,, then the speedthen the speed ofof the rotating field mustthe rotating field must bebe held held constantconstant.. This prevents the useThis prevents the use ofof the alternator rpmthe alternator rpm as aas ameansmeans ofof controlling the voltage outputcontrolling the voltage output..

3. Thus, the only practical method for obtaining voltage the only practical method for obtaining voltage controlcontrol is control the strengthcontrol the strength ofof the rotating magnetic fieldthe rotating magnetic field.The strength of this electromagnetic field may be varied by changing the amount of current flowing through the field coil.This is accomplished by varying the amount of voltage applied across the field coil..


Generator Voltage Regulation-3When the load on a generator is changed, the terminal voltage varies. The

amount of variation depends on the design of the generator.The voltage regulation of an alternator is the change of voltage from full load to

no load, expressed as a percentage of full-load volts, when the speed and dc field current are held constant.

• Assume the no-load voltage of analternator is 250 volts and the full-load voltage is 220 volts. The percent of regulation is

• Remember, the lower the percent of regulation, the better it is in most applications.


Generator Voltage Regulation-4Since the output voltage of an AC generator varies considerably with changes in load, some method must be employed to keep the terminal voltage at a constant level. On most generators, an auxiliary control device called a Voltage Regulator is used to maintain a constant voltage output. If the output voltage drops due to a load increase, the voltage regulator will automatically increase the DC voltage to the rotor so that the output voltage will be restored to its original value.If the output voltage tries to increase, the voltage regulator will decrease the voltage to the rotor and again restore the output to its original value.The rotor’s field is controlled indirectly by varying the voltage to the exciter’s field. Less current need be handled by the regulator in the exciter field than in the main generator field.


Generator Voltage Regulation-5The input to the regulator is connected to T7-T9 and the output of the

regulator in turn is connected to the exciter field assembly.When the output voltage decreases, the regulator will sense the drop and

increase the voltage to the exciter field which causes more voltage to be induced into the armature.

The increased voltage is rectified and applied to the rotor windings. Since the rotor now has a larger voltage applied to it, a greater voltage is induced into

the stator and the output voltage is increased to its original value.


Voltage Regulator Types which we use

Mecc AlteSR 7 UVR 6

StamfordSX 460 SX 440 SX 421 SA 465

S : Self excited

MX 341 MX 321 MA 325M: Permanent Magnet Generator

MarathonDVR 2000


GENERATOR EXCITATION SYSTEMS

The generators excitation system plays an important role to ensure trouble free operation when used to power non linear loads. There are three types of excitation systems mainly used on generators; ‘transformer controlled’, ‘self excited’ and ‘separately excited’ as shown in figures.


Transformer ControlledThe output current passes through the primary of a Current Transformer. The output of the Current Transformer’s secondary winding is rectified and supplied to the field winding.The transformer is designed to provide the generators required no-load output voltage by using the Current Transformer’s secondary winding as a choke.As load is applied to the generator the Current Transformer’s secondary winding produces increased excitation voltage, ensuring the stated voltage regulation is maintained. No electronics are used within this open loop control system making it suitable for use with small non linear loads.

N

S

Case

Laminatedsteel stator

Windings

Fan

Bearing

Shaft for rotationalpower input

Wound rotor

Electrical power output

NN

S

Exciter fieldRotatingrectifier

Exciter rotor

Transformercontrol

Transformer excited (TX) or series 5

Voltage Regulation to +/- 5%

*For Stamford Alternators


Circuit Diagram Of Transformer Regulated Generators


Self Excited

The power source for the AVR is taken directly from the generator output terminals and therefore if there is any disturbance in the generator output voltage, the thyristor in the AVR may interact with the load controlled thyristorsresulting in voltage instability. This type of system is not This type of system is not recommended for use with recommended for use with non linear loads.non linear loads.

N

S

Case


Windings

Fan

Bearing


Wound rotor


NN

S


Exciter rotor

AVR

Self excited (SX) or Series 4


Exciter Construction And OperationThe exciter consists of an armature,field assembly and rectifier assembly.The field assembly is cylindrical in shape and provides a statioanry magnetic field.The armature is located on one end of the main rotor shaft and provides the windings needed for magnetic induction.A three phase voltage is induced into the armature when it is rotated in the flux line created by the field assembly.TheThe three phase three phase AC AC voltage voltage is is converted toconverted to a DC a DC voltage by the voltage by the rectifier assemblyrectifier assembly..

Exciter


EXCITATION SYSTEM : SHUNT

ADVANTAGES DISADVANTAGES

POWER AND SENSING FROMALTERNATOR OUTPUT


Separately Excited (AREP –PMG)The power to the AVR is supplied via a Permanent Magnet Generator mounted outboard of the non drive end bearing, driven by the rotor shaft. This isolates the AVR power supply from the generator output waveform and therefore provides constant undisturbed excitation power regardless of the load condition. The only part of the AVR that is subject to the voltage distortion is the sensing circuit. To maintain close voltage regulation a sensing circuit incorporating an RMS comparitorcircuit is recommended.

PMG Excited (MX) or series 3

N

S

Case


Windings

Fan

Bearing


Wound rotor


NN

S


Exciter rotor

AVR

N

SPMG rotor

PMG stator

Stamford alternators which are HC6-7 series,are fitted with the PMG system.

Permanent Magnet Generator (PMG) Excited– AVR Controlled Generators


EXCITATION SYSTEM : AREP



EXCITATION SYSTEM : PMG



PMG Benefits-1Provides a separate fixed source impedence power to AVR & exciter field that is isolated from the generator output and is not influenced by external load conditions.AVR is fully protected against voltage transients caused by load switching devices and by thyristor loads.Provides positive voltage build up against all load conditions.The isolated PMG power supply of the excitation system allows the generator to meet low EMI / RFI suppression levels to meet MIL-STD.461C&VDE Class KPMG provides a good frequency referance for detecting overspeed and to operate starter motor control circuits during engine run-up.Isolated PMG power circuit simplifies the AVR & improves reliability by eliminating the need for ;

Separate build up componentsEMI suppression componentsTransient voltage protection components


PMG provides constant power to supply manual voltage control of the generator & to supply overvoltage , overcurrent & over excitation protection circuits.Provides full field forcing for good motor starting and is not influenced by the generator voltage dip during transient load applications.Provides excitation power to sustain short circuit current for fault clearance / discrimination under all line-line and line-neutral faults.

PMG Benefits-2

SUSTAINEDVOLTAGE (V)

LOAD %300%100% 200%

SUSTAINEDVOLTAGE DIP

U N

LOW OVERLOAD HIGH OVERLOAD - SHORT CIRCUIT

SHUNT

AREP

SHUNT

AREP

PMG


AREP OR PMGTHE ALTERNATOR CONTROLS THE SITUATION

DURING 10 SECONDSTHE DEFFECT IS RELEASED

THE BREAKER TRIPS

- THE POWER SUPPLY IS MAINTAINED

SHUNT or AREP or PMG ?

OVERLOAD OR SHORT CIRCUITON THE INSTALLATION

SITUATION

SHUNTTHE ALTERNATOR DOES NOT HOLD

THE SITUATIONDESENERGIZING OF THE ALTERNATOR

- THE POWER SUPPLY IS CUTTEN

AREP

SHUNT

PMG


COMPARE CHART OF EXCITATION SYSTEMS

SHUNT + PMG AREP SHUNT

ADVANTAGES

DISADVANTAGES

High startingcapacity

Short-circuitcapability

High startingcapacity

Short-circuitcapability

Self protectedagainst short circuit

Extralength

High numberof components

Low startingcapacity

No short- circuitcapability

Sensitive to distorting loads if thyristor controlled

Intrinsic build-up No extra length No extra length

Added cost

Small added cost

Specific winding

High startingcapacity ( LS version)


SHUNT or AREP or PMG ?

AREP / PMG ADVANTAGES COMPARED WITH SHUNT- THE SHORT CIRCUIT CAPABILITY THAT ENABLES A SELECTIVE PROTECTION

IN CASE OF OVERLOAD OR SHORT CIRCUIT ON AN INSTALLATION

WHEN TO CHOOSE AREP OR PMG ?- WHOLE INSTALLATION WITH SEVERAL CIRCUITS - POWER CUT FORBIDDEN- HIGH RATE OF DISTORTING LOADS.- STARTING OF A BIG MOTORMARINE, HOSPITALS, STAND-BY DUTY, STANDARDS IN SOME COUNTRIES.- AREP MINIMUM LENGTH REQUIRED-PMG EXISTING SHUNT MACHINE TO BE UPGRADED

WHEN TO CHOOSE SHUNT ?- SINGLE CIRCUIT INSTALLATION- POWER CUT ACCEPTABLE- SELF PROTECTION OF THE ALTERNATOR.


SHUNT

EXCITATION SYSTEMSCompetitors Competitors CComparisonomparison

Leroy-Somer Newage Marathon

10

20

50

100

200

500

1000

2000

10

20

50

100

200

500

1000

2000

SHUNT

AREPSHUNT

AREP

AREP

SHUNT

SHUNT

SHUNT

SHUNT+

PMG

SHUNT

SHUNT

SHUNT+

PMG

BC Range

UC Range

HC Range

HC Range

MAGNA +

MAGNA +

MAGNA MAX

PARTNER RangekW kW

Built in short-circuit capacity

Optional short-circuit capacity

Short-circuit capacity not available

BC Range


Voltage Unbalance


Transient Performance Of Alternators-1

When a load is suddenly applied to an ac generator the voltage will fall instantaneously to a level dependent upon the

amount of load applied.The AVR will monitor this voltage dip and increase excitation

to restore voltage level to nearly the original value, within a fraction of a second.

Similarly on load removal, there is a voltage overshoot and the AVR reacts reducing the excitation.


Transient Performance OfAlternators-2

The diagram illustrates the factors involved during load application and removal.


Transient Performance OfAlternators-3Transient Performance OfAlternators-3

Transient Voltage DipThe amount of transient voltage decrease due to the sudden application of a specified load usually expressed as a percentage of the original voltage level.

Recovery TimeThe length of time taken for the voltage level to recover to within 3% of the original value.

Transient Voltage OvershootThe amount of transient voltage increase due to the sudden removel of a specified load usually expressed as a percentage of the original voltage level.

Steady Stage RegulationA measure of the maximum permitted steady voltage changes over a wide variety of machine conditions (includes machine hot to cold variations : no load to full load applied, power factor 1.0 to 0.8 lag)


Transient Performance OfAlternators-4In certain applications, a voltage dip better than our standart may be required. ( for example 10% voltage dip on application of full load.)The most effective way of achieving, this is provide a a biggerbigger AC generator.


Alternators which we useStamford / England

Marathon / U.S.A.

Leroy-Somer / France

Mecc-Alte Spa / Italy

Sincro / Italy


Identification Of Leroy Somer AlternatorsThe alternator is identified by means of a nameplate the frame. The

machine name is defined according to various criteria Example ofdescription for :

LSA 37 M5 J1/4

• LSA : Leroy Somer Alternator

M : Marine / C : Cogeneration / T : Telecommunications.

• 37 : machine type

• M5 : model

• J : field excitation system

(J : SHUNT)

• 1/4 : winding number / number of poles.


Identification Of Stamford Alternators


Alternator Parts-1Mecc-Alte MR1 160/2 , J609b

1. Grid

2. Terminal box LID

5. Terminal board

8. Frame and stator

9. Drive end bracket

14. Rotor assy

15. Fan

17. Front bearing

19. Rear bearing

26. Diode

27. Varistor

29. Securing stud

39. Protection screen

40. Fixing ring

65. Capacitor

75. Rubber cup

107.Grid rubber cap


Internal Connection Diagram-1


Alternator Parts-2Mecc Alte ECO 37

NAME1 real seal

2 casing

3 grid

5 users terminal board

7 rear cover

8 frame with stator

9 front cover

9A front cover MD 35

10 exciting stator

11 rotating diode bridge

12 hub

13 exciting armature

14 rotor

15 fan

16 exterior flange bearing cover

17 drive-end bearing

18 interior flange bearing cover

19 rear bearing

20 terminal box

22 diode holder washer

NAME23 electronic regulator

24 auxiliary terminal board

28 cover stay bolt

39 protection screen

40 fixing ring

42 parallel device

59 coupling hub

60 disc plates

70 radio disturbs suppressor

94 rear case

95 termin.brd.side panel

96 termin.brd.front panel

97 termin.brd.rear panel

98 regulator carrying panel

99 disc blocking ring spacer

104 component-carryng panel

123 ring spacer

143 exciter stay bolt


Internal Connection Diagram-2


Stator Winding And Terminal Box


Rotor ConstructionRotor Construction in

alternators may beeither of two types.

1. The salient-polerotor is used inslower speed alternators.

2. The turbine driven-type is wound in amanner to allow high-speed use without flying apart.


Varistors (VDR’s)Varistors (VDR’s) are a mix of carbon materials that are a high resistanceuntil subjected to a high pressure[Voltage].They then becomes a low resistance path to bleed away excessive pressureby allowing lots of amps to momentarily flow through the VDR,which has become a momentary low resistance path. This means that the rating of thedevice based on it only being asked to conduct for VERY short period oftime and VERY intermittently. A VDR that is continually 'clipping‘excessive voltages will get hot and fail.


Varistors (VDR’s) - 2So a VDR is carefully chosen to protect the diodes from being subjectedfrom a damaging level of Peak Inverse Voltage [PIV], which would otherwisebreakdown the diodes P-N junction, and so make it a non-rectifying shortcircuit.A load related situation that causes a transient over current, or over voltage situation within the stator winding will by mutualinductance generate a high voltage transient in the rotor winding,which the VDR will attempt to eradicate by 'clipping', and so safeguard the rotating diodes from a damaging level of PIV.The additional mechanism that will compound the above-described situation is when there is a sudden change of rotor angular position relative to thestator.This could be due to a large load step change, resulting in a large rotorpositional load angle change.But the most common situation for this scenario is a sudden rotor positionalchange resulting from a generator being paralleled at a phase angle greaterthe recommended the displacement [ absolute max is +/- 10 electrical degrees]


Varistors (VDR’s) - 3So when Newage specify a VDR that will offer the required protection for a rotating diode assembly the decision process takes into account the Clamping Voltage, Voltage - Current curves, Maximum Energy rating, and Power Dissipation, and then most importantly Mechanical construction for its life on a spinning assembly. The VDR energy absorption required on HC6 &7 requires a matched pair of VDR's to be fitted to help with rotating diode assembly centrifugal stresses and rotor balance considerations.Note : It's imperative that if one VDR of a matched pair fails both arechanged for another matched pair, and in storage matched pairs are never separated.The VDR's used on the HC range are Z500PS single's on HC4&5,and same device but matched pairs on HC6&7, each device has amax energy of 420J, and a clamp V of 1420V @ 100A.As the HC6 &7 machines have two such devices in parallel the energy rating is doubled. The 1mA voltage is 800V.


Varistors (VDR’s) - 4Basic Fact....If a gen's VDR's are 'blowing' that gen is being subject to astressful, life-shortening, mode of operation, which may be the result ofpoorly commissioned equipment, or badly trained operators.Under a pole-slip, the relative sudden angular change between rotor andstator will cause massive changes to the gen's internal E. Therefore largechanges to stator current levels, and the cumulative effect of both statorampere turns. The pole slip angular change will induce into the rotor winding a high voltage. This will promote VDR clipping...it's then the duration of the clipping, driven by the duration of the most undesirable pole slipping, that decide the ability of the VDR to survive or become sacrificial with duty role.We don't want a generator to be subjected to pole slipping, and neither does the genset operator.If it happens it's negligence on the part of the operator, or gensets control system, and to offer generators fitted with VDR's rated for such extreme conditions would not be practicable.


Varistors (VDR’s) - 5Under fault conditions - overload - short circuit - the stator current ampere turns, and rapid air gap flux changes inthe time zero Sub-transient time zone would no doubt cause the VDR to become active.From experience a single short circuit applied to agenerator will not in itself cause the VDR to fail.But subject the gen to a sequence of overloads/faultssimulating a very poorly designed cascading protection system, or a micro-interruption when in parallel with amains supply, and then the VDR self-destruct.


Radio Frequency Interference - RFI

fCXc

π21

=


Over Temperature Protection Devices

Bi-metal Contact

PTC Thermistor

PT 100 Thermal Resistors


Parallel Device


Temperature Performance Of Alternators -1

Losses in the copper windings are due to the flow of load current througt the winding and the winding having electrical resistance.Those losses create heat and hence cause the winding and insulation temperature to increase, which in turn means that the winding resistance will also increase.If excessive loads are applied, the insulation temperature may increase beyond the temperature class normally specified, as in the case of standby duty rating.Continuously applied highly excessive loads will quickly lead to a winding burn out.


Temperature Performance Of Alternators -2

A.C. Generators are designed and insulated to operate on full load within maximum permitted temperature.It is the quantity of active material in the machine (lamination steel and copper) that primarily affects the temperature at which the machine operates when on a specific load.The insulation system must retain its properties over The insulation system must retain its properties over this operating temperature range for the lifetime this operating temperature range for the lifetime of of the machinethe machine..


Temperature Performance OfAlternators -3

Insulation materials are assessed on their ability to retain their insulation properties up to a maximum specified temperature for a specified lifetime.A usually accepted insulation lifetime is 100.000 hours of continuous operation at the maximum permitted temperature specified.

Insulation Class Insulation Class Of Of MaterialMaterial A E A E B F B F HHMaximum permissible temperature rise (°C) based on an ambient temperature of 40°C and the standart lifetime period.

60 75 80 105 125

(simplified from BS 4999 Part 32)


Insulation Material Life

B sınıfı izalasyon tahmini ömrü

65

85

105

125

145

165

0.57 1.21 2.25 4.25 8 15 29.2 42.5

yıl

sıca

klık

(°C)

A Class izolasyonlu bir makina 40 °C ortam sıcaklığında 40 °C sıcaklık artışında, en yüksek ısınan noktası; 40 + 40 + 15 = 95 °C olur. 95 °C sıcaklıkta tahmini ömür ortalama 29.2 yıldır. 10 °C sıcaklık artışında yukarıdaki ömür eğrisine göre ortalama ömrü 15 yıla düşmektedir.


AltitudeUp to 1000 m (3300 ft) above sea level, the change in air density is insufficient to radically alter the thermal transfer properties of the air.Above 1000 m the effectiveness of the air is reduced sufficiently to make de-rating necessary.Standarts are agreed that to avoid overheating due to this reduction in coolant effectiveness, machines operating at high altitudes must be de-rated.Unlike ambient temperature, the converse is not permitted. No greater output is allowed from a machine operating at sea level to one operating at 1000 m above sea level.

Altitude (m) Multiplier1500 0,972000 0,942500 0,913000 0,883500 0,854000 0,82 (For stamford alternators)


HumidityHumidity is a measure of the moisture content of the air in which a machine is situated.It is normally measured as “relative humidity” (rh) where 100% rh is air fully moisture saturated. (i.e. The point at which condensation occurs) and 0% rh is air absolutely dry.For successful operation in the high humidity levels found in tropical regions, machines are said to be “tropicalised”. This involves correct choice of the insulation materials and careful assessment of the impregnation varnish system and methods. (Anti-condensation heaters can be used)


Performance Of Mecc-Alte Alternators


Climate And EnvironmentAtmospheric contaminants such as gases and various chemicalsSalt water (sea) sprayDust or sand laden atmospheresSolar radiation and windRainfall and icing

Certain accessories Certain accessories can be can be added to the generator to provide added to the generator to provide adequate protection against particularadequate protection against particular problem problem climates and climates and environmentsenvironments..

Anti-Condensation heatersDrip-Proof LouvresAir Filters


Anti-Condensation Heaters-1Condensation occurs due to the change of water vapour into liquid.The point at which this change occurs is dependent upon actual water vapour pressure and particularly upon temperature.Consider Consider a a hot machine shut down hot machine shut down at at the the end end of a of a day shiftday shift..During the night the ambient temperature During the night the ambient temperature can can reduce quickly reduce quickly but but the machine surface the machine surface temperature will reduce much more slowlytemperature will reduce much more slowly..At At dawn the ambient temperature may rise dawn the ambient temperature may rise quicklyquickly, , probably to probably to a a level greater than the level greater than the machine surface temperature which will machine surface temperature which will begin to rise towads ambient temperature begin to rise towads ambient temperature only slowlyonly slowly..


Anti-Condensation Heaters-2Depending upon the actual water vapour pressure present in the local atmosphere, condensation may occur in the machine at any time after the ambient temperature exceeds the machine surface temperature.If the water vapour pressure is near or at saturation then condensation will occur during the rapid rise of ambient temprature at dawn.Condensation or dew will form on all surfaces which are cooler than ambient temperature.To avoid this, anti condensation heaters can be fitted which will ensure the winding temperature remains a few degrees above the ambient temperature and hence no condensation will form.Note thatNote that, , thethe antianti--condensation condensation heaters should heaters should be on be on only when the only when the set is set is offoff, , and they should and they should be be switched off whilst the switched off whilst the set is in set is in useuse. . They can be fitted to a machine at any time.


Protection Class IPIP (IIngress PProtection)The International Protection code, sometimes called the Ingress

Protection code, classifies the protection given by an enclosureagainst the touching of live parts, contact with moving parts and protection against the ingress of solid bodies.

It additionally specifies protection against the harmful ingress of liquids. Two (Sometimes 3) digits are used to describe its protection rating, called the IP code.

IP XXX*First number : Protection against foreign substances & contactSecond number : Protection against waterThird number : Stroke resistance(* =according to French norms)


Symbols Of IP Protection

http://www.interpower.com/scripts/wsisa.dll/WService=panel-pcc/p65list2.p?w_country=Europe

http://www.interpower.com/scripts/wsisa.dll/WService=panel-pcc/p65list2.p?w_country=Australia





Air FiltersSome site condintions are such that the air may be heavily laden with a very fine dust or sand, to an extend where the air passages become blocked.If moisture is also present then the dust may become saturated and so accelerate the insulation breakdown.Under these conditions we strongly recommend the fitting of inlet air filters.The sizing of these is important to avoid airflow restrictions and advice should be sought from the factory or the machine purchased complete with the necessary air filters.


Drip-Proof LouvresThe standart machine is drip-proof,

vertical drips of water cannot enter the machine.

Should the machine be used on uneven terrain then protection against water drops up to 60°C from the vertical can be provided by fitting drip-proof louvres.

These louvres can be fitted at any time.A deration of the generator output

(normally 5%) may be necessary.Our alternators standart which is

protection against water drops is IP 21-23

IP chart


Generator Ratings - kVAGenerator ratings are dependent on

the amount of current they are capable of providing at full output voltage; this rating is expressed asthe product of the voltage times the current.

A 10A 10--voltvolt alternator capablealternator capable ofofsupplyingsupplying 1010 amperesamperes ofof current current wouldwould bebe ratedrated at 100 voltat 100 volt--amperesamperes.

Larger alternators are rated in kilovolt-amperes. (kVA)


Electrical ComponentsResistors

Conductors&Wires are material that has a low resistanceInsulator are materials that have few free electrons so that their resistance is very high. Some common insulators are glass, rubber and ceramics.

Inductors are coil of wire that opposes a change in current. Inductors are used in motors to create magnetic fields needed for rotation.Capacitors consist of two metal plates separated by an insulator.A capacitor opposes a change in voltage.


DC PowerPower is the rate at which electrical energy is delivered to or used by an electrical device or circuit. The unit of electrical power is the WATT (W).The power used by an electrical component or circuit is equal to the voltage times the current.

P = V x IP : Power in wattsV : Voltage in voltsI : Current in amperes


P : True Power ( Watt)Inductance and resistance characteristics are both present in

industrial motors which consist of many coils of wire.The coils cause current to lag voltage as in an inductor and

because of coil length, the motor also has resistance.AC generator is used to provide power to a motor. The resistor is

the only component that comsumes power.The power used by a resistor is called True Power.True power is measured in watts and can be calculated by the

formula ;

(Watt) 2

2

RVRIIVP

RIV

=×=×=

×=


S : Apparent Power ( VA)The inductor does not use any true power. However, to the generator, the inductor “appears” to be consuming power because there is an opposition to current (inductive reactance) and voltage drop across it.To the generator, power is apparently used by the inductor.The total power used by the inductor and resistor is called appropriately. Apparent Power.Apparent power is measured in Volt-Amperes (VA) to distinguish it from true power.Apparent power for an inductive circuit can be found by multiplying the total current by the applied voltage;

Amperes)-(Volt tA IVS ×=


Power FactorThe efficiency of an inductive circuit is dependent on the ratio of true power to apparent power.The ratio of true power to apparent power is called the “Power Factor (PF)”. The PF can be determined by the ;

P (W)

Q (VAr)

S (VA)

ϕSPCosPF == ϕ


IVSCosIVP

tCostCosIVtPtCosItItCosVtV

mm

m

m

×=××=

−×××=−×=

×=

ϕϕωω

ϕωω

)()()()()(

)()(

AC Power

•V(t) : Instantaneous voltage (Vm=Vpeak)

•I(t) : Instantaneous current (Im=Ipeak)

•P(t) : Instantaneous power (watt)

•V : Vrms

•I : I rms

•P :Real power

• : Phase angle between voltage and current

Recall that rms (root mean square) values are the “effective” values of voltage and current that AC voltmeter and ammeters measure.

ϕ


Electric Formulas

Single Phase Circuits

Three Phase Circuits

VAr Watt

VA

ϕϕ

SinIVQCosIVP

IVS

××=××=

×=

VAr 3

Watt3

VA 3

ϕ

ϕ

SinIUQ

CosIUP

IUS

ff

ff

×××=

×××=

××=

−

−

ff −

P (W)

Q (VAr)

S (VA)

ϕ


Example-1

We will calculate full load current for 5 kVA Gen-Set at the CosØ=0,8 and CosØ=1.

P (kW)

Q (kVAr)S (

kVA)

ϕ ϕCosSPIVS

S

×=×=

= kVA5


Example-2Firstly we should calculate the active power output of Gen-Set.So..

Now..We can calculate full load current..

kW48,05 =⇒×=⇒×= PPCosSP ϕ

Amper 27,218,0235

4000

; 8,0

=⇒×

=⇒×

=

××==

IICosVPI

CosIVPCosFor

ϕ

ϕϕ


Example-3

Amper 02,171235

4000

; 1 ..kW 4

=⇒×

=⇒×

=

××==

=

IICosVPI

CosIVPCosFor

P

ϕ

ϕϕ


Starting And Stopping OperationsIMPORTANT :

When the system is set to work for the first time, whichhas to be done at a reduced speed, the operator shall check that no anomalous noises can be detected. If ananomalous noise is detected, stop the system immediately and improve the mechanical coupling.

THE STARTING, RUNNING AND STOPPING OPERATIONS MUST BE CARRIED OUT BY SKILLED PERSON-NEL WHO HAVE READ AND UNDER-STOOD THE SAFETY INSTRUCTIONS AT THE BEGINNING OF THIS MANUAL.


Starting Up - Electrical ChecksInspect also

that the machine to power supply interconnection is made according to the drawing. Make sure before start that terminal nuts are properly tightened.that the terminal links correspond to diagramthat the control panel protection equipment is correctly setfor separately fitted regulator, that the connections between alternator and panel correspond to wiring diagram,that there is no short-circvuit due to fautly connections either LL. or L.Nbetween the terminals of the alternator and the power switch or breaker(this part of the circuit is not protected by the breaker)


Starting Up - Mechanical ChecksBefore starting up

check that all foot and flange bolts are tightenedmake sure that the cooling air circulates freely around and

through the machine,check that all louvres, guards, etc .... are correctly fittedfor single bearing alternators the discs are fastened to the

coupling hub with boltsfor two bearing alternators that coupling is correct also.


Windings ConnectionTo reconnect from a star to delta connection (for ex. from 400V to230V), modify the linking arrangements on the output terminal board.It is not necessary to adjust the voltage regulator.The alternator must always be earthed by sufficiently rated cable, using oneof the inside or outside terminals.After completing output connections ensure that the terminal box cover is securely in place.


Measurement of resistance of stator windings

STATORUnscrew the top coverDisconnect capacitors leads in order to read auxiliary winding resistanceDisconnect leads fromterminal plate in order to read main winding resistances.


Measurement of resistance of various windings

Unscrew the top coverRemove the bracketUnsolder diode leads in order to read resistances of each winding


Checking The Diodes


Checking The Capacitors

Unscrew top coverDisconnect capacitor(s) leads and connect capacitor (s) to a 220/240 V mains witha switch and aammeter to read the current

Unscrew top coverDisconnect capacitor(s) leads and connect capacitor (s) to a 220/240 V mains witha switch and aammeter to read the current

70 micro F = 45 ohm

45 * 4.8 = 216 Vac


Checking the Windings and Rotating Diodes Using Separate Excitation-1

During this procedure, make sure that the alternator is disconnected from any external load and inspect the terminal box to check that the connections are fully tightened.

Stop the unit, disconnect and isolate theAVR wires.There are two ways of creating anassembly with separate excitation.



Assembly A

Connect a 12 Vbattery in series with a rheostat of approximately 50ohms - 300 W anda diode on both field wires (5+) and(6-).



Assembly BConnect a "Variac" variable

power supply and a diode bridge on both exciter field wires (5+) and (6-).

Both these systems should have characteristics which are compatible with the machine field excitation power (see the nameplate).


Checking the Windings and Rotating Diodes Using Separate Excitation-43) Run the unit at its rated speed.4) Gradually increase the exciter field current by

adjusting the rheostat or the variac and measure the output voltages on L1- L2 - L3, checking the excitation voltage and current at no load and on load(see the machine nameplate or ask for the factory test report).

When the output voltageWhen the output voltage is atis at its rated value and its rated value and balanced withinbalanced within 1 %1 % for the rated excitation levelfor the rated excitation level,,the machinethe machine is inis in good working ordergood working order..

The fault therefore comes from the AVR or its associated wiring (ie. sensing, auxiliary windings).


Before The MaintenanceBefore any cleaning, lubrication or maintenance operation, ensure that the genarator is stationary and disconnected from the power supplyThe people in charge of the handling must always wear work gloves and safety shoesDo not operate the generator with protective covers, access covers orterminal box covers removed.Disable engine starting circuits before carrying out maintenance.


MaintenanceCooling circuitIt is recommended to check that the cooling air circulation is not

restricted.

BearingsThe bearings are sealed for lifeMaximum grease life : 20 000 hours (Apx. 40.000 hours) or 3 years

Temperature rise of ball bearings :Periodically check that the temperature of the bearings does not

exceed 50°C above ambient temperature.If higher, it isnecessary to stop the machine to proceed to a generalinspection.


HandlingThe generously-sized lifting rings are for handling the alternator alone. They must not beused to lift the genset. Choose a lifting system which respects the positionning of the rings.


Ensure that the ambient temperature in the room where the alternator is placed cannot exceed 40°C for standard power ratings (for temperatures above 40°C, apply a derating coefficient).Fresh air, free from damp and dust, must be able to circulate freely around the air input louvres on the opposite side from the coupling. It is essential to prevent not only the recycling ofhot air from the machine or engine, but also exhaust fumes.

Location


StoragePrior to commissioning, machines should be stored :

Away from humidity : in conditions ofrelative humidity of more than 90%, the machine insulation can drop very rapidly, to just above zero at around 100%; monitor the state of the anti-rust protection onunpainted parts.For storage over an extended period, the machine can be placed in a sealed enclosure (heatshrunk plastic for example)with dehydrating sachets inside, away from significant and frequent variations intemperature to avoid the risk ofcondensation during storage.


Long Down timeIn order to avoid such troublesIn order to avoid such troubles, it is, it is recommended torecommended tofit fit anti condensation heaters and to run the machine anti condensation heaters and to run the machine periodicallyperiodically..During the long downDuring the long down time,time, the anti condensation the anti condensation heaters must operate fullheaters must operate full time.time.If the areaIf the area isis affected by vibrationaffected by vibration,, try to reduce the try to reduce the effecteffect ofof these vibrations by placing the generatorthese vibrations by placing the generator on on a dampera damper supportsupport ((rubber disc or similarrubber disc or similar)) and turn and turn thethe rotor arotor a fractionfraction of aof a turn onceturn once aa fortnight to avoid fortnight to avoid marking the bearing ringsmarking the bearing rings..


TransportingAlternators willAlternators will bebe packed for packed for shipmentshipment in ain a manner suitable to manner suitable to their modetheir mode of of transport andtransport and finalfinaldestinationdestination..Prior to handling goodsPrior to handling goods,, please please ensure that lifting equipmentensure that lifting equipment is ofis ofsufficient capacitysufficient capacity.. Under lifting Under lifting conditions machinery shouldconditions machinery should bebeelevated toelevated to a minimala minimal distance from distance from the groundthe ground..When lifting or moving goods by When lifting or moving goods by forklift apparatusforklift apparatus,, care shouldcare should bebetaken to ensure that forks are taken to ensure that forks are correctly positioned to prevent correctly positioned to prevent slipping or fallingslipping or falling ofof pallet or cratepallet or crate..


Cleaning And LubricationNEVER USE LIQUIDS OR WATER.DO NOT CLEAN THE INSIDE ELECTRIC COMPONENTS WITH COMPRESSED AIR,BECAUSE THIS MAY CAUSE SHORT CIRCUITS OR OTHER ANOMALIES.


Defects And RemediesMecc Alte ECO 37

ALTERNATOR DOES NOT EXCITESubstitute fuse.Increase speed by 15%.For an instant apply on “+” and “ -” of the electronic regulator a 12 V battery voltage with a 30 Ω resistor in series, respecting the polarities.Check PMG terminals on AVR P2,P3,P4.

These should be balanced and within 170-180 volts for 50 Hz generators.If these are unbalanced, check the PMG stator resistance between output leads.These should be balanced and within ±10% of 2.3 ohm.If resistances are unbalanced and/or incorrect,the PMG stator must bereplaced.If the voltage are balanced but low and the PMG stator winding resistances are correct,the PMG rotor must be replaced.


Defects And Remedies

AFTER BEING EXCITED ALTERNATOR DOES NOT EXCITE

Check connection cables as per attached drawings.



LOW VOLTAGE AT NO LOADReset voltage potentiometer.Check speed.Check windings.



HIGH VOLTAGE AT NO LOADReset voltage potentiometer.Substitute regulator.


Defects And RemediesAT LOAD CONDITIONS, VOLTAGE LOWER THAN RATED VALUE

Reset voltage potentiometer.Current too high, power factor lower than 0.8, speed lower than4% of rated speed.Substitute regulator.Engine speed is lowCheck “UFRO” settingIf these are correct, check rectifier diodes,surge suppressor and the main excitation windings (Measure each section resistance-values should be balanced and within ±10% of the value given resistance charts.



AT LOAD CONDITIONS, VOLTAGE HIGHER THAN RATED VOLTAGE

Reset voltage potentiometer.Substitute regulator.



UNSTABLE VOLTAGECheck uniformity of rotation.Regulate stability of regulator by acting on “STAB.” potentiometer.


Adjusting Of “STAB” PotentiometerUnbalanced

Critical

Good

Slow

Gen. Voltage

No Load Full Load


Defects And RemediesAbnormal noises

The generation of abnormal noises and vibrations may result from wear and tear of the ball bearings. It is better to proceed to their replacement so as to avoid any risk of seizure which could seriously damage the alternator.In the case of single bearing machines, the abnormal noise may also be caused by misalignment.Both single phase alternators and three phase alternators supplying unbalanced loads are more noisy and have more vibrations than three phase machines with balanced loads.The same for three phase generator connected in dog -leg,even with 3 phase balanced loads.


Troubleshooting For Alternators which are regulated by Condensers-1

Alternator excitation failureLow speedFaulty condenserFaulty windings

High No-Load VoltageSpeed too highCondenser with high capacity


Troubleshooting For Alternators which are regulated by Condensers-2Low No-Load Voltage

Speed to lowFaulty rotary diodesBreakdown in windingsCondenser with low capacity

U2U1



Proper no-load but low loaded voltageLow loaded speedLoad too bigRotary diodes short-circuited

Proper no-load but high loaded voltageHigh loaded (only for AR1)High speed in load condition (for MR1 and MR2)



Unstable voltageLoose contactsUneven rotation

Noisy generatorBroken bearingsPoor coupling


Parallel Operation Of Alternators-1

Alternators are connected in parallel to increase the output capacity of a system beyond that of a single unit serve asadditional reserve power for expected demands, or permit shutting down one machine and cutting in a standby machine without interrupting power distribution.


Parallel Operation Of Alternators-2When alternators are of sufficient size, and are operatingat different frequencies and terminal voltages, severel damage may result if they are suddenly connected to each other through a common bus.To avoid this, the machines must be synchronized asclosely as possible before connecting them together.This may be accomplished by connecting one generator to the bus (referred to as bus generator), and then synchronizing the other (incoming generator) to it before closing the incoming generator's main power contactor.


Parallel Operation Of Alternators-3

The generators are synchronized when the following conditions are set:Equal terminal voltages. This is obtained by adjustmentof the incoming generator's field strength.Equal frequency. This is obtained by adjustment of the incoming generator's prime-mover speed.Phase voltages in proper phase relation.

At this point, it is enough for you to know that the above must be accomplished to prevent damage to the machines.


Motor Starting Loads

Direct-on-Line (D.O.L.) StartingIn this case the full line voltage is switched directly to the motor terminals. The motor winding normally is connected delta. The maximum starting torque is available with this method, but a very high starting current is required.



• Direct-on-Line (D.O.L.) Starting• Assume

Ac generator overload capability 2.5 p.u.Motor starting current 6.0 p.u.Motor efficiency 0.9 p.u.

kW genr. = 2,67 kWmRatio S = 2,67


Motor Starting LoadsAuto Transformer Starting

The basic idea is that a low line voltage is tapped off the auto transformer and fed to the motor on start.As motor speeds up, the tap position is changed in any number of steps, increasing the line voltage until the full line voltage is directly across the motor terminals.Commonly used taps are 65% and 80% of full line voltage.



Auto Transformer StartingAssume

Ac generator overload capability 2.5 p.u.Motor starting current 6.0 p.u.Motor efficiency 0.9 p.u.

Tap Position 65 % 80 % 100 %

Reduction in line starting voltage

Value Of ratio S is

35%

1,12

20%

1,71

0%

2,67



• Star – Delta Starting• This system required that all ends of the 3 phase motor are brought to terminals. • Throught two contactors or a changeover switch, the windings are initially

connected in “star”, then usually after a preset time delay or when the motor has run up to a steady speed, the windings are reconnected into delta.

• This is the normal running condition at full line volts. This means that ;• The starting voltage is reduced to 1/1.73 of VL since VL=1.73xV l-n• Starting current is also reduced to 1/1.73 of the D.O.L. Value I• Starting kVA is reduced to 1/3 of the D.O.L. kVA• Starting torque is reduced to 1/3 of the D.O.L. Value


Motor Starting Loads• Star-Delta Starting

• AssumeAc generator overload capability 2.5 p.u.Motor starting current 6.0 p.u.Motor efficiency 0.9 p.u.

kW genr. = 6/(3x2,5x0,9) kWmRatio S = 0,889

The AC generator would be unable to supply the motor with its full load continuously rated steady state power.

In other word, values of S less than 1.0 are not practical.


Power Factor Correction-1The addition of the power factor correction bank can reduce the size of ac generator required to supply these loads under steady state conditions.The major problem with power factor correction banks is that, when all other loads are switched off, the power factor correction banks normally remain connected. This presents This presents aa purely zero power factor leading purely zero power factor leading load to the ac generator and load to the ac generator and as as such we have such we have already recommended already recommended ““refer to factoryrefer to factory”.”.One effect of having a comparatively large bank connected to an ac generator is for the terminal voltage of ac generator to rise dramaticallyrise dramatically.


Power Factor Correction-2VoltagesVoltages in in excess excess of 500 V of 500 V have been recorded from have been recorded from a nominal 415 V a nominal 415 V machine machine in in such casessuch cases..HoweverHowever, as a general , as a general guideguide, , providing the capacitor providing the capacitor bank bank rating rating is not is not greater than about greater than about 10%10% of of the ac the ac generator ratinggenerator rating, , then then no no real problems real problems of of this nature this nature should should be be encounteredencountered..


Non – Linear LoadsNon linear loads such as semi-conductor thyristor/rectifier loads generate harmonics in their current waveform which in turn leads to harmonic distortion of the supply voltage waveform. Depending upon degree of harmonic voltage waveform distortion, this may lead to either instability of the generators excitation system or to the control system of the loads applied to the generator.


Introduction Into Non-Linear LoadsA non linear load is a load that draws a non sinusoidal current from the electrical supply due to the inclusion of phase controlled power devices (usually thyristors) within its design. The firing of these thyristors results in notches in the power supply voltage waveform therefore distorting the waveform shape. The output of the thyristor system is a series of phase angled controlled, half wave pulses, the number of pulses dependant upon the number of thyristors.Therefore non linear loads are generally described by the number of pulses. For instance in a three phase, fully controlled, full-wave bridge circuit there are six thyristors providing six conduction periods, therefore a six pulse system.


Connection Of NLL’s to Mains and Generators

When a non linear load is connected to the mains, irrespective of the amount of current distortion, the voltage waveform is barely distorted due to the low source impedance of the mains supply.When these types of loads are connected to a generator, the higher source impedance, results in higher voltage waveform distortion.The resulting voltage waveform is then of a complex shape.


Which harmonics would be present in a specific system ?

The following formula provides a theoretical idea of which harmonics would be present in a specific system;

n = kp ± 1n = harmonic order.k = an integer , 1,2,3, etc.p = the pulse number.

For example a six pulse system would contain multiples of 6 ± 1, therefore 5th & 7th, 11th & 13th, 17th & 19th, etc. harmonics. Each harmonic will be a percentage of the fundamental, i.e. if the fundamental is 100% the 3rd harmonic will be in the order of 33%, the 5th 20%, etc. From this we can calculate typical current distortion values for different pulse combinations (see table 1).


Typical Current Distortion LevelsHARMONIC CONTENT %

Pulse number 2 6 121st Harmonic 100% 100% 100%

2nd - - -3rd 33% - -4th - - -5th 20% 20% -6th - - -7th 14.3% 14.3% -8th - - -9th 11.1% - -

10th - - -11th 9.1% 9.1% 9.1%12th - - -13th 7.7% 7.7% 7.7%14th - - -15th 6.7% - -16th - - -17th 5.9% 5.9% -18th - - -19th 5.3% 5.3% -20th - - -

Total Harmonic Content 45% 30% 14% Table 1


Harmonic ProblemsIncorrect operation of electronic equipment

as most electronic equipment requires an accurate voltage waveform in order to provide referencing signals for their control circuits. Harmonics distort the voltage waveform by increasing or decreasing the magnitude, mis-shaping the waveform or by causing zero volt crossings.

Noise and vibrationwithin electric motors as the presence of harmonics create torque pulsations.

Capacitor failureswhich result from higher than designed frequencies causing more than designed current to flow through capacitors.

Increased temperature riseswithin machines and transformers as the I2R losses are increased due to the extra, non load supporting harmonic currents resulting in higher operating temperatures. The insulation is stressed by the voltage harmonics. The two situations combine and can reduce equipment life.

Interferenceto other equipment can result from the presence of harmonics due to radiated and conducted high frequency signals.


Types Of Non Linear LoadsUPS systems,

Uninterruptible Power Supplies, which are becoming increasingly popular as more equipment is tending to be very sensitive to power disturbances. UPS systems basically consist of a converter, batteries and an inverter. The mains input to the UPS is converted to dc which is then used to charge the batteries and supply the inverter. The inverter then inverts the dc to a sinusoidal ac output. In the event of a mains failure, the batteries supply the inverter for a fixed period or until an ac supply is restored.

Variable speed drives,these drives contain converters and inverters and are used for speed control of ac motors.

Soft start systems,are an electronic method of reducing the high start currents encountered during motor starting. A pedestal voltage is set and applied to the motor, this voltage is then gradually ramped up to full voltage. These systems are usually bypassed once the motor has reached full speed/full voltage.

Switchmode power supplies,are electronic power supplies often found in computers and certain small battery chargers. These units contain capacitors and the current distortion levels can be quite high (in the order of 55%).

Telecom equipmentconsists of rectifier assemblies for battery charging and directly powering certain dc loads.


Harmonic FiltersHarmonic filters can be utilised in order to reduce the amount of current distortion created by the load.These filters usually incorporate capacitance and inductance. If a filter is fitted to a system, then often it is the first load applied to the generator.The active power will be zero and the generator will supply reactive, leading power factor current to the filter. When generators supply leading power factor loads a situation can occur where the generator begins to self-excite.In order to prevent this condition the amount of leading kVAr applied to the generator needs careful consideration. In order to establish the maximum kVAr that can be applied to the generator, reference must be made to the machines operating chart. This operating chart provides a guide as to the derating factors that must be applied for different operating power factors.


Operating Chart Of Generators

Pf. 0

(Le

ad)

175k

VAr=

0,35

*500


GENERATOR SIZING GUIDELINES - 1

The amount of voltage distortion is subject to the amount of current distortion and the generators source impedance. When determining the source impedance of a generator we can assume an inductance and resistance in series with a voltage source. The resistance values can be neglected as they are very small, leaving just the inductance (reactance) in series with the voltage source. As a generator is a dynamic system, any sudden load changes are subject to an initial value of reactance named the subtransient reactance (X”d). This subtransient reactance is therefore used as a measure of source impedance .



If the amount of current distortion produced by the load is fixed, the only method of reducing the voltage distortion is to lower the generators subtransientreactance. This can only be achieved on existing machines by increasing the operating flux level (voltage) but obviously remaining within the designed parameters.When considering a generator for such equipment the options are oversizing the generator or using a special winding designed to operate at a higher flux level.


GENERATOR SIZING GUIDELINES - 3A value of the voltage distortion due to each harmonic can be calculated using the following formula;

Vn = I n X”d p.u.

Vn - Harmonic voltage.I - Harmonic current.n - Harmonic number.X”d - Subtransient reactance.

For example, a 7th harmonic current equal to 0.1p.u. rated current passed by a machine having a mean subtransient reactance of 0.12p.u. will produce a 7th harmonic voltage of 0.084p.u. (8.4% of rated voltage).



The total harmonic voltage distortion can therefore be established by performing this calculation for every harmonic current present in the system and then taking the square root of the sum of each individual harmonic squared. By using the above method it is possible to estimate the required level typical values of subtransientreactance (X”d) required to achieve required level of voltage distortion. From this we can see that in order to limit the voltage distortion to 10%, when supplying a 6 pulse load with 30% current distortion, a generator is required with a subtransient reactance of 3.5%.

Required Value of Subtransient Reactance in order to limit Voltage distortion.

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GENERATOR SIZING GUIDELINES - 5The reactance values will be provided as a percentage or a per unit (p.u.) value relating to a specific base. These reactance values can then be re-calculated to provide the values specific to the expected maximum rated kVA of the non linear load to be supplied.This re-calculation is based on a proportional relationship, ie, (load kVA/kVA at which reactances provided) x reactance value (p.u.).The reactance values given will be provided at a base voltage, and therefore adjustment may be required in order to obtain the values at the system operating voltage.The reactances relate to the generator’s operating ‘flux level’, and vary as a square of the voltage ratio, i.e. (base voltage/operating voltage)2 x base subtransient reactance.


When sizing of non-linear loads the following information is required ;1. Number of system pulses, i.e. 6 or 12.

1. 6 pulse - 30%2. 2 pulse - 45%

2. Are harmonic distortion filters fitted?3. Maximum level of voltage distortion acceptable to electrical

system.Typical acceptable level of voltage distortion figures:1. UPS Systems 10%2. Inverter Drives 15%3. Soft starters 20%4. Rectifiers 20%

4. Supply voltage and frequency.5. Operating power factor and efficiency.6. Due to the extra heat produced by the harmonics as referred to

earlier, it is usual to limit the rating of the proposed generator to a class ‘F’ temperature rise.


Conclution Of Non-Linear LoadsThe best solution is to try to restrict the amount of current distortion produced by the load. This is slowly being enforced upon the manufacturers of equipment by EMC legislation. If the amount of voltage distortion is reduced by simply increasing the size of generator just to reduce the source impedance, operating efficiencies are decreased and the harmonic currents will still be present in the system, thereforeincreasing cable size unnecessarily.However as current legislation is continuing to regulate the amount of ‘pollution’ produced by non linear loads, it will soon be possible to handle non linear loads as standard loads.


Worked Examples For NLLThe most common question regarding the use of generators for powering non linear loads is the suitability of existing generators for supplying newly installed thyristor controlled equipment.The following worked examples are offered as guidance for the points previously discussed.It should be noted that subtransient reactance values do not follow a set pattern of either always being the same or in fact being lower for larger generators. The chosen two examples show typical values of subtransientreactance with the larger, higher rated generator having the higher subtransient reactance value at its class ‘H’ rated kVA.This situation often occurs when comparing the largest core length of a small frame size with a short core length of a larger frame size.


Worked Example-11. A 175kVA UPS is to be powered by a 415V,

3ph, 50Hz generator. The UPS is six pulse with 30% current distortion. Calculate the expected voltage distortion when powered by either of the following generators;

A) 1000kVA generator with a subtransientreactance of 14% at rated kVA, 415V.

B) 850kVA generator with a subtransientreactance of 0.10p.u. at a base of 800kVA at 400V.


Worked ExampleFigure 1

Required Value of Subtransient Reactance in order to limit Voltage distortion.

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Worked Example-11Note :The ratings quoted for UPS systems are usually

the output kVA. Therefore the operating efficiency, typically 95%, and the extra power required for charging the batteries, usually 25%, needs to be taken into account to establish the maximum input kVA.

Input kVA = 175kVA x 1.25 = 230kVA.0.95


Worked Example-12Generator A :

X”d of 14% (0.14p.u.) is quoted at a base kVA of 1000kVA and therefore it is necessary to re-calculate for the UPS load of 230kVA,

230kVA x 14% = 3.22% (0.0322p.u.)1000kVA

From the graph in figure 1, with a subtransientreactance, X”d, of 3.22% the voltage distortion will be in the order of 9%.


Worked Example-13Generator B :

X”d at 800kVA = 0.10p.u. (10%), therefore X”d at 230kVA,

230kVA x 10% = 2.88% (0.0288p.u.)800kVA

This reactance is given at a voltage of 400V and therefore also needs re-calculating for 415V,

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400 x 2.88% = 2.68% (0.0268p.u.)415

From the graph in figure 1, with a subtransient reactance, of 2.68% the voltage distortion will be in the order of 7.5%.


Worked Example-22. A 800kVA, 415V, 3ph, 50Hz generator with a subtransient reactance of 12%

is to be used to run a 250hp motor. The motor is to be started by the use of an electronic soft start system. The soft start system is 12 pulse with 14% current distortion. Calculate the level of voltage distortion during the starting of the motor when the start kVA is limited to

a) 1.5 times and b) 2 times run kVA.

Assuming the motor is approximately 92% efficient and has an operating power factor of 0.8, input kVA;

250 x 0.746 = 253kVA 0.92 x 0.8


Worked Example-21a) 1.5 times,

Start kVA = 1.5 x 253kVA = 380kVA

X”d = 12% (0.12p.u.) at 800kVA, therefore X”d at 380kVA,

380kVA x 12% = 5.7% (0.057p.u.)800kVA

From the graph in figure 1, with a subtransient reactance of 5.7% the voltage distortion will be in the order of 4.6%.


Worked Example-22b) 2 times,

Start kVA = 2 x 253kVA = 506kVA

X”d = 12% (0.12p.u.) at 800kVA, therefore X”d at 506kVA,

506kVA x 12% = 7.6% (0.076p.u.)800kVA

From the graph in figure 1, with a subtransient reactance of 7.6% the voltage distortion will be in the order of 6.2%.

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