INTRODUCTION TO GENERATORS , INTRODUCTION TO GENERATORS , PROTECTION SCHEMES / RELAYS & PROTECTION SCHEMES / RELAYS &

MAINTENANCEMAINTENANCE

PRESENTED BY PRESENTED BY Pawan BhatlaPawan Bhatla

BASIC PRINCIPLE OF GENERATORBASIC PRINCIPLE OF GENERATOR

AC GENERATORS CONSISTS OF ARMATURE & MAGNETIC FIELD.

ARMATURE WINDINGS MOUNTED ON STATIONARY ELEMENT CALLED STATOR.

FIELD WINDINGS ON ROTATING ELEMENT CALLED ROTOR.

MAGNETIC POLES ARE EXCITED BY D.C, WHEN IT ROTATES , STATOR CONDUCTORS ARE CUT BY MAGNETIC FLUX.

THIS CAUSES INDUCED EMF IN STATOR CONDUCTORS , WHOSE FREQUENCY DEPENDS ON THE NUMBER OF NORTH & SOUTH POLES MOVING PAST A CONDUCTOR IN 1 SECOND.

Generator Frequency f = Generator Frequency f = PN PN , , 120120

Where P = No. of Poles & N = RPMWhere P = No. of Poles & N = RPM

A

AA

A

LaminatedMagnetic

stator core Stator w indingslot

Rotor

Air gap Rotorw inding

Simplified tw o pole Generator cross section

AC GENERATORAC GENERATOR

SYNCHRONOUS MACHINESYNCHRONOUS MACHINE

SYNCHRONOUS MACHINESYNCHRONOUS MACHINE

TYPES OF GENERATOR EXCITATION SYSTEMTYPES OF GENERATOR EXCITATION SYSTEM

• BRUSH TYPE EXCITATION SYSTEM/STATICBRUSH TYPE EXCITATION SYSTEM/STATIC EXCITATION (JGP)EXCITATION (JGP)

• BRUSHLESS EXCITATION SYSTEM (RTR)BRUSHLESS EXCITATION SYSTEM (RTR)

EXCITERA.C

EXCITER FIELD D.C

GENERATOR ROTORD.C

GENERATOR STATOR (13.8KV)

EX2100

ROTATING DIODE

BRUSHLESS EXCITATION SYSTEM

TYPES OF GENERATOR COOLING SYSTEMTYPES OF GENERATOR COOLING SYSTEM

• AIR COOLED AIR COOLED

• WATER COOLEDWATER COOLED

• HYDROGEN COOLEDHYDROGEN COOLED

GENERATOR PROTECTIONGENERATOR PROTECTION INTRODUCTIONINTRODUCTION • Protection may be classiffied as

voltage based / current based / power based.

• Protection Function operates on :– Lower limit Lower limit – Upper limitUpper limit

Types of faults / abnormalities Types of faults / abnormalities that can occur on Generatorthat can occur on Generator

• Insulation failure of stator winding or Insulation failure of stator winding or connection leads. connection leads.

• Insulation failure of the exciter .Insulation failure of the exciter .• Failure of prime mover.Failure of prime mover.• Unbalance loading.Unbalance loading.• Over current.Over current.• Under voltage & over voltage.Under voltage & over voltage.• Under frequency & over frequency.Under frequency & over frequency.• Insulation failure of Gen. rotor.Insulation failure of Gen. rotor.• Stator over heating.Stator over heating.

Types of faults / abnormalities Types of faults / abnormalities that can occur on Generator that can occur on Generator

Transformer.Transformer.

• Inter turn short / winding Inter turn short / winding insulation failure.insulation failure.

• Over fluxing.Over fluxing.

Insulation failure of stator Insulation failure of stator winding or connection leads.winding or connection leads.Cause :Cause : Over heating, over voltage/surges, quality Over heating, over voltage/surges, quality

of insulating material.of insulating material. Damage to windings due to rubbing of rotor Damage to windings due to rubbing of rotor

on bearing failure / excess vibrationon bearing failure / excess vibrationEffect :Effect : Phase to ground short circuit.Phase to ground short circuit. Phase to phase and inter turn fault.Phase to phase and inter turn fault.Protection Functions to operate:Protection Functions to operate: stator earth fault, generator differential, stator earth fault, generator differential,

overall differential, back up impedance. overall differential, back up impedance.

Stator Earth Fault Stator Earth Fault ProtectionProtection

(0 - 95 % & 95 - 100 %)(0 - 95 % & 95 - 100 %)

64S

VL3

VN3

C1 C2 C3

PT TRAFO.GENERATORNGR

Third harmonic currnt

NGT

Stator Earth Fault ProtectionStator Earth Fault Protection( 95 - 100 % )( 95 - 100 % )

The 3 The 3rdrd harmonics voltages are plotted in a graph harmonics voltages are plotted in a graph with VN3 on X-axis and VL3 on Y-axis.with VN3 on X-axis and VL3 on Y-axis.

VN3

VL3

Fault on Neutral

Fault onPhase

Line-1Slope=m1

Line-2Slope=m2

Full load

No load

Generator differential Generator differential protectionprotection

GEN

Ia_B IA S

Ib_B IA S

Ic_B IA S

DIFF

DIFF

DIFF

C Ts C Ts

Generator differential Generator differential protectionprotection

Percentage bias -K2

NO TRIP

M ean bias currentIs2

Diff

. Cur

rent TRIP

Is1K1

Insulation failure of theInsulation failure of the exciter / PMG / cable. exciter / PMG / cable.

Cause :Cause : Over heating, over voltage/surges, Over heating, over voltage/surges,

quality of insulating material.quality of insulating material.Effect :Effect : Phase to ground short circuit.Phase to ground short circuit. Phase to phase and inter turn fault.Phase to phase and inter turn fault.Protection Functions to operate:Protection Functions to operate: Field failure, pole slipping relays.Field failure, pole slipping relays. Under voltage during Island condition.Under voltage during Island condition.

11 KV Cable fault.11 KV Cable fault.Cause :Cause : Mechanical damage- unprotected / running Mechanical damage- unprotected / running

near Hot surface, Electrical damage – near Hot surface, Electrical damage – improper termination /jointing , quality of improper termination /jointing , quality of insulating material.insulating material.

Effect :Effect : phase to ground or multi phase short phase to ground or multi phase short

circuit.circuit.Protection Functions to operate:Protection Functions to operate: Stator earth fault, overall differential, Stator earth fault, overall differential,

voltage restraint over current, back up voltage restraint over current, back up impedance. impedance.

Failure of prime mover.Failure of prime mover.Cause :Cause :• Due to failure of governing system / fuel / Due to failure of governing system / fuel /

steam failure.steam failure.Effect :Effect :• Generator will run as a Synchronous motor.Generator will run as a Synchronous motor.• Active power will be drawn from the Active power will be drawn from the

network.network.• May damage the gear box / turbine blades.May damage the gear box / turbine blades.Protection Functions to operate:Protection Functions to operate:• Reverse power protection.Reverse power protection.

Failure of prime mover Failure of prime mover ( reverse power)( reverse power)

P

-P

STABLEOPERATE

Generating power P = Generating power P = 3*VL*ILCOS3*VL*ILCOS, If , If increase above increase above 90 deg. then P becomes – P OR90 deg. then P becomes – P OR

P = P = 3*V3*VLL*I*ILLCOS (90+ COS (90+ ) = - P = Reverse power) = - P = Reverse power.

Unbalance loading.Unbalance loading.Cause :Cause :• Single phase / non-linear load on generator.Single phase / non-linear load on generator.• Unsymmetrical faults in the power system.Unsymmetrical faults in the power system.• Mal operation of the circuit breaker poles.Mal operation of the circuit breaker poles.Effect :Effect :• Causes dangerous heating of the cylindrical Causes dangerous heating of the cylindrical

rotor of turbo-generator.rotor of turbo-generator.Protection Functions to operate:Protection Functions to operate:• Negative phase sequence protection.Negative phase sequence protection.

Unbalance loading Unbalance loading (NPS)(NPS)

T

tmax

tmin

I2>> I2

K = I2In

2*t

In case of negative phase sequence, In case of negative phase sequence,

Heat = Heat = (I2)² (I2)² *t = K, and I2 = *t = K, and I2 = Ia+a²Ib+aIcIa+a²Ib+aIc (In) 3(In) 3

Normally K is dependent on type of generator, its cooling Normally K is dependent on type of generator, its cooling and type of rotor. and type of rotor.

Voltage restrained Over Voltage restrained Over current / Over loading.current / Over loading.

Cause :Cause :• Fault in power system.Fault in power system.Effect :Effect :• Over heating of the generator winding.Over heating of the generator winding.• Continues over current may damage Continues over current may damage

the generator.the generator.Protection Functions to operate:Protection Functions to operate:• Voltage restrained over current Voltage restrained over current

protection protection

Voltage restraint Over currentVoltage restraint Over current

KI>

Vs2 Voltage levelVs1

Cur

rent

pic

k up

leve

l

I>

Voltage restraint Over currentVoltage restraint Over current

The current pickup level for the voltage restrained function is ,The current pickup level for the voltage restrained function is ,

(1) (1) K*I> for V<Vs2K*I> for V<Vs2 (2) (2) I> for V>Vs1 I> for V>Vs1 (3) (3) K*I> + K*I> + I> - KI>I> - KI> * (V – Vs2) * (V – Vs2) Vs1 – Vs2 Vs1 – Vs2 for Vs2<V<VS1for Vs2<V<VS1

Where V = system existing voltageWhere V = system existing voltage

Under voltage & over voltage.Under voltage & over voltage.Cause :Cause :• Short circuit / earth fault in power system.Short circuit / earth fault in power system.• Excitation system failure in island Excitation system failure in island

conditions.conditions.Effect :Effect :• Voltage falls down in the system Voltage falls down in the system Protection Functions to operate:Protection Functions to operate:• Under voltage relay operates when voltages Under voltage relay operates when voltages

fall below the set point with time delay.fall below the set point with time delay.

Under voltage & over voltage.Under voltage & over voltage.Cause :Cause :• Excess voltage due to surges , AVR Excess voltage due to surges , AVR

failurefailureEffect :Effect :• Insulation failureInsulation failureProtection Functions to operate:Protection Functions to operate:• Over voltage relay Over voltage relay • Surge capacitor & lightning arrestor Surge capacitor & lightning arrestor

for surge voltage protection.for surge voltage protection.

Under frequency & over Under frequency & over frequency.frequency.

Cause :Cause :• Under frequency of generators will occur Under frequency of generators will occur

when the power system load exceeds the when the power system load exceeds the prime-mover capability of generators.prime-mover capability of generators.

• Effect :Effect :• System may collapseSystem may collapse• End users will get affectedEnd users will get affected• Protection Functions to operate:Protection Functions to operate:• First stage can be used to initiate load First stage can be used to initiate load

shedding and second stage to trip the shedding and second stage to trip the machinemachine..

Under frequency & over Under frequency & over frequency.frequency.

CCause ause ::• over frequency operation will occur due to over frequency operation will occur due to

sudden load throw off.sudden load throw off.Effect :Effect :• It may damage the bearing due to high It may damage the bearing due to high

vibrationvibration• End users will get affectedEnd users will get affectedProtection Functions to operate:Protection Functions to operate:• Generally, mechanical over speed devices Generally, mechanical over speed devices

are provided for generator protection.are provided for generator protection.• Over Frequency relayOver Frequency relay

Insulation failure of Gen. Insulation failure of Gen. rotorrotor

Cause :Cause : Over heating, over voltage/surges, Over heating, over voltage/surges,

quality of quality of insulating material.insulating material.

Effect :Effect :– Single earth fault in rotor is not harmful.Single earth fault in rotor is not harmful.– Further earth fault in the excitation Further earth fault in the excitation

circuits / rotor results in a double earth circuits / rotor results in a double earth fault fault

– Leads to Thermal effects on rotor due to Leads to Thermal effects on rotor due to high fault current. high fault current.

Protection Functions to operate:Protection Functions to operate:– Rotor earth fault relayRotor earth fault relay

Insulation failure of Gen. Insulation failure of Gen. rotorrotor

IE

M easurementM odule

RE

ROTORW NDG.

RV

RV

LowPassFilter

U H

Um Rm

CE

R

RELAY

TESTPB

RV = Coupling Resister, UH = Aux. VoltageCE = Earth Capacitance, RE = Eartth Resistance,Rm = Measuring shunt, R = Test series resistance

Stator over heatingStator over heating Cause :Cause : Chocking of cooling tubes or filters.Chocking of cooling tubes or filters. Improper circulation of cooling medium.Improper circulation of cooling medium. Over loading, short circuited lamination, Over loading, short circuited lamination, failure of core bolt insulation.failure of core bolt insulation.Effect :Effect : Insulation FailureInsulation Failure Protection Functions to operate:Protection Functions to operate: Compare inlet and outlet temperatures of Compare inlet and outlet temperatures of

coolant.coolant. Temperature indicating devices (RTD)Temperature indicating devices (RTD)

Generator Transformer Generator Transformer winding Inter turn short / winding Inter turn short /

insulation failure.insulation failure.Cause :Cause : Over heating, over voltage/surges, Over heating, over voltage/surges,

quality of insulating material.quality of insulating material.Effect :Effect : Phase to phase and inter turn fault.Phase to phase and inter turn fault. Phase to ground or multi phase short Phase to ground or multi phase short

circuit. circuit.Protection Functions to operate:Protection Functions to operate: Restricted earth fault, overall differential, Restricted earth fault, overall differential,

Buchholz, PRV, stand by earth fault.Buchholz, PRV, stand by earth fault.

Generator Transformer Over Generator Transformer Over fluxing.fluxing.Cause :Cause :

• Increase in voltage causes increase in Increase in voltage causes increase in working magnetic flux, there by increases working magnetic flux, there by increases the iron loss and magnetizing current.the iron loss and magnetizing current.

Effect :Effect :• The core and core bolts get heated and The core and core bolts get heated and

the lamination insulation is affected in the lamination insulation is affected in unit Transformer. unit Transformer.

Protection Functions to operate:Protection Functions to operate:• Over fluxing protection (v/f) is provided Over fluxing protection (v/f) is provided

for generator transformer where a for generator transformer where a possibility of over fluxing due to sustained possibility of over fluxing due to sustained over-voltages exists. over-voltages exists.

TYPES OF RELAYS : -TYPES OF RELAYS : -

• G60 : - G60 : - (GENERATOR PROTECTION)(GENERATOR PROTECTION)

• T60 : - T60 : - (TRAFO. PROTECTION)(TRAFO. PROTECTION)

• : - : - (UAT PROTECTION)(UAT PROTECTION) • • : - (TRAFO. SB E/F PROT)

G 60 G 60 (GENERATOR PROTECTION)(GENERATOR PROTECTION)

87G GENERATOR DIFFERENTIAL87G GENERATOR DIFFERENTIAL 51N STATOR EARTH FAULT51N STATOR EARTH FAULT 59N NEUTRAL DISPLACEMENT59N NEUTRAL DISPLACEMENT 67N SENSITIVE DIRECTIONAL EARTH FAULT67N SENSITIVE DIRECTIONAL EARTH FAULT 51V VOLTAGE DEPENDENT OVERCURRENT51V VOLTAGE DEPENDENT OVERCURRENT 32R REVERSE POWER32R REVERSE POWER 32L LOW FORWARD POWER32L LOW FORWARD POWER

46 NEGATIVE PHASE SEQUENCE46 NEGATIVE PHASE SEQUENCE

G60 G60 (GENERATOR PROTECTION)(GENERATOR PROTECTION)

40 FIELD FAILURE40 FIELD FAILURE27 UNDER VOLTAGE27 UNDER VOLTAGE59 OVER VOLTAGE59 OVER VOLTAGE

81U UNDER FREQUENCY81U UNDER FREQUENCY 81O OVER FREQUENCY81O OVER FREQUENCY 60 VOLTAGE BALANCE60 VOLTAGE BALANCE

VIEW OF GT XMER VIEW OF GT XMER PARAMETERS IN ECMSPARAMETERS IN ECMS

T-60 T-60 (TRAFO. PROTECTION)(TRAFO. PROTECTION)

• BIASED DIFFERENTIAL ELEMENTBIASED DIFFERENTIAL ELEMENT

• RESTRICTED EARTH FAULT PROTECTIONRESTRICTED EARTH FAULT PROTECTION

• OVER FLUXING ALARM AND TRIPPING OVER FLUXING ALARM AND TRIPPING FUNCTIONFUNCTION

T 60 T 60 (UAT PROTECTION)(UAT PROTECTION)

• PHASE FAULT PROTECTIONPHASE FAULT PROTECTION

• EARTH FAULT PROTECTIONEARTH FAULT PROTECTION

( STATOR EARTH FAULT )( STATOR EARTH FAULT )

Neutral displacement detector for 0 - 95%Neutral displacement detector for 0 - 95% protectionprotection

Third harmonics voltage comparator forThird harmonics voltage comparator for 95 - 100% protection95 - 100% protection

PERIODIC TESTING OF PERIODIC TESTING OF GENERATORS GENERATORS

NO DESCRIPTION OF TESTS REMARKSDC Absorption Test Generator StatorMeasurement of Capacitance and Tan delta Generator StatorRecording of Partial Discharges Generator StatorStudy of Non-Linear Behaviour of Winding Insulation Generator StatorMeasurement of Winding Resistance Generator StatorChecking of RTDs Generator StatorStator core healthines by Loop Test Generator StatorStator core healthines by ELCID Test Generator StatorWedge Mapping using Deflection Method suitable for Ripple Spring Wedges Generator StatorWedge Mapping by Knocking Method suitable for Non-Ripple Spring Wedges Generator StatorInspection of Mechanical response of end winding , Generator StatorMicroscopic & Endoscopic Inspection . Generator StatorVisual Inspection Generator Stator, Generator

Rotor, Exciter stator , ExciterRotor.

DC Absorption at low Voltages Generator RotorMeasurement of Winding Resistance Generator RotorMeasurement of Impedance Generator RotorRecurrent Surge Oscillograph Generator RotorInspection of Retaining Ring with Ultrasonic Method Generator RotorMeasurement of Impedance ,Winding Resistance and Insulation Resistance Exciter StatorMeasurement of Impedance ,Winding Resistance and Insulation Resistance Exciter RotorDiode and Fuse Checking Exciter Rotor