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Generator Operation and Protection
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7/13/2019 Generator Operation and Protection
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GENERATOR OPERATION, PROTECTION
& PROTECTION SYSTEMIOCL, PARADIP REFINERY
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Topics covered
Generator details
Checks during normal operation
Different capability curves of generator
Control & Monitoring Architecture
Overview of Generation & Distribution busControl philosophy of GIS
Brief about DAVR
Overview of Generator & Generator Transformer
ProtectionProtection chart of Generator & Generator Transformer
WHY & HOW of each type of protection
Generator CO2 system
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GENERATOR MODULES
Air Cooled Turbogenerator : TARIHydrogen Cooled Turbogenerator : THRI
Hydrogen/Water Cooled TG : THDF
MODULE NOMENCLATURE (EXAMPLE)
TARI 108/46 Paradip Refinery : TARI 1080-36P for GTGTHRI 108/44 TARI 800-20P for STG
THDF 115/59
MW CAPACITY RANGE OF TURBOGENERATOR
Air Cooled Turbogenerator : 80MW 240MWHydrogen Cooled Turbogenerator : 100MW 350MW
Hydrogen and Water Cooled Turbogenerator : 450MW 1000MW
GENERATOR DETAILS
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PARAMETERS OPERATION VALUES ALARMS
Stator teeth temp. 50-100 deg. C 120 deg.C
Generator winding temp. 50-100 deg. C 120 deg. C
Stator core temp.
50-100 deg. C
120 deg. C
Cold air temp. < 55 deg. C
Hot air temp.
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PARAMETER OPERATING VALUE ALARM TRIP
Bearing vib < 10 mm/sec 12.5 mm/sec. 25 mm/sec (peak)
Bearing temp < 85 deg. C 100 deg. C 120 deg. C
Load Limits : As per the capability curve
Rate of loading : Permissible rate of loading depends on the condition of the winding
Insulation
Space Heater : when generator is not running space heater should be ON
Monitoring:
a) Temperature monitoring of components (through temp scanner)
b) Generator hot air temp
c) Shaft grounding brushd) Rotor vibration
e) Fuse of brushless exciter with the help of stroboscope
Generator IR value : Min. IR value = (KV rating +1) M Ohm @ 40 deg C with 5 KV IR tester
Action required if IR value is less than min : Identification of low IR section , if found in winding
drying out to be adopted.
CHECKS ON GENERATOR DURING NORMAL OPERATION :
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PERMISSIBLE SYNCHRONISING CRITERIA
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PMG
Main Exciter
Rotor winding
Rectifier Wheel
Ring for rotor earth
fault
EXCITER ROTOR
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BRUSHLESS EXCITATION SYSTEM
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ECS panel
in CPP
C/R
I/O
panel
SCAP
Toshiba GIS
I/O
panel
ECS panelsin GIS
building
Operator
work
station
EEP panel
Control & Monitoring Architecture
FOcable
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66KV BUS 1
66KV GIS SLD CPP Generation Bus & S/S-303 Distribution Bus
66KV BUS 3
66KV BUS 4
11 /66 KV
10 MVA
(ONAN)
YnYn0,Z=12%
66KV BUS 2
To Transformers at downstream distribution sub-stations
X
118.3 MW
GTG 1 GTG 2
X
X
X
11 /69 KV
148/118 MVA
(ONAF/ONAN)
OCTC
YNd11,Z=14.8%
STG 2
X
X
STG 1
X
X
GTG 3
X
X X
X
X
X
3150 A 40 KA ,1 SEC 3150 A
11 /69 KV
37.5 MVA
(ONAN)
OCTC
YNd11,Z=11.2%
118.3 MW 118.3 MW 30 MW 30 MW
BS 1
BS 2
X
x xx
66KV BUS 2X X
x
x66KV BUS 1
SS 303 GIS -66kV,3150 A,40kA for 3 sec3150 A 3150 A
X X X X XX X XX
O
/
gF
D
R
O
/
g
F
D
R
O
/
g
F
D
R
O
/
g
F
D
R
O
/
g
F
D
R
O
/
g
F
D
R
O
/
g
F
D
R
O
/
gF
D
R
O
/g
F
D
R
O
/
g
F
D
R
Generation Bus
Distribution Bus
X
x
BC 1
X
x
BC 2
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GIS control philosophy
Synchronisation facility is provided to generators, sectionalisers, bus couplers and Tie-
transformer breakers
Synchronisation can be performed from SCAP as well as ECS in Auto as well as in manual
mode.
SCAP /ECS/OFF selection switch provided on SCAP
All breakers can be controlled from SCAP as well as ECS with Remote in LCC
All isolators can be controlled from SCAP as well ECS with Remote in LCC
All earthing switch can be controlled from LCC only with Local selection in LCC
All breakers can be controlled from LCC in maintenance mode (line & breaker side earthswitch connected) with Local selection in LCC
All isolators can be controlled from LCC with Local selection in LCC
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A section of 66kV TOSHIBA GIS Generation Sub-Stations Bays Local Control Panels
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CPP Synchronisation Control & Annunciation Panel (SCAP)
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Block Diagram of DAVR with Dual Auto (inbuilt Manual) Channels & Dual PLC
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21G,27G,32G,37G,40G,46G,50GDM,51G,59G,60G,64G(95%),64G(100%),64F,78G,81G,87G & 99GT
Y
G
x
P345 P345
P127
P633
P633
P141
P127
66 Kv GIS Bus
87GT
51GT/ 64RGT
870A/ 51NGT
P345
51VG 51VG
3 nos VTs for AVR Ch1, Ch2,
Met & Prot
To rotor E/F protection
GENERATOR & GENERATOR TRANSFORMER PROTECTION OVERVIEW
66/11 KV transformer
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Integrated Numerical generator protection relay
Areva Make Model P345 (two independent relay GR1 & GR2)
Protection code Description21G: Generator backup impedance protection
27G: Under voltage protection
32G: Reverse power protection
37G: Low forward power protection
40G: Field failure protection46G: Negative sequence current protection
50GDM: Dead machine protection
51G: Definite time overload protection
59G: Overvoltage protection
60G: Voltage balance relay (fuse failure)
64G(95%): Stator earth fault protection(95% winding)64G(100%): Stator earth fault protection(100% winding)
64F: Rotor earth fault protection
78G: Out of step(pole slipping) protection
81G: Under/Over frequency protection
87G: Differential protection
99GT: Gen & Gen Transformer Overfluxing protection
PROTECTION RELAYS
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Protection Relay Protection
Code
Description of protection
Areva Make P127 Numerical
protection relay(two
independent relay)
51VG Generator voltage restrained over
current protection
Areva Make P141 Numerical
protection relay
51GT/64RGT Generator Transformer HV side over
current & restricted earth fault
protectionAreva Make P633 Numerical
protection relay (1strelay)
870A/51NGT
Overall differential & Generator
transformer backup earth fault
protection
Areva Make P633 Numerical
protection relay (2nd
relay)
87GT Generator Transformer differential
protection
Areva Make VAEM21 relay 64F1A 1strotor earth fault relay
Areva Make CAEM33 relay 64F2 2ndrotor earth fault relay
PROTECTION RELAYS
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Important Accessories for
protection relays
Code Description of code
Areva Make P931 RGR2 low frequency square wave generator
for rotor E/F
Areva Make PR5104 REP Repeater for rotor E/F protection signal
Siemens Make 7XT3300 G20Hz 20Hz generator for 100% stator E/F
Siemens Make 7XT3400 FGR2 Band pass filter with built in voltage
divider for 100% stator E/F protection
PROTECTION RELAYS
OVERVIEW OF GENERATOR PROTECTION
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OVERVIEW OF GENERATOR PROTECTION
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GENERATOR PROTECTION
Electrical protection provided - To quickly detect & initiate shut down for
major electrical faults associated with the generating plant.Abnormalelectrical conditions arise as a result of some failure with the generatingplant itself,but can also be externally imposed on the generator. Commoncategories of faults and abnormal conditions to be detected are:
1. Internal Faults
Phase and /or ground faults in the stator and associated protection zone
Ground faults in the rotor (field winding)
2. Abnormal Operating Conditions.
a. Loss of field.
b. Overload.
c. Overvoltage.
d. Under and over frequency
e. Unbalanced Operation e.g. single phasing.
f. Loss motoring i.e. loss of prime mover.
g. Loss of synchronization (out of step).
h. Subsynchronous oscillation.
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GENERATOR DIFFERENTIAL (87G)
WHY
For protection of the stator windings against internal faults- to detect stator
winding multi phase and earth faults . Normally involves high fault current ,
so fast clearing required.
HOW Based on the principle of circulating currents. The difference of two currents
of the two sets of CTs (one set on the neutral side & other set on line side of
generator) flow through the relay.
Operates only with in the protected zone for internal faults.
Stability to be ensured for stability against out of zone fault
GENERATOR DIFFERENTIAL (87G)
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GENERATOR DIFFERENTIAL (87G)
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VOLTAGE DEPENDENT OVERCURRENT (51VG)
WHY
A fault close to the generator will result in a fault current decrement since
the armature reaction of the generator significantly reduces the fault current.
Provides back up protection for uncleared downstream faults with time
delay.
HOW
Voltage restrained over current relay. When voltage is low, relay will operate
on low current
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STATOR EARTH FAULT PROTECTION (64G)
WHY
Most faults in a generator are a consequence of insulation failure. They may
lead to turntoturn faults and ground faults. Required for the earth fault ingenerator stator windings, potential transformers, lightning arrestors, surgecapacitors & neutral bus duct. Fault current must be low as it may damage thecore , which is very costly affaire. Hence ground fault protection is veryessential for generators.
HOW Maximum resistive fault current limited to 7.8 Amp (under field forcing) by
neutral grounding transformer & secondary loading resistor.
95% of stator winding is protected by sensing voltage (overvoltage) acrosssecondary loading resistor.
100% of stator winding is protected by low frequency injection method.
100% stator earth fault protection can be provided by injecting an external lowfrequency alternating voltage into the starpoint or the terminals of themachine. Under normal healthy conditions only a very small current flows viathe stator earth capacitance due to the high impedance of this path at lowfrequencies (Xc = 1/2fc). In the event of an earth fault the measured currentincreases due to the smaller impedance of the earth fault path.
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STATOR EARTH FAULT PROTECTION (64G)
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ROTOR EARTH FAULT PROTECTION (64F)
WHY
An earth fault in the rotor winding does not cause immediate damage;
however, if a second earth fault occurs it constitutes a winding short-circuit of
the excitation circuit. The resulting magnetic unbalances can cause extreme
mechanical forces which may cause damage to the machine.
HOW
The rotor earth fault protection injects a DC voltage into the rotor circuit; the
polarity of the voltage is reversed at low frequencies and the frequency is
selectable by the user through a link selection.
Every time the DC voltage is reversed in polarity, a charging current is applied
due to the capacitance of the rotor windings to earth. Under no fault
conditions, the charging current should be discharged to zero.
When a rotor earth fault occurs, the steady state current will no longer be zero,
the magnitude of which can then be used to calculate the fault resistance.
Other method: -ve biased voltage injection(VAEM) for 1strotor earth fault and
potentiometer method(CAEM) for 2ndrotor earth fault.
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ROTOR EARTH FAULT PROTECTION (64F)
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REVERSE POWER PROTECTION (32G)
WHY
In the event of prime mover failure, a generator connected in parallel with a
power system - will begin to run as Motor . The active power is drawn fromthe power system to cover alternator & failed prime mover mechanical losses.
HOW
A time delay provided to reverse power protection tripping - to prevent false
tripping during some system fault conditions & power system swings.
A typical setting for reverse power protection - with 0.2% to 0.5% of the rated
power of the generator.
A time delay provided for operation without turbine trip.
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LOW FORWARD POWER PROTECTION(37G)
WHY
To avoid over speed damage to Large turbo alternators, with slender, low
inertia rotor designs like that of steam turbines - do not have high over speedtolerance , non urgent tripping of the generator breaker & the excitation
system can be interlocked with a low forward power function.
HOW
Measurement of the low power - done similar to that of reverse power
function
A typical under power setting : 0.5% of rated power.
A time delay provided for operation without turbine trip.
In gas turbine driven generators - Low forward power protection not required.
NEGATIVE PHASE SEQUENCE PROTECTION(46G)
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NEGATIVE PHASE SEQUENCE PROTECTION(46G)
WHY
Negative sequence currents create an mmf wave in opposite direction to thedirection of rotation of rotor. This cuts the rotor at twice the rotational speed,
and induces a 100 Hz eddy current flows in the outside skin of the rotor body, onthe wedges & in the top winding conductors and cause heating which can causesevere over heating and ultimately, the melting of the wedges in the air gap.
HOW
Negative sequence current is measured by the relay. An inverse-time overcurrent
relay excited by negative sequence current can be used for this protection. Themachine designer establishes constant k. It can be in the range of 550.
8% continuous negative sequence current can tolerated.
UNBALANCED LOAD TIME CURVE
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UNBALANCED LOAD-TIME CURVE
FIELD FAILURE PROTECTION (40G)
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FIELD FAILURE PROTECTION (40G)
WHY
When the excitation of a generator fails - its internal e.m.f. will decay. Thisresults in fall of active power output (accelerate to super synchronous speed)
& increasing level of reactive power being drawn from the system. In the lagging power factor-operating region, limits are determined either by
rotor field heating limit or by stator armature heating limit. During the leadingpower factor-operating region, it is the iron end region-heating limit due toeddy currents that is detrimental to the machine. Turbo-alternators may nothave adequate reactive power absorption capability. Hence, they are seldomoperated with leading power factor.
HOW
This protection function - measures the impedance at the terminals of agenerator to detect failure of the generators excitation.
During loss of excitation - the terminal impedance of the generator undergoesa transition from the first quadrant to the fourth quadrant.
Offset Mho relay Xa= 0.5 Xd , Xb= Xd
Time delay used. But in case of U/V no time delay.
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X
R-Xa
Xb
Load Point
Machine terminal
loss of fieldlocus
Field Failure protection function characteristic with typical machine impedance
TRIP
NO TRIP
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UNDER VOLTAGE PROTECTION (27G)
WHY
Under voltage - can be used to detect abnormal operating conditions, AVR failureor an un-cleared power system fault by other generator protection.
It can be interlocked with the field failure protection - to prevent its operation
during stable power swings.
Under voltage protection - not a commonly specified requirement for generator
protection.
HOW
Operates when the three phase voltages fall below the common set point. An
adjustable timer is available .
Under voltage threshold ( V< ) setting - set below the steady state phase-phase
voltage seen by the relay for a three-phase fault at the remote end of any feeder
connected to the generator bus.
70% of normal voltage.
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OVER VOLTAGE PROTECTION (59G)
WHY
Over voltage protection - set to prevent possible damage to generator insulation,prolonged over fluxing of the generating plant or damage to isolated power system
loads.
HOW
Over voltage operates when the three phase voltages are above their commonthreshold setting.
At 105% voltage , alarm with 2 sec delay
At 140% voltage, Trip without delay
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UNDER FREQUENCY PROTECTION (81GUF)
WHY
Under frequency operation of a generator - occurs when the power system
load exceeds the prime mover capability of the generator.
Under frequency running at nominal voltage - will result in over fluxing of the
generator.
Unsafe for turbine
HOW
The under frequency protection function of the relay - utilises the AC voltage
input signals as the frequency measurand.
Two independent time-delayed stages of under frequency protections.
First stage48.5 Hz, Alarm with 2.5 Sec delay
Second stage47.5 Hz, Trip with 2 sec delay.
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OVER FREQUENCY PROTECTION (81GOF)
WHY
Over frequency running of a generating set arises when the mechanicalpower in put to the generator is in excess of the electrical load & mechanical
losses.
Over frequency protection - a back up protection function to cater governor
or throttle control failure following loss of load & prevent over speeding.
HOW
Over frequency protection function of the relay - utilises the AC input signals
as the frequency measurand.
A single time delayed stage of over frequency protection , with an over
frequency threshold setting ( F> ) and a time delay setting ( t ). 51.5 Hz, Alarm with 2 sec delay.
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VOLTAGE BALANCE FUNCTION (60G)
WHY
Voltage balance function - provided to detect PT fuse failure so that an alarm
can be raised & unwanted generator shut down by the voltage sensitive
protection function can be prevented.
HOW
The voltage balance protection function - operates from signal derived fromthe relays two main PT secondary inputs and signals derived from an
additional pair of reference PT secondary inputs.
The level of voltage difference is determined between each of the two main &
reference voltage inputs.
When a voltage difference in excess of an adjustable threshold ( Vs ) isdetected - an alarm is raised.
( )
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GENERATOR BACKUP IMPEDANCE PROTECTION(21G)
WHY
Back-up protection must be applied at the generator so that faults are cleared
in the event of downstream protection/circuit breakers failing to operate. Also
current will come down with time.
HOW
Under impedance protection. This element is set to monitor the system
impedance at the terminals of the machine. If the impedance measured fallsbelow a set threshold then the element will operate.
System back-up protection must operate quickly during a fault and must not
operate for load conditions.
( )
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GENERATOR DEAD MACHINE PROTECTION(50GDM)
WHY
To provide fast protection for accidental energization of a generator when the
machine is not running condition.
HOW
Instantaneous overcurrent element that is gated with a three-phase
undervoltage detector and is blocked by the VT supervision element.
GENERATOR OUT OF STEP PROTECTION(78G)
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GENERATOR OUT OF STEP PROTECTION(78G)
WHY
A generator might pole slip, or fall out-of-step with other power system
sources, in the even of failed or abnormally weak excitation or as a result of
delayed system fault clearance.
HOW
To detect this condition, distance relay looking into the generator (or into the
transformer-generator unit) should be installed. Even a distance relay used forloss-of-field protection will pick-up on such power swing.
If the swing moves out of the relay characteristic, before the timer runs down,
then, no trip action will be initiated. However, if the swing persists for
sufficient time, the loss-of-excitation distance relay will operate on power
swing.
GENERATOR DEFINITE TIME OVERLOAD PROTECTION(51G)
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GENERATOR DEFINITE TIME OVERLOAD PROTECTION(51G)
WHY
To protect the generator from going out of the capability and safe operation
limit.
HOW
Thermal modeling of the generator as per the given data and
recommendation of supplier.
GENERATOR & GENERATOR TRANSFORMER OVERFLUXING
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PROTECTION PROTECTION (99GT)
WHY
High voltage or low frequency, causing a rise in the V/Hz ratio, will produce high
flux densities in the magnetic core of the machine or transformer. This could
cause the core of the generator or transformer to saturate and stray flux to be
induced in un-laminated components that have not been designed to carry flux.
The resulting eddy currents in solid components (e.g. core bolts & clamps) and
end of core laminations can cause rapid overheating and damage.
HOW
V/f element of the relay set as per the overfluxing withstand capability of the
generator & generator transformer.
Time delayed Alarm is used to take action
Inverse characteristics is used for trip
GENERATOR STATOR FRAME OVERTEMPERATURE PROTECTION
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(CO2 SYSTEM)
WHY
To provide protection against fire/ hot spots inside generator enclosure.
HOW
80 deg C & 100 deg C fire detectors installed at equal distance along the
periphery of generator frame /enclosure (Turbine end & Exciter End).
Logic formed to avoid mal-operation of detector for release CO2 in thegenerator enclosure and class A tripping.
CO2 is also released in case of actuation of generator differential protection.
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Fire Detector arrangement inside generator enclosure(Turbine side)
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Fire Detector arrangement inside generator enclosure (Exciter side)
GENERATOR CLASS A PROTECTION TABLE
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GENERATOR CLASS-A PROTECTION TABLE
ORlogic for class
A trip
GEN WINDING DIFFERENTIAL 87G
GEN TR DIFFERENTIAL 87GT
STATOR EARTH FAULT 64G
GEN TR REF 64RGT
OVERALL DIFFERENTIAL 870A
GEN FRAME TEMPERATURE 100 DEG
CELSIUS
ROTOR E/F 64F
Tripping of both generator breaker and turbine occurs for any of the following conditions
EMERGENCY PUSH BUTTON
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THANK YOU