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Transcript of Generator Course
8/10/2019 Generator Course
http://slidepdf.com/reader/full/generator-course 1/61
8/10/2019 Generator Course
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Generator Principles
Generator Construction
Excitation System
Operational aspectsGenerator Protections
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Alternator:
An Alternator is an equipment which
converts Mechanical Energy into
Electrical Energy.
8/10/2019 Generator Course
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Sources of Mechanical
Energy
Steam Turbines
Gas TurbinesHydraulic Turbines
Other sources
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This forms the basis for the conversion ofMechanical Energy into Electrical Energy.
This can be presented in two forms whichare applicable to the operation of
Generators.
8/10/2019 Generator Course
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•When a Rotating Magnetic Field cuts the conductors,
Voltage is induced in them.
N
S
RYB
•
This is applicable to the main generator
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•When a Rotating conductor cuts the Magnetic Field ,
Voltage is induced in the conductor.
N N
S
S
+
_
•This applicable to the Exciter.
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A DC Voltage is applied to the Rotor and itbecomes a Magnet
When this magnet is rotated,it inducesvoltage in the stator windings
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STATOR
ROTOR
EXCITER
SLIP RINGS
BRUSHES
BEARINGS
COOLING SYSTEM
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PROVIDED FOR EXTERNAL
EXCITATION
USED FOR ROTOR EARTH FAULT
PROTECTION
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SLEEVE BEARINGS ARE USED
THEY ARE MADE OF WHITE METALS
NDE SIDE BEARING IS INSULATED TO AVOID SHAFT CURRENT CURRENTCIRCULATION
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Stator frame : Mild steel
Stator core : Silicon steel
laminationsStator windings : Copper strips
End shield : Aluminum alloy
Rotor poles : Alloy steel
Rotor coils : Silver alloyed copper
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To take away the heat dissipated in thestator and the rotor
Maximum loading of the machine dependson the effectiveness of cooling system.
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AIR COOLING - For low ratings
WATER COOLING - For medium ratings
HYDROGEN COOLING - For higher ratings
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TO SUPPLY THE FIELD WINDING OF THEGENERATOR WITH DC CURRENT ANDCONTROL IT
THIS KEEPS THE TERMINAL VOLTAGECONSTANT
ENSURES PROPER REACTIVE POWERSHARING
IMPROVES STABILITY
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AVR
STATOR
ROTOR
STATOR
ROTOR
STATOR
STATOR
ROTOR
ROTOR
DIODE
RECTIFIER
+
-
11 KV
MAGNET
MAGNET
STATOR
STATOR
SHAFT
PoweringPT
Feed back
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AC - DC
CONVERTER
+
- TO EXCITERPOWERING
REFERENCE
PROCESSING
FEEDBACK
PROCESSING
CONTROLLER
FIRING PULSE
GENERATOR
Reference Feedback
Aux. power
Aux. power
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There are two identical AVRs present
The AVR will not come into line unlessthe turbine reaches 85% of full speed
One of the AVR will be on line and theother one will remain as standby.
If the main AVR fails , then the standby AVR will automatically come ontoline
A manual excitation control provisionalso exists
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Parameters List:
Voltage
Frequency
Active power
Reactive power
Excitation voltage / current
Power Factor
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Frequency - Real power
f
PFL
FL
NL
FSR 1
FSR 3
FSR 2
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Voltage - Reactive Power:
QFL
FL
NL
V
IF 1
IF 2
IF 3
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TURBINE REACHES FULL SPEED
CLOSE THE FIELD BREAKER
BUILD UP VOLTAGE TO 11KV
SYNCHRONISATION
INCREASE THE LOAD
ISLAND OPERATION PARALLEL OPERATION
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GT-A
LOADS
Real and Reactive power supplied will be the amount demanded by the Load.
GOVERNOR SET POINT DECIDES THE FREQUENCY
FIELD CURRENT DECIDES THE TERMINAL VOLTAGE
6 MW
6 MW
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More load in shared condition.
Increase in Reliability.
Flexibility in Maintenance.
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LOADS
GT-A GT-B
ARE THE VOLTAGES SAME?
ARE THE PHASE SEQUENCES SAME?
ARE THE FREQUENCIES SAME?
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LOAD
GT-A GT-B
7 MW
4 MW3 MW
LOAD DEMAND IS CONSTANT
7 MW
LOAD HAS TO BE SHARED BETWEEN THEM
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PP
GT-BGT-A
1MW6 MW
f
3 MW 4 MW
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TO SUMMARISE
Load demand is constant
Increase in Governor set point of one Generator
increases the system frequency and Real poweron that Generator
Increase in Field current of one Generator
increases the system voltage and Reactive poweron that Generator
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WHEN INCOMING FREQUENCY IS GREATER THAN GRID:
f
PP
GT-AAPTRANSCO
PGTPAPTRANSCO
GT-A TAKES PART OF LOAD
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P
f
P
GT-AAPTRANSCO
PAPTRANSCO -PGT
WHEN INCOMING FREQUENCY IS LESSER THAN GRID:
GT-A ACTS AS LOAD
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Voltage and Frequency are fixed by GRID
Governor set point decides the RealPower
Field current decides the Reactive power
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To prevent the equipment from severedamages during fault conditions
To continuously track the variousparameters and isolate the equipment
when they deviate from the set value
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Over current Protection
Stator Earth Fault Protection
Differential Protection
Unbalance Protection
Reverse power Protection
Loss of Excitation ProtectionOver / Under Frequency Protection
Over / Under voltage Protection
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R
Y
B
Winding
Winding
Winding
NGR RELAY
O/C OCCURS
I > 540 A or 1941 A
Relay operates in ‘ t ‘ sec
CTS
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It monitors the overloading pattern of the generator
and trips incase of heavy loadingIt follows an Inverse curve and so it trips in less time
for a higher current
• The set point initiates the relay typically at 540 A or 1941 A
t
I
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R
Y
B
Winding
Winding
Winding
NGR
CT
I >15.2 A or
20 A
Relay operates
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The star point of the Generator isearthed through a Resistor to limitEarth fault current
So whenever an Earth fault occurs , thefault current flows through NGR
When the neutral current exceeds theset value , the relay operates
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R
B
YWinding
Winding
Winding
RELAY
CTS CTS
I > 105 A (OR) 350 A
Relay operates
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This relay is to protect the stator
winding phase wiseThis is the fastest relay available
Under normal condition both the CT
currents are same and the differentialcurrent is zero.
But when there exists a fault in the
stator winding both CT currents differleading to a differential current
When this differential current is more
than set value the relay operates
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To avoid reverse flow of power i.e powerinto the generator
In this state Generator will act as a motorIf continues to operate , this will cause
overheating of turbine
Typically 3% ( 5% ) reverse flow
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To avoid running the machine withoutexcitation
It works on the principle,Impedance=V/I.
The terminal voltage falls if a suddenheavy load demand or AVR failureoccurs, this will cause the current toincrease and the impedance falls.
The relay is an Impedance relay and itoperates when Impedance falls below
certain limit.
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UNDER VOLTAGE = 7.4 KV ; 7.5 KV
OVER VOLTAGE ALARM = 12 KV ; 11.5 KV
OVER VOLTAGE TRIP = 12.5 KV , 12.5 KV
OVER FREQUENCY = 51.5 Hz , 52 Hz
UNDER FREQUENCY = 47 Hz , 47.5 Hz
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DIFFERENTIAL RELAY ACTS
STATOR EARTH FAULT OCCURS
LOSS OF EXCITATION HAPPENS