Generator PrinciplesGenerator Principles
Generator ConstructionGenerator Construction
Excitation SystemExcitation System
Operational aspectsOperational aspects
Alternator:
An Alternator is an equipment which
converts Mechanical Energy into
Sources of Mechanical
Energy
Steam Turbines
Gas Turbines
Hydraulic Turbines
Other sources
This forms the basis for the conversion of Mechanical Energy into Electrical Energy.
This can be presented in two forms which are applicable to the operation of
•When a Rotating Magnetic Field cuts the conductors,
Voltage is induced in them.
N
S
R Y B
•When a Rotating conductor cuts the Magnetic Field ,
Voltage is induced in the conductor.
N N
S
S +
_
A DC Voltage is applied to the Rotor and it becomes a Magnet
When this magnet is rotated,it induces voltage in the stator windings
STATOR ROTOR EXCITER SLIP RINGS BRUSHES BEARINGS COOLING SYSTEM
PROVIDED FOR EXTERNAL EXCITATION
USED FOR ROTOR EARTH FAULT PROTECTION
SLEEVE BEARINGS ARE USED
THEY ARE MADE OF WHITE METALS
NDE SIDE BEARING IS INSULATED TO
AVOID SHAFT CURRENT CURRENT CIRCULATION
Stator frame : Mild steel
Stator core : Silicon steel laminations
Stator windings : Copper strips
End shield : Aluminum alloy
Rotor poles : Alloy steel
To take away the heat dissipated in the stator and the rotor
Maximum loading of the machine depends on the effectiveness of cooling system.
AIR COOLING - For low ratings
WATER COOLING - For medium ratings
TO SUPPLY THE FIELD WINDING OF THE GENERATOR WITH DC CURRENT AND
CONTROL IT
THIS KEEPS THE TERMINAL VOLTAGE CONSTANT
ENSURES PROPER REACTIVE POWER SHARING
P T AVR STATOR ROTOR STATOR ROTOR STATOR STATOR ROTOR ROTOR DIODE RECTIFIER +
-11 KV SHAFT PoweringAVR STATOR ROTOR STATOR ROTOR STATOR STATOR ROTOR ROTOR DIODE RECTIFIER +
-11 KV MAGNET MAGNET STATOR STATOR SHAFT PT Feed backAC - DC CONVERTER + - TO EXCITER POWERING REFERENCE PROCESSING FEEDBACK PROCESSING CONTROLLER FIRING PULSE GENERATOR Reference Feedback Aux. power Aux. power
There are two identical AVRs present
The AVR will not come into line unless the turbine reaches 85% of full speed
One of the AVR will be on line and the other one will remain as standby.
If the main AVR fails , then the stand by AVR will automatically come onto line
Parameters List:
VoltageFrequency
Active power
Reactive power
Excitation voltage / current
Frequency - Real power
f P FL NL FSR 1 FSR 3 FSR 2Voltage - Reactive Power:
Q FL NL V IF 1 IF 2 IF 3TURBINE REACHES FULL SPEED
CLOSE THE FIELD BREAKER
BUILD UP VOLTAGE TO 11KV
SYNCHRONISATION
INCREASE THE LOAD
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
More load in shared condition.
Increase in Reliability.
LOADS
GT-A GT-B
ARE THE VOLTAGES SAME?
ARE THE PHASE SEQUENCES SAME?
LOAD LOAD GT-A GT-A GT-BGT-B 7 MW 7 MW 4 MW 4 MW 3 MW 3 MW
LOAD DEMAND IS CONSTANT
LOAD DEMAND IS CONSTANT
7 MW 7 MW
LOAD HAS TO BE SHARED
P P P P GT-B GT-B GT-A GT-A 1MW 1MW 6 MW 6 MW f f 3 3 MW MW 4 4 MWMW
Load demand is constantLoad demand is constant
Increase in Governor set point of one GeneratorIncrease in Governor set point of one Generator increases
increases the the system system frequency frequency and and Real Real powerpower on that Generator
on that Generator
Increase in Field current of one GeneratorIncrease in Field current of one Generator
increases the system voltage and Reactive power increases the system voltage and Reactive power on that Generator
on that Generator
TO SUMMARISE
Voltage and Frequency are constant i.e not in our control
f
P
V
WHEN INCOMING FREQUENCY IS GREATER THAN GRID: f P P GT-A APTRANSCO PGT PAPTRANSCO
P f P GT-A APTRANSCO PAPTRANSCO -PGT
WHEN INCOMING FREQUENCY IS LESSER THAN GRID:
f P P GT-A APSEB 1 MW 6 MW
WHEN THE GOVERNOR SET POINT OF GT-A INCREASES:
3 MW
Voltage and Frequency are fixed by GRID
Governor set point decides the Real Power
To prevent the equipment from severe damages during fault conditions
To continuously track the various
parameters and isolate the equipment when they deviate from the set value
Over current Protection
Stator Earth Fault Protection
Differential Protection
Unbalance Protection
Reverse power Protection
Loss of Excitation Protection
Over / Under Frequency Protection
R Y B Winding Winding Winding NGR RELAY O/C OCCURS I > 540 A or 1941 A
Relay operates in ‘ t ‘ sec CTS
It monitors the overloading pattern of the generator and trips incase of heavy loading
It 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
R Y B Winding Winding Winding NGR CT I >15.2 A or 20 A Relay operates
The star point of the Generator is earthed through a Resistor to limit Earth fault current
So whenever an Earth fault occurs , the
fault current flows through NGR
When the neutral current exceeds the
R B Y Winding Winding Winding RELAY CTS CTS I > 105 A (OR) 350 A Relay operates
This relay is to protect the stator winding phase wise
This is the fastest relay available
Under normal condition both the CT currents are same and the differential current is zero.
But when there exists a fault in the stator winding both CT currents differ leading to a differential current
When this differential current is more than set value the relay operates
Unbalance condition arises when the three phase loads are not same
This relay operates if the percentage of unbalance exceeds the set value
To avoid reverse flow of power i.e power into the generator
In this state Generator will act as a motor
If continues to operate , this will cause overheating of turbine
To avoid running the machine without excitation
It works on the principle, Impedance=V/I.
The terminal voltage falls if a sudden heavy load demand or AVR failure
occurs, this will cause the current to increase and the impedance falls.
The relay is an Impedance relay and it operates when Impedance falls below
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
