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
WATER
-
COOLING
HYDROGEN
COOLING
-
For low ratings
For medium ratings
For higher 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 IMPROVES STABILITY
STATOR STATOR
+
ROTOR
DIODE
ROTOR
SHAFT ROTOR
-
RECTIFIER
ROTOR STATOR
STATOR Powering
11 KV PT
AVR
STATOR
ROTOR
STATOR
+ DIODE
STATOR ROTOR
MAGNET
ROTOR
MAGNET
SHAFT ROTOR
-
RECTIFIER
STATOR STATOR
STATOR Feed back
11 KV PT
AVR
POWERING
Aux. power
AC - DC
+
CONVERTER
-
TO EXCITER
FIRING PULSE GENERATOR
Aux. power
CONTROLLER
Reference
Feedback REFERENCE
FEEDBACK
PROCESSING
PROCESSING
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 A manual excitation control provision
Parameters List: Voltage Frequency Active
power Reactive power Excitation voltage / current Power Factor
Frequency - Real power f NL FSR 3
FL
FSR 2 FSR 1
P
Voltage - Reactive Power: V
NL FL
IF 3 IF 2 IF 1
Q
TURBINE REACHES FULL SPEED
CLOSE THE FIELD BREAKER
BUILD UP VOLTAGE TO 11KV
SYNCHRONISATION
INCREASE THE LOAD
ISLAND OPERATION
PARALLEL OPERATION
6 MW
GT-A
6 MW
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
More
load in shared condition.
Increase
Flexibility
in Reliability.
in Maintenance.
GT-A
GT-B
ARE THE FREQUENCIES SAME? ARE THE PHASE SEQUENCES SAME?
LOADS ARE THE VOLTAGES SAME?
3 7 MW
GT-A
4 MW
GT-B
LOAD HAS TO BE SHARED BETWEEN THEM
7 MW
LOAD LOAD DEMAND IS CONSTANT
f
GT-A
P
6 MW
3 MW
GT-B
1MW 4 MW
P
Load demand is constant
Increase in Governor set point of one Generator increases the system frequency and Real power on that Generator
Increase in Field current of one Generator increases the system voltage and Reactive power on that Generator
Voltage and Frequency are constant i.e not in our control f
V
P
Q
WHEN INCOMING FREQUENCY IS GREATER THAN GRID: APTRANSCO
P
PAPTRANSCO
f
GT-A
PGT
P
WHEN INCOMING FREQUENCY IS LESSER THAN GRID: APTRANSCO
P
PAPTRANSCO -PGT
f
GT-A
P GT-A ACTS AS LOAD
WHEN THE GOVERNOR SET POINT OF GT-A INCREASES:
APSEB
P
6 MW 4 MW 2 MW
f
GT-A
1 MW 3 MW 5 MW
P
Voltage
and Frequency are fixed by GRID
Governor
set point decides the Real
Power Field
current decides the Reactive 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 Over / Under voltage Protection
CTS
Winding
R
Winding
Y
Winding
B O/C OCCURS
I > 540 A or 1941 A NGR
RELAY
Relay operates in ‘ t ‘ sec
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
I
Winding
R
Winding
Y
Winding
B
I >15.2 A or 20 A
CT Relay operates
NGR
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 set value , the relay operates
CTS
RELAY
CTS Winding
R
Winding
Y
Winding
B
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
Typically
8%
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 Typically 3% ( 5% ) reverse flow
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
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