Synchronous generator covert mechanical power into electric power in power plant. It is very complex and interesting machine for electrical engineers. In steam power plant, Generator coupled with steam turbine so when steam passes through turbine, it rotates which cause rotation of generator. Generator has field winding on rotor and 3 phase winding on it's stator, so when field rotate it induce 3 phase voltage on stator of generator.
For Protection and Measurement of big giant generator various CT and PT are mounted at different places. I have worked in many power plant, so this is just reflection of my work.
Generator detail:-
Rated Power = 22.5 MW
Rated Voltage = 6.6 kV
Power factor = 0.8 (lag)
Grounded with Neutral grounding resistor
For protection of generator two identical same relays placed which are in series. In that one is main relay GPR-1 (GROUP PROTECTION RELAY) and other is redundant relay GPR-2. if one is fail to operate during fault condition then other take care of that fault. Generator is connected in star, so it has two end points. One side is where you take power from generator and other side is where star point made.
Generator has two side, one is LINE side and other is STAR POINT side.
Generator LINE side CT:- As describe above, power taken from line side of generator.
Total 6 CTs are there, 3 CT (R-Y-B) for GPR-1 and 3 CT (R-Y-B) for GPR-2.
Each CT has 3 core.
Core-1:- used for differential protection have PS class and ratio of 3000/1.
Core-2:- used for metering purpose have 0.5 class and ratio of 3000/1.
Core-3:- used for AVR(Automatic Voltage regulator) have 0.2 class and ratio of 3000/1.
Generator STAR Point side CT:- This is where star point of generator made and ground through NGR.
Total 3 CT are there for R-Y-B. Each CT has two core.
Core-1:- used for differential protection have PS class and ratio of 3000/1.
Core-2:- used for other protection have PS class and ratio of 3000/1.
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| STAR POINT OF GENERATOR |
LA, SC, PT Panel:- Lighting arrester, Surge capacitor and PT panel.
There is PT which has 3 cores.
Core-1:- used for voltage protection have 3P class and ratio of 6.6kv/110V.
Core-2:- used for metering purpose have 0.5 class and ratio of 6.6kv/110V.
Core-3:- used in AVR for volage control have 0.2 class and ratio of 6.6kv/110V.
NGR Panel:- Neutral ground resistor panel has only one CT used for earthfault protection having ratio of 100/1 and have class of 5P10
Neutral CT in NGR Panel
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