~ 3 May 2010 ~

location : GT1B (PD1)

1) servicing GMCB (general main circuit breaker)

- GMCB is use to connect or isolate generator transformer from the grid.

- there are 3 unites of GMCB, one for each of the two GT's and ST's.
- GMCB uses a hydraulic spring mechanism in order to make or break the circuit.

2) step down the GT1B excitation transformer

generator (15kV) --> excitation transformer (830Vac) --> thyristor (change to DC) --> rotor

3) measure PI at the GMCB
- reading PI (polarization index) must greater than 1.5. it is better if can get greater than 2.

in the GMCB

PI test