One of our 24MW,13.8KV STG was tripped due to the stator earth fault causing the blackout of the plant and resulting in the damage of the stator windings(U,W).
Our grid is and island grid with 3 STGs connected to the grid (2 of 24MW and one of 10MW)
The stator winding were repaired and one turn of each phase (U,V,W) was bypassed and new rotor was installed.
Rotor healthiness was tested through RSO test. However, stator windings was checked by megger test and Hi-Pot test at 17KV for 1 minute and was found ok.
At startup, we decided to check the generator through open and short circuit test. While performing open circuit test , the AVR voltages were increased manually with some steps. When the terminal voltage (Vt ) of the generator reached 11KV , the NDE (non-Driven End) Bearing Temperature increases to 425 C resulting in the tripping of turbine.
While, same test was repeated, and the same result was obtained but this time we decreased the excitation voltages which decreases the temperature of the NDE bearing protecting the turbine from tripping.
Kindly suggest what can be the real causes on the issues on the generator and what checks need to be taken before attempting another start-up??
Our grid is and island grid with 3 STGs connected to the grid (2 of 24MW and one of 10MW)
The stator winding were repaired and one turn of each phase (U,V,W) was bypassed and new rotor was installed.
Rotor healthiness was tested through RSO test. However, stator windings was checked by megger test and Hi-Pot test at 17KV for 1 minute and was found ok.
At startup, we decided to check the generator through open and short circuit test. While performing open circuit test , the AVR voltages were increased manually with some steps. When the terminal voltage (Vt ) of the generator reached 11KV , the NDE (non-Driven End) Bearing Temperature increases to 425 C resulting in the tripping of turbine.
While, same test was repeated, and the same result was obtained but this time we decreased the excitation voltages which decreases the temperature of the NDE bearing protecting the turbine from tripping.
Kindly suggest what can be the real causes on the issues on the generator and what checks need to be taken before attempting another start-up??