Generator OV trip 1

[jimmy2times]

We have two identical MV generators on ship, 9MW each, after long period of maintenance we return to service. On paralleling they both trip on over volts. Then we test one on its own, sometime it trips on over voltage when energise mv/lv transformer (no other load on generator or secondary of transformer). Then for few days it is fine and no issues energising the same many times transformer. Then start some decent size reactive loads it is ok. But on one occasion it overvoltage trip with starting our largest compressor on LV side, which is soft start. The network voltage increased with the ramp of the soft starter until generator trip on overvoltage again.

Then we take all load off both generators and parallel at very low load (400kw], there was a reverse power trip, first time one generator, then next separate occasion the other gen trip on reverse power.

Then next we start with one gen and we put more load on 30%, then parallel, they sync ok. But load share is not the perfect, one 10% one 8%. But the kvar sharing is very bad 2 to 1 (normal is equal share in droop).

I wonder if this could be symptom of rotating diode failure? Open or short diode? Any thoughts?

Maybe two issues, the other being sync window of generator being too wide when at very low load.

 

[waross]

During maintenance someone may have changed the connections on the quadrature circuit.


Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!