Hello,

          As i obsered from the Crane,

1. First they start DGand waiting for 5 minutes, after that control and main power is switched on in the Control room. And when Control& Mains ON time i checked voltage is around 400V and Frequency is 58Hz (South korea is 60Hz). And those values are stable, there is no fluctuations.

2. Earthing and Grounding is ok.

3.They never use any electricity power source, they only use DG power. 

4. Only one drive have this problem. totally 2 cranes with 6 drives. So the problem looks strange......

Thanks and regards

Gopinath