I have come across one case where motors experienced damages during commissioning. motors are 11kV rated 650kW. motors are switched with vacuum CB. It is speculated that failure is due to high transient voltages while switching on and off.

Any comments

Is the feeder cable to the motor multi or single conductor and is it shielded and if so is it grounded?;p;

Feeder is single cable 3C150 mm2 and shielded, grounded.

Ok noble, what kind of test have you done to determine that the cause for the failure is due to high transient voltage. Just trying to get a feel for what might be taking place.:D

Hi

Maybe a little late, but rather late than never.

One possible reason for failure can be voltage spikes due to swithching of the vacuum breaker.

See this enclosed site:

http://www.joslynclark.com/downloads/Vacuu...rviewwithQA.pdf

check especially questions/answers on botom of page 3 and on top of page 4.

Regards
Ralph