Overvoltage Limit Alarm on Sag Mill

just to add on the above, the sag is usually loaded to about 70% load capacity.and runs at 7 RPM and the ball mill runs at 11 RPM.

Is the alarm coming up on start up?

I'm thinking back to a problem I had with a mill where it would stall after about ¼ of a turn and then run back slightly until the torque was high enough to continue. We sort of cured the problem by leaving a higher burden in the mill on shut down.

Is it a synchronous motor? If so, are you perhaps slipping a pole? If so, OV trips could be the least of your problems.

Have you monitored the line voltage during the event?

We also faced similar problems;

Detailed investigation in one case revealed that someone has changed transformer tap position during preventive maintenance and in another case the protection relay was contaminated with dust and moisture causing malfunction.

we kind of switched the excitation control cards from the ball mill to the sag and vice versa and it seems we have sorted out the problem though not very convinced. the problem has since stopped. no loose connections were found in the process so i still do not understand the problem. any way atleast it'e working for now. thanks for all you contributions