The Power to the 1050kW, 6kV motor is fed from VCB-->VFD-->Motor. We heard from the operator that the motor stops suddenly and starts after the 30s~1min. I feel that this might be due to the voltage fluctuations from the power supply side. The Under voltage protection at the VCB Panel has 50ms time delay but the VFD has only 30ms. Therefore the under voltage protection at the VCB panel may not have operated but the under voltage protection at the VFD may have operated and restarted again as the VCB which is feeding the VFD is still ON. The important point is to note that the VFD did not trip the VCB on the operation of under voltage function. There no other alarms/trips while this happened. I have not heard about the VFD showing any fault in it's display.
Has any experienced this type of problem? any comments?
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