Voltage and Frequency Affected by 5300-hp Sync Motor Start

Slip a pole?

OOOOPs--Slip a pole??

That can happen at pull-in, i.e. right when the field application relay closes to apply the DC to the rotor windings. Not supposed to, but it does.

Besides the possible reasons suggested by other friends, I feel the frequency measuring instruments can give erratic readings especially during the supply waveform clamping which is likely to incur during start-up of the heavy motor. The chances of this are more likely if the two separate multilins reffered above are of same type and brand.

In fact, the frequency cannot go to zero for the un-interrupted AC source for only one cycle especially while the AC Voltage is present and is recorded by the Voltage measuring instrument.

Perhaps it may be better repeat the test with another set of instruments.Frequency normally cannot go to zero on a infinity source.By the way what is the source?Thanks for bringing this to the forum.We may all gain some thing and have some interesting points in this thread.

Dear Sir,

The " Zero Hz " frequency phenomenon, so far , as major grid system to which your electric machine is connected is not possible SIR.

Otherwise the cascade tripping is just enevitable.

Regards,

Ulhas Pradhan

From my experience with Multilins the sampling time sometimes is not adequate to record high speed events in power systems.. As suggested obtain a high speed power monitor and try again..

Also, are the Multilins powered from DC source, or from the CPT in motor starter.. If CPT, the voltage dip / or surge, could cause the trending data in Multilin to become unreliable..

GA - I agree as this has also been my experience with GE Multilins. I wonder what kind of starting scheme is being used...

Say there dude, did you check to see if your instrumrntation will operate properly at 89% voltage? Got a battery powered model? Give that a try. If that still gives you the same result then you have indeed slipped a pole. No biggie.