Hi to all reading this!! I am new here and am seeking some input to a puzzler at work!
Our plant uses the typical ULIS. We noticed recently two of our load centers 600v/3ph showing a full scale deflection ground - 2 amps. When we turned 2 VFD's off (one on either bank - seperate metering), we observed both drop to normal levels. (incidently 1 VFD is a newer digital 1336 plus II - 25 amp, the other an older Relcon 400amp.
Q1. Is it correct that the harmonic distortion on our system would be likely a zero sequence current or a negitive sequence current? or a combination of A0, A1 & A2?? Note we are using the 3 light method and there is no indication of dimming on any phase.
Q2. The fact that there is an apparent ground - (FS deflection max grnd current - also phase to ground voltages 345 volts as expected), but no dimming . . . are we in a potential critical fault situation?
Also noteworthy, the other day we had an intersting grounded condition where we found 600v to ground on 2 phases and 16.5 volts to ground on the 3rd. We cleared that fault and voltages returned to normal. I have done some study on this but would appreciate any insight that you may be able to provide. With the information I receive I will be applying a power quality meter and testing to prove the theory.
Thanks again and looking forward to "hitting the ground" running.
Blair in the northern coastal rainforest of NW Canada!
Our plant uses the typical ULIS. We noticed recently two of our load centers 600v/3ph showing a full scale deflection ground - 2 amps. When we turned 2 VFD's off (one on either bank - seperate metering), we observed both drop to normal levels. (incidently 1 VFD is a newer digital 1336 plus II - 25 amp, the other an older Relcon 400amp.
Q1. Is it correct that the harmonic distortion on our system would be likely a zero sequence current or a negitive sequence current? or a combination of A0, A1 & A2?? Note we are using the 3 light method and there is no indication of dimming on any phase.
Q2. The fact that there is an apparent ground - (FS deflection max grnd current - also phase to ground voltages 345 volts as expected), but no dimming . . . are we in a potential critical fault situation?
Also noteworthy, the other day we had an intersting grounded condition where we found 600v to ground on 2 phases and 16.5 volts to ground on the 3rd. We cleared that fault and voltages returned to normal. I have done some study on this but would appreciate any insight that you may be able to provide. With the information I receive I will be applying a power quality meter and testing to prove the theory.
Thanks again and looking forward to "hitting the ground" running.
Blair in the northern coastal rainforest of NW Canada!