Well, I couldn't find the post I just posted, so here it goes again.
I've been having an intermittent ground issue on one of my 480V switchgear lately. What happens is that this ground alarm comes and goes. When it happens, it would actually last only for seconds, and then it would just go away. The whole duration could be 30-40 minutes, or it could be hours or half a day, and the problem will just repeat during the process. Because of the fact that it comes and goes, the alarm registry would actually register hundreds of the same "ground alarm" within hours. So far, there's no pattern, it's very erratic, and there's simply no way to predict.
Now, what's more interesting about this ground issues is that this one is not the one we normally see, i.e. one of the three lights off, and stays off until you keep switching off the right load the dead light will be lit again. Instead, when the ground comes, and because of the fact of the fast come-and-go, it makes all three lights flicker at the same time, but everything will be back to normal when the ground goes away.
I have used a FLUKE Power Analyzer to look at this. I wanted to rule out that it's not the swtichgear's instrumentation giving me this, and the result is: the ground alarm is telling me the truth. The FLUKE tells me that, when the ground happens, my phase B goes down to some 130V phase-to-gnd voltage, and phase A,C spike up to some 590V phase-to-gnd voltage. This makes sense as we have a 480V ungrounded system, and a normal phase-to-gnd voltage would be 277V, which is the right voltage observed when the ground goes away.
Now, the challenge is to find where this ground is. It's always a pain in the butt. I've looked at almost everything except for a few transformers. Thus my question is: can a ground (even intermittent) on one phase of my 2400V primary side cause a problem on the secondary 480V side? thus spike/dip the voltage? can the same thing happen to my secondary 120V side of the transformer and give me a problem on the 480V side?
Both 2400V and 480V in my plant are ungrounded system.
Any ideas and thoughts are very much appreciated!!
Thanks.
I've been having an intermittent ground issue on one of my 480V switchgear lately. What happens is that this ground alarm comes and goes. When it happens, it would actually last only for seconds, and then it would just go away. The whole duration could be 30-40 minutes, or it could be hours or half a day, and the problem will just repeat during the process. Because of the fact that it comes and goes, the alarm registry would actually register hundreds of the same "ground alarm" within hours. So far, there's no pattern, it's very erratic, and there's simply no way to predict.
Now, what's more interesting about this ground issues is that this one is not the one we normally see, i.e. one of the three lights off, and stays off until you keep switching off the right load the dead light will be lit again. Instead, when the ground comes, and because of the fact of the fast come-and-go, it makes all three lights flicker at the same time, but everything will be back to normal when the ground goes away.
I have used a FLUKE Power Analyzer to look at this. I wanted to rule out that it's not the swtichgear's instrumentation giving me this, and the result is: the ground alarm is telling me the truth. The FLUKE tells me that, when the ground happens, my phase B goes down to some 130V phase-to-gnd voltage, and phase A,C spike up to some 590V phase-to-gnd voltage. This makes sense as we have a 480V ungrounded system, and a normal phase-to-gnd voltage would be 277V, which is the right voltage observed when the ground goes away.
Now, the challenge is to find where this ground is. It's always a pain in the butt. I've looked at almost everything except for a few transformers. Thus my question is: can a ground (even intermittent) on one phase of my 2400V primary side cause a problem on the secondary 480V side? thus spike/dip the voltage? can the same thing happen to my secondary 120V side of the transformer and give me a problem on the 480V side?
Both 2400V and 480V in my plant are ungrounded system.
Any ideas and thoughts are very much appreciated!!
Thanks.
