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No, it's not a variable transformer. It is the star primary which has an over-wind to increase the star secondary voltage. Star point is floating. No neutral in the rectifier. What are your thoughts ? Thanks. Scrummer

Gunnar, Yes, I was thinking of capacitors, trying to give the delta bridge a 50Hz earth reference. I can see that varistors would do the job in a different way, actually conducting only when the voltage gets too high. Wye secondary is by an auto-transformer, so the actual earth connection is...

You need to look at the the alternator rating (kVA), and the engine rating (kW). Alternators are traditionally rated at 0.8 PF, so we have a relationship between kW and kVA. You may have to deduct the power needed to drive the radiator fan from the engine power (kW). However, it also depends on...

Silly question, which the utility should already know the answer to: It's not the carrier frequency for some sort of ripple control signalling, is it ? They shouldn't have chosen a line harmonic frequency, but stranger things have happened !

I have a feeling that it is the fact that the delta secondary is floating which is key to the matter. I wouldn't be expecting to measure 20 or 30 or 50 kV between these line terminals and earth. All I would be looking for is perhaps a trend, that this voltage creeps up, maybe to 1 or 2 kV...

Gunnar: Thanks for the explanation. I see what you are getting at now. I'll have a look at the photos and see if the snubbers Caps look blown. Yes, varistors may help. However, I can't help feeling that it is something to do with the fact that the delta is totally isolated. To explain a...

Thanks ghostbuster7. No, it's not a true delta connected 480 V system. It should be a 400 V star system with the N connected to E at the HV transformer. The 480 V comes from the rectifier input trafo which is a combined auto (star) and isolated delta. Only the delta feeding the delta...

Thanks for all the ideas. magoo2. No, it’s not a typo. If we say about 25 kV per centimetre, and this arc “jumped” about 2 cm, we have about 50 kV. Like you, I don’t know how I could get that high a voltage, which is why I’m looking for all the ideas I can. wbd. Environment is an air...

I am trying to find the phenomena (plural) which are causing my equipment to arc over. We are talking about a 400 Vac, 12 pulse, 50 Hz rectifier. We had all 3 phases of the delta rectifier arc to the nearest earthed panel. The equipment has been in service for about a month, and is one of 4...