PV Inverter - Voltage Rise on One Phase

[NJWVUGrad]

I'm troubleshooting a PV installation where we have 10 3Ø inverters tied into a single switchboard then running a few hundred feet to the point of interconnection at a dedicated pad mount transformer.

When the PV panel main breaker is off, all voltages are nominal L-G 277V range. When the inverters connect and begin to export, the voltage on phase B & C go up to 280 or so and voltage on Phase A keeps rising up until the inverter shuts off due to overvoltage (around 305V)

I know that voltage rise is to be expected (and conductors were upsized to account for this, the 280V values are in the anticipated range.

But what I cannot figure is the voltage rise on Phase A. My thoughts are that it has to be a cable fault, transformer issue, faulty fuse-link etc. Anything else would effect all 3 phases equally. Right?

 

[itsmoked]

At what rate is the voltage increasing?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[NJWVUGrad]

Its rises over time with the increase in power being exported (i.e. when the sun is shining). I cannot figure why it is only on one phase

 

[jfpe]

You are going in the right direction. The voltage rise you are seeing is a consequence of Ohm's Law, an there is a difference between phases. Look for lose or high resistance connections in A Phase. It could be that the main breaker is faulty in your panel, you could have a bad termination in the panel or transformer, transformer problem, etc. Work you way back through the system until you don't see the abnormal voltage rise on A Phase or you don't have the PPE to test safely.

I had a similar case a few months back where one of the medium voltage fuses was partially blown. I could measure normal voltage with all equipment off, but when I turned on an inverter B phase voltage rose rapidly. When I plugged in a shop vac, B Phase voltage dropped rapidly.

-JFPE