Transformer Questions

[PowerWagon]

Hello All, I haven't worked with transformers in PV systems that much so I'm a little out of my league here. Our client has an older Xantrex PV45208 inverter. As the name implies it uses 208 three phase with an isolation transformer. The inverter is going into a fault code 00000008 which the manual states is a ground fault on -B. I assume this means B phase. Since the grid goes through a transformer I'm not sure how to check for ground faults. In addition when I checked the voltage at the main panel I got 121VAC to ground as I would expect, but on the other side of the windings, Inverter side I get 111VAC, 92VAC and 133VAC. This doesn't look right. Anyone got any suggestions?

 

[jim dungar]

You need to know how the transformer is configured. Doe example, common non-utility 3-phase transformers have the high voltage windings connected in a delta while the low voltage are in a wye. This type of configuration prevents a ground fault on one side of the transformer from being passed to the other.

 

[PowerWagon]

Hi Jim, Thanks for your response. Tried to insert a picture from the transformer data plate I'm talking about. but it won't upload. The data plate says H.V 208Y/120 and L.V. 208Y/120. It's a Square D NO: 45TQ56367 if this helps. Is there a way to tell if there is a ground fault and why would I get the voltage readings I mentioned.

 

[jim dungar]

Is there a way to tell if there is a ground fault and why would I get the voltage readings I mentioned.

That is a non-standard, but not uncommon, wye-wye connected transformer.

Your readings might be due to a failure of your invertor, like it says, or from a bad connection to the invertor side wye point.

Have you disconnected the invertor and measured the transformer voltages?

 

[PowerWagon]

Good suggestion, I could try that.

 

[jaggedben]

Hello All, I haven't worked with transformers in PV systems that much so I'm a little out of my league here. Our client has an older Xantrex PV45208 inverter. As the name implies it uses 208 three phase with an isolation transformer. The inverter is going into a fault code 00000008 which the manual states is a ground fault on -B. I assume this means B phase. Since the grid goes through a transformer I'm not sure how to check for ground faults. In addition when I checked the voltage at the main panel I got 121VAC to ground as I would expect, but on the other side of the windings, Inverter side I get 111VAC, 92VAC and 133VAC. This doesn't look right. Anyone got any suggestions?

I'm not familiar with that inverter but I wouldn't assume. I'd reread the manual and try to make sure their not talking about a DC side ground fault. For one thing, I've never met an inverter that did ground fault detection on the AC side. Not saying you're wrong, just saying I wouldn't assume it.