Solar connection 277/ 4160 transformer

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epm

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When connecting a solar PV system to the grid using a 277/480 - 4160 transformer I am told that the transformer windings must exactly match the utility's. The reason for this is the 30 degree phase shift that would occurr with a wye/delta or delta/wye transformer. That part I understand.
The question I have is what would happen if this connection was made anyway, considering the 30 degree phase shift. Would it create power quality issues on the utility side or would it do more harm than that. It doesn't seem like there would be voltage between the two transformer outputs (utilty & customer) since they are both separately derived systems. Just tryng to understand.
 
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The shift is irrelevant in this situation because the inverter matches the utility on the 480V side anyway and to the inverter, it has no idea what's happening on the medium voltage side of the XFMR.
 
Right, the inverter does not care, its the utility. The problem is what could happen when the solar output exceeds what the customer is using. The phase shift after passing through the wye transformer back onto the utility delta grid. That is where the output would not be in phase with the utility power.
 
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epm said:
When connecting a solar PV system to the grid using a 277/480 - 4160 transformer I am told that the transformer windings must exactly match the utility's. The reason for this is the 30 degree phase shift that would occurr with a wye/delta or delta/wye transformer. That part I understand.
The question I have is what would happen if this connection was made anyway, considering the 30 degree phase shift. Would it create power quality issues on the utility side or would it do more harm than that. It doesn't seem like there would be voltage between the two transformer outputs (utilty & customer) since they are both separately derived systems. Just tryng to understand.
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The solar invereter will synchronize TO the point of connection, in this case the secondary of the transformer.
 
epm said:
Right, the inverter does not care, its the utility. The problem is what could happen when the solar output exceeds what the customer is using. The phase shift after passing through the wye transformer back onto the utility delta grid. That is where the output would not be in phase with the utility power.
Click to expand...

You aren't exporting through a seperate transformer. You are connected at the secondary. As a couple have stated, the shift is irrelevant. You will be importing energy that has had a 30 degree phase shift inside the transformer. When you export, the energy will shift the 30 degrees to match the utility.

I am trying to figure out how to tie this together to use a screw as an analogy, sort of a lefty loosey righty tighty thing...
 
Hv&Lv said:
You aren't exporting through a seperate transformer. You are connected at the secondary. As a couple have stated, the shift is irrelevant. You will be importing energy that has had a 30 degree phase shift inside the transformer. When you export, the energy will shift the 30 degrees to match the utility.

I am trying to figure out how to tie this together to use a screw as an analogy, sort of a lefty loosey righty tighty thing...
Click to expand...

Actually it does not make one bit of difference if you're exporting or importing.
 
weressl said:
Actually it does not make one bit of difference if you're exporting or importing.
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I realize that, I was trying to say that either importing or exporting will have the exact same shift.
 
Winding Tyoe and Phase Shift

Winding Tyoe and Phase Shift

If there is no attempt to parallel the low-voltage on parallel transformers, the phase shift is irrelevant. You can use wye-wye, delta-wye lag, or delta-wye lead.

However, utilities require a generator to be effectively grounded. That often means delta winding on the inverter side and grounded wye winding on the utility side. Essentially this is a grounding transformer.

A delta winding on the utility side poses a problem because if ther is a ground fault on the utility grid and the utility opens their supply, the inverter can continue to feed any load present (brifely) and this can lead to extreme over-voltages. The grounded wye-delta transformer solves this issue. An ungrounded wye on the utility side can also pose issues.

So, phase shift may not be the issue, effective grounding may be.
 
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