Three phase transformer for connecting 480/277V inverters to a 208/120V service

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wwhitney said:
Your diagram shows a factory H0-X0 bond on the transformer. Is that common, and is it ever non-removeable?

With such a H0-X0 bond, if you land the primary neutral on its terminal, you don't have an SDS, and so there would be no secondary side N-G bond, and the primary EGC would be the secondary EGC.
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Yeah the few wye-wye setups I have seen were factory bonded.

pv_n00b said:
The delta primary almost always fails loss of phase commissioning tests if you depend on the inverter sensing the loss of phase.
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There is a good reason to have the wye-wye right there.
 
tortuga said:
Seems like the neutral on the primary side would be grounded 250.24(A)(5)
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FWIW, previous discussions of this particular facet:

Wye Wye Transformer Bonding

Two things I've always held to: 1) Neutral and Equipment Grounding conductor are bonded at Service panel (point of origination) and NEVER to meet again. 2) With transformers creating a Newly Derived system, Neutral and Equipment Grounding conductor are Bonded at Secondary ONLY. Have run into...
forums.mikeholt.com

Wye Grounded Primary and Wye Grounded Secondary Transformer

What should be the grounding procedure for Wye-Grounded Primary and Wye Grounded Secondary TRANSFORMER to be considered as Separately Derived System?
forums.mikeholt.com

Wye to wye questions

Attached sketch shows from left to right: 600VAC inverters feeding customer owned 600V, 3000A service rated switchboard which has neutral to ground bond, GEC to ground grid and feeds 2000kVA 600VAC to 13.2kVAC customer owned transformer wye to wye. The transformer has no neutral to ground bond...
forums.mikeholt.com

It seems like the factory bond between HO and XO may be optional, at least in theory. I don't have experience to bring to bear on it.
 
pv_n00b said:
The delta primary almost always fails loss of phase commissioning tests if you depend on the inverter sensing the loss of phase. We have to put relay protection on the primary side to detect loss of phase to pass commissioning and get PTO. Maybe in theory it should work, but in the field, it does not.
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So just to be clear: You are saying that with an inverter fed from a delta wye transformer (delta on utility side), a phase loss on the utility side of the transformer will often not be seen by the inverter, but it will with a wye wye transformer? IF so, a few follow up questions:

1. Maybe im missing something obvious, but is there a problem if the inverter keep goings with a phase loss?
2. related to #1 but who is requiring the phase loss relay, the POCO?
 
electrofelon said:
So just to be clear: You are saying that with an inverter fed from a delta wye transformer (delta on utility side), a phase loss on the utility side of the transformer will often not be seen by the inverter, but it will with a wye wye transformer? IF so, a few follow up questions:

1. Maybe im missing something obvious, but is there a problem if the inverter keep goings with a phase loss?
2. related to #1 but who is requiring the phase loss relay, the POCO?
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Another followup question: In a delta - wye configuration, if losing a phase on the delta side isn't seen by an inverter on the secondary, does that mean that the line to neutral voltages on the secondary do not change? That doesn't seem possible to my admittedly rudimentary understanding of the inner workings of three phase transformers. If the inverter were to keep running and pushing its full power through two of the three lines on the primary side, at the very least that would trip the OCPD on those two lines where they interconnect with the service.
 
pv_n00b said:
The delta primary almost always fails loss of phase commissioning tests if you depend on the inverter sensing the loss of phase.
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I'm also having trouble understanding how this could be the case.

For the case of the OP, with a 208V delta primary and a 480Y277 wye secondary, wouldn't loss of one primary leg give you a single phase 416V secondary output, where H0 (secondary) is 277V from one ungrounded conductor and half that from the other two ungrounded conductors?

What kind of inverters are you dealing with, and can't they be programmed to trip out if any of the L-N voltages change from 277V to 138V? Or is it an issue that they don't trip out fast enough?

Cheers, Wayne
 
wwhitney said:
What kind of inverters are you dealing with, and can't they be programmed to trip out if any of the L-N voltages change from 277V to 138V? Or is it an issue that they don't trip out fast enough?
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All these inverters have fairly narrow operational voltage windows, and they shut down if/when the voltage strays out of them.
 
@ggunn I am curious do your 1000 volt and below wye-wye transformer designs have the HO and XO bonded? And are they wired like the diagram I posted in post #29?
 
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