Wye Wye configuration and Ferro Resonance?

Does anyone have any resource info on why- Wye- Wye connected transformers are used in certain situations and how they correlate to helping or hindering Ferro Resonance? After reading what I can find, and listening to the POCO, I am confused.

Situation we have- 34.5kv Ungrounded Delta service from the POCO to customer. Customer has 4160v generators and Wye- Delta (step up) transformers to generate the 34.5kv in the event of a utility outage.
POCO states that whenever they have a fault on their line, the fault current is seeking the H0 to ground bond on customer’s transformer, instead of going back to substation… and is burning up their static lines.
They state this is a case of Ferro Resonance and customer must replace both of their Wye Delta Transformers with Wye-Wye xfmrs.
Having never heard that term before, I started doing some hw and am now more confused than I was before! Any help understanding these topics would be greatly appreciated…

Ps- Eng. firms are being brought in to analyze the situation and recommend a solution, but I would really like to understand what’s going on…
Ty!

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Super interesting situation. Tbh I’m no expert in this area but I’ll take a stab at it.

The ferroresonance thing is completely not a concern. Here is a great video explaining ferroresonance.

I’m also not buying that changing a customers transformer wiring is going to prevent the “POCO”?? ( I assume this means utility co.??) from having issues. I’d say if the utility is burning up “static straps”?? (Again, sorry don’t know what you mean by this) they the utility needs to upsize those conductors b/c they are likely undersized.

It’s been a while since this post do you have any updates???

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The customer hired a 3rd party engineering firm and yes, they said they are the wrong types of transformers for the application, though I never heard why.
The original protection schemes were apparently never commissioned properly and didn’t provide the protection intended or advertised.
My employer has been hired to replace both transformers, associated cabling and upgrade the protection schemes to engineered requirements, though we have not seen them yet. The transformers are on order but still many, many months away.

Seems like there were multple issues all compounding together. Many hearsay tidbits of info have come out but none verifiable, such as “someone” received a kickback to buy the transformers they did, the commissioning company had new and inexperienced commissioning technicians…who, when they couldn’t get things to work as engineered, changed things to get their tests to pass… etc. idk

In short, sounds like they are going to be rebuilding almost the whole system.

My apologies that I don’t have a better answer or resolution to this matter.

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