Why do utilities like wye-wye transformers
Why do utilities like wye-wye transformers
(OP)
I overheard a conversation yesterday with someone trying to explain why utilities like or prefer wye-wye distribution transformers for supplying power to a facility. His explanation was basically saying that with a wye-wye transformer they didn't need a ground grid on the primary, and also explained that they tied the priamry and secondary neutrals together on these transformers.
Is there any truth to this or can someone please explain or give a reference why the utilities would prefer a wye-wye transformer for grounding purposes?
I understand that with a wye primary the utility can pass zero sequence current. Also from what I have read, wye-wye transformers are traditionally cheaper and also may lead to ferroresonace issues.






RE: Why do utilities like wye-wye transformers
Rafiq Bulsara
http://www.srengineersct.com
RE: Why do utilities like wye-wye transformers
RE: Why do utilities like wye-wye transformers
So, the great majority of their single transformers are rated for line to neutral voltage. For three phase banks, use what is in stock.
Bill
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"Why not the best?"
Jimmy Carter
RE: Why do utilities like wye-wye transformers
As for grounding the primaries, there is a ground at every pole connected to the transmission neutral line, though I still tend to see one in the transformer. Though in the cases where I have seen, the neutrals were not tied together.
RE: Why do utilities like wye-wye transformers
it works at distribution level to suppress ferroresonance by using wye-wye, but not at the transmission level
May you grow up to be righteous, may you grow up to be true...
RE: Why do utilities like wye-wye transformers
Connecting the neutral to the primary system neutral is required to stabilize the secondary voltages on most wye:wye transformers.
An example of the difference between grounding and connecting the neutral to the source neutral.
In many distribution systems the neutral is carried with the phase wires and is multiple grounded. A connection to the neutral conductor simultaneously grounds the transformer and connects it to the system neutral.
Now consider a hypothetical delta distribution system. A wye:wye transformer bank may have the primary neutral grounded but that will not necessarily stabilize the voltages on the secondary.
Note: the voltages may also be stabilized by a delta tertiary or to some extent by a three legged core. (phantom delta)
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Why do utilities like wye-wye transformers