Help on differences between 3 phase transformers

Discussion in 'General Electronics Chat' started by AESNJCOGEN, Oct 21, 2010.


    Thread Starter New Member

    Oct 21, 2010
    I am installing an induction generator in New York City which will operate in parallel with the local electric utility, Con-Ed. The utility requires that my 480 volt induction generator be stepped down through a 480Y / 208 volt Delta type transformer for interconnection to the utility grid @ 208 volts. I have purchased a transformer rated 112.5 KVA, 480Y x 208 Delta (star?). The installing electrician says this type of transformer is very different from a simple 480Y x 208 Delta type transformer. He says it is less efficient and could cause harmonics problems.

    The transformer has the following connections:

    H0 - H1 - H2 & H3 / X1 - X2 & X3.

    There is no low voltage side neutral connection. The utility requires that the high side neutral (H0) be bonded to the chassis frame and grounded to the building ground. Can anyone explain?
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
    "High side" as in the 480Y side? It should definitely be bonded to ground to keep the individual 277V legs from going into a floating condition where one might rise beyond the safety point of the transformer or generator's insulation breakdown point.
  3. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    The utility views your high side as a seperate service, and request the neutral be grounded. Code calls for such. Your low side is a load, and should not be grounded. Neutral on the low side is not important as you are not utilizing that voltage offering.

    In regards to efficiency/harmonics, if you provide 'dirty' power, the utility will ask you to leave. Effeciency will impact your returns.

    Watched a show where several Ontario farmers built substantial waste generators along with transmission lines, only to have Ontario hydro refuse to connect them. Shame.
  4. zgozvrm

    Active Member

    Oct 24, 2009
    Did you ever find the problem with the transformer?

    Perhaps it is an open-delta / open-wye transformer. Or more likely, it is a T-type transformer.
    I've attached a wiring diagram for a multi-tap delta primary, wye secondary transformer which is the reverse of what you're looking for.