Paralleling Transformers
Paralleling Transformers
(OP)
We are adding a 2nd 150/280MVA auto-xfmr to a 230/115kV substation. The xfmrs are to be run in parallel. Each has a delta tertiary. Through fault impedances are nearly identical on a 150MVA base. The intent is for each xfmr to be on taps so that ideal voltage ratios are identical.
There is one difference: Due to bus arrangement difficulties, there is a difference in which phase is connected to which bushing:
Auto 1: A to H1/X1, B to H2/X2, C to H3/X3 (1993 vintage)
Auto 2: C to H1/X1, A to H2/X2, B to H3/X3 (2008 vintage)
The phasing issue has been worked out.
The design has been questioned by some field people: Someone wondered if some unknown problem might arise, such an interplay of the excitation currents between the two xfmrs. My reaction is that I do not think any problems will arise, but maybe I just have insufficient experience. Does anyone have any experience with a problem that might arise?
There is one difference: Due to bus arrangement difficulties, there is a difference in which phase is connected to which bushing:
Auto 1: A to H1/X1, B to H2/X2, C to H3/X3 (1993 vintage)
Auto 2: C to H1/X1, A to H2/X2, B to H3/X3 (2008 vintage)
The phasing issue has been worked out.
The design has been questioned by some field people: Someone wondered if some unknown problem might arise, such an interplay of the excitation currents between the two xfmrs. My reaction is that I do not think any problems will arise, but maybe I just have insufficient experience. Does anyone have any experience with a problem that might arise?






RE: Paralleling Transformers
RE: Paralleling Transformers
If you are concerned about the LTC: I would think problems would happen if you have significent system unbalance. And with modern theory of not needing to transpose lines that is a real possibility.
This mainly applies to the cross connected CT method, and may not apply to the other methods.
RE: Paralleling Transformers
RE: Paralleling Transformers
They replaced a set up that used a transforme with minimal taps and an in series voltage regulator ( autotransformer).
I don't remeber seeing the tertiarys paralleled.
RE: Paralleling Transformers
RE: Paralleling Transformers