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Step-type Voltage Regulator Impedance

Step-type Voltage Regulator Impedance

Step-type Voltage Regulator Impedance

(OP)
I am trying to model some step-type voltage regulators for short-circuit calculations.  I have a couple of questions:

Does anyone have a source for typical regulator impedances?  This data is not on the regulator nameplate.  

Due to the limitations of the modeling software, I need to model these as two-winding transformers with load tap changers, even though they are really autotransformers.  Can someone explain how to translate an autotransformer kVA and impedance to an equivalent two-winding kVA and impedance for the purpose of short circuit calculations? (This has always confused me, for some reason)

Thanks.  

RE: Step-type Voltage Regulator Impedance

From Westinghouse T&D Reference Book, Chapter 11, page 395
TABLE 13 - Impedance of Feeder Regulators - Percent On                
Circuit KVA Base - Plus or Minus 10 Percent Regulation                
                                             Max.    Min.    Neutral Pos.
Induction                
    Single-phase..................... 2.5    0.7    1.5
    Three-phase...................... 1.5    1    ...
Step-Type                
    Single-core....................... 0.4    0    ...
    Two-core, three-winding......0.7    0.4    ...
    Two-core, four-winding...... 1.1    0.5    ...

RE: Step-type Voltage Regulator Impedance

Also from Westinghouse T&D Reference Book Chapter 5, page 117. The ratio between winding kva (Up or Us) and circuit kva (Uc) is,
Up/Uc = Ea x Ip/Ea x Ia  = Ip/ (N/N-1)Ip  =  N-1/N

For example, an autotransformer rated 1000 kva, with a circuit voltage ratio of 22 kv to 33 kv (N = 33/22 = 1.5) has an equivalent two-winding kva of
Up = Us = (N-1)Uc/N = (1.5-1.0)x1000/1.5 = 333 kva

To express the impedance in terms of Zps
Za = ((N-1/N)^2) x Zps

Sequence connections are shown in the appendix. I can e-mail the drawings to you if needed.

RE: Step-type Voltage Regulator Impedance

(OP)
Thanks, tgott.  I have the T&D Book, but I never thought to look in there.  I think I'm in business now - thanks again.

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