Electric Power Generation, Transmission, and Distribution

where

½Š¼aRVABC ½ŠaRVabc^1 (21:98)

21.1.4.6 Current Equations

IA

IB

IC

2

4

3

(^5) ¼
1
aRa
00
0
1
aRb
0
00
1
aRc
2
6
6
(^66)
(^64)
3
7
7
(^77)
(^75)
Ia
Ib
Ic
2
4
3
(^5) (21:99)
or
½Š¼IABC ½ŠaRIabc½ŠIabc (21:100)
also
½Š¼Iabc ½ŠaRIABC½ŠIABC (21:101)
where
½Š¼aRIABC ½ŠaRIabc^1 (21:102)
where 0.9aRabc1.1 in 32 steps of 0.625% per step (0.75 V=step on 120 V base).
Note: The effective turn ratios (aRa,aRb, andaRc) can take on different values when three single-
phase regulators are connected in wye. It is also possible to have a three-phase regulator connected in
wye where the voltage and current are sampled on only one phase and then all three phases are changed
by the same value ofaR(number of taps).
B
A

• 
  


• 
  

  −−
  VAn
  Van
  C
  IB
  Ia
  Ib
  a
  b
  Ic
  c
  IA
  IC
  FIGURE 21.18 Wye connected type B regulators.