21.1.4.7 Closed Delta Connected Regulators
Three single-phase regulators can be connected in a closed delta as shown in Fig. 21.19. In the figure, the
regulators are shown in the raise position. The closed delta connection is typically used in three-wire
delta feeders. Note that the potential transformers for this connection are monitoring the load side line-
to-line voltages and the current transformers are monitoring the load side line currents.
Applying the basic voltage and current Eqs. (21.77) through (21.83) of the regulator in the raise
position, the following voltage and current relations are derived for the closed delta connection.
VAB
VBC
VCA2
43(^5) ¼
aRab 1 aRbc 0
0 aRbc 1 aRca
1 aRab 0 aRca
2
4
3
5
Vab
Vbc
Vca
2
4
3
(^5) (21:103)
Equation (21.101) in abbreviated form can be written as
½¼VLLABC ½aRVDabc½VLLabc (21:104)
When the load side voltages are known, the source side voltages can be determined by
½¼VLLabc ½aRVDABC½VLLABC (21:105)
where
½¼aRVDABC ½aRVDabc^1 (21:106)
In a similar manner, the relationships between the load side and source side line currents are given by
Ia
Ib
Ic
2
4
3
(^5) ¼
aRab 01 aRca
1 aRab aRbc 0
01 aRbc aRca
2
4
3
5
IA
IB
IC
2
4
3
(^5) (21:107)
A
a
S
L
C
B
IA
IA
IC
Ibc IB
IB
IC
Ic
Ia
Ib I
b
b
Ic c
Ica
Iab
Ia
SL
L
S
L
SL S
SL
FIGURE 21.19 Delta connected type B regulators.