ABB Relion 670 Series Applications Manual page 86

Section 4
Analog inputs
In case of a solid ground fault close to the VT location the primary value of 3Vo will be equal to:
V
=
Ph Ph
3 Vo
EQUATION1927-ANSI V1 EN-US
The primary rated voltage of such VT is always equal to VPh-Gnd. Therefore, three series
connected VT secondary windings will give the secondary voltage equal only to one individual VT
secondary winding rating. Thus the secondary windings of such open delta VTs quite often has a
secondary rated voltage close to rated phase-to-phase VT secondary voltage, that is, 115V or
115/√3V as in this particular example. Figure
to make this measurement available to the built-in protection and control functions within the IED.
138
138 kV
3
115 V
3
138 kV
3
115 V
3
ANSI06000602 V2 EN-US
Figure 24: Open delta connected VT in low impedance or solidly grounded power system
80
- =
V
-
Ph Gnd
3
A
B
C
kV
3
115 V
3
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24 gives an overview of the actions which are needed
IED
2
13
AI07 (I)
14
15
AI08 (V)
16
17
AI09 (V)
18
1 3
19
AI10 (V)
20
21
+3Vo
AI11 (V)
22
23
AI12 (V)
24
1MRK 511 401-UUS F
SMAI2
BLOCK
^GRP2_A
# Not Used
# Not Used
^GRP2_B
# Not Used ^GRP2_C
^GRP2N
TYPE
4
ANSI06000602-2-en.vsd
Bay control REC670
Application manual
(Equation 7)
5
AI3P
AI1
AI2
AI3
AI4
AIN