Schweitzer Engineering SEL-387-0, Instruction Manual

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H.14
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Protection Application Examples
Transformer Winding and CT Connection Compensation Settings Examples
150 degrees. Figure H.19 shows the phase relationship of both the
primary system phase currents and the secondary phase currents as
seen by the relay.
Figure H.18 Delta-Wye Transformer With Non-Standard Phase-to-Bushing Connections
Select the delta winding as the reference winding. The H-side delta
current is connected to Terminal W1 of the SEL-387 Relay. Therefore,
set W1CTC = 0. The X-side currents are connected to Terminal W2, so
W2CTC must be determined.
Figure H.19 Primary Currents and Secondary Currents as Measured by the
Relay
IAW2 must be rotated 330 degrees (11 multiples of 30 degrees) in the
counter-clockwise direction for a system with an ABC phase rotation
to be 180 degrees out-of-phase with IAW1. Therefore, set W2CTC = 11.
The resulting compensation settings are W1CTC = 0 and W2CTC = 11.
Although the same transformer is used in Example H.1 and
Example H.2, notice that the non-standard phase-to-bushing
connections affect the compensation settings in both examples.
B (H2)
A (H3) C (H1)
Winding 1 Winding 2
A
B
C
a
b
c
IAW1
IBW1
ICW1
IAW2
IBW2
ICW2
H3
H2
H1
X3
X2
X1
IA
IA Relay Ia Relay
Ia
a (X3)
b (X2)
c (X1)
SEL-387
(Partial)
Primary
IA
Ia
330°
Secondary
330°
IAW1
IAW2
150°
IAW2
(Compensated)