Schweitzer Engineering SEL-387-0, Instruction Manual

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H.19
Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Protection Application Examples
Transformer Winding and CT Connection Compensation Settings Examples
Figure H.27 Direction of Compensation Based on System Phase Rotation
Thus, the compensation settings required for Example H.1 and
Example H.5 are the same. Following the settings guideline, the delta
side of the transformer is selected as the reference, so W1CTC = 0.
Figure H.28 shows IAW2 needs to be rotated 30 degrees (1 multiple of
30 degrees) clockwise for a system with an ACB phase rotation in
order to be 180 degrees out-of-phase with IAW1. Therefore, set
W2CTC = 1. The resulting compensation settings are W1CTC = 0 and
W2CTC = 1.
Figure H.28 Primary Currents and Secondary Currents as Measured by the
Relay
If the relay is set assuming an ABC phase rotation, but the actual
system phase sequence is ACB, the relay compensation settings do
not need to be changed. However, the calculated positive- and
negative-sequence currents will be incorrect unless the Global setting
for phase rotation, PHROT, matches the system phase sequence.
PHROT does not affect the compensation settings or the differential
protection.
EXAMPLE H.6 Delta-Wye Transformer With Standard
Phase-to-Bushing Connections, Standard CT Connections, and an
ABC System Phase Rotation With a Zig-Zag Grounding Transformer
Within the Differential Zone on the Delta Side
This example uses the same transformer and CT connections as in
Example H.1, except that it includes a zig-zag grounding transformer
within the differential zone on the delta side of the transformer. Zig-
zag transformers are typically used for grounding purposes and act
as a source of zero-sequence current. If the zig-zag transformer is
located outside of the differential zone on the delta side, it can be
ignored, and the compensation settings will remain the same as in
Example H.1. The same is true if the zig-zag transformer is present on
the wye side, be it inside or outside the differential zone. If the zig-zag
grounding transformer is within the differential zone on the delta
side, then it has to be accounted for when determining the
compensation settings.
The compensation settings in Example H.1 are W1CTC = 0 for the delta
winding (reference winding) and W2CTC = 1 for the wye winding.
When a ground current source is within the differential zone on the
delta side, the recommended compensation setting of W1CTC = 0
cannot be used. The zero-sequence current needs to be filtered to
avoid an operation of the differential element for external ground
faults. Therefore, set W1CTC = 12. Matrix CTC(12) has no phase shift,
but CTC(12) removes zero-sequence current from the differential
calculation.
WnCTC
(CW) WnCTC
Direction
WnCTC
(CCW)
ABC Rotation ACB Rotation
Primary
30°
IA
Ia
150
°
30°
IAW1
IAW2
Secondary
IAW2
(Compensated)