Schweitzer Engineering SEL-387-0, Instruction Manual

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H.9
Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Protection Application Examples
Transformer Winding and CT Connection Compensation Settings Examples
Figure H.11 Standard CT Connections
Standard CT Connections.
In Figure H.11 , the polarity of the CT
connects to the polarity of the relay current input, and the primary system
phase current connects to the same phase input on the relay (e.g., IA system to
IAW1 relay input). While the H-side currents connect to the W1-terminal and
the X-side currents connect to W2-terminal, they could be connected to any
two sets of current inputs on the relay.
Figure H.11 represents the standard
connections for the transformer, CTs, and relay.
Figure H.11 also shows the primary system currents (IA system, Ia system)
and the CT secondary currents seen by the relay (IA relay, Ia relay) based on
the currents of
Figure H.6 . For these connections, with power flow from the
H-side to the X-side of the transformer, currents enter the relay at the polarity
mark on the H-side, and leave the relay at the polarity mark on the X-side.
Thus, on the primary system, Ia lags IA by 30 degrees, but at the relay, IAW2
leads IAW1 by 150 degrees, as shown in
Figure H.12 . B- and C-phases follow
this relationship. Only A-phase is discussed for simplicity, but the concept is
the same.
Figure H.12 Primary System Currents and Currents as Seen by the Relay
B (H2)
C (H3) A (H1)
Winding 1 Winding 2
A
B
C
a
b
c
IAW1
IBW1
ICW1
IAW2
IBW2
ICW2
H3
H2
H1
X3
X2
X1
IA System Ia System
IA Relay Ia Relay
c (X3)
b (X2)
a (X1)
SEL-387
(Partial)
Primary
30°
IA
Ia
150
°
IAW1
IAW2
Secondary