Schweitzer Engineering SEL-387-0, Instruction Manual

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3.29
Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Restricted Earth Fault Element
Figure 3.14 REF Function, 32IOP Setting Guide
If you want to protect a single wye winding in, for example, a delta-wye
transformer, set 32IOP at 1, 2, or 3, which is the number of the relay winding
input associated with the line-end CTs of the protected winding. The relay
uses residual current from that single winding input as the Operate quantity.
Figure 3.14 shows neutral CT input connected to the Winding 4 input of the
relay, as it must be for every case where REF protection is to be used.
If you want to protect an autotransformer, set 32IOP at 12 and connect the
primary and secondary side CTs to relay winding inputs 1 and 2. You could
also use this setting for the single winding mentioned above, if that winding
had two breakers and two sets of CTs at the line end. You would also have to
connect these CTs to winding inputs 1 and 2. Such a connection would be
W1
W1
W1
W4
W4
W4
W2
W2
W3
W2
Delta–Wye
Autotransformer
Autotransformer
IOP
IOP
IPOL
IPOL
IPOL
32IOP = 2
(IOP = IRW2 • CTR2)
(IPOL = IRW4 • CTR4)
32IOP = 12
(IOP = IRW1 • CTR1 + IRW2 • CTR2)
(IPOL = IRW4 • CTR4)
32IOP = 123
(IOP = IRW1 • CTR1 +
IRW2 • CTR2 + IRW3 • CTR3)
(IPOL = IRW4 • CTR4)
Σ
IOP
Σ