2.40
SEL-751 Relay Instruction Manual Date Code 20170927
Installation
AC/DC Control Connection Diagrams
A core-balance current transformer is often referred to as a zero-sequence, ground fault, or window current transformer.
Directional control for an ungrounded system is selected with setting ORDER := U (see Table 4.19–Table 4.21).
Nondirectional sensitive earth fault (SEF) protection is also available.
Figure 2.31 SEL-751 Provides Overcurrent Protection for an Ungrounded System (Wye-Connected PTs)
TC
Trip
Coil
52A
52A
(+)
(—)
Trip
Circuit
IA
C
B
A
SEL-751 RELAY
OUT103
Forward Tripping Direction
Core-Balance CT
CC
Close
Coil
52B
(+)
(—)
Close
Circuit
IB OUT102
86
Lock
Out
86B
(+)
(—)
Breaker
Failure
Trip
Circuit
IC OUTxxx
OUT101
FEEDER
ABc
52
(+)
ALARM
(+)
(—)
Breaker Status
INxxx
IN
Ungrounded
TRANSFORMER BANK
+
+
to Annunciator, RTU,
or SEL Communications Processor
VCNVBVA