Sel SEL-351S - Page 72

2.36
SEL-351S Relay Instruction Manual Date Code 20080103
Installation
SEL-351S AC/DC Connection Diagrams for Various Applications
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 4.3–Tab le 4. 5 ).
Nondirectional sensitive earth fault (SEF) protection is also available.
The voltage inputs can accept open-delta PT (three-wire) connection (as shown) when Global setting PTCONN = DELTA.
VB (terminal Z10) must be externally tied to N (terminal Z12), as shown. (For Connectorized relays, this connection must be
made at the remote end of the wiring harness.)
The zero-sequence voltage 3V
0
(from the “broken-delta” connection) is shown coming from a step-down
instrumentation transformer, and connecting to voltage input VS-NS (terminals Z13 and Z14, respectively). To use this
connection, make global setting VSCONN = 3V0. Make group setting PTRS as shown in Section 9: Setting the Relay.
The step-down transformer is required when the maximum expected residual voltage exceeds the relay voltage channel
rating. See Voltage Input Rating on page 2.19.
The polarity of voltage input VS-NS connection should be verified prior to placing the relay into service. See Polarity
Check for VSCONN = 3V0 on page 2.20 for a suggested procedure.
Figure 2.28 SEL-351S Provides Overcurrent Protection for an Ungrounded System (Open-Delta Connected PTs,
Broken-Delta 3V0 Connection)
TC
Trip
Coil
52A
(+)
(—)
Trip
Circuit
IA
C
B
A
NVCVB
SEL-351 RELAY
VA
VS
NS
OUT101
Forward Tripping Direction
Core-Balance CT
CC
Close
Coil
52B
(+)
(—)
Close
Circuit
IB
OUT102
86
Lock
Out
86B
(+)
(—)
Breaker
Failure
Trip
Circuit
IC
OUT103
FEEDER
ABc
52
(+)
to Annunciator, RTU,
or SEL-2032/2030/2020
Step-Down
Transformer
(Some
Applications)
ALARM
(+)
(—)
Breaker Status
IN101
IN
Ungrounded
Broken-Delta
TRANSFORMER BANK
Open-Delta
52A