2.31
Date Code 20080213 Instruction Manual SEL-351A Relay
Installation
SEL-351A 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 Tab le 4 .1–Table 4 .3 ). 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 2.14.
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 2.16 for a suggested procedure.
Note: The SEL-351A-1 is not equipped for this application.
Figure 2.23 SEL-351A 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/SEL-2030/SEL-2020
Step-Down
Transformer
(Some
Applications)
ALARM
(+)
(—)
Breaker Status
IN101
IN
Ungrounded
Broken-Delta
TRANSFORMER BANK
Open-Delta
52A
Courtesy of NationalSwitchgear.com
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