Schweitzer Engineering Laboratories SEL-751 - Figure 2.24 SEL-751 Provides Overcurrent Protection for a Distribution Bus (Includes Fast Bus Trip Scheme) (Wye-Connected Pts)

2.33
Date Code 20170927 Instruction Manual SEL-751 Relay
Installation
AC/DC Control Connection Diagrams
Voltages are necessary for voltage elements, synchronism-check elements, voltage-polarized directional elements, fault
location, and metering (e.g., voltage, KW, KVAR). INxxx and OUTxxx indicate user-configurable optional digital inputs and
outputs. Voltage channel VS is shown connected with VSCONN := VS for use in voltage and synchronism-check elements
and voltage metering. You can use VS voltage channel for other voltage inputs such as 3VO from a broken delta PT
connection by setting VSCONN := 3V0 for use with zero-sequence voltage polarized directional elements. Setting
VSCONN := 3V0 disables synchronism-check elements.
Channel IN provides current I
N
for the neutral ground overcurrent elements. Separate from Channel IN, the residual
ground overcurrent elements operate from the internally derived residual current I
G
(I
G
= 3I
0
= I
A
+ I
B
+ I
C
). But in this
residual connection example, the neutral ground and residual-ground overcurrent elements operate the same because
I
N
= I
G
.
Although automatic reclosing is probably not necessary in this example, output contact OUT102 can close the circuit
breaker via initiation from various means (serial port communications, optoisolated input assertion, etc.) with desired
supervision (e.g., synchronism check).
INxxx is shown for use with a fast bus trip scheme. The fast bus trip scheme is often referred to as a reverse-interlocking
or zone-interlocking scheme.
Figure 2.24 SEL-751 Provides Overcurrent Protection for a Distribution Bus (Includes Fast Bus Trip Scheme)
(Wye-Connected PTs)
TC
Trip
Coil
52A
(+)
(—)
Trip
Circuit
IA
C
B
A
SEL-751 RELAY
OUT103
CC
Close
Coil
52B
(+)
(—)
Close
Circuit
IB OUT102
86
Lock
Out
86B
(+)
(—)
Breaker
Failure
Trip
Circuit
IC OUTxxx
IN
BUS
52
(+)
52A
to Annunciator, RTU,
SEL-2032/2030/2020,
or SEL-3530 RTAC
From Feeder Relays
(Fast Bus Trip Scheme)
ALARM
OUT101
(+)
(—)
Breaker Status
INxxx
(—)
INxxx
VCNVBVA
VS
NS
A
B
C
Forward
Tripping
Direction