Schweitzer Engineering Laboratories SEL-351A - Figure 2.13 SEL-351 A Provides Overcurrent Protection for a Distribution Bus (Includes Fast Bus Trip Scheme) (Wye-Connected Pts)

2.21
Date Code 20080213 Instruction Manual SEL-351A Relay
Installation
SEL-351A AC/DC Connection Diagrams for Various Applications
The fast bus trip scheme is often referred to as a reverse-interlocking or zone-interlocking scheme.
The voltage inputs do not need to be connected. Voltage is needed for voltage elements, synchronism check elements,
frequency elements, voltage-polarized directional elements, fault location, metering (i.e., voltage, MW, MVAR), and
frequency tracking. Voltage Channel VS (SEL-351A only) is shown connected for use in voltage and synchronism check
elements and voltage metering. See Synchronism Check VS Connection (Global setting VSCONN = VS) on page 2.15 and
Broken-Delta VS Connection (Global setting VSCONN = 3V0) on page 2.15. In this example, terminals VS-NS are connected
B-phase-to-neutral.
Current Channel IN does not need to be connected. 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 needed 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).
Figure 2.13 SEL-351A 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
NVCVB
SEL-351 RELAY
VA
OUT101
Forward Tripping Direction
CC
Close
Coil
52B
(+)
(—)
Close
Circuit
IB
OUT102
86
Lock
Out
86B
(+)
(—)
Breaker
Failure
Trip
Circuit
IC
OUT103
IN
VS
NS
BUS
52
(+)
52A
to Annunciator, RTU,
or SEL-2032/SEL-2030/SEL-2020
From Feeder Relays
(Fast Bus Trip Scheme)
ALARM
(+)
(—)
Breaker Status
IN101
(—)
IN102
Courtesy of NationalSwitchgear.com