Schweitzer Engineering Laboratories SEL-351A - Figure 2.25 SEL-351 A Provides Underfrequency Load Shedding, Overcurrent Protection, and Reclosing for a Utility Distribution Feeder (Single Voltage Connection)

2.33
Date Code 20080213 Instruction Manual SEL-351A Relay
Installation
SEL-351A AC/DC Connection Diagrams for Various Applications
Voltage must be applied between relay terminals VA and N (Z09 and Z12, respectively) in order for the underfrequency
elements to operate. Make group setting VNOM = OFF to allow the undervoltage block for the frequency elements to
operate off one phase only (if only connecting one phase voltage to the relay).
The phase of the single-phase voltage connected to VA-N does not matter. For example, it could come from VB, VCA, or
from a station service transformer (suitably fused). It should come from the same bus section that the associated
breaker is connected, preferably from the “normally hot” side.
In the configuration shown, only nondirectional overcurrent protection is possible. The fault locator logic and the load
encroachment element are also disabled.
Voltage Channel VS (in SEL-351A) does not need to be connected. Here, it 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.
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
.
Figure 2.25 SEL-351A Provides Underfrequency Load Shedding, Overcurrent Protection, and Reclosing for a
Utility Distribution Feeder (Single Voltage Connection)
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
TX
(—)
Comm.-
Assisted
Trip
Scheme
IC
OUT103
IN
VS
NS
LINE
52
(+)
OUT104
(+)
52A
to Annunciator, RTU,
or SEL-2032/SEL-2030/SEL-
ALARM
(+)
(—)
Breaker Status
IN101
RX
(+)
(—)
Comm.-Assisted
Trip Scheme
IN102
Courtesy of NationalSwitchgear.com