8-36
Application
BE1-951
are summarized in the following paragraphs.
&
A feeder relay detecting a fault will send a blocking signal to the BUS relay to prevent it from issuing
a high-speed trip. The 51 functions of the BUS and BACKUP relays are set to coordinate with each
other and the feeder relays.
&
An out of service feeder relay on a feeder with a fault will not send a blocking signal to the BUS relay
so the BUS relay will trip the feeder breaker via the 94 and 83 relay contacts. Fault clearing occurs
after the 2 to 4 cycle coordination interval set on the BUS relay 50T functions or after the BUS relay
51 time if the fault is further out. For this reason, the BACKUP relay 51 functions must be set to
coordinate with the BUS relay in this setting group.
&
A bus fault will cause the BUS relay to trip the feeder breaker with the relay out of service because
no blocking signal will be sent by any of the feeder relays. Since this won’t clear the fault, the
BACKUP relay will clear the fault with its 18 to 20 cycle coordination interval.
Table 8-17. BUS Contact Sensing Input Logic
Input
Purpose
Mode
Variable Label
State Labels
Closed (1)
Open (0)
IN1
51b breaker status
0
(disabled)
BREAKER
OPEN
CLOSED
IN2
Blocks instantaneous when feeder
relay picks up.
0
(disabled)
FEEDER_PU
PICKDUP
NORMAL
IN3
Signal from bus source relay using
BACKUP logic that a feeder relay is out
of service.
0
(disabled)
BACKUPMODE
BACKUP
NORMAL
IN4
Places the relay in Test mode so that
all trips are rerouted to OUT1 when IN4
de-energizes.
2
(on/off)
TESTDISABL
NORMAL
TSTMODE
Table 8-18. BUS Function Block Logic
Function
Purpose
BESTlogic
Expression
Mode Setting
50TP
Inhibit when feeder fault is indicated by feeder
relay pickup. Requires a 2 to 4 cycle coordination
delay. Used for high-speed bus fault tripping or for
feeder instantaneous tripping when in feeder
backup mode.
IN2
1
(enabled)
50TN
Inhibit when feeder fault is indicated by feeder
relay pickup. Requires a 2 to 4 cycle coordination
delay. Used for high-speed bus fault tripping or for
feeder instantaneous tripping when in feeder
backup mode.
IN2
1
(3-Phase Residual)
50TQ
Inhibit when feeder fault is indicated by feeder
relay pickup. Requires a 2 to 4 cycle coordination
delay. Used for high-speed bus fault tripping or for
feeder instantaneous tripping when in feeder
backup mode.
IN2
1
(enabled)
150TP
Not used
0
0 (disabled)
150TN
Not used
0
0 (disabled)
150TQ
Not used
0
0 (disabled)
51P
Not used
0
0 (disabled)
51N
Not used
0
0 (disabled)
51Q
Not used
0
0 (disabled)