Zone Coordination - GE 850 Instruction Manual

CHAPTER 8: CONTROL

Zone Coordination

850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
Path:
Setpoints > Control > Autoreclose 1 > Zone Coordination
The Autoreclose scheme can be programmed to maintain the coordination of sequence
and Overcurrent elements with a downstream recloser or sectionalizer as shown above. If
a downstream recloser or sectionalizer is programmed to use different protection settings
for different Reclose shots, it may be necessary to change the protection setpoints on the
850 each time the recloser 850 operates. To ensure that protection coordination is
maintained, each 850 reclosure shot must be coordinated with each downstream recloser
shot. In addition, the 850 Reclose shot counter must always match the recloser shot
counter. When a fault occurs downstream of the recloser and the 850 feeder breaker does
not Trip and Reclose, the reclosure shot counter is incremented. This external Reclose
detection eliminates the need for inter-relay communications specially when the recloser
is located far from the substation.
Once enabled, this scheme assumes an external reclose operation has occurred when the
phase or neutral current exhibits an increase in magnitude, due to a fault, followed by a
decrease in magnitude, due to a recloser opening for fault clearance. After the first
detection of an external Reclose, the shot counter is incremented by one and the
Autoreclose scheme Reset Timer is initiated. If needed, protection setpoint groups can be
changed as shown in the figure. Both the upstream and downstream relays should be
programmed with the same number of shots to lockout and number of trips before
protection is blocked. This will ensure that for a persistent downstream fault, both relays
will be on the same sequence count and will block protection at the same time.
Figure 8-37: Using Protection Setpoint groups with the Recloser
Recloser
CB Status
Sequence Number
1
Setting Group Number
850 Relay
CB Status
Sequence Number
1
Setting Group Number
If the fault is permanent and the recloser continues to Trip and Reclose, the coordination
feature continues to increment the shot counter. If this continues to the maximum number
of shots programmed in the 850, the Autoreclose scheme goes to Lockout. If the fault is
transient, then the Autoreclose scheme and shot counter are reset by the normal reset
mechanism.
For correct operation of the coordination scheme, the 850 instantaneous protection
elements must be set to have time delays longer than the maximum fault clearing time of
the downstream recloser. In addition, the Autoreclose reset timer must be set longer than
the maximum time for the recloser to reach Lockout.
t t
1 2
1 2
2 3
1 2
2 3
Open Closed Trip Autoreclose operation
AUTORECLOSE
t
3
3
3
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