Zone Coordination - GE Multilin 850 Instruction Manual

CONTROL

Zone Coordination

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Setpoints > Control > Autoreclose 1 > Zone Coordination
The Autoreclose scheme can be programmed to maintain the coordination of Overcurrent
elements with a downstream recloser. If a downstream recloser 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 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.
Once enabled, this scheme assumes an external reclose operation has occurred when the
feeder phase or neutral current exhibits an increase in magnitude, due to fault current,
followed by a decrease in magnitude, due to a recloser opening. 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.
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.
FUNCTION
Range: Disabled, Enabled
Default: Disabled
PHASE CURRENT PICKUP
Range: 0.050 to 30.000 x CT in steps of 0.001 x CT
Default: 1.000 x CT
The setpoint specifies phase fault current level, which when exceeded, signifies a
downstream fault.
These currents may be quite low for an end fault on a long feeder with a weak source.
NEUTRAL CURRENT PICKUP
Range: 0.050 to 30.000 x CT in steps of 0.001 x CT
Default: 0.300 x CT
The setpoint specifies neutral fault current level, which when exceeded, signifies a
downstream fault.
PICKUP TIME
Range: 0.000 to 6000.000 s in steps of 0.001 s
Default: 0.020 s
If the (phase or neutral) fault current exists for more than the Coordination Pickup Time
scheme, an increase in fault current magnitude is declared.
DROPOUT TIME
Range: 0.000 to 6000.000 s in steps of 0.001 s
Default: 0.020 s
If the (phase or neutral) fault current drops, the downstream Reclose opening is declared
for the duration of Coordination Dropout Time.
EVENTS
Range: Disabled, Enabled
Default: Enabled
850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS