GE 750 Instruction Manual page 286

14.8 AUTORECLOSE (760 ONLY)
14.8 AUTORECLOSE (760 ONLY)
The 760 has a very flexible autoreclose scheme that allows for the many different control strategies typical of
utility applications. Up to four reclosure 'shots' are possible with separately programmable 'dead times' for
each shot. Reclosure can be initiated from any 760 overcurrent element or from external sources. Between
each shot, overcurrent protection settings can be adjusted in order to co-ordinate with downstream devices. To
prevent breaker wear, a 'current supervision' feature can reduce the number of shots when the fault current is
high. A 'zone co-ordination' feature can maintain protection coordination with downstream reclosers. Logic
inputs are available for blocking and disabling the scheme.
Front panel LEDs indicate the present state of the autoreclose scheme. Note that display message group
STATUS \ AUTORECLOSE
RECLOSURE ENABLED:
RECLOSURE DISABLED:
RECLOSURE IN PROGRESS: An autoreclosure has been initiated but the breaker has not yet been closed.
RECLOSURE LOCKOUT:
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The reclosure scheme is considered enabled when all of the following conditions are true:
1. The
AUTORECLOSURE FUNCTION
2. Either a 52a or 52b contact is installed and has been programmed to a logic input function.
3. Neither the 'Block Reclosure' nor 'Cancel Reclosure' logic input functions are asserted.
4. The scheme is not in the lockout state.
5. The
AR BLOCK TIME UPON MANUAL CLOSE
Following is a simplified description of how the autoreclose scheme works. See the application example sec-
tion and logic diagrams at the end of this section for further details.
A fault occurs resulting in an overcurrent element tripping the circuit breaker and initiating a reclosure. Once
the breaker is detected open a 'dead timer' is started. Once this timer exceeds the value programmed for the
reclosure 1 setpoint
tiated using the '2 Close' output contact. At the same time, overcurrent element characteristics are modified
according to the reclosure 1 setpoints.
If the fault is permanent, subsequent overcurrent element(s) will trip and initiate reclosure. The scheme will
eventually go to lockout when the
occurs. If a breaker failure condition is detected at any time during operation, the scheme will again go straight
to lockout. When in lockout, the 760 disables the reclose scheme and returns all protection settings to their ini-
tial values. To re-enable the autoreclose scheme the relay must be reset via the front panel reset key, the
'Reset' logic input function, communications, or by a manual close operation. The latter resets the scheme only
after the
AR BLOCK TIME UPON MANUAL CLOSE
If the fault is transient in nature then no overcurrent element(s) will trip after the breaker has closed. The
scheme will automatically reset when the reset timer, started upon the first reclosure initiation, exceeds the set-
point
AUTORECLOSE RESET TIME
tings to their initial values.
An anti-pumping feature is built into the reset mechanism. Otherwise, breaker 'pumping' could occur when
the fault level is between the initial overcurrent pickup level and the adjusted overcurrent pickup level for a
reclosure shot. It prevents a permanent fault from continuously repeating the trip breaker, initiate reclose, close
breaker, automatic reset of autoreclose scheme, trip breaker sequence. If this condition is detected the anti-
pumping feature returns protection settings to their initial values without resetting the shot counter. The relay
will then continue to trip and reclose until lockout is reached.
14-
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can also be accessed to determine the present state of the autoreclose scheme.
The scheme is enabled and may reclose if a trip occurs.
The scheme is not enabled and will not reclose until the scheme is enabled.
The scheme has gone to 'lockout' and must be reset before further recloses
are permitted.
setpoint is set to Enabled .
timer is not active.
DEADTIME BEFORE RECLOSURE
MAXIMUM NUMBER OF RECLOSURE SHOTS
timer expires, and no overcurrent elements are picked up.
. This autoreclosure reset returns the shot counter to zero and all protection set-
750/760 Feeder Management Relay
, the shot counter is incremented and a breaker closure is ini-
14 S7 CONTROL
14.8.1 DESCRIPTION
has been met and another trip
GE Power Management
A1