AUTO RECLOSE BLOCKING OF POWER LINES

Blocking or disabling of autoreclosing on distribution circuits may be required for various circumstances. Requirements will vary depending on specific design features incorporated into the distribution system. The following are several conditions for which autoreclosing is blocked:

a) Line-side voltage supervision. 
Autoreclosing can be blocked if voltage exists on the line. Such supervision is usually provided if large motors, generators, or other sustained sources are connected to the line.

Autoreclosing is blocked if these downstream sources are maintaining voltage on the line in order to prevent possible damage to the associated rotating equipment due to being energized out of phase or to the establishment of an undesirable system operating condition.

b) Bus faults.
Autoreclosing of lines can be blocked for bus faults.

c) Underfrequency/undervoltage load-shedding schemes. 
When distribution circuits are tripped by action of load-shedding schemes, autoreclosing is blocked to avoid undesired load restoration during system overload conditions. Autoreclosing may be re-established when the frequency/ voltage condition has returned to normal and maintained that condition for some time.

d) Downed conductor protection.
Autoreclosing can be blocked when protective systems designed to protect for a downed phase conductor operate. A downed conductor represents a permanent failure and a safety concern––autoreclosing is undesired for such a condition (Rockefeller et al. [B13].)

e) Voltage unbalance.
Autoreclosing can be blocked if a voltage unbalance condition is detected at the station. A source-side open circuit can cause such unbalances. Restoring service under unbalanced conditions could cause damage to customer equipment.

f) Manual trips.
Autoreclosing is blocked if the breaker is opened manually at the station or by remote control. When a breaker is opened in this manner, it is desirable that it be under operator control for closure.

g) Breaker failure protection. 
Breaker failure protection typically trips all breakers connected to the bus directly or through the bus differential protection. Restoration of the bus is usually under an established procedure that includes isolation of the failed breaker. Autoreclosing of the healthy breakers are blocked until the failed breaker is isolated and the bus is restored.

h) Breaker failure to close.
If an attempt is made to autoreclose, and the breaker does not close (based on 52 auxiliary contact) or fails to close within the expected close time, or if a discontinuity (open circuit) is detected, then further attempts to autoreclose are blocked.

i) Hot-line maintenance.
Improve safety by disabling autoreclosing while line crews perform hot-line maintenance.

j) High-current faults.
A high-set instantaneous element can be used to block autoreclosing for close-in, high magnitude faults. This type of blocking is typically applied where these faults are likely to be permanent or in the substation equipment or exit cables, or exceed the damage rating of the source transformer or other equipment.

k) Breaker failure to trip or trip circuit monitor alarm.
If a relay trip has occurred, but the breaker stays closed longer than the expected breaker trip time (e.g., 6–10 cycles), block autoreclosing and initiate tripping of the backup breaker. Also, if trip circuit logic is available, then use this logic to block autoreclose if an open trip circuit is detected.

l) Cumulative operations lockout.
Used in locations with fault duty approaching adjusted circuit breaker rating to block autoreclosing after a predetermined number of operations until inspection and necessary maintenance can be performed.