Trip, Wait, Try Again: Recloser Sequences

8 min · difficulty 4/10

A recloser is programmed 1-fast-2-slow, 3 operations to lockout, 2 s dead time. Walk a temporary fault that clears after the first reclose, then a permanent one. At each step, is power back or is the line dead? Predict first.

On the temporary fault, the recloser trips fast on the first operation, the line goes dead, it waits the 2 s dead time, then recloses. Because the fault is gone, power stays on and the sequence stops. On the permanent fault, the recloser trips, recloses into the still-present fault, trips again, recloses again, and so on. It runs all 3 programmed operations, then locks out: it stays open and the line is dead until a person resets it.

A 1-fast-2-slow recloser sequence to lockout A current versus time timeline of a recloser clearing a permanent fault. The load-current trace sits at normal load, then jumps to fault current in red. The recloser trips open after a short fast operation, stays open for a 2 second reclose interval, then recloses onto the still-present fault. It trips again on a slow delayed operation, opens for 2 seconds, recloses, and trips a final slow operation, after which it goes to lockout and stays at zero current, hand-reset, ANSI device 86. One fast plus two slow equals three trip operations to lockout. A 1-fast-2-slow recloser sequence to lockout load current vs time on a permanent fault: 1 fast + 2 slow = 3 trip operations fault load 0 current time fast op 1 slow op 2 (delayed) slow op 3 (delayed) fault 2 s reclose interval 2 s reclose interval reclose reclose LOCKOUT hand-reset (86) stays open 1 fast + 2 slow = 3 trip operations to lockout fast op clears temporaries first; slow ops give downstream fuses time to clear the permanent fault
On a permanent fault, a recloser runs one fast then two slow trip operations with 2-second reclose intervals between them, then locks out and must be hand-reset.

A recloser runs a programmed sequence of trip-open, dead-time, reclose. The dead time, also called the reclose interval, is the open interval between operations, around 2 s in this setting. That open gap matters: it gives the fault arc time to de-ionize, so a temporary fault, like a branch that brushed a conductor and burned away, is gone before the line is re-energized. Most overhead faults are temporary, so most of the time the line comes right back.

“Operations to lockout” is how many tries the recloser makes before it gives up, commonly 3 or 4. Each trip is one operation. Run out of operations against a fault that will not clear and the recloser locks out. Lockout is the 86-equivalent: it stays open, hand-reset only, so a real permanent fault does not get re-energized over and over.

The order of operations is deliberate. Fast operations come first to clear temporary faults quickly, and with fuse-saving they trip before the lateral fuse minimum-melt so the fuse survives a temporary fault. Slow, or delayed, operations come later to give a downstream fuse time to clear a fault that keeps coming back, so a permanent lateral fault is isolated by its fuse rather than dropping the whole feeder.

So the two ends of the sequence do two different jobs. Fast operations save the line and the fuse on a temporary fault, slow operations let a downstream fuse clear a permanent one, and lockout stops the recloser from re-energizing a fault forever. A typical setting like 1-fast-2-slow with 3 operations and 2 s dead time blends both: it gives temporary faults a chance to clear and gives downstream fuses time to work before the recloser finally locks out.

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Question 1 of 3

A recloser is set for 3 operations to lockout (1 fast plus 2 slow). A permanent fault hits and never clears. After how many trips does the recloser lock out?

Educational material only. This is not engineering, safety, or procurement advice. Confirm any value against manufacturer documentation and a licensed professional before specifying equipment.