Recloser Lockout on a Branch with Suspected Conductor Slap
A 12.47 kV overhead feeder has a recloser at the substation and a sectionalizer midway down the main line. A lateral fused with a 25 K cutout feeds a rural branch. During gusty wind, the substation recloser trips and recloses twice, then locks out. The sectionalizer counts and operates. Field reports describe a flash near a span crossing a road on the lateral. You are the switching authority responding after lockout. The feeder serves a hospital on a different lateral that has its own transfer switch and generator. Available: a line truck, voltage detectors rated for the class, and a portable generator for the hospital if needed.
1. Explain what the recloser and sectionalizer operation tells you about fault location, and how you would narrow the search before patrolling.
Read the worked answer
The recloser tripping and reclosing twice before lockout indicates a persistent or recurring fault - a transient would typically clear on the first reclose. The sectionalizer counting and operating means it saw fault current through at least the programmed number of trips and opened during a dead time, isolating the section downstream of it.
Because the sectionalizer operated, the fault is most likely downstream of the sectionalizer - i.e., on the lateral or main line beyond it. The field flash near the road crossing on the lateral is consistent with conductor slap or a tree limb causing a phase-to-phase or phase-to-ground flash in wind.
Before patrolling:
- Confirm which devices are open and which sections are dead from the SCADA/records.
- Compare the fault-current magnitude (if available) against expected values to distinguish a lateral fault from a main-line fault.
- Prioritize the lateral span identified by the field report; check for conductor slap, damaged spacers, or a limb on the crossing span.
- Remember the hospital lateral is separate and has generator backup; do not delay its transfer unnecessarily.
2. The hospital is on a different lateral but shares the locked-out feeder. Describe your switching sequence and the safety considerations.
Read the worked answer
The hospital's transfer switch and generator should already have picked up the load on loss of voltage. Verify that transfer occurred and the generator is carrying the critical load before doing anything else. If transfer did not occur, coordinate with the hospital to start the generator and confirm it is online.
Switching sequence:
- Confirm the feeder is locked out and the recloser is open; treat all feeder conductors as energized until proven otherwise.
- Isolate the faulted lateral by opening its cutout/sectionalizer so the fault is removed from the feeder.
- Do not re-energize the faulted lateral until the fault is located and repaired.
- Restore the healthy portions by closing the recloser and sectionalizer in the proper order, checking voltage at each step.
- Verify absence of voltage on the isolated lateral before allowing crews to patrol or repair; apply grounds per procedure.
Safety: maintain MAD, use voltage detectors proven before and after, and ensure the hospital remains on generator or a verified alternate source until its lateral is restored.
3. The patrol finds a limb resting on the lateral span and a chafed conductor. What must be true before you re-energize that lateral?
Read the worked answer
Before re-energizing:
- The limb must be removed and the conductor inspected; a chafed conductor may have reduced ampacity or strand damage and may need repair or replacement, not just clearing.
- Clearance to other phases and to ground must be restored; slap damage often leaves reduced spacing that will fault again in wind.
- Insulators, ties, and spacers must be intact.
- The lateral fuse/cutout must be replaced with the correct rating; a 25 K that operated must be replaced, not reused, and the new rating verified against the load.
- The circuit must be tested for absence of voltage and grounded during repair, then ungrounded and the isolation removed in the correct order.
- After re-energization, verify voltage on all phases and monitor for a repeat trip. A chafed conductor that faults again under wind is a sign the repair was inadequate.