short-circuit-mitigation

name

short-circuit-mitigation

description

Senior power-engineer playbook for excessive fault current and breaker over-duty. Use whenever a short-circuit study shows fault duty above interrupting ratings, or a new interconnection raises fault levels near equipment limits. Triggers on "fault duty", "breaker over-duty", "short-circuit current too high", "interrupting rating exceeded", or "fault MVA at this bus". Gives an ordered sequence from study verification through operational fixes to equipment upgrades.

Short-circuit mitigation

Start with the over-dutied buses and breakers, the fault type, and the study assumptions that produced them.

Preferred action order

1. Confirm the duty is real: machine subtransient data, motor contribution, pre-fault voltage assumption, fault type (three-phase vs single-line-to-ground), and the X/R used for asymmetry — over-duty findings are often data findings.
2. Apply operational fixes first: split buses, open bus-tie or loop points, and re-dispatch nearby generation where switching alone relieves the duty.
3. Add impedance on the offending paths: series reactors or higher-impedance transformer choices for new connections.
4. Screen fault-current limiters where switching and impedance are not enough.
5. Recommend breaker replacement or uprating as the planning fix, with an interim operating guide until installed.

Working rules

• Check maximum (all-sources-in) and minimum (credible outage) fault cases — protection settings need the minimum, breaker duty needs the maximum.
• Single-line-to-ground duty can exceed three-phase duty near grounded transformer banks; do not screen on three-phase faults alone.
• Bus splitting changes power-flow transfer paths and N-1 performance; re-run the contingency screen after any topology fix and route findings to contingency-mitigation.
• Keep the protection engineer in the loop: any fix that changes fault levels changes relay reach.

Deliver

• The over-dutied equipment, its rating basis, and the computed duty.
• The mitigation sequence tried, from switching to reinforcement.
• The residual duty margin and any protection re-coordination still required.