HV Breaker Fault Basics: Training Guide for New Engineers

High-Voltage Circuit Breakers: Classification and Fault Diagnosis

High-voltage circuit breakers are critical protective devices in power systems. They rapidly interrupt current when a fault occurs, preventing damage to equipment from overloads or short circuits. However, due to long-term operation and other factors, circuit breakers may develop faults that require timely diagnosis and troubleshooting.

I. Classification of High-Voltage Circuit Breakers

1. By Installation Location:

• Indoor-type: Installed in enclosed switchgear rooms.

• Outdoor-type: Designed for external installation, with weather-resistant enclosures.

2. By Arc-Quenching Medium:

• Oil Circuit Breaker
  Uses insulating oil as the arc-quenching medium.

• Bulk Oil Circuit Breaker (Multi-oil): Oil serves both as arc-extinguishing medium and insulation between live parts and grounded enclosure.

• Minimum Oil Circuit Breaker (Less-oil): Oil is used only for arc extinction and contact insulation; external insulation (e.g., porcelain) insulates live parts from ground.

• Vacuum Circuit Breaker：Extinguishes arcs in a high-vacuum environment, leveraging vacuum’s high dielectric strength. Widely used in medium-voltage applications due to long life and low maintenance.

• Sulfur Hexafluoride (SF₆) Circuit Breaker：Uses SF₆ gas—known for excellent arc-quenching and insulating properties—as the interrupting medium. Dominant in high-voltage transmission systems for reliability and compact design.

• Compressed Air Circuit Breaker：Employs compressed air to extinguish the arc and provide post-interruption insulation. Less common today due to complexity and maintenance needs.

• Magnetic Blow-Out Circuit Breaker：Uses electromagnetic force to drive the arc into narrow slits where it cools and deionizes. Typically used in DC or specialized AC applications.

II. Common Faults and Troubleshooting of High-Voltage Circuit Breakers

1. Failure to Close (Refusal to Close)

This may stem from mechanical issues, control circuit faults, or operational errors. Check both electrical control circuits and mechanical components.

Electrical faults include:

(1) Indicator light not working or abnormal

• Check if control power voltage matches rated value.

• If red light does not illuminate when switch is in "close" position, likely causes: open closing circuit or blown fuse.

• If green light (trip position) turns off but red light (close position) fails to illuminate, check red lamp integrity.

• If green light extinguishes and relights: possible low voltage or mechanical failure in operating mechanism.

• If red light flashes briefly then goes out and green light flashes: breaker momentarily closed but failed to latch—likely mechanical fault or excessively high control voltage causing impact failure.

(2) Closing contactor does not operate

• If green light is off: check control bus fuses (positive/negative).

• If green light is on: use test pen or multimeter to inspect control switch, anti-pumping relay, auxiliary contacts, and check for coil open circuit or secondary wiring break.

(3) Closing contactor operates but breaker does not move

• Possible causes: poor contactor contact, arc chute jamming, open closing coil, or blown AC fuse in closing rectifier.

(4) Closing contactor operates, breaker moves but fails to close fully
Possible reasons:

• Mechanical failure in operating mechanism

• Low DC bus voltage

• Secondary wiring mix-up accidentally energizing trip circuit

• Improper operation (e.g., operator releasing control switch too early)

2. Failure to Trip (Refusal to Trip)

More dangerous than failure to close, as it can lead to upstream breaker tripping (cascade tripping), expanding outage scope.

(1) Causes of failed electric trip

• Red light not lit: indicates open trip circuit.

• Check: lamp integrity, fuse, control switch contacts, breaker auxiliary contacts.

• Check: anti-pumping relay coil, trip circuit continuity.

• Trip coil operates weakly: may be due to high coil pickup voltage, low operating voltage, stuck trip plunger, or coil fault.

• Trip plunger moves but breaker does not trip: likely mechanical jamming or detached drive linkage pin.

(2) Handling refusal to trip

• Manual trip fails: Immediately report to dispatch.

• If bypass switch available: transfer load to bypass, open bus-side disconnectors of faulty breaker, then trip bypass breaker to de-energize the circuit.

• Upstream breaker trips due to cascade fault:

• With power off, open disconnectors on both sides of the faulty breaker.

• Manually open all feeders on the affected bus.

• Report to dispatch for system restoration.

3. Unintended Opening or Closing (False Operation)

(1) Unintended Tripping (False Trip)
Occurs when breaker trips without protection activation or operator action. Possible causes:

• Two-point DC grounding in control circuit—check and eliminate ground fault before reclosing.

• Faulty interlock mechanism—isolate breaker (open source-side disconnector) and test close once.

• If evidence suggests internal fault despite no relay activation, investigate accordingly.

(2) Unintended Closing (False Close)
A de-energized breaker closes without command. Causes:

• Two-point DC grounding energizing closing circuit.

• Stuck auto-reclose relay contact.

• Low pickup voltage + high coil resistance, causing false closure during DC transient pulses.

4. Overheating of Circuit Breaker

Main symptoms: overheated tank (especially in minimum-oil breakers), heated frame.

• Cause: Poor contact or oxidation in conductive parts.

• Risks: Insulation damage, cracked porcelain, smoking, oil spraying, or even explosion.

• Action: Strengthen patrols, detect early, and address promptly.

5. Other Common Faults

(1) Oil Circuit Breaker Fire
Fire may result from dirty or damp bushings causing ground flashover, or internal arcing.

• If fire just started: Immediately remotely trip the breaker.

• If fire is severe: Use upstream breaker to isolate the circuit, then open disconnectors on both sides to fully isolate the unit. Extinguish with dry-type fire extinguisher (e.g., CO₂ or powder).

(2) Trip/Close Coil Smoking
Trip/close coils are designed for short-time duty. Prolonged energizing causes overheating and burnout.

• Action: Immediately report to dispatch and request replacement.

• If closing fuse blows during operation, replace only with specified rating—never use oversized fuse to prevent coil damage.

(3) Emergency Manual Trip Required
Immediately take oil circuit breaker out of service if any of the following occur:

• Severe porcelain insulator cracking, flashover, or explosion

• Melting or disconnection of conducting parts

• Loud internal arcing sounds

• Severe oil deficiency

Summary

This guide provides a comprehensive overview of high-voltage circuit breaker types, common operational faults, and corrective actions. Proper classification, regular inspection, and prompt troubleshooting are essential for ensuring system reliability, personnel safety, and equipment longevity.