- Circuit Breaker Maintenance Definition: Circuit breaker maintenance involves switching off, isolating, and regularly checking and servicing the breaker to ensure reliable operation
- Bulk Oil Circuit Breaker: Regularly inspect and clean contacts, lubricate mechanisms, and maintain the extinguishing chamber.
- Minimum Oil Circuit Breaker (MOCB): Monthly check for oil leakage and levels, and quarterly inspect the operating mechanism and painting quality.
- Air Blast Circuit Breaker: Regularly check for air and oil leakage and ensure the dew point of the operating air is within limits.
- SF6 and Vacuum Circuit Breaker: Monitor for gas leakage, check gradient capacitors, and measure the dew point every few years.
Maintenance of circuit breaker equipment, or circuit breaker maintenance, must be performed by qualified personnel under an approved safety procedure. Open the breaker and isolate every energy source with the relevant electrical isolator. Apply lockout or tagout, control stored spring, pneumatic and hydraulic energy and verify de-energisation before work begins.
Functional checks of the circuit breaker should follow the manufacturer’s instructions and the site’s maintenance programme. Where an authorised test requires temporary energisation, clear personnel and tools first, then isolate and lock out the equipment again before maintenance continues.
Bulk Oil Circuit Breaker Maintenance
For a bulk oil circuit breaker, inspect the main and arcing contacts against the manufacturer’s wear and alignment limits. Light deposits may be removed only by the approved method. Replace contacts, tips or arcing rings that exceed their specified erosion or damage limits, and tighten all parts to the stated torque.
Inspect the arc-control or extinguishing chamber for carbon deposits, cracks and erosion. Clean or replace it only with materials and procedures approved for that breaker and its insulating oil.
Clean the operating mechanism and inspect bearings, linkages, latches and gears. Apply only the specified lubricant, in the stated quantity and locations. For a minimum oil circuit breaker (MOCB), clean the insulators with an approved agent and inspect the oil for contamination or deterioration. The manufacturer’s manual controls each task.
Inspect tie-rod locking pins, foundation bolts and power-circuit terminals at the interval set by the maintenance programme. Remove corrosion by an approved method and tighten connections to the manufacturer’s torque values.
Check that the auxiliary switch indicates the correct normally open and normally closed states when the breaker is open and closed. Inspect and clean its contacts by the approved method.
Inspect the spring-charging motor, stored-energy mechanism and bearings. Clean and lubricate only where the product manual requires it.
Minimum Oil Circuit Breaker Maintenance
For an MOCB, inspect for oil leakage and confirm the oil level using the manufacturer’s indicator and limits. Find and repair the source of any leak before adding the approved oil.
Inspect the breaker, operating mechanism, enclosure finish, seals and kiosk-door gasket for damage, corrosion or contamination. Set the interval from the manufacturer’s schedule, service conditions, operation count and fault-interruption history.
Inspect any oil dashpot in the operating mechanism for leakage, correct level and smooth operation. Replace damaged seals with the specified parts.
Carry out operational and reclosing tests only under an approved test procedure. Confirm that the breaker’s rated duty and control sequence match the installation requirements.
Maintenance of Air Blast Circuit Breaker
An air blast circuit breaker needs the same mechanism and control inspections that apply to comparable oil circuit breaker, air circuit breaker, SF6 circuit breaker and vacuum circuit breaker equipment, plus checks specific to its compressed-air system.
Inspect piping, valves, reservoirs and seals for leakage. Confirm compressor operation and pressure against the manufacturer’s limits, then repair leaks with approved parts.
Inspect grading capacitors for leakage, damage and abnormal readings. Isolate and service or replace a defective unit rather than attempting a temporary seal.
Measure the operating-air moisture or dew point at the location and interval specified by the breaker or air-system manufacturer. Service the dryer if the reading is outside its limit.
SF6 Circuit Breaker Maintenance
Operating-mechanism and control inspections also apply to oil, air, SF6 circuit breaker and vacuum designs.
An SF6 CB also requires checks of its sealed gas system.
The SF6 circuit breaker needs recorded density or temperature-compensated pressure readings for its SF6 gas. Investigate any low-density alarm or downward trend. Trained personnel should locate leaks with suitable detection equipment and follow the manufacturer’s gas-recovery procedure. Do not vent SF6 to the atmosphere.
Inspect any grading capacitors for leakage, damage and abnormal test results. Remove a defective unit from service and follow the manufacturer’s repair or replacement procedure.
Measure SF6 moisture or dew point only at the interval and test point specified for that breaker. Product design, sealing system, service history and alarm records determine whether testing is required.
Maintenance of Vacuum Circuit Breaker
A vacuum circuit breaker has no oil or insulating gas in its interrupter, but it still needs product-specific maintenance. Inspect the operating mechanism, insulation, primary connections and contact-wear indication. Check interrupter travel, timing and vacuum integrity only by the methods and limits in the manufacturer’s manual for that circuit breaker.
