Condition Based Maintenance
Preventive maintenance activities for circuit breakers have historically been performed on a periodic basis. This is common for some low voltage circuit breakers. However, for medium and high voltage circuit breakers, a condition based maintenance program may be warranted. The main purpose of the overhauls of circuit breakers is to replace worn components. Through condition based maintenance, it may be possible to delay an overhaul to when it is necessary.
Normally, a circuit breaker overhaul is required when a specified number of operations, full load fault interruptions, or a recommended time interval has passed. The time interval may be recommended by either FIST 4-1B or the manufacturer’s O&M manual. A manufacturer’s requirement to perform maintenance based on time and number of operations is based on an expected lifespan of the breaker seals and other consumable components. Using this method will often result in maintenance being performed long before the breaker components are in need of replacement.
Ideally, Reclamation should be using condition based maintenance practices to determine when an overhaul, or at least an inspection, is required. Therefore, an overhaul is performed when the components of the breaker are actually worn and prior to a breaker failure.
A typical condition based maintenance program uses diagnostic testing to estimate the condition of the circuit breaker. By analyzing the results of the diagnostic tests and comparing the results over time, trends can be found and decisions made that may trigger specific maintenance procedures. These decisions are not based on any one diagnostic test. It could take several different tests to verify the decision to perform the maintenance.
Maintenance of Power Circuit Breakers
Power circuit breakers are essential components in electrical systems, designed to protect equipment and personnel by interrupting fault currents. Proper maintenance of these devices is critical to ensure their reliability, safety, and long service life. This article covers the importance, procedures, and best practices for maintaining power circuit breakers.
Importance of Circuit Breaker Maintenance
- Ensure Reliability: Prevent unexpected failures during fault conditions.
- Enhance Safety: Minimize the risk of electrical accidents and equipment damage.
- Extend Lifespan: Regular maintenance reduces wear and tear, prolonging the breaker’s operational life.
- Compliance with Standards: Ensure adherence to industry regulations like ANSI, IEEE, and IEC guidelines.
Types of Circuit Breakers
- Air Circuit Breakers (ACBs): Use air as the arc-quenching medium.
- Oil Circuit Breakers (OCBs): Use insulating oil to extinguish arcs.
- Vacuum Circuit Breakers (VCBs): Use a vacuum to interrupt the arc.
- SF₆ Circuit Breakers: Use sulfur hexafluoride gas for arc extinguishing.
Maintenance Frequency
The frequency of maintenance depends on:
- Manufacturer Recommendations: Follow specific guidelines provided by the manufacturer.
- Operating Environment: Harsh environments require more frequent maintenance.
- Usage Patterns: High-duty applications may need more frequent checks.
- Inspection Results: Schedule based on the condition found during inspections.
Key Maintenance Activities
Visual Inspection:
- Check for signs of physical damage, corrosion, or contamination.
- Inspect for oil or gas leaks in OCBs and SF₆ breakers.
- Verify the condition of insulation components and busbars.
Cleaning:
- Remove dirt, dust, and moisture from external and internal surfaces.
- Use approved solvents to clean arc chutes and insulating parts.
Mechanical Inspection and Testing:
- Check alignment and condition of moving parts such as operating mechanisms.
- Lubricate bearings, hinges, and contact surfaces as per the manufacturer's guidelines.
- Verify proper functioning of spring or hydraulic operating mechanisms.
Electrical Testing:
- Contact Resistance Measurement: Assess the resistance of breaker contacts to detect wear or pitting.
- Insulation Resistance Testing: Verify the integrity of insulation using a megohmmeter.
- Timing Test: Ensure that the breaker operates within specified opening and closing times.
- Dielectric Testing: Test the breaker’s ability to withstand overvoltage conditions.
Arc Chute Maintenance:
- Inspect arc chutes for wear or damage.
- Replace components showing excessive erosion or cracking.
Gas or Oil Checks (For SF₆ and OCBs):
- Check SF₆ gas pressure and refill if necessary to maintain proper insulation.
- Test the dielectric strength of oil in OCBs and replace if degraded.
Trip Unit Testing:
- Test and calibrate the breaker’s trip unit to ensure it responds correctly to fault conditions.
Recording and Documentation:
- Maintain detailed records of all maintenance activities, test results, and observations for future reference.
Special Considerations for SF₆ Circuit Breakers
- Ensure SF₆ gas is handled using proper equipment to prevent environmental impact.
- Test for gas purity and moisture content regularly.
- Follow safety protocols when working with high-pressure systems.
Safety Measures During Maintenance
- De-Energize the System: Isolate the breaker from the power source before maintenance.
- Lockout/Tagout (LOTO): Use LOTO procedures to prevent accidental energization.
- Personal Protective Equipment (PPE): Wear appropriate PPE, such as insulated gloves and safety glasses.
- Discharge Stored Energy: Release any stored energy in springs or hydraulic systems to avoid accidental operation.
- Follow Standards: Adhere to safety standards like OSHA and NFPA 70E.
Benefits of Regular Maintenance
- Improved System Reliability: Ensures uninterrupted operation of electrical systems.
- Cost Savings: Reduces the likelihood of costly repairs or equipment replacement.
- Enhanced Performance: Maintains optimal breaker performance during normal and fault conditions.
Conclusion
Regular maintenance of power circuit breakers is critical to ensuring their reliability and safety. By following a systematic approach that includes inspections, cleaning, testing, and timely repairs, electrical professionals can extend the life of these vital devices and protect the integrity of the power system.
