Circuit breakers are perhaps the least maintained electrical equipment in industrial power systems. This is unfortunate considering their safety purpose: to prevent arc currents from progressing to ejected arc flashes and tracking arc flashes that could cause building fires and electrocution. To prevent these occurrences, proper maintenance and testing are necessary. For medium voltage air, oil, and vacuum breakers, the following maintenance measures and tests are recommended.
Air
Air circuit breakers are the most common type of medium voltage circuit breakers in industrial buildings. Testing breakers that use air with contact resistance, insulation resistance, and dielectric voltage testing on an annual basis is recommended. After de-energizing the breaker unit, removing the pressure from its air receivers, and attaching ground leads, the following maintenance measures should be performed:
• Clean insulating components
• Check contact condition and alignment
• Check that terminal connectors such as bolts are firmly in place
• Check arc chutes for damaged parts
• Clean and lubricate operating mechanisms
• Check inner housing for signs of moisture and oxidization
These measures should be performed annually on air circuit breakers that operate at 600-15,000 volts.
Oil
Oil circuit breakers are the most prevalent type of medium voltage outdoor circuit breakers. They should be tested annually with the same tests used for air breakers. After de-energizing the breaker unit and attaching ground leads, the following maintenance measures should be performed:
• Check contact condition and alignment
• Remove oil accumulations from the tank and other parts
• Check the condition of the tank's gaskets and valves.
• Replace oil that has a dielectric strength of less than 22 kV.
• Replace oil that has carbon build up.
• Clean and lubricate operating mechanisms
• Check inner housing for signs of moisture and oxidation
These measures should be performed annually on oil circuit breakers that operate at 600-15,000 volts.
Vacuum
Vacuum circuit breakers have increased in popularity due to their compactness and arc resistant performance. They should be tested annually with the same tests used for air and oil breakers. After de-energizing the breaker unit and attaching ground leads, the following maintenance measures should be performed:
• Check arc chutes for damaged parts
• Clean and lubricate operating mechanisms
• Check that terminal connectors such as bolts are firmly in place
• Check contacts for erosion by measuring changes in shaft position
• Check the condition of the vacuum using a hi-pot test
• Check inner housing for signs of moisture and oxidation
These measures should be performed annually on vacuum circuit breakers that operate at 600-15,000 volts.
Prime Power maintains and tests breaker units
Proper breaker maintenance and testing is imperative to protecting a building and its workers from dangerous arc flash incidents. At Prime Power, we specialize in testing breakers and maintaining them as described above as part of our service to medium voltage power customers. If your breaker units need maintenance, retrofitting, replacement, NFPA 110 testing, or other types of testing, don't wait for an arc flash to cause a tragedy. Call Prime Power today.
