MAINTENANCE of VACUUM CIRCUIT BREAKERS

- Vacuum circuit breakers maintenance should be based on the manufacturer’s instruction , generally at least once a year or every 2,000 operations, whichever occurs first
- Breakers should be inspected every time after a severe fault interruption
- Remove breaker from its enclosure

- Use a clean, dry cloth to remove all dirt and moisture from the surface of vacuum interrupters and all insulating parts
- Check the contact erosion by measuring the spring plate over-travel
- Modern vacuum interrupter has an indicator or marking to show that the level that the interrupter need to be replaced

- Check the condition of vacuum by performing an A.C. high-potential test at 70% of final factory test value for 1 minute. If the test fails, replace a new vacuum interrupter
- If no factory test value, use the formula :
70% x (2 x rated voltage + 1 Kv) a.c. at power frequency ; or
(2 x rated voltage + 1Kv) d.c. if no a.c. test set is available

- Check other operating mechanism similary as with ACBs mentioned earlier
- Operate the breaker manually and electrically several times to make sure the breaker is operating properly

MAINTENANCE of AIR CIRCUIT BREAKERS

- Ensure the breaker is in the open position
- Record the number of operations
- Perform general inspection of the breaker and note any unusual signs or problems
- Put breaker in test position and use a test coupler to operate breaker electrically
- Check the operation of all relays, solenoid switches, charging motor, control switches

- Remove breaker from switchgear enclosure
- Wipe away carbon or grease deposit and dust from all insulating parts by using clean, dry lint-free cloth and vacuum cleaner
- Inspect condition of bushings, finger clamps, arc chutes, operating mechanism
- Inspect and test under voltage coils, shunt trip coils etc.

- Sand throat area of arc chutes with non-conductive and abrasive paper
- Ensure that arc chutes are clear of contamination and have no significant damage on grids or ceramics. Replace the arc chutes if ceramics are broken
- Ensure all Brazed, soldered or bolted electrical connections are tight

- Inspect the breaker contacts for uneven wear or damage.
- Smoothen contacts with a crocus cloth or sand light. Replace badly pitted or damaged contacts.
- Grease contacts lightly with an approved contact grease.
- Measure contact resistance.

- Inspect all moving mechanism to ensure that the cams, rollers, latches, bearings, etc.are in good condition
- Replace bearings and worn parts if required
- Apply light lubrication with SAE 20 or 30 machine oil on metal moving joints
- Check for proper operation function by closing & opening breakers a few times

- Oil circuit breakers should be maintained on a periodic basis similar to the ACBs
- Clean oil tank, barriers and tank linings to remove carbon deposit
- Analyse the dielectric strength of an oil sample. If visible carbon particles are evident in the oil, replace it with new transformer oil (mineral oil) and fill up to the indicated oil level.

CIRCUIT BREAKERS PROTECTIVE RELAY

Components of a Switchgear
- Circuit Breakers
- Fuses & MCBs
- Voltage and current transformers
- Protective relays
- Measuring instruments
- Busbars , insulators & other small parts
- Metal enclosure

Types of Circuit Breakers
- Air Circuit Breakers
**Main Incoming & Outgoing ACBs
**Moulded case circuit breakers (MCCBs)
**Miniature circuit breakers (MCBs)
- Oil Circuit Breaker
- Vacuum Circuit Breaker
- SF6 (Hexafluoride) Circuit Breaker

Ring main distribution system
- Oil or SF6 RMU
- Relative simple and economical
- Consist of circuit breaker or fuse taps with load-break isolator on either side

Function of a Circuit Breaker
- To isolate or connect the equipment or power supply from/to the power source
- To ensure the unimpeded flow of current in the network under normal operating conditions
- To interrupt the flow of excessive current in a faulty network through the protective relays
- Maintenance should be carried out every 2,000 operations or once a year whichever occurs first