Circuit Breakers

 Circuit Breakers are one of the critical "safety-valves" of electrical systems and basic maintenance procedures are essential to maintain maximum reliability.

 It is recommended that following measures may be incorporated in maintenance practices to improve reliability of circuit breakers

• Visually inspect the case to determine if any portion indicates overheating; replace the breaker if overheating indications are found. Use magnifying glass.
• Check connections for indications of overheating.
• Check temperature of all circuit breakers in every trip and replace if goes beyond    operating bench mark temperature. (to be decided by taking at least  readings of 20) circuit breakers).
• Cycle the breaker at least five times manually during every schedule examination.. Observe any reduction of spring tension or bad contact .Even if once it misses proper contact or power loss / fluctuation is observed in the circuitry; replace the circuit breaker with a tested circuit breaker. 
• Check circuit current with clamp meter at circuit breaker output end when loco is at starting condition during every schedule examination and the current value achieved must be significantly below the circuit breaker rating value. Circuit current trend must be observed and in case of any increase in current value from previous value of same loco or reading observed as bench mark in other locos, cause of excessive current should be investigated.
• Check and record the voltage drop across the breaker using a calibrated digital voltmeter (capable of reading three places to the right of the decimal point). Replace all circuit breakers during M24 schedule with test bench tested new circuit breakers. 

·         Remove all circuit breakers during M12 schedule and test on the test bench before   refitting. Effective circuit breaker maintenance requires well-organized, accurate testing. The ability to accurately compare circuit breaker tests with previous test results is essential. It is, therefore, imperative to conduct tests in exactly the same way and under the same conditions as those conducted earlier. Comparison can then provide a clear picture of any deviations and changes.

• Thereby indicating whether or not the circuit breaker should be kept in operation or taken out of service for further investigation
• The following parameters should be checked during test bench testing.

1.   Tripping current .The tripping current must be in the lower side of the MI value.

2.   Temperature rise and tripping time during testing 150%, 200% and 300% of rated Amp value .It should be in the lower side of MI value.

3.   Leakage current test.

4.   Freeness check of operating knob latching mechanism trouble. 

5.   MV drop test (also in situ during M4 schedule and above)

6.   Micro Ohm Measurement of Circuit breakers & Joints: Increased contact resistances of closed circuit breakers and joints can lead to circuit breaker failure. A periodic check (M2 and above) of the contact resistance in the system allows this kind of failure to be prevented.

• The load should be operated at full load for three hours, or until the breaker reaches normal load temperature; scan the breaker with an infra red type non-contact thermometer and record the readings.

Warranty should be raised against all rejected circuit breakers during schedule checking. RDSO should be advised with make wise and cause wise failure summary of circuit breaker failure cases.

You are advised to closely monitor the implementation of the above instructions and send feed back to HQ regularly through MCDO format M.MCDO.DSL.3.6.