Operating Cycle in a Breaker

Time in seconds = No of cycles x (1/frequency)

Example,

5 cycles time for 60 Hz system = 5 x 1/60 = 0.0833 second

5 cycles time for 50 Hz system = 5 x 1/50 = 0.1 second

In relay coordination, the relay operating time (or number of cycles) shifts the relay curve.

- MS

The OP has asked for the operating cycle or the Duty Cycle of a circuit breaker (e.g.) O-t-CO-t-CO. Whereas you have answered about the cycles in the supply frequency. The question is misunderstood and hence the answer is incorrect.

Now, coming to the OP's question, the 'O' in the duty cycle of the breaker means the total tripping time of the breaker (i.e.) from the instant of initiation of the trip command to the final arc quenching.

In relay co-ordination, the grading margin does take into account the opening time of the breaker.

Thanks for indicating it.

It all depends on what the OP meant by 'operating cycle'. If the OP means the circuit breaker duty cycle, then you are correct. However if it indicates circuit breaker interrupting time in cycles, my interpretation is not incorrect. I interpreted it this way since the OP asked for the relation of the cycle with time. Your interpretation is more intelligent and can be correct (I would never say it is incorrect) and maybe both answers could be helpful to the OP.

- MS

msamad and electricalexpert65

You are way too high calibre for the question...

_{What is the relation between operating cycle of a breaker with tripping time.}

i could not find the term "Tripping time" defined in IEC 60947-1. There is an "Opening time" (2.5.39) and "Break time" (2.5.41) the difference being arcing time.

"Tripping" would probably refer to the action of the relay, and the time would be very much dependent on the current.

Assuming that the OP is referring to the 'break time', the answer to the query would be - no relation.

Similarly, the second query also begs the answer that O-3 minutes-CO-3 minutes-CO has nothing to do with any coordintation.

msamad's expertise on US equipment and standards will give us some new knowledge, i hope.

There is a small relation between operating cycle of a breaker and its tripping time.

1 operating cycle = 1 ON(close) Cycle + 1 OFF(open) cycle.

the operating cycle of a breaker depends on mechanical durability & electrical durability.

Mechanical durability is with respect to mechanical wear and is expressed by the number of no-load operating cycles. With use, the operating mechanism becomes sluggish, resulting in delayed clearing times beyond that given in the manufacturer's published curves. The springs generally retain their strength for the life of the breaker and beyond. The lubrication, however, becomes the limiting factor. Grease and red oil used in the lubrication deteriorate, resulting in the slower clearing times. As shown in Figure 2, the manufacturer's published tripping curves are actually bands within which a good breaker is expected to operate.

electrical durability is with respect electrical wear and is expressed by the number of on-load operating cycles (the contact resistance is subjected to electrical wear).Worn out circuit breakers will constantly trip &turn themselves off, resulting in partial or total loss of power. There are two components that wear out with use: the copper contacts and the spring-loaded operating mechanism. The contacts wear out due to abrasion while closing and arcing while opening the breaker. In large breakers, the contacts are replaceable.

A possible shifting of this band is due to aging. If the tests reveal that the breaker operation is much above the original tripping band, then it is time to replace the breaker.

The current-carrying contacts consist of the main and the arcing contacts, the latter opening last when the breaker trips. The arcing contacts are easily replaceable. The condition of the contacts can be determined by measuring the contact resistance with a micro-ohmmeter, when the breaker is drawn out. A 4000 A, 480 V breaker in good condition should have a contact resistance of less than 30 micro-Ohms. The condition of the contacts can also be checked by infrared photography.

The operating mechanism requires greater attention, adjustments, and maintenance. Excessive pressure between the contacts would cause bending and misalignment. Inadequate pressure would lead to minute arcing and heating. Lubrication of the moving parts is the key to successful consistent operation of the breaker. Most manufacturers use red oil for both the current-carrying parts and the operating mechanism.

As the breaker ages, the oil dries out and flakes off. There will then be metal-to-metal sliding, which wears out the surfaces and can cause misalignment. Eventually the breaker will "seize," resulting in a failure to open or taking several seconds to open. This could be the beginning of a catastrophic failure unless there is an upstream backup breaker to clear the faulted condition. It is, therefore, essential to check out the mechanism, lubricate it, and exercise it on a regular basis.

the life of circuit breakers can be extended with preventive maintenance and testing. As a result, power circuit breakers are not normally included in the list of equipment to be replaced during renovation unless test results suggest otherwise or the breakers are antiquated and replacement parts become difficult to procure.

considering mechanical durability about 50K cycles are possible with normal circuit breakers (schneider, ABB, terasaki)

considering electrical durability about 30K cycles are possible at rated current & 50K at half the rated current with normal circuit breakers (schneider, ABB, terasaki)

In what way operating cycle of a breaker play role in Relay Co Ordination?

just a time delay (>200ms) is required for Breaker Relay Co-ordination.