Short circuit current& No. of operations relation

[safy2004]

Hi
Can any one help me to find the relation between the withstand short circuit current and the number operations relation for vacuum and SF6 medium voltage circuit breakers.
For example if I have circuit breaker with 31.5 kA at the manufacturing date (No. of operations = zero), what will be the withstand short circuit current after 2000 operations.
Thanks

 

[rbulsara]

31.5kA, provided the CB was designed for 2000 operations and was maintained per manufacturer's recommendations and NETA-MTS.

 

[rbulsara]

I do not beleive there is any established relationship between age or usage of the equipment and its withstand rating, as long as they have properly maintained and operated witin its useful life. You may want to ask the manufacturer's what do they consider useful life of the equipment.

 

[unclebob]

Checking and replacing closing springs on old Westinghouse
DS 600 V air breakers is something we do somewhat often during electrical maintenances. I've seen some of these built in 1980 in pretty good shape.

 

[apowerengr]

You may have to derate the breaker's interrupting rating not due to the number of operations but instead based on the breaker duty-cycle compared to any reclosing intervals you might have programmed into the reclosing relay (if applicable). If you reclose too fast or too often and don't allow the breaker to cool down you can cause failures. Most breaker mfg's provide information on how to derate their equipment based on reclosing intervals and total I2t accumulated vs. their duty cycle ratings.

 

[AusLee]

Hi,

I thought the number of maneuvers listed in the manufacturer's catalogs was based on full current making and breaking.

If you close the breaker (by chance) when the sine wave is at zero, then this maneuver practically do not count.

If an MV breaker is free standing and not connected (yet), then arming the lever and engaging / disengaging can only wear out the springs, which is not very critical as in these will wear out after the number of maneuvers has passed.

Note that Merlin Gerin SF6 circuit breakers are rated for 10,000 operations, 5 times more than the above mentioned 2,000 which may be based on other rating standard.

If the above is correct, then there is no derating on the current carrying capacity of the breaker. If the above is not true, please correct me.

 

[stevenal]

The interrupting ability doesn't change, but your maintenance interval will depend on the number of operations and the KA interrupted. The instruction manual should have a curve showing this inverse relationship.