breaking capacity of breakers 1

[144x]

If a vacuum type breaker with a breaking capacity of 31.5 KA and voltage level of 12KV is used in a system with a voltage level of 3KV would the breaking capacity change?

 

[dpc]

Maybe. This requires testing of the breaker - there is no theoretical calculation. ANSI-rated breakers have a "K" factor that provides this information. I'm not sure about IEC breakers. In general, the interrupting rating will increase as the voltage decreases, but only up to a certain point. It certainly does not increase without limit as the voltage decreases.

Refer to breaker testing standards and test data.

 

[jbartos]

Suggestion: Contact the breaker manufacturer for rating at 3kV since you did not post all necessary data, e.g. nominal 3-phase class MVA

 

[Modula2]

Didn't ansi eliminate the K factor and adopt a constant KA rating, regardless of voltage and because new breakers, particularly vacuum breakers have a capability that is constant KA.

 

[Kiribanda]

Hello,
From the data given, I presume that the circuit breaker you have mentioned should have been manufactured as per IEC60056(62271). Then 12 kV=Ur (rated voltage) is the upper limit of the voltage of which the CB has to operate. Then 31.5 kA should be the highest short circuit current, which the CB is capable of breaking under conditions of use. CBs using SF6 & Vacuum as the interrupting medium has got more constant current characteristics than the old air magnetic medium, which is having constant MVA characteristics. Therefore even at a lower operating voltage the short circuit rating should be the same. As such in my opinion, you can use the 12 kV vacuum CB at 3 kV, which can still break 31.5 kA. But it is always advisable to consult the CB manufacturer to get the required confirmation.

But if this CB is ANSI rated for 15 kV (there is no 12 kV in ANSI), then it can’t use for 3 kV because as per ANSI the voltage range factor K for a 15 kV maximum voltage is 1.30. Then the lower range of the max. voltage is 15/1.3= 11.5 kV and the modified short circuit breaking current has to be recalculated accordingly.

Regards!