Voltage Range K Factor understanding 2

[Eleceng01]

Hello all. I am trying to gain a better grasp of K-factor as associated with breakers and MCCs. It was mentioned to me by an associate that he had 15kV equipment being operated at 6.9kV so the K-factor would affect the short-circuit current available. This is a new subject to me so I am hoping someone can help with links to good sources or advice. Thanks.

 

[Skogsgurra]

K-factor, as I know it, has more to do with transformers and distorted waveforms. Are you sure you friend doesn't bull?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[davidbeach]

Skogsgurra, there was a k-factor (different from transformer k-factor) in an obsolete IEEE/ANSI breaker standard. It has been gone for quite some time and I don't know enough of the details to answer the original question, but it is a legitimate question.

 

[dpc]

The ANSI C37 K-factor provides a range of adjustment of short-circuit rating based on the ratio of the actual voltage to the maximum rated voltage of the breaker. So if a K-rated 15 kV breaker is applied at a lower voltage, such as 6900 V, there will be an increase in short circuit interrupting capability - up to a point defined by the K-factor.

New ANSI standards no longer use the K-factor, but it would still apply to any breakers tested and rated by that method.

As mentioned, this is unrelated to Transformer K-rating.

 

[Eleceng01]

dpc,

Thanks! I think I understand it now with your and davidbeach's feedback.

 

[Skogsgurra]

And I learned something, too!

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[RalphChristie]

dpc:

Although you've said it (k-factor) is not included in the new ANSI-standards, does some American switchgear manufacturers still use it?

Never heard of it (in the breaker-world) before.

Thanks
Regards
Ralph


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[rcw retired EE]

Here's my understanding.

K factor was for air and oil based circuit breakers with interrupting ratings given in short circuit MVA. As the operating voltage decreased, the short circuit current capability increased up to some maximum value given by the K factor. The interrupting MVA was constant down to some minimum voltage so the current value could be increased.

Oil and Air Blast circuit breakers could dissipate a given amount of arc energy. The interrupting current levels were not the limiting factor. The arc energy was the limit.

SF6 and vacuum interrupters use a different arc interruption phenomenon. They are limited by the current and not the arc energy. Their interrupting rating does not increase as the application voltage level drops. K=1.0

See Powell Electric’s website for a good white paper on this.

http://www.powellind.com/main/Uploa...ce of k factor in circuit breaker ratings.pdf

 

[Eleceng01]

All,

Thanks again for the discussion. GE still mentions K-factor in there literature.

http://www.geindustrial.com/publibrary/checkout/38652.30055.23350.12730/PDF/pvbkrpo.pdf

Glad I wasnt the only 'new guy' who had never heard of this. Thank you again.