Momentary asymmetrical vs peak evaluaton for K=1 breakers

[rockman7892]

When comparing momentary fault duty ratings for K=1 breakers to available system fault current do you need to compare the rms asymmetrical values or the asymmetrical peak value (or both)?

I'm evaluating a 63kA rated breaker that passes the interrupting rating however it fails the rms asymmetrical value (but passes the peak asymmetrical value).

Breaker peak momentary rating is 164kA but no specific rms rating is provided (assumed its 100kA ish?).

Does the breaker need to pass both the momentary asymmetrical rms and peak values?

I know the old ANSI standard used to be evaluated based on asymmetrical rating with the new standard using the peak value but never really understood the change or evaluating one vs the other?

 

[Kiribanda]

1) Asym peak current or the close & latch capability (2.6xk=1x63kA=164kA)of the CB has to be compared
with the rated momentary (peak) withstand current (Asy rms which includes the DC component) of the swgr/ MCC
of which the CB is going to be installed. (Because the swgr/ MCC is tested for sc forces etc for that
current so called bus bracing).

 

[dpc]

Medium- and high-voltage breakers have two ratings: Interrupting and Momentary(aka Close & Latch). As I understand it, the K factor adjusts the interrupting rating depending on the actual voltage vs the rated voltage. For newer vacuum breakers, K=1 and there is no adjustment based on voltage. The K factor does not have anything to do with the momentary rating.

Depending on the vintage of the (ANSI) Breaker, the momentary rating could be asymmetrical RMS or Crest (peak) current. I don't think a breaker will have both a rms asymm AND a creat rating for momentary. You would use whatever standard the breaker was tested to.

Cheers,

Dave