HV & LV breaker

[jasl]

I would like to know the standard time constants or X/R ratios of HV and LV circuit breaker. I am presently trying an IEC909 based short circuit calculation and have a value of X/R = 14 (for 50 Hz) for HV breakers. For LV breakers,I have a table with list of power factors, multiplication factors depending upon the capacity of switchear. Can someone guide me to the relevant ard/links for me to have a better understanding?

 

[mpparent]

I believe IEEE Ref. 1015 (IEEE Blue Book) might be where you could look.


Mike

 

[jasl]

An addition to my question :The short circuit analysis is IEC 909 based and I have found the relevant IEC standard containing the references to HV and LV breakers. Thanks for the posting.
Another question:
In HV switchgears the calculated symmetrical rms and peak are much lesser than the switchgear withstanding ability. However the calculated X/R ratio at this HV switchgear is greater than the X/R ratio as per IEC, ie. 14.
I would like to know whether any derating has to be applied on the switchgear rating?

 

[RajT]

You need not worry about the X/R ratios being ( calculated) on the high side. As far as the switchgear duty is concerned ,it is only important to ensure that the calculated rms/pk ratings do not exceed the switchgear suppliers nameplate ratings.