Symmetrical/Asymmetrical short circuit current
Symmetrical/Asymmetrical short circuit current
(OP)
We have a requirement for the 480V switchears and Motor control centres to have rating for 65kA (symmetrical) short circuit current and the main bus bracing for 100kA momentary short circuit current (Asymmetrical). I would like to know if the vendor provided 65kA (symmetrical) short circuit rated Switchgears and mcc's, will the requirement for bus bracing for 100kA momentary short circuit current (Asymmetrical) be met?






RE: Symmetrical/Asymmetrical short circuit current
LV switchgear up to 80kA symmetrical short circuit with stand (1sec) is widely available.
The Asymmetrical or momentary or making current rating is higher by a factor of 2.1 for switchgear at that voltage.
So, there shouldn't be any problem in procuring the switchgear with the said specifications.
RE: Symmetrical/Asymmetrical short circuit current
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RE: Symmetrical/Asymmetrical short circuit current
It is a factor to which all the low voltage switchgear (upto 1000V)must satisfy for the purpose of meeting the IEC requirement.
Incidently the factor increases to 2.5 for all the medium voltage switchgear (between 1kV - 56kV) having to meet the same Asy. current requirements.
RE: Symmetrical/Asymmetrical short circuit current
RE: Symmetrical/Asymmetrical short circuit current
RE: Symmetrical/Asymmetrical short circuit current
I think the topic you have talked is very interesting and sometimes not very clear.
My question is:
Do you know if there is any standar from ANSI/NEMA/UL concerning to busbars in any voltage rating?
I guess there should be something such as with the circuit breakers. . .
Regards
RE: Symmetrical/Asymmetrical short circuit current
A manufacturer may also have their own design subbmitted, tested, and aproved by UL.
RE: Symmetrical/Asymmetrical short circuit current
sorry for my ignorance
Flashover
RE: Symmetrical/Asymmetrical short circuit current
The worst SC case scenario will occur at the zero point of the voltage wave. An exponential decaying unidirectional current component (DC decrement) will be added to the AC symmetrical component forming the total asymmetrical current wave at a particular instant.
See the enclose article
http://polk-burnett.apogee.net/pd/dshe.asp