Hi,

I have consulted the IEEE 1584 standard but have not seemed to find any discussion regarding the impacts of PFC units to the incident energy.

From IEEE 551, it states that during fault conditions, the capacitor discharge takes place in the initial 1/30–1/8 cycles. Since the breaker protective device and contacts cannot operate in this time frame, capacitor discharge currents will have no effect on breaker parting or clearing operations. I take from this that the discharge current does not sustain long enough to effect the tripping of breakers, thus not having an effect on the arc duration.

But I wonder if the discharge contribution during the first cycle/s significantly impact the arc current, hence the incident energy?

Referring to IEEE 1584 again, they state that motors smaller than 50 HP can be ignored since they are not large enough to sustain their fault current for any meaningful length of time. Would this principle be applied for PFC units too? Also when modelling the system, are PFC units ignored?

I would appreciate your thoughts on this.

Kind regards,

studentengineer

Here is a response I got from EasyPower a while back concerning power factor caps:

I wanted to mention to you that the Capacitor banks are not considered as sources for short circuit studies and are only used in the Power Flow. With this in mind it is not as important to have the capacitor information filled out for short circuit studies.

Hi Barry,

Thanks for sharing the response you got from EasyPower. I wonder why they're not considered sources in short circuit studies? Is it that they're insignificant on their impact to short circuit faults?