Utility Information
Utility Information
(OP)
Hi,
Utility provided me with a Three phase fault level, zero sequence impedance and 3 Io for a new transformer connection. Why this three with ground fault current.
People from utility can put a word.
Thanks
Utility provided me with a Three phase fault level, zero sequence impedance and 3 Io for a new transformer connection. Why this three with ground fault current.
People from utility can put a word.
Thanks






RE: Utility Information
RE: Utility Information
My question is, I asked for ground fault current and three phase fault current....
I understand the three Phase but instead of Io they provided 3Io. We are in the preliminary stage of our design and need to set our Equipment withstand(Breaker) capability and grid design.
They also did not mention if this half cycle, or 3-5 cycle value.
Could you advise how to interpret this information.
Thanks
RE: Utility Information
If you do a symetrical fault fault calculation the standard termination for zero sequence current is 3I0 represented by three identical vectors.
The fault current is represented by adding a set of three identical vectors at 120degrees rotating clockwise to a set of three identical vectors at 129 degrees rotating counter clockwise and adding three IO vectors.
RE: Utility Information
Is this rms half cycle, 5 cycle or 30 cycle value ?
I need half cycle for my ground grid design and equipment withstand capability.
Thanks
RE: Utility Information
In what form did they provide the fault current? From what you wrote it looks like you don't have sufficient information to determine the X/R ratio. If the Zero sequence impedance is in X and R you have it for SLG faults but you'll still need it for 3-ph faults if you are to calculate the assymetric fault currents.
RE: Utility Information
I think most of the utilities use PSEE like packages for running load flow or short circuit information. and When
a customer asks for a short cicuit level...what value of current they provide ?
If they provide half cycle, technically they should not provide X/R because a half cycle already has accounted for that value.
I guess this was just an obersvation...people who work in utilities will comment better..
Cheers !
RE: Utility Information
Equipment rated for symmetrical fault levels account for asymmetry per ANSI/IEEE or other applicable standards or some multipliers. Refer to its full spec or you need to contact the manufacurer's technical support.