Utility Short Circuit Information
Utility Short Circuit Information
(OP)
How do you obtain accurate maximum and minimum shout circuit values from the utility companies? A lot of the smaller utilities in Colorado laugh with I ask. What is the best reference for oil filled transformer impedances?






RE: Utility Short Circuit Information
If you're on the secondary side of a transformer (480 V or lower), there will be very little difference between minimum and maximum. It will be basically a function of the transformer impedance.
The value that should be used will also depend on what you are doing with the data. For equipment ratings, I would assume an infinite bus on the primary and use the transformer impedance.
RE: Utility Short Circuit Information
Regards
Marmite
RE: Utility Short Circuit Information
For the transformer impedance, the best is to have it on the nameplate. There's a table with standard impedance in the IEEE buff book (1986, i think 1993 don't have the table anymore), but it can vary a lot. Transformer will have a great influence on the short circuit value, so i think it's important to have the accurate impedance.
Little question, how do you determine the minimum short circuit? The minimum will come from a 2 phase short circuit, but do you put a short circuit impedance too, like 10 ohms?
thanks
RE: Utility Short Circuit Information
More typically though, in the situation where the existing kVA size can be found, there are cases where the available designs have a significant difference in impedance. The numbers we give out are always based on the lower impedance situation.
RE: Utility Short Circuit Information
All transfoerm manufacturers publish the %sc.
RE: Utility Short Circuit Information
Someone knows! For "maximum" you can always use the infinite bus as a conservative back-up.
"Minimum" is trickier. I use it for arc flash calcs. I have had a more difficult time obtaining this value.
Good Luck.
RE: Utility Short Circuit Information
These values are constantly monitored by System studies groups in every Utility. Try to contact appropriate person.
RE: Utility Short Circuit Information
RE: Utility Short Circuit Information
Sorry experience you had!
The persons you have asked could be the wrong people! Suggest to take Auslee's advice, take a large short-circuit MVA (shall I say "infinite", meaning the utility is capable of delivering a large short-circuit contribution to your system during faults on your system).
glad to be of help.
RE: Utility Short Circuit Information
Again, Thank you.
cuhead
RE: Utility Short Circuit Information
min SC contribution could be significantly lower then max due to system configuration change in the upstream transformer stations.
Utility will provide you with "bolted" fault values, no resistance in the fault, and X/R ratio.
RE: Utility Short Circuit Information