Short circuit data for study modeling

[HamidEle]

Hi, Guys,
Thinking about something interesting. Upstream short circuit data are required to perform the short crcuit, load flow, motor starting, stabity and harmonic. By default, we have been using 1.5-4 cycle data( interrupting duty) data for years. Is is correct? Any thought are appriated!

Cheers.

 

[krisys]

1.5-4 cycle data is supposed to be the transient value. When you ask the Utilities, this is the value they normally furnish along with X/R ratio.

The steady state short circuit current (Ik in IEC Terms)is more significant for the relay coordination and short time withstand ratings.

 

[davidbeach]

Most utility customers are far enough away from generation that the source impedance at the customer location is essentially all lines and transformers, with no time dependent decay. For probably 90+% of our customers the biggest change in fault current will result from transmission switching, not from the transition from subtransient to transient to synchronous reactances. Don't, for even a moment, think that the utility supplies a constant level of fault current; but the day-to-day variations will be far greater than the cycle 1 to cycle 5 to cycle 30 variations. Even 2-3 buses away from generation sources I see fairly constant fault currents, changing when something trips, but not decaying as the generation contribution would. [highlight #FCE94F][/highlight]

 

[HamidEle]

Yes. In our case, the facility is a bit far from the generation, except when it is fed from the local generator only. Under the generator supply condition, the sub-transient and transient data will come into play. Thanks for the explanations.