seacraft18 said:
Could someone please provide the formula to calculate the short circuit current at the actual panel location ?
The utility company has provided me with short circuit current at the pole @ 10,846 amps.
What you ask, could be in actuality, a much more complex question then you may realize.
In order to know what the maximum three phase bolted fault current might be at a panel you would need to provide the rated voltage at which the 10,846 amps applies, and the one-line for the system showing any transformers with their rating, line/cable size, etc. Then the calculations can commence.
Be cautious, the responses herein, telling you that it should be OK are inaccurate because with the information you provided it is not possible to know for sure what it would be.
I recommend, as a minimum you sit down with someone trained to do these types of calculations and have a little learning session.
The short answer, the formulas are based on applying the rules of circuit analysis.
The long answer:
In ANSI/IEEE short circuit calculations, an equivalent voltage source at the fault location, which equals the prefault voltage at the location, replaces all external voltage sources and machine internal voltage sources.
Machines are represented by their internal impedances. Line capacitances and static loads can be neglected. Transformer taps are adjusted at nominal position or tapped position whichever applies. It is assumed that for 3-phase fault, the fault is bolted. Therefore, arc resistances are not considered. You can include fault impedances for single-phase to ground fault if desired. System impedances are assumed to be balanced 3-phase, and the method of symmetrical components is used for unbalanced fault calculations.
Three different impedance networks are utilized to calculate momentary, interrupting, and steady-state short circuit currents, and corresponding duties for various protective devices. These networks are: ? cycle network (subtransient network), 1.5-4 cycle network (transient network), and 30 cycle network (steady-state network).
ANSI/IEEE Standards recommend the use of separate R and X networks to calculate X/R values. An X/R ratio is obtained for each individual faulted bus and short circuit current. This X/R ratio is then used to determine the multiplying factor to account for the system DC offset.
Using the ? cycle and 1.5-4 cycle networks, the symmetrical rms value of the momentary and interrupting short circuit currents are calculated. These values are then multiplied by appropriate multiplying factors to finally obtain the asymmetrical value of the momentary and interrupting short circuit currents.
