ISC for IEEE 519

Since the short circuit current appears to be used mainly in determining the Short Circuit Ratio (Isc/I_L), I think I would use the single line to ground fault current, as most equivalent to the load current. Someone else can correct me if I'm wrong.

Here's some info that might be of help in general:

Interpreting IEEE Std 519

The standard seems amazingly clear to me. How that helps you remove line harmonics, I do not follow at this point, but I will be happy to play along for the booby prize.

It doesn't help in removing harmonics, it helps in determining how much mitigation you may need. The ratio of I_sc to I_l (load) current is used in determining an appropriate I-TDD (Total Demand Distortion) level, which then is used in pre-determining what effect adding a non-linear load(s) will have on your V-THD at the PCC and if you must do something about it. For example if you have a very high I_sc/I_l ratio and a small non-linear load, you may not need bother with harmonic mitigation because it's like a fly on an elephant's butt.

Now that last part, I understand, loud and clear, over.

Thanks.. But do you know which Isc should Iuse?

Not familiar with the term Iuse. Is that like Iload? Then there is the Iaim term.

Usually the Ifire term comes before Iaim though.

Iuse, new product from Apple?

Isc = I short current

Doesn't that smart - - a lot? Best not shunt off too much current.

Use the Short Circuit current that the load center allows for, surely you have a warning sign on the MCC panel that tells you?

I agree with you.In my opinion according to definition:

short-circuit ratio: At a particular location, the ratio of the available short-circuit current, in amperes, to the load current, in amperes.

and the note c [Table 2 or 4] :

Isc=maximum short-circuit current at PCC

it has to be 3 phase short-circuit [since IL has to be 3 phase load] and

maximum it has to be supertransitory short-circuit current. However, I don't think far from generators it has to be a significant difference from steady-state current.

From the attached by Peter T Interpreting IEEE 519 article ch.VIII. CASE STUDY the short-circuit three-phase [solid ] at low voltage transformer terminals [calculated at H.V. side] is considered.

Zxfm=12.5^2/3/(100/1000)*2.6%= 13.54167 ohm

Isc=12.5/13.54=923 A

The load is considered 200 HP IL=200*746/SQRT(3)/12500=6.89 A