Requesting Available Fault Current

[Revous]

Information needed from utility; the three phase short circuit MVA with the X/R ratio, and the single phase short circuit MVA with the X/R ratio. As an alternative to knowing the short circuit MVA and X/R, the system impedance (Z) and the X/R can be used to calculate the short circuit MVA. Also, the X and R components can be used.

Yeah that sounds exactly like what the SKM instructor said to ask for.

But do the utility companies even entertain the question "what is your short circuit MVA and X/R ratio?"

I feel like this information should be publicly available so we don't have to keep badgering utility engineers for all of this.

 

[jim dungar]

But do the utility companies even entertain the question "what is your short circuit MVA and X/R ratio?"

They usually do for their MV, primary metering, customers.

They often do not even know the transformer size feeding LV, secondary metered, customers without seeing the actual nameplate. And you can usually forget about getting actual %Z on the stock transformers supplied from their yard.

 

[Julius Right]

In my opinion 36 kA short-circuit current it is acceptable. If short-circuit current of a 100 MVA transformer 12.47kV rated is 36 kA then, the short-circuit voltage is 12.3% [usually possible].
I do not think the source of 12.47 kV may be more than 100 MVA power transformer.
However, in my experience, 20-40 MVA it is more expectable.

 

[electrofelon]

And you can usually forget about getting actual %Z on the stock transformers supplied from their yard.

I got it once. For a new 1200A 480V service, the POCO rep said "sure I can run out to the yard and take a picture of the 500 KVA unit we will be using" IT was a glorious day, I often think of that day and how wonderful it was. So sad it will probably never happen again.