Fault current

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
I have MHs fault current spreadsheet plus my own I made years ago. They compare with the answers given.

Competitor called yesterday with a question on a delta configuration. (I sent him on to the correct POCO contact)

He has three transformers and the POCO rep he talked to originally gave him the impedance of each. 50 KVA =1.9, 25 KVA =1.01, and 25 KVA =1.5.

What is the impedance I should use for my calculations, or is this where the limits of our relatively simple SSs become apparent?
 
F

Fitzdrew516

Senior Member
Location
Cincinnati, OH
ptonsparky said:
I have MHs fault current spreadsheet plus my own I made years ago. They compare with the answers given.

Competitor called yesterday with a question on a delta configuration. (I sent him on to the correct POCO contact)

He has three transformers and the POCO rep he talked to originally gave him the impedance of each. 50 KVA =1.9, 25 KVA =1.01, and 25 KVA =1.5.

What is the impedance I should use for my calculations, or is this where the limits of our relatively simple SSs become apparent?
Click to expand...

That's a great question. I guess theoretically you could calculate it out, but if I were you I'd use the lowest impedance as a worst case scenario, especially because the impedances are close.
 
kingpb

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
For equivalent 3-phase transformer I would use 75KVA, Z = 1.14%.

I have to be honest though, I let ETAP convert the 1-phase numbers. Could have done it myself but I like technology. :D
 
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
ptonsparky said:
I have MHs fault current spreadsheet plus my own I made years ago. They compare with the answers given.

Competitor called yesterday with a question on a delta configuration. (I sent him on to the correct POCO contact)

He has three transformers and the POCO rep he talked to originally gave him the impedance of each. 50 KVA =1.9, 25 KVA =1.01, and 25 KVA =1.5.

What is the impedance I should use for my calculations, or is this where the limits of our relatively simple SSs become apparent?
Click to expand...

You have two 25 KVA. Is one 15kVA?
 
kwired

kwired

Electron manager
Location
NE Nebraska
jumper said:
You have two 25 KVA. Is one 15kVA?
Click to expand...


High leg delta systems with unequal sized pots is more common to see a large pot for the 120/240 side of the delta which likely is more heavily loaded and smaller pot(s) to derive the high leg, which may have more limited load.
 
C

Carultch

Senior Member
Location
Massachusetts
kwired said:
High leg delta systems with unequal sized pots is more common to see a large pot for the 120/240 side of the delta which likely is more heavily loaded and smaller pot(s) to derive the high leg, which may have more limited load.
Click to expand...

What is a "pot" in transformer vocabulary?
 
C

Carultch

Senior Member
Location
Massachusetts
kwired said:
Some call them "pole mounted pigs"

Basically an individual unit that is single phase in - single phase out but they may use multiple units to build a multiphase bank.
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So it's one of those "buckets" up on the utility poles. And what it really is, is the enclosure that houses each pair of windings.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Carultch said:
So it's one of those "buckets" up on the utility poles. And what it really is, is the enclosure that houses each pair of windings.
Click to expand...
Well AFAIK it is a slang term and the meaning could vary, but most cases I believe that is what it is intended to mean.
 
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