electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
What is the lowest impedance you have ever seen in a pole or pad transformer? I dont recall seeing anything lower that 1.8%, but I am sure there are lower.
Lowest %Z transformer
- Thread starter electrofelon
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Iron_Ben
Senior Member
- Location
- Lancaster, PA
Off the top of my head, 1.7% for sure. When I would be poking around the yard looking at nameplates, the vast majority were 1.7 to 2.1 or so.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
This is an autotransformer @ 1%
Certainly odd for me to see this.
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iceworm
Curmudgeon still using printed IEEE Color Books
- Location
- North of the 65 parallel
- Occupation
- EE (Field - as little design as possible)
500kva, 208Y, 2%
69KA - freeking insane
69KA - freeking insane
If that autotransformer was re-connected as a two-winding transformer, the % impedance should be 2%.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
The lowest one I have seen was also a central maloney
wbdvt
Senior Member
- Location
- Rutland, VT, USA
- Occupation
- Electrical Engineer, PE
pole mounted transformers are typically in the 1-2% range from what I have seen.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Wow that's low for a 500 pad.
iceworm
Curmudgeon still using printed IEEE Color Books
- Location
- North of the 65 parallel
- Occupation
- EE (Field - as little design as possible)
What voltage?
yep, it was an existing transformer at a school where we were adding a building and pulling a second service out of the transformer.
208 secondary i believe. I'm not sure what they did about it, it wasn't my project i was just covering a meeting with the utility.
iceworm
Curmudgeon still using printed IEEE Color Books
- Location
- North of the 65 parallel
- Occupation
- EE (Field - as little design as possible)
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
The vault unit I posted in post #3, that was one of a 500 KVA 208y/120 bank, 1.8%. Available fault current is "healthy" to say the least, 77k. Pretty good for a non network service. Service equipment is only 25 feet away, but its well below 65k by the time it gets there.
wbdvt
Senior Member
- Location
- Rutland, VT, USA
- Occupation
- Electrical Engineer, PE
That 77kA is NOT available fault current. That is the infinite bus fault current. There is a difference and it is important to keep the nomenclature correct.
The available fault current would be based on what the utility is capable of delivering for fault current. This would be then result in an available fault current on the secondary side which is going to less, sometimes substantially so, and will be less than the 77kA.
The available fault current would be based on what the utility is capable of delivering for fault current. This would be then result in an available fault current on the secondary side which is going to less, sometimes substantially so, and will be less than the 77kA.
Correct. I plugged-in some numbers; assumed 1,000 MVA short-circuit power available at primary side, 300 feet of wires--> the available fault current I got was 74kA at the 208V side! I guess it is about that ballpark, IMO.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Yes I know
Two things.
1) That is crazy low for 500. Thanks for sharing that experience because I didn’t know they made them that low for something for that size.
2) We have strangely similar user names. I feel like I have to apologize to you since you joined long before I did.
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