Lowest %Z transformer

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Iron_Ben

Senior Member
Location
Lancaster, PA
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.

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.
 
15-25 KVA pads and poles I have seen are 1.9-2.3. Impedance seems to go up as the transformer size goes up. This is surprisingly low for a 166. Its a submersible vault unit:
 

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11bgrunt

Pragmatist
Location
TEXAS
Occupation
Electric Utility Reliability Coordinator
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.
This is an autotransformer @ 1%
Certainly odd for me to see this.
 

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mivey

Senior Member
I for sure recall 1.2%. Maybe 1.0x but I would have to look. Don"t ever recall one below 1.0
 

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.
 

topgone

Senior Member
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.
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.
 
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.
Yes I know
 

bwat

EE
Location
NC
Occupation
EE
500kVA pad mount at 1.9%

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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