transformer

[hondastang]

Hello new to the forum. When using a 112.5 kv delta 480 to a Wye 480 would i use a 200 amp breaker. Just want to make sure.
been a while figuring out this stuff. Thanks

 

[charlie b]

112.5 times 1000 divided by 480 and divided again by the square root of three gives a result of 135 amps. You can go up to 250% on the primary, but I usually stick with 125%. You can only go to 125% on the secondary. That value is 169 amps. You can go to the next higher standard size, which is 175 amps. So I would use 175 amps on both the primary and the secondary.

Welcome to the forum.

 

[Besoeker]

Hello new to the forum. When using a 112.5 kv delta 480 to a Wye 480 would i use a 200 amp breaker. Just want to make sure.
been a while figuring out this stuff. Thanks

I agree with Charlie's numbers.
But I assume you mean 112.5 kVA, not kv.
Important to get the units right old chap.

 

[augie47]

Keep in mind, when dealing with transformers, you must satisfy at least two Code Sections, Art 450 and Art 240.
Art 450 deals with protection of the transformer and your basic guide is 450.3(B) which, in this case, will require a primary OCP of 125% (or next larger) or a secondary protection of 125% (no larger).
Once you have selected your overcurrent devices for Art 450, then you need to apply Art 240, primarily 240.21(C) to protect the associated conductors.