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Thread: Transformer Terminal Ratings

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    Transformer Terminal Ratings

    I have a 150KVA transformer connected to inverter at 480V sec and utility at 208V pri. I am wondering if I can size the conductors based on 90C or 75C.

    On the spec it says, "Temperature Rise 150C with 220C Insulation System." Does this have anything to do with the terminal ratings? Or do I just assume that it's 75C?

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    Thanks for any help.

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    Quote Originally Posted by ryangittens View Post
    I have a 150KVA transformer connected to inverter at 480V sec and utility at 208V pri. I am wondering if I can size the conductors based on 90C or 75C.

    On the spec it says, "Temperature Rise 150C with 220C Insulation System." Does this have anything to do with the terminal ratings? Or do I just assume that it's 75C?

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    Thanks for any help.
    Those temperatures have nothing to do with terminal ratings. That is the winding temperatures. 150C is the full load temperature rise above ambient, and the insulation system rating is the maximum rated temperature at which the insulation system is safe (dielectric fluid and other internal electrical insulators inside the transformer).

    I would assume the 75C rating unless you know for a fact you can use the 90C rating.

    You do install on separately installed connectors, which are likely 90C rated, and that would lead me to believe I could use the 90C rating. But just because a connector is 90C rated, doesn't mean you can use the 90C terminal rating. The equipment itself needs that rating. The only time I anticipate using the 90C rating for anything other than derate calculations is if the termination is in an otherwise empty enclosure.

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    On what device do the conductors terminate on the other end ?
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    Quote Originally Posted by augie47 View Post
    On what device do the conductors terminate on the other end ?
    This is what I was going to bring up. The terminal temperature limitation is based on conditions at both ends of the conductors.
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    Quote Originally Posted by ryangittens View Post
    ... Or do I just assume that it's 75C?
    ...
    I would. And the following quote should help justify the assumption.
    Eaton recommends external cables be rated 75 °C for ventilated designs.
    Source: http://www.eaton.com/ecm/groups/publ...mz009002en.pdf, page 4 under Winding Terminations
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    Quote Originally Posted by Smart $ View Post
    I would. And the following quote should help justify the assumption.

    Source: http://www.eaton.com/ecm/groups/publ...mz009002en.pdf, page 4 under Winding Terminations
    This is gold... Thanks!

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