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Thread: Ungrounded wye to delta transformer - Padmounted

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    Ungrounded wye to delta transformer - Padmounted

    There were a lot of previous discussion about ungrounded wye to delta transformer bank. It seems most of the handbook suggest to float the wye primary if it is a wye-to-delta transformer bank. How about padmount transformer? We have a padmount 3-phase transformer; it is wye to delta; the primary wye side has a H0, which not internally bond to the tank or grounded. The H0 bushing insulation level is the same as the phase bushing. My question is, should I float the wye by just applying an insulation cap to H0, and not connect it to anything?

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    Quote Originally Posted by zhangbp View Post
    There were a lot of previous discussion about ungrounded wye to delta transformer bank. It seems most of the handbook suggest to float the wye primary if it is a wye-to-delta transformer bank. How about padmount transformer? We have a padmount 3-phase transformer; it is wye to delta; the primary wye side has a H0, which not internally bond to the tank or grounded. The H0 bushing insulation level is the same as the phase bushing. My question is, should I float the wye by just applying an insulation cap to H0, and not connect it to anything?
    Except in utility use where they have close control of the applied voltage balance, you must float the center point of a wye to delta transformer (or of a wye-wye transformer with a tertiary delta winding.) Otherwise you risk potentially damaging high circulating currents in both secondary and primary. The fact that there is an available neutral on the primary side makes no difference, and the fact that it is a three phase padmount rather than a set of single phase pots on a pole makes no difference either.

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