Aiming at the special winding connection of the new-type converting transformer, its connecting scheme of differential protection is proposed based on the establishment of the current transform equations. Adopting the ratio braking characteristic with three-broken line, and taking these effects into account including the unbalance current under the normal condition, current-transformer performance and existing output current when internal fault occurring, the setting values for the differential protection of the new-type converting transformer are calculated. At last, by the simulative calculation of various transformer operating states, the feasibility of the proposed scheme and the correctness of the setting calculation are verified.
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