Current equalising transformer for current balance in parallel-connected 12-pulse converter

There has been a serious problem of current out-of-balance in 12-pulse rectifiers between two 6-pulse groups. This has become particularly pronounced with semiconductor rectifiers where 12-pulse operation is obtained by two phase-displaced 3-phase bridge rectifier circuits operating in parallel. A current equalising transformer (CET) was introduced to overcome the problem. A new simpler variation of this has more recently been introduced and the paper describes this new variation and includes more complete and exact design current and voltage relationships than have previously been published.