The ANSI 49 Rectifier with Phase Shift

The ANSI 49 rectifier circuit given in the ANSI Standard C34.2-1968, Section 4 is a single-way three-phase input rectifier that has 120°rectifier conduction, six-pulse output, and does not use an interphase transformer. It is a very desirable circuit but has not been used extensively. Part of the reason for this is the need for separate phase shift transformers to cancel the source. harmonic currents when several of the rectifiers are used together. The ANSI 49 circuit, has a wye primary, six-phase star secondary, and is wound on three single-phase cores or the magnetic equivalent A modification of this circuit is described in which the wye primary is replaced with a partial zig-zag winding, where the zig. and zag windings have unequal turns. By selecting proper ratio of turns of the zig to zag winding, any desired phase shift can be secured. The new circuit is analyzed to show how it works, and test results of a laboratory model are described which fully verify that the circuit operates as theory predicts.