12-pulse Series-type Diode Rectifier

Study of THD(%) Spectrum of a 12-Pulse Series Type Diode Rectifier.

The 12-pulse rectifier is composed of a phase-shifting transformer with 2 secondary windings feeding
a set of identical six-pulse rectifiers.
The transformer primary winding is Y-connected and secondary windings are Y and delta connected. Due to delta windings at secondary side, we get a phase shift of 30 degrees. As a result, harmonics of the input line currents are greatly reduced and THD is greatly reduced as compared to the conventional 6-pulse rectifier.