Twelve-pulse rectifier cuts harmonic distortion by 80%
Fitted to the ACS 600 range of medium power ac drives, ABB's integrated
12-pulse input rectifier module will reduce total harmonic (THD) by up to
80% compared with conventional six-pulse supplies. The 12-pulse supply is
generated by two six-pulse rectifiers, connected to a three-phase system
via a three-winding, phase-shift transformer. Phase shifting the
secondary windings by 30o significantly reduces the sum of the secondary
currents in the primary windings, resulting in a current THD of between 5
and 15%. This would be more like 40 or 50% in a six-pulse installation.