12-Pulse Drive Cuts Harmonics

ABB has introduced an integrated 12-pulse bridge rectifier module for its ACS 600 range of medium power AC drives.

The rectifier produces a 12-pulse power supply that reduces total harmonic distortion by 80%, compared with conventional six-pulse supplies.

The module can be integrated within existing ACS 600 frame sizes and can now provide 12-pulse benefits to low power applications between 55 and 630 kW in 380 to 690 V.

The module is designed for use where the supply network is weak or where regulations limit the extent of harmonic distortion allowed in the electricity supply.

Two six-pulse rectifiers connected to a three-phase system, by a phase-shift transformer with a 30°-phase shift, generate the 12-pulse supply.

By phase shifting the secondary windings by 30°, the sum of the secondary currents in the primary eliminates, for example, the 5th, 7th, 17th and 19th harmonics. This can result in a THD of between 5 and 15% as compared with a THD of between 40% and 50% in a six-pulse installation.