WEG Electric Motors Corp. a global supplier of motors, drives, controls, generators and transformers, explains that the energy efficiency and process control benefits offered by frequency inverter drives with AC induction motors provide plant operators with many opportunities for increased profit and lower costs, but these advantages can be undermined by reduced motor life.
WEG Electric Motors R&D are continually trying to identify and implement practical solutions for improved motor life and better efficiency by improving motor designs for inverter operation.
“Our mission is to explore new lines of research to give us better insight into the different parameters and complex interactions that control energy efficiency and reliability in motor design and application,” comments Brian Keith, WEG automation manager. “By understanding these factors better, we can achieve useful advances and balance our findings against the cost-effectiveness of implementing them. Our developments in Optimal FluxT Technology are an excellent example.
“Recently, in collaboration with the Federal University of Santa Catarina, WEG has identified a new approach to coil design which could reduce premature aging of the coil insulation caused by inverter overvoltages.”
WEG’s approach lies in reducing the nominal supply voltage to the coil windings, by reducing the voltage pulse amplitudes of the pulse width modulation. For example, if the PWM amplitude is reduced by half, voltage levels on the motor terminals and the potential gradients between windings also will be reduced (especially on the initial windings). In this way, partial discharges at the terminals and initial windings can be virtually eliminated.
Meanwhile, the ampere-conductors required to create the magnetic flux are maintained by replacing pole group coils with a larger number of parallel path coils and applying lower voltages to the parallel path coils, thus obtaining the same mmf (magneto motive force).
Extensive studies of the impedances of each current parallel path show that certain amplitude or angular phase imbalances are allowable as they are effectively dampened by the impedance. This ensures an inbuilt self-regulating mechanism that tolerates minor variations, and increased losses are insignificant.
“This has been demonstrated in actual prototype two-pole three-phase motors,” continued Keith. “At this time, the complexity of the coil winding involved means further development work before a commercially useful result is available.
“However, this research-based and collaborative approach has already brought highly successful advances to the world markets, such as our coil insulation techniques, and our CWF-11 drive inverters based on our Optimal FluxT technology. By carefully matching inverter and motor design development, WEG has demonstrated that it’s possible to improve motor and inverter design offering reliability and lifetime benefits.”
For more information, call 678/249-2000 or visit www.weg.net.
