Improvements in energy efficiency of induction motors by the use of magnetic wedges

The key functions of magnetic wedges in the slots of large induction motors are to reduce the air gap flux distortion, magnetizing current, the starting (inrush) current and temperature rise. The benefits of magnetic wedges are the increase of motor efficiency (by reducing core losses, stray load losses and winding losses), improvement of power factor, improved energy conservation and thereby being more environmentally responsible. There can also be cost savings from potential reduction in active material or frame size. End users can make better purchasing decisions with an understanding of the cost impact of magnetic wedges. The paper investigates the impact on the motor performance by employing magnetic versus non-magnetic wedges during starting and normal operation. The type of induction motor, open (ODP, WPII) or enclosed (TEFC), along with the number of poles, influences the effect on the motor performance that magnetic wedges have. Magnetic forces (stresses) acting on the wedges are also investigated in this paper. This paper also discusses qualification processes that are necessary in order to avoid failures and ensure reliable magnetic wedge systems.