The Temperature Impact of Magnetic Wedges on TEFC Induction Motors

The key functions of magnetic wedges are to seal the open-slot design for form wound induction stators and reduce the air-gap flux distortion, magnetizing current, starting (inrush) current, and temperature rise. Supplemental benefits of magnetic wedges are an increase of motor efficiency and improvement of power factor 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. This paper investigates the impact on the motor performance by employing magnetic versus nonmagnetic wedges during a starting and normal operation. The type of induction motor, open (ODP, WPII) or enclosed (totally enclosed fan cooled), 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 the qualification processes that are necessary in order to avoid failures and ensure reliable magnetic wedge systems.