Replacing induction motors with caged rotor permanent magnet motors: application considerations & cost analysis

Efficiency improvements attainable with permanent magnet motors have been well documented. Some permanent magnet motors have been equipped with an induction cage in the rotor to allow direct on line starting. Designs of this type have been referred to as line start permanent magnet motors. A topic that has not received much attention is the use of this type of motor with an adjustable speed drive. This paper introduces the terminology Caged Rotor Permanent Magnet motor to describe motors of this type that can be used either direct on line or with an adjustable speed drive. Details of several installations of Caged Rotor Permanent Magnet motors are discussed. Each case study is documented from application selection, motor specification, cost justification, installation, operation and measured performance.