Copper in the Rotor for Lighter, Longer Lasting Motors

This paper reviews the advantages of substituting die-cast copper for aluminum in the motor rotor. This advance in motor technology has been long sought by the motor industry but short die life due to the high melting point of copper frustrated attempts to manufacture by pressure die casting. The nickel-base alloy hot die technology developed to solve the manufacturing problem is briefly reviewed. Development work done prior to the present program and commercial motors derived from that work have focused on the increased electrical energy efficiency achievable by using copper with its higher electrical conductivity in the rotor. Performance characteristics of example industrial motors are presented. Modification of the conductor bar shape to control in-rush current and starting torque to accommodate copper in the rotor will be discussed. Modeling by motor manufacturers has shown that by using copper in the rotor, a lighter motor than an aluminum rotor motor at the same efficiency can be built. An example of weight savings calculated for a 15 Hp (11 kW) motor is presented. Data presented here show that motors with copper rotors run cooler. Industry experience shows that cooler operation translates to reduced maintenance costs, improved reliability and longer motor life.