Lifetime Analysis of Copper and Aluminum Squirrel Cage Rotor of Asynchronous Machines

The squirrel cage of the rotor is frequently manufactured using aluminum and its alloys, as well as copper and its alloys. The number of requests from users demanding extended service life has increased, relating to the number of starting cycles. Requests, sometimes far above the conservative specifications existing in API 541 [15], which refers to 5,000 starting cycles. Users are questioning whether a machine equipped with an aluminum squirrel cage rotor, as opposed to a copper cage, can deliver the same performance and longevity when driving the same industrial application. In order to clarify this question, this paper will discuss in depth the performance and lifetime behavior of two squirrel cage motors (6.20 MW and 10.75 MW), one designed with aluminum in the rotor and the other designed with copper. This paper will also compare the environmental impact on the materials, the machine’s overall performance such as efficiency, power factor, torque curve behavior, starting performance and last, but not least, analyzing the number of starting cycles each motor can perform, comparing with API 541 Edition minimum number of starts. Aspects of failure mechanisms will also be addressed.