Rotor construction for alternating current induction motor

Abstract

The present invention pertains to an improved rotor bar design and method of fabrication of asynchronous motors using such rotor bars. The rotor bar design employs 'T'-shaped rotor bars that are interleaved around a magnetic core forming a rotor having a minimum amount of bonding interfaces between the rotor bars and end ring portions. The 'T'-shaped rotor bars may either be formed from a single piece or from multiple pieces of copper. The single piece rotor bar method provides N bonding interfaces per end ring, where N is the number of rotor bars used. Where the 'T'-shaped rotor bars are formed from three pieces for a rotor having N rotor bars, there will be 2N bonding interfaces for each end ring. Also, the 'T' shape of the rotor bars may be added after straight rotor bars have been installed in the rotor bar channels in the magnetic core with their end portions extending beyond the rotor bar channels. In addition, high-speed operation is facilitated by the addition of a shrink-fit beryllium-copper containment ring on each end ring. This containment ring acts to contain the copper end rings against outward forces developed during operation of the motor while having a similar coefficient of thermal expansion to copper (the end ring material) so that significant thermally derived differential forces are not developed between the end rings and their containment rings.