Copper versus Aluminum Induction-Motor Rotors: Which Contruction is Best?

MANY INDUCTION MOTORS IN SERVICE TODAY are running critical processes in which failure at any time can be very costly. Many times, these critical processes will not have a back up. As a result, a large portion of these processes will shut down until the motor is repaired and put back into service. Those aware of this situation will strive to purchase a motor that will maximize reliability. As a result of the strong push for maximum reliability, it is easy to over specify costly components not required for specific applications. These decisions will result in an unnecessarily high motor purchase price. To maximize reliability without overspending, large induction motors need to be properly matched to specific applications. With this consideration, the choice between various rotor constructions needs to be evaluated. It is generally assumed that copper bar rotors are the most reliable. In certain applications, this may be true; they can at times outperform aluminum rotors. But many times, the applications are such that there will not be any appreciable performance or reliability benefit from the use of copper bar rotors. It will be shown that the percentage motor cost increase can be very large on smaller machines but may not be as significant on larger machines.