Copper Rotors?


AC Squirrel Cage Induction Motors were originally invented with ‘Copper Bar’ rotors with ‘End Rings’ brazed to the Bars making it look like a cage and thus the name Squirrel Cage Induction Motors. This is how these Motors were made for almost 60 years world over from the year 1900. Then as a Technology improvement and enabling mass and defect free production the Die Cast Aluminum Rotors got developed totally eliminating bars insertion and end rings and brazing etc. This got readily adopted all over and today it dominates the entire world of LT Squirrel cage Induction Motors.

The Efficiency Advantage Using Die Cast Copper Rotors

The efficiency advantage that die-cast copper rotors bring to synchronous electric motors is understandably attractive to energy-conscious industrialized countries, but it’s doubly attractive in developing countries, where electric power is often in short supply and relatively expensive. India, the world’s second largest emerging energy market (after China), faces a chronic 10% energy shortage up to 20% during peak periods while energy use is growing at between 9% and 10% per year. The problem is especially felt in rural areas, where 63% of households do not have any electricity at all.

Motors with Copper Rotors Can Cost Less to Produce

Update readers know that simply substituting copper for aluminum in electric motor rotors can either: (a) increase electrical efficiency when motors are held at the same size, or (b) reduce size and weight when horsepower and/or efficiency are held constant. For example, Update recently reported that several motor manufacturers who directly substituted copper for aluminum saw significant increases in efficiency in an agricultural irrigation application (See Update, October 2004). Designers can also trade off efficiency, size and power against each other to optimize motors for given applications.

Motor Test Results, Copper Compared to Aluminum from CDA

Motor manufacturers have long realized that because the electrical conductivity of copper is nearly 60% higher than that of aluminum, substituting copper for alumi-num in the squirrel cage of the induction motor would markedly increase the elec-trical energy efficiency of the machine. Most motors larger than about 200 kW and a few special purpose smaller motors are built with copper squirrel cage struc-tures manufactured by a time consuming and costly fabrication process. The intri-cate squirrel cage of smaller motors is produced by pressure die casting aluminum. Alternative cost-effective manufacturing methods have not been devised.

DCR Final Efficiency Comparison between Aluminium Rotor & Copper Rotor

Aluminium Rotor

Copper Rotor

Designing Squirrel Cage Rotor Slots with High Conductivity

There has been, in recent years, an effort to make cast copper rotors for industrial use induction motors. The objective is to make motors more efficient because of the higher conductivity of copper. In addition, the reduced losses in such motors may lead to better design flexibility and therefor motors which are more compact.

In this paper we examine the tradeoff between running efficiency and starting performance. In order to understand how induction motors work it is necessary to have a good model for the conduction properties of the conductors in the slots of the rotor.