At the Emods meeting of the Global Motor System Energy Efficiency Forum (Eemods), Richard DeFay, Sustainable Energy Project Manager of the Copper Development Association, presented a report on the test results of copper rotor motors and permanent magnet motors.

Defi pointed out in the meeting: "The industry once believed that the efficiency of permanent magnet motors is better than induction motors, but this is not true." The Copper Development Association plans to compare relatively permanent systems of permanent magnet (PM) motors with copper rotor motors (CRM) using drives specified by permanent magnet motor manufacturers to determine the effectiveness of marketing claims.

The first phase of the test was compared using a 7.5 HP (5.5 kW) copper rotor motor and a permanent magnet motor from three different manufacturers. The test was conducted at the Advanced Energy Motor Testing Laboratory in North Carolina and the trial lasted for several months. The motor test is divided into three phases, all using the same frequency converter, and the efficiency is compared according to the motor load and speed.

The study found that the data comparing the test energy efficiency of permanent magnet motor and copper rotor motor at different speeds (1800, 1600, 1400, 1200, 1000 RPM) are as follows: (basket color represents copper rotor motor, red represents permanent magnet motor)

The data results show that the system efficiency of the copper rotor motor is higher than that of the permanent magnet motor at the level of the permanent magnet 90hz and the 60hz frequency of the copper rotor.

From the study of the second test phase, it can be seen that in the stage of permanent magnet 150hz, copper rotor 60hz frequency, the torque ratio of the copper rotor motor system is higher than that of the permanent magnet motor, but the torque percentage reaches 75%. At the time, the system efficiency of the copper rotor begins to be lower than that of the permanent magnet.

The third stage test shows that the copper rotor motor is more efficient than the permanent magnet PM motor when the frequency is the same.

“The results of this analysis are quite interesting and show that the motor must be further studied at different horsepower speeds,” Mr. Defi said. "We now have the opportunity to conduct further and larger assessments to more accurately evaluate copper rotor motor technology." Future tests may include: Motor rated power up to 20 hp (14.9 kW).

As can be seen from the above examples, the asynchronous motor using the copper rotor is not only far more efficient than the aluminum rotor motor, but also has an irreplaceable advantage compared with the permanent magnet motor, for example, short circuit, high temperature and strong vibration of the permanent magnet material. The environment is prone to loss of magnetism, and the magnetic protection cannot be extinguished when the fault occurs. Under abnormal conditions such as overspeed, the permanent magnet pole is easily affected. These inherent defects of permanent magnet synchronous generators make it difficult to meet the high reliability and maintenance-free performance requirements of the system, and the copper rotor motor has excellent performance in this respect. Motor manufacturer Reliance Electric believes that copper rotor motors are the only motors that meet the demanding requirements of the military.

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June 13, 2023