Reducing motor losses is one of the many challenges faced by motor engineers. The effective use of magnets is one of the methods to minimize motor losses.
Sources of Motor Losses
To reduce motor losses, it is essential to understand their sources.
| Copper Loss: This is a common and significant source of motor loss. When current flows through the copper windings of the motor, the resistance of the coils impedes the current, generating heat. The key point is that this heat loss is proportional to the square of the current. This means that if the current doubles, the copper loss quadruples. Therefore, any design that allows the motor to operate with a smaller current can reduce copper losses.
| Iron Loss: The invisible consumer, the core of the motor (stator and rotor), is not perfect. When the magnetic field constantly changes within it, the core material itself resists this change, thus consuming energy. This primarily includes two parts: the hysteresis loss, which overcomes the “friction” within the material, and the eddy current loss caused by the induction of small circulating currents (eddy currents) due to the changing magnetic field. Generally, the higher the operating frequency, the greater the iron loss.
| Magnet Loss: The permanent magnets on the rotor can also become a source of motor loss. Particularly in high-speed motors, rapidly changing magnetic fields can induce eddy currents within the permanent magnets, causing the magnet to heat up. Overheating not only reduces efficiency but may also demagnetize the permanent magnets, such as neodymium magnets.
The Role of Magnets in Reducing Motor Losses
| Using High-Performance Magnets: The efficiency of permanent magnet motors fundamentally comes from the strong and stable magnetic fields provided by the permanent magnets. A crucial parameter here is called “intrinsic coercivity (HcJ),” which can be understood as the magnet’s “ability to resist demagnetization.” When motor load increases or temperature rises, the coil current generates a magnetic field that weakens the permanent magnet.
If the magnetic steel has insufficient “demagnetization resistance,” the generated magnetic field weakens. To maintain output power, the control system must increase the current, which directly causes a spike in copper losses. Therefore, selecting high-performance magnets ensures that the magnetic field remains stable under harsh conditions. When this stability is achieved, there’s no need to increase the current, fundamentally curbing the primary copper losses.
| Controlling Heat Generation in Magnets: There are two common solutions:
Segmented Magnets (Laminated Magnets): This involves cutting a solid piece of magnetic steel into several smaller pieces, separated by insulating materials. This effectively interrupts large eddy current paths, changing significant eddies into many smaller, less effective ones, thereby reducing heat generation. These magnets are formed by bonding tiny magnetic particles with insulating plastics. Because each particle is insulated, eddy currents are nearly impossible to generate, resulting in minimal self-loss, making them particularly suitable for motors operating at extremely high speeds.
Selection of Silicon Steel Sheets: Using higher-performance, thinner non-oriented silicon steel sheets further reduces eddy current losses.
| Addressing High-Temperature Environments: In environments such as automotive engine compartments or certain industrial pumps, ambient temperatures can be high. In such cases, more heat-resistant magnetic materials are required. Samarium cobalt magnets are a typical example. Although their magnetic strength may not match higher-grade neodymium magnets at room temperature, they have a significant advantage: their “demagnetization resistance” decreases very slowly with increasing temperature. In other words, at high temperatures, samarium cobalt magnets can avoid efficiency losses due to demagnetization, fundamentally ensuring low losses and reliability in high-temperature conditions.
Magnets Manufacturer
At Tengye, we’re thrilled to be early participants in your new projects. Our passion for magnets extends from material selection and design optimization to providing magnetic solutions. We hope to bring our knowledge and experience to the forefront by actively engaging in your upcoming projects. Work with our magnet experts to get the right magnet solution.
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