Tom Bishop, PE
Senior Technical Support Specialist
Electrical Apparatus Service Association
St. Louis, MO
The paper "Emerging Technologies in the Motor Industry" by Tom Bishop, presented at the EASA Convention 2017, explores the potential successor technologies to the squirrel-cage induction motor. The focus is on permanent magnet (PM) motors, reluctance motors, and other emerging motor technologies that are nearing commercial reality. Bishop begins by acknowledging that while the induction motor will remain prevalent for decades, newer technologies are gaining traction.
Permanent magnet motors are categorized into those that can be started across the line and those that require a drive. They can have surface permanent magnets (SPM) or interior permanent magnets (IPM), and salient or non-salient rotors. High energy density rare-earth PMs, such as neodymium, offer high performance but are subject to price volatility and availability issues. Ferrite PMs are a lower-cost alternative but have significantly lower energy density. PM motors are more efficient at low speeds and typically smaller and lighter than comparable induction motors.
Hybrid permanent magnet (HPM) motors combine elements of switched reluctance and PM motors, offering high torque per input watt and nearly constant output torque with minimal ripple. These motors are used in applications like compressors and cranes. Across the line start PM (LSPM) motors can handle high inertia loads and are suitable for pumps, fans, and conveyors. They operate at synchronous speed and achieve high efficiency levels, but their violent starting "kick" can lead to accelerated wear.
High-torque, low-speed PM motors are used in cooling towers, paper drive machines, and slurry pumps, eliminating the need for gearboxes and reducing maintenance. Surface permanent magnet (SPM) motors require a VFD and offer high efficiency, while interior permanent magnet (IPM) motors provide exceptionally high efficiency and are used in applications like CNC machines and electric vehicles.
Reluctance motors, including synchronous reluctance motors (SynRM) and switched reluctance motors (SRM), offer unique advantages. SynRMs have distributed windings and rotors with low and high magnetic reluctance paths, providing high efficiency and low noise. SRMs have simple construction with salient pole windings and steel laminations, offering high dynamic response and fault tolerance but requiring electronic commutation and having high torque ripple.
Future technologies include the use of amorphous metals for stator cores, which can reduce core loss by up to 70%, and NovaTorque permanent magnet motors with dual PM rotors and axial flux. Axial flux ferrite PM motors are suited for direct drive applications, offering high efficiency with ferrite magnets and amorphous metal stators.
Key Points Covered:
- Overview of permanent magnet (PM) motors and their classifications
- Hybrid permanent magnet (HPM) motors and their applications
- Across the line start PM (LSPM) motors and their characteristics
- High-torque, low-speed PM motors and their benefits
- Surface permanent magnet (SPM) motors and interior permanent magnet (IPM) motors
- Reluctance motors, including synchronous reluctance motors (SynRM) and switched reluctance motors (SRM)
- Future technologies such as amorphous metals and NovaTorque permanent magnet motors
Key Takeaways:
- Permanent magnet motors offer high efficiency and reduced size and weight compared to induction motors.
- Hybrid and across the line start PM motors are suitable for various industrial applications.
- High-torque, low-speed PM motors eliminate the need for gearboxes, improving efficiency and reducing maintenance.
- Reluctance motors provide high efficiency and fault tolerance but require electronic commutation.
- Future technologies like amorphous metals and axial flux PM motors promise further improvements in motor efficiency and performance.
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