Cooling options for high-speed solid rotor machines

Did you know you can choose from a variety of effective cooling systems for our high-speed solid rotor electrical machines?

Solid rotor machines are a superb option for high-speed applications because they are robust, efficient and reliable. But because high-speed machines are characterized by high power density, even with the highest efficiency the loss density for large power ratings must be carefully addressed with proper design. Cooling is always needed.

We make sure proper design happens. We customize the cooling of our solid rotor machines for each application, taking into account temperature ranges, environmental conditions and process needs.

Solid rotors are temperature flexible

Solid rotor machines have no risk of thermal demagnetization as exists for permanent magnet machines. Nor do they suffer from the thermal bow of a laminate stack. Instead, solid rotors are quite tolerant to “running hot,” if necessary. They can adapt to temporary loss of cooling, momentary overloads and various ambient conditions.

As a rule, solid rotor machines are manufactured to meet insulation class 180 standards. Nonetheless, machine internals must be cooled in some manner. High power and high power density leave no other option.

Temperatures are monitored by default in the stator and bearings with PT100 sensors, as most common standards, such as IEC 60034, require. Temperature rise is limited to 155 °C, although higher limits may be considered case by case.

Overview of cooling options

We offer many cooling solutions with our solid rotor machines and can consider more specialized solutions when needed. In consultation with the client, we do a careful cooling analysis and choose the best cooling method for the specific situation and application.

  1. Our standard solution is open-air forced-ventilation cooling with an external fan. This is suitable in constant torque applications with low-speed overloading requirements where cooling flow is not dependent on speed.
  2. We can also provide ventilation through shaft fans. This is the solution for applications with a quadratic torque envelope such as compressors, pumps and turbines where the need for cooling flow depends on speed.
  3. When closed-loop cooling and an increased protection class is required, the cooling system of the solid rotor machine requires a heat exchanger. Our standard solution is an air-to-water heat exchanger. We can also use other medias such as oil, salt water or an air-to-air heat exchanger for special cases.
  4. For special cases, we also offer water jacket cooling with closedinternal air circulation. This provides very compact cooling, as less room for air circulation is needed around the active parts and heat exchanger of the machine. However, because it requires a completely tailored cast frame, water jacket cooling is only available for high volume projects.
  5. In machines requiring special integration, it is also possible to utilize process gas directly to produce very efficient cooling. These situations require active magnetic bearings (AMBs), and the entire system – including the compressor unit and the electric machine – must be hermetically sealed.

This is only a very brief overview of the considerations and possible options. Please get in touch with any questions or to discuss your particular situation in more detail. We are very interested in solving the challenges facing your high-speed applications.

Product Manager, Solid Rotor Machines

Panu Hava

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Panu Hava currently works as Product Manager, solid-rotor machines at The Switch. He has over a decade of experience in product development of electric machines, including industrial induction and synchronous machines as well as high-speed induction machines. Today, his main responsibilities are technical sales support for new tailored products and leading product development of high-speed electric machines. Hava holds a M.Sc. (Tech.) in Mechanical Engineering from Lappeenranta University of Technology.