Published on: 
Turbomachinery Magazine, September/October 2022,

Solid-Rotor Technology for Turbomachinery Applications

Yaskawa Electric Corp. is one of the world’s leading manufacturers in the fields of drive technology, industrial automation, and robotics. Founded in 1915 and based in Kitakyushu, Japan, Yaskawa strives to optimize the productivity and efficiency of machines and industrial systems via innovation. Today, Yaskawa has 14,500 employees worldwide and a business volume of EUR 3.7 billion.

In 2014, Yaskawa became the sole owner of The Switch. Yaskawa Environmental Energy / The Switch focuses on electrical drive train products, capabilities, and solutions. Included within its portfolio are electrical machines and high-power converters to original equipment manufacturers and system integrators for selected wind, marine and turbo (high-speed) applications.

Its solid-rotor technology integrates with high-speed machinery, and is designed to improve the efficiency, simplicity, and robustness of turbomachinery. A solid rotor is built of a single piece of steel that is not sensitive to thermal cycling. This offers stable and effective bending stiffness combined with an ability to retain its same balancing class. As a comparison, in case the rotor would be made of a plate stack shrink-fitted to a shaft, its stiffness would rely on the axial compression of such a stack. Therefore, it can change over time or when operating in fluctuating temperatures.

“We are known as a provider of robust high-speed electrical machines using solid-rotor technology,” said Markus Silventoinen, Mechanical Engineering Manager at Yaskawa Environmental Energy / The Switch.


The company also supplies complete high-speed machines for integrated turbomachinery, such as impellers directly on its machine shaft, as well as standalone machines that connect to adjacent machinery via a flexible coupling. Additionally, it delivers active part components for electric machines that can be integrated with turbomachinery.

The standard solution is to equip the rotor with a copper squirrel cage for improved efficiency and power factor. Efficiencies up to 97% can be reached, depending on the rating of the machine. The cage is made only from solid materials. Further, the company can provide feasibility studies of direct drive electrical machine solutions along with commissioning and service for its equipment.

“Our simplified electrical drive technology and products help optimize the performance of turbomachinery,” said Silventoinen. “The high-speed machine can be coupled directly to the system without other mechanical parts, like gear-boxes, even as a hermetic compressor motor or turbine generator unit. The variable frequency drive (VFD) supports operational optimization via energy savings.”


Some of the key turbomachinery use cases for this technology include:

• New designs for compressors, turbines,
or pumps
• Test benches with wide speed ranges
• Replacing old steam or gas turbine prime movers with standalone machines

Making heat or converting it to electrical energy is a hot topic today, added Silventoinen. New technologies for industrial-size (> 1 MWe) heat pumps are needed to increase efficiency in processes that generate heat for district heating.

“Whether you’re looking for efficient heat pumps or high-speed generators in Organic Rankine Cycle (ORC) applications, solid-rotor technology is a good fit,” he said. “Both solutions typically use radial turbomachinery in >1 MWe powers and need high rotational speeds of 10,000 rpm.”

Solid-rotor technology can also raise the robustness and simplicity of integrated high-speed motors in heat pump applications and high-speed generators in ORC applications.

The organization is currently looking into opportunities for its high-speed technology to be implemented in hydrogen-related applications. And its low-speed permanent magnet machines are being used with generators for offshore wind and with direct-drive shaft generators and propulsion motors for marine applications, both of which can be a part of the future hydrogen economy.

Its latest technology is in-house active magnetic bearings (AMB), which are currently being tested by a pilot customer. Contact-free bearing technology can simplify machines, maximize robustness, and minimize losses for better system efficiency. 

For more information, visit: www.theswitch.com