Advancing asynchronous motors

In order to reduce power consumption and the resulting CO2 emissions, it is necessary to continue optimising known and established concepts. Gerhard Thumm shares how asynchronous motors can become more efficient and advanced.

Government regulations require lower and lower levels of CO2 emissions in various areas. To meet these requirements, the overall energy consumption needs to be continuously improved. This includes electric motors. Approximately 38% of the world’s electricity is consumed by electric motors in buildings and industrial applications. A common type of electric motor is the three-phase induction Motor. Improvements to this type can provide efficiency and sustainability benefits.

Asynchronous machines (ASM) are built up of two components: the outer, fixed stator and the inner, rotating rotor. Unlike permanent magnet synchronous motors, these machines do not require expensive rare earth materials. As a result, their use in automotive applications has been on the rise in recent years. The compact size of the ASM is another advantage over a synchronous motor. This makes it ideal for small, lightweight machines with little space for larger components. This is where simple math enters the picture: Getting more power out of less weight will result in a higher overall efficiency.

The potential for further development of this machine is particularly noteworthy. One way to increase circumferential speeds and, more importantly, efficiency is to use copper materials. Studies have shown that it is possible to increase the performance of ASM systems by a factor of 2 to 3.

Using this knowledge, a redesigned short-circuit ring consisting of segmented end rings was developed by the Wieland Group.

The fact that the shading rings consist of multiple disks is the key feature of this design. These discs are pierced by the forming rods in a new configuration that allows the cage assemblies to be beam welded together. Welding bars and discs forms a closed cage, allowing for a flexible rotor design that can be tailored to meet the specific requirements of the application while remaining cost effective.

This high degree of geometric freedom comes with a certain amount of complexity, which can only be mastered by drawing on the experience gained from previous projects. In order to meet new requirements in the best possible way, Wieland’s project managers and engineers can access a large pool of successfully implemented geometries.

By allowing the use of different materials in the end ring, this new design is well suited for applications requiring high power densities, high efficiency classes and high circumferential speeds. Primary applications include automotive and railway traction machines, and machine tool spindle drives.

The robust design allows for a wide range of possibilities for development and improvement, as simply choosing the right material can make a big difference in thermal and energetic performance.

Wieland offers rotor components as well as complete rotors made of copper. Copper has about 50% higher electrical conductivity and better mechanical properties compared to aluminium, and also improves the efficiency of ASMs. So, rotors made of copper are a key component in high-speed machines, where temperature, power and energy density are critical.

In most other manufacturing processes, the high levels of thermal shock and temperatures during the rotor manufacturing process are critical to the tools and cage components that are used. Thermal fatigue of components and tools is usually unavoidable due to the high temperatures. The microstructure of the component is typically very soft after production, whereas in the new design the shorting rings are composed of several individual disks. After the forming bars have been inserted into the stack of sheets, the end rings are mounted on top of the stack of sheets over the profiles of the forming bars. This design allows “hybrid” end ring geometries. That is, different copper materials or steel end rings can be combined.

The advantage of ASM is that the cages are fabricated by established industrial methods, making it possible to produce any shape with high mechanical strength. The copper profiles of high-speed ASM rotors can therefore be adapted to the electrical and mechanical requirements, creating fine-grained and highly conductive microstructures.

The right rotor

As described in a previous article in International Transport Manufacturer on the Zero Porosity Rotor, this process can ensure 0% porosity. However, casting processes that meet high industrial standards mean that the components of the built ASM can also have the same material properties.

Wieland offers both types of rotors ready for immediate use, but they differ in their area of application. The ZRP rotor is intended to be used primarily in the high-power range. The built rotor, on the other hand, is more suitable for more specific requirements, as the assembly method creates more engineering space, allowing more variations in strength and design to meet customer requirements.

Gerhard Thumm is Business Development Engineered Products at Wieland Werke.