This website gives a short overview of electrical machines used as high speed motors and generators, their advantages and some application fields.
Furthermore, the challenges of developing and manufacturing high speed motors and generators are explained. With
e+a located in Switzerland, there
is a competent partner with more than 28 years of experience in designing and producing customized asynchronous and synchronous high speed motor elements for various application areas.
Various requirements are actually leading to a growing demand for high speed motors. First of all, the continuous need for an increased power density.
Due to the quasi linear relation between rotational speed and shaft power of an electrical machine, increasing the rated speed is an effective way to
boost power density and efficiency. Hence this approach takes advantage of increasing shaft power without changing the size of the machine. On the other
hand, the same performance can be provided in a smaller volume. The latter is paramount in the field of machine tool applications for example. Thus
spindles or the machine tool in a whole become smaller, weight is reduced and dynamical behavior is enhanced. Another point in this industry is the
cycle time that a machine tool needs to complete a specific operation. The faster a tool can be moved and rotated the faster it is able to complete its
task, not taking into account that high speed cutting operation rely on top speed to machine time efficiently respective parts.
Further interesting operation fields of high speed motors are applications where a standard gearbox is used to translate the rotational speed of conventional
power grid frequency (50/60 Hz) driven motors to higher speed levels. A replacement of this gearbox and the related conventional motor with a speed controlled
drive consisting of a high speed motor and a rectifier increases the overall efficiency and reduces the maintenance significantly.
The compressor industry is an example, where high efficiency, oil-free operation and no emissions make electric high speed motors the most environmental
friendly compressor drives. In the context of emission free application energy storage systems with high speed flywheels not only take advantage of high
speed generators. Thus fossil generators with unwanted emissions can be avoided and maintenance costs can be reduced significantly. Cryo applications actually
experience a very similar revolution of its drive technology. Directly driven motor elements replace a set of a gear box and a 50/60Hz standard motor.
Efficiency can be increased, the needed space is by far downsized and maintenance costs are reduced. Hence energy recovery systems e.g. become more and
more interesting from a financial and an ecological point of view. Thus high speed motor elements contribute partly to the ongoing development of green energy applications.
The mentioned advantage of high speed motors can only be achieved by using high quality motor elements. The reason for that is that due to the high rotational
speeds, the centrifugal forces on the rotating motor part (rotor) can be very high leading the materials to the edge of mechanical stress resistivity. Failures
in motor elements can result in crashes affecting the environment or at least damage the spindle, where the motor is built in. To prevent this, various physical
aspects need to be calculated in a challenging development process, taking electromagnetic, thermal, mechanical stress and structure dynamic aspects into account.
The applied computational methods need to be combined with a long experience, to extend actual operation limitations with keeping safety in mind as highest priority.
Furthermore, the interaction of the rectifier and the high speed motor needs to be known, because the rectifier has a deep impact on heating, noise, clogging,
and power consumption of the machine. Especially the interaction of various converter systems with a high speed motor element demands very specific knowledge
and experience. Hence tests of above described applications are crucial to succeed. They require an intense relation between the power electronic and high speed
motor specialists. Furthermore the infrastructure enabling performance tests are highly complex and usually not available on the market. Very often the related
costs exceed by far the costs incurred during the whole development process of a new motor element product line.
Typical inverters are working on base of the pulse wide modulation method, where a continuous switching of voltage or current controls the output waveform.
Due to the need for faster high speed motors, the switching frequency increases as well (in modern inverters, IGBT's are used). Although noise and efficiency
improve as the number of pulses increase, the inverter leads also to a few drawbacks, especially because of fast switching transients which can be understood
as a significant source of stray losses. Additional time harmonics caused by a switching mode inverter has a negative impact on the air gap flux distribution.
These harmonics cause additional eddy current losses in the motor elements especially in the rotor, which lead to higher temperatures and a possible degrade of
the mechanical behavior. The switching frequency has another impact on the high speed motor, namely on the insulation, which is severely stressed by the repetition
and the steepness of the pulse wave front. When IGBTs are used, the high rate of voltage rise of typically 0 - 650 V in less than 0.1 µs leads to approximately
10,000 V/µs. This fact results in adverse effects on the motor insulation. These steep rising and falling pulses lead to an uneven distribution of voltages within
the motor, especially during switching transitions. Without a deep knowledge of the motor insulation system and the inverter itself an insulation deterioration
and subsequent failure of the motor can occur. In this context partial discharge effects and rotor over heating are well known failure sources. The latter can
lead to an unwanted carbon fiber burst due to thermal a mechanical stress in the respective resin carbon fiber compound (synchronous machines).
Asynchronous and synchronous high speed motors offer several advantages like decreased installation space for higher power and unnecessary gearboxes. These advantages
apply for several fields and are intensively used in the machine tool, compressor, cryo and energy generating industry for example. Designing and producing these
asynchronous and synchronous high speed motors is an exciting task, where the usage of most modern computational methods for the development process is as important
as a wide range of experience and expertise to extend actual operation limitations in a safe way. Not only the knowledge of high speed motors is necessary but also
a deep inside in inverter technology, partial discharge phenomenon and so called stray or additional losses.
e+a in Switzerland offers a wide product portfolio of high speed motors or generators respectively. With more than 28 years of experience and more than 150,000 different
high speed induction machines and permanent magnet synchronous machines running,
e+a is one of the world leaders in developing and manufacturing highly customized high
speed motors. Furthermore, a professional equipped test bench with all the newest inverters and a partial discharge test system allows detailed analysis and adaptation
of rectifier and motor and a very well support for system integrators.