Magnetic bearing

Magnetic bearings are used in several industrial applications such as electrical power generation, petroleum refinement, machine tool operation and natural gas handling.

An active magnetic bearing works on the principle of electromagnetic suspension based on the induction of eddy currents in a rotating conductor.

The power amplifiers in a modern commercial application are solid state devices which operate in a pulse-width modulation configuration.

Jesse Beams from the University of Virginia filed some of the earliest active magnetic bearing patents[12][13] during World War II.

However, magnetic bearings did not mature until advances in solid-state electronics and modern computer-based control technology with the work of Habermann[14] and Schweitzer.

[15] In 1987, Estelle Croot further improved active magnetic bearing technology,[16] but these designs were not manufactured due to expensive costs of production, which used a laser guidance system.

[19] During the decade starting in 1996, the Dutch oil-and-gas company NAM installed twenty gas compressors, each driven by a 23-megawatt variable-speed-drive electric motor.

By using active magnetic bearings and a direct drive between motor and compressor (without having a gearbox in between) and by applying dry gas seals, a fully dry-dry (oil-free) system was achieved.

[21] These inventions provide the technological basis for a number of practical applications, some of which have reached the stage of industrial series production under licence from Forschungszentrum Jülich since about 1980.

The electronic control system is also smaller and requires less electrical power because the bias field is provided by the permanent magnets.

As the development of the necessary components progressed, scientific interest in the field also increased, peaking in the first International Symposium on Magnetic Bearings held in 1988 in Zürich with the founding of the International Society of Magnetic Bearings by Prof. Schweitzer (ETHZ), Prof. Allaire (University of Virginia), and Prof. Okada (Ibaraki University).

Joining the hall of fame and earning lifetime achievement awards in 2012 were Prof. Yohji Okada, Prof. Gerhard Schweitzer, and Michael Swann of Waukesha Magnetic Bearings.

Magnetic bearing advantages include very low and predictable friction, and the ability to run without lubrication and in a vacuum.

Magnetic bearings are also used to support maglev trains in order to get low noise and smooth ride by eliminating physical contact surfaces.

In the field of vacuum metrology the spinning rotor gauge (SRG) was introduced as a reference standard by BIPM, Paris 1979.

For rotating systems it is possible to use homopolar magnet designs instead of multipole Halbach structures, which reduce losses considerably.

An example that has bypassed the Earnshaw's theorem issues is the homopolar electrodynamic bearing invented by Dr Torbjörn Lembke.