Magnetic Bearing - History

History

The table below lists several early patents for active magnetic bearings. Earlier patents for magnetic suspensions can be found but are excluded here because they consist of assemblies of permanent magnets of problematic stability per Earnshaw's Theorem.

Jesse Beams from the University of Virginiafiled some of the earliest active magnetic bearing patents during World War II. The patents dealt with ultracentrifuges intended for the enrichment of isotopes of elements needed for the Manhattan Project. However, magnetic bearings did not mature until advances in solid-state electronics and modern computer-based control technology with the work of Habermann and Schweitzer. Extensive modern work in magnetic bearings has continued at the University of Virginia in the Rotating Machinery and Controls Industrial Research Program. The first international symposium for active magnetic bearing technology was held in 1988 with the founding of the International Society of Magnetic Bearings by Prof. Schweitzer (ETHZ), Prof. Allaire (University of Virginia), and Prof. Okada (Ibaraki University).

In 1987, E. Croot further improved AMB technology, but these designs were not manufactured due to expensive costs of production. However, some of those designs have since been used by Japanese electronics companies. They remain a specialty item where extremely high RPM is required.

Since then there have been nine succeeding symposia. Kasarda reviews the history of AMB in depth. She notes that the first commercial application of AMB’s was with turbomachinery. The AMB allowed the elimination of oil reservoirs on compressors for the NOVA Gas Transmission Ltd. (NGTL) gas pipelines in Alberta, Canada. This reduced the fire hazard allowing a substantial reduction in insurance costs. The success of these magnetic bearing installations led NGTL to pioneer the research and development of a digital magnetic bearing control system as a replacement for the analog control systems supplied by the American company Magnetic Bearings Inc. (MBI). In 1992, NGTL's magnetic bearing research group formed the company Revolve Technologies Inc . to commercialize the digital magnetic bearing technology. This firm was later purchased by SKF of Sweden. The French company S2M, founded in 1976, was the first to commercially market AMB’s. Extensive research on magnetic bearings continues at the University of Virginia in the Rotating Machinery and Controls Industrial Research Program .

Starting from 1996 the Dutch oil and gas company NAM installed over a period of 10 years 20 large E-motor driven (with variable speed drive) gas compressors of 23 MW fully equipped with AMB's on both the E-motor and the compressor. These compressors are used in the Groningen gas field to deplete the remaining gas from this large gas field and to increase the field capacity. The motor-compressor design is done by Siemens and the AMB are delivered by Waukesha (owned by Dover). (Originally these bearings were designed by Glacier, this company was later on taken over by Federal Mogul and now part of Waukesha) By using AMB's and a direct drive between motor and compressor (without the gearbox in between) and applying dry gas seals a full so-called dry-dry (oil free) system has been installed. A few of the main advantages of applying AMB's in the driver as well as in the compressor (compared to the traditional configuration with a gearbox, plain bearings and a gasturbine-driver) is a relative simple system with a very wide operating envelope, high efficiencies (particularly at partial load) and also, as done in the Groningen field, to install the full installation outdoors without the need of a large compressor building.