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Standards Development
The scope of the standard is to clarify the interpretation of load capacity in Active Magnetic Bearing (AMB) systems. With traditional passive bearings of the rolling element or fluid lubricated journal types, load capacity is the maximum load or force that the bearing can experience in a machine before permanent deformation or fatigue failure. In contrast, an AMB operates with a magnetic gap and may be designed to have a maximum load capacity for a particular application. An AMB has the added feature of being controllable, hence, to be able to apply a spectrum of controllable forces over a prescribed frequency range. The scope of this document covers the following attributes of an AMB:
• The static force capacity when the journal is statically centered with zero offset.
• The static force capacity when the journal is at its maximum offset position.
• The dynamic force capacity as a function of frequency and force direction.
• The peak transient load capacity over a limited time period.
• Limitations of force capacity arising from operating temperatures and available power amplifier capacities of voltage and/or current.
• The operational conditions of a machine that give rise to loss of stability margin, or journal/rotor contact with touch-down bearings, or variation of the journal/rotor levitation position.
Rotating machine designers commonly select passive bearing components from supplier catalogues to react against the loads expected during operation. When the rotating machine is delivered to an enduser there is usually a specified service life before machine maintenance is required. AMBs are more complex, though justify installation in certain applications requiring high rotating speeds, high efficiency, high power density, low maintenance, vacuum installation, oil-free operation, and low disturbance force transmission to the external environment. Applications include energy storage flywheels, compressors, turbines, pumps, motor-generators, machining spindles and biomedical VADs.
There is often a misconception that machines designed with passive bearing components may simply be modified with AMBs of appropriate load capacity. This is not the case and to ensure that AMB levitated machines shall be operated reliably and without unexpected malfunctions, the force requirements covered by the scope of this document are necessary. This provides the justification for generating ISO 14839-6 as a published standard.
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