Therefore there is no mechanical wear, no excessive heat generation, no rotating speed limit and it is more efficient. The obvious advantage of magnetic bearings is that they allow the rotating shaft to rotate almost completely free of friction. This ensures that intervening corrective action such as the increase or decrease of electric power on a particular magnetic element (electromagnet) can be taken automatically through the main controller - which is typically a microprocessor nowadays.Īpplications and Advantages of Magnetic Bearings So the distance from the rotating shaft to the inner edge of the bearing is detected. To aid the overall operation, active magnetic bearings also feature gap and rotation sensors. This is because electromagnets are easier to control and adjust, so the operation is more reliable and predictive. The control laws that are programmed in the control system determine the characteristics of the active magnetic bearing.Īctive magnetic bearings are the most popular type of magnetic bearings. The error signals through the amplifiers control the currents in the electromagnets to return the rotor to the nominal (center) position. Thus, in addition to electromagnets, the control system also includes position sensors (as well as rotational speed sensors), which produce the error signals. The currents that are applied to the windings of these electromagnets vary depending on the position of the rotor in space, in accordance with a given control law. These electromagnets are located on the stator of the electromagnetic bearing.Electromagnetic fields, in turn, are generated by controlled electromagnets.The rotor is held in a certain position in the radial or axial directions by means of electromagnetic fields.The principle of the active magnetic bearing ensures that:. The stable position of the rotor is a consequence of the action of magnetic attraction forces. However, permanent magnet bearings are not preferred over active magnet bearings and are generally considered to be less effective.Īn active magnetic bearing is a controlled electromechanical device. These help reduce the vibrations and disturbances that can cause instability and imbalancing of the rotating shaft. Passive magnetic bearings can perform very well when combined with temperature range limiters and extra dampening elements. Each set is devoted to the role of stabilising different directions in the degrees of freedom of the rotating shaft such as:. Ferromagnetic objects can steadily levitate only in an environment with a higher magnetic permeability (for example, in a ferromagnetic fluid).įor this reason, passive magnetic bearings are usually utilised in sets. These laws and statements lead to the fact that in a constant magnetic field (under normal conditions) only physical objects made of diamagnetic or superconductors can steadily levitate. Brownback’s statements (stable levitation of a physical object in the constant magnetic field is possible if the magnetic permeability of its material is less than a magnetic permeability environment).Earnshaw’s theorem (the equilibrium position of the active element in a static force field is unstable if force and distance are related by the inverse square law).This restriction is a consequence of the:. The main disadvantage of permanent magnet bearings is that it is impossible to create a magnetic levitation of a rotor using only permanent magnets. However, there is no such thing as a perfect magnetic bearing and it is impossible to reach an absolute electrostatic field stability. Due to the inability of magnetic force regulation, these bearings must be designed and manufactured with great precision. The first type of magnetic bearings are the passive ones that use permanent magnets. Active – with electromagnets and a control device.The most common are two different types of magnetic bearings, namely: Magnetic bearings can be grouped into eight types in accordance with the principle of operation:. Two conductors with electric current can both mutually attract and also repel each other. The conductive non-ferromagnetic material and the alternating magnetic field source are always repelled. The force of interaction between a ferromagnet and a source of a magnetic field is always a force of attraction.
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