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Concept
Motor drive
Résumé
Motor drive means a system that includes a motor. An adjustable speed motor drive means a system that includes a motor that has multiple operating speeds. A variable speed motor drive is a system that includes a motor and is continuously variable in speed. If the motor is generating electrical energy rather than using it – this could be called a generator drive but is often still referred to as a motor drive.
A variable frequency drive (VFD) or variable speed drive (VSD) describes the electronic portion of the system that controls the speed of the motor. More generally, the term drive, describes equipment used to control the speed of machinery. Many industrial processes such as assembly lines must operate at different speeds for different products. Where process conditions demand adjustment of flow from a pump or fan, varying the speed of the drive may save energy compared with other techniques for flow control.
Where speeds may be selected from several different pre-set ranges, usually the drive is said to be adjustable speed. If the output speed can be changed without steps over a range, the drive is usually referred to as variable speed.
Adjustable and variable speed drives may be purely mechanical (termed variators), electromechanical, hydraulic, or electronic.
Sometimes motor drive refers to a drive used to control a motor and therefore gets interchanged with VFD or VSD.
Induction motor and synchronous motor
AC electric motors can be run in fixed-speed operation determined by the number of stator pole pairs in the motor and the frequency of the alternating current supply. AC motors can be made for "pole changing" operation, reconnecting the stator winding to vary the number of poles so that two, sometimes three, speeds are obtained. For example a machine with 8 physical pairs of poles, could be connected to allow running with either 4 or 8 pole pairs, giving two speeds - at 60 Hz, these would be 1800 RPM and 900 RPM.
Source officielle
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