Linear motors move in a straight line with linear force and speed. Linear motion is needed in many types of systems, but linear motors aren’t commonly used by makers or professional engineers. That’s because these motors aren’t well-understood, there aren’t many manufacturers, and they’re expensive. For these reasons, designers frequently obtain linear motion by connecting […]
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Development of Induction Motor Equivalent Circuit Physically, the construction of the wound-rotor induction motor has striking similarities with that of the 3-phase transformer, with the stator and rotor windings corresponding to the primary and secondary windings of a transformer. In the light of these similarities, it is not surprising that the induction motor equivalent circuit
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Influence of Rotor Current on Flux Up to now, all our discussion in previous articles has been based on the assumption that the rotating magnetic field remains constant, regardless of what happens on the rotor. We have seen how torque is developed, and that mechanical output power is produced. We have focused attention on the
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Torque Production in Induction Motor In this article we begin with a brief description of rotor types, and introduce the notion of ‘slip’, before moving onto explore how the torque is produced, and investigate the variation of torque with speed. We will find that the behaviour of the rotor varies widely according to the slip,
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Rotating Magnetic Field of Induction Motor Like the d.c. motor, the induction motor develops torque by the interaction of axial currents on the rotor and a radial magnetic field produced by the stator. But, whereas, in the d.c. motor the ‘work’ current has to be fed into the rotor by means of brushes and a
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Inverter Fed Induction Motor Drives Induction motor can only run efficiently at low slips, i.e. close to the synchronous speed of the rotating field. The best method of speed control must therefore provide for continuous smooth variation of the synchronous speed, which in turn calls for variation of the supply frequency. This is achieved using
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Speed Control of Induction Motor To operate efficiently an induction motor must run with a small slip. It follows that any efficient method of speed control must be based on varying the synchronous speed of the field, rather than the slip. The two factors that determine the speed of the field, are the supply frequency
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Generating and Braking of Induction Motor Having explored the torque–speed curve for the normal motoring region, where the speed lies between zero and just below synchronous, we must ask what happens if the speed is above the synchronous speed, or is negative. A typical torque–speed curve for a cage motor covering the full range of
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Influence of Rotor Parameters on Torque Speed Curves We know that the rotor resistance and reactance influence the shape of the torque–speed curve. The designer can vary both of these parameters, and we will explore the pros and cons of the various alternatives. To limit the mathematics the discussion will be mainly qualitative, but it
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Stable Operating Regions of Induction Motor In addition to having sufficient torque to start the load it is obviously necessary for the motor to bring the load up to full speed. To predict how the speed will rise after switching on we need the torque–speed curves of the motor and the load, and the total
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