Stepping motors are attractive because they can be controlled directly by computers or microcontrollers. Their unique feature is that the output shaft rotates in a series of discrete angular intervals, or steps, one step being taken each time a command pulse is received. When a definite number of pulses has been supplied, the shaft will […]
Switched Reluctance Motor Drives The switched reluctance drive was developed in the 1980s to offer advantages in terms of efficiency, power per unit weight and volume, robustness and operational flexibility. The motor and its associated power-electronic drive must be designed as an integrated package, and optimised for a particular specification, e.g. for maximum overall efficiency
Operation of Synchronous Motor Drives As soon as variable-frequency inverters became a practicable proposition it was natural to use them to supply synchronous motors, thereby freeing the latter from the fixed-speed constraint imposed by mains-frequency operation and opening up the possibility of a simple open-loop controlled speed drive. The obvious advantage over the inverter-fed induction
Synchronous motors provide a precise, specific and constant speed for a wide range of loads, and are therefore used in preference to induction motors when constant speed operation is essential. Such machines are available over a very wide range from tiny single-phase versions in domestic timers to multi-megawatt machines in large industrial applications such as
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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Equivalent Circuit of Real Transformer We turn now to the real transformer, with the aim of developing its equivalent circuit. Real transformers behave much like ideal ones (except in very small sizes), and the approach is therefore to extend the model of the real transformer to allow for the imperfections of the real one. For
Ideal Transformer Because we are dealing with balanced 3-phase motors we can achieve considerable simplification by developing single-phase models, it being understood that any calculations using the equivalent circuit (e.g. torque or power) will yield ‘per phase’ values which will be multiplied by three to give the total torque or power. A quasi-circuit model of
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
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,
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