A hysteresis motor is a single-phase synchronous motor whose operating principle is based on the effect of magnetic hysteresis. According magnetic hysteresis, the magnetic flux density in a ferromagnetic material lags behind the magnetising force.Construction of Hysteresis MotorA hysteresis motor consists of a stator and a rotor (see the figure).The stator of the hysteresis motor has a main winding along with an auxiliary or starting winding. When the stator winding is fed from a single-phase supply, it produces a synchronously revolving magnetic field. The revolving magnetic field is accomplished by using a permanent split capacitor type construction of the motor. ... Read More

Operating Principle of Single-phase Induction MotorA single-phase induction motor consists of a squirrel cage rotor and a stator carrying a single-phase winding. When a single-phase AC supply is fed to the stator winding, a pulsating magnetic field (not the rotating) is produced. Under these conditions, the rotor does not rotate due to inertia. Hence, a single-phase induction motor is inherently not self-starting, but requires some auxiliary starting means.If the stator winding of a single-phase induction motor is excited and the rotor is rotated by an auxiliary means and the starting device is then removed, the motor continues to rotate in ... Read More

The differences between a single-phase and a three-phase induction motor are given below −A 1-phase induction motor requires single-phase AC supply, whereas a 3-phase induction motor need a source of 3-phase AC supply for its operation.1-phase induction motors produce low starting torque, whereas 3phase induction motors produce high starting torque.The efficiency of a 1-phase induction motor is less as compared to a 3phase induction motor.The power factor of a 1-phase induction motor is low, while the power factor of a 3-phase induction motor is high.1-phase induction motors are simple in construction, reliable and economical as compared to 3phase induction motors.1-phase ... Read More

A capacitor-start induction motor is a type of single-phase induction motor in which the starting torque is produced by using a starting capacitor and an auxiliary winding. The capacitor-start induction motor consists of a starting winding (S) and a main or running winding (M). Both the winding have the same number of turns. A starting capacitor (C) is connected in series with the starting winding as shown in the circuit diagram of the motor.The value of the starting capacitor is so chosen that the starting current Is leads the main winding current Im by an angle (α) of 90°. The ... Read More

The capacitor-start capacitor-run motor is a type of single-phase induction motor. The capacitor-start capacitor-run induction motor is also known as two value capacitor motor. The schematic diagram of a capacitor-start capacitorrun induction motor is shown below.The capacitor-start capacitor-run induction motor consists of a squirrel cage rotor and its stator has two windings, viz. the starting or auxiliary winding and the main or running winding. The two windings are displaced by an angle of 90° in the space.This motor uses two capacitors − the starting capacitor (CS) and the running capacitor (CR). The two capacitors are connected in parallel at the ... Read More

An AC servomotor uses AC electric input to produce mechanical output in the form of precise angular velocity. For low-power applications, the two-phase squirrel cage induction type AC servo motors are used. The three-phase squirrel cage induction motors have been modified for application in high-power servo systems.Two-Phase AC ServomotorThe schematic diagram of a two-phase AC servomotor is shown in the figure.The stator of a two phase AC servomotor consists of two distributed windings which are displaced from each other by 90° electrical.One winding is known as reference phase and is supplied from a constant voltage source.The other winding is known ... Read More

A single-phase repulsion motor consists of a stator carrying a single-phase exciting winding and a rotor which has a closed type armature winding with a commutator and brushes. The brushes on the commutator are short circuited. By adjusting the position of short-circuited brushes on the commutator, the starting torque can be developed in the motor.Working Principle of Repulsion MotorThe figure shows the operating principle of a two-pole repulsion motor with its two short-circuited brushes.Case 1When the brush axis is parallel to the stator field and the stator winding is energised from a 1-phase supply, then an EMF is induced in ... Read More

There are very few single-phase motors which run at true synchronous speed and they do not require any external DC excitation for the rotor. Therefore, these motors are also called as unexcited single-phase synchronous motors.The efficiency and the torque developing capability of the single-phase synchronous motors is low and the output power of the commercial single-phase synchronous motors is only a few Watts.The reluctance motor is a 1-phase synchronous motor which does not require DC excitation to the rotor.The operation of the reluctance motor is based on the following principle −"When a piece of ferromagnetic material is located in a ... Read More

Let suffixes "s" and "r" be used for stator and rotor quantities, respectively. Then, 𝑉𝑠 = Stator applied voltage per phase𝑁𝑠 = Number of stator winding turns in series per phase𝑁𝑟 = Number of rotor winding turns in series per phaseϕ = Resultant flux in air gap𝐸𝑠 = Stator induced EMF per phase𝐸𝑟0 = EMF induced in the rotor per phase when the rotor is at standstill𝐸𝑟𝑠 = EMF induced in the rotor per phase when the rotor is rotating at a slip 𝑠𝑅𝑠 = Resistance of stator winding per phase𝑅𝑟 = Resistance of rotor winding per phase𝐿𝑟0 = Rotor ... Read More

The rotor speed (Nr) of an induction motor is given by, $$\mathrm{𝑁_𝑟 = (1 − 𝑠)𝑁_𝑠}$$And the synchronous speed is given by, $$\mathrm{𝑁_𝑠 =\frac{120𝑓}{𝑃}… (1)}$$Therefore, the rotor speed of the motor is given by, $$\mathrm{𝑁_𝑟 = (1 − 𝑠) (\frac{120𝑓}{𝑃}) … (2)}$$It is clear from eqn. (2) that the speed of the induction motor can be changed by varying the frequency (f), number of poles (P) or slip (s).Speed Control of Induction Motor by Variable Frequency ControlFrom the eqns. (1) and (2), it can be seen that the synchronous speed and hence the speed of the motor can be controlled ... Read More