Schrage motor is an inverted 3-phase induction motor with primary winding on the rotor and the secondary winding on the stator. The schematic diagram of a 2-pole Schrage motor is shown in the figure.In a Schrage motor, a 3-phase supply is fed to the rotor circuit. The resultant air-gap flux runs at synchronous speed Ns with respect to the rotor and the rotor runs at a speed Nr in the opposite direction with the short-circuited rotor windings. As a result, the magnetic field runs at slip speed with respect to the stator inducing current in it which is having frequency ... Read More

A hybrid stepper motor combines the features of the variable reluctance and the permanent magnet stepper motors. In the hybrid stepper motor, an axial permanent magnet is provided in the middle of the rotor. The permanent magnet is magnetised axially to produce a pair of poles marked N and S as shown in Figure-1.The end caps are fitted at both ends of the axial magnet. The end caps have equal number of teeth which are magnetised by the respective polarities of the axial magnet. The cross-sections of the two end caps of the rotor are shown in Figures-2 and 3.Let, ... Read More

A permanent magnet (PM) stepper motor has salient pole stator. The stator has concentrated windings placed over the stator poles. It has cylindrical rotor and consists of permanent magnet poles made up of high retentivity steel. The construction of a 4/2-pole (i.e., 4-poles on the stator and 2-poles on the rotor) permanent magnet stepper motor is shown in the figure. Here, the concentrated windings on diametrically opposite poles are connected in series to form two-phase stator windings.In a permanent magnet stepper motor, the rotor poles align with the stator poles depending upon the excitation of the winding. The two coils ... Read More

A multi-stack variable reluctance stepper motor having m-stacks can be considered to be made of m identical single-stack variable reluctance stepper motors with their rotors mounted on a single shaft.In the multi-stack variable reluctance stepper motor, the stators and the rotors have the same number of poles or teeth and hence the same pole pitch. Therefore, for an m-stack stepper motor, the stator poles in all m-stacks are aligned, but the rotor poles are displaced by $(\frac{1}{m})$ of the pole pitch angle from one another.All the stator pole windings in a given stack being energised simultaneously and thus, the stator ... Read More

The motors that can be used with a single-phase AC source as well as a DC source of supply voltages are called as universal motors. A universal motor is a commutator type motor. If the polarity of the line terminals of a DC series motor is reversed, the motor will continue to run in the same direction. Therefore, it might be expected that a DC series motor would operate on AC supply also, therefore, it is also known as AC series motor. However, some changes must be made in a DC series motor so that it may operate satisfactorily on ... Read More

The torque-pulse rate characteristics of a stepper motor is the graph plotted between the electromagnetic torque and the stepping rate. It gives the variation of electromagnetic torque as a function of stepping rate in pulses per second (pps). A stepper motor is usually described by two characteristic curves as shown in the figure.Curve-1 represents the pull-in torque characteristic of the stepper motor and it gives the maximum value of stepping rate at which the motor can start, synchronise, stop or reverse for different values of load torque.Curve-2 represents the pull-out torque characteristic and it shows the maximum stepping rate at ... Read More

Basics of ServomotorsServomotors are the electromechanical energy conversion devices. In other words, a Servomotors is a rotary actuator or linear actuator which is used for precise control of linear or angular position, velocity and acceleration.A servomotor consists of an electric motor coupled with a sensor for position feedback. Servomotors are used in feedback control systems as the output actuators. Hence, servomotors are also called as control motors.Servomotors are not used for continuous energy conversion. The power ratings of servomotors vary from a fraction of a watt to a few hundred watts. The servomotors have low rotor inertia and hence they ... Read More

Basics of Stepper MotorThe stepper motor or stepping motor is an electromechanical energy conversion device which has a rotor movement in discrete steps. The number of pulses fed into the control circuit of the motor determines the angular rotation of the rotor.Each input pulse initiates the drive circuit of the motor which produces one step of angular movement. The drive circuit has inbuilt logic which causes appropriate windings to be energised and de-energised by the solid state switches in the required sequential manner. In a stepper motor, the angular movement of the rotor is in steps, so this motor may ... Read More

A stepper motor is an electromechanical energy conversion device which converts electrical input power into mechanical output power. Basically, it is a brushless motor that can divide a full rotation into an equal number of steps and the operation of the motor can be accurately controlled with no-feedback system when the motor is properly sized to the application.Practically, the stepper motors are manufactured in sizes ranging from milli-watts to hundreds of watts and the maximum torque values upto 15 N-m and the step angle from 1.8° to 90° mechanical.Types of Stepper MotorsDepending upon the rotor arrangement, the stepper motors are ... Read More

A split-phase induction motor is a type of single-phase induction motor in which the stator is provided with a starting or auxiliary winding (S) and a main or running winding (M). The starting winding is displaced by 90° from the main winding as shown in the figure.The starting winding operates only during the brief period when the motor starts up. The starting and the main windings are so designed that the starting winding (S) has a high resistance and relatively low reactance while the main winding (M) has relatively low resistance and high reactance so that the currents flowing in ... Read More