Found 1006 Articles for Electronics & Electrical

In an alternator or synchronous generator, the actual generated voltage consists of the summation of two component voltages. One of these component voltages is the excitation voltage  (𝐸exc); it is the voltage that would be generated because of the field excitation only. The excitation voltage is the voltage that would be generated when there is no armature reaction.The other component of the generated voltage is the voltage that must be added to the excitation voltage to take care of the effect of the armature reaction on the generated voltage. This component voltage is known as the armature reaction voltage and ... Read More

In a synchronous machine, the short-circuit ratio (SCR) is an important factor. The SCR affects the physical size, operating characteristics and cost of the synchronous machine.Low Value of SCRWith a low value of SCR, the synchronous machine is very sensitive to the load variations, i.e., the alternator has a large variation in terminal voltage with a change in load. In order to keep the terminal voltage constant, the field current of the machine is to be varied over a wide range. Also, for a small value of SCR, the synchronising power of the machine is small. The synchronising power keeps ... Read More

What is Hunting in Alternator?When an alternator or synchronous generator is running under normal condition, the armature field and the rotor magnetic field will be rotating in the same direction at synchronous speed.When either a sudden change in the load of the alternator or a change in the torque of turbine occurs, then the speed of the rotor decreases with respect to that of armature (or stator) field by some angle called as load angle. Once this happens, the alternator rotor starts to hunt, i.e., search for a new equilibrium position. Although the rotor has high inertia, it cannot achieve ... Read More

Why doesn't a Single-Phase Induction Motor Self-Start?A single-phase induction motor consists of a squirrel cage rotor and a stator carrying a single-phase winding. But, a single-phase induction motor is not self-starting like a 3-phase induction motor since it requires some starting means.When a single-phase supply is fed to the stator winding of the single-phase induction motor, it produces a magnetic field that pulsates in strength in a sinusoidal manner. The polarity of the magnetic field reverses after each half cycle but the magnetic field does not rotate in the space.As a result, the alternating flux cannot produce rotation in a ... Read More

The working principle of a single-stack variable reluctance (VR) stepper motor is based on the property of the flux lines to occupy the low reluctance path. Therefore, in a variable reluctance stepper motor, the stator and rotor get aligned such that the magnetic reluctance is minimum.Construction of Single-Stack Variable Reluctance Stepper MotorA single-stack variable reluctance stepper motor consists of a salient pole stator. The stator has concentrated windings placed over the stator poles. The number of stator phases depends upon the connection of stator coils. The rotor of the single-stack variable reluctance stepper motor is a slotted structure made up ... Read More

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