Found 1006 Articles for Electronics & Electrical

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

Torque-Slip Characteristics of Double-Cage Induction MotorIn a double-cage induction motor, it is assumed that the two cages develop two separate torques. Thus, the total torque developed in the double-cage induction motor is equal to the sum of the two cage torques. The torque-slip characteristics of the two cages and the total torque of the motor is shown in the figure.By changing the individual cage resistances and leakage reactances, the resultant torque-speed characteristics can be modified according to the requirement. The resistances can be changed by changing the cross-sectional area of the rotor bars while the leakage reactance can be changed ... Read More

The graph plotted between the torque and slip for a particular value of rotor resistance and reactance is known as torque-slip characteristics of the induction motor.The torque of a 3-phase induction motor under running conditions is given by, $$\mathrm{\tau_𝑟 =\frac{𝐾𝑠𝐸_2^2𝑅_2}{𝑅_2^2 + (𝑠𝑋_2)^2}… (1)}$$From the eqn. (1), it can be seen that if R2 and X2 are kept constant, the torque depends upon the slip 's'. The torque-slip characteristics curve can be divided into three regions, viz.Low-slip regionMedium-slip regionHigh-slip regionLow-Slip RegionAt synchronous speed, the slip s = 0, thus, the torque is 0. When the speed is very near to the ... Read More

A 3-phase induction motor is an electromechanical energy conversion device which converts 3-phase input electrical power into output mechanical power.A 3-phase induction motor consists of a stator and a rotor. The stator carries a 3-phase stator winding while the rotor carries a short-circuited winding called rotor winding. The stator winding is supplied from a 3-phase supply. The rotor winding drives its voltage and power from the stator winding through electromagnetic induction and hence the name.Working Principle of a 3-Phase Induction MotorThe working principle of a 3-phase induction motor can be explained by considering a portion of it as follows−When the ... Read More

The torque (τ) developed by the rotor of a 3-phase induction motor is directly proportional to −Rotor current (I2)Rotor EMF (E2)Rotor circuit power factor (cos ϕ2)Therefore, $$\mathrm{\tau \propto 𝐸_2𝐼_2 cos \varphi_2}$$$$\mathrm{⇒ \tau = 𝐾𝐸_2𝐼_2 cos \varphi_2 … (1)}$$Where, K is the constant of proportionality.Starting Torque of 3-Phase Induction MotorLet, Rotor resistance/Phase = 𝑅2Rotor reactance/Phase at standstill = 𝑋2Rotor EMF/Phase at standstill = E2∴ Rotor impedance/Phase at standstill, $$\mathrm{𝑍_2 = \sqrt{𝑅_2^2 + 𝑋2^2}}$$Rotor current/Phase at standstill, $$\mathrm{𝐼_2 =\frac{𝐸_2}{𝑍_2}=\frac{𝐸_2}{\sqrt{𝑅_2^2 + 𝑋2^2}}}$$And, Rotor power factor at standstill, $$\mathrm{cos\varphi_2 =\frac{𝑅_2}{𝑍_2}=\frac{𝑅_2}{\sqrt{𝑅_2^2 + 𝑋2^2}}}$$∴ Starting torque, $$\mathrm{\tau_𝑠 = 𝐾𝐸_2𝐼_2 cos\varphi_2 = 𝐾𝐸_2 × (\frac{𝐸_2}{\sqrt{𝑅_2^2 + 𝑋2^2}}) ... Read More

Circuit Diagram and Working Principle of Star-Delta StarterThe figure shows the connection diagram of a 3-phase induction motor with a star-delta starter. The star-delta starter is a very common type of starter and is extensively used for starting the squirrel cage induction motors. It is used for starting a squirrel cage induction motor which is designed to run normally on delta connected stator winding.When the switch S is in the START position, the stator windings are connected in star. When the motor attains a speed about 80 % of rated speed, then the changeover switch S is thrown to the ... Read More