Found 1006 Articles for Electronics & Electrical

Crawling in Induction Motor (or Effect of Harmonics on the Performance of 3-Phase Induction Motor)The flux in the air-gap of an induction motor set up by the 3-phase stator windings carrying sinusoidal currents is of non-sinusoidal wave shape. According to the Fourier series analysis, any non-sinusoidal flux is equivalent to the combination of a number of sinusoidal fluxes of fundamental and higher order harmonics.Since the wave shapes of the air-gap flux have half-wave symmetry, hence all the even harmonics (i.e., 2 nd, 4th, 6th, … etc.) are absent in the Fourier series. Thus, a non-sinusoidal flux wave can be resolved ... Read More

A 3-phase induction motor has two main parts − Stator Rotor The rotor and stator are separated by a small air gap ranges from 0.5 mm to 4 mm depending on the power rating of the motor. Stator of Three Phase Induction Motor The stator is the stationary part of the motor. It consists of a steel frame which encloses a hollow cylindrical core. The core of the three phase induction motor is made up of thin laminations of silicon steel to reduce the eddy current and hysteresis losses. A number of equally spaced ... Read More

Complete Equivalent Circuit of Induction MotorIn order to obtain the complete per-phase equivalent circuit of an induction motor, it is required to refer the rotor part to the stator side frequency and voltage level.The transformation of the rotor circuit of the induction motor can be done by the means of effective turns ratio of the induction motor.The figure shows the complete equivalent circuit of the induction motor.Let suffixes "s" and "r" be used for stator and rotor quantities respectively.Then, $$\mathrm{𝑎_{𝑒𝑓𝑓}= Effective\:turns\: ratio \:of \:induction \:motor}$$$$\mathrm{𝑅′_{𝑟} = Resistance \:of \:the \:rotor\: winding\: per\: phase\: referred \:to \:stator}$$$$\mathrm{𝑋′_{𝑟0} = Standstill \:rotor \:reactance ... Read More

Circle Diagram of Induction MotorThe circle diagram is a graphical representation of the performances of an induction motor. It is very useful to study the performance of an induction motor under all operating conditions. The construction of the circle diagram of an induction motor is based on the equivalent circuit of the motor which is shown in Figure-1.By applying KCL in the equivalent circuit, we can write, $$\mathrm{𝐼_1 = 𝐼_0 + 𝐼′_2 … (1)}$$If the phase voltage V1 is taken along the vertical axis of OY as shown in Figure-2. Then, the no-load current (I0) lags behind the voltage V1 ... Read More

The figure shows the circuit diagram for the blocked rotor test of an induction motor. The blocked rotor test enables us to determine the efficiency and the circuit parameters of the equivalent circuit of a 3-phase induction motor.In the blocked rotor test, the shaft of the motor is locked so that it cannot rotate and the rotor winding is short circuited. In a slip-ring induction motor, the rotor winding is short-circuited through the slip-rings while in a squirrel cage induction motor, the rotor bars are permanently short-circuited with the help of end rings.In the blocked rotor test, a reduced voltage ... Read More

Circuit and Working Principle of Autotransformer StarterThe circuit diagram of an autotransformer starter for starting a 3-phase induction motor is shown in the figure. The autotransformer starter can be used for starting both star and delta connected 3-phase induction motors. In this method, the starting current of the motor is limited by using a 3-phase autotransformer to decrease the initial applied voltage to the stator. The autotransformer is provided with a number of tappings to obtain the variable voltage.In the autotransformer starting method, the starter is connected to a particular tapping of the autotransformer to obtain the most suitable starting ... Read More

Applications of 3-Phase Wound-Rotor Induction MotorThe slip-ring or wound-rotor 3-phase induction motors are used in the following applications −Slip ring induction motors are suitable for loads requiring high starting torque and for applications where the starting current is low.Slip ring induction motors are used for loads having high inertia, which results in very high rotor energy losses during acceleration.The slip ring induction motors are also used for loads which require a gradual build-up of load.They are used for loads that requires speed control.Typical applications of wound rotor or slip ring induction motors are crushers, plunger pumps, cranes & hoists, elevators, ... Read More

Rotor Current FrequencyThe frequency of current and voltage in the stator of a 3-phase induction motor must be same as the supply frequency and is given by, $$\mathrm{𝑓 =\frac{𝑁_{𝑆}𝑃}{120}… (1)}$$But, the frequency of the current and EMF in the rotor circuit of the 3-phase induction motor is variable and depends upon the difference between the synchronous speed (NS) and the rotor speed (Nr), i.e., on the slip. Thus, the rotor frequency is given by, $$\mathrm{𝑓_{𝑟} =\frac{(𝑁_{𝑆} − 𝑁_{𝑟} )𝑃}{120}… (2)}$$Now, from the equations (1) and (2), we get, $$\mathrm{\frac{𝑓_{𝑟}}{𝑓}=\frac{𝑁_{𝑆} − 𝑁_{𝑟}}{𝑁_{𝑆}}}$$$$\mathrm{∵ \:Slip, \:𝑠 =\frac{𝑁_{𝑆} − 𝑁_{𝑟}}{𝑁_{𝑆}}}$$$$\mathrm{∴ 𝑓_{𝑟} = 𝑠𝑓 … ... Read More

The torque is defined as the turning moment of a force about an axis. It is measure by the product of the force (F) and perpendicular distance (r) of the line of action of force from the axis of rotation, i.e., $$\mathrm{Torque, \: 𝜏 = 𝐹 × 𝑟 \:… (1)}$$The torque is measured in Newton-meters (Nm).Armature Torque of DC MotorIn a DC motor, a circumferential force (F) at a distance r which is the radius of the armature is acted on each conductor, tending to rotate the armature. The sum of the torques due to all the armature conductors is ... Read More

Swinburne’s test is an indirect method of testing DC machines, named after Sir James Swinburne. In this method, the losses are determined separately and the efficiency at desired load is predetermined. The Swinburne’s test is the simplest method of testing of shunt and compound DC machines which have constant field flux.The connection diagram is shown in the figure and the machine is run as a motor at rated voltage and speed.Let, $$\mathrm{𝑉 = Supply\:voltage}$$$$\mathrm{𝐼_{0} = No \:load \:line\: current}$$$$\mathrm{𝐼_{sh} = Shunt\: field \:current}$$$$\mathrm{\therefore \:No \:load\: armature \:current, \:I_{𝑎0} = I_{0} − I_{sh}}$$And$$\mathrm{No load input power = 𝑉𝐼_{0}}$$This no-load input power ... Read More