Found 1006 Articles for Electronics & Electrical

The torque-speed characteristics of a 3-phase induction motor is defined as the curve plotted between torque developed and rotational speed of the motor. It gives the information about variation in the motor torque with the change in its speed.As the torque of three-phase induction depends upon its speed but the relationship between them cannot be expressed by a simple equation. Therefore, we use the torque-speed curve to express the relationship between them.Refer the torque-speed curve, it reveals the following facts −If the full-load torque is τ, then the starting torque or locked rotor torque is 1.5 times of τ and ... Read More

A three phase induction motor has a stator and a rotor. The stator carries a 3-phase winding called as stator winding while the rotor carries a short circuited winding called as rotor winding. The stator winding is fed from 3-phase supply and the rotor winding derives its voltage and power from the stator winding through electromagnetic induction. Therefore, the working principle of a 3-phase induction motor is fundamentally based on electromagnetic induction.Consider a portion of a three phase induction motor (see the figure). Therefore, the working of a three phase induction motor can be explained as follows −When the stator ... Read More

There are two types of three phase induction motors viz. squirrel cage motor and slip ring motor. Both have different methods of starting, let see each of these one by one.Squirrel Cage Induction Motor Starting MethodsThe following four methods are available for starting squirrel cage motors −Direct On-Line (D.O.L.) StartingAs the name suggests, the induction motor is started by connecting it directly to three-phase supply. In this method, the motor draws a high starting current (about 4 to 7 times of the rated current) and at low power factor. Therefore, DOL starting is suitable for relatively small motors (up to ... Read More

Electric PowerElectric power is defined as the rate of doing work in an electric circuit. In other words, the electrical power is the energy expanded per unit time in an electric circuit, i.e.Electric Power, $$\mathrm{p=\frac{Work\:Done}{Time}\:\:\:\:...(1)}$$The electrical power is measured in watts (W).Three Phase Electric PowerAs the single phase instantaneous power (for lagging load) is given by, $$\mathrm{p=\frac{V_{m}I_{m}}{2}\cos\varphi-\frac{V_{m}I_{m}}{2}\cos(2\omega\:t-\varphi)}$$If the RMS values of voltage and currents are V and I respectively, then$$\mathrm{p=VI\cos\varphi-VI\cos(2\omega\:t-\varphi)\:\:\:\:...(2)}$$Now, consider a balanced three phase system, then the above expression can be applied for each phase of the three phases of the three-phase system. Therefore, the instantaneous power in three phases ... Read More

A solid state relay circuit has following main components −Input Circuit ComponentsControl Circuit ComponentsOutput Circuit ComponentsInput Circuit ComponentsThe input circuit of solid state relay (SSR) is part to which the control circuit is connected and the control voltage is applied to this circuit. The input circuit of SSR performs the same function as the coil of an electromechanical relay. The input control voltage of a solid state relay is controlled by means of mechanical switches, transistors, logic gates, low-voltage signals etc. The input circuit is activated by applying an input control voltage to the SSR that being higher than the ... Read More

A relay is nothing but an electrically operated switch. To switch power on and off, a relay requires a low power electrical signal. Therefore, a relay is an automatically operated switch that uses low power electrical signal to control a high power electrical signal.Electromechanical Relay (EMR)As the name implies, an electromechanical relay is one that uses physically moving contact to control the flow of power in the output circuit. The movement of moving contact is generated using electromagnetic forces created by a low power input signal to the relay, which allowing the completion of the circuit that contains high power ... Read More

Basic Theory of Solid State StartersA solid state starter (or soft starter) controls the starting torque and current of an AC motor electronically by controlling the applied voltage. A solid state motor starter is made of solid state devices like SCRs or triac, which allows the current flow when they are conducting and stops the flow of current when they are not conducting.The solid state motor starters have the ability to control the starting characteristics to match the application requirements such as acceleration and deceleration time, starting and overload current and the motor toque etc.The solid state motor starters control ... Read More

Construction of Single Phase TransformerA single phase transformer consists of two windings viz. primary winding and secondary winding put on a magnetic core. The magnetic core is made from thin sheets (called laminations) of high graded silicon steel and provides a definite path to the magnetic flux. These laminations reduce the eddy-current losses while the silicon steel reduces the hysteresis losses.The laminations are insulated from each other by enamel insulation coating. The thin laminations are stacked together to form the core of the transformer. The air-gap between the laminations should be minimum so that the excitation current being minimum.For a single ... Read More

There are various types of single phase motor. Depending upon their construction and operation, they are having different characteristics. Let us discuss characteristics of each single phase motor one-by-one.Characteristics of Split-Phase Induction MotorThe single phase split-phase induction motor has following characteristics −The starting torque of split phase induction motor is 1.5 to 2 times of the rated fullload torque and the starting current is 6 to 8 times of the full load current.The cost of split phase induction motors is very low, due to which these are very popular in the market.The starting winding of split phase induction motor is ... Read More

The resistances that range from about 1Ω to about 100 kΩ are classified as medium resistances. The resistances of most of electrical apparatus are the examples of medium resistances.Measurement of Medium ResistancesTo measure the medium resistances following methods are used −Ammeter-Voltmeter MethodSubstitution MethodWheatstone BridgeCarey-Foster Slide-Wire Bridge Method.Ammeter-Voltmeter MethodIn this method, current through the unknown resistor (Rx) and the potential drop across it are simultaneously measured. The readings are obtained by ammeter and voltmeters respectively. There are two ways in ammeter and voltmeters may be connected for measurement as, Case 1 – When voltmeter is directly connected across the resistor, then the ammeter ... Read More