## Solid State Relay vs. Electromechanical Relay

Updated on 29-Aug-2022 13:01:49
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

## Solid State Motor Starters

Updated on 05-Jul-2021 09:28:30
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

## Single Phase Transformer – Construction and Working Principle

Updated on 05-Jul-2021 09:21:29
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

## Single Phase Motors Characteristics

Updated on 05-Jul-2021 09:15:00
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

## How to measure medium resistances? (Resistance Measurement Methods)

Updated on 05-Jul-2021 09:13:23
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

## How to measure low resistances? (Resistance Measurement Methods)

Updated on 05-Jul-2021 09:04:16
The resistances of the values of less than or equal to 1 Ω are classified as low resistances. For example, the resistances of armatures and series windings of large machines, ammeter shunts, contacts, etc.Measurement of Low ResistancesFor the measurement of low resistances, the following methods are used −Ammeter-Voltmeter MethodPotentiometer MethodKelvin Double Bridge MethodAmmeter – 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 ... Read More

## How to measure high resistances? (Resistance Measurement Methods)

Updated on 05-Jul-2021 08:58:50
Resistances of the order of 100 kΩ and upwards are classified as high resistances. For example, insulation resistances.Measurement of High ResistancesThe following methods are employed for the measurement of high resistances −Direct Deflection MethodLoss of Charge MethodMegohm BridgeMeggerDirect Deflection MethodIn this method, a very sensitive and high resistance (more than 1 kΩ) PMMC galvanometer is connected in series with the resistance to be measured and to a battery. The deflection of galvanometer gives the measure of unknown resistance. This method is mainly used for the measurement of insulation resistance.Let us take an example of direction deflection method for measuring insulation ... Read More

## Resistance and Impedance in an AC Circuit

Updated on 05-Jul-2021 08:52:36
Resistance in an AC CircuitConsider the circuit diagram, containing an AC sinusoidal voltage source and an unknown passive element (K). The element K will be a resistance, only if the voltage across it and the current flowing through it, are in phase with each other.ExplanationLet the equation for alternating voltage is$$\mathrm{v=V_{m}\sin\omega\:t\:\:\:...(1)}$$As a result of this voltage, an alternating current i will flow through the element. Now, the applied voltage has to overcome the drop in the element only, i.e.$$\mathrm{v=i\times\:k}$$$$\mathrm{\Rightarrow\:i=\frac{v}{k}=\frac{V_{m}\sin\omega\:t}{k}\:\:\:...(2)}$$The value of current will be maximum, when sin(ωt) = 1.$$\mathrm{\therefore\:I_{m}=\frac{V_{m}}{K}}$$Thus, the equation (2) becomes, $$\mathrm{i=I_{m}\sin\omega\:t\:\:\:...(3)}$$It is clear from the eqns. (1) ... Read More

## Purpose of Grounding the Utility Power Distribution

Updated on 05-Jul-2021 08:48:20
One of the remarkable discoveries in the field of electrical engineering is the grounding of electric current. In an electric circuit, there be an active wire, which supplies current and a neutral wire, which carries that current back. An additional grounding wire can be attached to outlets and other electrical devices and also securely connected to the ground. This ground wire provides an additional path for the current to return safely to the ground without danger to anyone, when short circuit occurs.The purpose of grounding the utility power distribution becomes clear from following points −Protection against electrical overloadOne of the ... Read More

## Power Transformer Characteristics

Updated on 05-Jul-2021 08:41:25
The power transformers are design to operate with an almost constant load which is equal to their rating. The maximum efficiency being designed to be at full load. Therefore, the fullload winding copper losses must be equal to the core losses.Actually, all the transformers are the same that is same design formulae apply for small signal transformers to the power transformers. In case of power transformers, the designer needs to consider both voltage and current, to remember that heat will need to be dissipated and the series resistance is a cause of low efficiency.Therefore, a power transformer has the following ... Read More