Electron Articles - Page 13 of 20

The magnetic reluctance (S) is defined as the opposition offered by the magnetic circuit to the magnetic flux (ΦMagnetic Reluctance FormulaCase 1 – When physical dimensions of the magnetic circuit are knownThe reluctance of a magnetic circuit depends upon its length (l), cross-sectional area (a) and permeability (μ) of the material. Thus, for a magnetic circuit (as shown in the figure), The reluctance is directly proportional to the mean length of the magnetic circuit, i.e.$$\mathrm{Magnetic\:reluctance, S\varpropto\:l\:\:\:\:....(1)}$$The reluctance is inversely proportional to the cross-sectional area of the mag. circuit.$$\mathrm{Magnetic\:reluctance, S\varpropto\:\frac{1}{a}\:\:\:\:....(2)}$$The reluctance also depends upon the nature of material that makes up ... 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

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

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

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 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

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

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