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Electronics & Electrical Articles
Page 35 of 47
Types of Solid State Relay (SSRs)
Depending on the applications and switching methods, the solid state relays (SSRs) are of following types −Instant ON Solid State RelayZero Switching Solid State RelayPeak Switching Solid State RelayAnalog Switching Solid State RelayInstant ON SSRsThe instant ON SSR instantly switches on the load circuit when a sufficient input voltage is applied. It turns off when the input voltage is removed and the load current crosses the next zero. The instant ON SSRs are designed to control the inductive loads. The practical applications are in switching of contactors, magnetic valves, starters etc.Zero Switching SSRsA zero switching SSR switches on when an ...
Read MoreMagnetic Reluctance: Definition, Formula & Examples
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 MoreThree-Phase Electric Power
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 MoreSolid-State Relay Circuit Components
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 MoreHow to measure low resistances? (Resistance Measurement Methods)
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 MoreHow to measure high resistances? (Resistance Measurement Methods)
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 MoreResistance and Impedance in an AC Circuit
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 MorePurpose of Grounding the Utility Power Distribution
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 MorePower Triangle and Power Factor in AC Circuits
Power in AC circuitActive Power (P)The product of voltage (RMS) and current (RMS) with the cosine of the angle between them, in an AC circuit is termed as active power. It is measured in watts (W). For a pure inductive and pure capacitive circuit, the active power being zero.Active Power, P = VI cos φReactive Power (Q)The product of voltage (RMS) and current (RMS) with sine of the angle between them, in an AC circuit is known as reactive power. It is measured in VAR (Volt-Ampere Reactive).Reactive Power, Q = VI sin φApparent Power (S)The product of voltage (RMS) and ...
Read MorePower Transformer Characteristics
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 ...
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