Electronics & Electrical Articles - Page 40 of 56

When a current carrying conductor is placed at right angles to a magnetic field, it is found that a force acts on the conductor in a direction perpendicular to the direction of both the magnetic field and the current.ExplanationConsider a straight conductor carrying a current of I amperes. If the magnetic flux density is B, the effective length of the conductor is l and θ is the angle which the conductor makes with the direction of the magnetic field.It has been found by experiments that the magnitude of the force (F) acting on the conductor is directly proportional to −Magnetic ... Read More

An English electrical engineer and physicist Sir John Ambrose Fleming established two rules, known as Fleming's Left-Hand Rule and Fleming's Right-Hand Rule which are widely used in electrical machines.When a current carrying conductor is placed in a magnetic field, a mechanical force acts on the conductor. The direction this force is determined by Fleming's Left-Hand Rule. The left-hand rule is mainly applicable in electric motors.Also, when a conductor is moved in a magnetic field, an emf is induced in the conductor due to which an electric current flows in the conductor. The direction this induced current is determined by Fleming's ... Read More

Faraday’s Laws of Electromagnetic InductionMichael Faraday (an English scientist) performed a series of experiments to demonstrate the phenomenon of electromagnetic induction and he summed up his conclusions into two laws, known as Faraday's laws of electromagnetic induction.First Law of Electromagnetic InductionThe first law states that "when a magnetic flux linking a conductor or coil changes, an EMF is induced in the conductor or coil". Therefore, the first law tells about the condition under which the emf is induced in a conductor or coil.Second Law of Electromagnetic InductionThe second law states that "The magnitude of the induced emf in the conductor ... Read More

A doubly-excited system is the type of magnetic system in which two independent coils are used to produce magnetic field. Examples of doubly-excited systems are synchronous machine, separately excited DC machines, loudspeakers, tachometers etc.Consider a doubly-excited system as shown in the figure, it consists of a stator wound with a coil having a resistance of R1 and a rotor wound with a coil of resistance R2. Both the coils are excited by independent voltage sources.Following assumptions are made to analyse a doubly excited system −For any rotor position the relationship between flux-linkage (ψ) and current is linear.Hysteresis and eddy current ... Read More

Electric Power: DefinitionThe rate at which work is done in an electric circuit is known as electric power. In other words, the energy used per unit time in an electric circuit is called as electric power.Electric Power: FormulaAs, the electric power is the rate of doing work in an electric circuit, thus, $$\mathrm{Electric\:power, P=\frac{Work\:done\:in\:elecric\:circuit(W)}{Time(t)}}$$Consider an electric circuit shown below. An electric current flows in the circuit, when a voltage is applied to it. So, work is being done in moving the charge (electrons) in the circuit. This work done in moving the charge per unit time is known as electric ... Read More

A voltmeter is a measuring instrument which is used to measure voltage across the two terminals in an electrical circuit.A voltmeter has a very high resistance and it is design in such a way that when connected in parallel to circuit for measuring voltage it does not take appreciable current, so that power consumed is small.Voltmeter – Working PrincipleWhen a voltmeter is connected in parallel to a circuit element (load), across which the voltage is being measured. Since the voltmeter has a very high resistance, therefore the combination will have almost same impedance that of the load. As we known, ... Read More

Star (Wye) Connected SystemLet VR, VY and VB represents the three phase voltages while VRY, VYB and VBR represents the line voltages. Assume that the system is balanced, so$$\mathrm{\lvert\:V_{R}\rvert=\lvert\:V_{Y}\rvert=\lvert\:V_{B}\rvert=\lvert\:V_{ph}\rvert}$$From the circuit and phasor diagram of star connected load, it can be observed that the line voltage VRY is a vector difference of VR and VY or the vector sum of VR and –VY, i.e.$$\mathrm{V_{RY}=V_{R}+(-V_{Y})=V_{R}-V_{Y}}$$Applying parallelogram law to obtain the magnitude of this, we get, $$\mathrm{V_{RY}=\sqrt{V_R^2+V_Y^2+2V_RV_{Y}\cos\:60^{\circ}}}$$$$\mathrm{\Rightarrow\:V_{RY}=\sqrt{V_{ph}^2+V_{ph}^2+2V_{ph}^2\cos\:60^{\circ}}=\sqrt{3}V_{ph}}$$Similarly, $$\mathrm{V_{YB}=V_{Y}-V_{B}=\sqrt{3}V_{ph}}$$$$\mathrm{V_{BR}=V_{B}-V_{R}=\sqrt{3}V_{ph}}$$$$\mathrm{\because\:V_{RY}=V_{YB}=V_{BR}=V_{L}=Line\:Voltage}$$$$\mathrm{\therefore\:V_{L}=\sqrt{3}V_{ph}}$$Therefore, in a star connected system, Line Voltage = √3 × Phase VoltageAgain, refer the circuit of star connected system, it can be seen that ... Read More

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 More

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