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Electron Articles
Page 12 of 19
Force on a Current Carrying Conductor in a Magnetic Field
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 MoreFleming's Left-Hand and Right-Hand Rules Explained
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 MoreVoltage and Currents in Star and Delta Connected Systems
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 MoreWhat is Electric Power?
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 MoreTypes 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 ...
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