Definition and types of alternator

Alternator is an electrical dynamic device which converts mechanical energy to electrical energy form. According to faraday’s 1st law either magnet or armature must be in motion condition to induced emf. Alternator is also known as synchronous generator. We can categorize Alternator in many ways, but according to the design of field system it can be divided into… Read More »

Construction of DC machines

The D.C. generators and D.C. motors have the same general construction. Any d.c. generators can be run as d.c. motor and vice versa. A d.c. machine consists of two main parts- Stationary parts-It is designed mainly for producing a magnetic flux. Rotating part- It is called the armature, where mechanical energy is converted into electrical (electrical generator) or… Read More »

Principle of operation of DC Generator

Introduction- Although a far greater percentage of the electrical machine in service are AC machines, the DC machines are of considerable industrial importance. The principle advantage of DC machine, Particularly the DC motor, is that it provides a fine control of speed. However, DC generators are not as common as they used to be, because direct current, when required,… Read More »

Megger method for measurement of high resistance

Construction- A megger is a portable device which is used for the measurement of high resistance. The component of megger are Permanent magnet C shaft Hand driven generator Resistances RC and RD Two Coils- Control coil (Cs) Deflection Coil (Cd) Working Principle- As current provided by the hand driven generator flow through the coil C because of which… Read More »

Direct deflection method for measurement of high resistance

From fig 1 we are going to measure the resistor value of a cable with outer metallic sheath available. The galvanometer measures the current between the outer sheath and the conductor current. The galvanometer is very much sensitive to the current because the current value is in the range of nanoampere. If the applied voltage is of 1KV… Read More »

Voltmeter-Ammeter method for measurement of medium resistance

In the figure let us assume the voltmeter to be ideal (internal resistance Rin=infinite). So current Iv=0A I= IA+IV I=IA       [IV=0A] V=VA+VK V=I×RA+I×Runknown Ammeter is  not ideal here. V=I(RA+ Runknown) V/I= RA+ Runknown            [V/I= Measured value of resistance] RM=RA+ Runknown So the measured value of resistance is greater than the unknown value of resistance exceed by the value… Read More »

Method of substitution for measurement of medium resistance

E= External battery R= resistance to be measured S= Variable resistance R= Turning resistance Sw= Switch A= Amperemeter The position of the switch is at a point 2 with the battery E makes a close loop with resistance r, ammeter and the unknown resistance R. There will be a deflection of ampere meter. The deflection an ammeter can… Read More »

Wheatstone bridge method for measurement of medium resistance

Wheatstone bridge- Balanced Bridge condition R1/R2=R3/R4 I1=I3 and I2=I4 Vbc=Vde and Vab=Vad Vbc=I3R3 Vdc=I4R4 As        Vbc=Vdc I3R3=I4R4 I3/I4=R4/R3 Vab=I1R1 and Vad= I2R2 As        Vab=Vad I1R1=I2R2 I1/R2=I2/R1 As        I3=I1 and I2=I4 I3/I4=I1/I2 R4/R3=R2/R1 R1/R2=R3/R4 R3=R4×R1/R2      (Proved)  Advantages- It can measure the medium range resistance (1 Ω <R<1 kΩ). The design is comparatively simpler compared to another bridge circuit. Calculation and… Read More »