Measurement of Resistance (Resistivity) by Simple DC Galvanometer Galvanometer is first calibrated by use of standard resistance of the values 10 MΩ with tolerance ± 0.5 to ± 1 %. Calculations The resistance of the specimen (RP) is given by RP = V / D x G Where D = deflection in cm with specimen G = Galvanometer sensitivity A … Read more

Measurement of D.C. Resistivity D.C resistivity can be measured by various methods such as using Galvanometer using D.C. Amplifier and using wheatstone bridge. Prior to study the above methods, let us take the idea of shape of specimen of insulation, and electrode system.Specimen and Electrode For facilitating calculation of D.C. resistivity, the shape of specimen … Read more

Aim of Testing the Insulation Properties (Non destructive Testing) Q. What non destructive testing of insulating materials ? State briefly the characteristics of these methods. Prior to use the insulating materials as the part of the equipment, its quantity is to tested by taking a sample of it so that it shall not create a … Read more

Capacitance Voltage Transformer  The high voltage measurement is possible by utilizing the concept of resonance. The setup used for it is often known as capacitance voltage transformer. The capacitance voltage transformer is shown in Figure A its equivalent circuit is shown in Figure B.It consists of  C1 – High voltage capacitance (value is in few thousand … Read more

High AC voltage Measurement Following methods can be used Electrostatic Potential divider Potential transformer (Voltage Transformer) Electrostatic Sphere gap Impulse voltage Measurement Following methods can be used : 1. Voltage dividers.  (a) Resistance with CRO  (b) Capacitances and current, voltage transformer  (c) RC 2. Peak voltmeters 3. Sphere gap For RMS value measurement methods used … Read more

Measuring Capacitors / Peak Voltage Measurement According to Chubb and Fortescue As opposed to sphere gaps, the circuit suggested by Chubb and Fortescue in 1913 is capable of measuring the peak value of a high AC voltage continuously and accurately. Figures A and B shows the circuit with its current and voltage curves. (a) Circuit … Read more

Peak Reading AC Voltmeter In some cases peak valve of an ac wave from is more important. (necessary to obtain maximum dielectric strength of insulating solids etc.) When waveform is not sinusoidal RMS valve of the voltage multiplied by √2 is not correct. Hence separate peak valve instrument is needed. Series Capacitor Peak Voltmeter : When … Read more

Factors Affecting on Measurement Influence of humidity : atmospheric condition : Spark over voltage increases with humidity. The increase in humidity is about 2 to 3 % over normal humidity range of 8 g/m3 to 15 g/m3 Humidity effect increases with the size of sphere and is maximum for uniform field gaps. The spark voltage increases … Read more

Measurement of High Value DC Current by Hall-Generator Q. With a neat sketch explain Hall generators for measurement of high currents. What is Hall effect ? If an electric current flows through a metal plate perpendicularly located to the on magnetic field Lorenz – forces will deflect the electrons in the metal structure in a … Read more

Measurements of High Value D.C. and A.C. Currents Reasons for High Current Short circuit Lightning discharge Switching transients surge currents Where high current measurement is required ? For conducting temperature rise, heat run test on power equipment like conductors, cables, circuit breakers Short circuit current measurements. Methods of Measuring High Currents (Devices used in High … Read more