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

Resistive Shunts There are various types of resistive shunts used in “Impulse current measurements”. Such shunts are : Low ohmic resistive shunt Bifilar flat-strip type resistive shunt Co-axial Tubular / Park shunt Co-axial squirrel cage type resistive shunt Characteristics of such shunts and their limitations Low ohmio resistive shunt : Large dimentions and hence it … Read more

Potential Divider Across Low resistances arm R2 electrostatic voltmeter or high impedance voltmeter is connected. Low resistances arm R2 and potential divider are connected as shown in the Figure. Due to sudden changes in voltage caused by Switching operations Flash over of test voltage Short circuit flash over or damage may occur divider elements. This is due … Read more