Category: Testing of Materials

Partial Discharge Measurements

Partial Discharge Measurements: Earlier the testing of insulators and other equipment was based on the insulation resistance measurements, dissipation factor measurements and breakdown tests. It was observed that the dissipation factor (tan δ) was voltage dependent and hence became a criterion for the monitoring of the high voltage insulation. In further investigations it was found […]

Schering Bridge Theory

Schering Bridge Theory for Three Terminal Measurement: For two terminal measurements the bridge is grounded at its junction points. The supply transformer, detector, and all the components of the bridge are enclosed in earthed shields. For Schering Bridge Theory for Three Terminal Measurement, it is necessary to avoid stray capacitances, for accurate measurements. Hence, a […]

Dissipation Factor in Schering Bridge

Dissipation Factor in Schering Bridge: Extension of range of the Dissipation Factor in Schering Bridge can be achieved by connecting in parallel an additional large capacitance across C3. But to avoid expensive and large-size decade capacitances the C3R3 arm is modified as shown in Fig. 9.15a. R3 is made as a slide wire along with […]

High Voltage Schering Bridge

High Voltage Schering Bridge: In the power frequency range (25 to 100 Hz) High Voltage Schering Bridge is a very versatile and sensitive bridge and is readily suitable for high voltage measurements. The stress dependence of K′ or εr and tan δ can be readily obtained with this bridge. The schematic diagram of the High Voltage […]

Mole Bridge for Low Frequency Measurements

Mole Bridge for Low Frequency Measurements: The bridge that is usually used for low frequency measurements is the Mole Bridge whose schematic diagram is shown in Fig. 9.10. This is primarily devised to measure the dispersion in insulation of installed equipment and gives a reliable measure of the moisture content in the insulation. It is […]

Dielectric Constant and Loss

Dielectric Constant and Loss: Many insulating substances have dielectric constant greater than unity and have Dielectric Constant and Loss when subjected to a.c. voltages. These two quantities, namely, the dielectric constant and the loss depend on the magnitude of the voltage stress and on the frequency of the applied voltage. When a dielectric is used […]

Direct Current Resistivity Method

Direct Current Resistivity Method: The specimen shape and the electrode arrangement should be such that the Direct Current Resistivity Method can be easily calculated. For a solid specimen, the preferable shape is a flat plate with plane and parallel surfaces, usually circular. The specimens are normally in the form of discs of 5 to 10 […]