Dielectric measurements of semi-insulating liquids and solids

Abstract

Sinusoidal steady state and transient decay measurement techniques were used to monitor the dielectric properties of electrical insulation, Impedance measurements of an air-gap capacitor, immersed in Shell Diala A transformer oil and driven with a 1 V peak sinusoidal signal (5 mHz-10 kHe), showed that the oil conductivity increased with temperature ( 15-70°C) and aging in air but was independent of the oil moisture content (2-30 ppm). Interfacial double layer effects were also observed.Surface charge effects were studied in a cylindrical electrode apparatus with EHV-Weidmann Hi-Val pressboard on the inner cylinder and transformer oil filling the gap. The pressboard dielectric properties were obtained from time transient decay measurements of the open-circuit voltage after disconnecting a DC voltage source from across the cylinders. These measurements indicate that the conduction mechanism through the pressboard follows a drift dominated unipolar conduction law rather than ohmic conduction.Further frequency sweep dielectrometry measurements using a three-wavelength interdigital electrode sensor confirm the dispersive properties of oilimpregnated pressboard. This sensor was also used to measure the time and space distributions of moisture diffusion into oil-impregnated pressboard.

Interdigital sensors and transducers

“…In many cases, the interpretation of the sensor response depends on simple calibration procedures, yet in other cases, it requires sophisticated signal processing algorithms [120] and deep understanding of the physics and chemistry of the dynamic processes that are being monitored [121].…”

“…The voltage source generated a sinusoidal signal having a peak amplitude of 1 V at a frequency that could be varied from 5 mHz to 10 kHz. The gain and the phase measurements were performed by a data acquisition unit designed to perform gain-phase measurements with interdigitated dielectric sensors [121].…”

Dielectrometry Measurements of Moisture Diffusion and Temperature Dynamics in Oil Impregnated Paper Insulated Electric Power Cables

“…Many of these techniques were developed in part for the analysis of oil impregnated transformer board used in industrial power transformers [16]. In fact this is one of the original applications of dielectrometry [17][18][19].…”

“…In this case the sensors have different wavelengths [37], or spatial periods which affects the sensitivity to material properties further away from the plane of the electrodes. This design has been used extensively for determining permittivity profiles normal to the surface of the electrodes [19,31,[38][39][40]. Care should be used in estimating material properties far away from the sensor.…”

Optical, electrical, and electro-mechanical measurement methodologies of electric field, charge, and polarization in dielectrics

“…Preliminary dielectrometry measurements have determined the diffusion coefficient and Debye length in transformer oil samples [23,24]. A parallel plate capacitor of area A was immersed in transformer oil and the impedance was measured over a range of frequencies at various temperatures.…”