Space charge dynamics investigation based on Kerr electro-optic measurements and processing of CCD images

Abstract

The Kerr electro-optic technique is used to investigate electric field and space charge effects using large Kerr constant propylene carbonate as the dielectric liquid with Kerr constant B≈1.22×10 -12 m/V 2 . However, improved accuracy of this technique to measure space charge distributions remains an important goal. This paper describes inversion algorithm research on obtaining accurate space charge distributions from Kerr measurements. The original charge-coupled device (CCD) image of light intensity was converted into grayscale values for improved calculation. The grayscale CCD image was transformed into the frequency domain through a two-dimensional Fourier transformation. Butterworth filtering techniques were employed for edge enhancement algorithms. The most important parameter for calculation of space charge distributions are the integer fringe numbers n in the sequence of light and dark fringes measured by the CCD camera. Comparison of the improved algorithm and traditional methods for calculating electric field and space charge distributions between a pair of stainless steel parallel plate electrodes was investigated. The space charge dynamics were also calculated after processing the CCD images with some improvements. The results showed the electric field was essentially uniform at early times of pulsed high voltages. This uniformity indicated the absence of space charge during the early transient interval, while a bipolar charge injection was found in the central region between electrodes at later times. For longer times the electric field and space charge distributions slowly became uniform again. Grayscale processing and Butterworth filtering played an important role in the improvement of the algorithm for better image quality and edge enhancement.

Space charge inhibition effect of nano-Fe3O4 on improvement of impulse breakdown voltage of transformer oil based on improved Kerr optic measurements

“…The traditional Kerr electro-optic field mapping technique can only be used to measure space charge in liquid dielectrics with high Kerr constants. 11,12 The Kerr electro-optic field mapping technique with AC modulation can be used to measure electric field and space charge distributions in transformer oil under high DC voltages, but this method cannot be applied to electric field and space charge measurements under impulse voltages. [13][14][15] In power system, switching impulse overvoltage, which is caused by switching operation on power apparatus, could lead to serious damage to the transformer oil-paper insulation system of transformers, and thus endanger the security of the power system.…”

“…The electric field and the space charge density distribution characteristics throughout impulse processing of the samples can be determined based on the light intensity measured by the photodetector arrays. 12 In this study, a positive impulse voltage (150/5000 µs) is applied with a 57.6 kV voltage peak on plate electrodes with gap width d = 3 mm, and is used for the Kerr measurements of the space charge and the electric field. The Kerr electro-optic effect principle can be described as, light parallel to the direction of the electric field and the polarized light perpendicular to the direction of the electric field.…”

“…Figure 7(a) and 7(b) demonstrate the space charge distributions of pure and nano-modified transformer oils, respectively, which were calculated on the basis of the relationship between the electric field and the space charge density. 12 At 150 and 1500 µs, the space charge in both the pure and modified transformer oils is small. At 3500 µs, the space charge densities in pure and modified transformer oil are −0.125 and −0.076 C/m 3 , respectively, at a distance of 0.4 mm from the cathode electrode.…”

Direct observation of electric charges at solid/liquid interfaces with the pressure-wave-propagation method

“…This is well adapted for studying flowing liquids but less for studying still liquids. And little studies use direct and local measurement methods for determining intrinsic space charge buildup at solid/liquid interface [18,19,20,21,22]. These latter use either the Kerr effect, which restricts the studied liquid to transparent and electro-optic materials, or thermal diffusion, which may produce thermal convection inside the liquid.…”

Effect of Fe3O4 nanoparticles on space charge distribution in propylene carbonate under impulse voltage

“…[10][11][12][13][14][15][16] By using the birefringence effect of the liquid, a polarized light that goes through a liquid dielectric while HV is applied will split into two perpendicular polarized lights with a phase difference δ = 2π(∆n•L)/λ = 2πKLE 2 . This can be detected by a pair of polarized lenses with polarization directions parallel or perpendicular to each other.…”