Pulsed Electro-acoustic Space Charge Measurement Research Articles

Study on Space Charge Characteristics in XLPE Under DC Voltage Superimposed by Impulse Voltage

In direct current (dc) transmission lines, power cables are susceptible to the invasion of switching overvoltage or lightning overvoltage. This causes the accumulation of space charge in the insulation due to the higher transient composite electric stress. Space charge is an important factor in dielectric breakdown, especially under high electric stress. However, until now, there are few reports on space charge characteristics under the composite stresses of dc voltage and impulse voltage. In this article, a modified pulsed electroacoustic space charge measurement system used for dc voltage superimposed by impulse voltage is developed by reasonably choosing resistor and capacitor elements in the measuring system. Then, space charge characteristics in cross-linked polyethylene (XLPE) are measured under dc voltage, impulse voltage, and dc voltage superimposed by impulse voltage. The test results show that hetero-charges dominated in the XLPE bulk under a positive dc voltage, whereas homo-charge injection occurred from the semiconductor (SC) electrode under a negative dc voltage. However, a continuous impulse voltage with high amplitude can cause a large degree of homo-charge injection from both electrodes. Moreover, greater homo-charge injection appeared under the negative impulse voltage than that under the positive impulse voltage. Under a dc voltage superimposed by an impulse voltage, the superposition of voltages with the same polarities facilitated homo-charges injection from both electrodes to a greater extent than did the superposition of voltages with opposite polarities. Furthermore, regardless of the polarity of the applied dc voltage, greater space charge accumulation appeared in XLPE when a negative impulse voltage is superimposed.

Effect of Space Charge Density and High Voltage Breakdown of Surface Modified Alumina Reinforced Epoxy Composites

The incorporation of 90 nm alumina particles into an epoxy matrix to form a composite microstructure is described in present study. It is shown that the use of ultrafine particles results in a substantial change in the behavior of the composite, which can be traced to the mitigation of internal charges when a comparison is made with conventional <TEX>$Al_2O_3$</TEX> fillers. A variety of diagnostic techniques have been used to augment pulsed electro-acoustic space charge measurement to provide a basis for understanding the underlying physics of the phenomenon. It would appear that, when the size of the inclusions becomes small enough, they act cooperatively with the host structure and cease to exhibit interfacial properties. It is postulated that the <TEX>$Al_2O_3$</TEX> particles are surrounded by high charge concentrations. Since <TEX>$Al_2O_3$</TEX> particles have very high specific areas, these regions allow limited charge percolation through <TEX>$Al_2O_3$</TEX> filled dielectrics. The practical consequences of this have also been explored in terms of the electric strength exhibited. It would appear that there was a window in which real advantages accumulated from the nano-formulated material. An optimum filler loading of about 0.5 wt.% was indicated.

Internal charge behaviour of nanocomposites

The incorporation of 23 nm titanium dioxide nanoparticles into an epoxy matrix to form ananocomposite structure is described. It is shown that the use of nanometric particlesresults in a substantial change in the behaviour of the composite, which can be traced tothe mitigation of internal charge when a comparison is made with conventionalTiO2 fillers. A variety of diagnostic techniques (including dielectric spectroscopy,electroluminescence, thermally stimulated current and photoluminescence) have been usedto augment pulsed electro-acoustic space charge measurement to provide a basis forunderstanding the underlying physics of the phenomenon. It would appear that, when thesize of the inclusions becomes small enough, they act cooperatively with the host structureand cease to exhibit interfacial properties, leading to Maxwell–Wagner polarization. It ispostulated that the particles are surrounded by high charge concentrations in theGouy–Chapman–Stern layer. Since nanoparticles have very high specific areas,these regions allow limited charge percolation through nano-filled dielectrics.The practical consequences of this have also been explored in terms of the electric strengthexhibited. It would appear that there was a window in which real advantages accrue fromthe nano-formulated material. An optimum loading of about 10% (by weight) is indicated.