Abstract
Non-pressurised air is extensively used as basic insulation medium in high-voltage equipment. Unfortunately, an inherent property of air-insulated design is that the system tends to become physically large. On the other hand, the application of dielectric barriers can increase the breakdown voltage and therefore decrease the size of the equipment. In this study, the impact of dielectric barriers on breakdown voltage enhancement is investigated under both direct current (dc) and alternating current (ac) applied voltages. For this purpose, three kinds of dielectric barriers in two different high-voltage electrode structures are investigated. In the first structure, several experiments are carried out with four different electrode arrangements, keeping the inter-electrode gap constant while varying the position of the dielectric barrier between the electrodes. In the second structure, the inter-electrode gap is varied while the high-voltage electrode is covered with dielectric materials. The influences of different parameters such as inter-electrode spacing, electric field non-uniformity factor, and dielectric materials on the breakdown voltage are investigated for applied 50 Hz ac and dc voltages. In addition, a simulation model to approximately calculate the breakdown voltage is proposed and validated with the experimental results.
Highlights
In gas-insulated high-voltage (HV) systems, non-pressurised air is mainly used as the basic insulation medium
Dielectric materials in a circular shape were inserted in the air gap of electrodes for four different electrode arrangements
A dielectric barrier was parallel to the grounded plane and was vertically moved in the constant inter-electrode air gap
Summary
In gas-insulated high-voltage (HV) systems, non-pressurised air is mainly used as the basic insulation medium. Redistribution of the electric field in the air gap, due to accumulated surface charges on the dielectric barrier, affects the breakdown voltage of the gap. These surface charges are the result of impact ionisation near the HV electrode. Blennow and Sjoberg [4] presented a model for describing a uniform electric field distribution in a plate–plate electrode configuration where the ground plate was covered by a dielectric layer They showed that the surface charges over the barrier decrease the electric field in the air gap and increase the breakdown voltage. Several studies explored the insulating performance of polymeric materials, there are many obstacles for using these materials in HV applications due to lack of understanding of their behaviour and performance in the presence of surface charges [18]
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