In the 1970s and 1980s, gas insulated equipment was of major interest due to the trend of higher voltages and power in transmission and distribution lines. SF6 was the most commonly gas used due to the higher breakdown strength, high purity of gas and it is non-flammable. However, the use of SF6 will decrease in the future because it is believed that SF6 contributes to the greenhouse effects. This prompt further investigations on using other gases as insulating medium. Air has been the subject of interest after SF6, because air is a natural insulating medium and that at normal state, air is a perfect insulator. Since then, many studies have been carried out to study the air breakdown phenomenon in order to improve the dielectric performance of air.
In this thesis, the characteristic of air was investigated. It is known that it is possible to achieve a higher breakdown voltage of air by covering the electrodes in high voltage application with a thick dielectric covering.
In order to determine this, experiments were carried out with a set-up of two crossing insulating conductors. The air breakdown between the insulators were measured. The result were compared with the breakdown of air obtained for the set-up using bare metals electrodes. For the experiments, AC and impulse voltages were used as the test voltage.
An investigation process that involves the collection of data to analyze the effects of space and surface discharges on the breakdown were also be covered. Following that all the results obtained will then be analyzed and discussed. Finally, a conclusion of the results drawn and recommendations for future studies were provided.