Abstract ▼ AI-Helper

SF6 gas has been widely used in electric equipment as gas insulation because of high dielectric strength and arc extinguishing performance. However, because SF6 gas is one of the green house effect gases, alternative insulation such as SF6 mixture, extremely low temperature gas, vacuum, liquid and s...

SF6 gas has been widely used in electric equipment as gas insulation because of high dielectric strength and arc extinguishing performance. However, because SF6 gas is one of the green house effect gases, alternative insulation such as SF6 mixture, extremely low temperature gas, vacuum, liquid and solid insulating are being investigated. The focus of this paper has been on breakdown of hybrid insulation in inhomogeneous fields under lightning impulse voltage stress. The principle idea behind hybrid insulation is the intentional use of surface charge to re-distribute the electric field within an insulation system. Theoretically, it is shown that the in homogeneous electric field in a rod-plane electrode system can be reduced if the electrodes are covered with a dielectric coating. Free charge will be affected by the electric field between the electrodes and are deposited at the dielectric surface. As a consequence, a counteracting electric field is forced into the dielectric coating by the charge. This effect gives important implications in high voltage engineering. The concept has been experimentally addressed by means of a hemispheric rod covered with solid insulation. In case of bare and coated rod - plane electrode breakdown voltage in air was measured. The experimental conditions are as follows: In case of bare rod – plane electrode, gap distance is between 5, 8, 12 mm and pressure of air is 1∼6 atm. Also in case of coated rod –plane electrode, gap distance is 5, 8, 12 mm and pressure is 1.5, 3.5, 6 atm. The experiment result show that the increase in positive/negative lightning impulse breakdown voltage of cated electrode system increase compared to uncoated electrode system. This increase breakdown voltage at coated electrode system in positive lightning impulse is ranged from 125 to 250 % and the voltage is ranged from 111 to 150 % in negative lightning impulse. In addition to that coated electrode system punctured, the increasing rate is much higher compared to uncovered. In coated electrode system the experiment at results show that the increase rate in positive breakdown voltage higher than that in negative breakdown voltage.