Effects of air pressure and humidity on the corona onset voltage of bundle conductors

On the condition of adjusting air pressure from 58.7 to 98.7 kPa and air humidity from 5 to 17.3 g/m³ in the multifunctional artificial chamber, experiments on AC corona performance of scaled models of three kinds of bundle conductors are conducted and the mathematical model of corona discharge is proposed to calculate the corona onset voltages. Results indicate that the corona onset voltage of bundle conductors will decrease obviously with the decrease of air pressure, but the effect of air pressure on the corona onset voltage will decline with the increase of absolute humidity. When absolute humidity rises from 5 to 15 g/m³, the corona onset voltage increases slowly. Furthermore, the lower air pressure is, the more obvious effect of absolute humidity on the corona onset voltage is. Yet, the corona onset voltage drops remarkably when absolute humidity reaches 17.3 g/m³, owing to the condensation, which distorts the surface electric field, on the surface of conductors under high-humidity condition. In light of the condensation effect, the mathematical model of corona discharge is improved, which helps yield agreement between the measured results and the calculated results. Moreover, formulas for predicting corona onset voltages under various bundle configurations, air pressure and air humidity are also obtained. Calculated results from these formulas along with from mathematical models are compared with the measured results.