Research on environmental factors of positive DC corona inception voltage of overhead transmission lines

The corona discharge effect is one of important problems in the design and operation of transmission lines. The transmission lines pass by the high altitude region with low air pressure, which brings many special problems to the design and operation of the transmission lines. Temperature and humidity also have obvious effect on the corona characteristics of the transmission lines. Consequently, it is significant to study the impact of air pressure, temperature and humidity on the corona characteristics and discharge mechanism of transmission lines. A computation model is adopted for evaluating the corona inception voltage on conductors, which is established according to the gas discharge theory. The charge simulation method is introduced to the computation model to calculate the electric field intensity. Then the criterion of corona inception voltage which considers whether the number of positive ions in the secondary avalanches is greater or equal to that in the primary avalanche is used to calculate the corona inception voltage of conductors. The influence of air pressure, humidity and temperature on the corona inception voltage of conductors is analysed systematically. Corona inception voltage decreases as air pressure is lowered or temperature is raised. It is mainly due to the enlargement of ionization zone as a result of the increase of effective ionization coefficient. Simultaneity, corona inception voltage decreases with humidity increasing for strengthening of collisional ionization intensity.