Calculation of townsend second ionization coefficient for photoemission at different humidities

The evaluation of direct current (DC) corona inception voltage in humid air is of importance for high-voltage equipments and high-voltage DC transmission lines, when the occurrence of DC corona in humid air is taken into account. The secondary electrons to sustain a negative DC corona discharge are produced primarily by photoemission from the electrode surface. The process of photoemission in a negative DC corona discharge can be described through the Townsend second ionization coefficient due to photoemission (γp). In this work an approach for the calculations of the Townsend second ionization coefficient γp at different relative humidities has been proposed. Using the presented approach, γp as a function of relative humidity has been calculated and compared with the experiments. The good agreement between the calculated results and the experiments are obtained. The present method is an efficient one for the calculation of γp at different relative humidities, especially for the humidities considered practically, and can be further used for the evaluations of negative DC corona inception electric fields in humid air.