Investigation of Sinusoidal Phase Voltage Effect on SFR Calculation of HVAC Transmission Lines

Objectives: In this paper, the conductor's voltage effects on shielding failure calculation of high voltage transmission lines are investigated. A new criterion for distinguishing the stable upward leader formation is also proposed. Methods/ Statistical Analysis: Charge simulation method is used for modeling of the 3-D step wise movement of lightning downward leader. For determination of striking point and Shielding Failure (SF) calculation, a new criterion for distinguishing the stable upward corona-leader system formation is proposed. The proposed criterion is developed in a way that the effects of operating voltage including the magnitude, phase and the sign of voltage are considered in the stable upward leader formation. Findings: The results of the simulated lightning, using the proposed criterion show that the proposed model simulates the lightning stroke phenomenon close to reality. The amount of the required electric field for stable upward leader inception from the phase wires with various voltage levels and signs, are calculated by proposed criterion. The results, in line with field experiments, revealed that the probabilities of upward leader inception and also lightning strokes change with variation of operating voltage of conductors. In the conductors with positive voltage, the required electric field for upward leader inception is far lower than the conductors with zero or negative voltage. Moreover the SF of a 500KV-HVAC transmission line is obtained and compared in two cases i.e., with consideration and without consideration of voltage effects. The result showed that SFR and maximum return stroke current increase 19% and 14%, respectively, by consideration of phase voltage effects. Which means voltage has great effects on SF calculation and should not be neglected. Novelty/Improvements: The proposed method improved SF Calculation by 1-Considering the effects of operating voltage including the magnitude, phase and sign of voltage2-Accurate modeling of downward leader and its charge in space.