Lightning Impulse Breakdown Characteristics and Correction of Long Air Gap at High-Altitude Field Site

With the rapid development of new energy projects in high-altitude regions, transmission lines are increasingly required to traverse mountainous terrain to deliver power. However, field measurements indicate that ambient humidity in these high-altitude areas often falls outside the recommended range specified in current standards, posing potential risks to the performance of external insulation under complex environmental conditions. In this study, extensive tests are conducted at a high-altitude field site to systematically investigate the lightning impulse breakdown characteristics of rod-plane gaps under long gap distances (2–6 m). The effects of atmospheric pressure, humidity, temperature, and other environmental factors are comprehensively examined. In particular, the influence of humidity on the ionization and attachment coefficients is analyzed, and its impact on the positive polarity lightning impulse breakdown voltage <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> is evaluated. The results show that the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> has a power exponential relationship with air gap distance and humidity. Humidity influences the critical breakdown electric field through ionization coefficient and attachment coefficient. Considering the influence of atmospheric pressure, humidity and temperature on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub>, and the correction method is proposed and analyzed.