Modeling of Proximity Effect on Positive Leader Inception and Breakdown of Long Air Gaps

The paper presents the first effort to mathematically model proximity effects on continuous leader inception and breakdown of long air gaps under critical switching impulses. Three aspects of proximity with considerable practical importance are addressed. These include wall proximity in high voltage switching impulse tests, effects of protrusions and surface roughness on switching impulses performance of large electrodes and finally determination of critical ground fields for upward leader inception of a vertical rod under an energized plane electrode. The model results provide quantitative tools to assess proximity effects as well as means to keep such effects within acceptable limits. Whenever possible the model findings are compared with experimental results and internationally recommended practice and with view of the complexity of the problems, the agreement is quite satisfactory.