Observation and analysis of the sparkover around grounding electrode under impulse current

Abstract

Soil sparkover is one of the key factors that affect the impulse characteristics of grounding devices under lightning current. In this study, the polyester-based sensitive films are applied to observe the morphology features of the sandy sparkover around a horizontal grounding rod 1 m in length buried in a hemispheric pool 8 m in diameter under impulse current. Moreover, the releasing current distribution of the grounding rod is measured by modular multi-channel simultaneous signal acquisition system. Along with injected impulse current increasing, the ratio of current released from two ends of the rod increases because the spark discharge leads the redistribution of the dissipating current. The discharge in the sand becomes more intense with current increasing. The discharge on middle segments spreads around the electrode-like cluster, while sparkover at the terminal develops into tree creeping discharge finally. Analysis based on combining observation images with current measurement result suggests that sparkover morphology is related to not only electric field value but also electric field distribution. The sparkover strength is determined by electric field intensity, while the sparkover concentration depends on electric field uniformity.