Influence of Rate-of-Rise on Distribution Arrester Protective Characteristics

Lightning causes 30% to 50% of all distribution system outages, and accounts for a similar percentage of distribution equipment failures, according to studies reported by several Utility Engineers. Equipment failures, distribution transformer failures in particular, have been difficult to explain because the published protective levels of distribution surge arresters are so low compared to the equipment Basic Impulse Level (BIL). The object of this paper is to show that distribution arresters may exhibit voltages high enough to endanger transformer insulation if reasonable assumptions are made regarding the magnitudes and rates of rise of currents through arresters.