Critical issues in distribution system surge protection

The past ten years have produced some dramatic advances in overvoltage protection for electricity distribution systems. Research into the nature of lightning-flash characteristics, especially the characteristics of distribution arrester discharge currents, now permit a greater understanding of the magnitudes of impulse voltages that impact the system and its connected equipment. Zinc oxide use has emerged during this same time period as a protective technology that is unequaled in its ability to minimize impulse voltage. Its improved characteristics make it a requirement for riser pole application, and its simple gapless structure makes it ideal for application within the transformer tank. On the other hand, a significant cable failure problem has surfaced with an alarming number of underground residential distribution (URD) cable failures occurring, which has led to premature replacement of a considerable amount of cable. It is concluded that while the causes of this cable failure problem are multiple, excessive impulse voltage is a contributor and requires evaluation of available methodology that can minimize the magnitude of impulse voltage on underground circuits