External grounding design to reduce effects of lightning damage in distribution system

This paper presents an external ground design in distribution system for improved lightning performance. Lightning protection is a set of features typically designed into grounding systems at locations subject to lightning damage. Basically, back flashover occurs when the amplitude of the lightning overvoltage experienced by insulator strings in response to direct strikes to a tower or to the shield wires at tower vicinities exceeds the insulation withstand of the line. The objective function is to reduce the effects of lightning overvoltage from back flashover is an attachment of external ground wire connected between the overhead ground wires and a ground rod. This paper analyzes the effects of lightning performance of 69 kV circuit in Metropolitan Electricity Authority (MEA)´s distribution system of Thailand. The proposed ATP-EMTP model for simulation and analysis of lightning in terms of pole top voltage, critical current and back flashover rate. The study results show that external grounding system design can reduce the effects of lightning and improve distribution system reliability.