Economic assessment of lightning performance improvement of 69 kV subtransmission and 24 kV distribution line in power system

The back flashover generated from a lightning stroke hit at different locations: either at the end of pole top or the middle of the span of the overhead ground wire (OHGW), is one of the major causes of sustained interruption in Metropolitan Electricity Authority (MEA)´s distribution system, Thailand. One effective way to reduce the effects of such lightning overvoltage from back flashover is an addition of external ground wire connected between the overhead ground wires and the ground rod. This paper analyzes the effects of lightning performance of 69 kV and 24 kV circuits installed on the electrical concrete pole by ATP-EMTP. The lightning performance is evaluated through 3 parameters: pole top voltage, critical current and back flashover rate. The case studies illustrated the lightning strike directly to either the top of the pole (pole top) or the middle of OHGW span (mid span). The study results show that external ground wires can contribute toward improvement of the above mentioned parameters and therefore offers a promising solution to improve reliability of subtransmission and distribution lines in MEA´s power system.