![]() This line configuration will be used to visualize the concept of electromagnetic surge impedance coupling. Assume the 115 kV transmission circuits have 1.0 m insulators and the 50 kV distribution circuits have the minimum recommended dry arc distance of 0.5 m. The lightning performance of a structure with four circuits, arranged as per Fig. Each steel pole is grounded but soil resistivity varies considerably from tower to tower so each pole will have a different value of footing resistance. Lightning protection for this line is provided by a single overhead groundwire (OHGW), mounted at the top of the pole. ![]() 1: Beton-Dribenenmast multi-circuit transmission line with twin HV, twin MV and single OHGW. 1 shows a visually appealing arrangement of “delta” transmission circuits and “horizontal” distribution circuits, with 1-2-3 conductors balanced on each side. With appropriate selection, arresters on the lower circuit can also mitigate cross-system contact faults.įig. William Chisholm explains that line surge arresters offer an opportunity to retain the benefits of improved electromagnetic coupling of lightning to the HV circuit above while mitigating induced and backflashover overvoltages on the MV circuit below. In this edited 2019 contribution to INMR, Dr. Often, the lightning performance of the HV circuit improves, while the trip-out rate of the MV circuit is disappointing. Distribution system engineers sometimes take advantage of existing transmission right-of-way to route their medium voltage (MV) circuits when standards show there is adequate vertical clearance to high voltage (HV) transmission circuits above.
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