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Q3. How do you calculate the induced voltage in a power distribution network caused by an indirect lightning strike? The induced overvoltage caused by a lightning strike can breakdown a distribution network. To prevent this failure and install proper insulation, we need an accurate estimate of lightning induced overvoltage. Lightning induced overvoltage would depend on various parameters: Rate of rise of lightning current(inductance) Magnitude or peak value of current Soil to strike point resistance Indirect Strokes mainly causes over voltages and thereby causing line outages. In case of indirect Stroke, the return stroke in nearby lines generates electromagnetic field which produces lightning induced over voltages. There are several methods through which over voltages induced by indirect lightning strokes can be calculated. The methods employed practically can be subdivided into two main categories: 1. Time varying horizontal and vertical electric fields are calculated from the magnetic fields, generated by the lightning channel, using analytical formulas. Afterward, lightning induced overvoltage are computed from these computed electric fields using coupling models that are based on telegraph equations of overhead lines. 2. Maxwell’s electromagnetic equations are numerically solved to calculate the electromagnetic fields radiated from the lightning channel and, hence, the lightning-induced overvoltage are computed. Different numerical methods are employed for these calculations such as the method of moments, finite-element method, hybrid electromagnetic model, and finite-difference time-domain (FDTD) method. #Evolution of Rusck formula: Rusck relation is the main formula for calculating induced over voltages caused by an indirect lightning strike in power transmission lines. It includes two basic assumptions, perfect ground conductivity and a vertical stroke channel. where v, c are the velocities of the return stroke and light, respectively; Ip is the peak value of the lightning current, h is the height of the overhead line and d is the distance between the return stroke channel to the overhead line. Since Rusck formula is applicable to only idea soil, Hence, for it to be valid for an actual soil, an additional term is added to eq.(1): Where Pg is the ground electrical resistance and k is a numerical factor between 0.15 and 0.25 according to IEEE standard 1410-2010. Reference: [IEEE 2019 27th Iranian Conference on Electrical Engineering (ICEE) Yazd, Iran (2019.4.30-2019.5.2)] 2019 27th Iranian Conference on Electrical Engineering (ICEE) - Investigation of the Induced Overvoltages Caused by the Indirect Lightning Strike in Power Distribution Lines