Lightning protection zones in substation using shield wires

Abstract

Lightning protection system in substation may employ mast, shield wire or both.  Calculation of lightning protection zone (LPZ ) is based on striking distance to ground, object and mast or shield wires.  LPZ generated by mast looks like a tent and is different from that of shield wire.  Equipment in substation is safe if it is covered by LPZ.  Calculation of the LPZ is complicated especially when there are more masts or parallel/convergence shield wires making it more difficult to picture LPZ.  This paper proposes Zone Apportionment Algorithm (ZAA) to apportion the LPZ into two zones corresponding to mast and shield wire, and further sub-apportion in two zones corresponding to non-overlapped and overlapped zones.  The maximum height of protected equipment at each point in substation is then calculated.  Integrating all points, results in a visual roof representing the LPZ. Equipment with its size and height is then laid in substation.  If there is an emerging part above the visual roof, it displays the part that may encounter lightning strikes.  ZAA is tested on five cases: one shield wire, two to three parallel shield wires and two to three convergence shield wires.  Numerical results show that ZAA can produce visual LPZ correctly in all cases and illustrate verification of protection.