The development of a 3-D rolling sphere algorithm for lightning protection

When designing Lightning Protection Systems (LPS), the effectiveness of an air termination structure(s) may be assessed by using the rolling sphere method. This method is outlined in standards BS6651:1999, IEC 62305, and IEEE 998-1996. A number of 2D methodologies are presented in these standards illustrating how to apply the rolling sphere method. This paper proposes a new 3D approach to the application of the rolling sphere method. This new approach analyses the designated air termination structures and forms stationary shapes around the air terminations. This approach focuses on where a rolling sphere can not go rather than where it can go. For example, a concave cone, as shown in Figure 1, will describe the protected area provided by a single lightning mast. Different shapes are required depending on the nature of the air termination system. All shapes will be a combination of sections of concave cones, spheres and cylinders.