Computer tool for comparison of classical and non-conventional lightning protection designs for electric substations

Electric substation physical plans are developed with consideration given to lightning protection. To develop these plans utility design engineers use various methods. This thesis focuses on developing a computer program for two methods/models for substation shielding against direct lightning strokes. The first method is being used currently in the industry to protect the substation structures. The second model is a new and more physics based approach towards lightning phenomenon. Both the methods consider only direct lightning strikes that can hit the substation equipment. Hence, the travelling waves, indirect strokes or over-voltage arriving at the substation equipment are not considered. The Electro-Geometric method (EGM) based Rolling Sphere Method (RSM) is used to develop first part of the program. The aim of the program is to design the protection system for the substation equipment quickly and error free. The protection system uses lightning masts and/or shield wires to protect the station equipment. These are grounded solidly with low impedance to earth. The MATLAB based program gives a two dimensional visual representation of the zone of protection and therefore helps utility engineers to position shielding system. As this program is converted further into an executable file, it can be used on any computer to produce the results without need of any other software. The second part of the thesis focuses on developing the MATLAB code for protection of substation equipment using the Rizk model which is not used as of now for shielding system design in industry. Using more physics based model, simulation of downward lightning leader and connecting upward leader is shown.

Finally both the methods are compared. This includes consideration of a 220 kV substation layout arrangement. The equipment are protected using shielding masts and the comparison is made in terms of number of the protective equipment needed. It is found that the classical rolling sphere model gives more conservative results than the physics based model. Hence the results shows that it is possible to use present methods and still protect the equipment sufficiently.