Controlling overvoltages in high voltage system networks, has always played a central role in network design. It is important that overvoltages should not result in damage to the equipment or cause intteruption of the energy supply.In Malaysia, where power systems operate at 275 kv or less, lightning overvoltages become a major factor to be reckoned with. A possible protection is to lomit these overvoltages below the basic impulse level (BIL) of the substation.Chapter 1 gives an introduction of the system being studies and the objectives of carrying out this project. A brief account on how protection againstlightning overvoltages can be achieved are mentioned.Chapter 2 deals with the theory of lightning surges and the propagation of lightning waves entering a substation.Chapter 3 discusses the parameters of transmission lines and cables mainly the capacitance and inductance needed in obtaining the surge impedance.Chapter 4 describes the propagation of travelling waves in transmission lines and cables. The determination of node voltages (total voltage at the termination) is explained by means of Bewley lattice diagram.Chapter 5 deals with propagation of lightning surge striking on the tower top. The effect of tower footing resistance on the tower top potential is briefly explained.Chapter 6 discusses the principle of lightning arrester and insulation coordination in the protection of substations. Chapter 7 and Chapter 8 describe in detail how the project is being done. the methodology of obtaining the computer programme for the analysis is explained in Chapter 8. The discussions and conclusions of the results obtained from the analysis is given in Chapter 9 and lastly in Chapter 10, the author gives some proposals for improving the computer aided analysis.