The problem__of switching surges in recent years has been a great -- concern to transmissi. on line engineers since, with the raising of transmission voltages to 30P-40P kV-and above, the stage has been reaphed where switching surges become of importance equal-to, or greater-than,. those caused by lightning for the selection of insulation and protective levels. This theBiS seeks to increase the knowledge on switching suges, particularly, those due to line energisation and re-energisation during which the highest overvoltage magnitudes are generated. The mathematical model used in the anlysis-has been the theory of nitural, modes as applied to symmetric transmission lines in conjunction with the Fourier transform'technique which tpLkes into account the frequency dependence of the elemlents. Sequential energisation and-high speed re-energisation of three-phaia lines as modified by the system configuration on both sides. --of the circuit breaker has been analysed. Surge magnitude reduction techniques by speciaAy designed circuit-breakers such-as resistor and synchronous ewitchit'99 and the protective characteristics of lightning arresters are presented* In insulation coordinationt statistical methods are being introduced to design for the most economical arrangement of the insulation structures taki, 39 I into account that the hig1jeqt overvoltages--have a low frequency of appearancs' In order to assess the sto-. -hastic behaviour of switching overvoltages, a fast and accurate method has been developedp and the distribution curves of some of the switching surge problems are presented.