Encouraged by the successful removal of continuous earthwire on overhead transmission lines by some foreign power utilities, such as Bonneville Power Administration in U.S.A., British Columbia Engineering Company in Canada and Electricile De France in France, and a few recent attempts by some Electricity Boards in this country for omission of earthwires on their transmission lines particularly at 66 KV an attempt has been made to maize a detailed analytical study of the various aspects of the problem with a view to investigating the feasibility of omission of continuous earthivire in this country on a large scale. Prevalent concepts of the mechanism of lightning stroke, the frequency of occurrence and the amplitude of lightning stroks are discussed. Analytical methods for calculation of areas of exposure of transmission lines to lightning strokes are presented. Number of strokes to phase conductors and towers are worked out. Strokes to towers will be drained into the ground for which maximum values of tower footing resistance to obviate flash-over are worked out. While majority of strokes to phase conductor’s will be self-cleared through circuit breaker switching and automatic reclosing, there will be some unsuccessful reclosings which will result in line outages. Permissible line outage values are then selected and the values of maximum IKL to give desired performance of unshielded lines are then worked out. Other aspects of omission of earthwire, such as inductive interference, breaker maintenance, etc., are discussed.
