In this paper, state-space method is applied to compute transients in power transmission lines by considering corona effects. Transmission line is modeled by lumped parameter identical sections to simulate the distribution nature of the line and nonlinear corona branches are combined with these sections'. The whole system is composed of RLC elements, sources and switches. The response of the system is calculated using state-space method which has been developed for the analysis of nonlinear power electronic circuits with periodically operated switches. (C) 2002 Elsevier Science Ltd. All rights reserved.