An efficient algorithm for transient analysis of lightning protective device installed in AC source systems

For the increasingly serious problem of lightning overvoltage in electronic equipment, a realistic circuit is proposed in this paper for the lightning protective device installed on AC source lines of electronic equipment. Based on the circuit, an efficient algorithm is presented to simulate the transient behavior of the protective device. The volt-ampere curve of metal oxide varistors is represented by an improved expression that has the capacity of describing the strong nonlinearity of the characteristic curves in a more accurate manner. Following a discretization treatment of the linear elements, the equivalent calculating network of the protective device is obtained for transient simulation. The simplified parameters of the residual multiport network are determined by removing the metal oxide varistors from the equivalent calculating network. According to these simplified parameters, the nonlinear equations are formed for the branches of the metal oxide varistors. A modified Newton iteration formulation is employed to solve the nonlinear equations. Then, the transient calculation for the linear part of the equivalent calculating network is performed in terms of the voltage responses of the metal oxide varistors. A better agreement is shown between calculated and measured results, which confirms the validity of the algorithm.