Simulation of chopping current effects upon capacitive switching transients

Transient overvoltages and overcurrents arise due to the switching action in high voltage electric power systems. Consequently, high electric field strengths occur because of the modified electrical patterns. Transient overvoltages and overcurrents are one of the main concerns of insulation coordination and short circuit analysis; whereas high electrical fields are primarily related with the environmental and biological issues. Transients due to the switching action depend on the network configurations as well as loading schedule. Unloaded line switching (capacitive switching) is one of the most important switching type from the point of substantial transients. On the other hand, chopping time of the current generally dominates the time dependent behavior of the transients. This paper presents a different method to analyze the effects of current chopping upon capacitive switching transients. Traditional frequency dependent T-model is changed by the proposed frequency dependent T-model to simulate the transmission line. The proposed model is applied and the transients for several different chopping currents are evaluated by using EMTDC/PSCAD software. All simulations are conducted for a practical power transmission line used in 380 kV Turkish National Power Transmission System. The results are compared with MATHCAD simulations. It is shown that the proposed model achieves more accurate calculations.