Frequency modeling of trapped charge source for transmission line switching studies in presence of shunt reactor using EMTP/ATPDraw

Insulation coordination studies are of great importance in power grid reliability. In this paper, a new method is proposed for modeling trapped charge sources (TCS) in switching transient studies. The TCS is used to take account of the voltage stored in line capacitors during reclosing operation after fault occurrence. The proposed model is designed based on the active filter concept, so it does not have the limitations of conventional TCS for simulating transient states in EMTP/ATPDraw. Given the natural frequencies of the transmission line to which the proposed TCS (PTCS) is connected, the PTCS injects the appropriate frequencies and eliminates voltage oscillations, which limit the use of TCS. To verify the efficiency of the PTCS, it is implemented in a real system with a shunt reactor, and the results are then compared with field measurements. A comparison of the results shows that the PTCS eliminates the voltage oscillations in the simulation before closing and provides a smooth voltage with the desired amplitude. Using the proposed model, the maximum line switching overvoltage is correctly calculated; this, in turn, results in a more accurate transmission line insulation design, which is technically and economically beneficial.