Application of solid state fault current limiting and interrupting device for voltage sag mitigation on 33 KV Tegeta distribution networks

Tegeta substation feeds four feeders from its 33 kV bus bar. One feeder of 50 km length is installed with autoreclosers, however in the course of distributing electricity to its customers, Tegeta 33 kV distribution network experiences tremendous voltage sags at the point of common coupling (PCC) due to the application of autoreclosers on one of its feeders. In this study, the distribution network was modeled using, Solid State Fault Current Limiting and Interrupting Device (SSFCLID), autorecloser and the developed SSFCLID controller. MATLAB simulations were performed with autorecloser and the SSFCLID used for operation during the network fault conditions to determine the voltage sag effect. Also, a varistor was used to limit the fault current during fault conditions in order to determine the voltage sag effect at the PCC. Finally, MATLAB/Simulink and Power System Block set were used to model a single phase distribution network with the SSFCLID and autorecloser applied on the single phase 33 kV distribution network at different fault locations. Voltage sag results were obtained for the various scenarios. When the varistor was used to limit the fault current during fault conditions, resulted in the mitigation of voltage sag at the PCC. With the application of autorecloser, the simulation results obtained under fault condition at different locations had voltage sag values far below the recommended value of 90 % set by equipment manufacturers. The worst voltage sag value of 62 % was recorded at a distance of 5 km from the PCC. However, with application of the SSFCLID, the simulation results obtained under fault condition at different locations had voltage sag values well above the recommended value of 90 % set by equipment manufacturers. According to the results obtained from the application of the SSFCLID, it showed clearly, the ability of the SSFCLID in mitigating the voltage sag to a safe value of 94.7 % well above the recommended value of 90 % set by manufacturers even at a distance of 5 km from the PCC. For proper operation of distribution networks, it is recommended to employ the SSFCLID in order to solve the problem of voltage sag occurrence at the PCC due to fault conditions.