Effect of transformer on stochastic estimation of voltage sag due to faults in the power system: a PSCAD/EMTDC simulation

Voltage sags in the electric power system are mostly due to faults in the power system. Voltage sag is characterized by its magnitude (the retained voltage), phase-angle jump, unbalance in the sag in the three phases, and duration. Type of transformers in the electrical system is the important parameter influencing the characteristic of sag at the node where sensitive loads are connected. For sensitive loads it is necessary to estimate how many times in a year the voltage at their terminal will experience sag to avoid tripping of operation. In this paper the effect of transformer on stochastic estimation of voltage sag is studied. Several stochastic methods for the estimation of number of sags have been developed in recent years. Various methods of sag prediction require lengthy programming or calculations. In the present work the PSCAD/EMTDC software package is used to estimate number of sags assuming uniform distribution of faults along the lines.