A Method to Estimate Voltage Sag Caused by Transformer Excitation Inrush Current

Due to excitation inrush current, no-load transformer accesses system can cause different degree of voltage sag. Therefore presents a method to estimate voltage sag caused by closing no-load transformer. Firstly, accord to the point of saturation magnetic flux and transformer core general single value curve equation to establish general nonlinear magnetization curve. Use the linear features of saturated magnetization curve segment to estimate the maximum inrush current and calculate the maximum depth of voltage sag. According to the magnetic flux decay time to estimate the duration of voltage sag. Simulate closing no-load transformer in a 10kV distribution network, and compare the simulated result with the calculated result. The results show that the proposed method is validity and accuracy.