Unbalanced Current Analysis of 220 kV Short Line Loop Network

With the strengthening of grid structure and the tt type connection,the short line increases and short line ring network appeared in transformer substation changes the structure of the grid and causes unbalanced current in many lines.According to the imbalance current under the 220 kV short circuit line in the 750 kV power grid,this paper makes equivalent line by using PSASP and individual phase modeling for multiple-circuit transmission line on same tower by EMPT,and also analyzes and modifies the related parameters,finally using EMTP to analyze and calculate the unbalance current under different operation modes.The results show that the adjustment of the circuitry phase sequence and reasonable choice of operation mode can effectively restrain the unbalanced current.