Analysis of unbalanced current in a 220kV short double-circuit line

With the growing electricity demands of the grid, more and more new power plants and substations have been connected to long transmission line through short lines, which results in current imbalance since that short lines are generally erected without transpositions and the inherent parameter asymmetry of them leads to the unbalanced electromagnetic coupling between paralleled lines. In order to analyze the reason of unbalanced current in a 220kV short line in Jiangxi Grid, the paper made equivalent grid network using PSASP and modeled the double-circuit transmission line by EMTP. Then unbalanced currents of different working conditions were simulated by EMTP. The results revealed that the adjustments of bundle spacing of each conductor, the reduction of the three-phase load imbalance, the rational arrangements of phase sequence and the reasonable choices of operation mode could constrain the unbalance current effectively.