Calculation and Analysis of Unbalanced Currents in Ningxia Northern 220 kV Power Gird

In double-circuit line on the same tower,three phases are unbalanced due to three-phase asymmetric parameters of each circuit and electromagnetic coupling between two circuits,which may endanger power equipment.Therefore,it is of great significance to calculate the unbalance degree and to analyze its influential factors of double-circuit transmission line.The unbalanced currents in Ningxia northern 220 kV power gird are large.Taking Ningxia northern 220 kV power gird as an example,we use ATP to build models for the ring network and to calculate the unbalanced currents of transmission lines based on practical power flow distribution,and compare the simulation results with measured data.The model includes the electromagnetic coupling between parallel lines and the topology of the ring network,which can simulate the real power grid effectively.The unbalanced currents under various operation conditions are obtained,consequently,the way to limit the current unbalance could be analyzed.The simulation results are in good agreement with the field data,and show that,by rationally adjusting the phase-order arrangement way of double-circuits transmission lines at the outlet of substation,the current unbalance in Ningxia northern 220 kV power grid can be effectively decreased.