The Research Of Individual Phase Electrical Characteristics Of 220kv Transmission Lines And Its Influence Power Grid

In order to decrease the asymmetry of current and voltage of the power system, the high voltage transmission lines should be transposed in principle. Design and operation experience has shown that, the transposition of high voltage transmission lines would weaken the mechanical strength and increase the cost of its construction and operation. For the double circuit transmission line, it is more difficult to be transposed completely because of the coupling of electromagnetic and electrostatic almong the lines.With the strong growth of electricity load and accelerating of the urbanization process, lots of short or ultrashort 220kV double-circuit trasmission lines in regional power grid emerge, which are without transposition generally. In recent years, the imbalance of three-phase current caused by double-circuit trasmission lines without transposition is increasingly prominent.The imbanlance of three-phase current increases the loss of network components or even may lead to maloperation of generator negative sequence protection or zero-sequence protection,and then brings about large area lackouts. Therefore, the research of the imbanlance of three-phase caused by the asymmetry of transmission line parameters is important.For the asymmetric three-phase parameters transmission lines, under the sequence domain the parameters are still coupling. So the modeling of three-phase parameters must be done under the phase domain.This paper research individual phase modeling of un-transposed high voltage transmission lines consulted Carson model. It introduces the caculationg method of inductance and capacitance of each phase and the processing method of overhead ground wire and bundle conductor, and a simplified model against 220kV transmission lines is proposed. On this basis, the influences to unbalance current of line tower type, wire parameters and phase sequence arrange are analyzed.For the double-circuit trasmission lines, this paper studies the asymmetric parameters by studying the asymmetry of mutual inductance matrix and elaborates the principia mathematica of decreasing current unbalanced degree by phase sequence arrange.From 36 kinds of phase sequence arranges,6 kinds of phase sequence arranges are attributed. When the length of lines, loads etc are changing, the impacts on the current unbalanced degree of these 6 kinds of phase sequence arranges are compared, and the kind of it which is general and applicable to decrease the unbanlance current is found.On the background of ring network in the power system, the impacts on unbalance current of power phase and powerflow of lines are researched. Finally, the unbalanced current in Shenzhen power grid is reproduced by simulation with EMTDC. Based on conclusions of earlier studies, a solution is proposed and it is proved by simulation.