Research On Integrated Protection And Quasi-Three-Phase Operation Of Double-circuit Transmission Line

With the growth of power demand, transmission lines on the same tower have been widely used in countries and regions with a large population and relatively arable land, for its narrow corridors, large transmission capacity and high reliability of power supply. The number of Double-circuit lines with voltage level of 220 kV and above was growing day by day, and most of them were constructed in parallel throughout. As the preferred primary protection of double-circuit line, single-phased differential protection was constrained by the longitudinal communication channel, needing protection based on single-end electric parameters as backup. While applied to double-circuit lines, traditional phase selector and measuring impedance element were likely to make mistake because of interline fault and mutual inductance between parallel lines. This thesis proposed that taken the double-circuit lines as the basic unit, configured integrated protection with single-end electric parameters of double-circuit. The major research included integrated phase selector, measuring impedance element and integrated tripping and reclosing strategy.The fault component of ideal transposed double-circuit lines was resolved into synclastic and opposite phasor. It was discovered that synclastic phasor was mainly related to fault phase and opposite phasor related to asymmetric phase, which referred to phase with same name and different fault state. Combined with the characteristics of superimposed component of different phase wire and zero sequence, specific fault types can be distinguished, thus forming the comprehensive integrated phase selector.Decomposing the voltage-current equation between the bus and failure point with phase domain method, the zero sequence compensating coefficient both this line and adjacent line could be contained in the integrated measuring impedance element. And there are six single-phase grounding measuring impedance element for single-phase ground fault, and twelve different-phase measuring impedance element for multiphase faults.The quasi-three-phase(QTP) operation was equivalent to two-point disconnection fault, and the main operation indicators were analyzed with the help of MATLAB. The comprehensive evaluation index of QTP operation was proposed with traverse maximum overload ratio, negative sequence current unbalance degree and transmission power limit as reference, becoming the basis of QTP mode selection and transformation. To achieve accurate QTP operation, the integrated tripping and reclosing strategy was put forward based on the removal of fault electrical characteristics. The integrated strategy made full use of structure advantage of double-circuit lines and minimized the resection and reclosing.