Research On Adaptive Autoreclosure Of Transmission Lines With Shunt Reactors

Adaptive autoreclosure technology can not only improve the stability of parallel operation of power system, but also avoid causing secondary attack on power system in a short time, which plays an important role in security, stability and economic operation of power system. The research findings on single-phase and three-phase adaptive autoreclosure so far are summarized and analyzed in this paper. Due to the complexity of engineering applications, the existing research findings have problems in practical applications more or less. In order to make up for the deficiency in the existing research findings, some extended researches on single-phase ground fault and interphase fault of transmission lines with shunt reactors will be carried out in this paper.Firstly, three-phase uniform transmission line equation is analyzed in this paper. Theoretical analysis shows that because of capacitive coupling and electromagnetic coupling between any two phase, when asymmetrical fault happens, the complexity of calculation and analysis will greatly increase. For the sake of simplifying calculation, Karranbauer transformation is used to work out the steady state equation of voltage and current, so as to provide a reference for the new proposed criteria.Secondly, for single-phase ground fault of transmission lines with shunt reactors, based on the transmission characteristic of transmission lines, a new algorithm to calculate transition resistance through uniform transmission line equation is presented in this paper. Whereas in the case of permanent fault, the transition resistance is nearly a low value, while in the case of transient fault, after the arc is extinguished, the calculated value of transition resistance increases to a large value immediately, as a result, we can distinguish the fault nature in this way, and also the extinction time of secondary arc can be assessed. This method can work just by making use of the current of shunt reactors and the non-fault-phase at one terminal, and fault locations results, and is easy for application. ATP simulation results and analyses show that the method is hardly affected by fault location, load current and transition resistance, and can be applied to transmission lines with shunt reactors at one terminal and at both terminals. What’s more, the method can withstand the inaccuracy of fault location, transmission lines parameters, and system frequency to some degree.Thirdly, for interphase fault of transmission lines with shunt reactors, the waveform characteristics of differential mode currents in shunt reactors is analyzed thoroughly in this paper, especially for two-phase or three-phase transient fault and permanent fault at EHV transmission lines with shunt reactors: After breakers of three phases tripped, in the case of transient fault, the differential mode current consists of attenuation periodic component after the arc is extinguished, while in the case of permanent fault, the differential mode current is composed of attenuation DC component. Based on the waveform characteristics of the differential mode current, a new criterion is proposed to identify interphase fault nature for three-phase adaptive autoreclosure, the criterion can work just by making use of the currents of shunt reactors at one terminal, and also the extinction time of secondary arc can be assessed. Large numbers of ATP simulation results show that the criterion can identify fault nature rapidly and accurately, and is hardly affected by fault location, transition resistance, sampling frequency, load current, fault time, tripping time and arc extinguishing time at fault point, and can be applied to transmission lines with shunt reactors at one terminal and at both terminals.