Research On Adaptive Reclosing Technology Of Transmission Lines

At present,the traditional automatic reclosing method is widely used in EHV transmission lines which usually adopts fixed reclosing time interval scheme.However,if ireclosing on a permanent fault or before transient faults arc extinguished,it will cause a second shock to the electrical equipment and power systems.Adaptive reclosing technology,Witch has the ability to distinguish the fault type and detect the secondary arc extinction time,can solve the problem of auto-reclosing fundamentally,further improve the power system transient stability and shorten open-phase operation time of single phase reclosing.In order to realize these two kinds of key technolog of adaptive reclosing of transmission lines,this paper analyzes the time domain and frequency domain characteristics of the line side voltages after transmission line isolation under various fault types such as single-phase ground short circuit,phase-to-phase short circuit and phase indirect short circuit.This paper focus on studying the adaptive single-phase reclosure of the transmission line with shunt reactors and without shunt reactors,and the adaptive sequential reclosure of transmission line with shunt reactorFirst,the research background and research status of adaptive single-phase reclosure and adaptive sequential reclosure are introduced.The dynamic characteristics of single-phase ground fault arc are studied.The transient fault arc model is built by ATP/EMTP simulation software and the fault phase voltage waveform is obtained.Secondly,for single-phase ground fault,the all-phase FFT(apFFT)spectrum of the terminal voltage of faulty phase is analyzed.It is found that,before the secondary arc extinguishes,the apFFT phase spectrum is not smooth,because of outstanding variation of high-frequency components which are caused by the highly non-linear transition resistances.Whereas,after the secondary arc extinguishes,the apFFT phase spectrum is flat,because the transition resistance disappears and high-frequency signals change smoothly.Utilizing the difference of flatness characteristic in high-order harmonic apFFT phase spectrum before and after the secondary arc extinguishes,this paper proposes a method based on the flatness characteristics of apFFT spectrum to detect the arc extinction time.Simulations using ATP-EMTP have verified the correctness and effectiveness of the proposed method.Besides,the proposed method is almost insusceptible to fault location,transition resistance and power angle.The validity of the method is verified by the analysis of the actual wave data.Finally,for interphase fault of transmission lines with shunt reactors,the spectrum characteristics of the fault phase voltage is analyzed thoroughly in this paper.For transient faults,after the fault disappeared,the tripped phase side voltage consists of the power frequency component and the free oscillation frequency component which is close to the power frequency component,and cause the misjudgment phenomenon.For the permanent fault,the tripped phase side voltage only contains the power frequency periodic component.Based on this difference and using the theory of all-phase FFT to identify the dense spectrum,an adaptive sequential reclosure scheme based on apFFT phase spectrum recognized dense frequency signals is proposed.The method does not need to calculate the free oscillation frequency in the voltage accurately,so the computation is small.The validity of this method is also verified by ATP/EMTP simulation.