Research On The Adaptive Auto-reclosure Method Of Transmission Lines

Auto-reclosing technology has been widely used in high voltage transmission lines which usually adopts fixed reclosing time interval scheme.However,reclosing on permanent faults or before transient faults arc extinguished may cause the risk of a second shock to the electrical equipment and power system stable operation.The adaptive reclosing technique aims to discriminate the fault nature and detect the arc extinguishing time which can avoid second damage of blind reclosure and shorten open-phase operation time of single phase reclosing.In this paper,the time domain and frequency domain characteristics of line side voltages and shunt reactor currents after transmission line isolation are analyzed,and the adaptive reclosing technology under different operating conditions is also discussed.Furthermore,the adaptive single-phase reclosure and sequential reclosure of transmission line without shunt reactor as well as the single-phase adaptive reclosing and adaptive three-phase reclosing for transmission lines with shunt reactor are mainly studied.An adaptive single-phase reclosing method based on the reactive power of sequence component is proposed.For the transmission lines without shunt reactors,the secondary arc current is large,and the traditional voltage amplitude criterion can not accurately distinguish the secondary arc voltage from the recovery voltage.Furthermore,the phase criterion is easily affected by the load power factor.In this paper,we first define the reactive power of sequence component which can both reflect the amplitude and phase characteristic of fault phase voltage;then the influence of the amplitude characteristics of the secondary arc voltage and the phase angle characteristic of the power frequency capacitance coupling voltage on the the reactive power of sequence component are deeply analyzed.It is found that the positive and negative reactive power have the opposite variation before transient fault arc extinguished,and jump in the reverse direction at the moment of arc extinguishing.As for permanent faults,each reactive power of sequence component remains as a constant.Accordingly,the fault nature is identified by the increment of the reactive power of sequence component,and arc extinguishing time is detected by incremental mutations and polarities.The analysis of simulation results and a recorded data show that the proposed adaptive single-phase reclosing method is less likely to be affected by fault transient resistance and the line power factor,therefore,it still has high sensitivity under the heavy load of the line.For transmission line with shunt reactor,a method of adaptive single-phase reclosing based on the voltage inner product and current inner product is proposed.The recovery voltage of fault phase and current of shunt reactor have free oscillation frequency component which is close to the power frequency may cause the misjudgment when the criterion is based on power frequency component.The criterion based on the time domain integration only applies to the recovery voltage stage.In this paper,healthy phase voltage and fault phase voltage as well as its first derivative voltage are used for defining voltage initialization inner product and compensation inner product respectively,similarly the neutral current and faulted phase current of shunt reactor as well as its derivative current are used for defining current initialization inner product and compensation inner product respectively.As for permanent faults,the voltage initialization innner product is less than voltage compensation inner product,and the current initialization product is lager than compensation inner product,two inner product curves will not appear intersection point.However,as transient faults after the arc extinction,two inner product curves will appear intersection point because of free frequency component.Therefore,the adaptive single-phase reclosing can be achieved by the intersection of initialization inner product and compensation inner product curves.The proposed method has clear start-up time and does not require artificial tuning threshold,so it can achieve full adaptive protection.The simulation results and the actual fault recording file verify the feasibility of the method which can be applied to heavy load lines.An adaptive sequential reclosure scheme based on the ratio of the voltage DC component to the fundamental component is proposed.A simplified model of fault circuit with one faulted phase isolation is established,and the time domain expression of the open-phase voltage is deduced based on the simplified model.It is found that the open-phase voltage has a higher DC offset component after transient faults arc extinguished,and the polarity of the DC component is mainly related to the polarity of the inter-phase coupling capacitor voltage at the moment of the arc extinguishing.However,as for permanent faults,there is no apparent DC component of the open-phase voltage.Accordingly,the fault nature can be accurately identified.The simulation results verify the correctness of the theoretical derivation and the feasibility of the proposed scheme.An adaptive three-phase reclosing scheme based on spectrum leakage effect is proposed.As for single or two-phase-ground faults of the transmission line with shunt reactor,the spectral characteristics of the fault phase current flowing through the shunt reactor after breaker three-phase trip are deduced in detail.Under the permanent fault,the fault phase currents of shunt reactor only contain one periodic component and exhibit the attenuation oscillation characteristic.However,after the transient faults arc extinguished,it will appear another two different periodic components.When the frequency of the faulted phase current of shunt reactor under the permanent fault is used as the reference frequency for sampling,the abrupt increasing of even harmonic content whcih caused by the spectral leakage under non-synchronous sampling of discrete Fourier transform can be used to detect the arc extinction time and then determine the nature of faults.The method does not need to accurately isolate the free oscillation frequency in the current,so the time window is short and the computation burden is small.The simulation results show that the method can accurately and promptly capture the time of fault arc extinction,which is beneficial to the rapid restoration of power supply and improve the stability of power grid operation.The adaptive reclosing method proposed in this paper has been applied to self-developed equipment—"Transmission lines optimal reclosing device" and passed through scientific research and identification.