Research On Adaptive Reclosing Technique For HV Transmission Lines

Reliable adaptive reclosing technique can not only improve the reliability of the power system, but also play an important role in security, stability and economic operation of the power system. In order to solve the problem of existing criterion such as inaccurate results and long determining time, the following areas are deeply discussed in this paper by theoretical analysis and simulation:The voltage amplitude and voltage phase criterion of adaptive single-phase reclosing are deduced in this paper. From the process of the deducing, we can conclude that the recovery voltage at open-phase has a different nature in different property fault cases, the impact of various factors on the criterion and the application scope of the criterion.In order to further understand the potential characteristics of the recovery voltage at open-phase during the time of adaptive single-phase reclosing in transmission line with non-shunt reactor, exact expressions of terminal voltage at open-phase are concluded through distributed parameter model, while the electromagnetic coupling voltage and capacitive coupling voltage, as well as the various factors associated with which are comparative analyzed. This provides a reliable reference for developing an accurate and reliable adaptive reclosing criterion in transmission line with no shunt reactors.Considering that there are so many shunt reactors with neutral small reactors in HV transmission lines to compensate for the capacitive current, this paper detailed analysis the transient characteristics of recovery voltage at open-phase during the time of adaptive single-phase reclosing by the laplace frequency domain analysis in transmission line with shunt reactors. Because of the existing shunt reactors with initial energy, the terminal voltage at open-phase contains more components than only fundamental frequency component. For transient fault, the terminal voltage at open-phase not only contains fundamental frequency component which is incented by the power generators, but also contains the free oscillation component which is produced by the initial energy in shunt reactors. But for permanent fault, the terminal voltage at open-phase contains only fundamental frequency component, because the free oscillation component have decayed to zero quickly through the grounding resistance. Based on this different nature in recovery voltage, this paper presents a new algorithm to distinguish the properties of fault. The principle of this method is to make an integral of the recovery voltage during a fundamental frequency cycle. The new criterion is simple for implementation, and it obtains results fast with high sensitivity, reliability and accuracy. The performance of this new criterion will not be affected at all by transition resistance, integral initial time, initial phase of free component, integral harmonics and so on.Considering that circuit breakers in 220～500kV transmission line have the function of sequential operation and fault phase selection, it makes adaptive sequential reclosing possible. Through qualitative analysis and simulation results, we found that the characteristics of terminal voltage at open-phase when single phase is opened are similar with that when multiphase are opened, which both contains fundamental frequency component and free oscillation component. So the new criterion is extended to the area of adaptive sequential reclosing. A large number of EMTP simulations and data validate its feasibility and reliability. Now, the technique of adaptive single-phase reclosing and adaptive sequential reclosing are unified by the new criterion and the mode that distinguishes the fault property in different fault type is completely broken down.