Research On Dynamic Physical Characteristics And Suppressing Technology Of Secondary Arcs Of UHV Transmission Lines

Single-phase auto-reclosure (SPAR) is widely used in extra high voltage (EHV) and ultra high voltage (UHV) transmission lines to improve the stability and reliability of the power systems. Reliable extinction of the secondary arcs is a critical issue for the UHV transmission lines, otherwise, the circuit breaker would be re-closed at grounded arc faults, may will result in failure of the re-closing operation. Hence, investigation on the formation mechanism and physical characteristics of the secondary arcs, as well as development of effective suppressing technologies, are of great significance in both theory and application arenas.Based on the ongoing UHV transmission project in China, secondary arc physics and corresponding suppressing technologies are systematically researched in this dissertation. The research contents cover several aspects as follows, namely establishment of the test platform for physical simulation of the secondary arcs, physical and mathematical modeling methodology of the secondary arcs incorporating the extinction and re-ignition mechanisms, development of novel suppressing technologies of secondary arcs and so on.Low voltage physical simulation is an effective approach to study secondary arcs. Based on an established experimental system, high speed images as well as the arc current and voltage waveforms are recorded as to explore the unique and intrinsic mechanisms of the secondary arc inception, development, movement, extinction and re-ignition. The motion characteristics of the arc root and arc column as well as their impacts on arc current and voltage are also fully elucidated and illustrated through the high-speed imaging equipment.Specifically for the secondary arcs of half-wavelength transmission lines (HWTL), exploratory research are also carried out, for which a new test topology is proposed via Thevenin transform of the established equivalent circuitry. With physical experiments, two critical points of the arcing time are obtained as to present useful reference for optimization of the high speed grounding switch (HSGS) arrangement along HWTL. Further, wind impacts on the secondary arc physics are given full account through large numbers of experiments.Secondary arc physics during zero-crossing stage of arc current plays a unique role to determine the arc extinction and re-ignition mechanisms, where the rate of rise of the recovery voltage (RRRV) across the arc path is one of the most important parameters to influence secondary arc extinction. The whole process of a single-phase-to-ground fault are divided into four stages, based on which corresponding equivalent circuit of the transmission lines is established in the complex frequency domain. The impact factors and their interacting mechanisms on the RRRV of secondary arc path are studied in details. The research results present theoretical basis for parameter optimization and auto-reclosing strategy development of the UHV transmission lines.The parameter determination of the four-legged shunt reactors within UHV transmission lines is a multi-objective issue of optimization. With a dynamic secondary arc model being taken into account, the impacts of the initial arc length and the neutral reactor on the arcing time of the secondary arcs are studied as to set up a guide criterion for parameter optimization of the four-legged shunt reactors. In addition, with full consideration of secondary arc suppression as well as resonant over-voltage mitigation due to out-of-phase operations, further optimization methodologies are presented for the four-legged shunt reactors.To achieve preferable suppression of the secondary arcs, a novel scheme based on paralleled impedance to line circuit breaker is proposed, which is applicable to both EHV and UHV transmission lines. An algorithm for topology parameter design and optimization under different conditions is given based on equivalent circuit transform. Simulation results indicate that the proposed arc suppressing theme can greatly reduce the forced components of the secondary arc current and the recovery voltage, thus resulting in quick extinction of the secondary arcs. The proposed scheme may be an applicable alternative and supplement of the traditional secondary arc suppressing measures prevailing within EHV and UHV transmission lines.The research work in the dissertation presents further development in both fundamental theories and analyzing methodologies for secondary arc study, and is of great significance for future development of the UHV transmission technologies.