Research Of Deicer For Overhead Ground Wire Based On SVC Unbalance Compensation

Icing hazards of overhead transmission line is one of the most serious threats to the safe operation of the power system. It may cause ice flash-over of transmission line and insulated equipment in substations, or even factures the wires and collapses the towers, and worst of all, it may result in the paralysis of the entire grid in disaster area. When the ice storm occurs, climatic conditions are very harsh in most cases, roads are blocked and communication is interrupted, maintenance work is very difficult. That easily leads prolonged, large-scale power outages, causing serious damage to the local economy, bring great inconvenient to the local people. At present, domestic and international anti-icing measures are mainly divided into:mechanical method, heat melting and natural de-icing. The AC short circuit ice-melting method is widely used in various types of de-icing project by reason of its high efficiency, low cost, safe and reliable advantages. When the de-icing target is three phase transmission conducting wire, short circuit ice-melting method can fully use its strengths to solve the problem of icing on transmission line efficiently. However when the target is overhead ground wire, it will generate the phase unbalance of current in substation due to the access of the equivalent single-phase load, which limits the application of AC short circuit scheme in the overhead ground line.By the addition of SVC with phase unbalance compensation function among the ice-melting power source which also is the low voltage terminal of main transformer in the substation, the new method of ice-melting designed in this thesis effectively solves the problem. The SVC mentioned above is used as reactive power compensation device to compensate reactive power fluctuation and to stable bus voltage in normal state of power system, which is closely linked to the demand of reactive power compensator in FACTS cause of the strategic goals of smart grid and strong grid. Around the new ice-melting method of overhead ground line based on unbalance compensation and its core device which is SVC, we detailed discussed the physical& mathematical model of wire ice-melting and the calculation of its parameter, the design of SVC main circuit and the control hardware modules, the algorithm of reactive power compensation and unbalance compensation. Using the PSCAD simulation platform and partial prototype experiment, the correctness and feasibility of corresponding content and conclusions are logically verified.Among them, this thesis focuses on the draw-out power circuit of high-voltage switching thyristor and unbalance algorithm based on instantaneous reactive power theory and symmetrical components method. The draw-out power circuit mentioned above is designed into two parts which are voltage draw-out power module and current draw-out power module. The energy extracting target of voltage module is common cathode thyrsitors, which using full-wave topological to improve system reliability. Working with each other in switching state, the two secondary windings in current module stabled the charging voltage and reduced draw-out power transformer core loss. We applied symmetrical components method in Steinmetz load balancing theory to obtain the expression of compensation admittance. Combining with instantaneous reactive current detection techniques, the expression can be converted to calculating formula of measurable parameters.