The Study On Contact Failure Mechanism Of Gas Insulated Bus Connector

Gas insulated bus (GIB) has been widely used in modern power system as power transmission and distribution equipment. The GIB equipment with the compact design has high operation reliability by SF6 insulation gas. There are series of plug-in connectors inside GIB equipment which are used for absorbing assembly misalignment and thermal stress on conductors and disc-type insulators. Reliable connection of plug-in connector is essential for safely operating of the GIB equipment and power system. In spite of the current carrying capacity, and the thermal/mechanical strength under short current impact of GIB plug-in connectors have been considered during component design process, however, contact failure of GIB plug-in connector can be induced during equipment operation, leading contact overheating fault even short circuit fault. Thus research on contact failure mechanism of GIB plug-in connector under different operation conditions is helpful for optimal designing and contact overheating monitoring technologies thus enlarge working performance, and ensure safely operation of the equipment and power system.The basic contact parameters (electrical, thermal and mechanical performances) are chosen as original points, and research work on contact failure mechanism of the GIB plug-in connector has paid attention on three topics:multi-physics numerical modeling, contact failure mechanism under cyclic thermal loading and short circuit current impact, and contact failure physical simulation and experiments.During GIB equipment operation, power frequency current can make alternating electromagnetic field thus induce eddy current in metal enclosure, temperature rise and vibration of GIB equipment can be generated by power loss and electromagnetic force which are produced by interactions between current carriers and alternating electromagnetic field. Contact forces and contact radiuses among contact spots in GIB plug-in connector which exerted by the contact spring holding force and conductor gravity have been analyzed, based on analysis, the current constriction effect and electromagnetic force in plug-in connector are simulated by modeling contact bridge between contact surfaces. A electromagnetic-mechanical coupled FEM model of GIB which is constrained by the external circuit has been developed by A-I field-circuit coupling method. Electromagnetic force which is derived from electromagnetic field calculation is used as load inputs in mechanical dynamics analysis, and validity of calculation model is demonstrated by comparing with semi-analytical imagine current method and GIB tank vibration tests.The operation conditions of GIB plug-in connectors are often influenced by the interactions among electromagnetic, thermal and mechanical force effects. An electromagnetic-thermal-mechanical coupled FEM model has been developed based on analyzing the contact condition and influence factors of GIB plug-in connector, the relationship between contact material properties and temperature rise has also been considered. The validity of calculation model is demonstrated by temperature rise tests with different currents. Distributions of electromagnetic, thermal and mechanical field of GIB plug-in connector have been analyzed by numerical model, results show that there are significant differences of contact forces, current densities and temperature rise among individual contact spots under action of conductor gravity, proximity effect and skin effect thus seriously affect the reliability of GIB plug-in connector. The established numerical model can reflect the contact status under different operation conditions, and provide an effective tool for contact failure analysis and design of GIB plug-in connector.During equipment operation, cyclic thermal loading induced by alternating loading currents and environment temperature may make relative motion between conductor and connector thus cause contact failure of GIB plug-in connector. A friction-sliding numerical model of GIB plug-in connector has been developed by low-velocity friction theory, and relative motion characteristics between conductor and connector under cyclic thermal loading (alternating temperature by loading current and environment temperature) has been analyzed. Theory research results are verified by physical simulation experiments, and the contact failure mechanism of GIB plug-in connector can be summarized as relative motion between conductor and connector under cyclic thermal loading (alternating temperature by loading current and environment temperature) thus make insufficient conductor insert depth. At the same time, typical contact failure field case has been analyzed by the numerical model, and further validates the theoretical research on contact failure mechanism.The electromagnetic force and temperature rise of GIB plug-in connector under short circuit current impact will make accelerated contact degradation. Focus on the contact failure mechanism of GIB under short circuit current impact, the dynamic electromagnetic force behaviors in different parts of GIB under different short circuit conditions have been analyzed by the FEM calculation model. Results show that short circuit electromagnetic force characteristics in GIB equipment are influenced by fault conditions and arrangement of conductors. Under the impact of short current, relative displacement between conductor and connector can be induced, contact force can be significant decreased and temperature rise in some contact spots can reach melting point of contact material, which accurate the contact failure process thus reduce operation life of GIB plug-in connector. Results can provide theoretical basis for dynamic stability and thermal stability of GIB plug-in connector.Internal electric field distortion even flash over of GIB equipment can be induced by the contact failure and then melting of GIB plug-in connector. For analyzing the influence of connector failure and melting on electric field distributions, A static electrical field calculation model of GIB equipment which contains the connector contact failure has been developed. Electrical field distributions of the GIB equipment with needle on shield, melting metal droplets and melted metal particle on inner surface of tank have been obtained by numerical model, the progress from contact overheating to break down has been deduced on analysis results.Contact failure mechanisms of GIB plug-in connector under cyclic thermal loading and short circuit current impact has been researched by the theory analyzing, numerical modeling and physical simulation experiments. Research result may guide design, manufactory and field delivery of GIB plug-in connector, besides bring theory supplements for operating maintenance and condition monitoring of equipment. With engineering significance and practical application value, clearly research on contact failure mechanism can prevent overheating fault of GIB connectors, thus ensure stable operation of power system.