| Gas insluated switchgear (GIS) can reduce insulation space and save the substation area through enclosing all typical equipments of power substation besides the transformer, such as the circuit breaker, disconnecting switch, voltage transformer (PT), current transformer (CT) and the bus into metal tank filled with SF6gas. Compared with conventional air insulated substation (AIS), GIS has the advantages of higher reliability, less space and stronger ability to resist environment contamination, therefore in recent years has widely used in the power system in our country. However, as the early operation of the GIS equipment aging and the defects of new equipment design and installation, GIS busbar connector overheating fault occurs frequently on the rising, which may seriously burn the connector and lead to discharge between the conductor and shell or nearby conductors and cause short circuit accident, threat the safe and stable operation of power system. And the accident treatment must disintegrate GIS equipment to the maintenance, power supply recovery time and the degree of environment pollution, which are greater than the conventional substation. So the research of GIS bus connector overheating fault analysis have important engineering significance and economic benefits. In this project, on the basis of GIS bus connector overheating fault mechanism research and analysis, the electrical contact theory and multi-physics field coupling finite element method were used to calculate the GIS busbar connector’s contact resistance and contact temperature rise. The GIS busbar joint overheating fault mechanism was proposed by studying the load current, short circuit current impact, environmental temperature changes, the contact resistance degradation, insert depth of GIS bus conductor on the temperature rise of the connector’s busbar.In terms of GIS bus connector’s contact resistance calculation, the different mechanical structures of GIS busbar connectors was firstly analyzed and the experience formulas for calculation of contact stress and contact resistance. Through the study of related theory and algorithm of contact mechanics, contact area of GIS busbar connector was calculated, respectively, based on smooth macro elastic contact Hertz contact model, rough elastic surface contact GW contact model and rough plastic surface contact Bahrami contact model, and GIS busbar connector contact resistance were calculated according to the theory of Holm constriction resistance. The calculation results of different models are compared with the field test results, and the results showed that the Bahrami contact model based on rough plastic surface contact model can reflect the physical phenomenon of GIS busbar connector accurately, the calculation result is close to the value of the loop resistance test results. Suitable GIS busbar joint contact resistance calculation method provides the necessary input parameters to calculate the temperature rise of GIS busbar connector.In terms of GIS bus connector contact temperature rise calculation, the project firstly analyzed the basic theory and computation process of finite element method of current conduction, thermodynamics and solid mechanics. The method to study the multiple physical coupled field and the methods of matrix and the load transfer in finite element algorithm, an electrical-thermal-structucal coupling model was also established to calculate the temperature rise. The electrical contact resistance (ECR) and thermal contact resistance (TCR) between the conductor and connector were calculated through analyzing structure fields. The power loss was obtained using the current conduction analysis and as a heat source in the calculation of temperature field in GIS busbar connector. The calculation model can reflect the influence of electrical-thermal-structural coupling on GIS busbar connector contact temperature rise, so that they can reflect the dynamic change characteristics of contact resistance and contact temperature rise in GIS busbar connector. A prototype of three-phase enclosed GIS busbar temperature experiment physical model was designed and entrusted in order to verify the correctness of the calculation model. Temperature rise experiments under different load currents were carried out at indoor experiment field cable room at Wuhan High Voltage Institute of China Electric Power Research Institute and the experiment results with the calculation result have good consistency, which showed that the calculation model can accurately calculate GIS busbar connector’s temperature rises under different contact pressures and load currents, can provide a new means for the GIS busbar overheating fault analysis and monitoring.In terms of GIS bus connector thermal fault mechanism research, comprehensive analysis and research mainly focused on GIS busbar connector temperature rise during load current changes, contact resistance degradation and short circuit impact using multi physics field coupling finite element calculation models. Special research was taken out to study the influence about the insert depth of GIS bus conductor on the temperature rise the busbar connector. Research results showed that the load current, the normal range of contact resistance degradation and the short circuit current shock could not cause the thermal damage and the GIS busbar connector overheating fault. On the basis of the actual GIS busbar joint burned accident investigation, the influence of insert depth of GIS bus conductor on the temperature rise of the busbar connector was analyzed. The results showed that the insufficient insert depth of conductor completely may cause abnormal temperature rise and overheating fault of GIS busbar connectors, which laid a foundation of further study for the mechanism of GIS bus connector overheating fault.GIS busbar connector temperature rise calculation and overheating fault mechanism research based on multi physics field coupling finite element analysis provide theoretical basis for overheating fault mechanism analysis and on-line monitoring of GIS busbar connector, which has a practical significance in ensuring the GIS equipment security and the stability of power system. |
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