Research On Calculation And Monitoring Method Of Temperature Rise In Gas Insulated Bus Bars

Gas insulated bus bars (GIBs) are one of the paramount components in power systems. Once failures happen to GIBs, huge metropolitan areas will suffer the loss of power supply, affecting the reliability of power system and leading to large economic loss and negative social impact. Overheat caused by contact degradation is one of the most frequent failures in GIB. The contact resistance becomes larger than normal value after contact degradation occurs, which increases the contact temperature and will worsen the contact condition. Contact degradation is a self-accelerated process that after a long period of gradual increasing contact resistance escalates rapidly, causing local melting and finally leading to short circuit failure. Thus, in order to avoid catastrophic fault of GIB, substantial efforts need to be devoted to develop techniques for overheat condition monitoring of the equipment after it has been put into service.In this paper, four perspectives which are the numerical calculation method of temperature rise, three-dimensional (3-D) temperature field distribution, prototype experiment and temperature-rise monitoring method of three-phase enclosed GIB are investigated. The main research works of this dissertation are shown as follows:The electric resistivity of GIB is temperature dependent, which makes the thermal analysis a coupled multi-physics problem.3-D numerical model of steady-state eddy current field based on A, φ-A method is established, which is discretized with Galerkin finite element method (FEM). The boundary conditions and mesh method proper for multi-physics of the solution region are given. As the contact resistance is difficult to be modeled, the structure of the contacts is simplified and the contact resistance is considered as a resistor between the contact and the conductor. For better accuracy, temperature dependent electric resistivity is considered and iteration method between eddy current and temperature fields is used to calculate the power losses in GIB. The result shows that contact power loss cannot be ignored in the thermal analysis for it is40%of the total loss in GIB.Numerical calculation methodology of temperature rise based on the multiple species transport technique is proposed, in which the temperature dependent thermal properties of the fluids are considered, and the ambient air is introduced into the solution region. The conjugate heat transfer problems both inside and outside the GIB are simultaneously analyzed, eliminating the need of convective boundary condition on the tank surface and the calculation of convective heat transfer coefficients. The proposed method is validated against the analytical method, traditional single-species FEM model and experiment. It is proved to be more accurate and able to show the reality of heat transfer both inside and outside the GIB. The convective heat transfer coefficient distribution on the tank surface shows that the convective heat transfer is less understood in the traditional methods. The proposed mothodology provides a new method for the thermal analysis of power apparatus.Considering the contact power losses,3-D coupled fluid and thermal model of GIB is established. The boundary conditions are given and the temperature distribution is calculated. The contacts are proved to be necessary in the thermal model of the GIB. The influence of the ambient temperature, load current and contact resistance on the temperature rise of the GIB is investigated with the proposed model, providing guidance for the overheat condition monitoring of GIB.The effectiveness of the3-D coupled fluid and thermal model of GIB and the reasonablility of the equivalent contact resistance are validated against prototype experiment in the conditions of both balanced and unbalanced load currents. According to the experimental results, the influence of unbalanced load current on the temperature distribution of GIB is small and can be ignored, and the relationship between the contact and tank temperature rises is determined.The temperature distributions of the outer tank surface under different load currents and overheating positons of the contacts in GIB are investigated. The best installation scheme of the temperature sensors on the tank surface in the condition monitoring process is determined and the fault diagnosis method is established. The overheat failure happened in either phase of the contacts can be detected with the two sensors installed on the hot spots corresponding to the contacts of phase-A and-C. Based on the whole temperature rise, the temperature difference in the length direction and the symmetrical temperature distribution of the tank, the overheat failure can be diagnosed and located. The results will provide technique support for the condition monitoring of temperature rise in GIB.