Application of computational fluid dynamics to predict the temperature-rise of gas insulated switchgears
Accurate temperature-rise prediction in gas insulated switchgears (GIS) is necessary to reduce the number of heat-run tests during the product development process. An electromagnetic-thermal-fluid coupled model using computational fluid dynamics (CFD) is developed to predict the temperature-rise of a 110-kV three phase GIS in common tank type. The GIS includes the three-position isolation/ground switch and the circuit breaker insulated with SF6 gas at 5 bar. In this model, the contact resistance, eddy current, skin effect, thermal flow, and thermal radiation are considered. The ohmic losses generated in the conducting components are calculated through the harmonic electromagnetic analysis with MAXWELL 3D software. Then, the predicted losses are imported to the commercial CFD software ANSYS Fluent to fulfill the thermal simulation. Based on this model, the distributions of heat generation, gas velocity, and temperature-rise are obtained. The results show that the maximum power density and temperature-rise both occur at the contact zones of the three-position isolation/ground switch. To verify the developed model, the temperature-rise tests of the GIS are carried out at 2200 A. The simulation and measurement results are close with a maximum error of 3.99 K.
Influence of mechanical faults on electrical resistance in high voltage circuit breaker
Abstract The health of contact sets is one of the most critical factors for the breaking capacity of the high voltage circuit breaker. Dynamic resistance measurement is considered to be an effective method to assess the erosion degree of the contact sets. However, the electrical resistance may be influenced by many other mechanical faults which will cause the misdiagnosis of the contact sets. At present, the influence mechanism has not been clarified. Therefore, the influence mechanism and degree of mechanical faults (stress relaxation, fatigue, friction) of contact sets is studied in the present paper. Firstly, the accelerated stress relaxation experiments of CuW alloy, the fatigue experiments of contact sets, and the mechanical friction experiments are carried out to obtain the relationship between the fault degree and the electrical resistance. Secondly, the fatigue fracture, micromorphology, energy dispersive spectroscopy, and metal loss of the contact sets are investigated. Thirdly, the stress distribution and fatigue fracture of the contact finger is analyzed by the finite element method. Based on the above works, the fatigue damage, and the partial loss of the contact fingers are considered to be the most distinct influence on the electrical resistance curves.
Thermal Analysis of Sealed Electromagnetic Relays Using 3-D Finite Element Method
Up to now, it is difficult to test the inner temperatures of sealed electromagnetic relays. In this paper, the temperature distribution of a sealed electromagnetic relay is obtained by using 3-D finite element analysis. The quality of thermal simulation results depends on the accuracy of both the modeled heat sources and heat sinks. Due to the high performance requirements of sealed electromagnetic relay it is interesting to know not only the temperatures of the conducting parts but also the thermal impact on the plastic components. Therefore, the non-metallic parts of the sealed electromagnetic relay (including the air within the device) are now part of the model. In order to improve the accuracy of simulation, the contact radius is calculated in advance. The relationship between convection heat transfer coefficient and temperature and how to consider connecting wires boundary condition are also researched here. Finally, the temperature distribution of a sealed electromagnetic relay is obtained by this method. Comparisons with experimental results confirm its validity.