| Capacitor Voltage Transformer, or CVT is an important electrical equipment in power system of 110 kv or above voltage levels. Since CVT is mainly composed of capacitance and nonlinear inductance components, subharmonic ferroresonance is easily stimulated under transient conditions. At present, the main methods of inhibiting ferromagnetic resonance is to install dampers in the secondary side of CVT. Considering the high performance of quick-magnetic saturated damper, it is used more widely among several kinds of dampers.Research on selection of resistance value, which plays a vital role in the damping effect of dampers has hardly been found. We can only get a large upper range of resistance value by some formulas. Since the calculation model is too simple, calculation result is often very different from engineering practice. Actually, the optimal value of resistance of damper is usually determined by plenty of ferromagnetic resonance tests which cause a lot of manpower, material resources of the waste. Besides, the research on CVT simulation model of ferroresonance which based on electromagnetic transient calculation software ATP-EMTP has improved the accuracy of selection of damping resistance, meanwhile cost too much calculation.Considering ferro resonance and oscillation circuit, an optimized calculation model of the selection of damping resistance value was built. According to the equivalent circuit of CVT, the thesis established the loop equation of this equivalent circuit first. Then damping conditions were derived with this loop equation. Finally a damp condition was derived theoretically. Combined with the data of 220 k V CVT obtained from Nissin Electric(Wuxi, JiangSu) Co., Ltd, the value of series resistance was calculated. Simulation results were consistent with the experimental, which showed that the proposed theory is validated and it can be use to design CVT with no ferro-resonance under any condition.In order to fully demonstrate the correctness of the optimization model, the range of resistance value calculated by the optimized calculation model was verified by means of modeling and simulation and field experiments. In simulation, a simulation model of CVT was built in EMTP-ATP to obtain the range of resistance. Then the ferroresonance simulation was conducted in this range of resistance. In experiments, the ferroresonance experiments were conducted with a series of damping resistance selected from the range of resistance determined by the optimized calculation model. The results of simulation and experiments proved that the model can solve the problem of the selection of CVT damper damping resistance. The optimized calculation model provided a new idea for the selection of saturation damper damping resistance and has important guiding significance for the design of CVT. |
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