Study Of Ferroresonance Overvoltage In Distribution System Based On LabVIEW

In order to watch three phase-to-ground voltages, inductive Potential Transformers (PTs) are connected to the bus of power substation or generator in ungrounded power distribution system. As the iron core of inductive Potential Transformer (PT) has a nonlinear magnetizing characteristic, if the inductance of it matches the line-to-ground capacitance under transient impact, ferroresonance may be caused in ungrounded distribution system. Ferroresonance not only causes system over voltages, but also may cause PT damage even explosion, so it is a serious threat to the safe operation of power distribution system. Therefore, researching the mechanism of ferroresonance, simulating it and exploring effective measures for ferroresonance suppression, have important practical significance to the safe and stable operation of power distribution system.Firstly, the mechanism of ferroresonance overvoltages was analyzed in theory in the paper. Then an equivalent mathematical model of a 10kV simplified distribution system was established. On the basis of the work done above, a simulation model of a 10kV simple distribution system for simulating ferroresonance was built using the saturable transformer model in MATLAB\Simulink. Factors influencing ferroresonance, such as the line-to-ground capacitance, magnetizing resistance, DC resistance of the high-voltage winding and magnetizing characteristic of the potential transformer, were simulated respectively. Simulation results revealed as follows:the line-to-ground capacitance mainly determined types of ferroresonance caused by system faults; magnetizing resistance, DC resistance of the high-voltage winding and magnetizing characteristic of the potential transformer principally determined whether ferroresonance occurred or not and its amplitude.And then functions of a power quality monitoring system based on LabVIEW were extended further. On the basis of the original functions, the program that could detect and analyze ferroresonance overvoltage was realized using LabVIEW, with the wavelet transform as core detection algorithm. After function extension, the power quality monitoring system not only could monitor many traditional power quality indexes, but also could identify the type of ferroresonance and locate the time when the ferroresonance suddenly occurred exactly. Therefore, the ratio of performance to price and practicality of the whole monitoring system were improved greatly.At last, homologous simulation models of four measures for ferroresonance suppression, such as neutral point on the high-voltage side of PTs connecting with nonlinear resistor, neutral point on the high-voltage side of PTs connecting with single PT, neutral point of system grounding via arc suppression coil and open delta winding of PTs connecting with damping resistor, were built respectively. According to the simulation results, the advantages and disadvantages of each measure for ferroresonance suppression were analyzed further. Next, an intelligent system for ferroresonance suppression based on LabVIEW was designed, based on the principle of open delta winding of PTs connecting with damping resistor for ferroresonance suppression. The intelligent system for ferroresonance suppression could automatically judge the run status of power distribution system. After the occurrence of ferroresonance, the devices of the intelligent system for ferroresonance suppression were started quickly. So the result of ferroresonance suppression was very good. When the intelligent system for ferroresonance suppression based on LabVIEW designed in the paper is integrated with the power quality monitoring system based on LabVIEW extended in the paper, many functions can be realized in one system and the cost of critical places in power system such as automation substation is reduced greatly. The integrated system will have wide application prospect and practical value.