Ferroresonance Phenomena in Medium Voltage Systems
The paper deals with the analysis of the formation of ferroresonance in MV systems. The analysis is focused on ferroresonance caused by instrument voltage transformer (IVT) connected to the outlet of the tertiary winding 10,5 kV autotransformer 400/110 kV. A non-linear element in this case is the magnetic circuit of IVT Ferro-resonance, in this case exhibits similar to the imperfect ground connection. The two phases may arise overvoltages in two phases and undervoltage in one phase. The rate of these adverse events is given by the initial conditions and load of switched circuits when circuit is switched on. Similarly, other exhibit nonlinear chaotic circuits. The main adverse effects include overvoltage that can damage the power system components well as a significant harmonic distortion. For prevent this problem the authors conducted the case study resonant circuit as a whole. In this case it is magnetic circuit of the IVT, in which saturate a hysteresis the magnetic flux depending on the winding currents. In the article before are described two approaches to determine hysteresis curves. The first approach is based on laboratory measurements of the properties of IVT, the second approach, developed by the authors is based on the measurement of nonlinear resonant circuit as a whole. The developed method additionally incorporates speech hysteresis. A non-linear circuit is described by the set of differential equations. Based on the knowledge of the basic parameters of the individual elements of the system is possible to analyze the resulting ferroresonance by solution system of differential equations in software Wolfram Mathematica. The analysis shows that the circuit can be for certain parameters even behave chaotically. It is, however, only certain ranges of the parameters. The simulation also confirms that ferroresonance is manifested like ground failure. To limit the exposure of ferroresonance is based on the analysis carried out several possible actions. The first measure is the choice of another type of the measuring voltage transformers with higher rated voltage, which is contrary with the applicable standardization. The purpose of the working area where the linear ITV report, therefore, no saturation of magnetic flux. Another possible measure is to increase the load the measured outlet or secondary circuit IVT. This measure does not prevent ferroresonance, but can't restrict it. The bottom line is dumping of resonant circuit.