Study Of Ferroresonance Overvoltage And Its Suppression Method

In medium voltage power supply system, in order to monitoring voltage at the substationbusbar, potential transformer is usually equipped at the busbar, which neutral is directlygrounded. Due to the nonlinear excitation characteristics of electromagnetic potentialtransformer, under the external disturbances, ferroresonance overvoltage may be caused. Inungrounded distribution systems, the ferroresonance that results from the saturation ofpotential transformer (PT) occurs frequently and harms the power systems. Some methodshave been put forward to depress ferroresonance. But because the theory of ferroresonancehas not been studied clearly, and ferroresonance is very sensitive to the system parameters,these methods are not very universal. So it has not only academic significance, but alsopractical value to carry on in-depth research on ferroresonance phenomenon and suppressionmethod.In this paper, the principle of ferromagnetic resonance is analysised. Based on this basis,the ferromagnetic resonance condition is given, and ferro-resonance process for qualitativeanalysis of the actual system is studied. When simulating ferroresonance, the accuracy of thePT model is very important. A new PT model is put forward in this paper considering thenon-linear of exciting characteristic and core losses. The practical modeling algorithm is alsoworked out. The model and parameters of over head line are studied, and the model of a35kVpower network is built up. The ferromagnetic overvoltage caused by lightning is simulated.The simulated results shows that As the loop parameters and the different conditions ofexternal excitation, the may bring the subharmonic frequency, power frequency or highfrequency ferromagnetic resonance. Harmonic elimination scheme of ferroresonance35kV system is proposed, and put theminto practice field running proves that the theoretical analysis, simulation and harmonicelimination scheme is correct and reasonable.