Study And Analysis Of PT Low Frequency Non-line Oscillation And Suppression Measure In Power Distribution Networks

Along with the development of city distribution network, grounded capacitance of power system larger as overhead lines lengthen and cables enlarge. Ferroresonance and low frequency non-liner oscillation caused by potential transformer and grounded capacitance always occur in the system neutral ungrounded. Appears high pressure insurance of PT frequent fuse even to burn down phenomenon, it is enormous threat to the safety of electrical power system.The existing each kind elimination way have the good suppression effect to ferroresonance, but for longer system line, the parameter ratio of PT inductance and grounded capacitance has surpassed the ferroresonance region, it enters low frequency non-liner oscillation region, it can produce large overvoltage and overcurrent in PT.In this paper, a systemic simulations using Electro-magnetic Transient Program is presented. It is simulation about all kind of ferroresonance and low frequencynon-liner oscillation caused by single-phase earth fault disappeared in 6kV isolated neutral system. It presents some correlation curves connected system parameters with overvoltage and overcurrent, and some representative wave forms diagrams about overvoltage and overcurrent. It discussed suppression effect of the existing each kind of elimination way to ferroresonace and low frequency non-liner oscillation. A new elimination resolve overvoltage and overcurrent caused by ferroresonance and low frequency non-liner oscillation, and it cans guarantee the safety and the reliability of power system.