Mechanism Study Of PT Fuse Breaking Caused By Switch Type Arc Extinguishing In Distribution Network

With spreading use of cable lines in 10 kV distribution network,the single-phase earthing capacitance and current increases rapidly,and the traditional arc suppression coil is faced with shortage of capacity and poor effect of arc suppression.Thus a sort of switch type arc extinguishing is gradually promoted.However,over-current occurs frequently on traditional PT(potential transformer)during arc extinguishing,which threaten the stability of power system operation.Therefore,by using electromagnetic transient calculation and high voltage test,the mechanism of fuse breaking is identified and the most optimal suppression measure is figured out in this thesis,which brings significant theoretical and engineering value in promoting safety and reliability of this equipment.Combining with actual structure of switch type arc extinguishing device,the thesis theoretically describes the single-phase grounding and disappear action during arc extinguishing,which is likely to motivate ferroresonance and low frequency nonlinear oscillation.The thesis also theoretically analyzes the characteristic of those two kinds of transient process,and concludes both advantages and disadvantages of common suppression measures.Based on actual substation parameters,an improved single phase PT model which considering hysteresis loss,eddy current loss and deeply saturated excitation characteristic is used in calculation.The ?-i data is accurately calculated by using piecewise linearization and recursive method.Based on the magnetic circuit of three-phase three-limb transformer,a simplified circuit model is proposed to simulate One-piece resonance resistance 4PT,while the positive sequence and zero sequence parameters are acquired through corresponding experiments.Considering the rapid increase of the single-phase earthing capacitance and current,both ferroresonance and low frequency nonlinear oscillation are simulated to study the characteristic of current through PT.Simulation results show that low frequency nonlinear oscillation is the main cause of PT fuse breaking,and the capacitance and the zero sequence damping value are the major influencing factors.A test platform of 10 kV neutral-ungrounded system is also established,and series of single-phase grounding and disappear experiments are carried on under two different capacitance current value and three kinds of single phase PT.The test results coincide with the simulation results,which verifies the accuracy of the simulation model.Research results show that ferroresonance is likely to happen even when system parameters exceed Peterson resonance section,causing half wave inrush current and endangering PT fuse.Research results also show that when system parameters are suitable,even quasi-periodic resonance can be motivatedwith high amplitude of inrush current.Considering two types of ferroresonnce suppression measures are commonly used,simulation,high voltage test and field confirmatory test are carried on to compare both ferroresonnce suppression and inrush current elimination effect,and to analyze their advantages and shortcomings.Finally,the effect of frroresonnce suppression measures on accuracy of zero sequence voltage measurement is researched.Research results show that 4PT wiring is the most optimal measure of suppressing ferroresonnce and fuse breaking when switch type arc extinguishing is on operation.