Active Interference Arc Suppression Method And Technology In Neutral Ungrounded Distribution System

Compared with neutral grounding by arc suppression coil and small resistance,neutral grounding system has great advantages in power supply reliability,but there are still some problems such as intermittent arc overvoltage,low accuracy of phase selection and low accuracy of line selection.The active interference arc suppression technology not only transfers the fault point current through bus grounding,so as to plays a good role in arc suppression.Moreover,active line selection is adopted in the process of bus grounding,which greatly improves the accuracy of fault line selection.But the operation of fault phase selection is added,and fault line selection can only be carried out on the premise of correct fault phase selection.Therefore,phase selection and line selection in neutral ungrounded distribution system will be the key technology of arc suppression device.In this paper,arc extinguishing method and technology for neutral ungrounded distribution system are studied in the following aspects.(1)Firstly,in the introduction part,this paper summarizes the application scope,basic principles and advantages and disadvantages of arc suppression methods and fault line selection technology at home and abroad.Then in the second chapter,the working principle of fault phase grounding technology and its advantages in fault line selection in distribution system are introduced.Then,the working characteristics and components of active interference arc suppression device using fault phase grounding technology are introduced.Finally,the technical difficulties existing in the arc suppression technology applied to the arc suppression device are analyzed.(2)An accurate model of single-phase-to-ground fault in neutral-point ungrounded system is established.Considering the three-phase voltages under different transition resistances,a phase selection method suitable for various transition resistances is proposed.Then,the phase selection method is improved according to the unbalance existing in the actual system,and the pre-fault system is considered comprehensively.Phase voltage vector method is used for fault phase selection in the original unbalance.At the end of the phase selection,it is necessary to judge whether the phase selection is correct or not.If the phase selection error occurs,it is necessary to quickly detect and correct the phase selection results to prevent further expansion of the fault scope.Finally,simulation in PSCAD/EMTDC shows that this method has high phase selection accuracy.(3)After the action of active interference arc extinguishing device,the magnitude and flow direction of capacitive current in distribution system will change greatly.The zero sequence current of fault line and non-fault line is calculated before and after switching-on.According to the difference of zero sequence current between fault line and non-fault line,three methods of line selection are proposed.According to the advantages and disadvantages of the three methods,the strategy of route selection is designed.In addition,in the process of fault line selection,it is also necessary to distinguish between line fault and bus fault.Finally,the correctness of the route selection method and process is verified by simulation in PSCAD/EMTDC.(4)The operation of fault phase selection and fault line selection combined with fault detection,fault type discrimination,signal sampling time point,permanent fault and transient fault are designed respectively,and integrated into a complete operation process.And the process is developed into an arc suppression device,which is tested in a practical system to verify the practical application value of the technology.