Research On Fault Line Selection System And Fault Location Method For Distribution Network

The 10 KV distribution network in China is mostly a radial network and adopts the non-neutral grounding system.When the common single-phase-to-ground fault occurs,the fault line selection problem has not been well resolved because of the small fault current.The implementation of DGs changes the traditional single-power centralized power supply structure,which makes the network turn from a traditional one-way flow radiation network into a two-way power multi-source network.The fault location problem of DG distribution network should be solved urgently.When the single-phase-to-ground fault occurs in the neutral-ungrounded system,it is very important to accurately determine the fault line.This will improve the operational reliability and reduce the economic losses caused by power failure.In this paper,we designed a faulty line selection system of the radial neutral point ungrounded power network,which includes several parts such as the fault line selection platform,the local intelligent zero sequence transformer,the integrated automation protection system and the remote diagnosis server,and it realizes the detection,selection,control,storage and other functions.The fault line selection algorithm is the core of fault line selection platform.The system adopts zero sequence current ratio method,zero sequence current phase method,first half wave method and wavelet analysis method to improve the line selection accuracy.Local intelligent zero-sequence transformer,integrated automation protection system and remote diagnosis server connect with the fault line selection platform through communication channel,to achieve data transmission,system monitoring,remote assistance and other functions.The fault line selection algorithm requires the data synchronization between the local intelligent zero sequence transformers,so in this paper,a method of data synchronization based on CAN bus is proposed.Finally,the experiments show that data synchronization method can meet the requirements of line selection algorithm and can select the line correctly.For the fault location problem of DG distribution network,this paper presents a fault location method based on the current phase difference in different protection point after fault,which is realized by the communication network.The symmetrical fault can be located by using the phase difference of the A-phase current calculated by the protection of both ends of the line after fault.If the asymmetrical fault occurs,we use the current phase angle information after the fault in three protection points.This method only needs to use the current information of the protection point and does not need the voltage,which reduces the transformation of investment costs.The simulation results show that this method is applicable to symmetrical three-phase short-circuit and asymmetrical two-phase short-circuit fault.It can correctly judge the fault in the zone,the fault outside the zone and the bus fault.In this paper,the problem of fault line selection and fault location in DG distribution is solved.In this paper,the fault line selection system developed for the radiation distribution network and the research on the fault location of the multi-power network after DG access is of great significance to discover and deal with the fault of the distribution network and improve the reliability of power supply.