Research On Detection Technology Of Single-phase Grounding Fault With Line-broken In Distribution Line

As an important part of the power system,distribution network is mainly responsible for the function of power distribution.The reliability and quality of power supply directly affect the social production and economic development.It is also closely related to people's daily life.In order to improve the reliability of power supply,non-effectively earthed neutrals is widely used in MV and LV distribution network in China,which mainly includes neutral point direct grounding mode and neutral point through arc suppression coil grounding.The fault of distribution line is a major factor threatening the safe and stable of power system,because of the complicated distribution network,the gap between urban and rural construction,the imbalance of maintenance and the unreasonable structure of the distribution network etc.In the research field of distribution line fault,small current grounding fault(Single-phase grounding fault)is the focus all the time.However,there are few studies on single-phase breaking fault and the complex fault caused by the live wire grounding after breaking.Accordingly,lacking protection against the damage caused by unbalanced voltage and current after fault is a short board for the development of distribution automation and smart distribution grid.With the intensification of the energy crisis and environmental pollution,the Distributed Generation(DG),which is based on the clean energy,has developed rapidly.More and more DG is connected through distribution network,which makes the fault characteristics of traditional distribution network changed and the traditional fault protection strategy inapplicable.The output characteristics of Inverter Interfaced Distributed Generation(IIDG)are closely related to the control strategy,and the fault features are more complex.Therefore,we should give full consideration to the impact of IIDG on fault characteristics when analyzing.In order to solve the problem of fault detection and fault type diagnosis for single-phase grounding fault with line-broken in distribution network,this paper takes full account of the influence of neutral grounding mode and transition resistance,and analyses the fault of traditional distribution line by symmetrical component method.According to the analysis of the traditional distribution line,the selection criterion of single-phase broken fault and the diagnosis criterion of the type of single-phase grounding fault with line-broken are summarized.Then,analyzing the control strategy and output characteristics of IIDG,and establishing the IIDG mathematical model.The main research content is as follows:(1)In order to solve the problem of fault line detection of single-phase broken fault in traditional distribution lines,a sequence network is established by using the boundary condition and symmetric component method.Through the analysis of sequence network the change of voltage and current can be obtained.Summary of fault features: The positive sequence current of the faulted line is the same as that of the negative sequence current,and it is half of the positive sequence current amplitude before the fault.The change of positive sequence and negative sequence current of non-faulted line is not obvious.(2)In order to solve the problem of fault line detection and fault type diagnosis for single-phase grounding fault with line-broken in traditional distribution network,based on existed analysis,two kinds of single-phase grounding faults with line-broken are further analyzed,one is the grounding points on the power side,the other is the grounding points on the load side.Considering the influence of neutral grounding mode and transition resistance,the change of zero sequence voltage is obtained by symmetrical component method.Then,based on the amplitude and phase information of zero sequence voltage,a diagnosis criterion of the type of single-phase grounding fault with line-broken is presented,and verified by simulation.The criterion can detect whether the grounding fault occurs after single-phase broken fault and determines the type of fault.(3)In order to determine the output characteristics of IIDG,the control strategy of IIDG is analyzed,and the IIDG mathematical model is established.When an asymmetrical fault occurs,in order to control active and reactive power and inhibit negative sequence components,the decoupling control strategy using double DQ transform is adopted.This control strategy can control the positive sequence and negative sequence components of the inverter control system respectively,so that the inverter control system can always output positive sequence active power whether or not the line has a fault.Establishing a mathematical model and building a simulation model.(4)In order to analyze the influence of grid-connected IIDG on diagnosis criterion of the type of single-phase grounding fault with line-broken,the IIDG is equivalent to the form of controlled current source or controlled negative value resistance.The equivalence is based on the control strategy and output characteristics of IIDG.Rebuilding the sequence network with IIDG equivalent model by using symmetric component method and analyzing the single-phase grounding fault with line-broken in the distribution network.The influence of grid-connected IIDG on the diagnosis criterion of the type of single-phase grounding fault with line-broken is summarized.The correctness of the theory is verified by simulation.The works done in this paper will provide theoretical support for improving the fault protection system of distribution network and the analysis of broken line fault in distribution network with grid-connected IIDG,and promote the development of distribution automation and intelligent distribution network...