Research On Single-Phase Grounding Protection Of Distribution Network Containing DG

At present,renewable energy such as solar,wind,geothermal,tidal energy has been vigorously developed in the world through government guidance,policy incentives and other measures.Most of these environmentally friendly new energy sources are connected to the grid through distributed generation.Most of the faults in distribution network are single-phase grounding faults,and other faults are mostly developed from single-phase grounding faults.Traveling wave protection technology can effectively solve the detection and removal of single-phase grounding fault.Based on this,a single-phase grounding fault traveling wave protection scheme on distribution network containing DG is proposed,and applicability of traveling wave protection to single-phase grounding fault in distribution network with DG is analyzed and verified.The output current characteristic of distributed generation when short-circuit fault occurred in distribution network is studied,which is a current source model controlled by positive sequence voltage of PCC after fault.The current characteristic of the theoretical analysis is verified by PSCAD simulation.When short-circuit fault occurs in distribution network,the output current characteristic of distributed generation can be equivalent to the current source model controlled by positive sequence voltage of PCC after fault.So it has no effect on traveling wave protection,which detects high frequency transient component to determine the faulty feeder.It is proposed that traveling wave protection is suitable for single-phase grounding fault of distribution network with DG.The applicability of traveling wave protection is verified by PSCAD simulation.By analyzing refraction reflection characteristics of faulty traveling wave and wavelet transform,it is concluded that the polarity of initial voltage and current traveling wave of fault line is opposite,and the initial traveling wave can be detected by the modulus maxima of wavelet transform,which is the basis of traveling wave direction criterion.According to the refraction characteristics of traveling wave at discontinuous point of wave impedance,the refraction of initial traveling wave in distribution network with DG is analyzed,and the traveling wave direction criterion is proposed to apply to single-phase grounding fault in distribution network with DG.The simulation results show that the maximum polarity of fault line wavelet transform is opposite.Traveling wave protection can effectively monitor and remove single-phase grounding fault in distribution network with DG.Based on the above conclusions,by analyzing the criterion of traveling wave protection,considering the influence of lightning wave,operation wave and other non-fault waves,as well as the characteristics of small amplitude of fault traveling wave signal,the power frequency action criterion is proposed as a supplement.The influence of arc grounding on protection is analyzed.The single-phase grounding arc characteristic based on cybernetics model is analyzed,and the criterion of arc grounding is proposed as a supplement.Based on the above criteria,a complete single-phase grounding fault protection scheme of distribution network with DG based on traveling wave protection is proposed.Based on ATP-EMTP,the DG-containing distribution network is modeled and simulated,and the applicability of the proposed protection scheme is verified.For single-phase faults occurring in the upstream,downstream and adjacent feeder locations of DG,the proposed traveling wave criterion is satisfied and the protection scheme is reliable.The simulation results show that the proposed protection scheme is not affected by the number of feeders,the length of healthy feeders and the fault distance.The simulation analysis of the operation characteristics of protection schemes under different fault conditions shows that traveling wave protection will be unfavorable under extreme fault conditions.