Analysis And Protection Based On Fault Transient Characteristics Of Distribution Network With Distributed Generation

With the continuous maturity of distributed generation grid-connected technology,the impact of distributed generation on grid operation is becoming more and more prominent.In terms of relay protection,the diversification of distributed generation control strategies,flexible grid-connected locations and weak feed-in characteristics during faults all make the short-circuit current distribution characteristics of traditional distribution network more complex.At the same time,due to the vulnerability of power electronic devices to withstand overcurrent,protection devices need to locate fault conditions more quickly and accurately.These factors make the protection scheme of traditional distribution network face great challenges.Therefore,for the distribution network with distributed generation supply,the research on the transient protection scheme with richer information and faster positioning is conducive to improving the "four characteristics" of relay protection,which is of great practical significance for helping the construction process of new power distribution system.In order to solve the problems of inaccurate selection results of characteristic frequency band near the phase voltage crossing point of the low-current grounding system with distributed generation supply,and the sampling of the protection device is not synchronized,the phase frequency characteristics of the distribution line under the zero-mode network are analyzed in detail,and a new line selection method based on the transient reactive power correlation detection in the characteristic frequency band is proposed.Firstly,the transient zero-mode current of each outlet line and the differential zero-mode voltage of the bus are cross-wavelet transformed,and the area with strong correlation and stable phase difference is used as the time-frequency window for fault selection.Then,the transient reactive power is calculated by using the amplitude and phase information of the transient voltage and current signal in the time-frequency window.Finally,according to the characteristics of the opposite flow direction of the transient reactive power of the faulty line in the characteristic frequency band and the transient reactive power of the non-faulty line,the correlation function algorithm is used to detect the correlation of the transient reactive power of each outlet line and determine the faulty line.Theoretical analysis and simulation results show that the proposed method is not affected by the initial angle of faults,synchronization error,noise interference and other factors,and has strong adaptability to high resistance and arc-flash grounding.In order to solve the problem of fault section location after phase short circuit and indirect short circuit in distribution network with distributed generation supply,combined with the characteristic difference between line mode voltage and current fault components in the upstream and downstream networks of fault points,a centralized protection scheme of master station based on fault direction information is proposed.Firstly,starting from the analysis of the phase frequency characteristics of each component in the line die network,it is concluded that they all have the first inductive frequency band,and the selection principle of the characteristic frequency band is elaborated accordingly.Secondly,according to the polarity relationship between the transient line-mode voltage and the differential line-mode current at each node in the characteristic band,the fault direction information is given to the switch.Finally,each node uploads the local switching information to the master system,and uses the integer linear programming algorithm to locate the fault segment with high fault tolerance.The simulation results show that the data required by the protection scheme is short in time,which is not affected by the control strategy and access location,and is suitable for the situation that there is a T branch in the distribution line.