| From the perspective of energy crisis and environmental protection,countries have turned their attention to the development and utilization of renewable energy.Photovoltaic power generation technology emerged as the times require.With the increase of photovoltaic gridconnected scale,the integration of photovoltaic power sources has changed the original system structure,and has brought many impacts on the operation of the original distribution network,affecting the electrical energy quality and the stability of the power grid,etc.,and have a great impact on the relay protection and ranging.In view of the influence of the photovoltaic power supply access system on the protection of the distribution network,this paper first deduces through theoretical formulas,and concludes that the grid-connected position of the photovoltaic power source,the photovoltaic capacity and the short-circuit position all have an impact on the protection of the upstream and downstream.The distribution network model and actual simulation verify the correctness of the theory.Aiming at the impact of photovoltaic integration into the system,this paper adopts a new setting method for current protection after photovoltaic power plants are connected to the distribution network.This method is based on the output current of the photovoltaic inverter control strategy and real-time monitoring of photovoltaic Output power,use the intersection of the two to get the output current of the photovoltaic at the moment,use this value to superimpose,and re-set the original current protection calculation,and the simulation calculation shows that this scheme improves the current protection to a certain extent.Based on the complex characteristics of the distribution network,in order to quickly isolate the fault in the event of a fault,this paper improves it by learning from the longitudinal differential protection used in the main network and combining the characteristics of the photovoltaic power supply.With the increase of electricity load,it is more and more common for the power supply to be connected to the system in the form of T connection.The existing literature studies the situation that multiple photovoltaic power sources are connected to the system in the form of T connection.Therefore,this section analyzes the characteristics of the distribution network.A pilot protection scheme suitable for multiple photovoltaic power sources connected to the distribution network is proposed,which are an improved pilot protection method based on impedance criterion and an improved pilot protection method based on voltage criterion.The simulation results show that these two schemes are Both are suitable for the situation where multiple photovoltaic power sources are connected to the distribution network,and all have high sensitivity.In order to improve the efficiency of emergency repairs by distribution network personnel,it is not enough to isolate the fault.Therefore,it is necessary to accurately locate the fault location of the distribution network with distributed photovoltaic power supply connected to the grid.This chapter proposes an accurate fault location method for distribution network with distributed photovoltaic power based on multi-terminal traveling waves,analyzes the characteristics of traveling waves in the system with distributed photovoltaic power,and discusses the feasibility of the traveling wave positioning method.By choosing two measuring points in the network,a set of fault distance values independent of traveling wave velocity is calculated,the variance is used to characterize the discrete degree of the set of data,the fault branch is identified,and then the quartile method is used to accurately locate the fault point..The simulation analysis shows that the method can realize the precise location of the fault point,and can overcome the influence of inaccurate wave velocity error or unknown wave velocity. |
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