Research On The Relay Protection Method Of Agricultural Network With Distributed Photovoltaic Power Generation

Photovoltaic power generation system with its clean,efficient characteristics has gone into thousands of households in vast rural areas.As people enjoy the convenience brought by the photovoltaic power generation,too much grid-connection has also brought a considerable challenge to the control and operation of the distribution network.Therefore,it is imperative to improve and upgrade the relay protection scheme of the traditional rural distribution network in order to improve the safe operation level of the rural distribution network.This paper takes Sihedang 66 kV substation in Chaoyang as an example.The influence of photovoltaic power generation system on distribution network fault current and relay protection is analyzed,different relay protection improvement schemes are proposed for different load types of circuits based on the analysis before.Firstly,this paper describes the operation status,wiring mode,main electrical equipment and protection configuration of Sihetang 66 kv substation.Then,takes the Zhengzhangzi line and Fuyuan #1 line as examples,the fault current calculation of three points of faults occurred in the case of photovoltaic power sources not connected and two distributed connected respectively is carried out,and the influence of photovoltaic power supply capacity on the fault current is analyzed.In addition,the influence of the access of distributed photovoltaic power on current protection and distance protection in MATLAB was simulated by taking the 10 kV Zhengzhangzi line and Fuyuan #1 as examples.Simulation results show that the location and capacity of photovoltaic power supply have obvious influence on current protection,and even lead to protection misoperation.Therefore,it is necessary to improve or upgrade the original current protection.Combined with the reclosing configuration of 10 kV Zhengzhangzi line,the influence of distributed photovoltaic power supply access on reclosing is analyzed and improvement measures are proposed.Sihedang 66 kV substation has different types of lines,which are represented by 10 kV Zhengzhangzi line and Fuyuan #1 line.According to these two different types of lines,different optimization and transformation schemes are proposed in this paper.According to 10 kV Zhengzhangzi line,current protection scheme based on communication means is introduced.Based on the idea of pilot protection,the improved scheme can accurately judge the faults inside and outside the zone according to the direction of electric quantity,and only cut the fault lines by means of communication.It not only meets the selectivity of protection,but also can reliably and accurately remove faults,reduce the probability of customer power failure,and improve the reliability of power supply.Distance protection is introduced for 10 kV Fuyuan #1 line,which can quickly locate the approximate location of faults,providing guarantee for important load users to quickly locate the fault location,reduce the loss of power failure and improve the quality of power supply.In this paper under the environment of MATLAB,photovoltaic system access to the distribution network distance protection improvement scheme simulation is carried on,simulation results show that the distance protection transformation scheme will not cause malfunction by the short-circuit current direction changes due to the access of distributed photovoltaic power supply.It will not lose selectivity due to the increase of short-circuit current caused by the access of distributed photovoltaic power supply,which verifies the feasibility of protection and transformation scheme.The two improved schemes above effectively solve the potential misoperation of traditional current protection in the case of distributed power supply access,improve the reliability of the protection,and control the unnecessary investment cost,which has certain application prospects.