Research On Network Relay Protection Technology Of Medium Voltage System Based On Smart Substation

When the interphase short circuit or single-phase grounding fault happened in the bus or line of the medium voltage distribution system,the traditional relay protection has some problems such as selectivity and poor speed.Based on the smart substation GOOSE message network to realize the interaction and sharing of the fault information of each interval protection unit,this paper aims to realize the network protection technology by using the multi-source information fusion method.Firstly,based on the "two layers and one network" architecture of smart substation,this paper analyzes the network protection objects and information domains.It also designs the network protection organization structure and implementation strategy of the intelligent substation medium voltage system.Secondly,this paper analyzes the information standardization process of smart substation,the message transmission mechanism of GOOSE and the information transmission network latency.The OPNET simulation software is used to analyze and model the data flow of intelligent substation.The simulation research is carried out on the effects of different networking modes,network bandwidth,load and other factors on the real-time performance of the information transmission network under fault conditions.The simulation results verify that the network protection has good real-time performance.The paper also makes a research on the technology that can further improve the real-time information transmission.Based on the principle of directional comparative longitudinal protection,the information acquisition process of network power direction and the initiation criterion and protection algorithm of interphase short circuit network protection are studied in this paper.At the same time,this paper analyses the protection fault-tolerant algorithm in the case of incomplete information acquisition.The model of 110/10 kV power supply system is built by MATLAB /Simulink.The simulation results prove that the designed network protection can meet the "four requirements" of relay protection in all kinds of short-circuit situations.Meanwhile,it has good fault tolerance.Integrating with the advantages of the traditional ground fault steady-state protection principle,this paper proposes the principle of ground fault comprehensive protection that based on network zero-sequence full-current power direction information.According to this principle,the single-phase ground fault network protection algorithm is proposed.The failure support degree and fault melting value coefficient are introduced in the algorithm,in which the fault lines can be more accurately identified.This paper also takes the fault-tolerant algorithm under incomplete fault information acquisition into consideration.The simulation results show that the protection decision results are accurate.