Monitoring Of AC Intrusion In Substation DC System

The power and power system of substation includes AC system and DC system,and DC system is the guarantee for safe and reliable operation of substation.Failure of DC circuit grounding,short circuit or alternating interference may cause malfunction of relay protection device.In the actual operation process,the power supply circuit of the power plant and substation is more complex,and the accident frequently occurred in the AC channeling into the DC circuit,which threatens the security of the system.How to prevent communication into DC circuit and reduce the loss caused by communication and channeling into the DC circuit is a problem that must be solved by various operating units.Therefore,the continuous on-line monitoring of the DC system must be carried out,and the rapid diagnosis of DC system failure must be realized.Starting from the composition and structure of DC system,this paper makes theoretical analysis of AC channeling into DC.Because of the diversification of alternating current into DC system,the equivalent model of DC system is set up in this paper.The main factors that affect the voltage of the relay coil are analyzed and discussed under the different position of alternating current entry point in the DC system,and some suggestions on preventing the misoperation of protection from AC crosstalk in practical engineering are put forward.In recent years,during the operation of the domestic power network,there are many accidents caused by the inrush and rejection of relay protection and control devices caused by the AC incoming DC system.In this paper,starting from two typical protection misoperations caused by alternating current and direct current,the process of accident is described in detail and objectively,the causes of the accident are analyzed in depth and the solutions are put forward.Then,the principle of AC channeling into DC monitoring is expounded,and the two monitoring methods of AC channeling into DC system: differential voltage method and isolation capacitance method are described and analyzed respectively.Finally,this paper proposes a monitoring device for DC system inrush AC fault in substation,which can monitor DC system inrush AC voltage,realize the monitoring and alarm function of AC inrush DC system in substation,and improve the reliability of DC system operation.All functions of the device are modular design,including voltage sampling module,control module,alarm module,power supply module,display module,command input module,etc.The function and working principle of each module are described in detail in this paper.Finally,through field experiments: voltage test and alarm test,the function of the monitoring device is verified,which proves that the monitoring device can realize the predetermined function.