Adaptability Of Relay Protection During Start-up Process And Equivalent Model For AC Protection Setting Calculation Of MMC-HVDC

As a new generation of DC transmission technology,MMC-HVDC has broad application prospects in the power grid.The startup of MMC-HVDC is a complex transient process.The fault characteristics during startup process may be different from the fault characteristics during normal operation process,which has an impact on the relay protection setting.In addition,due to the low voltage ride-through capability,the MMC-HVDC system still runs on the network,which has an impact on the AC short-circuit current.In this context,this thesis studies the fault characteristics of MMC-HVDC suring startup process and the adaptability of relay protection,and establishes an equivalent model of MMC-HVDC suitable for AC protection setting calculation.In section ?,the DC-side fault characteristics and the adaptability of DC pole protection during start-up of MMC-HVDC system is studied.The dynamic process of MMC-HVDC is described theoretically,and the fault characteristics of DC unipolar grounding and bipolar short-circuit are analyzed in detail.For the typical DC pole protection,the difference of protection related quantities between fault in start-up process and fault under normal operation is analyzed.The adaptability of the ex-isting protection to the start-up process fault is analyzed.Through simulation based on detailed electromagnetic transient model of the MMC-HVDC system,the fault characteristics of DC-side fault and adaptability of typical protection is verified.New suggestions are put forward for the setting calculation of protection relay.In section ?,the AC-side fault characteristics and the adaptability of typical protection during start-up of MMC-HVDC system is studied.Based on the control characteristics,the fault characteristics of MMC-HVDC during start-up process and nomal operation under AC side faults is analyzed.Through simulation based on detailed electromagnetic transient model of the MMC-HVDC system,the fault characteristics of AC-side fault and adaptability of typical protection is verified.The simulation verifies the fault characteristics of the AC side fault during the startup process,and analyzes the adaptability of various types of protection to the startup process fault.In section ?,equivalent model of MMC-HVDC for AC protection setting calculation during AC side fault is proposed.From the standpoint of AC protection setting calculation,principles of simplifying analysis of MMC-HVDC are proposed,and an equivalent model of MMC-HVDC is established.Based on the control strategies,the response characteristics of MMC-HVDC under access bus faults is analyzed.And a quantitative index for evaluating the influence of MMC-HVDC on AC protection setting calculation is proposed.