Research On Overvoltage Characteristics Of HVDC's Main Equipment Based On ASCCC

As the core equipment of HVDC transmission system,converter directly determines the performance and stability of HVDC transmission system.Traditional LCC systems usually have vibration and noise problems of converter transformer and the power grid commutation problem,while CCC technology's overvoltage and other defects also limit its application.Based on the above background,a new type of converter is proposed by the project group.Because the converter has the function of absorbing harmonic and reactive power compensation,it is called Absorption and Shunt Capacitance Commutated Converter(ASCCC).This paper mainly studies the overvoltage characteristics of the main equipment in the converter station under the converter.It is of great significance to the insulation level and the safe and reliable operation of the later master system.The main work is as follows:Firstly,the types of overvoltage in converter stations are studied,and the forms and hazards of temporary overvoltages and operating overvoltages are expounded.The mechanism of overvoltage transmission to the DC side and the overvoltage mechanism in the converter station are emphatically analyzed.Then the topology,working principle and advantages of ASCCC are analyzed.The mathematical model of ASCCC and the interconnection model of ASCCC and AC system are derived from the features of ASCCC circuit.According to the characteristics of reactive power compensation of Absorption and Shunt Capacitance(and Shunt Capacitance),the parameter selection principle of ASC and the ASC configuration scheme of the converter station are studied,and the influence of ASC into the HVDC system on the voltage and current parameter of the primary device is analyzed.Then based on the actual engineering parameters of Jiuquan Hunan + 800kV UHV direct current transmission project,the inverter side is changed to ASCCC structure,and the electromagnetic transient simulation platform of the ASCCC-HVDC system is set up through the PSCAD/EMTDC simulation software.A mathematical model is established for different equipment.The steady state voltage characteristics of converter transformer,converter valve and shunt capacitor are derived.The relationship between the steady-state voltage characteristics of the main equipment and the value of the shunt capacitance is analyzed.The transient overvoltage of main equipment in converter station of ASCCC-HVDC system is studied,and the influence degree of several typical faults on ASCCC-HVDC operation is analyzed.Finally,based on the knowledge of circuit theory,the changing and transient characteristics of the ASC switching operation are analyzed and calculated,and the possible overvoltage of the ASC reclosing operation is analyzed by simulation,and the influence of the ASC reclosing on the change of the flow and the voltage on the converter valve.