Study On Overvoltage And Overvoltage Protection Schemes For Thyristor Controlled Reactance Series Compensation By Adjustable Coupling In High Voltage Transmission Lines

A study for overvoltage protection of TCSC(Thyristor Controlled Series Capacitor)device is an important part of series compensation device design, which directly affects investment and safe function of the whole series compensation device. Thyristor Controlled Reactance Series Compensation by Adjustable Coupling is a new-style thyristor controlled series compensation method. This thesis mainly introduces overvoltage and overvoltage protection design of the device.Firstly, overvoltage protection problems of FSC(Fixed Series Capacitor) and TCSC are introduced. The main contenst of a study on overvoltage and overvoltage protection of the device are concluded. Then overvoltage is analyzed theoretically under different working conditions of the device such as throw-in , tap changing and fault.. The analytical method of over-current and overvoltage of the device at different short-circuit fault spot is put forward. An effect of thyristor control on over-current and overvoltage of the device is analyzed. Aimed at serious overvoltge of short-circuit fault, relevant overvoltage protection schemes and effectual thyristor control strategy are introduced. Electromagnetic transient program PSCAD/EMTDC is used to simulate and analyze overvoltage of line breaker throwing-in the device, over-current and overvoltage of representative short-circuit fault spot with thyristor control or no. Overvoltage protection level and maximum allowable energy dissipation of MOV are ascertained.The study results show that voltage of capacitor is not high and in allowable area. The transient overvoltage peak value of mutual inductance exceeds its maximum work voltage magnitude, but its duration is very short and there is no risk. For internal three-phase short-circuit fault, over-current and overvoltage of the device is quite serious. After thyristor control strategy is adopted, over-current and overvoltage drop dramatically, as well as the capacities of MOV. After Spark Gap is equipped, the pass-current capacities of MOV further decrease and cost of overvoltage protection effectively reduces.