Reactive Power Compensation Of Controllable Reactor Of Transformer Type In EHV/UHV Transmission Line With Series Capacitor Compensation

Development on the technologies of Extra high voltage(EHV) and Ultra high voltage(UHV) transmission are promoted by the needs of long-distance and large-capacity transmission, and the reactive power compensation based on controllable shunt reactor is an important issue for EHV/UHV power transmission system. Controllable reactor of transformer type(CRT) is essentially a high-impedance type(multi-winding) transformer in which the conducting state of controlling- winding can be realized continuously. In this dissertation, the characteristics of reactive power compensation and the arrangements on harmonic-suppressed winding of CRT are analyzed in depth, and the compensation degree of controllable shunt reactor are studied deeply in the case of uniform series capacitor compensation. In addition, the influence of compensation on power transfer and maximum efficiency of transmission are researched.(1) The body structure, working principle and operating characteristics of CRT are obtained by the theory analysis of core reactor and the reactor core. Two kinds of different arrangements on harmonic-suppressed winding with LC filters are studied in this dissertation in terms of the equivalent circuit of three-winding CRT and then the MATLAB simulation model of CRT with harmonic-suppressed winding is built. And it can be concluded that the effect of harmonic-suppressed is optimum when harmonic-suppressed winding is placed between control-winding and work-winding through the analysis of the total current harmonic distortion rate for two different winding arrangement of CRT. For CRT with harmonic compensation winding, the studies suggest that capacitive currents will generated through filter branch and injected into circuit by CRT even reactive capacity of LC filter reaches minimal when control loop of control thyristor winding is completely disconnected, which showed that CRT has a capacitive reactive power compensation performance.(2) The basic theory, the voltage distribution of transmission line, as well as the principle of active power transmission and reactive power compensation with a series capacitor are researched symmetrically in the dissertation. The impact of series capacitor on the compensation degree of sectional placement controllable shunt reactor is analyzed deeply then the amended mathematical expressions of compensation degree of controllable reactor with uniform series capacitor compensation are derived carefully. The results of mathematical analysis and simulation show that series capacitor compensation expands further compensation range of shunt reactors, and the segmented distance of controllable reactor is effected by the compensation degree of series capacitor and with the increase in the degree of series compensation, segmented distance increases.(3) The structure arrangement and characteristics of the different lines with shunt reactor are researched and summarized. The influences of shunt reactor placement on maximum power transfer and maximum efficiency of transmission are derived mathematically based on the equivalent circuit of distributed parameters and two-port model of long EHV/ UHV transmission lines under the conditions of series-parallel compensation when shunt reactors are placed on the sending or receiving end and the different positions toward the midpoint of the line with series capacitor compensation continuous changes. And the results of mathematical analysis and simulation with aid of some typical data of 500kV、1100kV transmission lines show that maximum power transfer and maximum efficiency of transmission will vary continuously with the location of shunt reactor when it is located between sending or receiving end and the center series capacitor.Furthermore the power transfer is also affected by the compensation degree of shunt reactor,and the maximum power transfer and maximum efficiency of transmission will decrease with the increase in compensation degree.In addition, the power loss of compensate line for shunt reactors and the impacts of voltage sensitive loads on the series-parallel compensated transmission lines are studied deeply.(4) The definition of compensation effectiveness of shunt reactor is proposed firstly in this dissertation. The influence of shunt reactor placement on compensation effectiveness are studied numerically and then the effects of line length and parallel reactance compensation degree on the effectiveness of compensation are analyzed further under the condition of series compensation.The results show that maximum compensation effectiveness was obtained when shunt reactor was located at the central of transmission line. The degree of compensation effectiveness will decrease gradually with the location of shunt reactor approaching to sending or receiving end, and they were same at sending and receiving end. The compensation effectiveness will decrease with the increase in length of transmission line. Furthermore in the range of compensation degree compensation effectiveness will decrease with the increase in shunt compensation degree but it is hardly affected by the series compensation.