Reactive Power And Voltage Control Of UHV AC Transmission System Based On MCR

In order to develop long distance bulk transmission system, and optimize allocation of the interregional resources, the research work on UHV AC transmission technology is vigorously conducted in our country. The reactive power balancing and voltage controlling problem play a vital role in the following construction of UHV AC transmission system. It is a critical technical problem pressing for solution, and further study should be conducted in order to propose solution as early as possible. Among the shunt compensation technology available now, the compensation technology based on magnetic control reactor is a fairly ideal compensating schema in solving the reactive power balancing and voltage controlling problem of ultra high voltage transmission system.The working principle and structure of magnetic control reactor were analyzed briefly. Using the piece-wise linear model of the magnetic characteristic curve, the magnetic characteristics of the ferromagnetic material was depicted. On the basis of the model, analysis of the magnetic valve was made and its magnetic equivalent circuit model was established. According to the magnetic equivalent circuit model, mathematical model of the reactor was founded. Besides, the simulation model of the magnetic control reactor was established using the UMEC transformer model of the power system electromagnetic transient simulation software PSCAD. The characteristics of the reactor were analyzed particularly, including control characteristics, responding speed and harmonic characteristics. In order to solve the low responding speed problem under the traditional control method, the control method of using DC chopper composed by IGBT was proposed to improve its responding speed. As for the current wave distortion problem of the reactor, a harmonic suppression method using inter-phase coupling reactor was proposed also. Intensive study on phase shifting principle of the inter-phase coupling reactor was made through simulation and experiment analysis. The winding turn determination problem was solved for a certain phase shifting angle. Detailed analysis of the harmonic suppression principle of inter-phase coupling reactor was made also.Using the distributed parameter model of transmission line, the overvoltage effect caused by distributed capacitance of UHV transmission line was analyzed and the line voltage distribution law was concluded. Study on overvoltage limit effect of the shunt compensation reactor was made based on the UHV AC pilot project. In order to solve the reactive power balancing and voltage controlling problem of UHV transmission system, comparative analysis was made for the shunt compensation strategy. Simulation analysis correspond to two conditions were made and the short comings existing in the two conditions were pointed out. One condition is that only fixed reactor was used, the other is fixed reactor coordinate with low voltage reactor and capacitance. At last, the compensation strategy was proposed that fixed reactor coordinate with controllable reactor. And the capacities of each kind reactor were determined. Through adjusting the controllable reactor with voltage close loop control strategy, the voltage of the system can be stabilized and the transmission ability can be improved. At the same time, the strategy is a relatively economical one for the capacity of the controllable reactor accounts for only part of the total capacity of the compensation reactor.