Research On Principle And Technology Of Relay Protection For UHV Transmission Line

The serious fault transient process of UHV transmission line brings many new problems to relay protection, some of which haven’t yet be solved well so far. By comprehensive and systematic researches on the fault process, practical scheme of relay protection for UHV line is studied, and meantime filtering algorithm and protection scheme with better performance are discussed in this thesis.The main contents are shown as follows.By studying on main frequency component of the transient noise during the fault, a novel estimation method is presented in this thesis, which can accurately and quantitatively analyse the transient characteristic of UHV line, and provides base for researching the performance of protection scheme and filtering algorithm.Aiming at the problem of transient overreach while applying the traditional algorithm and scheme of distance protection for UHV line, two novel smooth algorithms based on Half Fourier algorithm are put forward to mend the extent of overreach. A practical scheme for preventing transient overreach of distance protection for UHV transmission line is presented and the corresponding threshold parameters are obtained by comprehensive simulation. The protection scheme presented in this thesis has been adopted in the microcomputer protection equipment for high voltage transmission line, and the operating result is satisfactory.To improve the range and operating speed of distance protection, the thesis discusses the least square algorithm with the model of main frequency and presents a real time estimation method of main frequency. Based on this, a novel self adapting scheme of distance protection is presented, which can effectively reduce the extent of transient overreach for external fault, increase the protection range and meantime quicken the operating speed for internal fault.To know the algorithms of relay protection better and advance their filtering capability, phasor algorithms composed with a pair of orthogonal filters are systematicly expounded. By regarding the coefficient of window function as the independent variable, the universal discrete time-domain expression and maximum amplitude frequency characteristic of the phasor algorithm based on the orthogonal Sine and Cosine filters are deduced. According to the filtering demand for some characteristic harmonic in relay protection, the thesis presents a design method of searching for the optimal coefficient of window function by taking the interturn protection of generator as an example, which makes the algorithm can efficiently filter the characteristic harmonic as well as suppress other noncharacteristic harmonic components.Based on analyzing different selection methods for the zero-sequence current compensation factor and their influences on the operating range of protection, the measured impedance along the line is simulated and analysed when the fault occurs in the UHV1000kV Huainan-Shanghai project with double-circuit parallel line on the same pole. Basd on this, the practical setting scheme of distance protection for the UHV1000kV Huainan-Shanghai project is presented in this thesis; that is to say, the zero-sequence current compensation factors of both zone Ⅰ and Ⅱ protection are set to the high value, which ensures not only the security for zone Ⅰ protection but also the sensitivity for zone Ⅱ protection of distance relay.