Study On Problems Of Relay Protection In Four Parallel Lines On The Same Tower

With the development of power system, four parallel transmission lines appear quickly. Because it can save the transmission corridor areas and has the capability of taking larger capacity, four parallel transmission lines would be used widely in the power system. As there are many kinds of complicated faults and mutual impedance, the relay protection of four parallel lines will face lots of new challenge. Aiming at some problems of relay protection on four parallel lines, this paper has done some research as follows:1. The performance and application of the distance relay protection in the four parallel lines are discussed. The simulation model of the four parallel lines based on EMTP-ATP and corresponding programs for different kinds of distance relay are developed. After that, the paper compares the performance of those protections.2. Through analyzing the network characters and different operation conditions, the influences of mutual impedance between different lines on zero impedance distance relay protection are discussed. Remarkable improvement of grounding distance protection can be achieved by calculating the zero sequence compensating coefficients under different operation conditions. And a new grounding distance protection using the zero-sequence currents of normal lines as compensation component is also introduced.3. Based on the characters of the negative sequence current network with a single line asymmetry fault of four parallel transmission lines, the formula of negative current can be figured out. Analysis results indicate that when the asymmetric fault occurs, the phase angle of negative currents ratio between fault line and normal line will be about 0°or 180°.This character can be used to identify fault types, and the fault line can be selected according to the magnitudes of the currents of fault line and normal line. Moreover, the ratio of different loops'negative current can be obtained, which shows that the ratio value is only present as linearly with the fault distance. By using this function and the measured values of currents, the fault location can be obtained. The location algorithm and fault line selection method avoid complex decoupling calculation and can be applied conveniently. Lots of simulations have testified the validity of the new method.4. Taking account of the zero-sequence network of parallel transmission lines, a new fault location method is proposed. It eliminates the effect of the transition resistance in principle. The analysis and calculation of the algorithm are simple and convenient. The simulation result indicates that the algorithm is useful and not influenced by the fault resistance.5. At last, the paper summarizes the results of the study and puts forward the directions of future study. impedance, negative sequence current...