A New Compensation Scheme For Second Arc Current On Four Circuit Parallel Transmission Lines

As the development of power grid, the cost of the construction of transmission lines is increasing rapidly because of the land is more expensive, especially in some developed area in China. The land needed for the transmission lines now is a restraint for the development of the power grid. The four circuit parallel transmission lines can be constructed in the future power grid as they are more economic and can save the land and enhance the capacity of the transmission line. For four circuit parallel transmission lines, the coupling between different circuits is very considerable, and this can bring large secondary arc current, which means that the traditional secondary arc current compensation scheme using the one-circuit compensation is not effective.In this paper, the four circuit parallel transmission lines with completely transposed condition for every circuit are analyzed. According to the coupling between the transmission lines, the calculation method for secondary arc current and recovery voltage is proposed for different kind of faults. As the coupling parameters of the three phases in one circuit are symmetrical and parameters between different circuits are not totally symmetrical, we take the average coupling parameters into consideration to get the symmetrical parameters and decouple the symmetrical parameters.According to the decoupling parameters, the secondary arc current compensation and recovery voltage limiting scheme using four circuit shunt reactance is proposed. The mew scheme is compared to the traditional one circuit shunt reactance, and the results by PSCAD/EMTDC show the effectiveness of the new compensation. The new compensation can limit second arc current to 10A in 100ms after fault, which is a low level within the threshold for practical engineering in China. The optimized compensation using some switch is proposed for maintenance condition. And the compensation scheme can be effective for both ordinary condition and maintenance condition by changing the switch.For multiple voltage four-circuit parallel transmission lines, the lines with different voltage level can’t be combined by shunt reactance, so this paper analyze the effectiveness of one-circuit compensation scheme and two-circuit compensation scheme. The results by PSCDA/EMTDC shows the proposed compensation scheme is effective to limit the secondary arc current to 10A for transmission lines within 285km. The compensation scheme for four circuit parallel transmission lines is significant for the construction and safety of four circuit parallel transmission lines.