Detection method for single-pole-grounded faulty feeder based on parameter identification in MVDC distribution grids

Detection of the single-pole-grounded faulty feeder in ungrounded or high-impedance grounded MVDC distribution systems is a challenging task, because such fault cannot provide persistent and considerable fault current. To solve this problem, zero-mode fault network of radial MVDC system is analyzed and an algorithm based on identification capacitance to ground of the feeder's zero-mode fault network is proposed. Then on the premise of external fault, the mathematical model of zero-mode network is built for each feeder. The transient zero-mode voltages and currents of each feeder are utilized to calculate the capacitance to ground of zero-mode fault network. For the healthy feeder, the zero-mode fault network is its own zero-mode network and the calculated capacitance to ground is positive. But zero-mode fault network of faulty feeder is an equivalent zero-mode network of its background healthy system and its calculated capacitance to ground is negative. This characteristic is the basic theory of the proposed algorithm. Considering the calculation error, the polarity of the average value and deviation of calculated capacitances and the number of positive calculated capacitances are used to detect the faulty feeder. The simulation results have shown that the proposed algorithm is accurate, reliable and more sensitive to detect high impedance ground faults.