Suppression strategy for rail transit ground current in transformer neutral points

Abstract

The ground current of rail transit contains direct and harmonic components, which will lead to many undesirable effects on substation transformer neutral points. The traditional suppression strategy can only suppress the direct current in the ground current. At the same time, the traditional switching strategy does not consider the dynamic changes of the direct ground current and may cause the direct ground current at the surrounding neutral point to passively exceed the limit. Firstly, in this paper, the change of the direct and harmonic ground current and the influence of the rail transit passenger load on ground current were analyzed based on the measurement data. Then, considering the harmonic ground current of rail transit, a suppression strategy of harmonic ground current was designed. Besides, a calculation model for neutral point direct ground current distribution was established. Finally, an optimal switching strategy of the blocking device was presented to minimize the global direct ground current and maximize the economy of overall devices. Using the test case of 220kV substations surrounding an actual metro line, the ability of suppressing the harmonic ground current was verified. Compared with conventional switching strategy, the effectiveness and correctness of the optimal strategy for the direct ground current based on blocking devices were verified.