Abstract:

The resonant grounding system will go through a transient state when phase to earth fault occurs in Coal mine 6kV network, and the zero-sequence current of all the lines will generate a transient pulse in this period. In order to analyze the relationships between the initial amplitude, duration of the transient pulse and the earthing resistance, the earth capacity, and fault time, the paper deduces zero-sequence current expressions when phase to earth fault occurs in single substation mode and multi-substation mode. Meanwhile, related expressions are also given. It is found that the transient pulse polarities between the fault lines and normal lines are completely opposite, and the transient pulse’s amplitude of fault line is the largest among all the lines. Moreover, the amplitude of transient pulse is proportional to the sin of fault angle and inversely proportional to earthing resistance. Besides, all the normal lines have the same width of transient pulse, which is smaller than that of fault line, and which is proportional to earthing resistance. Last, the simulation by matlab proves the correctness of these conclusions.

Key words: transient state, pulse polarity, pulse amplitude, pulse width, resonant grounding system