Abstract:

The technical level of grounding design of stepdown substation of Metro station in China has to be improved so as to accord with the IEC standards and ChinaNational standards. In this paper, the disadvantages of multipoint grounding and the advantages of onepoint grounding are analyzed based on studying the grounding scheme of neutral point in low voltage side of stepdown substation of Metro station; and then a rational grounding scheme is proposed. The power frequency overvoltage and fault voltage of 0.4 kV system induced by grounding fault of 35 kV system and the resistance of weak current system are analyzed. It is concluded that the demand of grounding power resistance value of less than 1 Ω is irrational;the structural reinforcing bars should be used as natural grounding electrode; therefore the manual grounding network is not necessary.

Key words: Metro station, multipoint grounding, onepoint grounding, grounding resistance, equipotential bonding