Discussion Of Incorrect Action Of Zero-sequence Current Protection In Low Resistance Grounding System In Dongguan 10kV Power Grid

For a 10kV distribution system mainly comprised by electric cables, grounding system with neutral connecting point grounded by small resistance is widely used in Dongguan distribution lOkV network for many of its advantages as follow:first it can minimized the effects of a grounded fault on equipment; secondly the cost for such equipment is comparatively lower; thirdly for some overhead conductors, it can be accompanied by some automatic-reclosing protection equipment to enhance the power reliability.During the past few years, grounding faults in the 10kV distribution network vary significantly in terms of types, also are more and more complicated, which resulting in protection system malfunction and consequently harm the reliability of the system operation. This paper, based on the Dongguan lOkV distribution network, which utilizing the grounding system of neutral point grounded by small resistance, introduces the mechanism and operation principles of the grounding system with small resistance grounded, analysis in depth about the malfunction of the of the protection system, and points out the reasons for this miss-operation in terms of objective reasons and subjective reasons such as design imperfections, equipments inadequacy and installation errors. Solutions to the problems are also pointed out in the paper. The proposed solutions can be used to regulate the operation of the zero sequence protection system, thus enhance the reliability of the lOkV distribution systems and prevent future possible similar failures.