Transformation scheme of neutral grounding mode for distribution network with high cable ratio

With the development of city scale and the demand of city beauty, transforming overhead lines into underground cables is becoming a new trend in distribution network, especially in urban areas. The distributed capacitance current of power cable is much greater than that of overhead line. The traditional neutral point grounding mode of distribution network, such as the neutral point ungrounded and grounded through arc suppression coil is under greatly challenged. The increase of the capacitance current in the distribution network during fault conditions will enhance the capacity and volume of the over compensated arc suppression coil, which will bring inconvenience to the maintenance and operation of the power grid. At present, many distribution networks are transforming the neutral grounding mode, some of which are grounded by low resistance or large capacity arc suppression coil. Being grounded by a low resistance has a good performance of limiting the over-voltage of the system and improving the operation characteristics of the relay protection. The impact of the power cable on the capacitance current was analysed in detail in this paper. Taking Suzhou distribution network as an example, this paper analyses the neutral grounding mode in urban power grid transformation. The result shows when the power cable ratio reaches a certain degree, the neutral point of distribution network must be grounded through low resistance or distributed arc suppression coil. The grounding scheme is helpful for the smooth transition of urban distribution network transformation, and improves the stable and reliable operation of power system.