Neutral point treatment and earth fault suppression

Earth fault management in medium voltage networks involves assessing of customer interruptions, challenges in fault clearing processes and safety issues. The major advantage by allowing sustained earth faults is the avoidance of customer interruptions. However, the network operation with sustained earth faults does not only include welfare. The paper will generally discuss the advantages and disadvantages of operating the network with sustained earth faults. In addition, in the paper, the Helsinki medium voltage network and the developments in neutral point treatment and network operation during earth faults will be outlined. The paper presents the earth fault analysis in the Helsinki 10 kV network and compares the results to a reference analysis. Based on the analysis, the paper presents the possibilities and limitations of a sustained operation with earth faults. The paper also presents the strategy steps of managing sustained earth faults as well in the 10 kV and 20 kV areas and the required long term development steps.