Mitigation of Stray Current Intrusion by the Neutral Series Capacitance of Transformer

Subway stray current invades urban power grid, causing dc bias of transformer. In this paper, the simplified model has been used to quantitatively analyze the division coefficient of stray current at the neutral of transformer, and the method has been proven by using the measured data. Furthermore, this paper analyzes the principle of neutral series capacitor blocking dynamic stray current, and puts forward the analysis model of transformer neutral dc blocking capacitor method. The suppression efficiency is defined to quantify the effect of neutral series capacitance. The results show that the neutral series capacitor suppression efficiency is over 99% for dynamic stray current in the spectrum range of 0 ~ 2.5 Hz.