Analysis of sequence impedance of 345 kV cable systems with special bondings using ATP

Zero sequence impedance is an important parameter for accurate estimation of unbalanced fault current in power systems. In case of high voltage cable systems, there are various kind of bonding schemes resulting in more complicated zero sequence circuit compared to that of overhead transmission systems. Besides, the zero sequence circuit can be much more complicated when the cable system has a single-point bonding because of the rather complicated distribution of zero sequence current between cable sheaths grounding and the earth. In this paper, sequence impedances of 345 kV 4 circuits cable system with various bonding schemes is analyzed using ATP (Alternative Transient Program). The calculation results showed that the conventional method of zero sequence calculation can be erroneous in case of underground transmission lines mainly caused by its complicated and nonlinear return path of ground fault current.