Abstract

AC subsea cables are grounded at both ends via two metal layers, namely metallic screen (normally made by lead for high voltage subsea cable as radial water barrier) and armor, which consists of wires. This topology leads to induced current in the two grounded layers. Field test shows that occasionally unbalanced induced current is observed in grounded layers (lead and armor) between two cable ends. The difference of induced current between two cable ends can be as high as half of the load current. The cause for such unbalance is not clear and it may endanger the cable system. To analyze the phenomena and prevent potential failure, detailed analytical modeling assisted with finite-element method (FEM) is proposed in this paper to accurately analyze the unbalanced induced current for AC subsea cable. FEM is utilized to model the armor wires as an equivalent homogeneous layer. With this validated method, comprehensive analysis is performed for unbalanced induced current of AC subsea cable. It is shown that the unbalanced current is due to the inequal impedances between grounding points at two cable ends and/or the extra introduced resistor between lead sheath and armor. Based on these findings grounding status and connection status between lead and armor can be evaluated via the induced currents. An evaluation tree is then proposed to help identify the cable defects.

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