Medium voltage single core cable armor grounding issues and solutions

In medium voltage installations, grounding grid is often considered insufficient to provide a reliable fault return path. To create better continuity of the grounding system and better conditions for operation of protective relays, it is common practice to ground medium voltage cable armor at both ends, or to use a separate grounding conductor in parallel with the main power circuit. When single core cable armor is used as grounding medium, the point and the method of armor grounding becomes critical. If single core cable armor is grounded at both ends through cable glands, continuous high circulating armor currents may create high temperatures at armor termination points. Standards do not require cable glands to be rated for continuous currents, and therefore, it is important to eliminate high continuous armor currents from the glands. This paper illustrates possible issues in armor grounding in single core medium voltage cables with the help of relevant data, measurements and thermal images. The paper discusses methods of single core medium voltage cable armor grounding, their advantages and disadvantages and solutions to avoid possible issues.