MV Cable Shield Grounding - Save Energy, Mitigate Cable Derating, and Avoid Cable Shield Corrosion

Certain electrical fire events that have occurred in the last 2 years in California and other parts of the world have led us to consider using underground cables instead of more hazardous overhead bare distribution/transmission lines. This would minimize fire and life safety hazards that have occurred from broken live conductor falling on dry grass and trees. Techniques for bonding underground cable shield/sheath (S/S) to ground to minimize circulating current in S/S are included in IEEE Guide 575–2014 [1]. This guide suggests applying surge voltage limiters (SVLs) to ground S/S at one end of each section of underground cable. Such a grounding technique stops circulating current through S/S during normal load flow current as SLVs will not be conducting, they will conduct only under transient surge current flow through the cable to release the induced surge current on S/S to ground to protect S/S from damage. Medium-voltage (MV) cable protection from lightning and switching surges at overhead to underground locations remain the same when SVLs are applied at S/S of the cable sections. This paper discusses selection criteria for SVLs based on the underground cable voltage, cable parameters, suppliers' cable specifications, and published test data regarding SVLs' capability to mitigate expected surges without damage to S/S or the SVLs.