Sheath Bonding Copper Cable 11KV

SOLIDLY BONDED SCHEME SOLIDLY BONDED SCHEME SOLIDLY BONDED SCHEME Cables with solidly bonded sheath connections are common in distribution circuits, but rare in transmission systems. The schematic below shows a typical arrangement, where the sheaths are connected to ground wherever they are accessible. This scheme eliminates standing voltage at the end of each sheath section . The significant characteristic of this scheme is that current flows in each of the cable sheaths whenever the cables carry current. The sheath current is proportional to the cable load and requires a 20% to 30% reduction in cable load rating compared to schemes that eliminate sheath current. Cables with solidly bonded sheath connections are common in distribution circuits, but rare in transmission systems. The schematic below shows a typical arrangement, where the sheaths are connected to ground wherever they are accessible. This scheme eliminates standing voltage at the end of each sheath section . The significant characteristic of this scheme is that current flows in each of the cable sheaths whenever the cables carry current. The sheath current is proportional to the cable load and requires a 20% to 30% reduction in cable load rating compared to schemes that eliminate sheath current. Cables with solidly bonded sheath connections are common in distribution circuits, but igh-voltage power cables are provided with an outer concentric conductor in the form of a metal screen and/or a metal sheath which surrounds the main conductor and insulation layer. Metal screens and metal sheaths are collectively referred to as the sheath. The sheath also includes any metallic armour layer(s) in the cable. The purposes of a cable metal sheath include to provide fault current return path, return path for the induced capacitive charge currents, earth (zero touch voltage or thereabouts) potential for human safety, and moisture barrier for cable insulation. For high-voltage cable circuits carrying more than about 500 A, sheath bonding arrangements are implemented to reduce (often significantly) sheath current losses. Whilst the bonding arrangements come with an additional cost for equipment and maintenance, they will often result in considerably smaller cable sizes to be used for supplying the same load currents. The metal sheath bonding arrangement selected for high-voltage cable systems has the second highest impact on cable current ratings, second only to the external thermal resistance (the installed environment) to the cables. High voltage cable current ratings are calculated using the IEC 60287 Standard series. A sheath bonding system is used for protecting the insulation of various cable system components during normal operation as well as from transient overvoltage from lightning, switching and fault surges. Moreover, the sheath bonding arrangement is also important from a safety point of view. In this report we explain the following types: solid bonding, single-point bonding, cross-bonding, and impedance bonding.