Sheath Bonding Design Information for Excessive Voltage Cables

Excessive-voltage energy cables are supplied with an outer concentric conductor within the type of a steel display screen and/or a steel sheath which surrounds the principle conductor and insulation layer. Steel screens and steel sheaths are collectively known as the sheath. The sheath additionally contains any metallic armour layer(s) within the cable. The needs of a cable steel sheath embody to supply fault present return path, return path for the induced capacitive cost currents, earth (zero contact voltage or thereabouts) potential for human security, and moisture barrier for cable insulation.

For prime-voltage cable circuits carrying greater than about 500 A, sheath bonding preparations are carried out to scale back (typically drastically) sheath present losses. While the bonding preparations include a further value for tools and upkeep, they are going to typically end in significantly smaller cable sizes for use for supplying the identical load currents. The steel sheath bonding association chosen for high-voltage cable methods has the second highest impression on cable present scores, second solely to the exterior thermal resistance (the put in setting) to the cables. Excessive voltage cable present scores are calculated in response to the IEC 60287 Customary collection.

A sheath bonding system is used for shielding the insulation of assorted cable system parts throughout regular operation in addition to from transient overvoltage from lightning, switching and fault surges. Furthermore, the sheath bonding association can also be vital from a security standpoint.

Sectionized cross-bonding (defined under) is the commonest bonding association for HV and EHV transmission traces besides if the road size is brief then single-point bonding (additionally defined under) is generally used.