Tuesday, November 10, 2009

The design of Termination fulfills the following functional requirements

Electrical Stress Control
In a radical field (screened) cable, operating on AC system the distribution of voltage along the surface of insulation from the conductor to screen terminating point is not uniform. This results in degradation of insulation at this point, leading to premature breakdown. The qualitative graphic representation of electrical stress distribution is shown in the diagram.
Occurrence of high electrical stress is avoided by means of a heat shrinkable stress control tube having a closely controlled impedance characteristic per unit length built into the material. The qualitative graphic representation of smoother electrical stress distribution with stress control tube is shown in the diagram below.
Protection from the action of tracking and weathering
Any termination with exposed insulation operating under humid and contaminated condition tends to 'track' due to the flow of surface leakage current which leads to dry bands. The formation of 'track' which are conductive carbonaceous paths over the surface of cable insulation ultimately leads to a surface failure by flashover. This is avoided by provision of heat shrinkable protective tubes over the cores which do not track and withstand the action of weathering. A total seal is provided at crotch by means of a heat shrinkable breakout.
The termination are sealed against ingress of moisture and contamination by application of sealant to form environmental seals at interfaces.
Armour and Screen Bonding
Armour and screen bonding arrangement for XLPE cables is designed to provide a permanent and low contact-resistance between armour, screen and earth bond. This limits the raise in temperature at bonding points even during the flow of high earth-fault currents.

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