Introduction: In 2000 – 2002 midlife refurbishments were carried out on several cable circuits, mainly within London. As part of these refurbishment works the old link boxes were to be removed and new above ground pillars were fitted. At this time system studies were carried out and it was found that the length of major electrical sections could be extended, therefore reducing the number of link pillars that were required, eliminating the need for extra easements to be obtained and reducing ongoing maintenance requirements. However it has been found that circuits where the length of the electrical sections has been extended are suffering from multiple failures of the SVLs fitted to the cable bonding system. These SVLs are generally installed in public places and are critical to the circuit operation. As a result of this multiple circuits have been placed on enhanced maintenance regimes. These regimes require a major maintenance to be carried on the affected circuits annually opposed to being carried out every 3 years. Long electrical sections are also of interest as several new cable circuits are proposing to be installed with long electrical sections.

Objectives: This project will provide National Grid with:

• An understanding of the steady state and transient performance of cables with long electrical sections

• An awareness of the failure mechanisms and life limiting factors of cable sheath voltage limiters (SVLs)

• Recommendations for the future of operation and maintenance of cables with long electrical sections.