Case Study 2: Link Box

The LV Linkbox fault indicator is a specialized instrument designed for locating faults in low voltage (LV) Linkbox junctions. It provides efficient and accurate fault detection for LV underground cables, offering different sensitivity settings for easy fault location and fault passage indication.

Bowdens have been making reliable and feature rich earth fault indicators (EFIs) and overcurrent indicators for many years. These include EFIs connected to split core or band CTs for fault detection and reporting on underground 11kV cable systems, and the Pathfinder range of FPI for fault detection and reporting on 11kV overhead lines.

Bowdens was approached by UKPN, who had previously used a 20 year old Linkbox fault indicator from EDSL that is no longer in production, to design a modern version with improved speed of detection and implemented with modern processor technology and production methods. A specification was provided that set the physical constraints, environmental requirements, battery life, service life, electrical ratings and operational requirements.

Early trials conducted by UKPN of the new Bowdens Linkbox fault indicator produced very positive results. Following feedback from UKPN, the design was optimised for use on UKPN Linkbox installations in London and beyond.

The Linkbox fault indicator uses modern microcontroller technology from ARM to use minimum power from the internal battery whilst waiting to detect faults, giving exceptionally long service life once deployed. A custom enclosure was designed to withstand the possible high temperatures of a Linkbox installation and this is sealed to provide an IP67 seal.

The Bowdens Linkbox fault indicator has selectable trip current levels, a reset time of three hours and a battery life that will exceed 10 years in normal use.

Once it was shown that the Bowdens Linkbox fault indicator design met the UKPN Specification Statement of Conformance and performed well in field trials, the design was approved for use.

UKPN subsequently placed their first production order in 2023.