Case Study 1: LV FPI

by Ian Bowden 

The LV underground cable fault finder is a specialized instrument designed to provide efficient and accurate fault detection in low-voltage (LV) underground cables, offering different sensitivity settings and recording capabilities for easy fault location and analysis.

Says Ian Bowden, former director of Bowden Bros Ltd: "The concept of using electromagnetic detection to find faults on LV cables is not a new one. When Bowden Bros Ltd operated out of my parents' house in Bromley (circa 1970) it was not hard to persuade my father to apply a fault to the house supply, fitted with a quick blow fuse, to see if a transient current could be detected using early portable Pathfinders placed above the LV cable that we knew to run in the pavement outside our house. The current was detected, but by Pathfinders placed both upstream and downstream of the fault, so we concluded that the multiple earths often applied to LV networks give rise to multiple paths for the transient earth current to flow. However, we did get calls from engineers over the years to say that they had used the same technology, the Pathfinder MK7A and MK8, effectively on finding LV faults."

In 2017 Bowden Bros was approached by SSE (who had successfully used MK8 Pathfinders to find a high profile LV fault that had occurred on Cowes High Street) to collaborate on designing a device that could become part of the fault engineer’s tool kit. Bowden Bros put forward a proposal to change the instrument from a digital ‘yes/no’ flag to one that would measure the electro magnetic field, enabling the user to map the points of highest and lowest readings to pinpoint the fault. 10 prototypes were produced for experimentation by the SSE to determine how best to deploy them.

A meeting at the New Forest Depot in May 2019 provided enough positive feedback to prompt SSE to order 20 more units to extend the trial. These were delivered in October 2019. Further testing resulted in the LV-FPI, which successfully finds which spur off a main LV line carries the fault.

Another test was carried out at a site in Salisbury in 2021 where a fault had permanently welded two phases together but did not affect supplies to local houses. The results were inconclusive as far as the instrument was concerned, but what the test did highlight was the fact that a single engineer could not be expected to run up and down the street at night looking at the results of each detector. The solution was to link each detector to a hand-held tablet.

In July 2021 SSE applied for NIA funding to develop the equipment to incorporate a comms link from each detector, a receiving tablet that would display the results, and a suitable disguise for each detector that may have to be left in a public place during testing. The application was successful, with the contract finally being signed in December 2022.