Tony Davies High Voltage Lab invited by Prysmian to validate cable location hardware using a commissioned circuit

A research expedition to Edinburgh was recently completed by Dr Jack Hunter of the Tony Davies High Voltage Laboratory (TDHVL) with the aim of verifying the performance of a cable location rig using an operational cable circuit. The objective of the trip was to record the magnetic field produced by a buried 275 kV cable circuit at road surface level using a portable sensor array. The data acquisition system was developed as part of the EPSRC funded, "Mapping the Underworld" project. The system consists of 24 search coils on a portable frame, multiplexer, multi-channel sampling unit and a Laptop. The coils are distributed in a range of orientations such that a 3-D estimation of the magnetic field generated by the cable can be recorded over a period of 10 power cycles (0.2 s). A number of data sets were generated from several locations on the road in order to comprehensively map the magnetic field. The concept of the system is such that, if the geometry and configuration of the cables are known, an estimation of the cable location can be calculated from the recorded magnetic field distribution by solving a minimum fitting error problem. The next stage of the project involves developing a model for the cable configuration and finding if the estimated circuit depth is accurate.

The double circuit used in this study was laid in 2006/2007, energised in 2012 and is operated by Scottish Power; they consist of two sets of single-phase cables with extruded polymeric insulation and were manufactured by Prysmian. The double cable circuit connects Kaimes primary substation on the outskirts of the city to Dewer Place substation in the city centre (a distance of around 7.7 km). The cables are generally installed in trefoil formation at a depth of 825 mm. Several sections of the cable length had to be buried at a shallower depth due to local conditions – at these locations, steel plates were used to provide additional protection. Due to the varying layout of the cable circuits, it was identified as a useful test case to validate the operation of the cable mapping system.

Trials are also being carried out at test sites near Bristol and Wigan “The mapping the underworld project has had several successful outcomes and at Southampton we have developed a sensing tool that allows accurate estimation of buried power cable depth”. Said by Prof. P. L. Lewin – head of the TDHVL.