Project: Switch gear and transformer change

Location: Buckfastleigh substation

This contract involved the replacement of 2No remedially bunded transformer bases for new transformers and replacement of indoor switch gear in two phases.

The accessibility and terraced nature of the site presented additional challenges, both for the sensitive demolition and the new construction.

Demolition included the safe felling and disposal of 2No 7m high concrete floodlighting columns. Extensive trenching works were required within the switch yard, with careful stockpiling and due heed to existing live apparatus.

AIZAG personnel were also engaged in the cable pulling operations, working under the control of WPD as part of the working party. All AIZAG work and WPD work had to be closely integrated, so good communications were vital.

The original design had not fully appreciated the changes in level at each terrace. Therefore, we designed in house a bespoke retaining wall at one elevation of each bund, with expansion joints at the transition back to the general bund wall height.

These retaining walls incorporated filter drainage behind, linked to the existing land drainage system.

The retaining wall design for the second bund also incorporated a flight of concrete steps.

In order to joint onto the existing HV cables, it was necessary for us to provide a large joint pit of 20m2, extending half inside and half outside of the compound gateway. This called for plywood security measures where the gates were undermined and safe access across the pit.

The pit was temporarily backfilled between phases; reopened using a specialist suction excavation team to sensitively expose the live HV’s; and ultimately permanently reinstated to match the existing anti-skid surface finish.

Internally, the switchboard was replaced half at a time to suit the phasing, with full dust screening of the section remaining live.

The HV trench was enlarged by diamond floor sawing the slab into squares for careful removal. Existing HV cables in the floor trench remained live throughout the internal demolitions and were protected using sandbags + plywood boarding.

On the sustainability front, we reused all existing tubular handrails and the pebbles from the former bunds were utilised in a pathway serving the temporary accommodation.

Client: WPD
Duration: 16 weeks overall phases from January 2019
Value: £160k
Role: Contractor to WPD