Caithness Moray HVDC CASE STUDY-CAITHNESS MORAY HVDC The Caithness-Moray transmission reinforcement project is the single largest project ever undertaken by Scottish and Southern Energy (SSE). To put it into context, the cost of the project is similar to the construction of the new Forth Road Bridge. The project involves the installation of a 160km submarine cable under the Moray Firth to connect new or expanded substations at Spittal in Caithness and Blackhillock (Keith) in Moray. The project was the first in the North of Scotland to use HVDC cables in place of the usual AC. HVDC cables were used because they are more efficient in transmitting large volumes of power over long distances. Converter stations are needed at both ends of the cable to convert the high-voltage direct current to high voltage alternating current or vice versa. The HVDC cable reaches the Moray coast at Portgordon. Nicol of Skene was commissioned by Daviot Group, an Inverness-based civil engineering contractor, to undertake major directional drilling works on the twelve mile Portgordon to Blackhillock element of the project. A second contractor was already on site but was struggling to cope with the complex demands of the project and this was holding up the project. Frack-outs had also led to pollution incidents in local river courses. The chain of command on the project was: End client: SSE plc Prime contractor: ABB (ASEA Brown Boveri) Civil engineering contractor: Daviot Group Ltd (Daviot ceased trading in October 2017 due to cumulative losses and cash flow problems across multiple cable laying projects) Directional drilling subcontractor: Nicol of Skene Ltd Route of the Caithness-Moray transmission project The project consisted of two parallel 360mm boreholes. The HVDC cables (140mm diameter) have a solid copper core and, when in operation, generate considerable heat. Ground temperatures increase with depth, until they stabilise at about 10˚C at 15m below the surface. The combination of heat generated by the cable and ground temperatures at depth means that separation, the distance between the two cables, is critical to successful project delivery. This separation has to be achieved within tight constraints imposed by the wayleaves negotiated with landowners. In the drill undertaken by Nicol, the separation required at one point was 22m within a wayleave of 22.5m. Separation means the drill operator has to focus on both the depth and lateral direction of the drilling head. This makes the drilling operation far more complex. The approach adopted by Nicol was to pin out the line the drill team had to follow on the surface and then use ranging poles in conjunction with sondes to ensure the correct drill path was being followed. One of the drills was across wetlands. The bog could not be drained, however, as it fed a freshwater spring that fed one of the many local distilleries; Moray is one the world’s principal locations for Whisky production with brands such as Cardhu, Glenlivet and Glen Moray. Great care had to be taken to ensure there was no pollution of the water course. Ditch Witch all-terrain rigs were used on the project. The JT60 rig (https://www.ditchwitch.co.uk/all-terrain.php?s=jt60-all-terrain-directional-drill) was used on the drill through the wetlands and used standard Kodiak solid carbide reamers. The second borehole involved considerable rock drilling and the JT100 rig (https://www.ditchwitch.co.uk/all-terrain.php?s=jt100-all-terrain-directional-drill) was used. Security was a major issue on site due to the high value of the HVDC cables. Each 800m drum of cable weighed 52 tonnes and had a value of £1.2m. Further background information on the project can be found on the SSE video embedded in the following web page: https://www.ssen-transmission.co.uk/projects/caithness-moray/ KEY BENEFITS Innovation There was no specific innovation on the project per se. The key to success was the combination of detailed planning prior to arrival on site, drilling rigs which could adapt to changing ground conditions, experienced skilled drilling teams, attention to detail in terms of tracking drilling progress and close liaison with the client (Daviot) and prime contractor (ABB). Environment The project has an extremely high profile in Scotland. The decision to bury the HVDC cable is directly linked to concerns over the visual impact of overhead transmission lines. Due to its high profile the client had to be satisfied that Nicol’s approach to the project, supported by its method statement and risk assessment, met the strict criteria imposed after earlier frack-out incidents. The fact that local watercourses feed springs accessed by local distilleries – whisky is a major employer and economic driver in the local economy – meant great care was taken to ensure there were no frack-outs and that drilling mud was carefully controlled. Community impact and customer care SSE has invested considerable resource, both locally and nationally, in keeping all stakeholders informed of the progress of the project. Whilst Nicol was not directly involved in communications with the general public, all visible elements of the drilling programme (compound, entry and exit pits etc) were all designed and maintained to minimise visual impact. Project management Nicol was awarded work because the land-based civil engineering elements of the project were running behind schedule. This meant there was considerable pressure and client focus to maintain momentum across the duration of the drilling. An additional level of complexity over and above the project itself, was that the Swiss ABB Project Manager had a limited English technical vocabulary: a challenge compounded by the beauty of the local Doric accent! Legislative compliance The project complied with all relevant construction legislation, including CDM. The high value of the cable on the project meant that site security was extremely strict. The Nicol difference Nicol’s involvement was fundamental in helping Daviot Group claw back lost time. Its ability to develop a plan of work that met the client’s challenging technical requirements, mobilise to site quickly and efficiently, and complete the project within time, to budget, and with no environmental issues set it apart from earlier drilling contractors that had worked on the project. This was the first HVDC contract in Northern Scotland, and the focus on separation was a fascinating and challenging aspect of the project from a technical perspective.