HDD outfalls for high voltage cables in Scotland

This summer, Brownline surveyed two pilot bores in Scotland. These were outfalls to install high voltage power cables. In order to improve the electricity connection between Carradale and the Isle of Arran, the submarine cable was replaced. It was brought to shore with a horizontal directional drilling.

Several years ago, the existing submarine high voltage cables between Carradale and Arran were inspected and found in need of replacement. The grid operator ordered the replacement of the cables, named the Arran to Carradale Interconnector Project. Considering the electricity production of offshore wind turbines in the area, reliable infrastructure is an absolute must.

A large part of the 6.3 km / 3.9 mi long cable connection is installed under the sea floor by way of jet trenching. For the shore approach, Visser & Smit Hanab carried out two HDDs. One of the installed ducts will go into operation right away, while the other is there as a contingency. These drillings were surveyed using Brownline’s Drillguide GST.

The drills had to penetrate many layers of hard quartz on the steep Scottish coast, which represented a challenge on this project. Contractor VSH could rely on Drillguide’s Gyro Steering Technology’s accuracy during the pilot drillings. The length of the bore was over 400 m / 1300 ft and reached a depth of 80 meters below the entry point. While drilling, the pressure in the borehole was carefully monitored using the GST’s Pressure-While-Drilling module. With PWD, the client has an optimal insight into the pressures measured downhole.

Thanks to the accuracy of the GST’s measurements, all involved parties could be certain that the cable was installed according to plan. With this updated connection, the green energy produced by the wind turbines can be transported safely and responsibly.

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