Field trials of 400 kV internally oil-cooled cables

An account is given of two cable trials successfully completed at West Thurrock, which have proved the basis for the design of an internally oil-cooled underground cable system utilising one cable per phase, and capable of matching the rating of a 400 kV 4 × 400 mm2 overhead line. The design and construction of the aluminium and copper conductor cables, stop joints, sealing ends, straight joints and the hydraulic systems for both oil and water cooling and heat exchanger installations are described. The supervisory equipment and measurement equipment are outlined, together with the monitoring procedures for the cable oil, cable and accessories. The installation and commissioning experience and salient results of the trials which included 100 load cycles are given. The current-loading objectives of the trial were fully achieved and showed no constraints of the cable system which would limit the development of the system for higher ratings.