Benmore Pole 3 HVDC Upgrade

Drumreed Construction were contracted to carry out the concrete works for the South Island portion of the HVDC Pole 3 project at Benmore Dam. The project was located in a remote area, 50km from the closest resources, in a region renowned for extreme weather. The construction of a new converter station and switchyard structures at the Benmore Substation for Transpower's HVDC Pole 3 project was not only a phenomenally complex structure, but also a once in a lifetime project for the team at Drumreed Construction. 

The Pole 3 project has increased the capacity of the HVDC inter-island link, critical for enabling renewable generation to supply the North Island, and for supporting South Island electricity demands in dry years. Using state-of-the-art thyristor technology, the new station replaced the 45-year-old Pole 1 equipment. 

Three thyristor valves weighing 17 tonnes each were suspended from the ceiling of the 19-metre high valve hall. Six-metre long bushings transfer electricity between the valves and the outside converter transformers, which weigh up to 330 tonnes each when installed and operating. The converter building was constructed on a floating slab, which was connected to a 600mm-deep raft slab (approx. 1850m²) by 33 bearing plinths and 50 slider stools; thus allowing the structure to move up to 750mm in the occurrence of a major seismic event. A 100-year design life was placed on all elements of the converter and surrounding buildings, which led to strict QA regimes on tolerances and materials used. 

Adverse weather conditions, with temperatures down to 8 degrees in winter and up to 35 degrees in summer, made the job challenging at times. 

Enquire now