HVDC Inter-Island Link Pole 3 - Infrastructure / Civil

Client:          Siemens/ Transpower

Project Brief

Transpower is carrying out a project to replace Pole 1 of the inter-island HVDC link with a new pole by 2012.
The new pole (to be known as Pole 3) will be a state of the art thyristor valve unit and together with the existing Pole 2 will increase the capacity of the overall HCDV link to 1000 MW from 2012, and 1200 MW from 2014. Once Pole 3 is built, the old Pole 1 will be fully decommissioned and removed.
Mainzeal is the civil subcontractor for this project. We are contracted to Siemens who in turn is working for Transpower. Mainzeal is working at both the Haywards and Benmore sites.
Mainzeal is constructing a control building of approximately 1,400 m2 in footprint at both the Haywards and Benmore sites.
Central to the building is the valve hall and along its side are the three transformer rooms. At one end are the support spaces including areas for the safety systems and the control room.
A floating slab sits on base isolators and sliders sourced from America. The building is designed to move 750mm in all directions on the horizontal plan and return to its original position after the event.
Months were taken off the original build programme by changing the major spine walls and buttress walls from insitu concrete to 50 tonne precast wall sections. The main spine wall on each site is 40m long by 20m high and 300mm thick. The tower cranes were replaced with 200 tonne mobile crawler cranes to handle the heavy panels.
Prefabricated roof sections which were fully clad, lined and fitted out were another time saving construction feature Mainzeal employed to assist the programme. The roof sections were built on the ground and lifted into position when the main valve hall foundations and wall structures were complete. Using prefabricated roofs meant there was minimal time needed to complete the internal fitout once they were in place.