Transpower says its $602 million upgrade of the HVDC link has improved utilisation of the country’s low-cost South Island hydro resource and will lower reserve and frequency-keeping costs.

The 44-month project was completed $70 million under budget and with only four lost-time injuries reported after 1.9 million hours of work – much of it in live environments.

Transpower had to overcome a number of key design and construction challenges to complete the country’s most significant electricity infrastructure build in the past 40 years.

It says the biggest challenge was protecting the integrity of the existing pole - Pole 2 - while building a new convertor station right beside it at two locations, Benmore and Haywards, all in a live environment.

The upgrade involved replacing the original mercury arc valve Pole 1 with a new thyristor-based Pole 3 and an upgrade of Pole 2’s control system.

Pole 3 has a nominal continuous power transfer capacity of 700 MW, a continuous overload capacity of 770 MW and a 30-minute overload capacity of 1000 MW. Pole 1 provided only 250 MW of northward capacity during emergencies when it was decommissioned in 2012.

The improved functionality of the upgraded link helps to better integrate New Zealand’s two island electricity systems. More capacity is available in both directions, while the ‘round power’ capability of the new assets will improve frequency and voltage control nationwide.

Contracts, planning

But the project needed innovative contracting, construction and planning to build the new asset in one of the world’s toughest seismic environments and test it in a live market.

To minimise risk for all parties, Transpower undertook all below-ground site stabilisation and strengthening. An innovative disputes review board - used only once - was also set up to quickly deal with any issues without triggering the formal mediation or arbitration clauses in the agreement with lead contractor Siemens.

Stringent seismic requirements on site meant individual items of plant and buildings and their interfaces needed to accommodate high accelerations and movements of up to 700 mm. This was achieved through solutions including the use of base isolators and hydraulic damping together with large circuit breakers.

Transportation of high value items with long procurement lead-times was carefully planned to minimise the risks of damage or late delivery. As a further risk management measure, Siemens invested in a duplicate control system to test in Germany while the original tested control system was delivered to site.

Transpower also invested in a full real-time digital simulator for ongoing maintenance and development studies, which proved to be valuable to Siemens in carrying out testing.

In order to test the new assets in the market, Transpower set up a specialist trading team to contract with generators and major users. Just on 1,179 contracts - more than five a day - were needed to complete 80 per cent of the 400 scheduled tests. In contrast, the whole industry transacted 721 over-the-counter deals in 2012.

Since commissioning and handover of the project from Siemens, Transpower says it has not had any systemic issues to resolve with either Pole 3 or the new combined control systems for it and Pole 2. 

The Energy Project of the Year category is sponsored by ITL