Transpower, New Zealand, submitted an investment proposal with the Electricity Commission on May 2, 2008, to replace Pole 1 of the HVDC inter-island link. The new pole will be a state-of-the-art thyristor valve unit and will increase the capacity of the overall HVDC link to 1000 MW from 2012, and 1200 MW from 2014.

The HVDC link, which links Benmore Substation in the South Island and Haywards Substation just north of Wellington, consists of two separate circuits, each with its own major converter system at each end. The converters are called Pole 1 and Pole 2. The current Pole 1 includes equipment that is 43 years old and was shut down late last year. Half of that pole has now been returned to service for use in critical periods. Pole 2, which was fully commissioned in 1992, continues to operate reliably and has been able to carry additional electricity since Pole 1 was shut down.

The HVDC link also includes three undersea cables across the Cook Strait – two connected to Pole 2 and one to Pole 1. These three cables are in good condition.

The HVDC inter-island link is a key part of New Zealand’s electricity makeup. It provides:

• the South Island with access to the North Island’s gas and coal generation, (important for the South Island during dry winter and summer periods)
• the North Island with access to the South Island’s large hydro generation capacity (important for the North Island during peak winter periods).

Transpower’s Chief Executive Patrick Strange said that the technology that the existing Pole 1 uses was ground breaking technology when developed but has now been superceded by better, more efficient thyristor technology.

“The investment proposal for a new Pole 1, estimated to cost around $700 million, follows many months of consultation and engagement with interested parties on the approach, assumptions, methodology and options in investigating the need for a replacement.”

“The HVDC link is an important link for New Zealand as it balances the energy use between islands, which is more sustainable for the country. It also helps to facilitate renewable generation.”