New HVDC Pole 3 Commissioned

29 May 2013

Transpower announced today that the latest addition to the National Grid – HVDC Pole 3 – has been commissioned and will be put into full-time service from 8pm tonight.

Pole 3 is the new Siemens-developed, state-of-the-art High Voltage Direct Current (HVDC) converter system installed at Benmore in the South Island and Haywards just north of Wellington. It replaces the 47-year-old Pole 1 (decommissioned last year after running in restricted mode since 2007).

Pole 3 joins the existing, 20-year old Pole 2 in operating the inter-island link. Together, they will allow up to 1000 MW transfer capacity between the islands. Transpower’s Chief Executive Patrick Strange said that construction of the $672 million project, underway since early 2010 has not been easy. Building a new HVDC Pole in the middle of an operating power system, and in one of the world’s most extreme seismic zones, has been a huge challenge for Siemens and Transpower.

“This is the first time worldwide that such a major link has been commissioned ‘in the market’. Usually, these things are built on a greenfields site, tested, and then hooked into the power system. We didn’t have that luxury,” he said.

“With over three months of intensive on-site testing, all undertaken in the live New Zealand electricity market, it has been a tough challenge to commission such an important artery in the country’s transmission network.”

“Low lakes during the nationwide drought held our testing back, and we considered commissioning Pole 3 to a lower capacity in time for winter.  Fortunately, a little bit of recent rain gave us the ability to get it fully commissioned.”

“One of the big positives has been the cooperation from the whole industry during the project. We would like to thank them for their continued support in enabling us to get this critical asset commissioned,” he said.

With Pole 3 commissioned, attention turns to upgrading the Pole 2 control system in spring and adding further equipment to boost the overall link to 1200 MW by the end of the year.

“The new Pole 2/Pole 3 controls will provide more capability and flexibility, allowing us to operate the power system much more effectively in the future, producing savings across the whole power system for the benefit of New Zealand consumers”, Patrick Strange said.

Background

Pole 3 Facts and Figures

  • Total approved cost - $672 million
  • Capacity of new Pole 3 - 700 MW
  • Capacity of Pole 2 – 700 MW
  • Capacity of Pole 1 when retired last year - 250 MW (north transfer only)
  • Total capacity of the link by end of 2013 – 1200 MW
  • Key equipment contractor – Siemens
  • 2.3 million hours worked
  • Approximately 3,000 staff and contractors involved
  • Construction duration: 3 years 6 months.

What is Pole 3?

Pole 3 is the name of the new equipment at either end of the interisland HVDC link that changes the voltage from alternating current (AC) to direct current (DC) and back again. DC is the preferred means for transporting power over long distances because it is more efficient. The Pole 3 equipment includes three state-of-the-art thyristor valves housed at a new Pole 3 valve hall at each location (Benmore and Haywards), four transformers at each location, and a control system to make it all work.

How much did it cost?

When funding was approved by our regulator, the maximum amount approved was $672 million. We expect our final cost to be less than this.

Why did Transpower have to contract in the market for the testing?

For many of the tests we were able to rely on what would normally happen on the HVDC link – what we call natural transfer.  However, for some of the larger tests where we needed to send lots of power south or north, we needed to contract with parties in the electricity market to make those transfers happen at the time and duration needed. The difficult hydrological conditions did mean that we contracted for more tests than we had originally anticipated.

If Pole 3 and 2 are both 700 MW capacity why isn’t the full capacity of the link for this  winter 1400 MW

The number and capacity of the submarine cables in Cook Strait limit the full capacity of the link to 1000 MW (or 1200 MW by the end of this year).  A potential later development would be to lay a further submarine cable or cables, and the timing of this will be assessed further once we have completed the Pole 3 project.