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Transmission

Background

The national grid transports electricity from the generating stations to distribution networks and major industrial users at around 200 grid exit points across New Zealand.

The grid includes the inter-island direct current link ('HVDC link', colloquially 'Cook Strait cable'), which can transport power either north or south. There are a number of factors affecting the direction of flows, but the dominant one is the level of South Island hydro storage. When South Island storage levels are high, flows across the link are typically northward, and when South Island storage is low, flows are typically southward.

Current Transmission Situation

Looking forwards over the next few months, there is no expectation that transmission constraints will lead to regional energy shortages. We are not aware of any reason to expect that transmission might be restricted beyond the current known assumptions on circuit availability, line ratings, grid configuration and maintenance.

Inter Island Transfers

The ability to transfer electricity from one island to the other is an important aspect of managing security of supply, particularly as there are no thermal stations in the South Island to call upon in times of low hydro storage.

The graph shows the last 12 months of HVDC inter-island transfers up to 20 May 2012. The blue bars represent transfers from the South to the North Island and the orange bars represent transfers from the North to the South Island. It is not unusual for transfers in both directions to occur within a week, although north transfer is the predominant mode of operation. 

Transmission Investment

Transmission capital investment is planned to increase sharply in the next few years, driven principally by the following major upgrade projects:

• North Island Grid Upgrade between Whakamaru and South Auckland (the "Waikato line")
• New HVDC Pole 3 to replace the existing Pole 1
• North Auckland and Northland Project reinforcing supply through the Auckland CBD to the north.
• Wairakei to Whakamaru Replacement Transmission Line this project will build a new double circuit transmission line between Wairakei and Whakamaru

Many of the current issues with transmission constraints will be resolved as these and other investment comes on stream.

For a full listing of transmission projects see the Grid New Zealand website.

Related Information

Graph of the Last 8 Days HVDC Transfer