New Zealand's transmission system is made up of over 12,000km of high-voltage transmission lines and more than 170 substations. Comprised of a long trunk with smaller side branches, it connects power stations owned by generating companies to substations feeding the local networks that distribute electricity to homes and businesses. Some large industrial users of electricity receive their power directly from the national grid.

Most of the grid operates on alternating current (the high voltage alternating current (HVAC) system), but there is also a direct current (high voltage direct current or HVDC) link for long distance transfer of power between Benmore in the lower South Island and Haywards, near Wellington, which includes the Cook Strait cable.

The national grid is owned, operated, maintained and developed by Transpower, a state-owned enterprise.

Transpower's responsibilities

Transpower is responsible for working with us to ensure the national grid meets required reliability and service levels.

Transpower is also responsible for grid planning, including proposing transmission investments to the Commerce Commission, and reporting on asset management plans and forecast grid capabilities over time. It has contracts with transmission customers who are directly connected to the grid, setting out the terms they must follow to connect to the grid and use the grid services provided. Transmission customers include generators, distributors and large industrial companies that are directly connected to the grid.

As a state owned enterprise, Transpower is required to operate as a successful business, including earning a commercial return on its assets. However, Transpower is also subject to the Commerce Commission administered targeted price control regime, which has the objectives of limiting the ability of lines companies (Transpower and distribution companies) to exercise monopoly power, and increasing incentives on these businesses to improve efficiency and share efficiency gains with consumers.

The processes and responsibilities for transmission, which includes comprehensive arrangements for connecting to the grid, transmission pricing, and transmission services are set out in Part 12 of the Code.

Transpower website