The Blog

NZ's power supply: transmission and distribution

It’s something of a mystery to most of us just how electricity gets from its many sites of generation to the million or so households and businesses around NZ. Sure, the powerlines and pylons dotted around the place are somewhat of a giveaway, but really, a good portion of us know very little about it.

Here in NZ, we have three main stages in the production of our energy. The first step is Generation, or the various ways that we generate our electricity from things like water, wind and geothermal activity (check out our ‘Talkin’ about our Generation‘ blog for some good information).

Next in the chain are Transmission and Distribution. These two stages are the backbone of our electricity industry; the super-highways that get electricity from Point A to Point B. So, to enlighten you further…

What’s transmission?

Also known as the national grid, the transmission network consists of a system of lines spread down the country between populated areas, and a very large cable that joins the North and South Islands.

Lines and pylons

The lines are different sizes and can carry alternating currents, ranging between 50 kV right up to 400 kV, though most lines in NZ run at either 110 or 220 kV. They connect each generator (for example, Lake Karapiro’s hydro dam) with one of the 170 substations, and then the smaller distribution networks which branch off into each area. The transmission network is carried by the big pylons (25,000 of them!) and lines you often see throughout the countryside.

The HVDC cable

An integral part of the grid is the HVDC cable (or High-Voltage Direct Current cable) which connects the North Island to the South. This cable is a biggie, able to transfer 1050 MW northwards and 750 MW southwards. With more of our population in the North Island, the cable primarily transfers power northwards during the day and southwards during the night (you can view which direction electricity’s being tranferred, and how much, here!). It runs only between the Haywards substation in Wellington and Benmore Hydro Station in Canterbury – there are zero off-shoot lines along the way.

The national grid is owned by the Crown, and run by state-owned enterprise Transpower. They’re in charge of developing and maintaining the grid, and ensuring it can meet our growing demands.

What’s distribution?

You can think of this as the little brother of the larger transmission network. It feeds directly off the national grid, and is made up of the smaller power lines and power poles we see around our more populated areas.

From the grid to you

The role of the distribution network is to carry electricity from the bigger transmission network to individual homes and businesses. They have the job of getting the electricity to the ICP, or Installation Control Point, at each home or business. Once it’s at that point, it then becomes the responsibility of your electricity retailer (like Flick!).

Lines companies

Keeping the network in reliable, working order is the job of distribution (or lines) companies. There are around 29 lines companies, and each region of NZ has an allocated company; for example, Wellington Electricity in Wellington, Powerco in Tauranga and Westpower on the West Coast. They’re responsible for maintaining the power lines and power poles (both above and under ground) in their area, and making sure the lines have enough capacity to cater for each customer. Not such an easy task!

Complicated? Just a bit! That’s why we think it’s so important that our mahi helps to share knowledge and bring transparency to this remarkable industry and essential service that we all use, every day.