Outages – Who, What and Why

Questions and Answers

Who's responsible for my power?

There are many steps involved in getting power to your home or business, and different companies are involved at each stage. A power outage or ‘power cut’ can be caused by a complication at any step along the way.

Sometimes there’s an issue with Transpower’s equipment that causes an outage; sometimes your local distribution company has an issue with their equipment that causes the power to go out.

Who manages what?

  • National grid: Transpower owns and operates the national transmission grid, bringing bulk power from areas of generation (like the Waikato River) to towns and cities across New Zealand via large transmission lines and towers. Transpower connects at our substations with local distributors.
  • Local distributors: These companies (also known as ‘lines companies’) move electricity from our substations to homes and businesses across their regions. They own and manage the power lines and cables in your neighbourhood, e.g. Vector in Auckland; Aurora Energy in Central Otago. Click here to find out who’s in charge of distributing power in your region.
  • Electricity retailers: This is the company your pay your power bill to. They don’t own the lines that supply power to your house and business, but they can help you find out more information if your power goes out.
  • Generators: This is the company that generates bulk electricity utilising wind, hydro, geothermal or thermal fuel sources. Our large generation companies also are electricity retailers.

Why is my power out?

An unplanned power outage may be due to one of the following common causes:

  • Objects: Foreign objects coming into contact with lines or equipment, such as a bird’s nest, broken trees or foliage. These objects can cause equipment to ‘trip’, which causes the power to go out.
  • Pests: Rodents or other pests interfering with equipment, causing it to ‘trip’ and the power to go out. Sometimes a short maintenance outage is required to remove this risk or install deterrents.
  • Weather: Severe storms, wind and snow can damage or bring down power lines, cutting power to the town or neighbourhood that line feeds. This is more often an issue for local distributors’ lines, although even Transpower’s heavy duty transmission lines can be susceptible to damage from heavy snow.
  • Technical: Despite thorough maintenance programmes, sometimes equipment fails unexpectedly. Without backup electricity supply, this can cause a power cut to the area it supplies.

How can bird poo cause a trip?

  • Bird excrement can enable flashovers (arcs of electric current that can pass from the wires to the steel towers into the earth) by providing a path across the insulation that separates the wires from the steel towers causing the line to trip.

  • One likely cause is the bird emptying its bowels upon taking flight from perching on the tower, letting loose a long jet of droppings onto the insulator.

Why can it take so long to get the power back?

  • Crews are on standby 24/7 across New Zealand, however geography and weather can affect response times. Outages in remote areas can involve long travel times for crews, especially if there has been a severe storm.
  • Safety is a priority. Sometimes this can mean waiting for daylight until a crew can enter a site and start their investigation.
  • Some issues can be very complicated, even for highly-skilled engineers – they work as fast as they can, as safely as they can, to restore power.
  • Where there is little or no alternative supply, a spare needs to be sourced, supplied and installed to enable restoration.
  • In any event, Transpower will work with the local lines company to minimise the impact of any outage.

Why do we seem to have more power outages than other people?

  • This generally comes down to location. In some places there is only one transmission line that supplies an area. When that line and/or associated substation equipment experiences a fault, or we have to carry out maintenance work on that equipment, then the local power supply will need to be temporarily switched off.
  • We work closely with your local distributor to see if we can route alternative power supply to keep the lights on, but in some locations this isn’t possible. Routing alternative power supply is more commonly available around urban centres.
  • This sort of ‘traffic management’ is happening all the time, which is how we can carry out maintenance work on the grid every day without disconnecting everyone.

Why do you have ‘planned’ outages?

  • There are many ‘planned’ outages on the grid happening every day. These are needed so we can safely maintain our equipment or fix problems to reduce the risk of ‘unplanned’ power outages.
  • In many cases, we can work with your lines company to route an alternative power supply to keep the lights on, but in some locations this isn’t possible and an outage is unavoidable.
  • Planning an outage takes a lot of work and co-ordination – these can take up to 12 months to organise.
  • We know there is never a good time for the power to go out, which is why we work closely with  the local distributor and local community to consider what community events are going on, to lessen any disruption.
  • We need to coordinate with other work that might be happening on the grid, and with local distributors who may also be planning work during an outage. We also need to consider when our workers are available to carry out the job.
  • Weather and conditions are also a consideration – we try to avoid outages in winter when everyone needs their heating or at the busiest times of the week.
  • Of course, we can do all this planning and then bad weather comes through and we have to change our plans. That is why we also tend to have an alternative day for the outage – again determined in conjunction with the local lines company.