Gisborne power outage shows need for back up lines


By the time you read this, hopefully power will have come back on in Gisborne, which is suffering through a black out that has affected the entire city of 40,000 people. Aside from having entirely tragic circumstances (see below)causing it, the complete black out of a New Zealand urban area raises questions about the reliability of the local power grid when placed under stress.

Except that this was not caused by a natural disaster. In fact  this was not caused by a disaster – although it was certainly disastrous for the families of the victims –  at all, but by a fatal plane crash that killed two men. It struck the 110kV link which has six lines. All were affected and outages reached as far north as Tolaga Bay.

I cannot recall a time prior to yesterday when an entire New Zealand urban area has gone dark because of one event/incident that was not an act of nature. On 22 February 2011, 80% of Christchurch lost power as a result of the seismic activity that day, but this is an exception rather than the norm. Some of the major power cuts in the last 25 years include:

  • In May 1991 a power cut affected Christchurch sending 2/3 of the city into darkness, affecting around 220,000 people, but this lasted only an hour.
  • In 1998 Auckland C.B.D. had black outs that cost millions of dollars in lost revenue for businesses and lasted five weeks before the last customer was reconnected
  • In 2006 a power cut in Auckland affected 700,000 people, or about 3/4 the total population of the city
  • In 2014 a power cut caused by line failure at Penrose Substation in Auckland lead to nearly 80,000 without power for several days

Much of the time these cuts have been traced back to substandard equipment at substations, or substandard maintenance of equipment at substations and switch yards. Following the 1998 and 2006 power outages in Auckland, pledges to improve reliability of supply were made. In accordance with these pledges additional switch yards were established and existing lines upgraded from 110,000kV to 220,000kV, thus doubling their capacity to carry power.

In the case of Gisborne’s power cut, an event such as a plane crash has shown how one incident can affect the entire distribution network of a particular link. Whilst the physical impact of the plane onto the infrastructure at the crash site could not realistically be controlled, how the network reacts to the accident could have been controlled better had there been an alternative link carrying the required power supply.

 

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