Protecting electric grid against storms could take decades

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Extreme weather this past summer has caused repeated electricity blackouts affecting tens of thousands of households. The interruptions to service are caused mainly by falling trees cutting power lines, and there have been increasing calls to place power lines underground. Some consumers in the southeast of Finland were left without electricity for a month.
      Reliability of the electricity supply could also be improved by moving power lines out of the middle of forests onto roadsides. However, the process is likely to take decades.
      “We have taken as a starting point that by 2030 we will have reached a situation in which the likelihood of interruptions will be reduced significantly, and their duration would be considerably shorter”, says Kenneth Hänninen, executive director of Finnish Energy Industries (ET).
     
Especially susceptible to storm damage is the medium voltage grid, which winds through forests in the form of three parallel lines.
      If the line breaks, hundreds of users can be left without electricity.
      Slightly over 10 per cent of the medium voltage cables are underground. The proportion has gradually increased, as electric companies have replaced obsolete power lines with underground cables.
     
Finland has about 140,000 kilometres of medium-voltage power lines, and it is expected to take decades before the cables are all buried. It also costs much more to bury electric power lines than it is to hang them on poles.
      Simo Nurmi of the Energy Market Authority says that society needs to consider how much it is willing to pay for reliability.
      “In the short term there will be no great changes without investing huge amounts of money”, Nurmi says.
     
Researcher Jukka Lassila of the Lappeenranta University of Technology has calculated that a comprehensive underground network of power cables could raise the price of a kilowatt hour of electricity by one cent, which would lead to an increase of five to ten per cent in consumer prices of electricity.
      Another way to reduce storm damage would be to move airborne power lines to the sides of roads. This would mean that the lines would be susceptible to damage from falling trees only from one side. Also, the improved access means that any damage that does take place would be easier to fix.
      Electric utilities have long wanted to place cables underground along roads. There has been resistance to this because road maintenance authorities are concerned of possible damage caused during road work.


Previously in HS International Edition:
  Tens of thousands of households without electricity after new storms (5.8.2010)
  Thousands in rural areas of Eastern Finland still without electricity after Friday storm (2.8.2010)

Helsingin Sanomat