Towards a Baltic Sea Region Strategy in Critical ... - Helsinki.fi

CHAPTER II: ELECTRICITY
• The network suffers severe damages that take time to repair.
• Several repair actions are normally required on the same location due to
multiple damages that affect the network independently of each other.
• There are many minor damages spread out over a large area; however
only affecting a small number of customers. These are normally the last
damages to be repaired.
The assumed rate of occurrence of a storm corresponding to a class II major storm
is once every twenty years.
Customers without electricity
Time (h)
Figure II—10 Customers without electricity in class III major storm.
(Partanen et al. 2006) 46
A class III major storm is a disturbance that leaves customers without power for
as long as 18 days (2.5 weeks). The affected area may be as large as the entire
country, with severe damages on the inter-regional distribution networks, causing
blackouts in cities and population centres as well. It is estimated that as many as
95 % of the customers may lose their power before any repair actions can be taken
According to a model more than 50 % will still be powerless three days after the
zero hour. After two weeks, 90 % will have their power back.
Storms of class III require a full mobilization of all available personnel.
Reinforcements may have to be flown in from the neighbouring countries. The
time of recovery is not only affected by the huge number of damages; the rate at
which vendors are able to deliver replacement components becomes an important
factor.
The assumed rate of occurrence of a storm corresponding to a class III major
storm is once a century.
46 Mathematical model is only theoretical without statistical background, but if we compare this
mathematical model to information from Gudrun-storm, we can notice that the scale is right.
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