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

CRITICAL INFRASTRUCTURE PROTECTION IN THE BALTIC SEA REGION
powerless customers may vary locally from all to none. According to a model,
roughly 40 % of the customers in the area will be powerless at the zero hour (the
time when the number of powerless customers no longer increases). After 12
hours, the percentage has dropped to 10 %. In 48 hours, all customers have gotten
their power back.
A big impact on the time of recovery is the amount of required clearing
(fallen trees and other debris) preceding the actual repairing actions. The number
and severity of the damages as well as the number of available repair personnel
also affect the recovery time.
The assumed rate of occurrence of a storm corresponding to a class I major
storm is once every five years.
Customers without electricity
Time (h)
Figure II—9 Customers without electricity in class II major storm. (Partanen
et al. 2006) 45
A class II major storm is a disturbance that leaves customers without power for a
maximum of five days, given the current network structure and available
resources. The affected area normally covers the entire network of the power
distribution company and there is little local variation. The only exception is the
customers connected to the ground cable networks in cities and population centres;
they are normally not affected. According to a model roughly 50 % of the
customers will be powerless at the zero hour. After 12 hours, the percentage has
dropped to 23 %. Within a day, roughly 90 % of the customers will have their
power back; however, it may take as long as 120 hours before all customers have
been reconnected. In addition to the class I impacts, the recovery time is mainly
affected by three factors:
45
Mathematical model is fitted to the statistical information on Unto -storm from Suur-Savon
Sähkö electricity company’s information system. Actual percentage of customers in coloured
points and fitted function in black
78 NORDREGIO REPORT 2007:5