What makes the storms of this winter unusual is that the ground is not frozen. When the ground is frozen, this attaches trees to the ground so that even in strong winds, they stay upright better than when the ground is not frozen. In July and in the autumn, these situations are common and to some extent expected.
During storms, we sometimes get a lot of customer feedback wondering about the reason for electricity breaks still occurring even though electricity network cabling has been taken underground at quite a fast pace. So, what are the reasons for the power cuts? Our customers are annoyed. Let's give some clarification on what is behind the power cuts.
The electricity network is a long chain in which every link has an impact on the security of supply.
Caruna has many kinds of networks – high, medium and low voltage – in several network areas, and despite cabling, there is still plenty of overhead lines left. In total, Caruna has about 87,000 km of electricity network in Finland.
Electricity travels along a 110 kV high voltage electric line from power plants to the distribution network of electricity distribution companies and to heavy industry. Primary substations transform the voltage of the electricity network and connect two electricity networks with different voltages to each other. The medium voltage network (1 – 20 kV) distributes electricity to both small industries and to supply transformers located near inhabited areas. The low voltage network (0.4 kV) connects households to the electricity distribution network of an electricity distribution company.
After storms, the first faults to be repaired are always faults in the medium voltage network, because that network has the biggest customer impact. A faulty medium voltage network may cause disturbances to electricity distribution even tens of kilometres from the fault location.
There are several points where failures can occur in the long electricity network chain. Sometimes, substations and distribution boards suffer from the weather in addition to electricity poles. And vandalism is not unheard of either. Animals can also cause breaks with their activities, unfortunately most often to the detriment of the animal.
Without continuous development of the network, there would be significantly more faults
Of our network, about a half has now been cabled, so there is still much to do in the improvement of the network's weatherproofing. The entire electricity network will not be cabled – about twenty kilometres of overhead lines will continue to distribute electricity. This is why, in addition to cabling, we maintain the nearby areas of the networks, for example by felling trees.
"We have been cabling since 2015, mainly focusing on the medium voltage network, and now we will increasingly be taking the low voltage network underground to protect it from the weather. Of course, we will also apply other cost-effective alternatives in areas where cabling is not the best solution. We can well understand the irritation of our customers when electricity is cut off as a result of a storm. Our preparation for these situations means that we call electricians to work at a short notice so that faults occurring in the terrain can be repaired as quickly as possible," says Kosti Rautiainen, Head of Electrical Network Unit at Caruna.
Why does it take so long to repair faults?
Caruna's electricity network in South, Southwest and West Finland is fragmented in the archipelago and the coastal region. In the archipelago, it may take a long time to repair faults. Often, the reason is that archipelago locations are inaccessible for example because of rough seas.
"The safety of fitters is the most important thing in all circumstances, so sometimes, we have to wait for the wind to die down and for the daylight. In the terrain, work is sometimes carried out in very difficult circumstances, in the cold and dark," Rautiainen reminds us.
February's storms brought a lot of work for numerous professionals in our customer service, in our control centre, as well as in the terrain. Everyone takes care of his or her part so that electricity supply can be returned as quickly as possible to all our customers.
Our network keeps getting better, but the fact is that our society, which is increasingly dependent on electricity, will to some extent suffer from breaks in electricity distribution also in the future. However, the breaks will be less frequent and last for a shorter period of time. We work continuously to accomplish this so that the daily lives of our customers will also in the future run even more smoothly.