Electricity networks are built to last decades

20 February 2012, 14:28 EET

Fortum has 77,600 kilometres of electricity networks in Finland. About 1,600 kilometres of new electricity networks are built yearly. Most of our electricity networks built in the 1960s and 1970s are aerial networks. Today, however, underground cabling is Fortum’s primary mode of network construction, and over half of the new electricity networks are built underground. Old aerial lines are being moved underground also in conjunction with redevelopment work. Underground cabling accounts for 29% of Fortum’s electricity networks, which is more than average compared to peer companies. The lifetime of an electricity network is several decades, so a network must be designed for current and future needs.

New electricity networks are built in public areas and along roads when possible. Not only does this make it easier to repair malfunctions and to service and maintain the network, it also causes fewer disruptions for customers. In accordance with the Land Use and Building Act, landowners receive compensation for the use of their land if the placement and maintenance of the network causes harm or losses. Fortum’s goal is for national land-use agreement terms that are fair and reasonable both for landowners and network companies. Reasonable network construction costs also benefit transmission customers.

Regular maintenance of networks and power line corridors

Fortum inspects and services its electricity networks in accordance with its servicing and maintenance programme. Among other measures, preventive maintenance ensures that electricity network control equipment functions during network construction as well as in outage situations.

The purpose of clearing power line corridors is to prevent trees from growing into power lines and thereby endangering people or causing power outages. Clearing is done using manual labour or with forest machines and helicopters. In 2011, we used various methods to clear a total of about 7,000 kilometres of power line corridors in Finland. Machinery was used for about 300 kilometres of this clearing work.

The clearing of trees around power lines is prescribed in previous regulations and in current standards. In accordance with power line corridor agreements, electricity companies have both the obligation and the right to clear trees from an area 6-10 meters wide around a power line. Ground-level clearings are carried out at six-year intervals.

Power line inspections and clearings generally do not require the electricity to be shut off. Repair work or preventive maintenance sometimes requires short interruptions in the supply of electricity to customers; they are always informed about these outages in advance.

Fortum is shifting to a risk- and reliability-based servicing and maintenance programme in which network target sites are inspected and serviced in different cycles depending on the location and vulnerability of the target sites.

A fallen tree is the most common cause of a power outage

When installing power lines, the aim is to take into consideration the reliability of electricity distribution and the assimilation of the lines into the landscape. Roadways and fields are preferable to forests as installation sites for power lines. However, more than a third of the power lines are still located in forests, and thus trees can fall or lean on power lines as a result of strong winds, storms or heavy snow. In fact, the most common cause of a power outage is a tree that has fallen or is leaning on a power line, or a branch that has blown onto a power line.

The condition of forests adjacent to power line corridors are inspected every six year or so in conjunction with the inspection of the electricity network condition. Electricity companies have the right to remove bordering trees that jeopardise the power line, but the details regarding the tree removal must be agreed on with the landowner when possible. General electrical safety prohibits the storing of logs under power lines. It is safest to store logs far away from power lines.

Proper maintenance of adjacent forests benefits both the forest owner and the network owner. When adjacent forests are properly maintained, electricity delivery reliability increases significantly without added expenses or losses to the forest owner.

The more extensive forest management measures that are consistent with the Finnish Energy Industries, the Central Union of Agricultural Producers and Forest Owners (MTK) and the Central Union of Swedish-speaking Agricultural Producers in Finland’s (SLC) adjacent forest management recommendation, aiming to improve the electricity delivery reliability of the power line owner, require a separate agreement with the landowner.

When felling trees, they must always be felled away from power lines for the safety of the feller and to prevent interruptions in power distribution. If this isn’t possible, the electricity company can provide no-cost tree-felling assistance. However, tree-felling assistance doesn’t mean the actual felling work, it means assistance in the form of a wedge, felling jack or cable hoist to fell the trees away from the power lines; the actual tree felling is the responsibility of the one requesting assistance.