Transmission line maintenance

Fingrid's transmission lines are mainly constructed using guyed towers. These days, the material is steel, but in the past, wooden tower feet were also used in 110-kilovolt (kV) lines and in some 220 kV lines. Towers in 400 kV lines, however, have always been made of steel. Free-standing lattice towers are used in urban areas. So-called field towers have also been used in new transmission lines. The oldest lines still in use were built in the 1940's.

As the owner of a transmission line, Fingrid has an obligation to maintain the line in the condition prescribed by electrical safety regulations. For the maintenance of the line, the company has the right to move in the transmission line area on foot and by using machinery and vehicles, to use roads and paths leading to the transmission line area and to use other areas, if necessary. The condition of the transmission line and the height of the vegetation in the transmission line area are monitored with the help of regular inspections.

Transmission line inspections are mainly carried out by walking in the terrain every 1 to 3 years.
The following issues, among others, are observed in the inspections:

• Vegetation in the transmission line area, new structures, excavations
• Possible inclination of tower structures, condition of steel parts, birds' nests, woodpecker holes
• Integrity and condition of insulators and conductors.

Special inspections are also carried out whenever necessary. These inspections are for issues such as decay damage in towers, earthing, insulators and couplings. Check out flights of the powerlines are carried out after storms if needed. During winter, in conjunction with hoar frost patrols by helicopter, ice loads are dropped off ground wires if necessary.