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Fingrid’s mission is to maintain and develop Finland’s high-voltage electricity transmission system. The nationwide grid includes some 14,300 kilometers of power line. A significant portion of the grid is located in areas where trees grow underneath the lines. On average every five years the vegetation gets cleared in order to prevent trees from interfering with the power lines, causing power outages or other dangers.

The regularly cleared coppice growing beneath the power lines consists mainly of deciduous trees originating from sprouts. The growth rate of sprouts is affected by various factors and therefore the predefined clearance cycle cannot blindly be relied on. The Natural Resources Institute Finland (Luke) has assisted Fingrid in creating models and an application, with which the growth rate of trees can be reliably estimated.

voimalinja sähkölinja fingrid runkoverkko tutkimusmetsä
Finland’s power grid consists of 14,300 km of power line, considerable share of it in forest lands.

Contractor’s inspectors walk through Fingrid’s lines every few years. The inspectors monitor the tower structures and wire conditions. At the same time they observe the coppice and use tables for interpreting how long the trees will safely fit underneath the wire. The observations are recorded with a mobile application and submitted into an asset management system. The system informs when it spots objects that should be cleared.

“If the system notifies that some tree cannot wait until the planned clearance, it will get a targeted treatment,” says Mikko Nykänen, an expert in vegetation management at Fingrid.

Luke’s model brings estimation charts to the next level

Fingrid has had models for predicting vegetation growth already since the 1990s, but the new model will bring more reliability in the estimations. Soil fertility has impact in the growth rate of the trees, as has tree species.

Jouni Siipilehto.

“A young alder sprout grows the fastest but among older sprouts silver birches have the highest growth rates. Also climate warming has an impact on tree growth,” describes Jouni Siipilehto, Luke’s senior scientist who was in charge of developing the prediction models.

“We had investigated and developed growth models for trees already before this project. However, this was a completely new application area for us. Typically, one looks for average growth rates, but now we needed to come up with a maximum growth rate for tree sprouts,” says Luke’s research professor Jari Hynynen, who was planning and preparing the project.

The model helps mitigate risks

According to Nykänen, the major benefit of the model and the application is related to managing and mitigating risks.

“We are not aiming to optimize our clearance cycles. Instead, we seek to avoid situations where a tree hits a power line. Recovering from a power outage is on a whole other cost level than organizing a clearance work. In addition, Fingrid has an obligation written in the electricity market act to perform in a way that electricity transmission is not impacted by a tree falling over a wire.”

The model and the application to run it were implemented in 2018. During 2019 the work was finalized and since the end of the year Fingrid has started to roll out its usage. The first experiences of the model’s predictive power are very promising.

“Luke maintains lots of long-term measurement data and in addition we perform cross-sectional inventories around the nation’s forests. We also have the needed skills and knowledge to perform the needed research. This Fingrid case is just one example area where we can apply our know-how,” Hynynen sums up.

Photos: Erkki Oksanen.