Landowners in Wales and Shropshire have been warned to assess the potential impact on their businesses of a 30-mile long overhead power line project.

National Grid is planning to build an electricity substation on a 7.6ha site at Cefn Coch in Montgomeryshire, which will link to six proposed wind farms in the area.

Dozens of farms are likely to be affected by the substation and the 100 pylons needed to carry the overhead line from Lower Frankton in Shropshire down the picturesque Vyrnwy valley.

Jonathan Wilkinson, chairman of campaign group Montgomeryshire Against Pylons, said that he was “disappointed but not surprised” by the chosen route.

“If they wanted to choose a route to maximise opposition, they’ve chosen it. If they wanted a fight, they’ve certainly got one now,” he said.

Landowners affected by the project are being urged to look carefully at the likely implications for their land and businesses.

CLA Wales director Ben Underwood said the development would have huge implications for farmland and could greatly affect the ability of landowners to carry on their businesses.

“There will be a substantial impact on the countryside along the route and every farmer and landowner will need to assess the effect on their own business, both on the construction work and other losses associated with the pylons, including environmental and other surveys,” he said.

Sheep farmer and NFU Cymru county chairman for Montgomeryshire, Edward Chapman, said that the union opposed the project in its current form.

He said NFU Cymru and believed the only acceptable solution was for the cables to be laid underground, without impacting unduly on the ability to farm the land during and after installation.

But Jeremy Lee, lead project manager for National Grid, told the Guardian newspaper: “We understand people have concerns about overhead lines, but where they are used, we will work hard to reduce any visual effects by routing the line carefully and using appropriate pylon designs which could include the new T-pylon.”

It will take at least three years of planning before work begins on the substation and cables in Powys.