Scottish Hydro Electric Power Distribution (SHEPD) is carrying out work worth approximately £500,000 on the 33 kilovolt lines.
The lines will serve 1,200 customers across Coigach in Wester Ross and Assynt in Sutherland.
The work includes renewing wood poles where required, installing replacement metal bindings suited to the coastal environment and fitting enhanced lightning protection.
The programme aims to reduce the impact of future severe weather on the electricity supply to local homes and business, while helping engineers restore power faster if disruption does occur.
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The Deputy First Minister was shown preparations under way to fit one of 28 'spark gaps' which will help reduce the impact of lightning strikes in the vicinity of the power line.
Where lightning strikes the ground close to the line, the new equipment will allow the induced current to flow safely to earth, adding to the measures already in place to protect against direct strikes during electrical storms.
Following the visit, Mr Swinney said: "I welcome SHEPD's work to strengthen the electricity grid and make the network more resilient when severe weather strikes.
"The investment should help cut the number of customers affected by power cuts during storms and lightning strikes, and will also help engineers get the network up and running more quickly."
John Shanks from SHEPD added: "It was great to be able to show the Deputy First Minister the work we are carrying out to strengthen our network in advance of severe weather.
"The work which will go ahead at the end of August should make a real difference for our customers in the area for years to come. If high winds and lightning do cause disruption, the new equipment will help our local team as we battle to get the lights back on as quickly as we can."
(LM)
