The company will also start work at Dounreay to allow the connection of the refurbished overhead transmission line which will run south to Spittal through Thurso South, near Geiselittle in Scotland.
The commencement of work at Mybster and Dounreay follows on from Thurso South last month.
The substain works are part of is SHE Transmission’s £1.1bn Caithness-Moray project.
SHE Transmission project manager for the Dounreay-Mybster package of work Ian Clark said: "Mybster substation has seen significant activity in recent years associated with connecting wind farms in the area, while Dounreay was renewed completely a few years ago.
"The work now beginning will build on the investment that has already been delivered and result in a stronger onshore transmission network for Caithness as a whole."
The project intends to deliver 1.2GW of renewable electricity through a new subsea transmission link between Caithness and Moray in Scotland.
Construction work on the link, which will connect the electricity grid on either side of the Moray Firth, is expected to be completed in 2018.
Upon completion, the Caithness-Moray link will provide enough energy for about 2,000,000 residents in Scotland.
Image: The work at Dounreay will enable the connection of the upgraded overhead transmission line. Photo: courtesy of SSE.
