The deal was secured from project developer Beatrice Offshore Windfarm (BOWL), which is 50%-owned by SSE Renewables.
The remaining interest in BOWL is held equally by Repsol Nuevas Energias UK and Copenhagen Infrastructure Partners.
Construction on the Beatrice project is expected to start in 2016 subject to a final investment decision.
The development in the Outer Moray Firth was awarded an investment contract by the UK Government in May 2014.
HiDef commercial director Kit Hawkins said: "Beatrice is a hugely important project for the UK’s offshore wind industry, being one of the first to be granted a Contract for Difference by the Government and as such it will be a standard bearer for the new support regime.
"We are proud to be supporting such a key project at a transitional time for the UK renewables sector."
Onshore transmission works for the Beatrice project includes the installation of all infrastructure required to connect the Beatrice Offshore Wind Farm to the onshore National Grid.
The offshore cable is proposed to fall onto land at Portgordon and is expected to connect from there, through underground cables, at Blackhillock substation, near Keith.
The grid connection route was approved in principal in February 2013 by Moray Council’s Planning and Regulatory Services Committee.
Image: The 664MW Beatrice offshore wind farm is located in Outer Moray Firth, Scotland, UK. Photo: Courtesy of SSE.