Carillion, Costain and Electricity Network Solutions will refurbish and rebuild existing 33,000 and 132,000 volt power lines in the South East and East of England.
New fibre optic cables will also be installed to send essential signals to equipment.
The contractors’ responsibilities will include design, feasibility and construction works involved in replacing electricity lines, increasing capacity and renewing components on steel pylons.
The contracts come into effect immediately.
Nirmal Kotecha, director of capital programme, said: “We are delighted to be working with three contractors, including two new suppliers, which bring a depth and breadth of knowledge and experience to our business. Together, we will deliver essential improvements to our electricity networks to maintain reliable power supplies.
“Our aim is to deliver exceptional levels of performance in customer service, safety, quality and sustainability.
“We hope our suppliers will implement innovative ideas which fit in with our vision to be a respected corporate citizen, sustainably cost-efficient and an employer of choice.”
Andrew Wyllie, Chief Executive of Costain, added: “The upgrade of the UK’s electricity distribution system and the installation of fibre-optic infrastructure to improve connectivity are both major national needs.
“The appointment to this framework contract for a new customer demonstrates the success of Costain’s focus on blue chip customers who are investing billions in meeting these needs.”