Transpower will undertake a lengthy programme of work on the High Voltage Direct Current (HVDC) link, which allows power to be transmitted between the North and South Islands, to improve the resilience and security of the national grid.
The link allows South Island's hydro electricity to supply the North Island, and the North Island to send power to the South Island when water levels are low.
The 13-week programme will enable major work to be done to rewire parts of the HVDC lines and replace the control system equipment at Benmore and Haywards that converts high-voltage AC to DC, and back again at the other end.
Planning for this work has been underway since 2017 and had been timed to coincide with warmer weather when demand was lowest, Transpower's general manager grid services Mark Ryall said in a statement.
"The outages will see limits on the transfer of power northwards from the South Island power stations for use in North Island during this period," Ryall said.