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.
"Transpower as New Zealand's power system operator does not expect the outages will affect supply to households and businesses," he said.
The works include replacing aging transmission lines in Wellington's Churton Park area and updating control system equipment at our Benmore and Haywards converter stations for Pole 2, as well as some routine maintenance.
A spokesman for Transpower said the upgrade was not linked to the possible closure of the Tiwai Point aluminium smelter, the country's biggest power consumer, by its majority owner, Rio Tinto.
Early this month, Transpower said work would start on a network upgrade that will help mitigate the risk to their businesses if the Tiwai Point aluminium smelter closes.
Rio Tinto's report on Tiwai is due in the first quarter of 2020.
Transpower said that speculation over the future of the Tiwai prompted it to restart construction of projects that will allow the increased transmission of power in the south of the South Island to points north.
The grid operator said it had entered into separate agreements with Contact and Meridian to commence further work on Clutha Upper Waitaki Lines Project (CUWLP).
Chief executive Alison Andrew welcomed the agreements with Contact and Meridian who, for $5 million each, will fund the immediate start of work on the link.
CUWLP consists of five projects approved by the Electricity Commission in 2010. Two critical projects were completed in 2016 before work ceased.
The project was to recommence once an increased northward transfer of South Island generation was expected to be required.
"Recent speculation and uncertainty regarding the future of the Tiwai aluminium smelter has led to a review of the transmission network and a decision by Transpower to recommence work on two of the remaining three projects," Transpower said in this month's statement.