Transpower's applying for Commerce Commission approval to invest 1.1 billion dollars in replacing ageing electricity cables linking the North and South Islands

It includes work on three Cook Strait cables, adding a fourth to boost electricity capacity, and the building of new stations on either side of the water.

The cables are deteriorating to the point they must be replaced by the early 2030s, and are playing a more important role in balancing the power being generated by solar and wind farms.

The money spent by Transpower would be gradually recovered by the company via transmission charges.