Transpower has successfully erected a temporary tower and transferred a 220 kV transmission line across, further restoring electricity supply to Northland.
A transmission tower near Glorit fell during maintenance on Thursday, causing outages across the region.
While most of Northland was connected later that afternoon, supply was limited and a number of households remained without power for a time.
Transpower had been re-routing power through its 110 kV network, but demand ramping back up on Monday was expected to put pressure on this supply.
Transpower executive general manager grid delivery Mark Ryall said they'd been working "around the clock" to fix the issue.
"With electricity supply into Northland at reduced levels, it was critical we got this tower up and supply restored through our 220 kV network over the weekend," he said in a statement on Sunday.
"Our design engineers worked through the night Thursday to plan the work and once we had necessary equipment in place Friday our crews began the complex and challenging work of putting up the tower and transferring the transmission line across."
This was completed and the circuit re-livened shortly after 2pm.
But while transmission capacity has been restored, full security of supply won't be restored until the second 220 kV circuit is back in service.
Ryall said more temporary structures need to be installed and the remaining circuit transferred to them. This circuit is under the fallen tower and the work is more complex than for the first circuit.
"We will be doing everything we can to get this completed as quickly as possible and hopefully before Friday," Ryall said.
"This means there is increased risk of short power cuts if faults happen to one of our three circuits currently supplying Northland but, depending on the cause, any disruption is likely to be short-lived."
Investigation underway
Transpower CEO Alison Andrew apologised for the disruption.
"What happened was unacceptable and we apologise to all those that have been impacted by the outage caused by the fallen tower," she said.
"It is never easy to be without electricity and we know that Northland has been through a lot in recent years."
Andrew said Transpower is commited to investigating what caused the tower to fall, and has appointed an external party to lead this.
"Something has gone terribly wrong for a tower to fall over, and we need to make sure it doesn't happen again," she said.
"We have been gathering information about what happened in parallel, but it is critical that we take a measured and informed approach to our investigation."
The Electricity Authority has announced it is also conducting a review after being instructed by the Minister for Energy.
"We welcome the review and will work closely with the Authority to ensure everyone understands what happened and we can take the lessons to prevent something like this happening again," Andrew said.
