Monday, April 22, 2024

Trees took toll on powerlines in cyclone: report 

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‘Out of zone’ trees falling onto lines were the single largest cause of outages.
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A review of Cyclone Gabrielle’s impact on electricity supplies through Northland,  Tairāwhiti and Hawke’s Bay has found outages were caused by fallen trees, wind conditions above line design limits and flooding. 

At its peak the cyclone inflicted outages across almost a quarter of a million customers around the North Island and kept some customers offline for over two weeks due to the breadth of damage.

The Electricity Networks Association commissioned a review of distribution impact and response to Cyclone Gabrielle, something Richard Krogh, the report’s principal author, said is critical given New Zealand’s increasing reliance on electricity as a key energy source.

“Electrification is going to reduce energy diversity in NZ, so the resilience of the sector is something we need to be mindful of,” he said.

“Out of zone” trees falling onto lines are a long-standing area of frustration for electricity lines companies, with rules only allowing them to trim within 3.5m of the affected lines.  They were the single largest cause of outages across the regions during Gabrielle.

Electricity Networks Aotearoa CEO Tracey Kai said the issue of untrimmed privately owned trees falling onto lines is an ongoing one for companies. 

She said the Ministry of Business, Innovation and Employment is reviewing legislation around the ability of companies to do more to manage privately owned trees outside the 3.5m limit.

“There is a continuum of how people respond to companies wanting to trim them back; some are happy for the companies to do so, through to those who want them left alone.”
The review also found there were strong links between the ability to restore electricity in rural areas and damage suffered by roading and communications infrastructure. 

A report earlier this year on Gabrielle’s impact on telco companies highlighted a lack of co-ordination between authorities, telcos and electricity companies as a key barrier to more rapid re-connection through the regions. 

Only two cell towers were actually damaged by the weather events, with the remainder simply running out of battery supply before electricity was restored. 

“The failure of roading access was material on the east coast, Hawke’s Bay, and Auckland rural regions. The communications failure on the east coast was a material factor, combined with access issues resulting in delays and impacting on restoration,” said Krogh.

To improve responses in coming years Krogh said upgrading power assets as they are renewed would deliver incremental improvement. But having alternative power arrangements like microgrids for more remote communities will also reduce risks. 

The small Tairāwhiti community of Ruatoria is an example. Community leaders there have pushed for an emergency reserve that includes Starlink satellite pods, generators, and mini water treatment plants. 

The report also suggests the need to increase companies’ ability to incentivise landowners to enable companies to better manage trees out of the 3.5m zone, or change the regulations.

Generally, company assets withstood the event well, but Krogh pointed to a lack of clarity around standards for flooding nationally. 

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