Damage at the Redclyffe substation in February. Photo: RNZ / Lauren Crimp
Transpower is still looking at relocating a key substation near Napier despite completing repairs and raising electrical gear after February's deluge.
The Redclyffe substation, submerged in Cyclone Gabrielle, was cut off the national grid for a month, and is only now back to its pre-cyclone state.
"We are continuing to consider options for either further strengthening its resilience or relocating it to a new site," general manager of grid delivery, Mark Ryall, said in a statement.
"Key considerations include the timescales involved in relocating ... costs, logistical challenges and making sure we have sufficient resilience in place now in case another major event happens."
It had investigated engineering options, and new flood modelling was now being done.
They had done "a huge amount of work" across Hawke's Bay since Gabrielle, Ryall said.
Redclyffe was one of a dozen substations nationwide that Transpower rated in 2020 as "vulnerable and critical" to flooding.
Its 2020 report into resilience also rated another 32 substations as "vulnerable" to flooding.
During Cyclone Gabrielle, power cuts took out phone and internet communications across several regions.
Up to 75,000 customers in Hawke's Bay were without power at any one time.
Flooding at Redclyffe substation. Photo: Transpower
Prior to the cyclone hitting, Transpower had been aiming in July 2023 to do more detailed investigations at all dozen substations rated critical.
Even if it had brought Redclyffe up to the current standard, that was to resist a 1-in-450-year event, and Gabrielle exceeded a 1-in-500-year event.
"The new standard would have not have entirely mitigated all of the impacts from Cyclone Gabrielle," Transpower told the Commerce Commission.
Some older substations have just 1-in-100-year resilience levels.
Transpower has said it was looking at accelerating an investment plan that had been due for 2025-30 for the two-to-three highest priority sites.
It had aimed for spending $110m on resilience of the grid overall, and its new investigations into the 12 substations would help it decide whether to seek the commission's OK at the end of next year, to spend even more.
Transpower's spending flows through into higher lines company charges to consumers.
"As Redclyffe substation has a large proportion of connection assets, any significant changes to it must be agreed and supported by our customers as they bear the costs," it said.
The 12 "vulnerable and critical" substations are:
- Albany, Auckland
- Edgecumbe, Bay of Plenty
- Redclyffe, Napier
- Whakatu, Hastings
- Whirinaki, Hastings
- Southbrook, near Rangiora
- Bromley, Christchurch
- Temuka, north of Timaru
- Studholme, north of Oamaru
- Frankton, near Queenstown airport
- South Dunedin
- Gore, Southland
Transmission towers - pylons - are another problem. The resilience report said 35 of these were vulnerable to flooding, and 14 were "vulnerable and critical", while landslides and other land instability posed risks to over 200 towers and poles.
In particular, braided rivers in the South Island pose problems, and have taken out towers, such as when five failed and four were damaged in the 2019 Rangitātā River flood.