Andrew Laxon puts the critics' main questions on the pylon plan to Transpower chief executive Patrick Strange
Will this mean no more power failures in Auckland?
You can never say never, replies Strange, but combined with other upgrades it will make the city a lot safer. The main benefit is bringing more power into Auckland, which is using more electricity each year. Running the first leg of the new transmission line into Pakuranga also gives an alternative supply route if the Otahuhu substation breaks down, as it did in 2006.
In separate developments, a second substation opens at Otahuhu next month to guard against any repeat failure and by 2013 a new cable will run from Pakuranga to Albany, via Vector's Penrose-CBD tunnel and the Harbour Bridge. This will create a ring around Auckland instead of the highly vulnerable single line which now feeds the city and Northland.
Is the new line necessary?
No one really knows because the answer depends on how much electricity Auckland will use in the next 50 years or longer and where it's likely to come from. Key factors include demand for electricity (which could change for many reasons, ranging from population growth to improved energy efficiency), alternative transmission routes and methods and the possibility of new power stations close to the city.
Transpower's critics say the grid operator has not addressed these questions seriously. Former Electricity Commissioner Roy Hemmingway was scathing about what he called the company's "weak analysis" and lack of creativity in solving the country's power problems. Rejecting its original plan in 2006, he acknowledged a new line would be needed but said it could wait until at least 2017 and cost up to $240 million less.
The following year another former commission board member, Graham Pinnell, questioned Transpower's reliance on old demand forecasts when more recent information showed lower demand and more local power stations. Pinnell, an engineer and a farmer, also worried that a 400kV line could be more likely to fail because of its high load.
Strange responds that Transpower has to look up to 70 years into the future because transmission lines last that long. It will take at least 40 years to know if the project is over-engineered or not but past experience suggests that taking the long view works. "Quite a few of the lines round the country, which we're now upgrading to 220kV, were built as 110kV lines, 220kV-capable, and thank God they did."
Couldn't they have used other methods?
Critics suggest many technical alternatives to Transpower's plan. They include high voltage direct current (HVDC) cables, which reduce energy loss, and rapidly developing technology based on superconductors, which have zero resistance to the current.
On the demand side, the new buzz words for electricity planners are "smart grids" - an interactive system which allows household appliances to feed information back into the national grid. In theory, dishwashers and washing machines can automatically switch on when power is cheap and turn off when it is expensive, saving home owners money and reducing the peak load for Transpower.
While most of these developments are still new or untested, Transpower's critics say they threaten to make its pylons obsolete within decades.
Strange says he's as keen on the new developments as anyone but the company can't afford to take chances, especially as earlier predictions of "a power station on every corner" - such as domestic solar panels or wind turbines - haven't worked out.
"The reality is some of the trouble we got into was because people relied on distributed generation occurring and it didn't. So we have to keep our options open. What we can't do is suddenly get to 2025 and say 'sorry Auckland but superconductors were 20 years late, so you're going to have rolling cuts for the next 20 years'."
Is it safe?
Transmission lines produce electric and magnetic fields which may affect health.
The actual effects and safe exposure levels are hotly debated.
A board of inquiry into the pylon project concluded there was weak evidence of a slight link between long-term exposure and childhood leukaemia - accepted by most expert groups including the World Health Organisation - but no evidence that exposure caused the cancer.
Hunua resident Chris Woods, who will see three of the new pylons from her back door, has a blunt challenge for anyone claiming the technology is safe. "Would they allow their children or grandchildren to live underneath electricity lines? Until you can yes to that, why put those in somebody else's back yard?"
Strange says we'd all prefer not to live close to power pylons, just as we'd all prefer not to live next to a motorway. "But if you ask me, is it safe? These lines have been designed to international health standards and the overwhelming evidence is; Yes."
He says the company has done checks for a few concerned homeowners and found a higher level of exposure from their underfloor heating.
How does Transpower have the right to build pylons on privately owned land?
The state-owned enterprise can build on the 318 properties "directly affected" by the new pylons (a sore point for some, as having to look at a 70m pylon on your neighbour's property does not count) but it has to negotiate compensation with landowners first.
Most of this money is for easements, which give Transpower the legal right to enter a property and build the pylon or carry out maintenance on the line.
The price is partly determined by how much the work drives down the property's value. In some cases the property is so badly affected that Transpower has to buy it.
The company plans to spend $125 million on easements and has so far spent $185 million buying 92 properties. Strange says this represents 80 per cent of affected landowners and the remaining 20 per cent will be mainly compensation, rather than buyouts. He admits only a handful of properties have been resold so far, some at a loss, but is confident the market will pick up in future.
A more pressing issue is reaching settlements with the 20 per cent of owners still holding out. Pylon building is now under way but the timetable must work around those properties still in negotiation.