Auckland’s central business district has been caught in the grip of not one but two separate electricity crises in the past few days, but matters should be resolved shortly, says Mercury Energy’s general manager of networks, Richard Gibbons.
Gibbons knew Mercury was in for a tough time when a 110,000-volt cable failed two weeks ago. When a second cable failed, that left only a smaller 22,000-volt cable to serve as backup.
“We’ve been trying to work out what the statistical probability of both failing at the same time is,” says Gibbons with a wry smile.
A new 22,000-volt overhead cable will temporarily ease the pressure until one of the main cables is restored.
Finding and fixing the problem isn’t an easy matter. The damaged circuits consist of oil-impregnated paper-surrounded gas pressure cables. “You have to take down the insulation, test it all, then rebuild it. It takes a minimum of a week to re-pressurise the cable so that it’s safe to re-energise.”
The cables are both about 40 years old and should be fine for another 20, although Gibbons says they have had problems with them in the past. “We can only deduce that there’s a problem with this particular design or there’s been some problem with the pressurisation.”
The long-term answer, hopefully, is to be found in the Penrose tunnel project, which will see two new plastic-insulated cables replacing the older 110,000-volt cables. With a higher wattage capacity, these cables are intended to carry Auckland’s CBD power needs well into the next century.