Engineers repaired a fault on a transformer at Penrose substation which had caused two days of supply disruption.
About 74,000 households and businesses in the eastern suburbs were without electricity on Tuesday, due to the transformer fault and rolling cuts to reduce demand were made on Wednesday.
One Penrose transformer was out of service for maintenance when a second suffered a fault on Tuesday, and a third transformer shut down automatically from overloading.
The third transformer was soon restored, but heavy electricity use overloaded the system on Wednesday
Transpower chief executive Dr Patrick Strange said engineers repaired the second Penrose transformer on Wednesday night.
The national grid operator is also dealing with a second fault in its network. A breakdown at the Otahuhu substation has left the site working with just one transformer.
The cable fault at Otahuhu is unrelated to the power outages caused at Penrose, but Transpower admits it would rather not be dealing with it at this time.
In 2006, a fault at the Otahuhu station cut power to about 700,000 customers.
Prime Minister John Key said the latest power outages show just how vulnerable Auckland is, and investment must take place. He said the role and effectiveness of the Electricity Commission is also being reviewed.
Former Meridian Energy chief executive Keith Turner said the commission has played a part in delaying Transpower's equipment upgrades
Dr Turner said the commission has stopped several Transpower projects, despite a huge growth in electricity demand since the 1990s.
Power cuts to reduce demand
On Wednesday, Transpower instructed the lines company Vector to implement rolling outages in Auckland suburbs to reduce demand.
It said power was cut in residential parts of St Heliers for a short time and about 4,500 customers in Orakei were without power in the afternoon.
Power was restored to all suburbs just before 3pm and Vector said on Wednesday that hot water was back on in parts of south-east Auckland.
Beaches safe, shellfish ban
Auckland City Council on Thursday said eastern beaches are now safe for swimming.
Beaches at Okahu and Mission bays St Heliers and Kohimarama were closed on Tuesday after the power outage caused sewage pumping stations to fail and overflow.
However, Auckland Regional Public Health Service has advised people not to collect shellfish from St Heliers and Okahu bays.
'Tin-pot' network, says mayor
Auckland City Mayor John Banks and the business community say the crippling power outage on Tuesday was unacceptable.
Mr Banks said Transpower must find the money to replace its 35-year-old transformers.
"This is tin-pot infrastructure that doesn't work, lets us down, everyone loses," he said.
The head of the Newmarket Business Association, Cameron Brewer, said the power cut on Tuesday was is a blow for businesses - particularly in the third quarter of a major recession.
The power cuts on Tuesday are estimated to have cost millions.
Energy Minister Gerry Brownlee said he has already signed off a significant upgrade to Transpower's network.
Mr Brownlee said he has made the commitment to get the work done, and is confident Transpower can do it.
The Government is also reviewing the regulatory arrangements that sometimes hold up such improvements.
