Two independent reports have been released examining last month’s major power outage in New Zealand. On June 12, a blackout caused chaos in Auckland, leaving about 750,000 without power and resulting in US$52 million lost in trade. Roads were gridlocked, phones lines were down and hospitals closed, according to a Reuters report.

Heavy snow loads caused line tripping in the South Island, and at 8:32 a.m., major tripping at the Otahuhu substation caused 1000 MW of supply to be lost resulting in power outages in Auckland. Transpower, the owner and operator of New Zealand’s national grid, dispatched contractors to the site, and crews confirmed that two earthwires had broken, dropping onto three 110-kV buses and one 220-kV line. This resulted in the fault that contributed to disruption in the major portion of electricity supply to Auckland.

By 10: 45 a.m., Transpower had reconfigured the network to begin re-supply, and power was progressively restored by Vector throughout the afternoon.

“The outage of June 12 was a rare and catastrophic event; but underlines the importance of having a robust, flexible National Grid to provide for the long-term security of electricity supply, not only to Auckland but to all of New Zealand,” said David Gascoigne, Transpower chairman.

The two reports included one from Sinclair Knight Merz, which reviewed the incident, and the PriceWaterhouseCoopers report, which examined the operational response.

The SKM incident report found that high winds triggered the failure of connection equipment at Otahuhu Substation that led to the failure of the two earth wires and loss of load—and that this occurred because of the poor condition of the connection equipment (shackles). Transpower’s maintenance schedule and records have been checked and found to be adequate, but the report states that Transpower’s maintenance contractors should have identified the poor condition of the shackles and replaced them.

Transpower commissioned PWC to provide an assessment of the operational performance of Transpower in managing the events leading up to, during and following the incident. The key findings concluded that Transpower operational staff performed well throughout the unfolding situation on the day, particularly given extreme weather conditions in South Island that resulted in a significant increase in operational activity.

“Transpower is proceeding quickly to undertake actions identified in reports on the outage, and these remedial actions will contribute to greater security of operations. Transpower managed this serious situation effectively, and with no loss of life, particularly within the challenging environment on the day,” Gascoigne said.

Transpower has proposed upgrades to improve the reliability of supply to Auckland and the Northland regions.

A 400-kV project from Whakamaru to Auckland would provide significant strengthening of supply into the Auckland region. This proposal has been rejected by the Electricity Commission, and Transpower has indicated that it is in the process of revising the proposal to operate initially at 220 kV, migrating to 400 kV over time.

“Our concern with the amended staged proposal is the timeframe. We believe reliability of supply will be affected if Transpower’s line is not built by the earliest possible date and favor building the line by 2011,” said Gascoigne. “But even if we present our revised and rephrased proposal on the basis of implementation in 2011, we do not believe our proposal will meet the requirements of the Grid Investment Test as currently applied by the Electricity Commission.”

Transpower has also developed supplementary proposals that specifically address reliability of supply into Auckland. These projects assume, however, the completion of the initial phase of the staged 400-kV project on time by 2011.