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Major upgrade of Otahuhu substation proposed

Transpower proposes major upgrade of Otahuhu substation

11 Aug 2006

Transpower has submitted a proposal to the Electricity Commission that will modernise and provide greater diversity of supply at the Otahuhu substation.

Chief Executive Dr Ralph Craven said Transpower had responded to the concerns raised about Auckland’s heavy reliance on the existing substation equipment at Otahuhu.

“We had planned to upgrade the Otahuhu substation by 2011 as part of the proposed new transmission line into Auckland. We have now separated out the Otahuhu substation development and submitted it separately for approval.

“At a cost of up to $77.3 million it is in itself a significant project but Transpower believes it can be completed within two years of receiving approval.”

Dr Craven said the project addresses historical issues.

“For many decades Otahuhu substation has been the key link in the network, where electricity comes into Auckland from the south and is then distributed throughout Auckland and Northland. But the Otahuhu facility is ageing.

“The current design of the substation evolved between the 1930s and the 1960s. 110 kV and 220 kV outdoor switchyards are located side by side and a number of connecting transmission lines cross over those switchyards.

“While these overhead crossings met the design practices of the time, modern practice is to avoid this situation,” Dr Craven said. It was an earthwire coming free from one of these crossings that caused the June 12th outage.

The proposal submitted to the Electricity Commission includes undergrounding the 220 kV circuits that cross over the existing switchyards. A new physically separate, enclosed, high reliability 220 kV switchyard will be built on the Otahuhu site. The main incoming and outgoing 220 kV circuits will be shared between the old and new switchyards, which will also be connected to permit switching and load sharing flexibility.

“This project is an important step in a long-term strategy to provide much improved diversity of supply into and across Auckland,” Dr Craven said. “We anticipate that the Electricity Commission will give consideration of our application a high priority.”

View the full Otahuhu project application

What is the justification for this project?

Transpower considers this project to be an urgent reliability upgrade to reduce the possibility of low probability-high consequence events disrupting power supplies to the Auckland area. The existing substation configuration is not up to current international best practice for a major load centre.

How much will the upgrade at Otahuhu substation cost?

The mid-range estimated capital cost, in 2006 dollars, is $60.5 million. The upper range cost, adjusted for inflation and allowing for project and financial contingencies, is $77.3 million. This represents the maximum cost that Transpower will be seeking to recover. Transpower will only recover the actual costs if they are lower than $77.3 million.

What does the project include?

New indoor 220 kV gas insulated switchgear (GIS), physically separate from the existing outdoor switchyards
Remove all crossovers of transmission lines
Underground cable for all transmission line entry and exit points
Reconnect half of the existing 220 kV circuits to the new switchyard
Underground cable connections between the new and existing switchyards
What is Gas Insulated Switchgear (GIS) and why is it being proposed?

GIS technology has been preferred over air insulated switchgear (AIS), which is currently used at Otahuhu. GIS has a higher capital cost but has a number of advantages:

GIS is much smaller than AIS and greater physical separation can be achieved from the existing equipment
GIS is housed indoors, in a building similar in size or possibly smaller than the existing warehouses on the Otahuhu site
As the GIS is fully enclosed it is a controlled environment that is more protected from outside influences
Using GIS will leave room for future upgrades at the Otahuhu site.
How does this project fit into a strategic long-term plan for Auckland’s electricity supply?

There are two important projects that will impact on the medium-term (5-6 years) development at Otahuhu substation:

A new high capacity transmission line into Auckland from the south
Enhanced supply across Auckland
At Otahuhu substation these developments will require new connections for additional incoming and outgoing circuits, new transformers and voltage support equipment. In the longer-term, Transpower intends to replace the existing outdoor switchyard with modern new equipment.

What approvals are needed?

The Electricity Commission has been asked to approve the project as a core grid reliability investment, which is consistent with good industry practice for a substation supplying a critical load centre. The Commission is expected to respond within six weeks with a decision or a request for more information.

Transpower owns the land at Otahuhu substation but some existing property rights will need to be re-negotiated.

A resource consent will be required from the Manukau City Council, with whom initial discussions have been held.


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