Completed Projects

Cromwell Zone Substation Transformer Upgrades

Aurora Energy is upgrading the Cromwell Zone Substation Transformer. Project status: Starting December 2019, target completion August 2020


The Cromwell Zone Substation is in Barry Avenue, Cromwell and supplies Cromwell township and the surrounding regions such as Pisa Moorings and Lowburn. It is connected to Transpower’s Substation along Bannockburn Road and the site is shared with our maintenance contractor.

What is a Zone Substation?

A Zone Substation is a key part of the total electricity supply system that supplies electricity from generation sources (such as wind farms and hydro power stations) across the national grid transmission system to the local distribution system then to consumers. A Zone Substation usually consists of one or more power transformer(s) that converts high voltage electricity to lower voltages for distribution throughout the local community. Distribution transformers in the street reduce the voltage further to supply customers at their premises.

Why was the upgrade needed?

The existing Cromwell substation was established in 1981 and has undergone various upgrades throughout the years including replacement its switchboard with safer arc flash rated equipment, the introduction of an electronic hot water and streetlight control unit, and a bay to house Aurora’s mobile substation when not deployed elsewhere.

The demand for power in this area is increasing rapidly and is now near to the capacity of the existing power transformers. Installing larger units will ensure Aurora meets the needs of our customers now and in the future. The old outdoor structure will be removed and replaced with ground placed equipment to improve reliability and reduce the visual impact of the site and we are installing two additional circuits to supply the local area. The additional circuits will benefit the long-term reticulation plan of the region.

Beyond the Cromwell Zone Substation itself, two new vacuum enclosed circuit breakers will be installed in the line connecting Transpower’s Cromwell Substation and Pioneer Generation’s Roaring Meg Hydro. These new switches and operable from either of Aurora’s Network Control Centres at either Cromwell and Dunedin resulting in faster restoration of supply if a fault occurs.

Further Details

There will be two new 12/24 MVA power transformers at the Zone Substation. Physically they are at least twice as large as the existing units. To accommodate these, the Zone Substation’s switchyard will be expanded (in the direction away from Barry Avenue). This upgrade will ensure there is sufficient control in place to avoid oily water being discharged into the public system in the unlikely event of oil spillage from the two new power transformers, each containing approximately 9,000 kg of oil. Civil structures such as bunds, underground oil containment tank, and an oil separator unit are included for this purpose, on top of fire spread prevention. Most of these construction work will be contained within the fenced substation site, so we do not expect any disruption to local residents.

All existing six 11 kV feeder cables will be upgraded to larger size cables to meet the increased capacity. This will involve certain level of earthwork including trenching within the switchyard and also in the road reserve of Barry Avenue, where new cables will have to be jointed onto existing cables. There is also an existing 33 kV cable along Barry Avenue that has to be recovered and re-routed. There is likely to be some temporary disruption to Barry Avenue and its road shoulders from time to time while the work is being carried out. Traffic management will be in place to ensure the safety of everyone.

For works outside the switchyard, along Bannockburn Road, there will be new fiber optic cables being installed into existing ducts for approximately 500m, unless the existing duct cannot be used for unforeseen reasons there should be minimal disruption for this work. Where the two pole mounted vacuum breakers are to be installed, there will be deep driving of three separate rods into the earth. Aurora is in the process of obtaining approval from the Otago Regional Council for this work and ensuring the integrity of the aquifer in the vicinity.

Noise level during construction will be minimised and working hours will adhere to CODC’s consent requirements. For permanent noise, the new power transformers are located further away from Barry Avenue and the noise level from the equipment fans will comfortably adhere to the site designated requirement.


What electricity outages are planned?

Measures will be taken to ensure that interruption to our customers are minimised and it is likely that there will be multiple power outages planned for this work. In the event that planned power outages are required to ensure the safety of our contractors you will receive individual notification from the contractor or your electricity retailer advising the specific date and time in advance. We appreciate your patience and understanding that this is a significant upgrade for this site and many equipment will be subject to some level of works especially during the commissioning process.

Indicative project timeline

Oct Nov Dec Jan
Feb Mar Apr May Jun Jul Aug Sep Oct Nov

Design Complete


Enabling works, Civil and Earthworks


Ongoing Electrical Work








Thank you

We thank the local community for their understanding as we carry out this improvement work and apologise in advance for any inconvenience and disruption that may be caused.

More information and feedback

We welcome your feedback. For more information, please contact Aurora at 0800 22 00 05 or send us an enquiry.