Omakau Zone Substation Upgrade

This project will require a new substation at a different location, as the current substation on the Ida Valley-Omakau Road is in a flood risk area with no room for expansion. The upgraded substation will be relocated to a new site, next to the Omakau stockyards on Lauder-Omakau Road, State Highway 85.

This project was to be completed by mid-2024, however it will now be later in the year. Large infrastructure projects can sometimes take longer than planned due to procurement and shipping delays etc, and we look forward to giving our customers an update as this project nears completion.

The current substation will be decommissioned and removed once the new substation is up and running, apart from the surrounding power poles. This will require a power outage. We will plan the outage as best as we can to avoid the irrigation season and to align with other work that may be happening in the area, to minimise customer impact.

What are the benefits?

• We are splitting the current single 11 kV feeder at the Omakau substation and reconfiguring it into four new feeders. This will mean that if a fault was to occur, only the customers on that feeder will be impacted rather than the wider area, which is the case at the moment.
• A larger transformer will double the supply capacity, ensuring it can meet the growing demands of the community.
• The substation will provide more options during planned and unplanned outages, with the four new feeders creating alternative ways to configure the network. This will mean customers will have a reduced exposure to unplanned outages and we will have improved flexibility to re-route supply and restore some customers sooner than we could previously. It will also give us more options when we are doing planned maintenance on the network.
• The new substation location creates an opportunity to install new reclosers and to relocate existing reclosers on the overhead line network. This will further reduce the number of customers impacted if a fault occurs and speed up the time it takes to restore power. This project will be completed once the new substation is live.

The diesel generator

• The new substation has a permanent generator that can provide power supply for most of the central Omakau community if we need to take the single main sub-transmission supply line out of service to undertake maintenance, i.e for planned power outages.
• It can provide some backup generation if an extended unplanned outage occurs to the main sub-transmission supply line. However, the generator cannot be used for every unplanned outage due to the delicate balance required to manage load fluctuations in real time as well as the location of the fault on the network relative to the generator.
• The generator needs someone onsite to operate it and, depending on the type of fault, it is often faster to fix the fault than getting a qualified person to site and undertaking the necessary start-up routine.
• In situations where the generator has been used for an unplanned power outage, we will need to take customers briefly offline before the usual network power supply is restored.

Other projects that will improve electricity supply

We have a number of projects either recently completed, underway, or coming up that will help to improve your electricity.

• We are in the process of implementing a new technology trial on the supply line from Alexandra to Omakau to detect emerging faults in real time, so we can remediate the defect before it causes an outages.
• Lauder Flat back-up supply: We will be upgrading the 11 kV conductor between Omakau and Lauder Flat. This work will improve the performance of the network in two ways. Firstly, the new power lines will address age-related defects and thereby reduce the fault rate and the number of outages. Secondly, this upgrade will increase the back-up support between the Omakau and Lauder Flat substations. To have full back-up support to Lauder Flat substation, we are exploring a second feeder option to Lauder Flat from Omakau.
• Investigate the feasibility of a staged additional Alexandra to Omakau link: The first stage would provide better back-up from Alexandra into the Chatto Creek area, which could then be extended into Omakau in later stages. Please note it may not be economic to implement this, and could have a significant impact on line charges, however the feasibility study will help with decision making.
• Investigate options for a new distribution line to Ida Valley: The valley is currently supplied by a single line from Omakau and therefore a fault on the line can cause an outage to all of Ida Valley until the repair work can be completed. We are investigating the feasibility of a second line into the area, enabling the network to be split with a back-up from each line. Please note it may not be economic to implement this and could have a significant impact on line charges, however the feasibility study will help with decision making.
• We also have ongoing power pole, cross arm and line replacements planned.

While we expect this work will improve the reliability of your power supply, it will not resolve unplanned outages caused by third parties, major weather events, vehicles damaging assets, ‘fall zone’ vegetation, animal interference, and occasional equipment faults.

Once the 11 kV feeder has been split into four feeders, we will do some analysis on the expected number of unplanned outages each feeder can reasonably expect each year and share this information with our customers. We will continue to monitor the performance of the Omakau electricity network and give updates to the community.

How electricity is supplied to Omakau and the wider area

The Omakau and wider area network has fewer customers per kilometre of line than any other part of our network throughout Otago. It is fed via a single supply line from Alexandra and then redistributed by a single line from Omakau.

The area is geographically challenging, prone to extreme winds, and much of the network is not easily accessible from the roadside. While this creates challenges, we have additional focus on this part of the network so we can make it as resilient as possible, given the current limitations.

Supply line

• The main supply line is a one-way sub-transmission (33 kV) overhead line spanning 25km between Alexandra and the Omakau substation.
• It extends a further 12km to the Lauder Flat substation (37km in total)
• If a fault occurred on this line, power would be lost in Omakau, Lauder Flat and surrounds

Distribution line

• The distribution line is a high voltage (11 kV) line, which distributes electricity to around 690 customers in Omakau and the surrounding area.
• At 235km, this is the longest line on Aurora Energy’s network, and one of the most remote.
• This line supplies customers in Chatto Creek, Omakau, Ophir, Poolburn and Moa Creek, while Lauder, Becks, and St Bathans are supplied from the Lauder Flat substation

No back-up supply

• Because the area only has one supply line, there is no current back-up supply for the main line, unlike other larger Central Otago towns such as Cromwell and Alexandra.
• With no alternative source of electricity, power cannot be restored until a fault response crew can drive to Omakau, patrol the line, find the fault, and repair it.

Impact of irrigation

• When the original line was installed between 1953 and 1968, there was little to no powered irrigation in the area. With the introduction of centre pivot irrigators, this now means irrigation pumps are our major load in the area. These pumps can draw a lot of power when they start, sometimes up to six times their normal load. This can cause voltage drops or fluctuations on our network.
• We have installed voltage regulators to improve the voltage for customers who are supplied further away from the substation; the voltage regulators make automatic adjustments to keep voltage levels steady.
• Voltage regulators were installed in 2022 to resolve low voltage issues occurring during the irrigation season from Chesterman Road towards Devonshire Road.