Last updated: 21 Jul 2025
What are we doing?
Transpower is investigating possible electricity infrastructure investments for the upper South Island, north of Twizel, to ensure a reliable power supply for the future as the region grows and more homes and businesses switch their energy use to electricity.
Why are we doing it?
Electricity use across the upper South Island has been rising steadily, particularly during summer, when power is used for irrigation. With the growing shift toward a lower carbon, more electrified way of life and forecast electrification of South Canterbury primary processing, demand for electricity is expected to increase further.
In the upper South Island, there is not enough electricity generation to meet demand. Electricity is supplied into the upper South Island through high-voltage transmission lines coming north from the Waitaki Valley.
Long distance transmission like this requires additional voltage support to help maintain a reliable supply of electricity. Voltage support tools and equipment include bus couplers, switching stations and dynamic reactive support.
In 2012 we began investigating long-term development plans to ensure voltage stability is maintained in the upper South Island. As the immediate need was relatively urgent, but the longer-term outlook was uncertain, we decided to split the investment into stages:
- Stage 1, a low-cost investment for a new bus coupler at Islington Substation – a short-term deferral
- Stage 2, a second (and potentially much larger) investment.
Timeline and updates
Stage 1
The Stage 1 project sought funds to install a sixth 220 kV bus coupler at Islington Substation. This was a low-cost measure which allowed end-of-life voltage stability equipment at Islington to be decommissioned and at the same time ensured no voltage instability issues in the short term. The project also sought funds to investigate future switching station options further. We submitted our Stage 1 proposal in June 2012, and it was approved by the Commerce Commission in February 2013. The project was delivered and the bus coupler commissioned in 2014.
Following the switching station investigation that was part of Stage 1, in 2015 we sought and received an approved Output Amendment to our Stage 1 proposal from the Commerce Commission to add the ability to secure designations and property rights for potential switching stations in the future at two locations, Orari and Rangitata. This was to ensure that switching stations could be commissioned in time, if switching stations proved to be the preferred option to meet the voltage management needs for Stage 2. We actioned this as part of Stage 1. This Output Amendment has allowed this option to remain possible, but does not preclude the Stage 2 investigation process, which will involve long-listing and short-listing processes and consultations, and which may result in a different preferred solution.
Stage 2
We are now in Stage 2 of this project. Following an initial shortlist consultation of investment options which concluded in February 2025, we undertook further consultation in May 2025 to reflect revisions in our initial thinking, which now incorporate a more detailed understanding of the activities, resources and scope of work required. These revisions have resulted in our preferred option increasing to approximately $164 million, compared to the $77 million presented in our shortlist consultation. Click here to read our consultation documents and summary of submissions.
We held a long-list consultation in August-October 2023. This was the first consultation to seek feedback about our thinking, assumptions, and possible early options for upgrades on the high-voltage electricity transmission network for the Upper South Island region.
Hearing from those interested in potential new generation, planned commercial or residential developments, and industrial conversions from fossil fuels to electricity helps us better understand what is happening, and what the future need for electricity will be. The information received will help us refine our thinking and planning about the options we are looking into to provide for future growth.
What happens next?
Transpower will submit a proposal to the Commerce Commission for transmission infrastructure for the upper South Island later in 2025.
Keep an eye out for updates on this webpage or email us at [email protected].
More information
- Click here to view the documents from our further consultation on our short-list of options.
- Click here to view the initial short-list consultation documents.
- Click here to view the long-list consultation documents.
Transpower's Notice of Intention to the Commerce Commission.
This letter outlines our planned Major Capex Proposal project for the upper South Island upgrade project to the Commerce Commission, identifying the envisaged approach to staging investments and suggesting a timeline.
Letter from the Commerce Commission agreeing preliminary matters and timeframes.
The Commerce Commission responds formally to our Notice of Intention, expressing comfort with proposed approach and agreeing a timeline for the process, as is required under cl 3.3.1(3) of the Capex IM.
Transpower's update to our Notice of Intention to the Commerce Commission.
This letter requests that our Upper South Island Upgrade project is treated as a major capex project (staged). It is an updated notice under clause 3.3.1(1) of the Transpower Capital Expenditure Input Methodology Determination 2012 (Capex IM).
Letter from the Commerce Commission agreeing with Transpower's update to our Notice of Intention.