MainPower Electricity Network Infrastructure and Operations
MainPower manages a comprehensive electricity network spanning 11,180 square kilometres (4,320 sq mi) across the Waimakariri, Hurunui, and Kaikōura districts. This extensive infrastructure ensures a reliable power supply to several key towns, including Kaiapoi, Rangiora, Oxford, Woodend, Pegasus, Amberley, Waipara, Culverden, Cheviot, Hanmer Springs, and Kaikōura.
Key Facts
- Service Area: 11,180 square kilometres covering three districts.
- Customer Base: 44,918 total customer connections.
- Infrastructure: 5,234 km of total line length supported by 56,430 poles.
- Energy Delivery: 640 GWh of energy delivered with a peak demand of 117 MW.
- Grid Access: Electricity is sourced from Transpower via five grid exit points (GXPs).
Network Architecture and Distribution
The network operates by taking electricity from Transpower's national grid at five specific grid exit points (GXPs): Kaiapoi, Southbrook, Ashley, Waipara, and Culverden. From these points, power is moved through a tiered system of voltages to reach the end consumer.
MainPower operates 4,873 km of circuits dedicated to subtransmission and distribution. Subtransmission occurs at 66,000 and 33,000 volts, while distribution is handled at 22,000 and 11,000 volts. Following New Zealand standards, the final delivery to residential homes is provided at 230/400 volts (phase-to-neutral/phase-to-phase).
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Strategic Upgrades and Expansion
To improve reliability and capacity, MainPower has undertaken several strategic acquisitions and infrastructure projects. In 2011, the company purchased the Kaikōura GXP and the 66 kV transmission line from Culverden to Kaikōura from Transpower.
Further enhancements include the 2015 up-rating of the network west of Rangiora toward Oxford, which increased capacity from 33/11 kV to 66/22 kV. Current ongoing projects focus on upgrading the 33 kV subtransmission line between Cheviot and Kaikōura to 66 kV. Additionally, MainPower is preparing a new "Rangiora East" GXP between Rangiora and Woodend to supply the Woodend and Pegasus areas, which will reduce the load on the Kaiapoi GXP.
Operational Performance and Financials
The network's efficiency is measured by its Regulatory Asset Base (RAB), which stands at $328 million, and its annual energy throughput. While the system is robust, performance metrics for the 2023/24 period were impacted by an extreme windstorm in October 2023, leading to higher interruption rates.
These interruptions are tracked via SAIDI (System Average Interruption Duration Index), measuring the average outage duration, and SAIFI (System Average Interruption Frequency Index), measuring how often the average customer experiences an outage.
| Parameter | Value |
|---|---|
| Regulatory asset base | $328 million |
| Line charge revenue | $60.5 million |
| Capital expenditure | $37.3 million |
| Operating expenditure | $24.7 million |
| Customer connections | 44,918 |
| Energy delivered | 640 GWh |
| Peak demand | 117 MW |
| Total line length | 5,234 km |
| Distribution/low-voltage overhead lines | 3,668 km |
| Distribution/low-voltage underground cables | 1,191 km |
| Subtransmission lines and cables | 390 km |
| Poles | 56,430 |
| Distribution transformers | 8,493 |
| Zone substation transformers | 24 |
| Average interruption duration (SAIDI) | 937 minutes |
| Average interruption frequency (SAIFI) | 2.88 |
Frequently Asked Questions
Which areas does MainPower serve?
MainPower covers 11,180 square kilometres across the Waimakariri, Hurunui, and Kaikōura districts, including towns such as Rangiora, Kaiapoi, and Hanmer Springs.
How does MainPower receive electricity?
Electricity is sourced from Transpower's national grid through five grid exit points (GXPs) located at Kaiapoi, Southbrook, Ashley, Waipara, and Culverden.
What is the standard voltage for home delivery?
In accordance with New Zealand standards, electricity is delivered to homes at 230/400 volts (phase-to-neutral/phase-to-phase).
Why were the 2023/24 interruption rates high?
The high SAIDI and SAIFI values for the 2023/24 period were primarily caused by an extreme windstorm that occurred in October 2023.
What is the purpose of the new Rangiora East GXP?
The new GXP is being prepared to supply Woodend and Pegasus, which will help offload the existing Kaiapoi GXP.