17,700), most of the district is rural with a high usage of irrigation, with the associated water pumps responsible for more than 85 percent of EA Networks' peak summer demand.

In 1924, the AEPB's network was connected to the national grid and Coleridge Power Station when a 110/11 kV substation was established in central Ashburton.

After the Second World War, the AEPB established a production facility and reticulation network to supply coal gas to Ashburton township, and was subsequently renamed the Ashburton Electric Power and Gas Board.

As a result, Electricity Ashburton decided to concentrate on the distribution business, and sold its retail base and the Montalto power station to Tauranga-based generator-retailer TrustPower in April 1999.

Dividends from the shares are paid out in proportion to the amount of line charges each consumer pays.

[5] EA Networks' subtransmission and distribution network covers the Ashburton District, a 6,187 km2 (2,389 sq mi) area of the South Island, bounded by the Rakaia River in the north, the Rangitata River to the south, and the Pacific Ocean to the east.

[2] There are 17,800 customers connected to the network, the largest of which include a plastics manufacturer (RX Plastics), two meat processing plants (Silver Fern Farms at Fairton and Canterbury Meat Packers at Seafield), a vegetable processing plant (Talley's at Fairton), a skifield (Mount Hutt), and a large water pumping station at Highbank (taking water from the Rakaia River into the Rangitata Diversion irrigation race).

In summer where load is high and local generation is low due to irrigation (the largest local generator, Highbank, has limited water supply in summer as most of it is being diverted for irrigation), if one transformer is out of service, then the other transformer will overload during peak demand.

As a result, EA Networksn is in negotiations to install a third 120 MVA 220/66 kV transformer at the Ashburton substation around 2015 to secure supply to the network.

The proposed grid exit point would be located approximately where Transpower's Livingstone to Islington 220 kV transmission line crosses Thompsons Track between Methven and Rakaia (approximately 43°45′03″S 171°50′46″E / 43.7507°S 171.8460°E / -43.7507; 171.8460 (Transpower Thompsons Track substation (proposed))), would connect to both the Livingstone to Islington line and the nearby Tekapo B to Islington 220 kV (via a short tie-line), and have two 220/66 kV transformer - one new and one relocated from the Ashburton substation.

However, generators and step-up transformers are still vulnerable to severe damage if a network event causes an out-of-phase synchronisation.

[8] Highbank Power Station is potentially exposed to a risk of out-of-phase synchronisation resulting from manual or automatic switching on the 66 kV network.

These precautions add complexity to network operations and can delay restoration of circuits after a fault.

EA Networks plans to install phasor measurement units (or synchrophasors) on their 66 kV network in 2025 to enable automatic re-closing of 66 kV circuit breakers if the conditions for closure are suitable and will not produce an unacceptable out-of-phase synchronisation.