Railway electrification in New Zealand
Earlier NZR electrified routes from 1923 to the 1940s operated at 1,500 V DC, but the NIMT (1986) and Auckland suburban services (from 2014) use 25 kV 50 Hz AC; all with overhead catenary supply.
The system used 275 V DC from a low overhead line via trolley poles, and 915 mm (3 ft) gauge track.
[4] The 1925 report by the English consulting firm of Merz & McLellan was commissioned by the Minister of Railways Gordon Coates to investigate electrification of suburban services in the four main centres of Auckland, Wellington, Christchurch and Dunedin.
The firm's partner Charles Merz of Newcastle upon Tyne had reported on Melbourne suburban electrification in 1908 and 1912.
[7] In February 1946, it was decided to electrify the remaining Wellington suburban lines to the Hutt Valley as there was a shortage of coal for locomotives, and also to replace commuter steam trains with EMUs, as the Hutt Valley was now largely residential with new state housing replacing market gardens.
The sections of these lines that were retained were mainly used for suburban commuter services, with initially some stock traffic to Johnsonville (later to Raroa).
From 1967, diesel locomotives (DA class) replaced electric locomotives (EW class) on freight trains south of Paekakariki on the Kapiti Line after the track in some older tunnels on the North–South Junction were lowered, so diesels could run under the catenary into Wellington.
[citation needed] In 1950, electrification of the entire North Island Main Trunk (NIMT) from Auckland to Paekakariki (the terminus of the Wellington electrification) was proposed by the General Manager Frank Aickin; the system comprised 657 route miles or 1,000 km (620 mi) of track.
[14][15][16] In 1974, a study was undertaken to consider the looming problem of "traffic saturation" on the mountainous central section, particularly the Raurimu Spiral.
Work started in late 1984 and was completed in 1988 though on 24 June rather than March as planned,[18] with an official train traversing the whole section.
[26] In 2021, New Zealand rail operator KiwiRail secured independent panel approval of the resource consents for the main works related to its electrification project in South Auckland.
In 2008, a paper was produced by former New Zealand Rail senior managers Murray King and Francis Small,[29] on the extension of the NIMT 25 kV electrification from Te Rapa to Papakura and Hamilton to Tauranga.
[29] It concluded that money would be better spent on grade and curvature easements, removing speed restrictions and increasing the length of passing loops.
[29] The 2023 New Zealand budget set aside $369.2 million for 4 years between 2023 and 2026 for the Rail Network Improvement Programme, which included funding for a detailed business case for the electrification of the North Island Main Trunk.
