HVDC > HVDC References > Oceania > New Zealand HVDC link
A unique HVDC project that was decided when the first 20 MW Gotland link was the only HVDC transmission in operation and where new additions have been made.
The AC systems on the South and North Islands of New Zealand were interconnected in 1965 by a ±250 kV, 600 MW HVDC Interisland Link. In 1992 the grid owner Transpower upgraded the HVDC link to 1240 MW. The existing link, with its mercury arc valves, was modified to operate in a bipolar "hybrid" scheme together with a new thyristor converter. The first stage of the upgrade was to add the 700 MW thyristor converter, and the second step was to operate the old and new equipment as a hybrid bipole
rated 1240 MW. The two mercury arc valve poles were connected in parallel to form an upgraded pole 1.
Bird's eye view of Benmore converter station. Pole 1 in the front and Pole 2 in the background. | 
Pole 2 valve hall interior, Haywards |
On average 80 per cent of New Zealand's electric energy production is from hydroelectric sources, most of which is produced on the South Island. However, the North Island accounts for almost two thirds of the total electric energy demand, and has a peak load almost twice that of the South Island. After the upgrade of the HVDC transmission as much as 25 per cent of the North Island's electricity demand is met by South Island hydro capacity.
| Main data |  |
| Pole 1 and 2 1965 - 91 | |
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| Commissioning year: | 1965 (mercury arc valves) |
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| Power rating: | 600 MW |
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| No. of poles: | 2 |
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| DC voltage: | ± 250 kV |
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| Pole 2 after 1991 | |
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| Commissioning year: | 1991 (thyristor valves) |
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| Power rating: | Nominal 560 MW,
Continuous overload: 700 MW |
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| DC voltage: | -350 kV |
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| Pole 1A+1B and 2 after 1992 | |
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| Commissioning year: | 1992 (hybrid sceme) |
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| Power rating: | 1240 MW |
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| DC voltage: | +270 and -350 kV |
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| Complete transmission | |
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| Length of DC submarine cables: | 42 km |
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| Length of DC overhead line: | 575 km |
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| Main reason for choosing HVDC: | Long distance, including sea crossing |
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