Benmore Dam

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Benmore Dam
Benmore Power Stn NZ.jpg
Benmore Dam is located in New Zealand
Benmore Dam
Location of Benmore Dam
Location Canterbury Region, New Zealand
Coordinates 44°33′50.92″S 170°11′49.92″E / 44.5641444°S 170.1972000°E / -44.5641444; 170.1972000Coordinates: 44°33′50.92″S 170°11′49.92″E / 44.5641444°S 170.1972000°E / -44.5641444; 170.1972000
Construction cost $62 million
Dam and spillways
Type of dam Earth-filled dam
Impounds Waitaki River
Height 110 m (360 ft)
Length 823 m (2,700 ft)
Width (crest) 10.6 m (35 ft)
Width (base) 490 m (1,610 ft)
Dam volume 28 million tonnes
Spillway capacity 3,400 m3/s
Reservoir
Creates Lake Benmore
Total capacity 1.25 km3 (1,010,000 acre·ft)
Surface area 75 km2 (29 sq mi)
Max. water depth 120 m
Power station
Operator(s) Meridian Energy
Commission date 1965
Hydraulic head 92 m (302 ft)
Turbines 6 x 93 MW
Installed capacity 540 MW
Annual generation 2,215 GWh

Benmore Dam is the largest dam within the Waitaki power scheme, located in the Canterbury Region of New Zealand's South Island. There are eight other power stations in the Waitaki Power Scheme.

The dam is the largest earth-filled water-retaining structure in New Zealand. Its core is low permeability clay material, supported by two massive shoulders of river gravel. Lake Benmore has a volume of 12.5 million cubic metres, about 1.5 times as much water as Wellington Harbour. The dam's spillway can cope with 3,400 cubic metres of water per second, about 10 times the mean river flow. With a generating capacity of 540 MW, Benmore Power Station is the second largest hydro station in New Zealand behind Manapouri, and the largest dam in the country.

The $62 million construction of the dam and hydroelectric station began in 1958. It was commissioned in 1965, and officially opened by Prime Minister Sir Keith Holyoake on 15 May that year.[1] It was built for the New Zealand Electricity Department; since 1999 it has been owned and operated by Meridian Energy.[1]

From 2008 to 2010 the six turbines are being refurbished at a cost of $67 million. This will enable a 5% reduction in water use for the same generation capacity, increasing annual generation by 70 GWh. New switchboards and an upgrade to the switchyard are also planned.[1]

Benmore is the South Island terminus of the HVDC Inter-Island link between the North and South Islands of New Zealand. The HVDC converter stations are on the west side of the tailrace, and convert 220 kV AC power to ±350 kV DC for the 610 km (380 mi) journey to the North Island converter station at the Haywards in Lower Hutt.

Otematata is the small town that supports the dam, although with advances in technology the staffing needed to maintain the dam is drastically smaller. Due to this the town is now a small holiday community, with only around 200 permanent residents. The dam is about 8 kilometres (5.0 mi) up the valley from the township.

Key statistics[edit]

  • Lake Benmore area: ~ 75 square kilometres
  • Lake Benmore shoreline: 116 km
  • Dam crest length: 823 metres
  • Dam crest height: 100 metres
  • Dam width at base: 490 metres
  • Dam width at crest: 10.6 metres
  • Dam fill: 28 million tonnes
  • Head (hydraulic): 92 metres
  • Average river water flow: 340 m³/s
  • Nominal annual generation: 2,200 GWh
  • Installed capacity: 540 MW
  • Machinery: 6 x 93,000 kW vertical Francis turbines (Dominion Engineering, Canada), coupled to 6 x 90,000 kW 112,500 kVA generators (Canadian General Electric); 6 transformer banks totalling 1,150 MVA
  • Penstocks: Concrete
Benmore Dam from the south lookout, near the spillway

Transmission[edit]

Main article: HVDC Inter-Island

Benmore is a major switching point in the New Zealand national grid and one of two major switching stations in the Waitaki Valley (the other being Twizel sub-station). The importance is largely due to the location at Benmore of the southern terminal station of the HVDC Inter-Island link.

The main AC switching station is on the east bank of the tailrace, and electricity generated at Benmore Power Station is injected into the national grid here. Three major 220 kV lines containing five circuits run from the Benmore substation. Clockwise from south, they are: [2]

  • A double-circuit line to the Twizel sub-station, with one circuit going via Ohau C power station and one circuit going via Ohau B power station.
  • A single-circuit line to Islington sub-station in Christchurch, via Twizel sub-station and Tekapo B power station.
  • A double-circuit line to Aviemore Dam

The HVDC converter stations are located on the west side of the tailrace, connected to the AC switching station by lines over the tailrace. The +270 kV mercury-arc Pole 1 has its valve hall on the north side of the site, near the powerhouse. The -350 kV thyristor Pole 2 has its valve hall on the south side of the site. A new +350 kV thyristor Pole 3 is currently under construction to replace the ageing Pole 1, and its valve hall is located adjacent to the existing Pole 2 valve hall.

See also[edit]

References[edit]

  1. ^ a b c Bruce, David (30 October 2008). "Benmore gets more with first full rebuild". Otago Daily Times. Retrieved 2008-10-30. 
  2. ^ "South Canterbury Region Plan - Annual Planning Report". Transpower New Zealand. Retrieved 31 December 2010. 

Further reading[edit]

  • Martin, John E, ed. (1991). People, Power and Power Stations. Wellington: Bridget Williams Books Ltd and Electricity Corporation of New Zealand. pp. 316 pages. ISBN 0-908912-16-1. 
  • Reilly, Helen (2008). Connecting the Country – New Zealand’s National Grid 1886 - 2007. Wellington: Steele Roberts. pp. 376 pages. ISBN 978-1-877448-40-9. 
  • Sheridan, Marion (1995). Dam Dwellers – End of an Era. Twizel: Sheridan Press. pp. 392 pages. ISBN 0-473-03402-6. 

External links[edit]