Строительство гидроэлектростанции в Новой Зеландии: история и инфраструктура.

Historical records showed that the long term flow of the river was and that a controlled flow of would be possible through the power station. The designers estimated that with an overall efficiency of 85% the mean output would be 160 MW and assuming an annual power factor of 50% the station could deliver a maximum output of 320 MW. In October 1949 at the request of the Ministry of Works, Dr. John L. Savage a former Chief Design Engineer of the United States Bureau of Reclamation visited the site and provided advice on the proposed design options. While an earth dam was more suitable at the wider Pleasant Valley location after considering various options it was decided in October 1950 that due to the geology at Tamblyn's Orchard a solid concrete gravity dam would be more appropriate.

The MOW was the government department responsible for designing and constructing the government power station in New Zealand. Though it was still unresolved who would be designing and building the dam and power station Fritz Langbein the engineer in chief of the MOW assumed that his organization would be undertaking the design and would at the least build the diversion channel. Therefore, he put in place plans to build a construction village and in July 1949 had the MOW commence work on the excavation of the diversion channel. This channel would eventually be 2000 feet (610 m) long, 100 feet (30 m) wide and 70 feet (21 m) deep which required the removal of of material. By the end of 1950 720 workers were being employed on site.

To house the workforce the Ministry of Works first built in 1947 a single men's camp and cookhouse on the west bank of the river. In 1950 work began on erecting 100 workers' cottages. The following year began on building a YMCA hall, shops, a hospital and nurses accommodation and a further 225 cottages. Eventually the village grew to 724 houses complete with a 90 bed hostel, a 600 child primary school, a cinema, a social hall, 17 shops, three churches, a fire brigade and ambulance building, four tennis courts, a swimming pool and a piped sewage scheme. In addition there were four single men's camps (two on the east and two on the west bank) containing a total of 1000 huts. These facilities cost a total of NZ£2,241,925. As the Otago Central Electric Power Board's network could not provide sufficient power to the village and the project, the government built a temporary power station containing two 1 MW and one 0.4 MW diesel generators, to supplement the supply.

In May 1946 the PWD and the New Zealand Railways Department held a meeting to determine what would be needed to transport materials to the proposed site of the power station. The main loads associated with the first four generating units were as follows: thirteen generator transformers, each 39.5 tons (40.1 tonnes), 15 ft 6 in (4.72 m) long, 10 ft 4 in (3.15 m) high, 8 ft 2 in (2.49 m) wide; twenty four stator sections; each about 19 tons (19.3 tonnes) gross, 14 ft 9 in (4.5 m) by 9 ft 1 in (2.77 m) by 6 ft (1.83 m); four shafts and thrust plates, each 33½ tons (34 tonnes) gross, 20 ft (6.1 m) long by 6 ft 6in (1.98 m) by 7 ft 10 in (2.39 m); four turbine runners, each 25 tons (25.4 tonnes), 12 ft 10 in (3.91 m) diameter, 6 ft 7 in ( 2 m) high; four generator bottom bearing brackets, each 20 tons (20.3 tonne) gross, 12 ft (3.66 m) by 12 ft by 6 ft 1 in (1.85 m). The most direct rail route was via the Roxburgh Branch line to its terminus at Roxburgh. However this line had an uncompensated 1 in 41 grades and five chain (100.6 metre) curves that would limit the loads to 180 tons per engine. As well, four tunnels In May 1949 the government reluctantly accepted that overseas contractors may have to be employed to meet the planned construction programme. This admission lead to an unsolicited bid being received from a British consortium consisting of civil engineering contractors Richard Costain, electrical manufacturers and contractor English Electric and Insulated Callender Cables to design and build the Roxburgh and other New Zealand power stations. Meanwhile, work continued on site on completing the construction village and creating the diversion channel. However progress was slow, with completion of the diversion not expected until 1953 instead of the planned 1951.

In 1949 the newly elected national government, which ideologically favoured private enterprise, appointed Stan Goosman as both Minister of Works and Minister of the State Hydro electric Department. By 1951 the projected project delays were serious enough to draw criticism from the Electrical Supply Authority. By now aware of the projected energy shortfalls and the shortage of government resources to complete six other hydroelectric projects that were underway as well as complete Roxburgh, Goosman's response was to announce on 25 September 1951 that tenders would be called from interested parties to undertake the civil aspects of the project. This required the rapid production of tender documents and specifications by a short staffed government design staff. Bidders had the choice of offering on either a bill of quantities basis or by nominating a 'target estimate' plus a 4% fee. In this type of contract the Government met all costs and the contractor received a fee of 4% of the total cost up to the target estimate. If the cost varied from the estimate, then 25% of the change was added to or subtracted from the fee. A 'no loss clause' meant that if the cost overruns where high enough the contractor could lose their entire fee but would not suffer any further loss, other than those for not meeting agree completion dates. Eight tenders were received. Three were fixed price with a bill of quantities and the remainder were target estimates. The Ministry of Works had estimated that the work would cost £10,198,000 and the average for seven of the bidders was £10,068,838. The target completion date was 1 June 1955. By late August 1952 the Ministry of Works had completed the two cableways that were to be used to carry concrete to the workface. To manufacture concrete on site the Ministry of Works purchased a Johnson concrete batching plant that had been used by the United States Navy in the reconstruction of Pearl Harbour after the Japanese attack in 1941. This came into operation in early April 1953. Upon completion of Roxburgh the plant was transported first to Benmore power station and then later to Aviemore power station and the Pukaki dam to mix aggregate for the penstocks, spillways and other concrete structures. The consortium bought from overseas 82 engineers, supervisors and administration staff and 322 workmen to the project and took over the civil aspects from the Ministry of Works on 29 Sept 1952. In an attempt to improve progress the contractor replaced a number of senior project staff. Labour relations were also deteriorating due to uncertainty over the management changes, reduction in working hours to 40 per week and the impact of cost overruns on the workers pay. In November 200 British workers demanded either a 70 hour working week or their tickets back to Great Britain.

With it having been necessary in 1953 to introduce power rationing in the South Island due to a shortage of generation the government decided the slow progress couldn't continue and requested two directors of Downer & Co, a major New Zealand construction company to attend in two days time a meeting at the Prime Minister's summer cottage on 24 April 1954. At this meeting which was attended by representatives of the consortium, Arnold Downer and Arch McLean from Downers were requested by the government to enter the project as the managing partner with a 25% interest. After spending £4 million the existing contract was cancelled and a schedule of rates contract was agreed upon with the renamed Cubitts Zschokke Downer with a planned completion date of late 1956. As a result of the forming of this new consortium Arnold Downer was put in charge of all site activities.

The preliminary works for the diversion of the river got off to a bad start when the explosive charge used in mid June to remove the upstream dumpling damaged the steel sheet pile cofferdam downstream of it. This cofferdam has been constructed to ensure that water didn't carrying any blast debris from the upper dumpling into the sluice channel. Eventually the debris and the cofferdam were removed, allowing unrestricted flow down the diversion channel. Now it was necessary to block off the river so all of the water flowed down the diversion channel. The river's average flow was and by June it had fallen to , but by the time work had been completed to a stage that a firm date of 1 July had been selected to attempt the diversion the flow had increased to Extra bulldozers were allocated to the attempt as the steady increased to and then .

To connect the new power station to the major load centres, a 52 mile (84 km) long new 110 kV wood pole line was first built to Gore. The linemen then commenced constructing an 89 mile (143 km) long double circuit 110 kV overhead transmission line using lattice steel towers to the Halfway Bush substation at Dunedin which was completed in July 1955 at a cost of approximately £500,000. The principal connection, however, was a new 266 mile (428 km) 220 kV single circuit overhead transmission line built using lattice steel towers from Roxburgh to a new substation at Islington on the outskirts of Christchurch. By 1949 the surveys for this line were well under way with by 1951 the construction camps established and the material on order. By 1954 the first section of the line had been completed, which allowed it to carry power from Tekapo A to Christchurch. A second section as far south as the Waitaki Valley helped improve supply conditions during winter. The Roxburgh Islington line cost approximately £1,000,000 and was completed by the winter of 1956.

With power cuts being applied across the South Island by June 1956, the Minister of Works requested the contractors to concentrate all resources on work that would bring forward lake filling as far as possible. To encourage the workforce, the government offered a bonus of £2 per week plus £1 per day if the lake was filled before 19 August. At midnight on 21 July 1956, lake filling began and the lake level commenced rising at an average of 3 feet (1 m) an hour. As the lake began to fill, increasing levels of water began to flow from the drainage channels behind the grout curtain in the right abutment, which indicated that the grout curtain was faulty. Investigations concluded that further grouting would have to be performed (which took about a fortnight) before the lake could be raised to its final level. The decision was made to allow the lake to fill to no further than the crest of the spillway while the contractors began drilling and inserting more grout. Meanwhile at 12:30 pm on 23 July a speedboat driven by Ken Harliwich and accompanied by Willis Wetherall to leave Roxburgh for Alexandria making the first boat trip on the new lake. By 11:20 am on 23 July 1956, the lake had filled to the crest of the spillway water. With a desperate shortage of electricity affecting the South Island, commissioning of the generating unit 1 immediately commenced under the direction of electrical resident engineer Eric Gordon “Sandy” Sandelin. The commissioning of Roxburgh removed the need for power restrictions in the South Island and ensure a surplus of power for many years.

In December 1947 the government expected the project to cost a total of £11,500,000. By September 1949 when the final location and type of dam had been chosen the cost had increased to £17,000,000. A contract of £8,620,074 was awarded to Hannen, Holland & Cubitts in association with Conrad Zschokke. This was a target estimate contract with a 'no loss clause'. In May 1954 the contract was re negotiated to include Downer & Co as the principal. The new contract was based upon 'a schedule of rates' at a value of £10,120,000. The final total cost of the project was £24,102, 800 of which £19,151,700 was for civil engineering, £445,000 on the bulkhead caissons and stage 2 civil works, £4,506,100 on the purchase and installation and commissioning of the eight generators and outdoor switchyard. Included in the civil engineering cost was £900,000 for the early completion bonus and £35,900 on expediting the programme. A total of 3,500 drawings were produced between the Ministry of Works, the State Hydro Electric Department and contractors to build the power station.

In December 1965 a generator coil failed on unit 2, followed by a series of further failures between 1971 and 1973, which in an effort to correct, the windings were reversed. Units 1, 3 and 4 had their stators rewound in 1975 to 1976. The sluice gate No. 3 in 1996 and gate No. 2 in 2001 were modified to enable the power station to pass an increased maximum design flood of Gate No. 1 was also plugged with concrete. To improve the structure's ability to withstand seismic events the original heavy chain and counterweight spillway gate operating system was replaced with a hydraulic system while the dam's top bridge was strengthened and the gantry towers were lowered. In the 1990s the power station's control systems were automated with new control and protection systems which allowed it to be de manned. Control of the power station is now undertaken from a control centre at Clyde Power Station.

In 1987 the assets of the NZED (including Roxburgh) were transferred to the Electricity Corporation of New Zealand (ECNZ). On 1 April 1996 ownership of Roxburgh was transferred from the Electricity Corporation of New Zealand to Contact Energy a State Owned Enterprise which subsequently passed into private ownership in 1999. With the separation of Transpower a new control room was constructed on the former carpark to house the Transpower equipment needed to operate the transmission equipment. The original air blast circuit breakers were replaced with Sprecher & Schuh SF6 circuit breakers in the late 1980s.

The original generator design supplemented the fan pole generated air flow with through rotor air flow. During the factory acceptance tests one generator had been subjected to a heat run but in order to keep the windage and friction losses within the allowable 10 percent over the guaranteed value the manufacturer had blocked off the through rotor flow which reduced air flow in the generator, with the coolers in the closed circuit, to 19.5 m3/s, which was about 90 percent of the design flow. This modification was applied to all of the generators. The limited time taken to commission the generating units had meant that no heat runs were performed, which would have identified the impact of this modification on the stator winding temperatures. As a result, the Roxburgh generators always operated at higher temperatures than most other hydro generators in New Zealand. The traditional practice over summer to manage the generator temperatures was to open the generator air vents and use modified ducting to discharge the hot air outside the building, while also to open the main powerhouse door and start the extraction fans installed high in the wall at the other end of the machine hall. In 1995, it was becoming apparent that it was becoming difficult to maintain the stator winding temperatures within their rated 65 to 75 °C operating range when operating at their maximum output over the summer months from January to April. As a result, it was necessary to de rate the generators from 40 MW to 35 MW. This de rating limited the station's operational flexibility. Investigations found that the over heating of the stator windings was due to a breakdown of the stator winding insulation, thus reducing the heat transfer from the conductors, accumulation of dust and oil on stator winding and heat exchanger surfaces reducing their heat transfer as well as sustained high ambient air and river water temperatures over the summer, compartmentalization of the powerhouse to manage the fire risk, which reduced airflow through the powerhouse, all compounded by an inefficient generator ventilation system. The 110 kV and 220 kV systems were connected by a 50 MVA 220/110 kV interconnecting transformer supplied by Brown Boveri. The outdoor 220 kV and 110 kV circuit breakers were also supplied by Brown Boveri and were of the air blast type.

To ensure a reliable auxiliary to the power station two auxiliary generating units were installed below the unloading bay and supplied from a shared 3 ft (0.27 m) diameter 243 ft (22.6 m) long penstock which ran from the top of the dam. Each unit has a horizontal Francis 765 hp turbine supplied by Drees & Co of West Germany which drove via flywheel a 625 kVA 400 V generator supplied by General Electric. At full load each unit consumes of water. The auxiliary generating units were upgraded at a cost of NZ$2.5 to $3 million in 2017.

Lake Roxburgh, the lake formed behind the dam, extends for nearly towards the town of Alexandra.

Operation of the power station is covered by the requirements of six resource consents that expire in 2042. These require a minimum discharge of from the power station. With the commissioning of Roxburgh, the sediment which had previously flowed down the Clutha river became trapped behind the dam. Regular surveys commenced in 1961 to monitor this sediment. By 1979 the average river bed level downstream of the Alexandra bridge has increased by 3.6 metres since the lake was created in 1956. The completion of the Clyde Power Station in 1992 reduced the sediment inflows from the Clutha River, leaving the Manuherikia River as the principal source. Floods in 1979, 1987, 1994 and 1995 have led many residents of Alexandra to put pressure on the owners of Roxburgh power station to better manage the sediment build up. A major flood in 1999 caused flooding of large parts of the main business area of Alexandra. This led to Contact Energy and the government purchasing flood affected properties and flood easements over others as well as constructing a flood bank. Contact Energy has also introduced a program of drawing down the lake level during floods in an attempt to move flush sediment downstream. Between 1956 and 1979 the maximum operating level of Lake Roxburgh had been 132.6 m before being reduced to 132 m. In December 2009 Contact Energy was given permission by the Otago Regional Council to return to a maximum operating level of 132.6 m. This would increase the amount of electricity that the power station could generate. When Contact Energy's application was heard in October 2009 14 submissions were received on the application, eight in opposition, five in support and one neutral. The approval of an increased operating level came with the conditions to ensure that the power station's discharge flow matched naturally occurring flood flows. When the flow reaches , the level of Lake Roxburgh has to be lowered to below 132 m, by either releasing less water at Clyde Power Station or increasing the flow through Roxburgh power station. Other conditions addressed mitigating the effects on amenity areas and walking track as well as the protocols to be followed if historic artefacts are found. Since 2012 a trap and transfer programme and transported elvers (juvenile eels) around the power station. 2016 report