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The Story of Electrical Energy, Pt.8 The largest hydroelectric machines in Tasmania are in the Gordon River underground power station, in the rugged south western region. The subject of much controversy in the past, it is an impressive project by any standard. By BRYAN MAHER Exposed to the never-ending moist gales of the roaring forties , the southwest corner of Tasmania boasts Australia's wettest temp erate climate , with 200 rainy days each year. Flora and fauna, direct relics of ancient times , still thrive in the cold rainforests . Rugged parallel mountain .5es lying in a north west to south easterly direction and broad valleys cut by inaccessible gorges posed a nearly impossible task for the surveyors and engineers. Although recognised since World War 1, the hydroelectric potential of the Gordon River was not thoroughly investigated until 1961. In March of that year, a hydrology analysis station was established on the Serpentine River. Measurements of precipitation and runoff predicted that 500 to 1000MW could be generated from the Gordon, Huon and Serpentine rivers. That was easier said than done! Just reaching the site, let alone bringing in heavy machinery, was a major effort. A rough access track, suitable only for tracked vehicles , was constructed in 1960 to McPartlan Pass. Helicopters were necessary to build research stations on Lake Pedder and the upper Huon River. The region was accessible only in summer, when snowfalls and driving south westerly gales usually abated. To verify the choice of dam site on the Gordon (1.5km upstream from the Serpentine confluence), a camp was ·established. Here intensive surveying, geological mapping, exploratory tunnelling and drilling occupied the summers of 1963 and following years. Approval by parliament in 1967 of the $185 million scheme started construction destined to increase the state's electricity supply by 23 %. The ambitious plan involved a 140-metre high dam blocking the precipitous gorge on the Gordon river. The 260 square kilometres of Lake Gordon thus formed would join an elevated version of the existing Lake Pedder to create Australia's largest fresh water storage. After a road was built to the dam site in 1969, diversion tunnels were the next to be built. River diversion Taken when the Gordon Dam was almost complete, this photo shows the extreme curvature of the structure - a classic concrete arch dam. 92 SILICON CHIP To enable the building of the Gordon Dam, the river had to be temporarily diverted. This was done in two stages in 1969/70. First, a reinforced concrete coffer dam was built upstream from the main dam site. The water thus impounded flowed through a 350 metre long tunnel bored through the gorge cliff, exiting well down stream. Then a second stage diversion was built closer to the dam. Subsequently, the first diversion tunnel was sealed with a concrete plug and the coffer dam demolished in --:-·-~· <t~' )'t j, ·~ !i ""' Most dam projects require at least two dams, one a temporary coffer dam which lets construction start on the main dam. This upstream photo of the Gordon Dam during construction shows the remains of the coffer dam after it had been demolished. FEBRUARY1991 93 The arched design transfers most of the water force onto the steep rock cliffs which form abutments on each side. Begun in 1972, the dam was completed in 1974, but it took 4 years to fill. The weight of water exerts a pressure of 1.4 megapascals (ie, 14 kilograms per square centimetre) at the base of the dam wall. As the dam's security depends on the stability of the abutments, electronic transducers were buried within the concrete wall. Computers in Hobart monitor the electrical readings to constantly assess the conditions. At the same time as the dam was being constructed, an 80-metre high intake tower was built with an access bridge above spillway water level. At the top of the tower are controls for the 75-tonne cylinder gate valves, located at the bottom, which control the bulk water flow to the power station below. The flow of water (415 cubic metres/sec) can be totally stopped, if need be, by the cylinder valves in only 20 seconds. Water falls via the 8.23m diameter shaft, then runs horizontally to the turbines, as the cross section diagrams show. The 356-metre power tunnel was completed in 1973 and the following year the dam began to fill. Underground turbine room This photo shows the underground Gordon power station during construction. The inlet valve and turbine casing for the No.2 machine can be clearly seen. 1970. Similarly, the Serpentine River was diverted so its dam could be commenced. As the region was totally uninhabited, Strathgordon Village was built to house the workforce, while design of a twin 220kV power line to the east commenced. The proposed site of the underground power station proved to be unsuitable because of unfavourable rock structure. The geology of south west Tasmania consists of 700 million-year-old sandstone with limestone outcrops and ancient lava intrusions up to 300 metres thick. A quarry and cement plant was built on a knob hill overlooking the river and roads were built to the bottom of the 400-metre deep gorge. Roads and an overhead cable way 94 SILICON CHIP carried men and equipment to the dam site. Using twin haulageways and four tower cranes, by 1972 the first concrete was being poured in the Gordon Dam structure. The following year, the excavation of the re-sited underground power station began. The Gordon Dam Rising 140 metres above its foundations (higher than Sydney Harbour Bridge), the Gordon dam is a classic reinforced concrete arch; the largest of its kind in the southern hemisphere. Only 200 metres long, it tapers in thickness from 17.68 metres at the base to 2.74 metres at the top. Containing 280,000 tonnes of steel and concrete, the dam is constructed with its convex curvature facing upstream. The construction of a power station within the bowels of a mountain tests the expertise and experience of engineers to the limit. The procedure used was to excavate the underground turbine room from the top downwards. The artificial cave was first dug out down to crane rail level. The crane runway structures were set into the rock walls, then the cranes assembled and operated. The work then consisted of digging out the floor using tracked hydraulic boring equipment until the full 32metre depth was reached. As machinery was set in place, tiling contractors then lined the ceiling. The walls were faced and lighting was set in place. Various floor levels were then constructed; above and below the alternators, at basement and above the turbine runner height. Reinforced concrete busbar troughs were built around the walls to house the generator output conductors which run from each machine to the vertical shaft, thence up to the aboveground substation. The final appear- tured in Germany by Siemens and assembled on site. The heaviest component is the 269-tonne rotor; so heavy that it was lifted into place in sections by the two overhead travelling cranes. The 22-pole stators for each machine , weighing 168 tonnes when assembled, were lifted into position by both cranes. When fully assembled, the total 314-tonne weight of the rotor, turbine and coupling shaft hangs on one vertical thrust bearing and is aligned by a number of guide bearings. So accurate is the alignment and so smooth the lubricated bearings that two men can turn the total rotating mass by hand (at a very slow speed of course). Having done its work in turning the turbine, the water falls through the fabricated steel outlet draft tube to the tailrace tunnel. This huge conduit , 9 metres in diameter, carries the Hydroelectric alternators are very big machines, especially compared to those driven by steam turbines. This is one of the stators in the Gordon Power Station. ance of the main floor of the power station, high above the lop of the alternators, is shown in one of the photos. Only the exciters are visible from the operating floor; stairways give access down to all other levels. Simultaneously with the turbine room construction, the boring of the inlet and outlet water tunnels proceeded. As already noted, the inlet shaft has a diameter of 8.23 metres. This main water conduit and the branchings to each turbine are lined with concrete and a great deal of trouble was involved in obtaining smooth contours throughout. Smooth contours Smooth pipe contours are necessary to obtain laminar water flow with minimum turbulence. Turbulent flow implies a severe energy loss which must be avoided for best efficiency and least wear in the tunnels and turbines. The cross section diagram of the power station shows the water pathway. Controlling the flow through each turbine is a 2.8-metre diameter hydraulically operated rotary inlet valve. The station's two 90-tonne capacity cranes were used in tandem to lift these 116-tonne valves into place during construction. From each valve, the water flows into the tur- MAX . LA~f LE VEL $ .L. 30 &m bine at a rate of 86 cubic metres per second. Francis turbines Each 150MW Francis vertical shaft water turbine consists of a welded steel spiral casing in which the turbine runner rotates. The 100-tonne spiral casings were fabricated in the HEC workshops and were then lifted into position and embedded in concrete. In op eration, the water enters the spiral casing at the large diameter end. Flowing around the spiral towards the small diameter end, th e water is forced to flow through the turbine runner before falling downwards. The water thus rotates the turbine and the direct coupled alternator above. Each 3-metre diameter turbine runner, the most critical mechanical component, was cast by Fuji in one piece of stainless steel. These 23tonne castings must have smooth blades polished almost to mirror finish to reduce water friction and enhance efficiency. The chromium component in the stainless steel alloy inhibits pitting and corrosion which would otherwise increase losses. Each turbine runner is coupl ed by a long 22-tonne vertical shaft to the rotor of the alternator above. These 144MW generators were manufac- LAKE GORDON GAU. EI-H•' .... -•·· ~---,J~ GHOUl ,/ /.,,j COfHAIN t -. .,. ·-!--··· ORAINAG E I CURTAINS l The cross section of the Gordon Dam shows it to be a very thin structure, relative to its height. Note that it is curved vertically and horizontally. FEBRUARY1991 95 This photo really does show the scale of the Gordon hydroelectric scheme. This is the 8.23-metre diameter inlet water tunnel with the three raceways running off lo Lhe left. Note how smooth the concrete is, to minimise turbulence. total outlet water from all machines 1.6km downstream to the lower Gordon River. Scale working model To test the performance of the turbines and verify the design , the Fuji Electric Co of Japan constructed a true 118th scale working model. This model turbine used water flow and full load to ascertain the efficiency, speed characteristics , stresses, strains and the extent of cavitation. In any turbine of the Francis or Kaplan types (as with ships' propellers), water flow patterns are critical. Cavitation means a non-ideal action wherein the turbine or propeller generates bubbles of water vapour close to the steel blades. As this water vapour is compressable (whereas liquid water is not), less than ideal forces act between turbine blade and bulk 96 SILICON CHIP water. The result is that full power transfer cannot be realised from the machine. Thermodynamic theory shows that there will always be some cavitation. However, this effect can be minimised by optimum design of blade dimension, shape and contour. In operation, the generator runs at 272.7272 RPM (long term average). But as with all generators, the sudden application of a heavy load must cause a momentary reduction in speed until the water valve opens incrementally to compensate. Load reduction causes the reverse. However, the very heavy rotating mass of large hydroelectric generators provides a great spinning reserve of energy, helping to maintain system frequency during changes in load. The 18kV 5000A 3-phase output of the alternators is carried by hollow square aluminium busbars through a 190-metre vertical lift shaft to the aboveground substation. Here the power is stepped up to 220kV for transmission to Hobart. Each transformer weighs 194 tonnes, so heavy that a special technique was used to transport them to the site. Carrying frames Instead of an enormous trailer being used (which would be too long for manoeuvrability) a special pair of carrying frames were built. Each 160MVA transformer was supplied by the manufacturer, Reyrolle-ParsonsWilson, complete with special transporting frames . After being lifted from ship to wharf, the triangular frames were bolted to the front and rear of the transformer casing. Multiple road wheels supported each triangular frame, while a heavy Pacific prime mover hauled the assembly. The switchyard and power line in the Gordon regions were designed to _________ 23 · 165 METRES ,ii! ___, UHF HIGH GAIN ANTENNAS !I if ii H f/ ROCK BOLTS antenn existing systems triangul powder coated receiving elements ensures excellent UHF reception compared to other UHF antennas of similar size and price. Two models are available: the TVA 14 for Band Four and the TVA 15 for Band Five UHF reception. Both models are supplied with back reflectors to prevent ghosting as well as a waterproof entry box designed to accept 75 ohm coaxial cable without the need for addittional baluns. They also have predrilled holes for securing the tilt adjustable metal mounting bracket in either a horizontal or vertical position. 90 .i 10 T ON TWIN OVERH EAD C:__l'! A"'_~S ~········-····· , __;r~J?~s12y· l,ll IIJ ...cc w :lF 0 (jt 0 Imported and dlatrfbuted by: M ARIS'& ELECTRONICS Aval/able through the following retallera: Ritronlcs. 56 Renver Rd. Clayton. V/ctoria. 3168. (03) 543 2166. Bernys. Brldgepoint. Military Road. Mosman. 2088. NSW. (02) 969 1966. DRAFT TUBE ··- GATE CHRISTIAN BLIND MISSIQ~ ·d Re$toti~t t~~~,, M,~ This cross sectional diagram of the Gordon Power Station shows the scale of the project. The station capacity is 432MW, with provision for two more machines. blend as much as possible with the scenic surroundings. ACSR (Aluminium Conductor Steel Reinforced) conductors 25mm in diameter were used for the twin power feeders, using an average span length of 450 metres. In the sensitive Gordon River regions, towers were constructed of a special steel. This develops a uniform stable rust coating which inhibits further corrosion. The dark colour blends successfully with natural surroundings. The first two generators were completed and commenced supplying load in 1978. Full load commercial operation was achieved in 1978/79. After 3½ years work and an expen- diture of $38 million, the installation of the third turbogenerator at Gordon Power Station was completed in 1988. This raised the total station capacity to 432MW. The station still has provision for two more machines. If installed, these would raise the available peak load output. However, the total output in a year would not be increased as this is limited by the rainfall and snowfall within the catchment area. Lake Pedder To supplement the water storage of Lake Gordon, the level of Lake Pedder was raised by the Serpentine and Scotts Peak dams and the small Edgar COUPON Please cut and send to: CHRISTIAN BLIND MISSION INTERNATIONAL, P.O . .Box 5, 1245 Burke Road, KEW. Vic. 3101 Phone: (03)817-4566 e D Please send me further information about CBMl's work. As long as it is possible for me, I will help: monthly D quarterly D annually D to prevent blindness D to restore eyesight D to rehabilitate the blind Enclosed is my gilt of S _ _ _ _ _ __ D Mr/ Mrs, Miss, Street , __ . . City , _ _ .. . . P051code, FEBRUARY1991 97 The third machine, installed in the Gordon Power Station in 1988, raised the station's maximum output to 432 megawatts. levee. Though much smaller than the Gordon, these two additional dams are an integral part of the scheme. The Serpentine Dam, on the river of the same name near Mt Sprent, is a 38-metre high mass of concrete-faced rockfill 131 metres long. Much bigger is the Scotts Peak Dam, just over a kilometre in length but only 43 metres high and containing about a million tonnes of rockfill under its concrete skin. These two small dams, with the Edgar levee, impound the Lake Pedder catchment, raising the water to approximately the same level as Lake Gordon. The McPartlan Pass Canal, 2.66km long, was cut to allow water to flow either way between the two lakes. Normally water flows from Pedder to Gordon but flood rains in the Gordon catchment can also be stored in Lake Pedder. The Tasmanian parliament and the Hydro Electric Commission recognised that the intrusion of man into previous! y inaccessible wilderness regions must cause adverse effects. Certainly the flooding of the small but beautiful original Lake Pedder provoked serious environmental controversy. The Gordon power station contributes a large percentage of the total state power loading which reached an all-time peak of 1.4505 Gigawatts in June 1989. The control of the entire Tasmanian hydroelectric system requires many factors to be taken into account. Not only must power be immediately available at all times but also water resources must be carefully husbanded. Accurate weather forecasts must be taken into account. These factors and other Tasmanian dams and power stations will be investigated in a later chapter of this series. References (1). Tasmanian HEC literature. (2). "Australia the Beautiful Wilderness"; Bob Brown. (3). "Australia's Wilderness Heritage" Vol.1; Geoff Mosley. (4) . "Australia the Greatest Island"; Robert Raymond. Acknowledgements Big alternators require big transformers and these cause big headaches in transportation. This photo shows the solution used for the Gordon power station transformers - a special carrying frame hauled by a heavy prime mover. 98 SILICON CHIP Grateful thanks to the Tasmanian Hydroelectric Commission and to Liz Emson for data, photos and permission to publish. SC