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The Story of Electrical Energy, Pt.12 The first major sections of the Snowy Mountains Hydroelectric scheme to come on line were all underground. Huge caverns and tunnels had to be carved out of the mountains & mammoth electrical machinery installed. By BRYAN MAHER A shining example of the design ingenuity and the enormous size of the Snowy Mountains Hydroelectric project becomes apparent when we look at the Eucumbene-Tumut tunnel construction. Its complexity is typified in the control of water flow in two directions through the system. Twenty two kilometres in length, this is the longest tunnel in the scheme. Bored right through the Great Dividing Range, in places as much as 520 metres below the massif above, this tunnel traverses the worst fault zones found in these mountains. Excavated throughout its length to a diameter of 6.9 metres (22 feet 6.7 inches), the tunnel was steel and con- crete lined in regions of vertical faults and possible ground movement. This lining extends over 28% of the length of the tunnel. The first step in lining the tunnel was to install massive 250 x 125mm structural steel ribs. In the most critical sections, a cage structure of steel reinforcing rods was welded to the ribs and then the final concrete lining was sprayed on to form the finished tunnel walls. Because of its smooth bore, 6.4 metres in diameter, the concrete lined tunnel carries the 114m3/sec water flow as easily as the larger rough walled unlined sections. It's interesting to note that the 1-metre gauge railway tracks, used during construction to carry men and materials, still run down the centre of the finished tunnel floor. The diagrams of Fig.1 show the Eucumbene-Tumut tunnel and the Happy Jacks Junction. A huge bulkhead gate, together with a guard gate, each 6.4 x 3.91 metres, controls the water flow at the Lake Eucumbene portal. Similar hydraulically operated gates are installed at the Tumut Pond outlet structure. Fine control of the flow rate is achieved by a 6.4 x 3.9-metre regulating gate mounted back in the tunnel. The Eucumbene-Tumut tunnel passes approximately 100 metres bee low the confluence of the Happy Jack and Upper Tumut rivers. Here a small dam forms a pondage. From its floor, a 5.5-metre diameter vertical shaft brings water down to join the main east-west tunnel. Flow from Happy Jack is then regulated by a 6.2-metre gate valve. Siphon intakes Taken during the construction of the Eucumbene Tumut tunnel, this photo shows the heavy bracing installed before it was lined with concrete. In the foreground is a battery-operated locomotive which was used for transporting men and equipment. 74 SILICON CHIP Siphon intakes, whereby water can be collected by tunnels from rivers under which they pass, are used extensively in the Snowy. Up to 20 :ii I This is Tumut Pond, the reservoir for the Tumut 1 underground power station. It is held by an 86-metre high thin concrete arch dam which was completed in 1958. Tumut 1 was Australia's first underground power station. siphons operate in sequential order, carrying water down to the tunnel below. The purpose of the siphon system is to prevent the intake from scavenging the total river flow in times of low rainfall. As rain or snowmelt increases, more siphons automatically come into operation, conducting an increased share of the water down the shaft to the tunnel below - see Fig.2. The reservoir providing the water head for Tumut 1 power station is Tumut Pond, high above in the mountains. Sitting astride a broad fault zone, this reservoir is held by an 86-metre high thin concrete arch dam. Holding 53 gigalitres of water at a height of 1158 metres above sea level, this dam was completed in 1958. Thus, the Eucumbene-Tumut was the first transmountain section of the Snowy Scheme to be placed in service. Underground power stations A unique feature of the Snowy Hydroelectric scheme is the arrangement of two underground power stations in tandem. Fed in turn by essentially the same water, both power stations are buried deep within the granite moun- · tains. When it first came on line in December 1959, Tumut 1 ushered Australia into the age of underground power stations. Boasting the greatest water head for the day (292.6 metres), the four 82 megawatt Francis turbines were the first in operation on the western side of the scheme. Each turbine rotates at 375 RPM and drives a 16pole alternator mounted immediately above it. The machine hall was hewn from the mountain 's interior, 415 metres below the surface. It is 93 metres across and 34 metres high and required the excavation of over 100,000 tonnes ofrock. It is the equivalent of a large city building buried deep underground. Excavation commenced in May 1955 and the station was completed 4½ years later. Pressure shafts From Tumut Pond reservoir, the Tumut 1 pressure tunnel runs 2.4 kilometres north-westward through the mountain at a slight downward gradient. At 6.4 metres in diameter, this fully lined tunnel can carry as much as 125 tonnes of water per second. At a point almost above the underground power station, the tunnel divides into two 3.66-metre steel lined shafts which drop 240 metres to feed the power station's four turbines. The water regulating valves at the power AUG UST 1991 75 UMUT1 RESSURE TUNN INLET GATE -~-'< *" 4:, \ D AC GATESHAF ~t ~i \' - ~'r "'~ 2 3 .......__._.......____.___.____----' -__. . .4, y--r-<- ),.. -1--<'j SCALE OF MILES PLAN OF EUCUMBENE-TUMUT TUNNEL 6 0 0 0 ~ - - - -- - - - - - - - - -- -- - -- - - -- - - - - -- - -- - - - -- - - - - - - - - , 5000 i GATE SHAFT ~ 4000 0 ; EUCUMBENE-TUMUT TUNNEL C ~ 3 0 0 0 H - - ~ ~ = ~ - - - -- - - -- - - - -- - - - - - - -- - -- - - - -- - - - - - - - - - - - - t fil a: 20001--- -- - -- - - -- -- - ~- - -- - - - ~ 2 ~ - - - -- -4-- - -- - - - -- -----------j SCALE OF MILES 1 0 0 0 ' - - - - - -- - - -- -- - - - - -- - -- - - - - - - - -PROFILE OF EUCUMBENE-TUMUT TUNNEL Fig.1: these diagrams show the plan and cross-section of the Eucumbene Tumut tunnel which can transport water in either of two directions between Lake Eucumbene & Tumut Pond Reservoir. station are continually adjusted to control the turbines , as required by the varying electrical loading on the generators. At any partial or complete valve closure, the momentum of many thousands of tonnes of water rushing through the pressure tunnel must be safely controlled. This is done with the aid of a very large surge chamber. As shown in Fig.3, two 5.5-metre diameter shafts rise 82 metres to a much larger chamber 15.3 metres in diameter and 40 metres high. Electrical aspects Many innovations in electrical engineering are to be found in the Snowy Scheme. The four 80 megawatt alternators at Tumut 1 each produce a 12.5kV 3700 amp 3-phase output. This · must be stepped up to 330kV for transmission to the state grid system. From the underground alternators, the shortest path to the aboveground 76 SILICON CHIP high voltage switchyard is about 500 metres via the cable tunnel. This would be much too far to run the 12.5kV 3700 amp generator conductors because there would have been considerable resistance losses. Therefore, the 12.5kV /330kV step-up transformers were located underground in a chamber adjacent to and almost as large in floor area as the turbine hall. The transformer bay contains seven single phase, oil filled, water cooled transformers. Each is mourited on flanged wheels. These fit a set of rails via which any transformer can be wheeled out to the assembly bay. Here access is available to the two 110/ 10tonne capacity station cranes. But why have seven single phase transformers when the four alternators have 3-phase output? The unusual setup means that six transformers are always connected, with one as a spare. Each transformer has two 12.5kV 28MVA primaries and one - - - - - -- - -- -- -- - - ' 191kV 56MVA secondary winding. As the circuit diagram of Fig.4 illustrates, pairs of generators share one bank of three transformers to provide 330kV 3-phase output. The star connection of three 191kV secondaries produces a line-to-line voltage of 330kV (191kVx [sqrt]3 = 330kV). The delta primary connections, on the other hand, allow circulation of 3rd harmonic currents caused by the nonlinearity of the transformer core permeability. This delta connection is necessary as the three isolated iron cores do not allow 3rd harmonics in the magnetic flux to circulate between phases to stabilise the secondary neutral potential. Output cables The total output from Tumut 1 power station is carried by two 330kV 168MVA circuits. From the underground transformer hall, power is carried by six single core oil-filled paper insulated 330kV cables. These are laid within the cabltJ tunnel to the surface. DURING JULY - SEPTEMBER and only while stocks last WINTER SPECIALS TYPl~AL INTERMEDIATE INTAKE SHAFT GROUND SURFACE NOTE:-NUMBERING OF SIPHONS INDICATES SEQUENTIAL ORDER OF OPERATION SECTION THROUGH INTAKE INTAKE STRUCTURE TRASHRACK SLOT INFRA RED NIGHT VIEWER Similar to E.A project (May and Sept. 90) , but is smaller when assembled. Yes this kit includes an adjustable high quality long range mil spec lens with a built in IR filte r as well as a high quality eyepiece . The tubes are NEW IR types (BWB 258). The lenses and eyep ieces were removed from NEW mil spec night vis ion equipment and guara nteed not to have any b lemishes. You wou ld norma ll y pay over $2000 for a viewer which uses a sim ilar tube and optics! The lens, tube, eyepiece, are only part of the complete kit supplied. The Price of this bargain???: $ ... 299. 00 SHAFT What is in the kit : A BWB258 tube, an adjustable long range objective lens, an adjustable eyepiece, sufficient plastics for the case, a 775mm round IR filter, an electronics kit as per the E.A May 90 article, and the instructions.. Kit No. IRNW5 SPILLWAY CREST MORE BARGAINS?: Check our adds in the "MARKET CENTRE" of this ma azine. 2mW PHILIPS LASER HEAD WITH UNIVERSAL 12V POWER SUPPLY \ \ I \ FOUNDATION EXCAVATION LINES ~ DRAINAGE HOLES~ SECTION THROUGH TYPICAL DIVERSION DAM 10 $175. 00 for the pair!! 20 SCALE OF FEET VORTEX CHAMBER TOOMA-TUMUT TUNNEL Fig.2: a typical siphon intake system, as used to take water from the Happy Jack River to the Eucumbene Tumut tunnel below. In this scheme, a system of up to 20 siphons comes into operation sequentially, depending on the height of water in the river. From there, they run via by an arched bridge across the upper Tumut River gorge to the open air switchyard. These high voltage single core cables in the cable tunnel cannot have steel armouring. If they did, the AC magnetic field produced by the currents in the cable would induce eddy currents in the steel sheath. These eddy currents would lead to huge losses, manifested as destructive heating of the cable sheath. The electrical output from Tumut 1 power station ushered in the first 330kV substation on the NSW grid system. This was built at Yass in 1959, Uses a brand new. high quality, encapsulated and wired visible (red ) He-Ne Laser Head . The head is easy to handle and use. It has a very tight beam (0.95mR). making it intense at good distances, and more suitable for most applicat ions . Head dimensions: 37mm diameter by 260mm long. Supplied with our newest 12V "Universal Laser Inverter" kit which powers all He-Ne tubes. This inverter comes with a totally prewound transl ormer. instructions. and even some plastic casing. Very easy to construct. and very efficient. The Special July - Sept. Price?? An incred ible: where seven 330/132kV transformers were installed. Second use of the water Having done its work in Tumut 1, the water exiting from the four turbines flows via the tail water tunnel to Tumut 2 power station. With a width of 8. 53 metres and height of 7. 7 metres, this horseshoe section tailwater tunnel has the largest cross sectional area of any tunnel in the Snowy system. So large is the interior volume of this tunnel, that four Sydney suburban trains could fit in together; two 2mW PHILIPS LASER HEAD WITH MAINS POWER SUPPLY (Kit No. LK13) Alternatively you can purchase the same 2mW Laser Head with a very small profess ional (Illustrated) 240V power supply, th at even has a TTL interlock: needs 3SV approx. 3mA, across two isolated terminals (Opto isolator built in the supply). to sw itch the laser ON . Nor' mally you would pay over $250 for the supply alone , but ', during July August ., the price f or the ____ ______ _.,, , head and the 240V supply is an unbelievable: $210. 00 torthepeiir!! (KitNo.LK14) We also have a limited number o f some larger 24 mW "Mail es Griot" laser heads wit h a similar deal (dimensions: 45mm diameter by 275 mm long.) LK16 • 2•4mW Melles Head with universal 12v kit supply : $225 .00 LK17 - 2-4 m W Melles head w ith mains supply: $260.00 LASERS are not for kids: DANGER OATLEY ELECTRONICS PO BOX 89, OATLEY, NSW2223 Telephone: Fax No: (02) 579 4985 (02) 570 791 0 Certified p&p: $5 inAust. NZ (Airmail):$1 o Melbourne Distributor Electronics World (03) 723 3860 or (03) 723 3094 AUGUST 1991 77 a GROUNO SURFACE SECTION THROUGH TUMUT 2 SURGE TANK ANO PRESSURE SHAFT 100 200 100 SCALE OF FEET • RL2603 SURGE TANK 28' DIA EIGHT MILE CREEK,.,---PRESSURE SHAFT 11-6" DIA TOP OF STEEL LINING SHAFT-B RL2348 CROSS SECTION OF PRESSURE SHAFT STEEL REINFORCEMENT STEEL LINING PAY LINE STRUCTURAL STEEL 10 TO TUMUT 2 POWER STATION RL1761 15 SCALE OF FEET Fig.3: the surge chamber used for Tumut 2 power station. Surge chambers are there to stop the equivalent of "water hammer" in the pressure shafts feeding the turbines. When the water is shut off or reduced in flow, the surge chamber prevents a huge rise in water pressure which would otherwise occur due to the momentum of thousands of tonnes of water moving at high speed. abreast and stacked two high! This huge 300 metre length of tunnel forms the lower surge chamber. Tandem underground stations It is indeed unusual to find a tandem arrangement of underground power stations. Yet that is the way Tumut 1 and Tumut 2 are constructed. The Tumut 1 tailwater tunnel discharges into Tumut 2 pondage. This is a small surface holding stage in a cleft of the mountains, 20 hectares in area, held by a very small concrete dam 46 metres high. From this 78 SILICON CHIP pondage, a second pressure tunnel carries the water 4.8 kilometres through the mountains to Tumut 2 power station. Above Tumut 2 the pressure tunnel divides into two steel lined downcomer shafts. These slope downwards 230 metres to feed water to the four 71.6MW turbines. Water equalization Normally, both Tumut 1 and Tumut stations use exactly the same water flow. But provision must be made in the design for possible load shedding 2 Left: Tumut 1 power station during the excavation stage, in the mid-1950s. This was Australia's first underground power station . . ,,,:,;...-,.,_ ·.«~, l ,, • 5 10 15 20 SCALE OF FEET SECTION THROUGH TUMUT 2 POWER STATION Fig.4: cross section of the Tumut 2 power station which, like Tumut 1 station, is built entirely underground in a chamber excavated out of the rock. AUGUST 1991 79 A GENERATOR 1 8 C A 8 C 330kV ~T GENERATOR 2 or shutting down of any of the Tumut 2 machines. At the same time, Tumut 1 must be allowed to run at full power. For this contingency, a huge surge tank and overflow spillway was constructed at the junction of Tumut 2 pressure tunnel with the two downcomers (ie, exit pipes). The vertical surge tank, 8.5 metres in diameter and 76 metres high, was excavated within the mountain, steel reinforced and concrete lined. The top of this tank opens to a huge spillway capable of discharging 7474 cubic metres of water per minute. Exit Tumut 2 Fig.5: the novel transformer connection used for the Tumut 1 power station. Six single phase transformers (with one as a spare) handle the 3-phase output of the alternators. Having passed through the Tumut 2 turbines, water exits via the 6km long tail water tunnel to be returned to the Tumut River downstream. From this point on, the water flows aboveground, eventually to pass through yet more power stations. The rest of this story, including pump storage (effectively storage of AC electricity), the Murray system and the first interconnection of three states' electricity grids , will be left until next month. Power & energy Some readers may be puzzling over a small apparent discrepancy: Tumut 1 power station, with four machines, generates 320MW; using the same number of turbines and literally the same water, Tumut 2 only provides 280MW. Why the difference? The reason is to do with the head of the water. Tumut 1 turbines are driven by water at constant pressure caused by its 292 metre head. On the other hand, Tumut 2 works from a 262.1 metre head. Less pressure at Tumut 2 means that the turbines cannot produce as much power, even though the water flow rates of both power stations are equal. Interestingly, whereas Tumut 1 machines rotate at 375 RPM, the smaller machines at Tumut 2 run faster at 428.57143 RPM (long term average). Why? The alternators at Tumut 1 have 16 poles while those at Tumut 2 have 14 poles. Acknowledgement Tumut 1 power station as it is today - quiet, reliable and pollution free. 80 SILICON CHIP Special thanks and acknowledgements to Libby Langford and the Snowy Mountains Hydroelectric Authority for data, photos and permission to publish. SC