Harnessing tKe Waipori. Part I.

Progress, Volume III, Issue I, 1 November 1907, Page 15

Harnessing tKe Waipori.

Part I.

By W. G T. GOODMAN, A M I.E.E.

One cannot travel through New Zealand without being impressed with the fact that Nature has been extremely beneficent m her endowments of natural resources The magnficent lakes, rugged mountains with their everlasting covering of snow, extensive glaciers, and swift-flowing rivers, are a great attraction to visitors from all parts of the world. New Zealand has many rivers, some carrying large volumes of water with low heads, and others carrying smaller volumes with extraordinarily high and easily developed heads. The natural resources of New Zealand in the direction of valuable rivers that can be harnessed, have received the attention of the New Zealand Government during the last few years, with a prospect of development and utilisation for electrical purposes. The late Mr. P. S. Hay, M.lnst. C.E. who held the position of Engmeer-m-Chief to the Public Works Department of New Zealand, submitted a most valuable and instructive report to the New Zealand Government in September, 1904, in which he dealt exhaustively with the valuable resources available for hydro-electric development, and after making due allowance for all loss of head in races, conduits, and pipes, and allowing an 80 per cent, efficiency for all water motors, he showed that the enormous amount of 3,700,000, horsepower can be obtained, 500,000 horse-power being available from the rivers of the North Island, and 3,200 000 horse-power from the South Island rivers When one realises the true import of these figures it can be seen that New Zealand has been liberally treated with natural hydraulic resources. There are several small streams which have been used for generating electric energy in various parts of the country. It has been the good fortune of the author to carry out the development of an important hydro-electnc scheme contiguous to the city of Dunedm, and the object of this article is to present a description of the installation. The Waipori river is situated in the province 'of Otago, and has become noteworthy, be cause from it power is being obtained for the development electrical energy on a scale not attempted in the Australasian colonies. It is typical of many rivers of New Zealand, rushing down the steep slopes of the mountain ranges meandering through a comparatively level plateau ; again rushing through a rocky gorge, and subsequently forming a confluence with the Taieri river some five miles from the sea. The translation of the Maori word "Waipori" is "muddy water" and, as the name indicates, the water is of a dirty colour, caused by the mining operations m and along its banks and tributaries. It is the leceptacle of "tailings" from hydraulic sluicing and elevating. Perhaps one may be excused for reciting, inter alia, a brief history of the circumstances leading to the hydro-electric development of the river. Seven years ago the author on behalf of the firm he then represented, was invited by the City Council to

report on the electrification of the Dunedin tramways and recommend a system for generation of power, the latter consideration to be with the view of supplying the tramways and city and suburbs with the electricity for lighting and motive power. In this report consideration was given to alternatives of generating by gas, steam, and water-power. In connection with the hydraulic considerations, three propositions were reviewed, namely — The Taieri

river, with a head of 70 feet , the Lee stream, with a head of 700 feet ; the Waipori, with a head of 800 feet. The power station on the Taieri river for the Lee stream scheme would have only been 12 miles from the city of Dunedm , the power station for Waipori scheme in the location suggested by the author would have been 26 miles from Dunedm After consideration, the City Council decided to adopt the Taieri river scheme, but subsequently this proposition had to be abandoned as Parliament

would not grant the Council power to erect a dam 30 feet high across the river. The Corporation then adopted the Lee stream scheme, by the advice of a firm of consulting hydraulic engineers. This scheme involved the construction of a tunnel \\ miles long, which was proceeded with and constructed for about two-thirds of its length. In August, 1902, a company was formed to exploit the Waipori river scheme. This company immediaately proceeded with the construction of a portion of the hydraulic works, and in April, 1904, contracted for the necessary Pelton wheels, generators, and transformers for the power station. Their prospectus stated that they proposed to utilise the energy to be obtained from the Waipori river, to supply power on the Taieri plains, and in the city and suburbs of Dunedin. When they had proceeded thus far they applied to Parliament for the necessary Enabling Act. The Council realised that if the company secured powers to reticulate in the city of Dunedin, and suburbs, such powers would jeopardise the prospects of the Corporation undertaking, and in October, 1904, they bought out the rights for £12,500 and took over the liabilities of the Waipori Company, and abandoned the Lee stream scheme, on which they (the Corporation) had alreadyspent the sum of £18,000 on the tunnel works. Negotiations necessary for the completion of the purchase occupied several months, and in March, 1905, Messrs. Noyes Brothers were instructed to proceed with the designing and construction of the electric portion of the undertaking. At the time of the purchase by the Council, the company had constructed the weir and 82 chains of the flume, and, as previously mentioned, had let contracts for a portion of the generating plant The proposals of the Corporation were of a much wider range than those of the Company, and, with the view to meeting the requirements of such proposals, the scheme as designed by the Company was very materially altered and amplified in order to guarantee as far as possible permanent operation, and provide every possible means of eliminating risk of stoppage in supply. At the point where the Waipori river leaves its last elevated plateau and commences its final rush towards the sea, the site of the intake has been chosen, the height above sea level being 1125 feet. From this point the river rushes in numerous cascades through a vertical height of 700 feet, in less than two miles. The source of the river is in the Lammerlaw Mountains, a range running from 4000 to 6000 feet above the sea level. The length of the river above the intake is 22 miles, and the catchment area of the watershed is about 95 square miles. From careful observations taken during the last three years the discharge at point of intake has varied from a maximum of 50 cubic feet per square mile, to a minimum of 0 4 cubic feet per square mile. The information at hand shows the fluctuation in the river discharge October, 1904, to 31st May, 1907.

The location of intake was well chosen, and advantage was taken of a projecting spur of rock through which a tunnel 22 feet in length was cut. This tunnel leads into the wooden flume. On the opposite side of the river a similar spur formed an excellent key to the weir. Nature thus assisted the construction of the intake, as these rocks present practical immunity from damage by flood, and provide an easy method of handling the head-gates. The tunnel is rectangular in section, 8 feet by 4 feet at intake, tapering to 6 feet by 4 feet at the junction with the flume. The two head-gates are each 4 feet by 4 feet, and are operated by rack, pinion and pawl with ratchet levers. The wen is constructed of rock-filled crib-work, 76 feet long at the crest, 15 feet in depth, with a top width of 10 feet, and a bottom width of 32 feet. The timber used was obtained m the vicinity, and none ot the logs are less than 8 inches in diameter at the small end. The first bay of logs was run longitudinally with the current, and fastened to the bed rock by iron dowels run m with neat cement. The next tier was run^t right angles to the first bay, and attached to it by thin manuka trenails, the logs being adzed to present a neat seat at each intersection. The space was then filled with hand-packed rubble as large as could be conveniently placed in the structure, A spillway has been constructed on the opposite side to the intake, which tends to divert the current clear of the head-works durmg heavy floods, and an 18-inch scour pipe has been provided in order to draw orf silt accumulations. The object of the weir was to cause the deposit of material carried in suspension, the material thus deposited to form a water-tight structure and to reduce the pressure on the criD-work to a minimum. The results anticipated have been obtained, and a permanent wall of gravel, etc., now extends some 600 feet up stream. The conduit for the water embraces all ths features usually met with in an undertaking of this class, viz., earthworks, tunnels and pipes, and the total length from intake to water wheels is 2 miles 14 chains. The country alone which the flume is laid is mostly of micaceous schist formation eas-ly affected by weather, and shortly before the author left, some five tons ot rock fell an^l carried away 12 feet ol the flume. There is not likely to be any lurther trouble in this direction, as the rock is well benched back. The whole of the conduit from the intake to the penstock is wooden rectangular fluming, except where it passes through the tunnels, built upon a bench 10 feet wide, mostly excavated out oi solid rock. Where the flume crosses creeks and gullies, it is carried on masonry piers. Tt is (j feet by 4 f eet in the clear, and ha^ a uniform gradient of 8 feet to the mile. The joints in the longitudinals are butted and covered by battens 3in by -Jin. under which is placed a 3m. strip of tarred felt, the joint having received a coat of tar applied hot, and all butt joints were run m with boiling pitch. The length of wooden fluming is 130 chains and the six tunnels aggregate 11 cnains, total 147 chains Four spillways are provided in this distince , these are for the purpose of i-icilitatmg repairs to the flume. The flume i-j constructed of mountain birch, an abundance of which exists in the locality. A saw-mill was erected in the vicinity and worked by an impulse wheel, under a head of 120 feet, located on the

bank pf^therner, and the sawn timber was hauled 3,170 feet by cable tramway, rising 1 100 feet m that length. Four miles of wooden tramway were laid through the bush, on which the logs were hailed by horses to the mill. Nearly 1,000,000 super feet of timber was used in the flume construction, and 400,000 super, feet of sapwood was turned out and cut into suitable sizes for building purposes. The life of the flume is estimated at from 10 to 12 years but before the expiration of that time, no doubt, a tunnel will be constructed, about 5,000 feet long, through the hill, to conduct the water to the penstock.

Ihe tunnels, which are cut through the various spurs, vary m length fiom 2Uo ieet to 20 feet, and

they are made slightly larger tnan the ilume. One novel feature in the construction of the tunnels consists in increasing their capacity by dropping the invert lever 7|m. at the inlet, and rising conespond mgly at the outlet. It was found that owing to the decrease of fractional surface the discharge was increased by this means nearly 15 per cent. Three spillways are operated by rack, pinion and pawl ; while a fourth, from which all water discharged into the pipe line is regulated, is operated by a revolving screw, the nut being firmly fixed m a yoke piece which has two long arms with a cast-iron ball weighing 301bs. at each end. As the planes of the gates are at right angles, one leading to the spillway and the other leading to the penstock, the race man is able to stand in a position so as to operate both gates simultaneously with the assistance of the centrifugal force obtained by the cast-iron balls. In order to free the water of all materials carried in suspension, two catchment basins, to intercept stones, etc., have been constructed, each having a capacity of 53 cubic yards of silt. The flume terminates at the penstock, which is constructed of concrete, and is 13 feet long by 9 feet wide, and 10 feet deep below the sill of the flume. By this depth sufficient velocity was obtained in the falling water to overcome the head lost at the pipe entrance. Two pipes are built into the penstock, each 42m. in diameter and provided with 6m. air-vent pipes, located on the pipe side of the main gates. Before the water enters the penstock, it passes through two gratings, twenty feet apart, one formed by wroughtlron bars, l^m. apart, lying at an angle of 45 degrees, and the other of galvanised wire netting, l^in. mesh, at an angle of 60 degrees. The author found it necessary to fix the latter grating , as on one occasion trouble was caused by two rabbits' feet becoming jammed between the needle and nozzle. The pipe line presents some features of interest on account of the deviation from the usual practice. The steel pipes run from 42m. to 36in. internal diameter, alternate outside and inside courses, and vary m thickness from at the penstock to -|in. at the power station end, and the length of the pipe line is 1,776 feet. The following table gives the details of construction • — Thickness of plate, inches i 3-16 J 5-16 I 7-16 \ Diameter of rivet, inches 5-16 -| \ 11-16 5 13-16 '\ Pitch double rivetted seams Li \.\ \.\ 2 a 2|- 2} 2f Pitch single rivetted seams 1 1 1-16 l.f 2 2 2 2 Distance between rows, D.R seams 11-16 I It 1* 1-1- I I 11 Lap, centre of rivet to edge of plate 9-16 21-32 | l.i I.J- 1 5-16 ] ] The pipes are manufactured from " soft open hearth " steel plates, with a tensile strength of between 52,000 and 56,000 pounds per square inch. The rivets were of similar quality, with a tensile strength of between 44,000 and 51, 000 pounds per square inch, all materials being submitted to the usual bending , punching and cold hammering tests

iho pipo.!. weie made in 20 feet lengths m the saop, and were subjected to a test 15 per cent, in excess of that given in the foregoing tables, after which they were cleaned by sand blast, then heated to a temperature of 300° Fah., and dipped for 15 minutes m a bath of asphaltum mixture, containing H per cent, of pure linseed oil. The transport of the pipes and placing in position entailed a large amount of labour and risk to men and horses, owing to the inaccessibility of the country. After being placed m position m the trenches the pipes were jointed and hand nvetted, afterwards being caulked both inside and out , they were then covered with soil to a depth of 2 feet 6 inches, to prevent them being exposed to sun temperature, and thereby to dispense wjth expansive joints. The variation m temperature of the water between summer and winter is not more than 15 degrees Fahr., and the expansion due to this difference will not be more than 2 inches, which will be taken care oi by the vertical angles m the pipe line. Six anchorages prevent the line from creeping, four of which are solid concrete blocks, 6 feet x 4 feet x 6 feet Five air valves of the triple-cluster type are provided with shut-off gate and extension pieces to allow the influx and efflux of air, the balls being of hard wood with rubber seats. Five manholes are placed in the line to facilitate field rivetting and inspection. Owing to the physical features ot the country it was found impossible to s°lect a line wholly below the mean hydraulic gradient, and recourse had to be made to a tunnel at the lower end, in order not to rise above it This tunnpl is 187 feet in length, with a gradient of 1 in 3£, and large enough for three pipe lines, thus providing for future extension At the mouth of the lower end of the tunnel the last section of -£-mch plate pipe is attached to a cast iron "Y" branch piece, dividing the water into two 22m. cast iron pipes each to carry 20 cubic feet of water per second, one branch for each unit. On each end of the branch of the " V"a mam 22m. gate isplaced with a 4in. by-pass. The valves are enclosed in a tower, as they are operated by fine thread spmdles which require 2500 turns of the hand-wheel to open or close them ; a motor is installed to operate these. The balance of the pipe line is of cast iron, each leg of the 22-inch branch being 80 feet long, bifurcating by a cast iron " Y " piece into two 14-mch branches, each leading to the nozzle of the impulse wheel Each 14-inch branch is controlled by a 14-mch gate valve with by-pass The cast iron pipes were made of best grey iron, having a tensile strength of not less than 18,000 pounds, and were cast vertically m 6tt fan. lengths, weighing 25cwt.

It was of course necessary to erect the foundations for the engine beds before the pipes were laid, and considerable difficulty was met with in having to connect rigidly with two fixed points m the pipe line The closures were made £m short, and the final joints were run m with lead caulked against a wrought steel band shrunk over the flanges In the terminal pipe two extension pipes were placed, one being a 6-inch branch to operate the exciter units, and the other a 4-inch branch leading to the air receiver. The excitei pipe line is so arranged that any two of the three exciters may be operated m parallel with the same hydraulic head, this object being obtained with a system of " Y " branches and valves. Al! cast iron pipes were tested hydrostatically to a pressure of 4501b per square inch and the valves to 500tt> per square inch. The joints are made with round rubber high pressure gaskets, the flanges being rebated for that purpose. Generally the whole lay-out of the pipe system JS a departure from that usually adopted, more particularly m respect of the entire absence of receivers at the back of the power house. The deviation of water is made by the "V " branches It will be seen that the water has thus been put into tram with a minimum amount of obstruction and fnction, and the results o btamed from the efficiency tests are ample proof of the advantage of this system over that of water receivers. The weight of the column of water in the pipes is about 470 tons, which at full bore moves with a velocity of 5"66 feet per second , and m order to provide against accident due to shock from water hammer, an air receiver has been installed which consists of a shell 30 feet long by 36 inches m diameter. The air pressure is maintained equal to that m the pipe line by an air compressor operated by a 10 h.p motor, and the water is covered with a layer of oil to prevent aeration of the former. The capacity of the receiver was calculated to absoib the sudden stoppage of flow from an angle of 26 degrees from the one jet of the four main pipes, in six seconds at tull bore , the standard working pressure being 2881b per square inch The receiver reclines at horizontal, and is provided with an automatic float ■\\ hich operates the controller of the compressor motor. The receiver was placed at the end of the malleable line because it was impossible to place it nearer the nozzles ; the cast-iron pipes

had, therefore, to be made sufficiently strong to resist the shock arising from water hammer. • As previously mentioned, the mam supply of water carries a large amount of sludge in suspension, which renders it unsuitable for the operation of the hydraulic governors A supply of clear water was obtained from a small creek giving a hydraulic head of 400 feet at the power station. A small concrete weir 8 feet high to the sill of the spillway was constructed across the bed of the creek, and the water conveyed by a 4-inch pipe-line 1807 feet m length, to the governor. This pipe line is provided with the necessary air valves, gate valves, and stopcocks, and is buried and securely anchored. It is tapped at a height of 2W feet above the power station to supply the engineers' residences and fire hydrants for same, and in addition to supplying the governors the water is also used for cooling the transformers. The maintenance and operation of the flume is done by one man, "who has been provided with a small cottage located near the penstock It is th is ma )'s duty to record the water passing through the flume and over the weir and to patrol the whose length of the flume twice per diem. His residence is connected by telephone to the power station, and there are also telephone stations along the /lume to each spillway, and one at the intake! and the racemap reports to the power station from each pomt. When makmg the efficiency test the water was measured by passing it through a square orifice. Ihe head and aperture were accurately measured, and the co efficient of discharge used was 0.619, and the results agreed with the measurements of the water over a weir. The amount of water used during the experiments was 29 cubic feet per second, and allowing for frictional losses, etc., the total theoretical h.p. at the power house was 2185 This included the water for the main unit and exciter. The spouting velocity at the noz/les was 12 360 feet per minute , the peripheral speed of the water wheels being 5945 feet per minute. An ideal site for the power station was selected on the bank, of the Waipori river. The building is constructed of concrete re-inforced- with steel rods ; the metal, grave], and sand for the concrete were obtained from the opposite bank of the river and consequently only the cement and re-inforcmg lods had to b j transported from Dunedin. The power station building is 100 feet long by 64 feet in width (internal dimensions), and a temporary wall has been constructed at the down stream end to allow of future extensions Before commencing the work of clearing the site for the foundations the author deemed it advisable to clear the bed of the river in fiont of the power station of the large rocks and boulders, so as to provide a clear channel for the water in flood time This dangerous and arduous work took several months to complete, and the bed of the river was cleared for a, length of 8 chains, the result being that the normal level of the water was reduced 6 feet, thereby considerably reducing the cost of the power station foundations, as the floor level would have been 6 feet higher if this work had not been carried out. Concurrently with the work of clearing the river bed, the construction of a training wall at the upstream end of the power station was proceeded with,

to divert the flood waters from the power station site andjto form a permanent protection to the foundations from erosion during time of floods. The foundation for the wall of the building on the river front was taken down to the rock bottom 16 feet below the bed of the river, and is 8 feet wide at the base, tapering to 4 feet wide at the engine room floor level, which is 6 feet above the highest known flood level. The power station is divided into two portions • The front portioa forms the engme room and is 100 feet long by 30 feet wide ; the back portion is 100 feet long b}?- 29 feet wide, and has two floors On the ground floor adjacent to the engine room, is the L.T. bus bar corridor, which runs the whole length of the building, and is 7 feet 0 inches in width. At the rear of this is the transformer room, which is 63 feet long by 12 feet wide, and at the

rear of the transformer room is the H.T. bus bar corridor, which runs the whole length of the building and is 9 feet wide. These compartments are divided from each other by concrete walls, which also form the support for the floor of the oil switch [room above, which contains the H. and L.T. remote control oil switches, the L.T. in this case being 2400 volts. The whole of the walls and floor of the oil switch room are constructed of re-inforced concrete, the floor being calculated to carry a distributed load of 40 tons. At the down stream end of the building, in the rear of -the H.T. bus bar corridor, is the lightning arrester annex, which is 29 feet long by 5 feet G inches wide. The main walls of the engine room carry the 15-ton Krupp travelling crane which runs the whole length of the building on concrete girders, which are re- inforced with steel rods and partly supported on con crete corbels. The roof is constructed with framed iron principals at 12 feet 6 inch centres, and is sarked, felted and covered with galvarised iron. The engine room and the oil switch, room are lighted by means of skylights which run the full bugth of the building, and there are also large windows at the up-stream end. The foundations for the machinery are carried down to bed-rock • they are constructed of solid concrete and are entirely independent of the main building. The cast-iron pipes conveying the water to the engines are carried right through the building on independent foundations. There are two main generating units, each unit consisting of one General Electric 1000 K.W. 2400 vdt 50-cycle three-phase generator, revolving field t>pe, with 14 poles running at 429 r.p m. The regulation at full load and 100 per cent. P.F. is 7 per cent., and with 1000 X.V.A. and 75 per cent. P F. 15 per cent. The efficiency is 95.25 per cent, at full load. The generator is driven by two Pelton wheels each 4 feet b inches diameter, one at each end of the shaft, and on each Pelton wheel there aie 15 buckets and the wheels are out-hung. Leading to each water and on each Pelton wheel there are 25 buckets and the wheels are out-hung. Leading to each water wheel is the. 14in. pipe, so designed as to increase the velocity at the nozzles. The flow of water is controlled by the mam 14m. gate valves on each branch, which, under operating conditions, are left wide open, and the regulation is adjusted by means of movable needles within the nozzles. The needles are of bronze and operated by worm gear and hand wheels, so that the quantity of water flowing through the nozzles varies according to the area of the concentric apeiture between needle and nozzle tip, which is s\ in internal diameter. When operating at full load" the radial space is gin. The needles are provided with hea\ y re-action springs to ease the effort required to increase the annular opening.

Under full load conditions the nozzles are at the top position and the jet impinges on the centre of the buckets. At no load the jet is quite clear of the buckets and impinges against a heavy iron baffle plate which deflects the water into the bottom of the tail race. The jets discharge right across the river and strike the opposite bank. They act as an ejector, and special inducts are led into the water educts to admit air. The whole of the solid casting forming the nozzles is attached to the main pipe by a ball and socket joint, and is free to move in a vertical plane through an angle of four degrees. The nozzles are raised and deflected by means of a system cf levers, cat gearing and rack shaft operated by the hydraulic governors, w hich ai c Lombard

type " E." The deflecting portion of the nozzles, is counterbalanced by hydraulic pressure, so that quick action can be secured from the governor on account of the absence of inertia m heavy counterbalanced weights. The governors are proviled -with electric control motors operated from the table switchboard, which admit of instantaneous control of the speed of the water wheels This control is of great advantage when synchronising. The regulation of the governors is exceedingly sensitive and does not vary more than 4 per cent, from no load to full load, and from full load to no load. When the load is thrown off, the jets are deflected clear of the buckets.

This shows the seven 350 kilowatt transformers, which raise the voltage from 2400 to 34,700 These transformers weigh from five tons each, and are eleven feet high. The Pelton wheels are capable of driving the generators at 50 per cent, overload, but they aie designed to give the best efficiency at full load. The buckets are made of the highest grade cast semisteel, and the wheels aie guaranteed to safely withstand the highest run-awa\ speed attainable under the effective head of 6C5 ft. without damage, uith the nozzle adjusted to give the maximum stream.

The nozzles are pivoted on heavy trunnion pins and the ball joints are leather packed with oak tanned leather laid m tallow A re-action strut is provided for relieving the fulcrum bolts from thrusts, which are taken up on an independent journal in line with the axis of the joints The Pelton wheels are guaranteed to develop an efficiency of 80 per cent of the theoretical energy in the water delivered to each wheel at full rated load 75 per cent at three-quarters load and 70 per cent at half load. In the tests made by the author the efficiency obtained at full load was 83 per cent.

The main generating units are spaced 24ft. 4in. apart, centre to centre. At the down-stream end of the engine room are located tvo exciter units, foundations being pro vided for a third. Each unit consists of aG E. 40 K.W. 6 pole DC. J25 volts, 725 r.p m. generator, coupled to a 6J hp. Pelton w heel , coupled at the other end of the Pelton -wheel is a 60 h.p. induction motor, the object of the latter being to act as a regulator for the exciter, the position of the adjustable needles m the deflecting nozzles being fixed to take care ot the normal load on the exciters At the rear of the exciter units is the switchboard gallery, the flocr of which is Bft. above the engine room floor level. The centre of the gallery will be the ultimate centre of the power station when the plant is duplicated. On the switchboard gallery is located the main controlling switchboard, consisting of four generator panels, two exciter panels, one motor panel, one transformer panel, one regulating switch panel, and two line panels. In front of the gallery is a table switchboard inclined to a slight angle, on which are distributed the switches for contrthng the oil switches and. Lombard governors. These switches are provided with red and green lamps which indicate -whether the oil switches are open or closed, and the connections are engraved on the marble so that the attendant can see at a glance which line or bank of transformers he is operating. On each generator panel there is an A.C. ammeter in one leg, field ammeter, volt meter, polyphase inductor recording Watt meter, field switch and field rheostat, one four -point receptacle for synchronising plug, and two hand-operated oil switches. On each exciter panel there is one ammeter, one field rheostat, one volt meter receptacle and one double pole mam switch. On the induction motor panel there is one ammeter and one automatic oil switch On each transmission lire panel there are three ammeters, one in each leg one overload time limit relay, one controlling switch with signal lamps for line oil switches. The switchboard is of black enamelled slate, 18ft. 6m. long, supplied by the G.E. Company, and is a very handsome piece of work. In the L.T. bu^ bar corridor are located the 2,400 volt bus bars, which lead from the hand operated oil s\\ itches and bus bars on the switchboard to the remote control oil switches controlling the L.T. side of the transformers. In the transformer room there are 7 G.E. transformers, each having a rated capacity of 350 K.W., and arranged m two banks of three each, with the beventh as a spare. The transformer ratio is 2,400 to 20,000, and they are connected in " Delta " on the L.T. side, and in " Star " on the H.T. side, with neutral earthed giving a potential of 34,700 volts between places The primary full load current is 140 amperes and the secondary full load current 17.5

amp. The transformers are oil insulated, water cooled, and each tank contains 350 gallons of oil. They are guaranteed not to exceed a temperature rise of 35 degrees C. after 24 hours' run at f nil load and 50 degrees C. after 2 hours' run at 25 per cent, overload, and the tests prove that these guarantees were fully conservative. The efficiency of the transformers at full load is 97 per cent. /the regulation with non-inductive load 1.4 per cent., and at 90 per cert. P.F. 2.8 per cent. jEach transformer is 11 feet high by 4 feet by 3 feet weighing f" 7 tons, and connected to a system of oil piping by means of which the oil can be drained from the transformer to a well, and a small electrically-driven rotary pump lifts the oil to tanks overhead, from where it gravitates back to the transformers , they are also connected up to a circulating water supply. Each transformer is mounted on a small trolty and can be shifted off its bed on to a traverser and wheeled into the engine room, so that it can be dissembled with the aid of the overhead travelling crane. Theie are several small transformers m the power station for various purposes. Three 40 K.W. transformers for motors and lighting the potential being regulated by taps connecting to the dial switches on switchboard. Series transformers are m transmission lines for operatirg the overload relays and line ammeters In the H.T. bus bar corridor at rear of trans former room are the bus bars connecting the oil switches on the H T. side of the transformers to the oil switches controlling the live bus bars This bus bar corridor is constructed on the cellular principle with concrete partitions, and all H.T. wires are kept at a minimum distance of 12 inches from earth. In the oil switch room abo\e are located the remote control oil switches, which are of two tyres there arc four of the Westmghouse solenoid operated type which connect 2400 volt bus bars to the I, T side of the transformers, four G.E. motor operated type which connect the H.T. side of the transformers to the bus bars four of the Westmghouse solenoid type which connect the PI T. bus bars to the 35,000 volt line bus bars and two G.E. motor operated type which control the two transmission lines They are built up on concrete wall" separating each chamber, and the doors arej hung from the top, so that they are free to fly outwards m the event of explosion m the oil cells. The controlling circuits for motors, solenoids, and signal lights, are taken oft the D.C. 125 Y. exciter circuits, and the whole of the mechanism can be handled with safety. The switches can be opened or closed with hand levers m case of necessity and both types of oil switches are entirely satisfactory in operation. All oil switches throughout the entire system have disconnecting knife switches on either side of each leg, and the greatest care has been exercised with thejstation wiring, which is with open bare conductors throughout, the only insulated cables being those which connect the generators to the switchboard bus bars, and both sides of the transformers to the disconnecting switches above. It will be observed that the leads from the transformers are connected to double throw knife switches on the L.T. side and to plug switches on the H.I. side, m order to admit of the spare transformer being cut m to replace any one m service that may give out in either of the two tanks. The connections to the plug switches on the H.T. side are made by means of heavih insulated flexible cable to admit of safe handling with a potential of 20,000 volts to earth. The double throw switches and plug switches are all supported on an angle iron framework. On this framework are also carried the inter-connecting bus bars between the transformers and the oil switches on both sides. The wiring of the power station is on the duplex system throughout, and admits of either generator being connected to either transmission line through either bank of transformers independently, or in parallel. In the lightning arrester annex are six Westmghouse low equivalent lightning arresters, one set on each leg of the two transmission lines. Each arrester is of the standard type with a series of sparking gaps m series with a resistance between' them and the ground. Oil insulated choke coils are connected Detween the lightning arresters and the line oil switches, to protect the transformers from damage •due to surges. The hissing of the brush discharge from the H.T conductors is very marked, and the latter is visible at night. The author found it advisable to have all insulators carefully cleaned with dry cloths at regular intervals. The operation of the plant is extremely simple, and the orly electrical troubles the writer had was a puncture of an insulator on one of the selector switches and a burn out m one transformer, the latter due to a heavy surge on the line The generators were put into operation on 3rd November, 1906, and have been running almost continually ever since ; and though the water contains so much matter in suspension it is so fine that the paint is not even worn off the buckets.

The power was first sent througn to Dunedin on 19th March, and after the necessary" preliminary experiments, the whole was put into permanent operation on. 7th April, 1907. The power station staff consists of three engineers, three switchboard attendants, and one spare man, who divide the shifts between them. A gravitation tramway had to be constructed on the hillside to convey the material from a receiving shed at the foot of the practicable waggon road to the power station. The full truck descending hauls up the empty one. The horizontal length of the line is thirty chains and the total fall 722 feet, at ar average grade of 24 feet to the chau the steepest pmch being 1 m 1.43 The tramway is constructed of birch rails laid on transverse sleepers (To be continued )

Depth ft m Area sq ft Hydraulic Medn Depth Feet. Velocity m Feet Cub. Ft Per Sec. 0 C 1 0 1 6 2 0 2 6 3 0 3 6 4 0 3 6 9 12 15 18 21 24 4285 .75 1 0 1.2 1 36 1 5 1 (51 1 714 1 795 2.729 3 358 3 821 4 170 4 463 4.683 4 888 54 16 4 30 2 45 8 62 5 80 3 98.3 117 3

The following table shows the discharge for every Gin. ot water in the flume the calculations being based on Ganguillet and Kutter's formula using the co-efficient of rugosity of N 0 017 —

Diameter, j M'xm'm j Head. | Thickness 1 of Steel Length feet Lo=.s Feet V'lc'tyft. p rS'Cond 1 1 1 1 I t 1 nicies 42 40 36 36 36 36 36 36 feet 140 226 254 329 440 i 500 I 600 I 670 ' 670 inch. 1/8 3/16 3/16 1/4 5/16 3/8 7/16 1/2 258 136 I 58 ! 333 I 32S I 256 1 221 186 1 48 .33 4.16 4.58 5.66 • s.i^o 5 oS I I 776 6 30 I 5.06

The following table gives the various lengths of each size of pipe, maximum head, loss of head byfriction, and velocity of water when carrying 40 cubic feet of water per second —