WHERE THE POWER IS GENERATED

Timaru Herald, Volume CXXXVIII, Issue 19941, 27 October 1934, Page 10

WHERE THE POWER IS GENERATED

WELL EQUIPPED FOR RAPID DEVELOPMENT

The erection of the power house at Waitaki did not involve the same difficulties as the construction of the dam, but at the same time it formed an interesting section of the scheme. The powerhouse consists of two main buildings—the generator room and an annexe, the latter being superimposed on the back of the intake structure of the dam itself. Between the main structure and the annexe are huge horizontal beams of heavily reinforced concrete. These beams are for the purpose of minimising earthquake risk and it has been calculated that the powerhouse is able to resist an earthquake of as great intensity as has ever been recorded in New Zealand. Control Room On the top floor of the annexe is situated the control room, which provides the officers with the maximum comfort compatible with efficiency of operation. The great series of huge switchboards, with their wonderful recording instruments and gauges cf many kinds, are too intricate for a description to be capable of comprehension by the layman. Suffice it to say that the instruments are the most modern and efficient that it has been possible to procure. Night lighting comes from beautiful beaten copper inverted hanging lamps. The woodwork is of attractively grained oiled rimu and the floor is covered with heavy cork linoleum. Along a light, airy and wide passage are the splendidly equipped offices. The control room and offices are placed as far from the generating plant as possible, to ensure quietness and also, in case of a serious breakdown, to keep the switching staff aloof from the turmoil below and yet able, with the coolness of head thus engendered, to carry out necessary urgent duties at such a time without fuss or flurry. In the control room there is more than 26 miles of wiring, the work having been done by the electrical staff under Mr L. S. Payne, the electrical engineer, and Mr W. H. D. Watson, the station superintendent. Big Travelling Crane From the offices a well-built staircase, with attractive rimu and steel banisters, leads down to a big platform running along the whole length of the generator chamber and overlooking the huge machines. Above, running on great rails, one on each side of the chamber, is the huge 120ton crane. This machine was used in the installation of the turbines and generators and will be necessary when repairs are needed to some of the bigger parts, such at the rotors, which each weigh 116 tons. Two Small Turbines On the main floor, at the northern end, is a set of two turbo-generators of 600 horsepower. Each consists of a small turbine, a flywheel, an alternator and a direct current generator. They will produce current at 400 volts and will be used for domestic work, such as the lighting of the Power House and of the village, operate pumps and lifts, compressed air and so on, and also, in case of emergency, for supplying current to the “exciters” on the big generators. Their production of current would be more than ample to fill the needs of Oamaru. Batteries are also provided and, as a further safeguard against stoppage, it is possible to connect current from Lake Coleridge to the alternators and run from that. At the south end of the main room is a big area of floorspace for repairs and other work. Off this, again are other small chambers which have been provided for various minor functions. Careful Designing The machinery is extremely heavy and this weight is carried on the floor of the main chamber. It will thus be apparent that the floor is immensely strong. In fact, so much reinforcing had to be done that over 2000 tons of steel reinforcing rods are embedded in the concrete of the powerhouse. The calculation of strains and stresses, involving the most infinitesimal fractions, the provision for all sorts of contingencies such as heat and cold, water pressure, dampness, corrosion and many others, evokes admiration of the engineering minds that could conceive and then design such works. POWER PLANT Main Machinery Only two main turbo-generators have been installed, but provision has been made for five. The two installed are of the vertical Francis type, each of 23,000 brake horsepower and they will run at 125 revolutions per minute. The “runners,” acting something on the reverse principle to a ship’s propeller, are each 13 feet 7i inches in diameter and each weighs 211 tons. The carriage by rail of these runners to the works was a tricky job. The water consumption of each runner will be 2929 cusecs at full load. Each runner is housed in a circular compartment below the generators and

this is surrounded for a good part of its circumference with an interesting water gate. This gate forms most of the wall enclosing the runner housing and is a series of hinged leaves, or slabs of cast steel, wide and rounded at the outer edges and thinner at the hinge. Each edge overlaps the next leaf. Though it is not necessary for the “gate” to be absolutely watertight the leaves fit very closely. A compressed air system operates jacks which open and close the leaves of the gate, so admitted or shutting out water from the runner. This compressed air jacking system is connected with a governor, of the oil pressure, evolvent pendulum type, which automatically opens or closes the gate as the demand for power increases or diminishes. Each runner is suspended at the end of a vertical steel shaft, 24 inches thick, which is very similar in diameter to the propeller shaft of a battleship. This shaft itself weighs 10 tons. It connects the runner to the generator above, and passes through big bearings that carry no weight, but merely keep the shaft vertical. A Giant Top Each English Electric generator has a capacity of 16,666 k.v.a., producing current at a pressure of 11,000 volts. Its main parts are the rotor, stator and the Michel thrust bearing. The rotor is affixed to the vertical shaft, like a giant spinning top. It weighs 116 tons and its diameter is 24 feet. This great armature was assembled in the powerhouse and the task might be imagined when it is stated that there are 13.000 metal plates in its circumference. So tightly have these plates been pressed together that they look like solid blocks. The biggest job done by the crane was the carrying of these rotors and lowering them into position. The rotor rotates at 1255 revolutions per minute, its peripheral speed being over 100 miles an hour. An Outsize Bearing; This spinning section of the generator, and the shaft and turbine runner, are all suspended on one single bearing, which carries a total weight of 240 tons. The bearing consists of a highly polished steel face and bearing pads faced with white metal, separated by a film of oil, and that it is possible to operate so huge a mass on such a bearing is one of the most astonishing things about modern engineering. The weight is distributed by eight great steel arms, which extend out beyond the circumference of the stator, on to the specially reinforced floor. An Inspiring Sight The stator, or magnetic field, weighs 86 tons and, as its name implies, is the fixed outer part of the generator. The cost of the generators was £19,305 per unit. The two that have been installed are situated at the northern end of the main chamber. The chamber itself is an inspiring sight, with its whitepainted walls and lofty roof, which is supported by a latticework of steel. The Intakes After the water enters the penstocks, of intakes, of which there are 15 (three to each turbine), each 20 feet deep by 11 feet 8 inches wide (equalling 700

square feet per turbine) it rushes down inside the big tube at the rate of six feet per second and round the coned and streamlined chamber. The pressure exerted on the walls and roof of this chamber is enormous, about 1000 tons on the roof, and as the chamber proceeds round the gate it gradually narrows, proportionately to the amount of water consumed, until it ends altogether. These chambers called for some of the finest designing in the works.

Each penstock is equipped with a head-gate of the truck type, and a steel stop-log gate. For lifting, each gate has its own motor-driven winch, while a 15-ton gantry crane commands ail the gates, and can withdraw them bodily on to the top of the intake structure for painting or repair. Somewhat similar gates which are commanded by a 7J ton crane can be placed in position at the mouth of the draught tube, where the water discharges, and thus the whole great compartment above and below the may be locked against the entry of water from above or below and then be pumped dry for the purpose of inspection or repairs. The water having been admitted to the runner through the gate, the turbine then operates. But it is not only the water above the runner that provides all the power. After leaving the runner the weight of water falling in the draught tube below also exerts its force, which is almost as great as that of the water above. The water flows for a vertical distance of 70 feet.