POWER-STATION PLANT

Otago Daily Times, Issue 13890, 30 April 1907, Page 3

POWER-STATION PLANT

<«««?!?' iw ? vcr " statloll p,ant consists of two 1000-kilowatt generators, bo designed that they ore capable of maintaining an overload capacity of 25 per cent.—altogether, 2500 kilowatts. Each generator is driven by a pair of Pclton wheels, the wheels and generator hemg mounted on the one shaft ,yo exciter units arc installed, each driven bv a single Pclton wheel at one end of the shall, while at the other end they are couplcd to an induction motor, so that they may be driven either by water, power or electrically. At the downstream ond of tho room is located the switchboard gajlcry, on- which is mounted tho switchboard. This'is equipped with controlling devices, instruments, and.mctcrs for operating the electric generators and the various oil switches in the back portion of the building. 'Hie switchlward is a particularly fine piece of apparatus, made of Muck enamelled slate. At tho rear of tho engine room lies tho transformer room, this being on the first floor. It contains seven transformers, wcjghing 35 tons in all, and cach of 350 kilowatt capacity. These transformers aro massive pieces of station••'ry apparatus, each lift high by 4ft by Sit. ihoy are for the purpose of raising the pressure of the electric current, which is generated 2400 volts to 20,000 volts, and the connections aro arranged in the 'star,' so that tho lino voltage is 31,700 volts, at which pressure energy is transmitted to the outskirts of Dmiedin. The first floor of the rear portion of the' bunding 13 divided into three corridors—tho first, adjoining tho engine room, containing the low-tension bus-bara; tho centro containing tho transformers above referred to; and the rear the high-tension bus-bar?, which aro supported on special insulators encased ■in concrete chambers running the whole length of the building. Situated above these corridors is a oliambeiyßßft by 28ff. jfnside hero are the oil switches, disconnecting switches, lightning arresters, and ehede coils. The oil switches are heavy pieces of apparatus, electrically operated on the switchboard in the engine room, bv which means all high-tension apparatus'i 3 controlled with low potential current, thereby obviating any risk of accident to the switchhoard attendant. Tho watenvJicel unils are deflecting nozzle. The flow of water is controlled by an adjustable needle and regulated by the adjustable needle, which governs the area of tho eonccnlric aperture at the nozzle, and fluctuations of load aro taken care of by the hydraulio governor, which raises or lowers the deflecting nozzle. The nozzles aro geared to the hydraulic governor by a system of rods and levers, so tlmt these nozzles can impinge the jet of water direct oft the buckets of the Polio n wheels, or lower tho 3107.7,1e so that, tho jet may pass quite clear of tho biickcts. The governors are what are known as tho Lombard type, 15, and tho water which operates them is obtained from an indc|>endent supply, tho head utilised being 400 ft. " The whole of tho plant and machinery ,been installed under tho supervision of Mr W. ICcon, foreman in charge of the works.

TIIIS TRANSMISSION LINE. TJio transmission lino loaves the poworsiation building at tho lightning arrester annexe. Ifc is taken to a steel tower silimhxl on the hill at tho rear of tho station. .From tit fa point steel cablcs aro strctchcd across tlio rivc r to another tower ocald on tlio opposite bank 1700 ft above the level of tho stream. Tho seven wires Bpan 1500 ft from tower to tower. "From this point copper wires aro taken on a duplicate line of poles to the sub-station at Halfway Bush. The duplication is thought necessary to eliminate the risk of breakdown. Tlio poles which carry tlio wires arc of Australian hardwood, 35ft in length and 15flft apart. One wire is carried on tho top of tlio polo, tho other two at cither did of tho crossbar, so arranged that the wires, aro spared in tho form.of a triangle with 3ft 6in sides. The Touto is across Maungatua to tho top of Ivowhai Spur, thence following tho ridge, and crossMile Oreet until it reaches Munro's road. It follows this to tho Bcrwiek-Outrain road, thenco to Ontram, and along tho Oiitram-Mosgiel road to the North-west Taicri rood. Tlio black bridge at tho SfTveratream is then rcached, the lines' of polos being looatcd one on each side of tlio road. After reaching the Silverstream tho lino breaks oil' into private property, and the sub-staiion at .Halfway Bush is reached. This slalion contains tho transformers Mint have been installed, which lower tho voltage from 34,700 volts to 3300 volts, at which pressure it is trans-' nutted (o the convcrfer station in Cumberland street. The route taken by this lino' (which is known as tho low-tension trans-', emission line) lies along the Halfway BnsiC road, through Koslvn, and down" Stuart' SlreeUo just below York place. The cables are carried on poles to this joint. Here, however, a largo chamber has been excavated under tlio sidewalk which contains the necessary apparatus for changing the overhead lino to underground, and tlio cables aro conveyed in earthenware conduits to tho converter station, at which point the energy is utilised for operating the tramways and supplying electrical power.

THE CONVERTER STATION. Tiro converter station contains three motor generator units, each consisting of ono 440 h.p. synchronous motor couplod ilircct to ii ■ 300 kilowatt clectric pcncrator for generating direct currcnt at 550 volts for operating tlio tramways, Tho station jlso contains very extensive switchboards, which aro equipped with tlio necessary controlling apparatus for regulating tlio v.' .'ions circuits which will ho reticulated throughout Dunedin and suburbs.. MR GOODMAN'S STAFF. In reply io a (juration Mr Goodman said: "In conncolion with the construction and installation of the plant Mossrs Noves Bros, left mo to select my staff for ilia work, and I was fortunate in having the assistance of most able men. Mr Stark assisted me with the power-station equipment and high-tension transmission lino; Mr Shepherd with tlio sub-station at. Halfway llusli and the low-tension transmission line (o Dunedin; and Mr Ackland with the converter station and underground reticulation in and around the city."