TO THE SUB-STATION

Evening Post, Volume CVI, Issue 48, 25 August 1923, Page 13

TO THE SUB-STATION

POWER LINES TO THE , y city

BREAKING DOWN HIGH VOLTAGES

TRANSFORMERS AND CONVERTERS. ' ' ■

The work of carrying the heavy underground power supply cables from the Evans Bay Power Station to the main city sub-station at the Southern end of Jervois quay is nowon ite last lap; for the big. feeders are at the door of the converting station, and at present a subway, running the whole length of. the station, and later to be extended under the footpath towards the Fire brigade Buildings, six feet wide and deep, is being constructed for the more convenient housing outward-bound low tension cables. ' ' :

The power from Evans Bay will not make the whole trip underground, but will travel over, the: Mount. Victoria ridge overhead, and will go to earth at a spot on the- Town Belt juet before Majoribanks street is reached. Thence the route runs down hill to Courtenay ?lace, across Clyde quay square, and own .Wakefield street to the converting station. The main feeders from Mangahao hare started on their way from Shannon, to Khandallah by stranded copper cables" earned high -overhead, thence to be carried underground along the Hutt road, across to Customhouse quay and then to.Jervois quay and the sub-station. The whole of the power supplies for the .city irea will, there-. fore, pass through this station,' some of the .power; from- Evans Bay to be run through rotary.converters to be changed in from alternating to direct current for tramway, lift, and certain power purposes, Maagahao power to be watered down,, as it were, from overproof to'something less dangerous to allow out and-, about the city,' still as alternating, current. .The differentiation between direct and alternating current is that -.direct current ruris .continuously round: the. circuit,, a one-direction current while alternating .current .runs first clockwise and., then; anti-clockwise. Direct; current; runs : as, a riyeiv;- alternating current as the tides, but-the tides rim out .and,in with; wondtous speed, fifty times to,the second.; ■- ■ •'. . ■ The. converter will beiof 'the one-unit ■ rotary type, : .the... .alternating ■ .ciirrent bmi}s, «a.xn on.one-side and. direct, current leaving at the, other, a converter of quite a,'different "type from the doubleunit style, which; is-really a compound motor : generator,;' the first, unit >Ing a' motor actuated: by. alternating/current, and the second unit, coupled up directly a .generafor.of .direct current."; Tlie.rbtarvconverter, has certain-advantages • over the., double-unit -type, . -chiefly in ■ that .losses■are.mTich lower., It. will deal. with, alternative current at 408 volts,- -the .pur* supply-.at li; 000 -from -Evans Bay.,>ing first stepped down in great stationary transformers.- The rotary converters will .turn':alternatinecurrent of 400 volts uito! direct current at 050 .volts: '.■'••'

The, stepdown transformers for alternating current are. totally : different in in them no moving parts, the breaking i&J*"?" roUght' Mt:asa «sult of induction from, one' : set' of coila' to . another, ;t,he.number and arrangements of the coils bemg determined according to extent_"of. stepping 'down required. Such transformers can' Lndie alternating S 1 110*I?'*™™ there is no inductivl action when direct current flows smoothlj round a coil : The induction.coU, used either for medical purposes or by vouneer sons of the family7 or the sui| r Tshfg ?It «te t nSL mclei' who unwittingly takMrm hold of a. "loaded" doorknfb^ 'i. a BteP-FP transformer, and the mal chines which will handle the power aim Ply.as it reaches the city wi§°£ Zh. ing more or'^s. than elaborate i>Xcn°s?ead lnSiae °Ut steP down

WATTLVG. '.FOR 'THE ■tIHANGE- ■ : OVER. ;

form the power from Evans Bay toMA« nao will have a slower frquencv of % HN ifts§§i erini 7-^ 6^ IS an- °uter Protective-c^v enng, of bitumemsed material. Over these power lmes :11,000 volts; will run £ b*^em, »;.the-road trench are two.smaUer single-core cables,' lead-cov-cnlpW 8 .a ga« Protected by bitumen covering, to carry boosting power, divolts. These -are out,, not in), power hnes Particular care has been taker, m the,laying of these lines,.for complete insulation is of .first consideration. Upon the floor. ,of. the road trenchi a' couple of feet or so deep, are laid shallow .wooden trenches, upon the bottom ot those are placed at regular.' intervals squares of plate, glass, 1 and'on those squares are laid: the two smaller cables The • troughs' are then filled in with hot: bitumen, and by. .way of additional precaution against risk or injury by traffic stress from above a thick layer of concrete is. put down. ■' HIGH VOLTAGES. The Mangahao power, due in Welling, ton about the end of June next, if all goes well, will.also flood into the city at 11,000 ; volt pressure,, to . be sent out again from the sub-station, partially watered down, to under-strappers of breaking- down stations, to -be diluted yet again. ready for the consumer, a greater or less voltage, acording as to whether the power is to be' employed in lighting services of for factory or other power services. Electric current at 11,000 volte is best i left very strictly to the understanding

and 'handling of experts," whose respect for it, though it may not show on tho surface when one. is talking with-them, is really spmething remarkable, but 11,000 volts after all are a mere trifle in power as it is distributed to-day, and the genuine article will flood away from Mangahao at 110,000 volts. Even experts plainly show their respect for such current. Still, Mangahao will in nowise set a record in distribution voltage, as the new standard: for long dis-' tance in the States appears to be settling down at double that pressure, 220,000 volts, the advantage being that the higher the voltage the lower are the distribution losses, a very great consideration when power has to be transmitted for distances running up to two;or three hundred miles. Again, high voltages may be transmitted over .considerably smaller cables than lower voltages; and accordingly there is a big saving in the material .of which the cables are-composed, copper in the case of. the Mangahao lines. The lads of Khandallah and other: lads along the poWer route will be very well advised not to "birds-neat upon the power poles nor. to fly kites in'interesting fashion when strings are likely to be' damp, near the live lines, for .though" 110,000 is not' a world's record by a long'way, still for all practical purposes' it is one; of the moßt dangerous brands of electricity produced, unless treated with proper- expert respect. And so, for that matter, is every service voltage. The Mangahao power, then, w.ill make the first stage of its journey, to .Wellington at 110,000 volts, but at Khandallah will run through transformers and leave again by underground cable:along the Hutt road for the : city at one-tenth the ; pressure, but, to ;go back to!, the simile, of • bond and. commercial liquor, watered to.a greater volume.. With a high, voltage the volume (amperage) is low; with low voltage.the amperage is high. . . .■. ; .'.■•• , UNDERGROUND SERVICES. "■l* is.» more awkward job and a more expensive one to' transmit! power underground, than overhead, but the regula-tions-are- hard and- fast that high'"tension current must go "underground within city and town ' boundaries to 'minimise risk of accident. ■■ In 'many centres at Home and'in the States it is. the practice to carry practically alt street reticulation ■ underground :in the densest business' blocks' and to place the final; stepping - down' transformer boxes belowthe surface along the power routes' or,; under proner : saf eguardg, in basements: owned by ■' business firms- by arrangement between the' supplying body and the owners, the -cables in .such system's in many cases diving down to- very.considerable depths from -the road surface. One or two. of the larger American ■ cities have carried ' this underground street reticulation, service a step' further, and have given: private (Companies :the right 'to . tunnel, under the. city streets and handle lines-" on behalf of all suppliers^ .of". the 'city's electric services, power, Ught/telegraph, telephone, 'and "ticker, with- perhaps 'half a- dozen bodies supplying:power alpn'e;_ Each service has of its own-in .the-.tunnel,, and.everything., is get-atable without tearing; up" the road' surface.- An.even more ambitious scheme .was ■ put- forward -by 'one': American - coin--party promoter whose id'eaSyas'that:one •pompany" should be set up to iaridle, not only cable services, but 'water-and"sew- \ erage services as well, everything within one main road tunnel. America-finds | some such plan necessary; hot' merely be- ' cause'the' volume-of traffic .makes 'street. excavation, an. acutely .awkward -husiness, _ but because the... f erro-concrete road is the standard there, and a con--crete road is laid down ; to ■; last,' and is consequently a solid Job:- .^.i .'>_■/;.: " Anything like -a complete underground reticulation service in' Wellington is out of-the question, .for 'the' reason-that those parts of: thi; city '.where -current demands 'are heaviest,'that is, -in' the business ■ streets, are: largely built upon reclaimed land, through' which,-even . after.-all these years since '.the'■; reclamation was made, the sea water'runs remarkably freely— as./, witness the thousands of gallons pumpedout-- when nil-' ,ing is,being put down for a ■new/'buildmg well back from the waterfront—and sea water spells ruin for such, appliances as transformer boxes placed • wfthin reach of its .dampness. -Underground transformer, stations in; the cityproper are therefore probably' ruled out There is,, However, consolation, to. the man who objects to the.\ sight "of ', iron transformer' boxes perched* above :•' the footpath- at every few.hundred, yards or Jso, in that the new voltage .will enable: the corporation- to 'do; away! with the great majority ,of. these, possibjy all pf them, in the city .prop'er;\the higher voltage making it; possible 'to . carry power to the consumer. frbm ; transforming stations considerably ' further apart with comparatively, smill--loss. ' ' : Jervois quay ; sub-station ''is one of several, such stations' on the. plans; though- it is the-biggest,: Another.is now being built in' Riddiford street; and will do-much the same-work-though on a different: system,' for there the converter;.will ■be automatic?and will run without constant attention.--This converter ■ will: be one' of 'the latest types built and the: largest* of: its' kihd in" the .Dominion;. Christchurch has one or- two of these converters in • action, but they are; comparatively small. Another.' point about the Riddiford. street 'station ;is that-it;will be sound-proof, and 1 the passer r by '.will hear nothing' of -'the roaring, hum within... In that.; respect, perhaps,,-the'passer-by is ho very important person, but. those who live near the sub-station will certainly, apppreciate the virtues of. the; particular style of building foUowed.