MANGAHAO REVISITED.

Shannon News, 19 June 1925, Page 3

MANGAHAO REVISITED.

, * DEVELOPMENT AT. POWER STATION. EIGHT THOUSAND HORSE-POWER LINKED UiP. Following is the second purl ol an article on the present state of development of the Alangahao hydro-elec-tric scheme. The first portion, dealing with the Alangahaq date, . and tire new dam under construction appeared in our Wednesday’s issue. THREE MILLION FEET OF TIMBER. Returning from Mungahuo, the sawmill, where the whole of the timber used on the job tor hut-building, bridges, concrete boxing, etc., was, cut, the whole amounting to three million feet, is situated a mile above Arapeti. This is a small, but wellequipped mill, with a capacity ol 12,000 ft per day. It, is at present being run at low" pressure, turning out about 3000 ft daily, largely, at present, blue mountain rata poles and crossarms for transmission lines. Here will be cut also the 21. million feet of timber which the No. 3 dam is estimated to require, half a million feet of which is at present stacked in the yard. THE POWER HOUSE. No part of the huge Mangyhau undertaking is more impressive than the power house, which, probably from the very obviousness of its function, demands the attention .u; the visitor. Within the huge white building, three-storied, and despite its massiveness, practically glass-sid-ed from the huge windows which fill up the whole space between the great concrete buttresses, are the generators, to run which the whole vast scheme was undertaken. Under the guidance of the Supt. (Mr, A. C. Blackwood) an inspection of the powerhouse was made, the Working of the vast machinery with its amazing detail and intricacy being explained at length. The technicality of this however, precludes its being grasped in the condensed form which the space available to this article would only permit, and a general resume must suffice. THREE GENERATORS RUNNING. Three generators out of the fivp installed, are now operating, two of these being of eight thousand h.p., and one of four thousand. To the layman this appears incomprehensible when he is informed that the present horse power, consumed over the whole, of the district linked up to date is only eight thousand, or just what one of the large generators is capable of producing. It would appear, from Mr Blackwood’s explanations that the answer is bound up with the length of transmission line at present in use, and the light (pad carried ! ih proportion to its length. The extra generators are being run as, a saiety factor, for, should for any reason, the whole of the sub-station's shut off together, or even the greater

number of them, under present load conditions, such a sharp rise in voltage would occur that injury might be occasioned to the generators. This, it was explained, was only a subnormal load condition, and would disappear when the full load was taken on the generating plant, with the gradual linking up of the various districts which the scheme will embrace. EXTENT OF MANGAHAO DISTRICT. The service lines eventually will extend from Mangahao north to Wanganui on the one hand, and on the other to Napier, yml branching at Woodville, down to. Masterton. South, a line runs to Wellington. So far the district served is as follows: —Horouiienua, served from a sub-station at shannon, whence it is transmitted through tlie district on 11,000 volt lines; Wellington supplied through a sub-station at Khandalluh per medium of an 110,000 volt line'; the Mana-watu-Oroua Power Board, with a substation at Bunnythorpe; Wairarapa Power Board, at Masterton; Dannevirke Power Board with a sub-station at Dannevirke; and Tararua Power Board, whose sub-station is at Mangamaire. All of these places are supplied by 110,000 volt lines, and another fact which to the layman is more or less incomprehensible is whv, when the power is generated at 11,000 volts it should be raised from that figure to 110,000 volts for transmission purposes. TRANSMISSION PROBLEMS.

Shortly, it may be stated, that voltage (which is pressure) plus current, represents power, and that these factors are interchangeable. Thus, ten

units of current, plus a similar number of voltage, and giving a result, of 100, may be transformed effectively into one unit of current, plus one hundred of voltage, and this is, figuratively, what is being done. The advantage of the system is that a certain amount of current only may he transferred through a given sized copper wire, whilst the power expended in transmission is in direct ratio to the size of wire employed. By reducing current, therefore, a smaller wire may he used, whilst by

a reverse process at the receiving sub-station, the power is restored again to its original condition. Once one attempts to go beyond these few main facts one becomes involved in a maze of technicalities, which the expert finds the greatest difficulty in reducing to ordinary language, and which although decidedly interesting would necessitate a scientific treatise

to do them justice. SPACE AND MASSIVENESS. The general plan of the powerhouse is simple. A huge floor space only partly divided covers the whole ground area of the building, and rising from the centre of this and supported on two rows of massive concrete pillars, are two extra floors, occupying about a third of the width of tiie total building. These floors are protected only by hand-rails, and the remainder of the interior being open to the ceiling 70-odd feet above, the effect is striking in its suggestion of space and massiveness. White is the

prevailing colour, relieved by touches of red in hand-rails and machinery, and by a great splash of red for the floor of the generator space, in The midst of which the five generators in their even alignment are painted black. Only the ends of the shafts on which the rotors swing are visibly in motion. The whole of the remainder of the machinery is covered in, and

its immobility is striking when one realises that there is a capacity of 32,000 horse-power. Only the sustained and rather disconcerting roar oi the revolving machinery convinces the onlooker that here is energy of .surprising magnitude. THE SWITCH-BOARDS.

On the first floor of the central elevation is housed the controls. Here at huge switchboards stands an engineer with his finger, as. it wore, on the pulse of the whole sentient Mangahao scheme. In one place is recorded the voltage generated from each generator in operation, in another, the lines on which that power is being transmitted; in still another, the exciter generators which act as automatic regulators of voltage production, and an infinite mass of further minutiae, each part of which is an essential detail of the control of distribution over the hundreds of miles of lines radiating from the power house. Added to these are automatic safeguards for each particular portion of the lines .and machinery, for it will be readily understood that when dealing with machines each capable of generating 8000 h.p., no uncontrolled operation can be permitted for even one instant, whilst the effect of 110,000 volts, if once it got out of control is almost incalculable. THE STAFF.

The operating staff of the powerhouse will be, when in full running, a superintendent, first engineer, seven operators, three greasers, and station fitters, and two apprentices who are being trained as. engineers. Shifts will be in attendance night and day, each shift being of two! operators and U °TCctS6I\ PIPE-LINE AND CONTROL GATES. The pipe line which brings the water from the surge-chamber to the generators, has now passed its six months’ maintenance period, and come through the test very satisfactorily, the amount of leakage being indeed below that expected. The gates at the entrance of the surge-chamber, and at the outlet from the Arapeti dam, which at first gave some trouble, have been adjusted. These, under the initial test, refused to operate, and it was found that ihe winches supplied from England were inadequate for their purpose. Ting lias now been rectified 'by the New Zealand agents of the English manufacturers and the gates are lowered and raised each morning to insure their being in good order should a sudden emergency occur.

CONCLUSION. In conclusion it may be stated that although the Mangahao dam has been completed, the impression that the' undertaking no longer presents a subject tor interest is a mistake. Mangahao was never more interesting than at the present moment, and with tile completion o/f the road to I lie site of the No. 3 dam, it is certain that advantage will be widely taken during the coming summer mouths of what will undoubtedly be one of the finest, and most interesting motor runs in the Dominion.