POWER FROM ARAPUNI.

Waikato Times, Volume 102, Issue 17243, 31 October 1927, Page 9

POWER FROM ARAPUNI.

TRANSMISSION LINE.

IMPORTANT WORK DETAILED

CONSTRUCTION COSTING £220,000

METHOD OF TOWER ERECTION

In an apparently endless line across the Waikato is a chain of latticed steel towers which will carry the great voltage power to be generated at the Arapuni works as far as Penrose, to reticulate the wide area traversed. The work of erection has involved much constructional detail, and the undertaking is a responsible and important piece of electrical engineering, perhaps without parallel so far as the lino itself is concerned, in the Dominion. Good progress has been made with the work, which Is estimated to cost In the vicinity of £220,000.

Some indications of the work involved in the construction of the Arapuni-Penrose 110,000-volt steel tower transmission line were given by Mr T. MacLcnnan, Public Works Department district electrical engineer, in a paper presented on Saturday night at the annual conference of the Auckland branch of the New Zealand Society of Civil Engineers.

When the line is in service, there will be three circuits supplying power from Arapuni to Auckland. The lower line comprises two of the three circuits, the third being the pole line which has been in service since July. 1925 and which is insulated * for i 10,000 volts, but now operating at f,0,000 volts. This wood pole line and all the oilier lines shown, arc now in service and supplied by power from Hora Hora.

On completion of Arapuni the three circuits connecting Arapuni and Penrose will be operated at their full voltage of 110,000, and the 50,000-volt system of lines will be supplied by means of 110,000 1o 50,000-volt transformers at Arapuni, Hamilton and Bombay and 22,000 to 50,000-volt transformers at Penrose. The length of the line is 99.6 miles and the number of towers total 527. There are 425 standard line or suspension towers, 53 light angle towers and 27 heavy or strain towers, with two special lowers at the Tamaki crossing. The conductor used is 19/13 copper, weight 26201 b per mile. The steel towers have the advantage of greater durability ami being more reliable on account of fewer insulators. The landed cost of 50ft lowers of the three types is: Standard line. £6B 10s; light angle, £lO2 Gs; and strain, £l2l 16s. From the figures given the economy of using three different types of towers, according to requirements, is apparent. The use of any tower in various locations depends on the length of the span and consequent wind pressure, as well as on the angle. The suspension towers are designed lo stand wind pressure only on 19* chain spans, and on five-chain spans they can stand in addition the side pull due to an angle of 12} degrees. The light angle range is from a 121 degree angle on 25-chain spans to a 29 degree angle on five-chain spans, and the strain, or heaviest towers, range from a 64 degrees angle on five-chain spans to Hi degrees on 25-chain spans. With 70ft towers on level ground, spans of 17.8 chains give the regulation ground clearance of 22ft..

Building of Towers.

The towers are built to stand substantial strain from all angles, and weights are used to prevent excessive side swing of wires or uplift. The matter of foundations is important for a steel tower transmission line, and much additional investigation has been necessary before deciding that in addition to the standard grillage, three types of special foundations are necessary. The wood pole line built over the same country gave a lead as to where trouble could be expected. There are 208 concrete stub foundations of Various sizes. Investigation failed to find anything that could be called a definite hard bottom in some of Hie swamps, and floating foundations were designed to meet requirements. Their main feature was that they consisted of four primary beams of reinforced concrete joining the corners of a square 2 6M"t long and extended in each direction, making a total l)eam length of 39ft. The ends of the primary beams arc then joined with secondary beams and reinforced concrete. The foundation covers an area of 1080 square feet. These were used in the peat swamp at-Hor-sham Downs, and between Huntly and Rangiriri.

The progress of the work may be gauged by the fact that preliminary survey work was done in' November, 1924, to determine the general route for the line, and definite survey work commenced in March, 1925. The actual pegging of tower positions was commenced in May and completed in September, as many as five survey parties being employed at one time. There have been many minor alterations in the roiile since September, 1925, lint, the lowers were ordered on the basis of I his survey, after allowing for changes and replacements, ime all.crai.inn which makes the line cross the Tamaki basin in a different place from the. original survey, requiring four special towers, 85ft to the lowest wire,-'two for this line and two for the already existing line.

Work on Foundations.

The contract price for the lowers was about, £45,000. The other two main items of material were about £63,000 for copper wire and £II,OOO fur insulators. Stub-setting was commenced in April, 1926. Previous to this, in February, a start had been made on special foundation work, piledriving in the Mangatawhiri swamp, and the erection of gales and bridges, bushfelling and work on special foundations near Rangiriri. were commenced in March. Tower erection wis started in May, and in May the rise in the Waikato River practically stopped foundation work in the Mangatawhiri and Maramarua swamps, though it was still possible to do a little near Rangiriri, and I.ll c special foundation could be carried on fairly welt at Papakura. Stub-setting was continued throughout ilis wiSter months, but it was necessary to" shift the gangs about lo some extent lo keep them on the drier country. Stub-setting on the southern section (Arapuni-Rangiriri) was finished early in April, 1027, and on the northern section (Rangiriri-Pcn-rosc) it was finished, with the exertion of some special wor.k, early in May. Some 4 50 stubs were thus set in a little over 12 monllis, or at the rate of 36 monthly. The number of men employed in a stub-setting party was between 10 and 12, and two gangs, sometimes three, were engaged practically the whole lime. Tower erection, which began in May, 1920, was practically completed in May, 1927, on the southern section

and in June on the northern section. I After the first three months the towless. crs were erected at the rate of 45 monthly. The number of men on ! tower erection was a maximum of . about 40, but averaged considerably The wiring of the Line had been jj carried out for the most part under | adverse circumstances, owing to de- I lays with the towers. The weather | recently has been bad for this class j of work, but from the end of April I until the end of August (five months) | 221 of the 528 towers have been | wired, and in ail 310 were then com- jj pleted, including most of the swamp | portions and about 120 more were I completed in September. With fair j 1 cross-country going, a gang of about JI 14 men will do .I }_ miles a week, and i| with five such gangs it was •expected!! to complete wiring in October. About I 90 men arc at present employed on § wiring, and about 20 men on other | work indirectly connected. | Delivery' of material to the tower E sites was covered principally by four i main contracts, for amounts totalling | £2385. Tlic stubs for the main tow- j ers weigh about 5001 b each, and tower | erection has almost all,been done by l co-operative contract. A method of jj setting stubs with the theodolite was I worked out in connection with the | Mangahao lines, and lias proved much I preferable to the template method. | There are 23 5 separate members in j I one of the 70ft towers, the heaviest | being 2401 b, and 661 bolts, not in- 1 eluding the stubs. -• §

Estimate of Costs,

The final cost figures are not yet | known, but the following approxim- 1 ate figures can be given:— | Cost of special foundations £10,900, 1 consisting of 10 piled at average cost I of £320, 15 floating at £240, and 52 j blocked at £65, making a total of 77 f towers. Setting stubs on the remain- g ing 450 towers cost £6467, an aver- j age of £l4 7s. The 70ft tower costs | were approximately as follow: —£88 1 landed cost; £lO4 at site, after railage | and cartage, plus £l4 for stub-setting I and £l2 for erection, making a total of ij £l3O. Some of ttie foundations, it jj will be observed, cost nearly three 1 times as much as the towers built on i g them. 11

The total cost of towers erected, including the ordinary stub-setting, but not special foundations, is about £09,000. The landed cost is about £4 5.000. Insulators cost approximately £2 18s for suspension string (5 units) and £3 9s per strain string (0 units), the total cost for the line being about £II,OOO. Copper wire (COO miles allowed), cost about £03,500, landed approximately £73.000 on site, with an additional £BOOO to erect it, making a total of say £81,0.00. As far as can be seen at present the net cost of the line will be about £IBO,OOO. The cost of survey, use of equipment, stores and overhead charges, land compensation and other charges will bring the total cost to about £220,000.

The line was built by the hydro- [ i electrical branch of the Public Works !| Department. The engineer in charge : 1 of construction was Mr G. W. Samp-11 son, who had under him Messrs Mar- j shall and Earle in charge of the j f southern and northern sections ro- [ | spectiveiy. All design work was done i I by the Public Works Department head j office staff in Wellington, principally!! Messrs Creagh and Ingram, under the if direction of Mr Kissel, the chief dec-| j trical engineer. !J The'lantern slides for the address || wore made and shown by Mr George j| Cartwright. jj