Harnessing the Waipori. Part II.

Progress, Volume III, Issue 2, 1 December 1907, Page 54

Harnessing the Waipori.

Part 11.

By W. G. T. GOODMAN, A M I E.E.

The power station being at the bottom of a deep gor»e does not receive anj of the sun's rays for about three months of the 3 r ear, and in order that the residences for the attendants should not be subjected to this condition the author selected a site for them on a spur about 200 feet above the power station. It is also necessary that they should be away from the noise caused by the impact of the water on the impulse wheels, which is so deafening m the power station that conversation can only be held by means of a megaphone. There are three residences, with f?.miliar suggestive names affixed — Voltaire Villa, for the chief engineer and family , Ampere Cottage, for the second engineer and family , and Faraday House, for the third engineer, three switchboard attendants, and the spare man. These residences are all substantially built and furnished by the

Council and the barracks is provided with a billiard room and library for the benefit of those who have to live in',this isolated part of the country • *here is not another residence within eight miles, and on one occasion they received no communication for nearly a fortnight, on accrunt of snow. We will now p?ss on to a descriptirn of the H. T Transmission line. After leaving the power station the H.T. transmission line pioceeds for a distance of 21 miles to sub-statien No 2 Ihis sub-station is located en the Taien Plains in order to meet the conditions demanded by the Taien County Council for granting the right to the Dunedin Council to take the transmission lines along the reads •within the Taien County. The nature of the agreement is that so soon as the Dunedin Council have contracted for a demand that will take four-fifths of the capacity of installation, the remaining fifth may be utilised tor the benefit of the residents of the Taien County at a rate not exceeding that given to the most favoured consumer in the City of Dunedin under like condition of supply. In this sub-station, it is well te remember, the connections are so arranged that the transmission lines may be mter-connected in any manner. There will also be a bank of transformers for reducing the pressure to 3300 volts for reticulation in the neighbourhood. About 1J miles from this sub-station is the town of Mosgiel, where there is a large woollen factory, and several mills, which eventually w ill, no doubt, be connected to the system.

When fixing the route for a power transmission line, special consideration mus* be giveu the character oi the country, facilities for patrolling, climatic conditions, and the voltage. The voltage, of couise, depends upon the length of transmission, the price of copper, and the limit of line loss. The question of good regulation practically governs the latter, and after careful consideration a voltage of 35,000 was adopted as being reasonable for insulation and economical as regards weight of copper in the line. The total distance along the transmission route from power station ,to sub-station No. 1 is 27 miles 8 chains, and from the sub-station to the converter station, in the centre of Dunedm, two miles, the total length of transmission, being, therefore, 29 miles 8 chains.

The Council adopted the writer's lecommendation that the transmission line should be in duplicate tin ougho ut, and the lines entirely independent of each other. Ihe site of the power station is 436 feet above sea level, and the hills forming the banks of the nvei have an angular slope ranging fiom 30 degrees to almost vertical. These hills are covered with dense bush to about 1000 feet above sea level, and as it would h?ve been a very expensive matter to construct the transmission line on the slopes of the hills the route chosen was across the top of the divide between the power station and the Taien Plains. On the opposite bank of the river to the power station theie is a small plateau, and then the hill rises with an average angle of about 40 degiees to a height of 1095 feet above the sea level, and thence the country giadually rises to an elevation of 2000 feet above sea level At this altitude there is a fairly level tableland which is about two miles across and then the mountain, which is known as Maungatua, slopes towards the Taien Plains with a series of sharp spurs. The country on the top of the mountain is entirely open, and mostly used for grazing purposes In winter it is exposed to the severe south-westerly winds and covered for da^s with snow. This route was chosen as being the most direct to the Taien Plains, and at the same time because of the ease of construction fcr the line and facility of patrolling.

The transmission lines leave the power station at the top of the lightning arrester annex, the wires passing thiough fibre tubes held in glass shields. From this point the wires are taken to a terminal tower on a spur about 80 feet above and at the back of the power station. From this tower the -wires are taken right across the ravine to a steel tower located on the top of the first bluff on the opposite side. It was decided that the line should be taken across m one span, in preference to erecting poles at short intervals down the rugged face of the mountain side. 'Ihis span is 1700 feet in length, and the horizontal distance between the towers about 1600 feet, the upper tower being 650 feet above the terminal + ower. An experimental .span of steel cable" was strung up m approximately its peimanent position, and

the strain measured by a dynamometer was found to be 960 lbs , when the initial angle of sag was 54 degrees from the vertical at the upper end, and 85 degiees from the vertical at the lower end. It will be seen, therefore, that this span is not quite half of a natural catenary. The steel cables used for this span have a tensile strength of 6000 lbs., and are of sufficient size to carry ten times the line current without heating. The tower at the upper end, which w?.s specially designed, is constructed of angle steel throughout, and with the insulators arranged to take the angular strain of the long-span cable. The tower is a special piece of wcrk calculated to withstand the strain of the seven cables. The strain of each wue is taken up, fully and directly, by four pans of insulators. Around the neck of each insulator is a " U " bolt, the ends of which pass through a wooden cross-bar. The wire passes through a hole ai the centre of the cross-bar, and iron clamps arc clamped rigidly to the wire and rest against the upper side cf the cross-bar. By this means it can be seen that the strain on each pair of insulators can be equalised by means cf the nuts on the " U " bolts. Two pans of insulators are sufficient to take care of the strain on the wire, so that ample maigin of safety is provided. Se\cn wires are suspended r.cioss the span, three for each transmission line and cue spa,ie cable for use should am of those m service carry away. This provision wts necessary, as owing to the nature of the country at this pemt it would be a most difficult matter to

repair a span. JFour of the wires are of steel and three of No. 2 B and S gauge copper, and the latter appear to be as satisfactory as the former, except, of course, that there is not the same factor' of safety. ' ' , f^l'"! The tower is erected on solid rock, and the cables have a minimum clearance of 10 feet from the face of the hillside. The spans are not affected by the wind, which blows with great velocity at times through the gorge. They are spaced 10 feet apart triangularly, and each cable is drawn to the same tension. The lower terminal tower is made entirely of wood, consisting of six hardwood poles, as shown in Fig. 9. This tower is anchored by guys, so that the only work it does is to hold the cables off the ground; the same method of attaching the wires to the insulators was adopted as on the hill-i.op tower. After leaving the hill-top tower, the transmission wires are carried on Australian hardwood poles, those used on the mcuntam-top being 30 feet in length with 6 feet in the ground. The design cf the transmission pole is likewise special. The question of towers versus wood poles was carefully considered, but as the Taieri Council would not agree (and rightly so) to tcwers being erected along their roads, there was no alternative. The cost it. slightly in favour of wooden pole construction. The insulators are spaced 42 inches apart, triangularly, the tcp insulator being attached te the top of the pole. The bottom insulators are carried or irontark cross-arms gamed and bolted to the poles by two lag screws. The gams were cut slightly slanting, so as not to provide a pocket for moisture. The poletop pins, the cross-arms, and insulators were all specially considered and arranged for the work The cross-arms ?.re 4 feet 6 inches long' by 4 inches by 5 inches. The pcles are spaced 150 feet apart, and the two lines of poles' ,are 30 ,feet apart over the mountain top. The transmission wire is of two sizes, No. 2 B. and S. gauge, and No. "3 B. and S. gauge, and is of medium hard drawn copper with a tensile strength of 50,000 lbs. per square inch. The reason that two sizes of transmission wire a^e used is that the Courcil purchased some years previously, 72 miles of No. 2 B. and S. gauge for the Lee Stream scheme. This wire was sent out on reels and was used en that portion of the transmission line on the plains. The remainder of the wire was purchased later, and is No. 3 B. and S- gauge, and was sent out m bundles for ease of transport over the hills. There are 164 miles of copper wire in the transmission lines. After leaving the tableland referred to, the route of the transmission line is along the ndge of the Kowhai Spur or Razorback, and m this case it was also necessary to keep the pole line on the top of the ridge as the sines ore covered with dense bush. In a few places m crossing the tableland small creeks and depressions were crossed with spans ranging up to 300 feet in length. Before reaching the bottom of the Kowhai Spur another long span had to be adopted in order to cross a small valley. This span is 900 feet m length, and the wires are spread out to 6 feet spacing, the two lines bemg supported on long double cross-arms on three poles at the upper end.

The line then continues across private property until it strikes the mam road on the plains, secen miles from the power station. From this point the poles are erected along either side of the rond, being located in the tence line where the roads nrp 40 feet wide and 6 feet from the fence alignments where the reads are one chain wide. The line then continues on poles until it reaches the tounship of Octram HI- miles from the pewer station. At this point towers had to be erected for crossing the railway. These towers were special l y designed to meet the requirements of the Railway Department, who insisted on provision being made to prevent any possibility of a wire falling across the railway line, either due to breakage of msnl 'tor or wire The type of tower was also specially designed — to offer the advantage that the insulators are only sublet to compression strain. Steel wires are used for the crossing with a tensile strength of 6000 lbs., and as the working strain is only 400 lbs. the factor of safety is ample. It is impossible for the cable to fall frona the tower if all the insulators break ; the copper wires which terminate on the tower above the steel cables are connected to the latter by soldered clamps. After leaving the Outram Railway crossing, the lines are taken through private property in order to cut off a long detour and to avoid going through the township of Outram. The line proceeds along the Outram-Mosgiel road and -the, ' |North- west Taieri road until it reaches the site for' pub-station

No. 2, 21 miles from the power station, which has already been described. It then proceeds on steel towers across private property, m order to again avoid a long detour, crossing another line of railway, and proceeding thence along the North-west Taieri road to the Silverstream river, 23 miles from the power station. From this point the route leaves the plains, and is taken four and one-tenth miles through private property, ascending at an average grade of 1 in 8 ever a spur of Flagstaff mountain rising to an altitude of 1125 feet, and then descending until it reaches the sub-statun at Half-wav Bush, 645 feet above sea-level. At the pemt where the route of the transmission line is taken through private property at Outram and again after leaving sub-station No. 2, the lines are carried on steel tcwers because the propertyowners objected te a double line of poles running through their lands, as they held same would obstruct ploughing and farming operations. These towers are spaced £00 to GOO feet apart, and each tower carnes the six transmission wires and telephone line. The towers are rectangular structures, the length of the base parallel to the line is one fifth of the height, and the width is 14 feet. The towers vary from 40 to 50 feet in height, according to the nature of the ground, and the angle steel sections are in 10 feet lengths. The bracing stays consist of two No. 7 S.W.G. steel wires, twisted wi^h Spanish wind lass}, and Jwith eccentric washers in the bolts to j?rovideJfor L adjustment of the strain. Before the design of the tower was decided upon the writer had an experimental tower made, and put a strain of 2400 lbs. on +he extreme end of the tower, this strain being equal to the tortional strain that would be put on the tower in the event of five of the wires carrying away on one side. In the design of the line throughout a factor of safety of six was adhered to in all calculations , this factor was insisted upon by the Board of C ontrol as being sufficient to provide a s.ife margin against all snow and wind stresses. The spins were all strung in accordance with the table of sags specially prepared. The linesmen were provided with adjustable sighting pieces, which were hung at each pole and the cable strained with a sag to correspond with the length cf span and temperature of the atmosphere. The wires were tied to the insulator with No. 8 soft drawn copper, and all joints made with M^lntyre's figure 8 tubes, a specimen of which is exhibited. No ladders were used in the erection of the line, as the men climbed the poles with spurs, two types of which w ere used. These are special! Neither of the H T. lines are transposed throughout their length. One of the Government telephone lines runs parallel to the trinsmission line for a length of two miles, and at a distance of 20 chains from the line, and no trouble was experienced due to induction! only a very slight humming being perceptible. The insulators and pins were delivered along the line of route and deposited at the foot of the poles. (To be continued.)