Wellington, New Zealand
Harnessing the Waipori
BY W. G. T. GOODMAN, M.INST, C.E., M.I.E.E.
At first the pins were fixed in with litharge arid glycerine cement, as this is quick setting, but as the men complained it made their fingers very sore and it was found the public rod not damage the insulators, the litharge and glycerine cement were substituted by Portland cement, mixed one part to one part sand. arid the pins were allowed to stand four clays to set. The pins are of ordinary 2-inch galvanised iron pipe swagged in the usual way. Iron pins were adopted because the writer thought if wooden pins were used there would probably be trouble with digestion, owing to the very moist climatic conditions which prevail during a great portion of the year. The pins were made by the Johns Manville Co., and the insulators by R. W. Thomas and Sons, New York. The insulators were made of brown porcelain throughout so as not to provide a good mark for boys with pea-rifles.
The specification for the insulators was very lrastic. The porcelain ad to be thoroughly vitrified and be absolutely non-absorbent of moisture, and stand the voltage test without the surface glazing. Half of one per cent. of the insulators was subject to the following tests. The porcelain was broken into small pieces and kept in a dry place at a temperature of 212 degrees F for twelve hours, and then accurately weighed. The pieces were then soaked in water for twenty-four hours, and carefully wiped, after which they were again weighed and the porcelain rejected if the weight was different to that before soaking. No insulators Here accepted that showed any mechanical weakness before or after glazing. As a mechanical test the insulator was mounted on an iron pin, and a pull of 2500 lbs. exerted on the tie wire groove and parallel to same.
For the wet arcing test the insulator was mounted on an iron pin set in a metal cross-arm 4 in. wide and projecting 12 in. beyond the pin on either side. At right angles to the cross-arm a No. 3 B. and S. wire, 3 feet long, was tied to the insulator, and the voltage applied between the copper wire and the cress-arm. A spray of water sufficient to cover the insulator was then allowed to play on same from a sprinkler, under pressure of 50 lbs. per square inch at the nozzle placed at an angle of 30 degrees from the horizontal, and not over four feet from the insulator. Under these conditions the insulator must not arc from the wire to either pin or cross-arm at a less potential than 40,000 volts effective E,M.F., the tests lasting for one minute after reaching that voltage.
For break-down test, the insulators were placed inverted in a brine solution in a metal tank for a depth of 1 inch below the head. The pin hole was filled with brine and a metal rod placed therein. After the insulator had stood in the brine for one hour it had to stand an effective F.M.F. of 70,000 volts, applied between the metal rod and the metal tank, without either arcing across or puncturing or showing any sign of electrical weakness.
The inspection and testing of the insulators was carried out by Dr. F. A. C. Perrine.
In the line there are 1802 poles and 15 steel towers. All poles and towers are numbered with enamelled iron plates, and on every alternate pole there is a notice on enamelled iron offering £5 reward for information leading to the conviction of any person found damaging the lines or insulators.
At all road crossings there are 45-feet poles with double cross-arms and insulators, which are also used at all angles. The poles are mostly 35 feet in length, and rough dressed the wood being either blue gum, flooded gum, tallow wood, black butt or turpentine, and cost on an average £2 5s each, erected. All poles are ringed at the top.
There are two linesmen whose duty it is to patrol the line daily. They both reside at Outran and are provided with horses, one man proceeding over the 17 1/2 miles of line to the power station one day, staying there for the night, and returning to Outran the next day. The other linesman patrols the 9.6 miles of line from Outran to Half-way Bush, returning to Outran every night. The linesman on this section hands in both linesmen's daily reports on every alternate day to the sub-station attendant, who forwards them to the head office.
Each linesman has to call up and report to the power station and sub-station No 1 at each telephone box along the line, stating the direction m which he is going. These calls arc entered up in the log hooks. The linesman on the power station section has a very rough time during the winter months, as heavy snowstorms prevail, and the ascent and descent is very steep on both slopes of the mountain so much so, that many people prefer to walk instead of ruling. The writer on several occasions has ridden through two feet of snow when visiting the power station. During the month of June last there were several heavy falls of snow, but none adhered to the line wires and no line troubles arose from same.
The whole of the insulators were erected at the end of February, and up till the time that the writer relinquished control (May 18th) of the undertaking no insulators had been reported broken; in fact, there had been no line troubles of any description. Since that date three insulators have been broken, but it is not necessary to renew them immediately. In the author's opinion, so few breakages is extremely satisfactory, especially when it is borne in mind that 19 miles of the line is along public roads. It was found necessary to cut down no less than 1400 trees along the line of route, which endangered the safety of the line. These trees were mostly blue gums, ranging from 80 to 120 feet in height. With respect to the ten miles of transmission line through private property, the writer was able to secure the sole right of ingress, egress, and regress at all times for the moderate figure of £600.
The efficiency test of the line confirmed the calculated loss. As previously mentioned, each line consists of 12 miles No. 2 B. and S. gauge, and 15.1 miles No. 3 B. and S. gauge. The calculated resistance is 26.23 ohms. and the measured resistance is 27.11 ohms. Taking 1000 K. W. at 30,000 volts with 90 per cent. P. F. at the receiving station, the line current is 21.1 amp. the calculated voltage drop, allowing for inductance and impedance is 2192 volts, and in the test made by the writer the measured voltage drop was 2200. Each line is designed to carry 2000 K. W., with a loss of 8.75 per cent. at full load with 85 per cent. P.F.
On one occasion the writer made an interesting experiment by connecting the transmission lines at sub-station No. 1 and transmitting the power from Weapon by one line to Half-way Bush and back by the other, and driving the second generator as a motor, the total length of transmission being 54.2 miles.
A telephone line connects the power station to sub-station No. 1, and is carried on one line of poles on bracket insulators. It is a metallic circuit throughout, and the telephone wires are alternately 7 feet 3 inches and 7 feet 9 inches from the line wires. The wires are transposed vertically and across the pole every three pole lengths, so that a complete helix is obtained in every 12 pole lengths. On the towers as the spacing of the line wires is different to that on the poles and the interval between the towers is irregular, in order to keep the inductive effect on the telephone hue to a minimum, instead of the bare copper, as used on the poles, two ordinary insulated telephone service wires were twisted together and strung from tower to tower. The twisted insulated wire was supported on steel suspension wire, carried on the insulators on the towers. The result of the transposition is that with the full voltage and current on the main transmission line the telephone circuit is almost quiescent.
The telephone wire is 12 B. and S gauge, hard-drawn copper, tied to the insulators by No. 12 B. and S. soft drawn copper. The insulators were submitted to a wet arcing test with an E.M.E. of 4500 volts and a puncture test with an E.M.F. of 8000 volts the tests made in a similar manner to those specified for the main line insulators.
There are nine telephone stations along the line; these are arranged so that the linesmen stand on a platform supported on four main line insulators. The connections in the telephone boxes are made so that the linesmen can talk to either end or both ends simultaneously. The telephone instruments are protected with long fuses and grounding device, so that should the main line wire fall on the telephone, at the time the linesman is using the instrument it would be earthed and blow the fuse. This system was adopted by the writer as he did not deem it advisable for the linesman to carry portable telephones to connect the wires at any point, as it would be dangerous in the event of the line wire coming into contact with the telephone either accidentally or intentionally. At the power station and sub-station the telephone instruments are protected in a similar manner. The power-station telephone box consists of two independent cabinets, one inside the other, and each one lined with felt. This cabinet effectually insulates sound, and the noise of the pelton wheels cannot be heard from inside.
The telephone line is only used for service purposes and the operators have strict instructions that no conversation must be held over this line except in connection with the operation.
The sub-station at Half-way Bush is connected to the converter station by telephone wires running on the Government poles as the Board of Control would not allow the main line telephone to be taken right into town.
In order to provide a duplicate means of connecting with the power station, the writer installed another telephone line connecting the power station to the Government telephone bureau at Berwick. This line consists of two wires erected on an independent line of poles running parallel to the transmission line and the minimum distance of three chains from same over the Maungatua mountain to the bottom of the Razorback Spur. From this point it is taken along the main roads to Berwick; connection is then made with Dunedin by connecting on to the Government lines, the ordinary bureau charge of 3d being made for each conversation. The operatives can, therefore, use this line for private purposes.
[missing text with details of the power house and sub-station]