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