High Tension Insulators

Progress, Volume XIII, Issue 10, 1 June 1918, Page 233

High Tension Insulators

Mr. L. Birks, Electrical Engineer to the Public Works Department, gave some interesting information to a meeting of the Philosophical Societv in Christchurch early this month on the testing of high tension insulators. The lecturer stated that the importance of the Lake Coleridge hydro-electric system to Christchurch now could be gauged by the fact that the trams were run by it, the water and sewage pumping, three-fourths of the freezing works, the flour mills, the butter factories, and hundreds of industrial plants. If the Lake supply failed for long the city would have to be abandoned. The chief difficulty in maintaining continuity of service was the distance transmission line, and a breakdown in the line was distinctly serious if of long duration. Tne weakest links on this line were the insulators, and a good many breakdowns had occurred since the inauguration of the line, though the public only knew of a percentage of them. Tn 1915 there were 15; in 1916, 1.9; in 1917, 27 ; and during the current year, 7. These were the total interruptions, some of which, however, were not due to the insulators. The main trouble in dealing with an insulator in which the insulation had broken down AA r as in locating the faulty insulator, not in replacing it when

found, which was a comparatively simple job. Insulators behaved in an irritating and tricky fashion, often working well enough when the weather was dry and failing when there was rain or moisture about. A fruitful cause of the breakdown of insulators was. tree bark, especially the bark of bluegums. In the autumn this blew about in long strips, which hung on the line and caused “shorts,” and. often serious breaks in the insulators. Lightning was also troublesome sometimes, and one severe discharge caused four or five breaks on one occasion; one at the time of the flash and the rest later as,the weakened insulators gave way. The problem of insulation was rather an obscure one, and from investigations that had been carried out here and in other countries it seemed that the degree of excellence of the vitrification of the porcelain of the insulators was directly responsible for the degree of their excellence as insulators. Porosity in the porcelain was a bad fault, and usually porous insulators broke down in service, though this could not yet be stated as a rule. Very slight porosity seemed sufficient to weaken the effectiveness of an insulator, and for this reason it was difficult to detect porosity accurately. The speaker then described the mechanical and electrical tests to which insulators were subjected, and a very interesting demonstration of the tests was given by Messrs. Ferguson and Philpot, Mr. Birks’s assistants.