POWER LINE LEAKS

Radio Record, Volume I, Issue 11, 30 September 1927, Page 5

POWER LINE LEAKS

CAUGHT AND CURED GOOD WORK IN LAUNCESTON, for a considerable time radio listeners m and around Launceston, ‘Tasmania, have had to contend with electrical interference from high-tension supply | lines. ‘This interference took un the character of the noise of a waterfall, and it very soon became known fat and wide as the "Iaunceston Roar." One peculiarity about this electrical roar was that’ a few minutes’ rain would absolutely silence it for a bricf period. Actually the only time one could rely on getting good reception was while it was raining. Mr. George J. Mclélwee, assistantelectrical engineer, Launceston, writes to Sydtiey "Radio" of the cause of the roar and the successful means taken to cure it. He explains: High-tension Cables. "When the overhead high-tension cables were first erected in the city of Launceston in the early ‘nineties, they were put up to comply with the British. Board of Trade Regulations at that time; those regulations provided that the cables should have a rubber and braid insulation, atrd should be suspended from. a steel bearer cable by iron of steel elips at six foot intervals. ‘To prevent the clips from chafing the itsulation, a strip of tarred felt was wrapped round the cable, which, of course, added to the insulation between the copper and steel cables. Both cables were supported on porcelain insulators, the steel cable terminating at the shackle or anchor insulators, whicli were about every half-mile on a straight run, and the copper cable, of course, running right through to the point of utilisation. Insulation. Too Good. "With this arrangement of the two cables, it was thought that the steel cable would have a current induced in it which would be a good deal out of phase with the current in the copper cable; in other words, would be reaching its maximum potential when that in the copper cable was approaching its zero at every alternation ‘This, it was thought, would probably set up an ins visible discharge between the two cables in dry weather, when the insulation was good, and thus cause the interference, and when there was sufficient rain to reduce the insulation resistance, the discharge would cease and a much-appreci-ated silence be obtained on all receiving sets. "The obvious thing to do was to adopt some means of preventing a difference of potential building-up between the two cables. ‘To achieve this, the insulation on the copper cable was stripped for a few inthes about every quarter of a mile and the bare copper bound up fight to the steel cable with a copper binding wire. Supply Cut Off. "This, of ‘course, could not be accom plished withont causing some incon. venience to electricity users, and after one of the high-tension distribution cit« cuits was completely bonded in this way, the citizens were further inconvenienced by having the whole electricity supply cut off to put the theory into practical operation. ’ "Tt was on a Saturday afternoon when the ‘Roar’? was particularly bad, and it was found that the bonded circuit mtroduced no noise whatever into the | receiving sets, but immediately any of the other circuits were switched on the trouble started again, and when the whole supply was resumed, reception was impossible. "All of the circuits were similarly bonded as soon as the work could pose sibly be undertaken, with the result that vendors of wireless apparatus were otce more able to do business." *