[Trade Journal]
Publication: Electrical Review and Western Electrician
Chicago, IL, United States
vol. 56, no. 14, p. 691-692, col. 3, 1
Care of High Voltage Insulators.
Some instructions on the care of high voltage insulators are given in a recent issue of the Journal of Electricity, Power and Gas, by J. O. Hansen, superintendent of the Pacific Gas and Electric Company’s San Jose Power Division.
On the system of the Pacific Gas and Electric Company, says Mr. Hansen, there are more than 100,000 high-voltage insulators. Their efficiency must be great to avoid an average of one breakdown a week, and even that is too frequent. But at this rate the average life of an insulator would be nearly 1,000 years. This, of course, is not reckoning on breaks due to mechanical causes. The small boy with a stone is often the most frequent cause for a mechanic on the job, and the small boy is closely seconded by the unsuccessful hunter who must use his ammunition on something.
A few hundred insulators put under test will undoubtedly make a satisfactory showing. But there must be very general great reliability for all climatic conditions. In the intensely foggy and windy climate about San Francisco bay insulators are things that require careful watching and attention. Insulators made to stand a rain or wet test will render good service in fog and wind when they are clean, but, when dirty, their insulating quality becomes much impaired.
The heavy winter rains keep the insulators clean a part of the year. During a dry spell of from one to two months so much dirt will have collected on the insulators that when they become wet there will be enough current leak over to fire the pole. The soft redwood or cedar pole itself catches fire much more easily than the pine cross-arms. When iron pins are used, and are shorted by wire, the leakage current may be entirely between the wires over the insulators or the leak may be between a wire and the ground, and then fire the pole. But by running the shorting wire to the ground, the pole is thoroughly protected from such burning. Still the current is present, and, if allowed to become large enough, through the wetting of the accumulated dirt by fogs or light rains, an arc forms which either shatters the insulator or burns the transmission wire in two. In the majority of cases either of these accidents is easier to repair than a burned pole. With the iron insulator pins shorted and grounded, more current and consequently a greater accumulation of dirt and dampness are required more to start trouble, so that more time can be allowed between cleanings of the insulators. The dirt accumulates over all parts of insulator in an even layer. But an insulator that has been on the line through the winter has more dirt left on the protected parts than on the exposed parts where the rain has washed some of it off.
For this reason the suspension type of insulator is better than the pin insulators, because in the suspension type a larger-percentage of the entire surface may be washed off by the rains. The method of supporting by a large clamp is also probably better than by a small tie wire on the pin insulators, because of the difference in corona discharges from small and large diameter surfaces.
First dry cloths were used in cleaning the insulators. Later it was found more effective to apply gasoline on the cloths to cut the dirt and grease. But because gasoline evaporates so quickly kerosene is now being used with good results. The best cleaning is with clear water applied with a hose. All parts are then washed off without any residue being left on the surface.
An insulator made to hold up under all of the dirt that will accumulate on it during a season and have its surface so exposed that the winter rains will thoroughly clean it, should give satisfactory results.
