Publication: The Telegraphic Journal and Electrical Review
ALTHOUGH but little has been done within the last few years in the direction of improving the insulation of aerial wires, it can hardly be admitted that there is no room for improvement. In this country, especially, where moisture is so prevalent, the loss which occurs on the best insulated lines is very considerable, and any decided departure for the better from the existing patterns of insulators would prove a source of considerable profit to the inventor. Whatever the improvement may be, however, it must not be one which would add materially to the cost of the present forms, or the chance of its use would be small.
Insulator manufacturers, we are inclined to think, pay too much attention to the quality of the body of the ware of which the insulator is formed. If great mechanical strength, with a highly glazed and uniform surface can be obtained with a comparatively low class body, there is no reason why the latter should not be used. The insulating value of an insulator is practically entirely dependent upon the excellence of the surface and not upon the mass, as the normal leakage which takes place is superficial entirely. Owing to the fact that the ware must have a resting place in the baking kiln, it is usually the case that that portion which touches the rest does not become coated with glaze. We frequently find that the position of rest is such that the most important part of the insulator, namely, the "lip," is left bare, whilst the "crown," where a glazed surface is totally unnecessary, presents a highly finished surface. Length compared with small diameter would seem to be the correct form for an insulator, but practice does not confirm this ; not, however, because the normal leakage is great, but because of the great difficulty of keeping the insulators internally clean and free from the webs which spiders can spin so freely in a confined space. Many attempts have been made to increase the length of the external surface over which leakage can take place, by a system of corrugating; such an arrangement, although no doubt efficient in the case of new insulators, is liable to harbour dirt, and thus to eventually reduce the efficiency below that of the plainer patterns.
A great deal has been said with reference to the method of securing the line wire to the insulators as regards its effect upon the insulating capacity of the same ; experience has, however, amply proved that, whether the line wire touches at a mere point, or is secured to the insulator by folds of binding wire, yet the difference in the two cases is very slight.