[Trade Journal]
Publication: Ceramic Industry
Chicago, IL, United States
vol. 4, no. 6, p. 460-461, col. 1-3
Latest German Insulator Designs
This Article Tells in a Very Practical and Well Described
Manner What the Germans are Doing in the High Tension Field
Translated by DR. WALTER SCHULZ
National Enameling & Stamping Co. , Inc.
WHILE the development of the low voltage insulators has been considered as near completion, the work of developing insulators in the field of high voltage is steadily going forward. Included in the latter are most of the high tension lines conveying electricity great distances and those used in most transformer installations either outside or inside. These types of insulators are being continuously improved, due to the fact that defects frequently bob up.
The high voltage insulator for indoor use, however, is in general improved to such an extent that few defects will occur if the right design is used. Therefore the indoor assembly is being made without the use of cement. Nearly every firm has its own design. Formerly in the high voltage industry insulators for use indoors on high voltage lines were furnished with ribs to lengthen the creepway, but of recent years the plain design has been used more and more. Lately, due to the formation of flashovers in the case of over-voltage, the value of the ribs, which lengthen the creepway and limit the effect of condensed water on the right side of the design, is again being recognized. While the standards of the German Electrotechnical Society still show plain walls for this type of insulator, it Is probable that these standards will soon be changed to admit the ribs.
Need Not Avoid Tension in Insulators In outdoor suspension insulators, the development is heading in two directions, one of which is concerned with the compression of the porcelain and the other one to side pull. The two so-called cap insulators, are those of the first type shown in Fig. 1, while specimens of the second type, double cap insulators, are shown in Fig. 2. Formerly the strain from the side pull in porcelain was avoided, but due to the development of porcelain bodies many types now show good tensile strength under side pull. One must bear in mind, however, that today the compression strength of porcelain is higher than the tensile strength and according to those who are intimately acquainted with the problems of this field, it is not believed feasible to place the most unfavorable stress upon the porcelain. Several new designs of suspension insulators which are the result of much research are described below.
Fig. 1 shows the Goliath insulator of the firm of Hentschel & Muller in which the small blocks which carry the clapper are introduced thru a vertical split. In the manufacture of this vertical split a great deal of difficulty was met with. A disadvantage of this type of construction is the apparent weakening of the cross section by the split.
Fig 2 shows the conical insulator in which the clapper is split at its upper end so as to form six prongs. These prongs open up when a small cone is introduced in the hole of the clapper, causing the clapper to press against it. The introduction of the clapper should be given special attention as it is hard to make contact of the prongs uniform. A similar insulator is built by another porcelain firm, but in the latter case a special metal
ring is split like a ball. Fig. 3 shows the V type insulator of the Siemens Schuckert Co., where metal blocks are introduced thru the collar.
A Safe and Simple Insulator Those insulators manufactured by the Porcelain Union, Inc., are said to be simplest and also the safest. The different segments of the upper metal ring are introduced thru the collar and fall into the right position by means of. the correct selection of the point of equilibrium. Then the hole in the clapper is filled with lead alloy and heated porcelain powder. The porcelain powder retains the heat a considerable length of time so that the lead does not at once solidify along the cold walls when it is poured in but flows all the way thru.
Insulators subject only to side pulls were at first put into practical use in the wireless telegraphy. This was because the cap insulators have a considerable capacity for a current of high frequency.
There are cases in which the strain on the insulator is not borne by the porcelain itself, but by an insulated rod, which is Surrounded by a porcelain tube. This type is made by a special process of which very little is known. The space between the rod and the porcelain is filled with an insulating material of high quality.
Suspension Insulators Popular In Germany the suspension insulators are replacing more and more the outdoor pin type insulator. Recently small suspension insulators were constructed which may be considered economical even at average tensions of from 10 to 30 k.v. Their general design is exactly the same as those of the normal suspension insulators, with smaller dimensions. For instance, the diameter of the shade is 200 millimeters, while the tensile strength is about 3,000 to 4,000 kilograms.
It is interesting, from a ceramic point of view, to note the processes used to assemble the different parts of the insulators by the use of glazes. However, as the difficulties of manufacturing large insulators in one piece are overcome, the glaze bond will lose more and more of its value.
Translated from Keramisehe Rundschau.
