[Trade Journal]
Publication: Ceramic Industry
Chicago, IL, United States
vol. 5, no. 3, p. 219, col. 1-3
Late German Electric Porcelain Development
LOUIS E. THIESS
IN SPITE of the herculean efforts made by the German high tension porcelain manufacturers to standardize manufacture which was supposed to have been formed by a commission of The Institute of German Electrical Engineers there is a wide variance among the factories.
These differences are not to be found in prices (as these are strictly laid down by the Vereinigte Hochspannungs-Isolatoren) or on the shapes, quality of the porcelain bodies, glazes or colors. The main variance lies in the construction of the inner part and methods of assembly, while the forms, dimensions and so forth are practically the same in all factories.
A word or two will be said in comparing the different types in regard to their advantages and disadvantages. The insulator in Fig. 1 is made in one piece. As a matter of fact tests have proven that such pieces are difficult to make, as the body cannot be sufficiently worked thru by the turner. High tension insulators must be thoroly [sic] thoroughly vitrified, but the thickness of the shells on this type prevent the degree of vitrification desired. If this type of insulator fails it must be changed at once, even tho the inconvenience be great. Multiple type insulators maintain reliable working, even tho the head or other parts of the insulator be destroyed.
The Cemented Insulator A cemented insulator is shown in Fig. 2. This type is a source of worry because of the fact that it is cemented with a material that is not absolutely constant. Very often the expansion of the cement causes the head of the insulator to break off and a failure results. This failure is more abrupt due to the intermediate surfaces not being glazed. Owing to the frequent failure of this type another method of fabrication was attempted.
Glaze Used as Bond The insulator shown in Fig. 3 consists of two parts, but the advantage of this construction lies in the fact that all cementing material has been dispensed with. The two parts are glazed and fused together, forming a single piece. The union of these two parts is so complete that when the wires and pins are applied there is practically no danger of the head tearing loose. Many prominent German insulator concerns agree that this type of construction is one of the best.
A number of factories in Norway and Germany are now making this type of insulator.
Insulators Screwed Together Insulators are also made where the parts are screwed together, as in Fig. 4. No cement or glaze is used in this type. The parts of this type can be screwed together or they can be fastened with hemp. By winding the upper unglazed or roughened parts with long fiber hemp, dipped in a mix¬ture of oil and graphite a good union can be made.
This type may have the advantage that the single parts, for instance, the head after it has been destroyed by puncture, gunshot or other cause, may be screwed off and exchanged. But these insulators have the disadvantage that they are difficult to manufacture because of the threads and the hemp is an unhomogeneous material at best, and can be burned by a glimmer discharge or any puncture.
The insulators described in Figs. 3 and 4 seem to be the best and are said to meet the requirements, which are:
1. Absolute sufficient surface insulation.
2. Greatest dielectric strength against puncture.
3. Sufficient mechanical strength.
4. Unaffected by climatic conditions.
