Electrical porcelain: I. Testing with a high-frequency oscillator. II. The problematical points of manufacture. III. Experiences and experimental investigations

Part I treats of the reasons for using the high frequency oscillator for testing porcelain insulators. The oscillator is a combination of a 60-cycle transformer, a condenser, a spark gap, and an oscillation or coreless transformer. The 60-cycle potential charges the condenser and the condenser discharges through the gap and the coreless transformer. This sets up high frequency wave trains of the same nature as the wave trains that take place on the transmission line. This high frequency potential strain is the only kind that damages the insulators. The 60-cycle potential is always far below the puncture potential and arc-over potential of the insulators. In Part II it is shown that the principal factors in the manufacture of porcelain which affect the final product are: 1. The choice of ingredients, — ball clay, china clay, feldspar, and flint. 2. Is the problem involved in getting a homogeneous mixture of these pulverized materials. 3. Is the problem of drying out the moisture without causing unequal contractions which crack the green porcelain. 4. Is the early dehydration in the furnace in which as much as 14 per cent of moisture is given out. 5. Proper time and temperature for vitrification. The mechanical processes through which porcelain is carried are of the greatest importance in getting good electrical porcelain. It can be stated that defective porcelains are in general due to the accidents of manufacture, the dielectric strength of all the porcelains being passably good except for flaws. Part III includes data on tests carried out mostly with the high-frequency outfit. An electrical method is shown of producing failure along invisible cleavage surfaces in the porcelain body. This examination should be useful to the porcelain manufacturer to indicate how nearly the porcelain is approaching to a weakness which will cause the rejection of the porcelain piece. Another method, using potential gradient to investigate the homogeneity of the porcelain, may- be found of use in determining the efficiency of the pug mill which is used to mix the ingredients when the porcelain is in the early plastic stage.