Influence of construction and finishing on the electrical properties of tubular ceramic capacitors

The paper deals with a description of a field-distribution measurement technique using a conduction analogue of an enlarged capacitor cross-section. The results obtained in this way are used to draw some conclusions concerning the breakdown voltage and the variations in capacitance, temperature coefficient of the capacitance and dielectric losses caused by the construction and covering of tubular ceramic capacitors. A conducting medium was needed with two or three different resistances per square. For this purpose glass plates were used which we graphitized ourselves and to which electrodes were applied with conducting silver paint. By means of a simple electric device the equipotential lines could be measured and plotted rapidly. The above method directly showed the points of greatest field strength and their reaction to variation in capacitor construction, permittivity and resistivity of the encapsulating as well as the ceramic material. The capacitance increase due to lacquering is determined not only by the thickness and permittivity of the coating but also by the permittivity and wall thickness of the ceramic body. With this increment there is a change in the dielectric losses and in the temperature coefficient of capacitance. Formulae for tan ¿ and temperature coefficient were checked for correctness.