Abstract
The dielectric strength of some oiled paper under the various conditions of the humidity have been investigated and the following facts have been observed: -
(1) Under the relatively low humidity, the variation of the humidity of the air has a remarkable effect on the dielectric strength of the oiled paper in the puncture test with the D.C. source, while it has a feeble effect in the case made with the A.C. source.
Under the high humidity, however, the effect of the humidity becomes the same order independent of the source.
(2) Although the dielectric strength ratio between alternating and direct current voltages is greater than the unity at the relatively low humidity, (this case is more common) it is reversed, the higher the humidity is.
(3) The relation between the A.C. and D.C. dielectric strength of the oiled paper and the humidity is similar with the relation between the A.C. and D.C. dielectric strength of glass and the temperature obtained by L. Inge, N. Semenoff and A. Walther.
Although the dielectric strength ratio of A.C. and D.C. voltage in the case of them is always greater than the unity, the ratio in our case is not always greater than the unity. Such a difference in character of the dielectric strength of the solid insulation seems to depend on the different condition of the contact between the solid insulation and the e:ectrodes.
(4) As the history of the test sample exposed under the various condition of the humidity has a remarkable effect on the dielectric strength of the test sample, the D.C. conductivity measured with the Cathode ray oscillograph instead of the A.C. dielectric loss is utilized to express the effect of the humidity.
From such a Braun tube figure, it is ascertained that the direct current through the test sample is pulsating and the degree of the pulsation is very irregular.
