石油学会誌

The relation between breakdown voltage of silicone liquids and some factors, such as frequency, pulse duration, temperature and hydrostatic pressure were studied under pulsed high frequency field. The results can be successfully explained from the viewpoint of thermal breakdown mechanism.
It was found that the relation between breakdown voltage and pulse duration in significantly varied by electrode arrangement. For example, in uniform field the breakdown voltage varies greatly with pulse duration. On the contrary, in non-uniform field the breakdown voltage is little influenced by pulse duration. From these results, it was concluded that, in needle-plane electrode arrangement, the area of the local heat generation required for the breakdown to occur is as small as several microns, but, on the other hand, in uniform field that area covers almost between electrodes.

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Copper corrosion by sulfur compounds in transformer insulating oil is a very important problem in view of the interruption of electric power supply.
The factors considered to affect this phenomenon are oil temperature, surrounding gas, water content of oil, surface condition of copper, voltage stress imposed on copper surface and oil additive which will suppress copper corrosion.
To acquire some knowledge on the effect of these factors, the authors carried out many short time tests with the test conditions similar to ASTM corrosive sulfur test.
The results are as follows: 1. Corrosivity at low temperatures remains at a lower level in the air atmosphere than in the nitrogen atmosphere. 2. Water in oil promotes corrosion. 3. Oxide film on copper surface suppresses corrosion. 4. Voltage stress on copper surface heavily accelerates corrosion. 5. The addition of benzotriazole or 2-mercaptobenzothiazole suppresses corrosion over the temperature and voltage stress ranges which are ordinarily encountered in transformers.

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