@article{oai:soar-ir.repo.nii.ac.jp:00012987,
 author = {永野,  泰男 and 田原,  徳夫 and 加藤,  之敏},
 journal = {信州大学工学部紀要},
 month = {Jul},
 note = {When the contact in the insulating oil carries the high current for many hours, there is a case where the contact resistance increases considerably. In this case, sludge occurs at the contact surface. The origin of occurrence of the sludge has not been determined yet. In this study, this phenomenon is made to appear again with model contacts, and the mechanism of occurrence of the sludge, which is the first cause to worsen the electrical characteristic of the contact, is analyzed with measurments of electrical and microscopical techniques. The model contact which has the following constructions was employed in the experiment. Model Contact No. 1 : In order to obtain the high current density and the pressure at the area of real contact, the conducting area is made a point contact by putting a grain of copper between both electrodes. And to stabilize the static load, one of the electrodes is vibrated slightly by the constant frequency (60Hz). Model Contact No. 2 : The construction is the same as the No. 1 contact but one elctrode is transparent, so that it is possible to observe the phenomenon at the contacting surface directly while the current passes through there. The following became clear from these experimental results. Generally, in electrical contact, the area of real contact must be much less than the apparent area, and it can be considered that the conducting area consists of several circular contacts the radius of which is very small. (Usually, that contacting spot is called a-spot.) Therefore, the contact resistance appears owing to the constriction of the current at the microscopic area of the contact. It the high current passes through the contact, the temperature at the point of the constriction, where the current density is extremely high, can be raised sufficiently not only to soften but to melt the metal. On the other hand, in the case of the contact in the insulating oil, the magnitude of the conducting area and the number of the spots decrease owing to the oil wedge between the surfaces of both electrodes. So the contact resistance becomes high as compared with the contact exposed to air. Consequently, there are many possibilities that an a-spot is overheated by the joule heat. So that, the oil around the a-spots is decomposed by heating and carbides grow on the contact surface. From above results, the following conclusion is reached. The electrical characteristic of the contact in the insulating oil becomes worse owing to the accumulation of the carbides on the contact surfaces., Article, 信州大学工学部紀要 32: 183-198 (1972)},
 pages = {183--198},
 title = {油中接触子の通電特性劣化について},
 volume = {32},
 year = {1972}
}