| 摘要 |
PURPOSE:To improve the interrupting performance and the possible number of interruption, by making the width of a spiral groove in a part of annular contact portion of a spiral electrode less than that in the other part. CONSTITUTION:In an annular contact portion 14 at the central region of a spiral electrode 11, and in a portion near the inner end of a groove 12a formed in an arcing part 3 in the peripheral region of the contact portion 14, there is formed a groove 12b having a width smaller than that in the other portion. Accordingly, the groove width at the contact portion 14 is small, but the arc energy at the contact portion 14 is small too, so that the inner end of the groove can be made to be the electrode center side with almost no lowering of the intensity. Thus, the interrupting performance and the possible number of interruption can be improved simultaneously. |
