| 摘要 |
PURPOSE:To assure the transfer of arc to the main electrode by designating the difference in height between the coil of the main electrode and an auxiliary coil for start-up and the distance in radial direction between them in specific ranges. CONSTITUTION:The main elecrode 4a is made up by winding the electrode coil 21 around the electrode shaft 20, and the tip of the electrode 20 is projected toward the discharge space side, extending the tip of the electrode coil 21 of a coil diameter (d) and a coil length (L). The tip facing the discharge space side in the auxiliary coil 7a for start-up is formed so as to back it from the discharge space side for a distance as much as the dimension l from the tip of the coil 21 of the main electrode 4a, in which the dimension l is in the relationship L>=l>=0.3mm.. Also, the tip of the auxiliary coil 7a for start-up is separated from the main electrode 4a to the radial direction of a valve for a distance as much as the dimension S, in the relatioship S<=3d (d is the coil diameter of the main electrode 4a). |
