| 摘要 |
PROBLEM TO BE SOLVED: To prevent the increase in the number of components, assembling process, and assembling work time by using a return spring for standard kinds of devices, and reduce the dispersion of instantaneous tripping current values. SOLUTION: A heater 38 is inserted between both sidewalls 37d of a yoke 37, and connecting parts 44b of a primary conductor 44 are faced in the innermost wall 37c of the yoke 37. In this constitution, a magnetic fieldΦ1 is generated in the surrounding of the heater 38, and a first magnetic circuit A is formed between the yoke 37 and an armature 41. A magnetic fieldΦ2 is generated in the surrounding of the connecting part 44b, and a second magnetic circuit B is formed between the yoke 37 and the armature 41. Since a large attractive force acts from the yoke 37 to the armature 41, even if a return spring 42 for standard kinds of devices is used as is, the armature 41 is attracted to the yoke 37 at a low instant setting current value.
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