| 摘要 |
PURPOSE:To prevent the overheat of an overvoltage limiting element by connecting in parallel a series circuit in which an overvoltage limiting element and isolating means are connected in series, and a thyristor, and breaking a load current by the isolating means at the improper conduction time of the thyristor element. CONSTITUTION:When a thyristor element is interrupted and a load current flows to a series circuit of an overvoltage limiting element 24 connected in parallel with the thyristor element and a fuse 28, the fuse 28 is immediately molten and broken, thereby interrupting the load current. When the element 24 which is connected in parallel with the thyristor element is isolated in this manner, the sharing voltage of the all thyristor elements are applied to the both ends of the thyristor elements. Accordingly, it exceeds the withstand voltage of the thyristor element, and the element is broken in insulation, with the result that the thyristor elements becomes conducted state. Since the thyristor elements can have the capacity of flowing the load current even in this state, the operation can be continued. |
