| 摘要 |
<p>PURPOSE:To detect a flashover generated not only at the time of power running but also at the time of dynamic braking operation, and prevent its damage from being increased, by breaking a power circuit when the change rate of armature current exceeds a specified limit value. CONSTITUTION:When a flashover accident is generated under dynamic braking operation, then as shown by a broken line in figure,flashover current IF flows, and current to flow to a braking resistor 5 is short-circuited. Accordingly, the absolute value of accident current IT to flow to an armature current change rate detector 10 is reduced, and a current change rate dI/dt is a positive value and exceeds the limit value of 25,000A/sec, and 10msec or more is continuously kept,and so the change rate detector 10 is worked, and contactors 8 and 7 are interrupted. Then, a power circuit is interrupted, and field current If is set to be zero, and the induced voltage of an armature 3 is turned into nothing, and the flashover is canceled, and the accident is prevented from being increased.</p> |
