| 摘要 |
In a circuit embodying delayed excess current trip (7, 8) and instantaneous short circuit current trip (12, 13) the delayed circuit incorporates a Schmitt trigger (6) whose output energises the relay coil (7) and holds the contact (8) closed in the steady state. An increase in signal voltage (3) representing excess current in the current transformer (1) causes the trigger to turn off and the relay drops out. Similary, a loss of auxiliary power supply (14) turns the trigger off and opens the relay contact (8). The instantaneous trip is typically a latched relay. The two relay contacts (8, 13) are typically in series in an interposing relay circuit which controls the main circuit breaker. |
