| 摘要 |
<p>The earth fault protection circuit uses a transformer core which surrounds the supply cable to the appliance. In the case of an earth fault there is a current imbalance in the cable cores and a signal appears at the output terminals of the transformer (1). This alternating signal has a magnitude which is a function of the current imbalance. The alternating signal is transformed into a continuous signal by a rectifier (2) and is then applied to an OR gate (3). The output of the OR gate being applied to two step relays (4, 5). The signal is applied to one of the relays (4) via an adjustable timer (6). This relay (4) controls an alarm circuit. The operating level of the relay (4) is less than that of the relay (5) which controls interruption of the supply to the appliance. The timer (6) avoids operation of the relay for fleeting faults.</p> |
