| 摘要 |
<p>A ring main unit (200) for use in a local ring main electricity supply circuit comprises a T-off switch (213) for serving a T-off circuit and a pair of ring switches (211/231, 212/232) for connecting the ring main to the T-off circuit. The ring switches each comprise a disconnector (211, 212) in series with a fault-make/fault-break vacuum interrupter (231, 232) having closed and open positions. The ring main unit further comprises: (a) a controller (224) which outputs a trigger signal when a current in the T-off circuit exceeds a predetermined magnitude indicative of a fault in the T-off circuit, (b) an actuator (210) responsive to the trigger signal for actuating the interrupter from its closed position to its open position, and (c) further actuator means (e.g. 209) which sequentially (i) actuates the T-off switch (213) from a closed state to an open state after actuation of the interrupters (231, 232) from their closed state to their open state, and (ii) actuates the interrupters from their open state to their closed state upon actuation of the T-off switch device from its closed state to its open state. <??>In this way, the faulty T-off circuit is isolated from the ring main circuit and continuity of the ring main is maintained without appreciable interruption of the supply to other parts of the ring main. <IMAGE></p> |
