| 摘要 |
1280704 Protective arrangements BROWN BOVERI & CO Ltd 2 Sept 1969 [3 Sept 1968] 43387/69 Heading H2K An earth fault protection circuit for a threephase star-connected alternator 1, comprises a three-phase transformer 8 having a starconnected primary 81 and an open-delta secondary winding 83 connected to supply through a filter circuit 10, 12, 17 and a rectifier 14 a first signal dependent on the third harmonic of the alternator output voltage, a single phase transformer 7 having its primary winding connected between the alternator star point and earth and its secondary winding connected to supply through a filter circuit 11, 13, 18 and a rectifier 15 a second signal dependent on the third harmonic voltage at the star point, and a relay 16 responsive to the relative magnitudes of the first and second signals. Normally these signals balance and the relay 16 is not energized, but when an earth fault occurs on a winding of the alternator adjacent the star point the signals are unbalanced and relay 16 is energized and closes its contacts to energize a relay 23, which after a delay causes the opening of a main switch 3 and the closing of a field short-circuiting switch 5. Protection against other earth faults may be effected by a further relay 9 responsive to signals of the fundamental frequency derived from the transformer 7 and a star-connected secondary winding 82 of the transformer 8. |
