| 摘要 |
88/099 Protection method and protection device for detecting asynchronism during the synchronous starting of a synchronous machine. During the run-up of high-power synchronous machines (6), such as those used in pumped storage plants, in gas turbines sets and so forth, unwanted alternating currents with slip frequencies between those of the phase swings and the nominal frequency (50 Hz) of the synchronous machine (6) can also occur in the disturbed condition in addition to low-frequency plant-specific phase swings. These alternating currents are induced in the field windings of the synchronous machine (6) as a consequence of an unwanted asynchronous starting and can lead to inadmissible heating of the synchronous machine and to overvoltages in the field circuit. Alternating voltages (U1) associated with the slip frequencies are detected from use of a sensing resistor (4) in the exciter current (if) of the synchronous machine (6), separated from the high-voltage potential in an isolating converter (10), subsequently filtered in a bandpass filter (11), controlled for constant amplitude in a function generator (12), triggered in a Schmitt trigger (13) and selected by means of two timing sections (15, 16). If a slip frequency is detected uninterrupted for longer than a predeterminable minimum period (T3), field and highvoltage switches (5, 7) in the circuits of the synchronous machine (6) are opened by a RS flip-flop (19). (Fig. 1) |
