| 摘要 |
1,149,525. Coupling arrangements for A.C. networks. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 19 Sept., 1966 [29 Sept., 1965], No. 41336/65. Heading H2H. In a coupling arrangement between two A.C. networks of the type in which an L/C combination provides for a low impedance path under normal operating conditions and automatically increases the reactive impedance to prevent excess current flow upon the occurrence of abnormal (fault) conditions, a modifying circuit is provided to ensure that the normal (low) impedance of the coupling is rapidly restored as soon as the fault has been cleared. In Fig. 2 the L/C combination 4, 5 is normally series resonant to present a low impedance, but should a fault occur a switch 7 is closed to connect a damping resistor 14 and a non- saturable reactor 6 which de-tunes the coupling. When the fault has been cleared a signal from a control unit 10, obtained for example by monitoring the coupling current at point 11, closes a fast-action switch 9 to connect a capacitor 8 and damping resistor 15, members 6, 8 forming a high-impedance parallel-resonant circuit which restores the low impedance of the series resonant circuit 4, 5 and facilitates the subsequent opening of the switch 7 and the switch 9 in that order. The switch 7 may be omitted if the reactor 6 is replaced by a saturable reactor (36), Fig. 1 (not shown), which automatically de-tunes the combination 4, 5 when a fault occurs. In another arrangement, Fig. 3 (not shown), of the type in which members 4, 5 are in parallel, with member 4 alone forming the coupling impedance for normal operation and the combination 4, 5 forming a high impedance parallel-resonant circuit under fault conditions, the capacitor 5 is connected in parallel with a non-saturable reactor (16), through the fast-action switch, when the fault has been cleared. Two other arrangements are described one of which, Fig. 4 (not shown), is generally similar to the circuit of Fig. 2, but the combination 4, 5 is in parallel with a resistor (26) which forms the coupling impedance when members 4, 5 are de-tuned by closure of the switch 7. The other arrangement is shown in Fig. 5 and uses parallel-connected seriesresonant circuits 4a, 5a; 4b, 5b which normally by-pass a resistor 26 through a switch 47 to provide a low coupling impedance. Excess current causes closure of a switch 48 to increase the coupling impedance. After fault clearance the switch 47 is opened, followed by opening of the switch 48 and reclosure of switch 47 for normal operation. The switches used in the various embodiments may be of vacuum, sparkgap, valve or semi-conductor type, and their operation may be controlled by current parameters such as actual value, change of value or rate of change, or by the voltage across the capacitor 5. |
