GB1153999A - Improvements in and relating to Alternating Current Network Couplings - Google Patents

Abstract

1,153,999. Coupling arrangements for A.C. networks. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 28 Oct., 1966 [3 Nov., 1965], No. 46556/65. Heading H2H. In a coupling arrangement for two A.C. networks of the type in which a series inductance/capacitance combination is tuned to resonance during normal operation and detuned upon abnormal (fault) conditions to limit the current flow, part or all of the combination is shunted by an auxiliary impedance which carries little or no current during normal operation and substantial current during abnormal conditions. The nature of the impedance can be resistive, inductive or capacitive or various combinations of these, and is determined by the characteristics of the networks and by the fault conditions likely to be experienced. For example, a resistive impedance will damp oscillations consequent upon a fault; a reactive impedance will influence the power factor during "settled" fault conditions and immediately following fault clearance, and can be made inductive or capacitive as required. In Fig. 2, the auxiliary impedance 7 is connected to tappings A, B on the inductance and capacitance portions 3, 4 of the resonant combination, these tappings being chosen so that the series L/C circuit so formed is resonant like the overall L/C combination of which it is a part. The detuning circuit comprises a saturable reactor 5 and resistor 6, but may be a switch by-passing the capacitor 4 or a portion thereof and comprising a spark gap, a vacuum switch or controlled semiconductor elements. Another saturable reactor may be connected in series with the auxiliary impedance 7 to keep its current negligible when voltage oscillations occur between points A, B during normal network operation. In other embodiments the impedance 7 is connected across the whole L/C combination 3, 4, Fig. 1 (not shown) or between a tapping on the inductance 3 and the reactor 5, Fig. 3 (not shown). The impedance 7 or parts thereof may be transformer-coupled instead of directly connected.