GB262842A - Improvements in or relating to electric protective systems - Google Patents

Abstract

262,842. Electrical Improvements, Ltd., and Grant, L. C. Aug. 19, 1925. Addition to 216,924. Cut-out arrangements.-Relates to a balanced protective system employing wireless or wiredwireless methods (instead of the usual field wires) and oscillating circuits one at each end of the section to be protected to supply high-frequency oscillations to the other, such frequencies being modulated, detuned, or controlled in respect of output by variations in the conditions of the protected circuit at the respective ends as described in the parent Specification. According to the invention, the control circuits F associated with the end of the section to be protected are connected up to the grid circuit of the transmitting valve B so as to vary the potential of the grid in accordance with variations in the conditions of the protected circuit. In the arrangement shown, current transformers F<1> in the ends of the section supply the primary 1 of an ironcore transformer F<2> the secondary of which is connected across the condenser E<5> in the grid circuit of the transmitting valve. The impedances of the windings of the transformer are chosen to suit the circuits to which they are connected. A second auxiliary valve C in parallel with the first serves as a stand-by and comes into action automatically in substitution for the first valve when the latter fails. This automatic substitution is achieved by the arrangement of resistances B<2>, C<2>, D<1> controlling the supply to the filaments and is described in Specification 258,718, [Class 40 (v), Wireless signalling &c.]. The control circuit F has the effect of modulating the normal oscillations of the transmitting circuit to a degree dependent upon the current in the power circuit without affecting the frequency. The oscillations at the other end are similarly modulated and, as the transmitting circuits are connected through a capacity coupling A<2> to the feeder, these modulated oscillations normally balance one another even with heavy straight. through currents and have no effect upon the detectors G which operate the relays G<2>. In the event of fault, however, the modulated oscillations operate the relays G<2> at each end and bring out the main circuit breakers G<3>. The relays G<2> may be tuned relays with holding coils as described in Specification 261,115.