Patent GB-610610-A (GB)
Title: Improvements in or relating to electric protective arrangements for sectionalised a.c. circuits
IPC: H02H3/30
Filed: 1946-04-11
Abstract: 610,610. Protective cut-out systems. REYROLLE & CO., Ltd., A., and OLLERENSHAW, C. April 11, 1946, Nos. 11152/46 and 11588/47. [Class 38 (v)] In a protective arrangement for a sectionalised A.C. circuit, carrier-currents, controlled in accordance with the phase-angle of the line currents, are transmitted on fault from each end of the section to the other end where they are applied to electronic discharge devices in which they are compared in phase with currents derived from the line currents at the adjacent ends. The carrier currents are 180 degrees out of phase with each other when the line currents are in phase, i,e. on external faults, and substantially in phase on internal faults. The system comprises, at each end of the section, three star-connected current transformers B<1> ... B3, connected to tappings on a summation. transformer B<4>, which, or a transformer B<5> connected thereto, saturates at slightly more than full-load current. The output of an oscillator D is controlled by the output of a transformer B<7>, fed from a filter B<6> controlling the wave-form of this output. A half-wave rectifier D<2> ensures that only the negative half-cycles of the current from transformer B<7> are applied to the grid of a modulating valve D<1>, so that the signal transmitted thereby and imposed on the conductors A<1> ... A<3> consists of pulses of carrier-current during alternate half-cycles. The incoming signal, which is preferably of a different carrier frequency, is applied to an amplifier F and rectifier F<3>, and the negative pulses fed to the grid of a receiving valve G which is thus blocked during these half-cycles. The output of a transformer B<8>, in series with transformer B7, is also applied to the grid of valve G over a half-wave rectifier F<8> so that, on an external fault, this valve is blocked during the remaining halfcycles also. On an internal fault, however, the two currents applied to the valve will be relatively shifted so as to be substantially in phase. The valve G will now conduct during all or a large part of each alternate halfcycle and the A.C. component of the anode current is passed to a trip relay G\ either directly over a transformer G<3>, or an amplifier; Fig. 3 (not shown), and a rectifier bridge G<5>. A starting relay H, on fault, removes a negative bias from the grid of valve D<1> and completes the circuit of transformers B<7> and B<8>, and a second relay J, needing a higher operating current, prepares the trip circuit at contact J<1>. With an internal fault, fed from one end, the circuit-breaker at that end will be operated, since the valve G will conduct during alternate half-cycles due to the absence of a restraining current from the other end of the section. Figs. 2 and 3 (not shown) illustrate modifications of the transmitter and receiver circuits, respectively, wherein the tetrode valves D<1>, G are replaced by triode-hexodes. In Figs. 11, 12 (not shown), the carrier signals from both ends are mixed in the receiver and after rectification are applied together to the valve G so that the incoming signal is compared directly with the out-going signal, instead of with the output of transformer B<8>. If the carriercurrents are of the same frequency, a filter is provided to render each receiver insensitive to the outgoing signal. Specification 598,581 is referred to.