Patent GB-317018-A (GB)
Title: Improvements in and relating to control circuits
IPC: H02H3/06
Filed: 1929-08-08
Abstract: 317,018. British Thomson-Houston Co., Ltd., (Assignees of Cook, E. D.). Aug. 8, 1928, [Convention date]. Thermionic relays.-A trigger relay device comprises a pair of thermionic valves with their plate-filament paths in series, one being connected as an oscillation generator and the other having a control voltage applied to its grid, as in Specification 243,683. In the present arrangement the control grid circuit is also coupled to the oscillator, so that as oscillations start up they raise the average voltage of the control grid, allow more plate current to pass to the oscillator, and so strengthen the oscillations. The final relay is in the common plate circuit of the valves. Fig. 1 shows the valve circuit applied for the operation of an overload circuit-breaker 6 in an electric supply system. An impedance 13 in the supply line is connected through a transformer 11 to the grid circuit of the control valve 2, the grid being negatively biased by a battery 12. The oscillatory circuit 9 of the valve generator 1 is also variably coupled at 10 to the control grid circuit. The plate-filament paths of the two valves 1, 2 are connected in series with the source 3 and the relay 6, their filaments being separately energized by transformers 7, 8. When the voltage applied by the transformer 11 rises abnormally, current begins to flow in the common plate circuit of the valves, and oscillations are generated bv the valve 2. These are fed back to the grid circuit of the valve 1, and still further raise its potential, thus increasing the amplitude of the oscillations and further increasing the plate current through the relay 6. If the coupling 10 is close, the plate current builds up quickly in response to a slight stimulus from the impedance 13, and maintains its value when the stimulus is withdrawn. With a looser coupling the response is slower, and the relay is self-restoring. In a modification, the two valves 1, 2 are replaced bv a single valve with two grids, one for effecting the back-coupling for producing oscillations, and the other having in its circuit the input transformer 11 and the secondary of the coupling 10. Fig. 3 shows an arrangement for operating relays 6<1>, 6<11> when the control voltage moves above or below fixed limits. The relay contacts are connected in series in the circuit of a motor 21 which may drive a fuel pump for an oil-burning furnace, and the control voltages are tapped from resistances 15, 17 connected across an ignition arc 20. Pairs of valves 1<1>, 2<1> and 1<11>, 2<11>, each functioning as in Fig. 1, are controlled by the voltages at the respective resistances 15, 17 and operate the respective relays 6<1>, 6<11>. If the voltage across the arc is normal, relay 6<1> is energized and relay 6<11> is unenergized, and the motor circuit is complete. When the arc voltage drops below the lower limit, relay 6<1> is released, whilst if it rises above the upper limit, relay 6<11> pulls up, the motor circuit being opened in either event. A rotary interrupter 19 may be arranged in the common plate circuits of the valves; or the operation of the valves may be rendered intermittent by using A.C. supply for the plate circuits. In both cases, the relays 6<1>, 6<11> may be retained either by their inertia or by shunt condensers 22, 23. The voltage range over which the circuit of the motor 21 is kept closed may be varied by adjustment of the couplings 10', 10". Fig. 5 shows the trigger relay arranged to control the re-closure of circuitbreaking switches 30 on a power supply line 31. As indicated in Fig. 7, the line 31 is in the form of a loop either end of which may be connected to the supply source by switches 67, 68. When either of these switches is closed, the circuitbreakers 30 close automatically to connect further sections of the line 31 provided that the further section is in normal condition as regards its impedance to earth. Assuming that the switch 30, Fig. 5, is open, and that power is supplied to the left-hand line 31, the transformer 32 (which may be connected between line and earth, or may be an ordinary distribution transformer) is energized and the relay 34 pulls up. Current thus passes from the secondary through the backcontacts 64 of relay 30 to a motor 49 driving a platecircuit generator 43, and to transformers 51 for supplying the filaments of valves 1, 2, 38. The valve circuits are thus prepared for operation. The right-hand section of the line 31 is connected through an impedance 37 bridging the interrupter contacts, and the voltage on the secondary of the transformer 33 will depend on the conditions in this right-hand section. Should there be a short circuit, or a low impedance fault, this voltage will be low and insufficient to trigger the valves. Under normal conditions, however, this voltage, while insufficient to operate the relay 35, is applied through a resistance 41 to a valve amplifier 38. and thence to the trigger valves 1, 2, causing the plate-circuit relay 6 to close. The transformer secondary 32 now energizes a relay 45 through the back-contacts 64 of relay 30, contacts of relay 6, and upper contacts of relay 34. The closure of relay 45 then energizes the final relay 30 which connects up the right-hand section of the line 31. and opens the valve supply circuits at contacts 64. The right-hand section now receives the full voltage of the line 31, and relay 35 operates. opening the circuit of the transformer 40. The symmetry of the arrangement enables the circuit-breaker 30 to be operated in similar manner when power is applied from the right-hand end of the line. In a modified. arrangement, the grid of the control valve 2 is biassed by rectified alternating current obtained from a transformer, the primary of which is energized through back'contacts 64. The valve plates and filaments are supplied with A.C. from further secondary coils. Wired wireless systems ; tell-tale apparatus.- The operation of the successive switches 30 may be indicated in the power station by the lighting of a number of lamps 75, Fig. 8. These lamps are lit in turn by a step-by-step switch 73. As each line switch operates, oscillations generated by the corresponding valve 1 are sent to line through a coupling-coil 54<1> and condensers 53, 54; and at the power station, the oscillations are rectified by a detector 72, and caused to operate the switch 73, thus indicating the connection of each section, and enabling the operator to locate a fault. Should one of the switches 30 be itself faulty, a prolonged series of oscillations passes to line, and is indicated by the continued lighting of a lamp 78.