Patent GB-519403-A (GB)
Title: Improvements in electrical systems of remote control
IPC: H02J13/00
Filed: 1938-10-24
Abstract: 519,403.. Signalling over power circuits. GENERAL ELECTRIC CO., Ltd., and SMART, N. C. Oct. 24, 1938, No. 30638. [Class 40 (iv)] [Also in Group XXXVIII] In a system for signalling over D.C. or A.C. power lines, the voltage of the signal applied to the line is controlled in accordance with the response of a local relay FR of the same type as the distant receiving relays to compensate for varying load conditions. This relay may also control the duration of 'the signal. As shown, the mechanism of the relay is of the type described in Specification 491,980, [Group XXXVII], but controls movement of wipers over a contact bank instead of a mercury switch. The system is adapted for the transmission of signals of two frequencies, e.g., to switch street lights on and off, but may be modified to make use of more than two frequencies. When the switch 22 is thrown to the opposite position to that shown, ST pulls up in series with B and locks up. Voltmeter relay V is thus connected to the potentiometer tapping characteristic of the signal to be sent, the whole of resistance 11 is cut into the field circuit of the generator motor 8 and contactor MS is energized to connect the mains through rectifiers to the armature circuit. Relays STA and X are energized and the former cuts resistance 25 into the circuit of FR to make it less sensitive than the receiving relays proper. Relay X co-operates with relays Y, Z to give slow impulses to one of the driving magnets UF of a switch F which progressively inserts' resistance in the circuit of the motor field winding 10 to increase the motor speed until the proportion of the voltage of the tachometer generator 14 selected by the contact A<SP>1</SP> is enough to operate V whereon FC switches the impulsing circuit to magnet DF to drive the switch F in the opposite direction and so reduce the speed of the motor. FC also operates a contactor 1A, which locks itself, to cause the signal currents to pass out over the power network and impulses to be delivered to driving magnet VC of a switch for removing resistance from the circuit of the generator field 9 to increase the voltage generated. When the generator speed falls owing to the reversal of the direction of movement of F, V releases FC whereupon F again acts to increase the speed. The frequency generated is thus kept varying about the correct point to ensure operation of receivers the tuning of which is not. quite accurate. The relay FR responds to the signal, extinguishes lamp 18 and later releases AA to energize SG which locks and stops the voltage increasing switch VC. Subsequently FR energizes BB without effect and in its final position lights a lamp 17 and shunts out B, ST to send the switches VC, F home and shut down the apparatus. When the switch 22 is moved theother way, similar effects are produced but a different frequency is sent out since B is energized instead of A. The voltmeter relay V and tachometer-generator could be replaced bytuned relays. The signal may be applied to one or more phases of a low or high-tension network and may pass through one or more power transformers on its way to the receiving relays.