US2357995A - Remote control system - Google Patents

Description

Sept. 12, K. BLQMBER ETAL I REMOTE CONTROL SYSTEM Filed April 16, 1941 INVENTOR F/ 7 KH. fiLoMssxc,

CL PBnooME,

E A .DA user/v, AG. J'oHAA/ssoA/ AND R. 0, L U/VDHOLM ATTO R N EYS Patented Sept. 12, 1944 REMOTE CONTROL SYSTEM Knut Hugo Blomberg, Appelviken, Carl Ludvig Percy Broom, Stockholm, Fredrik Axel Dahlgren, Djursholm. Artur Gosta J ohansson,

Stockholm, and Ragnar Olof Lundholm, Djursholm-Ekeby, Sweden, assignors to Telefonaktiebolaget L. M. Ericsson, Stockholm, Sweden Application April 16, 1941, Serial No. 388,912 In Sweden April 19, 1940 2 Claims.

The invention relates especially to remote control in alternating current power supply systems, but can also be used in direct current systems.

The remote control over such a power supply system can be obtained by changes in the supply current or voltage or by means of separate superimposed signal currents e. g. of audiofrequency, in which case frequency-selective receivers will be used. In known systems changes in the supply current orvoltage will be maintained e. g. by momentary interruptions in one phase, by changes of the voltage, by modulation of the supply frequency or by phase-displacement of the voltage in one phase. In other known systems direct current impulses are used in connecting a direct current source of 6-12 volts in the neutral wire in an alternating supply system. In the receiver the direct current selected from the supply voltage by means of a choke operates a relay. Surely when transmitting the signals in such a system the voltage on the supply line will be L. raised, but the receivers will not be influenced by this raised supply voltage but only by the superimposed signaling voltage filtered out from the supply voltage.

The invention relates to a system, by means of which the remote control will be obtained through a rising of voltage. One object of the invention is to provide means by which the amplitude of the power supply voltage together with the imposed voltage will operate the receiver. It is thus unnecessary to use receivers responding to the character of the rising of voltage e. g. the

. difierence in frequency between the supply voltavoided. The signals will be produced through rising of the amplitude of the supply voltage to a value, necessary for amplitude-selective receivers without a corresponding equivalent rise of the R. M. S. value of the supply voltage.

The invention will best be understood by reference to the following description taken in connection with the accompanying drawing, in which Figs. 1 and 2 show diagrammatically how the rise of the supply voltage in an alternating current supply system can be obtained by the aid of a direct voltage resp. an alternating voltage. Figs. 3, 4, 5 and 6 show different forms of a transmitter and Fig. 7 shows by way of example an arrangement for passing a step-down transformer in the transmission of remote control signals from a main station over a high tension to a low tension line. 7

The necessary rise of voltage can as mentioned above be obtained through a direct voltage or an alternating voltage. By using a positive direct voltage V, as shown in Fig. 1, a displacement of the whole alternating voltage curve in positive direction is obtained, so that the positive amplitudes will increase and the negative amplitudes will decrease. By using an,alternating voltage, which forms the 3rd harmonic of the fundamental frequency, a distortion of the voltage curve will be obtained as shown in Fig. 2.

In an alternating current supply with a phase voltage of nominally 127 volts, the voltage at different points of the net-work can differ between and volts, corresponding to the amplitudes 163 and 198 volts. To ensure a margin in receivers the rise of the voltage amplitude must be ZOO-163:3? volts, 1. e. 20%. By the ris of tension, shown in Figs. 1 and 2 and by rise of tension in direct current net-works by the aid of alternating current, a relatively great rise of the voltage amplitude corresponds to a moderate rise of R. M. S. voltage. That will be shown below where R. M. Stension oi the fundamental frequency is E1 and the R. M. S. tension of the voltage rise is E3. The resulting R. M. S. voltage E=-\/E1 +E3 Thus a rise of 2,4 and 8% of the R. M. S. voltage corresponds to a riseof 20, 30 and 40% of the voltage amplitude. The above mentioned necessary increase of 20% of the voltage amplitude gives a rise of only 2% of the R; M. S. voltage. It is, however, possible to raise the amplitude with 35%, corresponding to the phase voltage limits 110-150 volts and to a rise of the R. M. S. voltage of about 6%.

A very simple way to raise the voltage amplitude in an alternating current supply is obtained as shown in Fig. 3, by connecting a direct voltage source in the neutral wire. .In the connection between the starpoint of the secondary side of a distribution transformer Td and the earth a low-ohmic resistance W is normally connected which is short circuited by means of a contact 1'. At the signaling the contact is moved into the signaling position, whereat the short circuit over W is broken and a direct voltage source B is connected in parallel to W. The amplitude value of the phase voltages is thus increased as shown in Fig. 1. Receivers which are connected between one phase and the neutral path are operated from the battery B over the corresponding transformer winding and line, receivers, neutral path, resistance W and back to the battery 13. This very simple way to raise the voltage (the direct voltage source can be a normal auto accumulator) can not be used in supply nets containing considerable inductive loadings connected between the phase and the neutral wire, as such a loading forms a low shunting impedance for the direct current. In this case it will be more suitable to use one of the methods for increasing of the supply voltage amplitude, described as below.

In Figs. 4 and 5 two circuits are shown by which the rise of the voltage is obtained by aid of the third harmonic. The transformer Td is a distribution transformer in the supply net. The remote control signals shall be sent out on the low voltage side by the aid of a rise of the voltage. For this purpose the one winding of a little signal transformer T), is connected between the starpoint on the secondary side of the transformer Td and the earth. One terminal of each of the three coils S can be connected to the phases 1, 3 on the secondary side of the transformer Td by the aid of a three-polar switch K. The coils are joined together and connected to the starpoint of the transformer Td over the primary winding of the transformer TI. The coils are dimensioned in such a way that by connecting the coils to the power line by means of the switch K the current causes very nearly a saturation of their iron cores. Thereby the current through the coils S is distorted and a current of the third harmonic of the power frequency appears between the joining point of the coils S and the star point of the transformer Td. A voltage of this third harmonic is thus imposed upon the other winding of the transformer T1, connected in the neutral wire, causing a rise of the amplitude of the phase voltage and the operation of the amplitude-selective receivers, connected between anyoneof the phasesand the neutral path of the power supply system. The phase voltages are deformed as shown in Fig. 2. The transformer T can also be replaced by a simple coil, at which the coils S are connected directly to the neutral wire.

The saturation of the iron cores of the coils S can also be obtained through a direct current by means of transductors, as shown in Fig. 5. The direct current source is constituted of a rectifier bridge L, containing four electrolytic rectifiers. One diagonal of the rectifier bridge is connected between the phases 2 and 3. The other diagonal is in state of rest closed over a spacing contact n in the relay Rand aseparate winding M in the signaling transformer Tj. At the signaling the relay R breaks the contact 11 and closes the contact r2, thus disconnecting the winding M from the bridge L and in return connecting the direct current windings of the transductor D. This causes a direct current fiow through these windings and a saturation of the transductors and the same effect is utilized as by the circuit in Fig. 4. In the state of rest, i. e. when no signals are transmitted and the relay R is unmagnetized,

a current is flowing through the winding M.

Thus the iron core of the transformer Tf will be saturated and the impedance of the winding in the neutral wire is decreased to an allowable value. It is, however, not always necessary to arrange such a saturation winding as the impedance at normal supply frequency also otherwise can be held suihciently low.

The deformation of the sinusoidal supply current can also be obtained by means of rectifier circuits. Such a circuit can by way of example be obtained by replacement of the coils S in Fig. 4 through rectifying elements (e. g. copper oxide rectifier) each of which is shunted with a condenser.. The rectifier circuit is connected to the transformer T over a condenser with a voltage which has the same course as the rectified threephase-voltage, but is displaced in relation to the zero voltage line so as to have both positive and negative values. This voltage is superimposed on the phase voltage and causes the desired rise of amplitude. It is also possible to cause a suitable deformation of the voltage curve by means of a three-phase grid controlled mercury-arc rectifier G as shown in Fig. 6, which is connected to phases 1, 2, 3 of the supply system by, means of a A-Y connected transformer Tic. The operations of the transmitter is obtained by means of a three-polar switch K. In the neutral wire of a distribution transformer Td the secondary winding of a signaling transformer T1 is connected. The primary winding of this transformer is connected between the cathode of the rectifier and the neutral point of the transformer Tic. The rectifier is controlled in known way by aid of the grids, indicated in the drawing, so as to produce a current in the form of a sawtooth curve. This current flows through the transformer Tf and produces the wanted voltage rise between each of the phases 1, 2, 3 and the neutral path.

To allow a centralized transmitting over a great supply system e. g. for air attack alarm over a great air alarm district, it can be necessary to connect the central transmitter to a main station. In this case a step down distribution transformer 'for the transforming to 220 volts must be passed by the signals. According to the invention this can be attained with a repeater circuit as shown in Fig. 7.

In the main station from the secondary side of the high voltage transformer Th voltage rise signals are transmitted in the form of the third harmonic of the supply frequency. This is obtained with an arrangement which in the said figure is indicated by 0, and which can be connected as shown in Figs. 4, 5 or 6. When the voltage amplitude on the high voltage line by transmitting of the signals over the signaling transformer Tj rises, an amplitude selective receiver, connected to the primary side of the distribution transformer "Idis operated. The latter is formed of a transformer Tfl, connected between one phase and the earth and a series connection of a glow lamp G and a relay R (corresponding to the relay, indicated in the same way in Fig. connected in the secondary circuit of the transformer. As soon as the voltage amplitude of the glow lamp exceeds the ignition voltage, a current is flowing through the lamp G and the relay R. Said relay is energized and over its contact r2 causes a current to flow through the direct current windings of the transductors D. A signal is thus transmitted to the low voltage supply system.

The above described circuits relate to alternating current supply systems. It is, however, possible to raise the voltage amplitude of a direct current supply system according to the invention by means of an alternating current without a corresponding rise of the R. M. S. voltage. In this case the transmitter consists of an alternating current generator, which is connected to the neutral wire in the three wire-net work. The receivers can be of the same sort, as above described, according to the alternating current system.

The described circuits should be regarded only as examples. Other ways may be used within the bounds of the invention, involving the rise of the amplitude of the supply voltage to a value, sufficient for, amplitude selective receivers without a corresponding rise of the R. M. S. voltage.

We claim: 1. In a remote control system, a distribution transformer, a control transformer including primary and secondary windings, said secondary winding being connected between the starpoint of the secondary of the distribution transformer and the earth, a group of coils connected at one end with one end of the primary winding, the opposite end of the primary winding being connected with said starpoint, and a switch for connecting the other ends of the coils with the phases of the secondary of the distributing transformer.

2. In a remote control system, a distribution transformer, a control transformer including primary and secondary windings, said secondary winding being connected between the starpoint of the secondary of the distribution transformer and the earth, a group of coils connected at one end with one end of the primary winding, the opposite end of the primary winding being connected with the starpoint, and a switch for connecting the other ends of said coils with the phases of the secondary of the distributing transformer, said coils being so dimensioned that when connected with the phases of the distribution transformer, the current causes substantial saturation of their cores.

KNUT HUGO BLOMBERG. CARL LUDVIG PERCY BROQME FREDRIK AXEL DAHLGR N. ARTUR G6s'ra JOHANSSON. RAGNAR OLOF LUNDHOLM.

Images