Carrier current system

Sept 25, 1945

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J.. L. WOODWORTH

CARRIER CURRENT SYSTEM

Filed July 27, 1943

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Fig. 2.

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TRANSMITTER

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RECEIVER

Inventor:

John L. Woodworth,

His Attorney.

Patented Sept. 25, 1945 2,385,673

UNITED STATES PATENT OFFICE

2,385,673

CARRIER CURRENT SYSTEM

John L. Woodworth, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York

Application July 27, 1943, Serial No. 496,299

Claims. (Cl.

The present invention relates to a carrier current system for application to a plurality of interconnected feeders each having a carrier current transmitter and one or more carrier current receivers. In such systems it is desirable that the 6 carrier current transmitter for one of the feeders affect only the receivers associated with that feeder, particularly in the case where the receivers are relays for carrying out switching operations. ¹⁰

Under some circumstances it has been found that the carrier current voltage at the Interconnection of the feeders from one of the transmitters is sufficiently great to affect receivers associated with another of the transmitters. ¹⁵

An object of my invention is to provide an improved system in which the respective carrier current transmitters serve as wave traps for preventing interference due to signals from another transmitter. ²⁰

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further ob- ²⁶jects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 represents a carrier current system embodying my invention; Fig. 2 is a modification of the transmitter for substitution in Fig. 1; and Fig. 3 represents another carrier current system.

Referring to Fig. 1 of the drawing there is shown a carrier current system comprising transmitters I and 2 and receivers 3 and 4 respectively associated with feeders 5 and 6 interconnected by a power transmission line 7. The transmitters I and 2 operate at or near the same carrier frequency and are intended to control only the receivers 3 and 4 respectively. Each of the transmitters comprises a generator 8 connected through a key 9 and a blocking condenser 10 across the primary II of a coupling transformer 12 having a secondary 13 connected in series with one of the feeders 5 or 6. When one of the keys 9 is closed, a carrier current voltage is impressed on the associated feeder through the coupling transformer and provides the signal for operating the associated receiver. A carrier current voltage is also impressed across the impedance of the circuit comprising the power generator 35 and the interconnecting power transmission line 7 and, while the voltage across the power transmission line is generally small, it is Under some conditions sufficient to result in the impression of a carrier current voltage on another feeder large enough to affect a receiver not associated with the sending transmitter. In the present system this is prevented by condensers 14 across the

177—352) primary windings 11 of the coupling transformers which parallel tune the coupling transformers to serve as wave traps. The parallel tuning of the coupling transformers presents a high impedance to carrier current voltages fed from one of the transmitters through the interconnecting power transmission line to a feeder associated with the other transmitter. For example, under the condition under which the transmitter I is sending and the transmitter 2 is idle, the carrier current voltage from the transmitter I encounters a high impedance at the coupling transformer of the transmitter 2 and accordingly cannot affect the receiver 4. For effective operation it is obviously necessary that the transmitters be arranged intermediate the associated receivers and the interconnection between the feeders.

The system of Fig. 1 does not provide protection for the case in which the transmitters I and 2 are simultaneously energized. For this condition, which may occur at infrequent intervals, the parallel tuning of the coupling transformers is impaired by the parallel circuit through condenser (0, key 9, and generator 8, and the carrier current voltage from one of the transmitters may affect a receiver associated with the other transmitter. This disadvantage is overcome by the transmitter shown in Fig. 2 which may be substituted for either of the transmitters in Fig. 1. ³⁰ In this transmitter the primary winding I I of the coupling transformer 12 is shunted by two parallel circuits each of which includes a condenser 14 or 15 and one of the poles 16 or 17 of a two-pole keying switch 18. The carrier cur³® rent generator 8, which has an inductance represented at 19, is connected across one of the poles 17 of the keying switch so that the generator is shorted when the keying switch is closed. When the keying switch is closed, the condensers 14 and ⁴⁰ 15 in parallel tune the coupling transformer 12 as a wave trap. When the keying switch is open, the circuit through the condenser 14 is opened and the condenser 15 is connected in series with ₄₅ the generator 8 across the primary winding I I.

The condenser 15 parallel tunes the coupling transformer as a wave trap. With the transmitter of Fig. 2 the coupling transformer 12 is at all times tuned as a wave trap to prevent interference 50 due to other carrier signals.

In the modification shown in Fig. 3 feeders 20 and 21, having respectively associated therewith receivers 22 and 23 and transmitters 24 and 28, are energized from a power transmission line 28 55 through transformers 27 and 28. Each of the transmitters comprises a carrier current generator 29 having an inductance represented at 30 connected through a keying switch 31 and a series circuit including condensers 32 and in60 ductance 33 across the feeder conductors. The keying switches 31 have two positions, one con2

2,885,673 rent signals from another source in both open and closed positions of the keying switch.

3. In a carrier current system, a feeder connected to , a power system, a carrier current receiver associated with the feeder, a carrier current generator having a predetermined inductance, a series resonant circuit shunted across the feeder intermediate the receiver and the power system for short circuiting signals of carrier current from the power system and thereby preventing false operation of the receiver, said series circuit including the carrier current generator.

4. In a carrier current system, a feeder con15 nected to a power system, a carrier current receiver associated with the feeder, a carrier current generator having a predetermined Inductance, a series resonant circuit shunted across ' the feeder intermediate the receiver and the 20 power system for short circuiting signals of carrier current from the power system and thereby preventing false operation of the receiver, Said series circuit including a keying switch in one position connecting the generator as part of the 25 circuit and in another position disconnecting the generator and connecting an inductance, of said predetermined value as part of said circuit.

5. In a carrier system, a coupling transformer having a secondary for connection in series with a feeder and a primary having shunt connected tuning means, switching means for connecting the carrier current generator to said primary and for switching said tuning means so that the transformer is a parallel tuned trap for carrier 35 current signals from another source when the generator is either connected to or disconnected from said primary.

6. In a carrier current system for a power system including a plurality of interconnected feed- ers, a carrier current receiver and a carrier current transmitter associated with each of Said feeders, each said transmitter including a carrier current generator, means for coupling eaid generator to its feeder intermediate the associated 45 receiver and the interconnection of said feeders, two-position keying means for selectively disabling said transmitter or rendering said transmitter operative to impress a carrier current signal upon the associated feeder, and means in50 eluding said coupling means for tuning each said transmitter as a wave trap for undesired carrier current signals from any other transmitter through said interconnection in both positions of said keying means.

7. In a carrier current system for a power system including a plurality of interconnected feeders, a carrier current receiver and a carrier current transmitter associated with each feeder, each said transmitter including a carrier current 00 generator, means for coupling each said generator to its feeder Intermediate the associated receiver and the interconnection of said feeders, and keying means for selectively disconnecting each said generator or connecting said generator to impress 65 a carrier current signal upon its feeder, said keying means including switching means for tuning the associated coupling means alone as a wave trap when said generator is disconnected and tuning said coupling means and a generator to70 gether as a wave trap when said generator is connected to its feeder, thereby to preclude the reception of signals by any receiver through said Interconnection.

JOHN L. WOODWORTH.

nected in series with the carrier current generator so as to impress a carrier current voltage from the generator across the respective feeder, and the other position in which the circuit to the generator is opened and the keying switch 5 is closed on an inductance 34, having the same value as the inductance 30, which completes an alternative series circuit across the respective feeder. In either position of the keying switch there is a series circuit across the feeders coil- 10 sisting of the condensers 32, inductance 33, and either of identical inductances 30 Or 34. These series circuits are tuned for resonance at the carrier current frequency and accordingdy short circuit carrier current voltages fed to the respective feeders from the transmission line 26. Since the transmitters are located intermediate the associated receivers and the interconnecting transmission line 20, a carrier current voltage fed from one of the transmitters through the interconnecting transmission line to another feeder is short circuited by the series coupling circuit associated with that feeder. This prevents undesired operation of one of the receivers by signals from a transmitter associated with another feeder.

It is important that the coupling circuit be tuned so as to short circuit the undesired carrier voltage at the points of connection of the series circuit to the feeder. If the tuning of the series circuit were such as to provide series resonance at carrier frequency for the circuit, which also included the feeder to the associated receiver, under some conditions the series circuit associated with the transmitter would increase rather than decrease interference due to carrier voltages fed through the interconnecting transmission line 26.

While I have shown particular embodiments of my invention, it will be understood that many modifications may be made without departing from the spirit thereof, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.