US1965674A - Carrier current communication system - Google Patents

Description

P. SPORN El' AL CARRIER CURRENT CQMMUNICATION SYSTEM July 10, 1934.

2 Sheets-Sheet 1 mw, mw um,

Filed Aug. 22. 1930 July l0, 1934.

P. sPoRN Er Al.

CARRIER CURRENT COMMUNICATION SYSTEM Filed Aug. 22. 1930 2 Sheets-Sheet 2 wvemtou Pff/UP .SPO/'ew /EA Y nl. WOL Fa@ 33513 MMM @Moz/nap R 1 -J- der all normal and emergency conditions.

Patented July 10, 1934 UNITED STATES CARRIER CURRENT COMMUNICATION SYSTEM Philip Sporn, New York, N. Y., and Ray H. Wolford, Elizabeth, N. J.

Application August 22, 1930, Serial No. 476,978

5 Claims.

This invention relates to carrier current communication systems, particularly for use as communication means on electric power transmission and distribution systems, and has among its ob- 5 jects the provision of such communication system in which the excessive costs and hazards of the present coupling arrangements between the high frequency communication apparatus at the stations and the power line conductors are reduced 1,3 and eiiicient coupling is secured with great decrease in cost, increase in reliability of service, and reduction of the number of operating devices at the coupling stations. The foregoing and other objects of the inl vention will be best understood from the following description of exemplications thereof, reference being had to the accompanying drawings wherein,

Fig. l is a diagrammatic View of a portion of Z9 a power transmission and distribution system provided with a carrier communication system in accordance with our invention;

Fig. 2 is a diagrammatic View of a transmission line tower showing the arrangement of the trans- :j mission line conductors of the system shown in Fig. 1; and

Fig. 3 is a sectional view through'a circuit breaker unit employed at the individual stations 'of the power system shown in Fig. l, illustrating w'the arrangement of the coupling condenser in the lead-in bushing by means of which the high frequency receiving and transmitting apparatus at the stations is coupled to the line conductors.

Experience has shown that carrier current y communication systems operating over power transmission and distribution lines constitute one of the most reliable means for maintaining continuous communication between the stations of a power transmission and distribution system un- One of the greatest diiiiculties in the practical application. of such communication systems resides in the excessive cost of the coupling equipment by means of which the carrier frequency energy is caused to enter or leave the transmission line at the individual stations, and also the complications involved in maintaining such coupling equipment in proper operating condition. At present, two types of coupling means are used. 3l One is in the form o f an antenna strung parallel to the power line, and the other is in the form of capacitors installed as separate and distinct units at the individual stations of the system. They are described in a paper entitled Experience 57 with Carrier Current Communication on a High Tension Interconnected Transmission System, which we presented before the American Insttute of Electrical Engineers in December, 1929, ,and which has been printed in the publications toof that Institute. Experience has shown that the antenna method of coupling is a source of many difficulties and accordingly it is now the almost uniform practice to use coupling capacitors, of which there are various forms now on the market. These coupling capacitors are installed as separate units and constitute an additional piece of apparatus 'at the stations, requiring additional space and making it necessary to provide proper clearances for establishing connections toy sulation. Instead, we utilize for coupling purposesV the ordinary equipment that is essential and must be provided for the operation of the power stations, such as circuit breakers, and combine relatively low voltage coupling means with the high voltage equipment of such standard operating apparatus in a way to secure satisfactory communication, comparable with that obtained by the use of separate coupling capacitors or antennae, in accordance with the prior practices. The details of the arrangement of our invention will be clearly understood from the following description of a carrier current communication system of which a section including stations A and B is shown in the drawings.

The power transmission system is, as usual, of the three-phase type and may, for instance, operate on 132 KV. At each station there is provided a set of high voltage bus bars 1, 2, 3 for` the three phases of the system. The stations A and B are shown interlinked by two parallel threephase circuits M and N, each circuit comprising three line conductors 1, r 2, 3, corresponding to the three phases of the system. There are also shown at station B, two additional outgoing highvoltage transmission line circuits O and P, each likewise including three line conductors l, 2, 3 corresponding to the three phasesof thesystem, the circuits O and P going to the next station of the system. From station A there is also outgoing a single circuit transmission line Q having three conductors 1, 2, 3 corresponding to the three phases of the system.

The power transmission lines are carried between the stations on transmission line towers as shown in Fig. 2, which also illustrates the arrangement of the line conductors of the circuits M and N on the tower. As seen in Fig. 2, the two transmission lines are strung asymmetrically on the tower, circuit M having phase 1 on the top, and circuit N having phase 3 on the top. This reduces the reactance of the transmission line.

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To control the transmission of power over the circuits there are provided at the-stations, sets of three-pole circuit breakers AM, AN, BM, BN, BO, BP and AQ, by means of which the individual lines of the transmission circuits may be connected or disconnected from the bus bars 1, 2, 3 at the stations. The individual circuit breaker sets AM, AN, etc. are all of a type well known in connection with high voltage power transmission.

Each circuit breaker set consists of three like units 10 illustrated with more detail in Fig. 3. Each unit comprises a large oil-filled metal tank 11 having mounted at its top two upwardly divergent lead-in bushings l2 through which extend lead-in conductors 13 terminating at their lower ends in contact members 14. The circuit between the contact members is completed by a conducting bridging element 15 which is moved down to open the circuit breaker and up to close the circuit breaker, by means of a rod 16 that is operated by suitable motion transmitting mechanisms 17 and actuated by an actuating device 19 that is common to the Ythree units of a circuit breaker. Such circuit breakers with the high voltage lead-in bushings 12 are common and standard equipment at each power station and must be provided whether there is a carrier communication system used or not. The bushings must provide insulation for the full line voltage, and one of the common types of bushings is the so-called oil-lled bushing", as shown in the drawings. The bushing as shown comprises a cylindrical supporting collar 20 of metal which is secured at the top to the tank. Over the top and bottom of this collar are mounted porcelain shells 21 which in conjunction with the collar, form a closed hollow chamber. The lead-in conductor 13 extendslongitudinally through the center of this chamber and is insulatingly held at its endby the ends of the porcelain shells 21. The interior of the chamber is filled with oil, so as to provide the necessary insulation against dischargesand break-down between the lead-in conductor 13 and the surrounding metallic portions, cylindrical barriers 22 of impregnated paper or similar insulating material serving to strengthen the insulation.

In accordance with our invention, such high voltage lead-in bushings of the standard apparatus used at the stations are employed to pro- 'vide the coupling means for the carrier current communication system. To this end, there is provided within the interior of the bushing an additional capacitive coupling member 23 which may be in the form of a cylindrically wound plate, preferably arranged so as to have its ends out of contact. 'Ihis coupling plate 23 is insulatingly held at a distance from the walls of the collar 20 of the bushing so that the plate has a capacitive coupling with the lead-in conductor 13 and also a capacitive coupling with the collar 20 of the bushing. As a result, the collar 20, coupling plate 23 and lead-in conductor 13 constitute two serially arranged condensers, one condenser being formed of the lead-in conductor 13 and the coupling plate 23, and the other condenser being formed of the coupling plate 23 and the supporting collar 20. A lead-in connection is provided to the coupling plate 23 on the bushing by means of a lead-in conductor 25 extending through a small bushing 26 on the collar 20 and then pass. ing through a suitably sealed port 27 on, the tank 11 of the circuit breaker to the exterior thereof.

The details of construction of the bushings as shown in Fig. 3 do not constitute a part of 011.1. n-

vention, and for more particulars as to their construction 'reference is here made to Eby Patent No. 1,657,249. It is of course understood that the description of the particular type of bushing is intended only for illustrative purposes as our invention is in no way limited to the use of any particular type of bushing, but is broadly applicable to the use of lead-in bushings for the station apparatus such as circuit breakers or transformers having embodied therein capacitive coupling means insulated from the leads to the bushings but having capacitive coupling therewith, for the purpose of coupling carrier current communication apparatus to high voltage power lines.

The several circuit breakers shown in Fig. 1 are of the type described above and are provided with lead-in bushings having capacitive coupling plates 23 as indicated in the drawings.

In accordance with our invention, we employ as a means for passing the high frequency signal energy of the carrier communication system between the line and the transmitting and receiving apparatus at the stations, the capacitive coupling plates mounted in the bushings of the circuit breakers or like `standard station apparatus that is used in connection with the transmission and control of power entering and leaving the station. .We have found that by proper arrangement standard bushings as they are now available on the market can be used satisfactorily for theprovision of such coupling means, and that capacitive coupling plates 23 may be provided in such bushings that will permit transfer of Sunicient energy into the line conductors for maintenance of reliable carrier communication. In a typical bushing of this type, for 132 KV, the capacity between the coupling plate 23 and the lead-in conductor 13 was found to be .0002 microfarads, the capacity between the coupling plate and the supporting collar 20 amounted to .004 microfarads, and the Vsystem according to our invention using such bushings for coupling purposes was found to give satisfactory and reliable carrier communication on an extended 132 KV power transmission system.

' The details of the arrangement of such system as practically operated are seen in Fig. 1. operating the carrier current communication system on the two parallel circuits M and N between the stations A and B, the carrier current is transmitted inter-phase and inter-circuit, i. e., two phases of each circuit are used to provide a closed communication circuitand the two cir-v cuits are used in parallel. In the instance referred to, phases 1 of circuits M and N are coupled in parallel to one pole of the carrier current communication apparatus and phases 3 of the circuits M and N are coupled in parallel to the other pole of the carrier current communication apparatus. The outgoing bushings of the circuit breaker sets at the two stations are used for coupling purposes,and as seen, the lead-in terminals 25 of the bushing coupling plates 23 of phase 1 of circuit M and of phase 1 of circuit N are connected in parallel to the conductor 31,

and the lead-in terminals 25 of the couplingv plates 23 .of the outgoing bushings of phase 3 ofV line Mand of phase 3 of line N are connected in parallel to conductor 32.

These conductors have associated therewith protective apparatus in the form of spark gaps 33, and the other usual protective devices which are as a rule in the coupling circuits between the carrier current communicationA apparatus and the transmission line. The conductors 31 and 32 lead to a tuning unit comprising variable inductances 34 and 35 and condensers 36, the circuit being completed by a coupling inductance 3'7, to which in turn are connected the leads 38 from the carrier frequency transmitting and receiving apparatus indicated in the drawings by a rectangle 39.

The details of construction of the transmitting and receiving apparatus and of the tuning unit do not constitute a part of the present invention and may be of the type heretofore used in carrier current systems'utilizing antenna wire or separate capacitive coupling. A fuller description of such tuning and transformer and receiver apparatus will be found in our paper on carrier current communication referred to hereinbefore.

In the station B of the system, the coupling plates in the outgoing bushings of the circuit breakers BM, BN, BO and BP of the two circuits M and O are connected pairwise to two coupling coils 37 in a similar manner asy in Station A, and as shown in the drawings, the two coupling coils are interconnected in parallel by means of coupling conductors 45, 46 to which in turn are connected the leads from the transmitting and receiving apparatus 39. Because of this arrangement, the circuits M and N will constitute a continuous communication line with the circuits O and P, so as to permit direct communication between station A and the stations on the circuits O and P. The tuning apparatus connected with the coupling plates of the bushings of the circuit breakers BM, BN, BO and BP, when properly adjusted, constitute thus in conjunction with the conductors 45, 46, a resonant by-passing circuit by means of which carrier current power is free to iiow between the circuits M-N and O-P, even when the bridging contacts in any of the breakers BM, BN, BO and BP are open. The provision of the by-passing circuit is desirable on stations in which Vcircuit breakers or other power apparatus having lead-in bushings provided with coupling plates as explained before are installed and connected to the high voltage power lines, regardless of whether or not carrier current communication transmitting and receiving apparatus is provided at the station. In this way, it is possible to provide a very positive communication tie between all the lines and circuits of the system by merely providing connections between the bushing taps, as explained.

l'Ehe usual frequencies used at present in 0perating carrier current communication systems on power lines lie within the range of about 50 kilocycles to about 150 kilocycles. In general, the higher the frequency, the easier it is to transfer the amount of power required to establish reliable communication through a given capacitor coupling. We have found that a system arranged as described in connection with Fig. 1 operated in a reliable and satisfactory way at frequencies as low as 49 kilocycles.

A particular feature of our invention is the utilization of combined interphase and intercircuit transmission of carrier frequency currents over parallel transmission line circuits. Heretofore, wherever carrier frequency communication was used between remote stations, there was employed either interphase of intercircuit carrier communication. In the interphase carrier communication, one conductor of the carrier frequency apparatus cuit. In the intercircuit system, which is usable where there are two independent circuits extending between the communicating stations of the system, euch as is now common practice, one conductor of the carrier frequency apparatus at each station was coupled to one phase of one circuit andthe other conductor to another phase of the other circuit. By combining the interphase and intercircuit coupling of the transmitting and receiving apparatus at the communieating stations with the utilization of the coupling plates in the bushings of the outgoing circuit breakers, We greatly increase the reliability of the communication system and at the same time enable efcient carrier intercoinmunication through the capacitive coupling of the condenser bushings already present in the station under elimination of additional costly capacitors.

The combined interphase and intercircuit coupling as used between the stations A and B of the arrangement shownin Fig. 1 is of course possible only where two circuits extend between the sta# tions. However, the broad principles of the invention vinvolving the utilization of capacitive coupling plates in the bushings of circuit breakers and similar standard power apparatus at the stations are not limited to the use in double circuit sections of the line, but are likewise applicable to single circuit line sections. Such arrangement is shown in connection with the line section Q extending from station A of the system, where the coupling capacitor plates of the circuit breaker bushings, on the line-side as well as on the station-side, on phases 1 and 3 of circuit Q alone are connected to the two conductors 31 and 32 leading to the transmitting and receiving apparatus in a manner similar to the Way the equipment on the circuits M and N is connected interphase-intercircuit tothe communication apparatus.

In order to secure maximum transmission of the high frequency carrier currents it is important to prevent loss of high frequency power by way of the condenser formed by the coupling' cuit having a very high impedance at the carrierl frequency used, and te act as an anti-resonant element and cause substantially most of the carrier frequency current to flow into the line conductor over which communication is desired. In

accordance with our invention, we. so design or tune the inductance coils 34 connected to the'I conductors 31 and 32 leading from the coupling plates 23 as to make the impedance to the flow:

of carrier frequency currents to the ground relatively large, thus securing a high degree ofv cinciency of transmission and utilization of the. capacity coupling between the coupling plates 23 and the lead-in conductors 13 in the bushigs.

The anti-resonant coils 34 may also beV used' fcr drainage, or separate drainage coils may be provided.

Although practical limitations may sometimes prevent the securing of an extremely high antiresonant impedance, nevertheless it is possible to secure an impedance value suiiiciently high to' prevent the loss of excessive carrier frequency I power through the condenser formed by the coupling plates in the bushingand the grounded metal parts of the circuit breakers.

By combining suitable capacity and inductance elements with the capacity elements formed by the coupling plates 23 and the metal collars 20 or other grounded metal parts of the bushings or circuit breakers, electric' wave lters of the band and high-pass types are secured which wave lters are useful in controlling the frequency band of carrier frequency energy passing from the carri-er frequency transmitting apparatus to the power conductors and from the power conductors to the carrier frequency receiving apparatus. According to our invention, we employ the capacity elements formed by the coupling plates 23 and the metal collars 20 as part of .the capacity elements of such electric wave filters.

It is of course understood that the apparatus andthe system of our invention are provided with all the devices and Xtu'res usually entering into a power station, such as transformers, lightning arresters, disconnecting switches, metering equipment, etc., but we have omitted these devicesfrom the description of the exemplication of theinvention for the sake of clearness.

Instead of using the lead-in bushings of the circuit breakers at the power stations, the lead-in conductors of other pieces of apparatus used at the stations may be employed for establishing the coupling connections with thetransmission line, inaccordance with the principles of our invention, avoiding the installation of separate devices for coupling apparatus and the expense of and diiioulties incidental thereto.

v rInstead of using only the lead-in bushings on theA outgoing sides of the circuit breakers for coupling of the carrier current apparatus with the transmission lines, it is of advantage to use in addition the bushings on the bus-bar side of the circuit breakers for coupling with the carrier current apparatus. To this end, the conductors 31 and 32 leading from the coupling plates 23 oi the 'circuit breaker bushings as shown in Fig. 1 are extended and connected also to the coupling plates 23 on the bus-bar sides of the individual circuit breakers, thus connecting the coupling plates on both the outgoing and incoming sides of the breakers in parallel. The capacity coupling between the carrier frequency equipment and the lines is thus doubled, but this doubled capacity is fully eiective only when the circuit breakers are closed. Such arrangement is shown in connection with the circuit breakers AQ on the circuit Q outgoing from station A, and the circuit breakers BO, BP, on the outgoing circuits O and P of station B. As arule, where parallel circuits are used, at least one set of circuit vbreakers is closed at a time so that the advantage of the increased coupling between the high frequency carrier equipment and the transmission lines is made use of practically all the time. n

`Furthermore, as an alternative, the coupling plates of the bushings on the outgoing side of the breakers may be connected to a tuning unit and the coupling plates on the incoming side of the breakers may likewise be connected to a separate tuning unit.

The invention is not limited to the particular details of construction or arrangements or method of operation described for purposes of eX- emplication hereinabove, but is susceptible of many other embodiments which will suggest themselves to those skilled in the art. It is ac- 4 cordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

We claim:

1. Ina carrier current communication system for high voltage power transmission systems, a plurality ofremotely located power stations, a pair of polyphase power transmission circuits extending between said power stations, each circuit comprising a set of polyphase high voltage line conductors, power apparatus at said stations controlling the flow of high voltage power' through said line conductors, high voltage lead-in bushings on said apparatus for effecting connection of the operative parts of said apparatus to said high voltage line conductors, carrier frequency communication apparatus at the stations having two pole terminals, coupling condenser means in two bushings of one phase in the two circuits connected to one terminal of said communication apparatus, and'coupling condenser means in two bushings of another phase in the two circuits connected to the other terminal-of said communication apparatus to effect carrier frequency communication between said-stations over said phase conductors.

2. In a carrier current communication system for a high voltage power transmission system, a plurality of remotely located power stations, a pair of polyphase power circuits extending between said stations, each power circuit comprising a set of three-phase high voltage line conductors, means for supporting said line conductors in insulated relationship along each other, power apparatus at said stations, said power apparatus including circuit breaker units for the individual lines, each circuit breaker unit comprising high voltage lead-in bushings, said lead-in bushingsv having a high voltage lead-in conductor connected to the high voltage line and an insulating enclosure for maintaining said lead-in conductors in insulated condition, carrier frequency communication apparatus at said stations Yhaving two' lll-5 closures constituting condensers in conjunction with the lead-in conductors extending through the bushings, connections from the coupling members in two bushings of one phase in the two circuits to one terminal of said communication apparatus, and connections from the coupling members in two bushings of another phase inthe two circuits connected to the other terminal of said communication apparatus to effect carrier frequency communication between said stations over said phase conductors.

3. In a carrier current communication system for a high voltage power transmission system, a plurality of remotely located power stations, a pair of polyphase power circuits extending between said stations, each power circuit comprising a set of polyphase high voltage line conductors, means for supporting said line conductors in insulated relationship along each other, power apparatus at said stations, said power apparatus including circuit breaker units for the individual line conductors, each circuit breaker unit comprising a high voltage lead-in bushing on the lineside and a high voltage lead-in bushing on apparatus-side of the station, said lead-in bushings having a high voltage lead-in conductor connected to the high voltage line and an insulating enclosure for maintaining said lead-in conductors in insulated condition, carrier frequency apparatus at said stations having two pole terminals,

low potential within said bushing enclosures constituting condensers in conjunction with the leadin conductors extending through the bushings, connections from one terminal of said communication apparatus to the coupling members in the line-side and station-side bushings of two circuit breaker units of one phase in the two circuits, and connections from the other terminal of said communication apparatus to the coupling members in the line-side and station-side bushings of two circuit breakers of another phase in the two circuits to eiect carrier frequency communication between said stations over said phase conductors.

4. In a carrier current communication system for a high voltage power transmission system, two remotely located power stations, a power circuit section extending between said stations comprising a plurality of line conductors of different high voltages, means for supporting said line conductors in insulated relationship along each other, power apparatus at each station including a set of bus-bars of different voltages corresponding to said lines and circuit breaker units for connecting and disconnecting the individual line conductors to the corresponding bus-bar at the station, each circuit breaker unit having a high voltage lead-in bushing on the line-side and a high voltage lead-in bushing on the bus-bar side, carrier frequency communication apparatus at each of said two stations coupled at the opposite section ends to one of said line conductors acting as carrier conductor maintaining carrier communication between said two stations, and a pair of coupling condensers in the line and busbar bushings of the circuit breaker unit of said carrier line conductor at one of said stations coupling through said two bushing condenser paths in parallel one terminal of the carrier communication apparatus at said station to said carrier line conductor to carry thereover carrier frequency currents between the communication apparatus at said one station and said second station.

5. In a carrier current communication system for a high voltage power transmission system, two remotely located power stations, a power circuit section extending between said stations comprising a plurality of line conductors of diierent high voltages, means for supporting said line conductors in insulated relationship` along each other, power apparatus at each of said two stations controlling the flow of high voltage power through said line conductors, high voltage lead-in bushings for effecting connection of the ends of said line conductors to the operative parts of the associated apparatus, carrier frequency communication apparatus at each of said two stations coupled to opposite section end portions of two of said line conductors acting as parallel carrier conductors maintaining carrier communication between said two stations, and a coupling condenser in the lead-in bushing of each of said two carrier line conductors at one c1" said stations coupling each of said two carrier line conductors to one terminal of the carrier communication apparatus at said station to carry through the parallel bushing condenser paths of the two bushings at said station, and the two carrier line conductors leading to the second station carrier frequency currents between the communication apparatus of said two stations.

PHILIP SPORN. RAY H. WOLFORD.

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