US1881574A - System for preventing interference between power wires and communication wires - Google Patents

Description

Oct. -1-1, 1932-.-

' A. HERZ SYSTEI FOR PREVENTING INTERFERENCE BETWEEN POWER WIRES AND'COXHUNICATION WIRES Filed Sept. 4, 1931 3 Sheets-Sheet 1 I my;

Oct. 11, 1932 V v A. HERZ 1,881,574

, SYSTEM FOR PREVENTING INTERFERENCE BETWEEN rowan WIRES AND COMMUNICATION WIRES Filed Sept. 4, 1931 3 Sheets-Sheet 2 0a. 11. 1932; v A, HE 1,881,574

'SYSTBI FOR PREVENTING INTERFERENCE BETWEEN POWER WIRES AND COMMUNICATION WIRES Filed Sept. 4, 1931 3 Sh'OtS-Sh66 t 5 Patented Oct. 11-,- .1932

UNITED STATES PATENT-OFFICE ALFRED HERZ, OF CHICAGO, ILLINOIS SYSTEM FORQPREVENTING INTERFERENCE BETWEEN POWER WIRES AND COMMUNICATION WIRES Application filed September 4, 1931. Serial No. 561,170:

My invention relates .to system and method of preventing interference between power conducting Wires and communication wires and the like. The present application 1s an 5 improvement upon my prior Patent No. 1,782,875, of November 25, 1Q30, and also upon my copending application, Ser. No. 382,025, 'of July 29, 1929.

When a modern power transmission line is built some consideration is given to'adjacent communication circuits already in existence by coordinatin the configuration and arrangement of the power line wires so that a minimum inductive influence is felt by the communication circuits while normal operating conditions exist on the power system. This minimizing of inductive influence is brought about by transposing the power wires at certain pre-determined points so that the influence exerted by the individual power wires has substantially equal effect on the wires of given communication circuits. Assuming the separation of the two lines to be strictly equal throughout the exposure, each of the power'line wires is caused to occupy a given position on the pole or tower line for one third of the total length of exposure. Naturally if the exposure is not strictly a physical parallel, as, indicated above, but so there is some variation in separation between the two systems, this can be compensated for, at least to some extent, by varying the length of the sides of the transposition barrel, this latter-being the recognized term which covers the equivalent of the three transpositions, in the ease .of a three phase power line, necessary to bring a given Wire back to the nominal location originally occupied by it. Thus, outside of slight unbalances due to variation in fl 40 height, sag, etc., a theoretical cancellation of the influence is obtained. The slight remnant is further reduced in the case of metallic telephone, circuits by a frequent transposition of the pairs constituting the latter system.

The above, as indicated before, relates to normal operating conditions of the power system. In case of abnormals, and most especially in the case of a short circuit to ground, the three phase field is so badly distorted that it usually essentially becomes a single phase field, the wire or wires in trouble constituting one side of a loop and the return path being under the surface of the earth, the plane of the return path often ex- 5; tending one or more thousands of feet under ground. Then the aforementioned coordination, i. e., transpositions, do not to any material extent mitigate influences felt by the communication wires. It is under this latter condition that the screen Wires are effective, since a counterflux' is generated by these which to a great extent cancels the single phase flux liberated by the fault current and its return through the earth.

Returning to the normal operating condition of the power system, the benefits derived from transpositions of the power conductors are based entirely on the principles of an uninfluenced three phase field spaced 120 electrical degrees apart andof equal magnitude. If a wire such as a screen wire is placed comparatively physically close to these power wires and'if this screen Wire in turn is grounded at more places than one, which is essential in order to make it perform as a screen wire, a current will be induced in it the same as a current is induced in the short circuited secondary of a transformer unless the screen wire is located in such a position that it is equally influenced b the field of all three of the power wires. TlllS condition is practically impossible with a line configuration which works out best for structural and economical reasons. Therefore a single wire can only occupy a position where the influence is unequal and therefore, as mentioned before, a current will be caused to ow. I have conceived the possibility that this contradictory condition, that is, where a screen wire offers both mitigating and harmful effect, can be alleviated if another harmful effect of equal magnitude but of opposite phase is caused to make its appearance. I propose, in brief, to employ two screen wires so arranged as to oppose the harmful influence of each other while gaining the beneficial effects of both.

e individual wires of the pair are so locatedthat the small voltage induced, when no the line is operating normally, in one screen wire, is compensated for by anequal voltage but in opposite phase in the other screen wire, these two being either transposed, and thus having the total effect nullified, or else not transposed andallowing the circulating current to flow between these two screen wires via the circuits between the wires at these grounding points. Thus, although the circulating current does flow it has no effect on a neighboring communication wire as long as the circulating current stays in the small loop consisting of these two screen wires. If, however, these two screen wires are not balanced by being in opposite phase, the circulating current will flow through the ground connection and through the earth, thus creating a large loop which does affect neighboring communication wires.

In accordance with the present invention I provide, also, a particular disposition of the shielding conductors with respect to the power conductors, so as to gain the-maximum neutralizing effect. That is to say, with the two conductors of the shielding system of my present invention, it is possible to dispose the shielding system in a more advantageous manner than where a single conductor is employed for that purpose. Also it is possible, according to my present invention, to employ a single pair of shielding conductors constituting the anti-induction system for two adjacent power lines upon the same transmission tower or other common support, all without appreciable change from the usual location of the power conductors.

Now, in order to acquaint those skilled in the artwith the manner of constructing and operating the system "embodying my invention and practicing my method, I shall describe, in conjunction with the accompanying drawings, a specific embodiment of the invention.

. In these drawings:

Figure 1 shows the shielding conductors as applied to a high voltage power line;

Figure 2 illustrates a shielding conductor applied to a communication system which extends parallel to the power system shown in Figure 1; the communication line of Figure 2 parallels the power line of Figure 1, as indicated in Figures3 and 4;

Figure 3 is a diagrammatic circuit representation showing a communication line which parallels a power line, and also the shielding conductors provided in-connection with these lines, the grounding points thereof, and the manner of transposition of certain shield conductors relative to the power conductors;

Figure 4 represents another diagrammatic circuit in which grounded shield conductors are shown to be arranged in sections and transposed with regard to the conductors of the power line; and

ssn574 Figure 5 shows a cross sectional view of a;

Referring now to Figure 1, this figure shows, somewhat, diagrammatically, one -tower of a high tension transmission system wherein the conductors are disposed in substantially the arrangementshown in Figure 5. Mounted on the tower 1 are the cross-arms 2, 3 and 1, all of the usual trussed or any preferred construction. The high voltage power conductors 5, 6, 7, and 8, 9, 10 of two feeders are suspended from the cross-arms in the usual or any preferred manner by means of high voltage suspension insulators 11, 12, 13 and 14, 15, 16, respectively. An electrostatic shield conductor 17 extends parallel to the power wires. This conductor is optional, so far as my present claimed invention is concerned. .In Figure 5 I show two such conductors, 17A and 17B.

This conductor 17 may be grounded at each of the supporting towers by a direct connection. It is provided for maintaining a ground potential above the power conductors. The grounding of this conductor 17, assuming the same to be continuous, would be in effect the same as an electrostatic shielding conductor, in that it is grounded by low resistance ground connections at numerous points along its length. Preferably I place an insulator 110 or resistance such as shown at 111, which may be of carborundum, thyrite or the like, in each section of the grounded conductor 17 between adjacent ground points and thereby prevent or limit the longitudinal flow of current but provide low resistance paths to ground. This eliminates or limits the objectionable effect upon the communication line of induced current flowing in this conductor but preserves the function of con ductor 17 as an electrostatic shield. The manner in which I separate this conductor in sections by means of interposing insulators or resistances at certain points is indicated in Figure 3.

The sections into which the electrostatic shield wire is dividedare to be either entirely insulated from each other or else connected with each other through such a high resistance that the current caused to flow by induction is reduced so that its effect upon neighboring communication or signal wires is negligible.

Referring again to Figure 1, it will-be seen that I have provided two anti-induction shielding conductors 18 and 19 in proximity to both feeders of the power line. The communication system to be protected by these shield wires is shown somewhat diagrammatically and on an enlarged scale in Fi ure 2.

In Figure 5 the relation between the power line and the communication line is indicated substantially to scale. Thepower linecomprises the two feeders, 5, 6, 7, supported atila'rly, the vertical sag of the phase conductor B'is indicated at 68 and similarly the vertical sag of the conductor"? is indicated at 78.

In addition to this, the conductor in each span, when thus permitted to sag verticall may swing sidewise through an angle indicated in conjunction with the insulator string 13 and conductor 7. While the swing is indicated only to the right of the neutral or vertical position it is understood that the swing may be as great to the left, or in a clockwise direction. Interference with the power does not occur because the sag occurs between towers and the extent of angular motion indicated will bring the conductor 7 at the tower only so close as the length of theinsulator string 13, as a radius, permits.

In the layout shown in Figure 5 the angle A is 45.

The dimension B between the nearest communication conductor and the swing of the nearest power conductor 7 is approximately 12 6". The other general dimensions have been indicated on Figure 5-to show the general proportions of a specific embodiment.

It will be observed that the three phase conductors of each feeder are disposed at the corners of a flat triangle on each side of the tower 1. The two conductors 18-19 which form the sides ofv an anti-induction loop are so disposed relative to the power conductors that they have substantially equal effect upon the two feeders, and also each anti-induction conductor 18 or 19 has substantially the same effect upon each line that the other has.

These two conductors 18 and 19 form a vertical loop which may be transposed as shown in Figures 3 and 4 or which need not be transposed under certain conditions, forming in effect a vertical ribbon conductor extending through a plane which is substantially equally effective upon both feeders. If an actual metallic ribbon were so disposed, only the upper and lower edges would, in fact, have much effect and therefore two spaced conductors such as 18 and 19 are substantially the equivalent of a vertical ribbon of metal. The two conductors 18 and 19 area as 113, which may be employed under certain circumstances to assist in limiting circulating currents.

I prefer to prevent circulating current occurring through ground and the two antiinduction shield wires such as 18 and 19, by transposing the said anti-induction shield wires between grounding points with very low resistance in the ground connections.

The residual field which might affect the two anti-induction shielding wires 18 and 19 within the length of power line between transpositions would induce voltages which would tend to set up current fiow in one conductor such as 18 in one direction, and in the other conductor such as 19, in the op posite direction, with the result that a circulating current would tend to flow. However, if within the length between transpositions of the power wire the two conductors 18 and 19 which are connected together at the transposition points of the power wire by ground connections are themselves providedwith a transposition connection, the two voltages oppose each other and substantially eliminate circulating current but at the same time provide a highly conductive path for ground return current in case of a single phase to ground fault.

Thus maximum usefulness of both conductors in parallel for ground return current, and the two conductors in opposition to each other for eliminating circulating current due to residual field, under normal conditions, is secured. Y

The communication line shown in Figure 2 parallels the power system shown in Fi ure 1 for a greater or lesser distance, depen ing upon the installation. The communication line may comprise pairs of conductors such as 20, 21, and 22, 23, for full metallic circuits. These conductorsare shown to be supported upon insulators 23, 25, 26 and 27, respectively, which may be mounted on the cross-arm 28. .Several such cross-arms carrying insulators and communication wires supported thereby may be mounted on the customary pole structure indicated diagrammatically at 29.

An insulator 30 is mounted on the pole 29 for supporting the shielding or screen wire 31. This shielding wire is a conductor of low resistance which extends parallel to the communication conductors and is grounded carefully at a number of points along its length, i. e., at the poles, for example, in a manner as is indicated at 32.

If it is desired to achieve only an electromagnetic shielding effect, this conductor 31 may be mounted on any convenient insulator, preferably centrally of the insulators. which support the communication wires. Its particular location relative to the service wires does not seem to matter materially. It will have a mitigating efiect upon the ele ch'omlgnetic fields. However, when the shield ill ' determined bylocal conditions.

wire. 31 is placed above the service wires, for example in the manner in which it is shown in Figure 2, its eflect will be to shield the communication system electrostatically as well as electromagnetically. It will re-- tain its mitigating eflect upon the electromagnetic fields, and it will at the same time render an a preciable efiect in screening the communication line from electrostatic interference.

Reference may now be had-to Figure 3 which shows a power system, a communication system extending in parallel thereto, and the shield conductors for eliminating the detrimental efi'ects of the first system upon the second system, as provided in accordance with my present invention. I

The conductors 83, 34, 35 of the power line are transposed at a number of points designated by the numerals. 36 to 42, inclusive. The distance between transposition points is The three conductors are in effect twisted about each other for a complete turn and then twisted back again a complete turn, etc. The length of power line between which the conductors are thus twisted for a complete turn is called a barrel. The length between the points 43 and 43 as shown in Figure 3 represents such a barrel, or, rather to say, these points are the uncture points between adjacent barrels of the power line. The transposition is omitted at these points because they are, in effect, the equivalent of transposition points because of the reversal of twisting. In each I barrel the three power conductors occupy the successive positions for substantially equal lengths, hence, other factors being equal, the inductive effect upon adjacent communication lines, insofar as the power cycle hum is concerned, and if spaced a substantial distance from each other, is substantially neutralized. The barrels may be of different length as conditions require.

Two conductors of a communication system are indicated in Figure 3 by the numerals 44 and 4 5. A shielding conductor 46 is shown adjacent the communication line. This conductor may be grounded at each of the transposition points of the power line and at points which are the electrical equivalent of the transposition points, such as the node points 43 and 4 3.- These grounding connections are indicated at 47 to 55, inclusive. The shielding wire 46 may correspond to the shielding wire 31 shown in Figure 2. -When disposed over the'communication line it will mitigate not only the electromagnetic forces acting upon the communication line, but it will also act as an electrostatic shield, as previously explained.

A low resistance path in each loop of this shielding wire is highly desirable and if good ground connections are not available it is advisable to resort to a metallic return wire connected to the foot of the tape 47 to 55, which Ihave shown in Fig. 3.

In order to maintain a ground potential at or above the power line, I employ one or more sectionalized shielding wires such as 17 in Fig. lor 17A17B in Fig. 5, the different sections being indicated at 56 to 68, inclusive. The various sections may be conductively sectionalized by means of insulators 110 or resistances 111 at points between the towers supporting the power line. Each section is connected by a low resistance connection to ground as shown. a

, This sectionalized conductor performs the function of an electrostatic shield. Due to the insulators 110 placed between the sections the flow of current is prevented between adjacent grounding points, and objectionable effects of current flow in this conductor are avoided while the electrostatic shielding function is fully preserved. Instead of a sectionalized conductor as described, individual sections of conductors may be provided if desired. It is, in some cases, not necessary to employ insulators 110, as resistances 111, which limit the longitudinal flow of current along the electrostatic conductor, are sufficient. The object in each case is to provide free paths for the sections to ground, but to limit or even prevent theflow of induced current longitudinally of the electrostatic shield wire. WVith either insulators 110 or resistances 111, impulse voltages may travel to adjacent sections and thence to ground.

The two anti-induction shielding wires such as 1819 may be conductively continuous conductors such as indicated in Figure 3 by the numerals 69 and 70. The relative location of these conductors with respect to the power conductors is apparent from Figures 1 and 5 and also from the diagram Figure 3. The manner in which these shielding conductors may be placed on the supporting towers of the power line may be varied. They maybe insulated from the tower and grounded by separate ground taps or they may rest directly upon the metallic parts of the tower and be grounded therethrough.

It will be first assumed for the sake of explanation that these wires are two separate conductors mounted on the towers of a power line, and that they are grounded at various points, for example, substantially at the points of transposition ofthe power line. It is further assumed that these conductors are continuous and that they are disposed sub stantially in parallel to each other and to the power line, including substantially the same sag, without any transposition relative to one another. If this condition is assumed to be the case .it will be understood that voltage induced in either one of these wires will shield wires and a loop formed by them is concerned, and this force will set up circulating currents in the shield wires. The effect of the circulating currents preferably should be neutralized in such a case where two shieldin" conductors are em *cd. If

a: l l

the resultant voltage of the two induced volages is permitted .to make the relatively 'large loop formed by flowing to and through ground, the disturbance upon the communication wire might be worse than if they were absent. This may be prevented by inserting enough resistance in the ground taps to limit the current flow or the two wires may be of low resistance. They are of a conductivity substantially equal to the phase conductors. The conductors are grounded at or near the points of transposition of the power line as shown in the diagram, whereby the phase of the E. M. F. on the shielding conductors is more closely adapted to the phase of the residual inducti'ng magnetomotive force of the particular section. The cross-connecting grounding connections for the shielding wires are indicated by reference numerals 72 to 78, inclusive. The shielding wires are twisted or transposed approximately midway between the grounding points, or at such-a point as will secure the desired opposition of the induced electromotive forces. The voltage induced in each half of a loop of these shielding conductors will thus be opposed and thereby cancelled by the voltage in opposition in the other half. Thus the anti-induction shield wires do not normally carry current. This means that they do not tend to cause loss from the maintenance therein of a current flow, the power for which would have to be supplied by the transmission line. However, in case of ab-- normal conditions such as a fault to ground, the two conductors 6970 form parallel paths for the return current.

In Figure 4 I have shown another embodiment of realizing the prevention of circulating current effects in the loops of the two shieldin conductors employed in conjunction wit a power line.

Numerals 79 and 80 in Figure 4 designate a communication line. A. shielding conductor 81, grounded at points 82 to 87, inclusive, may be provided for protecting this communication line against electromagnetic effects ofthe adjacent power line. If this conductor 81 is placed over or on approximately the same line as the communication lines, as previously explained, it will also act cross-connecting I as an electrostatic shield for the communication wires. The grounding points of this shield wire may substantially correspond to the transposition points of the power wires and to node points thereof, respectively, as illustrated.

The power line shown in Figure 4 comprises the conductors 89, and 91. These power conductors may be suitably transposed in accordance with the local conditions as previously outlined. One barrel of the power line is formed between the points 92 and 93.

I employ sectionalized or conductively discontinuous shield conductors in this embodiment. These shield conductors are indicated at 92'93', 9495, 9697 and 9899. They are cross-connected and grounded by means of the connections 100101, 102-103, l 04.-105 and 106107, and are transposed intermediate of the grounded cross-connections as shown, in order to neutralize the efl'ect of circulating currents which will be induced in the loops of the shielding wires. It is understood, of course, that the cross-connections and the grounding wires may be separate in this embodiment, as well as in the embodiment previously discussed with reference to Figure 3.

The function of the above described arrangement shown in Figure 4 is, in efi'ect, substantially the same as the function of the previously explained arrangement represented diagrammatically in Figure 3. Voltage will be induced in each half of the loops of the grounded shielding wires and the effect of the voltage induced in one half will be cancelled or neutralized by the effect of the voltage induced in the other half due to the transposition of the shielding wires.

The terms employed in the foregoing specification and also in the appended claims are intended to cover broadly the subject to which they refer. 'For example, as has been mentioned elsewhere in this s ecification, the

terms communication and signalling are 7" used to include telegraph, telephone, and all other systems in which equipment is actuated over lines by relatively weak currents either over full metallic circuits or by the use of ground return. Systems of this or of broadly similar character, including'systems operating phantom or superimposed circuits are understood to be also covered by these terms.

shown and discussed. What I consider new and distinguishing over prior inventions is particularly defined in the following claims:

I claim as my invention: 1. In an electric system wherein a power transmission system and a communication system parallel one another, means for preventing the induction of excessive'voltages in the communication lines due to curre t flowing in the power line, said means comprising shielding conductors disposed substantially parallel to and in the vicinity of the power line, said shielding conductors being intermittently grounded and transposed intermediate of the grounding points thereof. 2. In an electric system wherein a power transmission line and a communication line are disposed substantially in parallel to one another, a plurality of shielding conductors for preventing the induction of excessive voltages in said communication line, means for groundin saidshielding conductors at predetermined points, said shielding conductors being transposed intermediate of said grounding points for neutralizing the effect of currents circulating therethrough.

3. In an electric system wherein a power transmission line and a' communication line are disposed substantially in parallel to one another, a plurality of shielding conductors extending in the vicinity of said power line and substantially parallel thereto for reducing the effect of magnetic fields of said power line upon said communication line, means for cross-connecting and for grounding said shielding conductors at predetermined points, and means for neutralizing the electromagnetic effect of currents induced in said shielding conductors shielding conductors and circulating therethroug N 4. In an electric system wherein a power transmission line and a communication line are disposed substantially in parallel to one another, the condutitors of said power transmission line being transposed at predetermined points, means for reducing the effects of electromagnetic and electrostatic forces of said power transmission line relative to said communication line said means including a plurality of shielding conductors disposed in the vicinity of said power transmission line and substantially arallel thereto, said eing transposed at predetermined points, the points of transposition of said shielding conductors being intermediate of the points of transposition of said power transmission conductors, and means for'connecting said shielding conductors intermediate of the points of transposition thereof. 7 y

5. In an electric system wherein a power transmission line and a communication line are disposed substantially in parallel to one another, the conductors of said power line being transposed at predetermined points, means for reducing the effects of electromagnetic and electrostatic forces of said power line relative to said communication line, said means including a plurality of shielding conductors disposed in the vicinity of said power line and substantially parallel thereto, said shielding conductors being transposed at predetermined points, the points of trans position of said shielding conductors being intermediate the points of transposition of said power conductors, means for cross-connecting said shielding conductors intermediate of the points of transposition thereof, and means for grounding the points of crossconnection ofsaidshielding conductors, the grounding points of said shielding conductors being disposed substantiall coincident with the transposition points 0 said power conductors.

6. In combination witha power transmission line, means for reducing the inductive a' effect of said line relative to a communication line disposed substantially parallel thereto, said means including a plurality of shielding conductors transposed at a plurality of predetermined oints', and means for interconnecting and or grounding said shielding conductors lntermediate of said transposition points thereof.

7 In an electrlcsystem comprising a power transmission line and a communication line disposed substantially in parallel to said power line, the conductors of said power line being transposed at predetermlned po1nts, means for shielding said communication line against the efiect of electromagnetic and electrostatic fields created by the currents flowing in the conductors of said power l1ne, said means comprising a shielding conductor disposed over said communication 11ne, grounding connections for said conductor substantially coincident with the points of transposition of said power line, two shielding conductors disposed substantially parallel with said power line, said shielding conductors being' -transposed at predetermined points intermediate of the points of transposition of said power line, means for crossconnecting said shielding conductors intermediate of the points of transposition thereof, means for grounding said shielding conductors substantiallv coincident with the. transpositions of said power conductors an electrically discontinuous shielding con uctor disposed over said powerconductors, and ground connections for the sections of said discontinuous shielding conductor for maintaining a ground potential over said power conductors. I

8. In combination with an overhead power line, a conductor disposed above and parallel to said line, said conductor comprising a number of sections insulated from one another and connected mechanically end to end, each section being directly grounded to maintain each section normally at ground potential, a pair of conductively continuous shielding conductors disposed substantially parallel -to said line, said shielding conductors being transposed at predetermined points, means for cross-connecting said shielding conductors intermediate of said points of transposition thereof, and means for grounding said points of cross-connection of said shielding conductors.

9. A system of the class described, com? prising an alternating current transmission line having conductors, said conductors being transposed, a communication line having conductors influenced electromagnetically and electrostatically by said transmission line, a plurality of shielding wires adjacent said power conductors, said shieldin wires being transposed, and a shielding wlre disposed above said communication line, said shielding wires having ground connections atintervals corresponding substantially to the points of transposition of said transmission me. I

10. In combination with a power line and an adjacent communication line, an electrostatic shield wire comprising a plurality of sections, said sections being provided with individual low resistance ground connections and the sections being joined by connections of such high resistance as to reduce the current flow caused by voltage induced by the normal flow of power on the power line to a negligible value, said resistance providing a relatively free path for impulse voltages.

In witness whereof, I hereunto subscribe I my name this 2nd day of September, 1931.

ALFRED

Images