US1204407A - Protective means for transmission-lines. - Google Patents

Description

G. J. D. CENTERWALL.

PROTECTIVE MEANS FOR TRANSMKSSION LINES.

APPLICATION FILED APR. 19, 1912.

1 04,407. Patented Nov. 14, 1916.

/ 5 5 8 5 F/ a 5 2 l/ 4 Hz; 6. F/q] WITNESSES: S E T m/ I W B 2 M ATTORNEY UNITED STATES PATENT OFFICE.

GEORGE J'. D. CENTERWALL, STOCKHOLM, SWEDEN.

PROTECTIVE MEANS FOR TRANSMISSION-LINES.

Application filed April 19, 1812. serial No. 691,846.

To all whom it may concern Be it known that I, GEORGE J. D. CENTER- WALL, a subject of the King of Sweden, and a resident of Stockholm, in Sweden, have invented a new and useful Improvement in Protective Means for Transmission-Lines, of which the following is a specification.

My invention relates to electrical systems of distribution and transmission and it has particular reference to protective devices for use in connection with high voltage transmission systems for the purpose of preventing excessive peak voltages, and line surges.

The object of my invention is to provide a system of the above-indicated character which shall be simple in arrangement, effective and reliable in operation and shall embody adequate means for preventing momentary excessive voltages and disturbances.

It is well known in the art that considerable energy is dissipated in silent electrical discharges, known as corona, which are effected at very high potentials, and also that high-potential disturbances may be prevented to some extent when a system is working at the so-called corona voltage.

Abnormal voltages and surges in hightension transmission systems usually result from electric charges, traveling along the line wires in about the same way as waves of sound in a tube, being reflected and damped in accordance with similar laws. Reflection of the electric waves takes place when the waves encounter devices containing inductance and capacity in other proportions than the line itself, but the damping of the waves can be eflected only as a result of dissipation or loss of energy.

The simplest way of dissipating energy from static Waves is through ohmic resistance. Such resistance cannot however be directly connected between the wires or to ground for the reason that, with such an arrangement, a considerable loss of energy would be sustained continually, even at normal voltage. Consequently, it is necessary to have a spark gap in series with the energ consuming resistance. It is impossible, however, to disconnect the damping resistance immediately when normal conditions are restored, as a power are will follow in the path of the original static discharge, which will be maintained for a period many times longer than thetime which it takes for the wave or discharge to pass. For this rea a heat capacity suflicient to. accommodate an amount of energy very much larger than that of the traveling waves or surges. Different apparatus, have been employed for the purpose of rupturing the current through the resistance at the critical moment after the static discharge has passed, among the most important devices of which is the electrolytic lightning arrester.

In my invention, therefore, I propose to utilize the corona discharges for dissipating the excessive energy in case of abnormal surges and voltage waves. Corona produces an ionization and splitting-up of the air molecules around the wires and is accompanied by a dissipation of energy in connection with chemical processes in the formation of ozone and nitric acid. Part of the energy is also directly converted into light and heat. It is evident, that this is an entirely different way of dissipating energy from the voltage waves and oscillations than by means of ohmic resistance.

A study of the laws of corona shows, that the energy loss starts at a predetermined voltage which depends only on the voltage gradient in the air surrounding the wires. This voltage can be regulated at will by changing the size or the distance between the line conductors. In some cases, systems working at very high voltage will, to some extent, protect themselves against surges, z'. c. the oscillations will be somewhat more damped than through the resistance of the line wires alone. In most cases, however, it will be necessary to make special arrangements, in order to carry off or dissipate the desired amount of energy in corona discharges.

It is my purpose, therefore, to provide means for causing the formation of corona at a predetermined voltage, whereby the desired results are accomplished, and I attain these ends by employing, either directly or indirectly, with the transmission circuits,

conductors of relatively small section or of peculiar shapes that are particularly conducive to the formation of corona. By suitably choosing the size of these small protecting conductors or the particular shapes thereof, it is evident'that the formation of corona maybe effected at any predetermined voltage, whereby energy is dissipated and excessive and dangerous surges are prevented.

son, it is necessary to, provide resistances. of" My invention may'best be understood by Specification of Letters Patent. P t t N 14, 191

reference to the accompanying drawings, in which Figure l is a diagrammatic view of a portion of a transmission system embodying my invention. Figs. 2, 3, 4 and 5 are views similar to Fig. .1, showing various modifications which embody my invention, and Figs. 6 and 7 are sectional views of conductors of peculiar shapes that are particularly conducive to the formation of corona.

Referring to Fig. 1 of the drawings, a plurality of substations 1 and 2, or the like, are connected by a transmission line 3 which is here shown, for convenience, as a single conductor but which may comprise several conductors, as is the usual practice. At varying intervals, protecting conductors 4 are inserted in series with the transmission circuit 3, for the purpose of facilitating the formation of corona and thus preventing excessive voltages. These protecting conductors 4 may be of relatively small section in comparison with that of the conductor which constitutes the transmission line 3 or may be of one of the shapes shown in Figs. 6 and 7, or mayhave other suitable shapes that are peculiarly conducive to the production of corona.

At the right-hand end of the transmission circuit 3, a plurality of protecting conductors 4 are shown as being connected in multiple in order that the resistance of the transmission line may not be increased.

If the material of which the transmission line is composed is aluminum, a single protecting conductor of copper may be included in series therewith without increasing the normal resistance of the line, by reason of the greater conductivity of the copper conductor. Also. in some cases, in order to suppress rapid electrical changes, iron wire, or wire covered with iron or nickel may be employed.

In the operation of the system, if the voltage rises above the particular value for which the protecting wires 4 are designed, it is evident that the formation of corona is effected thereon which serves to prevent any surges or momentary line disturbances.

In Fig. 2, the transmission line 3, which connects the several stations 1 and 2. is provided with a protecting wire 4 similar to that hereinbefore described, said wire being connected in parallel wit-h a portion of the transmission line.

In Fig. 3, the stations 1 and 2 are connected by the transmission line 3 which includes a choke coil 5 in accordance with usual practice. A protecting wire 4 is connected to the transmission line 3 at one end and an auxiliary wire 6 is disposed in proximity thereto and is connected in series with resistance 7 to ground. By reason of this and by properly choosing the distance between conductors 4 and 6, as well as the value of the resistance 7, it is possible to cause the formation of corona at any predetermined voltage.

Another form of protective means embodying my invention is shown at the lefthand end of the transmission line 3 which comprises a plurality of protective conductors 4 which are segregated, one from the other, by means of suitable spark gaps 8, and which are decreased in section progressively from the extreme left protecting conductor 4 which is connected to the transmission circuit 3. Vith this arrangement of circuits, the various protecting conductors 4 are successively brought into circuit in accordance with line conditions, whereby a considerable amount of energy may be dissipated. Hence, this arrangement is of great protective value.

- Referring to Fig. 4, the transmission circuit 3, which connects the stations 1 and 2, is provided with a protecting wire 4 at one end thereof and, in connection with the wire 4 is an oscillation circuit 9 which includes a condenser 10, an inductance 11 and a spark gap 8, said oscillation circuit being grounded through a suitable resistance 7. By means of this arrangement, the formation of corona upon the protecting conductor 4 mav be greatly facilitated by effecting changes or distortions of the alternating current waves by means of discharges across the spark gap 8. This result is accomplished by suitable adjustments of the condenser 10 and the inductance 11 whereby resonant conditions are obtained. Discharges across the spark gap 8 are effected which correspond to the peak of each high-voltage wave, and this action tends to permit the voltage of the oscillation circuit to build up to a high value, at which corona is formed, which serves to protect the system from excessive surges or line disturbances.

Referring to Fi 5, the stations 1 and 2 are connected by a transmission line 3 of low or moderate potential which is much less than that at which corona is formed.

In order to perform the function of a protective device, in connect-ion with a sys tem of comparatively low voltage, the protective wire 4 may be associated with the transmission line 3 through a transformer 12, the windings 13 and 14 of which are adapted to step up the normal voltage of the system to a high voltage, which is increased sufficiently to produce corona discharges upon the conductor 4 in case excessive conditions obtain upon the transmission circuit.

For illustrative purposes, I have shown and described several particular arrangements of circuits embodying my invention, but it will be understood that various modifications may be effected therein without departing from the spirit and scope of my invention, and I intend to cover such variations in the appended claims.

I claim as my invention:

1. In an electrical power-transmission system, the combination with a line-conductor that is not conducive to the formation of corona thereupon under operating voltages and which is subject to abnormal highpotential disturbances, of means influenced by the potentials obtaining on said line-conductor for dissipating, through the formation of corona, the excess energy only that results from the abnormal disturbances.

2. In an electrical power-transmissi on system, the combination with a line-conductor which is so formed as to be non-conducive to the formation of corona under operating conditions and is subject to abnormal highpotential disturbances, of means influenced by the potentials impressed on said lineconductor for dissipating energy, through the formation of corona, only during the time that the abnormal disturbances maintain the potential of said line-conduc tor substantially above its working potential.

3. In an electrical power-transmission system, the combination with a line-conductor that is not conducive to the formation of corona discharges under operating conditions and that is subject to transient highvoltage disturbances, of means associated with said line conductor and comprising a protecting conductor that is under the influence of the abnormal potentials obtaining on the line-conductor and is effectively insulated from ground for damping said disturbances by generating corona discharges.

4. In an electrical power-transmission system, the combination with a line-conductor of relatively large cross-sectional area which is non-conducive to the formation of corona discharges thereupon under operating conditions, of a protective conductor from which discharges to ground are precluded and which is conducive to the formation of corona discharges when subjected to potentials above a predetermined value and which is influenced'by the potentials obtaining upon the line conductor for dissipating through corona discharges the energy of high-potential disturbances only that may be impressed on said line-conductor.

5. In an electrical power-transmission system, the combination with a line conductor which is not conducive to the formation of corona discharges under operating conditions and is subject to electrical disturbances, of a second conductor which is conducive to the formation of corona discharges when subjected to potentials above a predetermined value that is below the value at which corona discharges will emanate from said line conductor, said second conductor being influenced by the potentials obtaining on said line conductor, whereby the line conductor may be relieved, through the corona discharges emanating from said second conductor, of only the excess energy resulting from the high-potential disturbances.

6. In an electrical power-transmission sys- V tem, the combination with a line conductor which is not conducive to the formation of corona discharges under operating conditions and'is subject to electrical disturbances, of at least one conductor of relatively small cross-sectional area which is conducive to the formation of corona discharges when subjected to voltages above a predetermined value that is below the value at which corona may form on said line conductor, said sec ond conductor being influenced by the potentials obtaining on said line conductor in order to relieve the line conductor of the i excess energy resulting from the disturbances impressed thereupon through corona discharges emanating from said second conductor.

7. The method of protecting an electrical transmission system which consists in discharging therefrom the eXcess energy resulting from abnormal disturbances that may be impressed upon the system by the production of corona emanations in a portion of the system only when the voltage of the system is raised above a predetermined value.

8. The method of protecting an electrical transmission system, the conductors of which are not conducive to the formation of corona emanations under operating voltages, which consists in discharging from' the system only the excess energy that results from abnormal disturbances occurring in the system by the production of corona GEORGE J. D. CENTERVVALL.

W'itnessesz' DRETA PRIM, FREDR. NORDSJO.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents,

Washington, I). C. a I

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