US1171936A - Means for preventing corona losses. - Google Patents

Description

G. FACCIOLI- MEANS FOR PREVENTING CORONA LOSSES. APPLICATION FILED APII.2I, 191].

1,171,936. Patented Feb. 15, 1916.

2 SHEETSSHEET I.

Witnesses: Inventor g Giuseppe FaccioH, 524- fl y WM His )Tttorney.

G. FACCIOLI. MEANS FOR PREVENTING CORONA LOSSES. APPLICATION FILED APR, 27, I9II.

2 SHEETS-SHEET 2.

1. i f Wfl/ //7////i Inventor":

Giuseppe Faccsoh;

' His fittorneg Iatuted Feb. 15, 1916.

UNITED STATES PATENT OFFICE.

GIUSEPPE FACCIOLI, OF PITTSFIELD, MASSACHUSETTS, ASSIG-NOR TO GENERAL ELECTRIC COMPANY, A CORPORATION" OF NEW YORK.

MEANS FOR PREVENTING CORONA LOSSES.

Specification 0: Letters Patent.

' Patented Feb. 15, 1916.

Application filed April 27, 1911. Serial No. 623,630.

To all whom it may concern Be it known that I, Grosnrrn FACCIOLI, a subject of the King of Italy, residing at Pittsfield, county of Berkshire, State of Massachusetts, have invented certain new and useful Improvements in Means for Preventing Corona Losses, of which the following is a specification My invention relates to the prerention and to the reduction of the corona losses which appear when high potential is applied to electrical conductors and electrical apparatus of the type heretofore commonly used. The corona or luminous discharge from the conductor or apparatus into the air represents considerable loss of energy and also facilitates short circuits and discharges from the conductor to ground.

Ordinary insulating materials break down and become conducting if subjected to high enough voltage and if the voltage between a wire of the transmission line, for example, and either the other wire or the ground is gradually increased, it ultimately passes beyond the point where the air is insulating, whereupon corona is produced because the air surrounding the wire breaks down and becomes a conductor. The conducting air envelop surrounding the wire is in turn surrounded by non-conducting air, but as the voltage gradually increases still further, the area of broken down or conducting air surrounding the wire spreads farther and farther from the wire, thereby enlarging the luminous zone of corona until this area spreads to such an ext-e t that it merges with the corresponding area surrounding the other wire, or else touches a ground, and current can flow from the Wire th ough the conducting air to the other wire or to ground.

For any given size wire there is a certain critical voltage at which th ir around the breaks down and lunain sity begins.

- nous.

1 'Il 1 i there is practically id critical perfect darkness until the Wire begins to be luminous. It is found that the point between where the wire is perfectly dark and where it is luminescent can be measured within the fraction of one per cent.

Within the limits of the sizes ofwire ordinarily used in the construction of electrical apparatus and of transmission lines, the critical voltage of a small wire is lower than that of a large wire. In some kinds of apparatus, and particularly on a long transmission line, the corona losses on very high voltage conductors will be prohibitive unless the conductors are made much larger than would be necessary if their size were determined merely by the mechanical strength required or by the cross section of metal necessary to carry the current most economically.

The phenomenon of corona may also be considered with reference to the electrostatic field which surrounds a wire carrying current. When current is flowing the wire is surrounded by a magnetic field which may be represented by lines of force in the form of circles around the wire, while at the same time the voltage produces in the surrounding air a condition of electrostatic stress which may be represented by lines of eleo trostatic force issuing from the wire and perpendicular to its surface.

The density of the lines of electrostatic force will be proportional to the voltage gradient or the voltage per centimeter length of the electrostatic circuit, and if the number of lines of electrostatic force per inch in air rises beyond a certain,critical value the air ceases to be an insulator and becomes conductive, whereupon corona appears. At the critical voltage the density of the lines of electrostatic stress reaches thecritical value which is necessary to cause the air to break down.

The obiect of invention prevent all or practically all of the corona, losses which occur on the'conductors and in the loo electrical apparatus ordinarily used when high potential is applied c a conducto of which the 'han its actual uch higher potentials n nout 'oducing corona tn to cono store of the same current capacity and constructed in the orin a wall so that the conductor is brought titl tttl

dinary manner; to provide a construction by means of which conductors adjacent to ground, such as conductors passing through entrance bushings and walls, or passing near the metal towers of a transmission line, may be subjected to much higher potentials without danger of a breakdown to ground than is the case with conductors constructed in accordance with the practice heretofore followed; 'to provide means to eliminate the corona losses which occur at the point where a conductor passes from one insulating medium into another; and in general to provide conductors and apparatus of which the critical voltage is much higher than the critical voltage of the conductors and apparatus generally used heretofore.

My invention will best be understood in connection with the accompanying drawings, in which merely for purposes of illustration I have shown some of the various forms in which my invention may be embodied and in which Figure l is a conductor provided with disks or projections for the purpose of increasing the virtual diameter of the con ductor; Fig. 2 is a conductor made in the form of a "network with the longitudinal current conducting elements tied together by metallic or conducting cross pieces; Fig. 3is a form of the conductor shown in Fig. 2 but modified to prevent the appearance of corona at the edges of the conductor; Fig. 4 is a form of my invention as applied to a conductor passing through an opening close to ground; Figs. 5 and 6 show one form of my invention as applied to a conductor adjacent a grounded support or tower by which the conductor is supported; 1F ig. 7 is one form of an embodiment of m invention as applied to a conductor whic forms a terminal of an electrical device and passes from the air into an insulating medium, as porcelain, of which the characteristics differ from those of air; and Fig. 8 is a diagrammatic view illustrating one way of considering the electrostatic stresses present when a conductor passes from one insulating medium into another.

In the particular embodiment of my invention illustrated in Fig. l, the cylindrical conducting element or rod 1, such as is generally used as a. conductor of electricity, is

' so shaped by means of the cylindrical disks or enlargements 2 that the virtual diameter oi the rod 1 is substantially increased at high potential, so that when high potential is applied to the "rod it acts as though I its diameter were considerably greater than the diameter of the conducting element or red I... The extent to which the virtual -dianiei'zer of the rod 1 is increased is de gpendent upon the size and shape of the lidisks 2 and the way in which the disks nirneae tual or apparent diameter of the entire conductor is somewhat less than that of the disks 2 but is greater than that of the rod 1. The edges of the disks or enlargements 2 are preferably made rounded so that there will be no sharp points or corners from which corona-discharge will start. As an example of the effect upon the critical voltage of the size and distance apart of the disks or enlargements 2 it has been found that the critical voltage of No. 10 copper wire suspended parallel to a horizontal grounded iron plate, and about 22 inches from it, (equivalent to a line spacing of about 44 inches) can be greatly increased by using disks or enlargements about 2 inches in diameter with an annulus'one half inch in diameter spun about their edges and mounted on the wire as shown in Fig. 1. If these disks are placed about ten inches apart on No. 10 copper wire the critical voltage is 25 per cent. above the critical voltage of the same wire without the disks. Placing these disks 8 inches apart raises the critical voltage per cent., and placing them 6 inches apart raises the critical voltage 100 per cent. above the' critical voltage of the same wire when not protected by the disks. The disks or enlargements appear to exert upon the rod 1 a kind of shielding efiect which extends for a considerable distance on each side of the disks and apparently the presence of the disks or conducting enlargements renders the electrostatic field around the rod less dense at the surface of the rod than would be the case if the disks or enlargements 2 were omitted.

The presence of the enlargements or disks 2 along the rod or conducting element 1 renders the critical voltage of the entire conductor higher than the critical voltage of the conducting element or rod 1 without the disks or enlargements and therefore the conductor is much better adapted for high potentials than the rod 1 without the disks, while at the same time it is much lighter and contains much less metal than a conductor of the same diameter as the disks 2. The rod orconducting element is amply large to transmit current with the proper economy, while the enlargements or disks 2 make the outer surface of the conductor which is in contact with the air much greater than the surface of the conducting element or rod 1, so that the electrostatic stress due to the potential of the conductor is distributed over an area greater than the surface of the rod or conducting element through which the current is flowing.

The enlargement in the virtual or apparent diameter of rod 1 and the increase in its critical voltage, secured by means of the enlargements 2, permits rods constructed in this manner to be placed closer together without danger of short circuit than is the case with rods of the same size but without the enlargements. Rods or conductors constructed in accordance with my invention may therefore be used as bus bars and for the interior wiring in stations with a considerable economy in the size of the station on account of the closer spacing of the bus-bars and conductors which is rendered possible by making the bus-bars and conductors in accordance with my invention.

In Fig. 2 I have illustrated another form of conductor having a critical voltage much higher than. the critical voltage of awire such as ordinarily used and in this particular form of my invention a plurality of longitudinal wires or conducting elements 3 are connected at intervals to transverse conductors 4 so that the entire conductor is in the form of a coarsenetwork. I have found 1 that if the wire or conducting element, such as the conducting element 3, is joined to a transverse wire or conductor, such as the cross piece 4, both the conducting element 3 and the transverse conductor 4 are shielded or protected for a considerable distance from the junction, so that when the voltage applied to the conducting element 3 is gradually raised. until the appearance of corona, those portions of the conducting element or wire and the transverse conductor which are nearest the junction are the last portions to become luminous. In the form of conductor shown in Fig. 2 the transverse wires or conductors 4 are so spaced that the protected zones around each junction mergeor overlap to a limited extent so that the critical voltage of the conductor as a whole is much higher than it would be if the transverse conductors or wires at were not present and very considerably higher than the critical voltage of a solid cylindrical conductor having the same cross section as the longitudinal conducting element 3.

Under some conditions in which the potential on the form of conductor shown in Fig. is maintained at a point very close to the critical voltage of the conductor, it may be desirable to make the conductor in such a form that there will-be no sharp bends or points at which the electrostatic stress may concentrate suiiiciently to break down the air. In such cases the-conductor will preferably be made in the form of a cylinder, as shown in Fig. 3, in which the coarse network is shaped into substantially a cylindrical or tubular form to render the distribution of the electrostatic stress due to potential on the conductor as uniform as possible throughout the air surrounding the conductor.

In Fig. 4 I have illustrated one way in which my invention may be embodied in a conductor which is mounted comparatively close to ground. There-is a tendency for corona to appear on a conductor in the neighborhood of aground as the critical voltage of the conductor is approached and this breakdown of the air tends to produce a breakdown to ground. In Fig. i I have shown merely for purposes of illustration a wall 5, such as the wall.of a generating station, provided with an opening 6 through which extends a conductor or wire 7 of a transmission line. When high potential is applied to the wire 7 the electrostatic stress tends to concentrate on the conductor in the neighborhoodv of the wall or ground 5 and unless the opening 6 is made very large corona first appears on the conductor 7 where it passes through the wall 5. In accordance with my invention I enlarge the virtual diameter of the conductor 7 where it passes through the wall 5 and shield that portion of the conductor adjacent the wall by means of enlargements or disks 8 made of metal or other suitable conducting material provided with smooth outer edges and placed on the conductor adjacent the wall 5 in such a relation to each other and to the wall that the virtual diameter of the conductor 7'where it passes through the wall is substantially as great as the diameter of the disks or enlargements 8. Although the disks or enlargements 8 usually make the distance between the live metal of the conductor and ground less than it would be if the enlargements were not present, the critical voltage between ground and all parts of the conductor, including the edges of the disks or enlargements 8, is higher than it would be between ground and the conductor 7 if the enlargements were absent. These disks 8 may be made as large as desired and the virtual diameter of the conductor can be made so great that corona will appear in other parts of the conductor before appearing in the neighborhood of the wall 5. The distance apart of the disks 8 will depend upon the critical voltage which the conductor? should have where it passes through the wall 5, upon the sizeof the disks and other conditions which affect the amount of shielding exerted by the disks or enlargeinents 8.

Fig. 5 shows a similar application of my invention to transmission lines. In the particular embodiment of the invention shown in this figure the metallic arm of the sup porting tower is provided with a suitable in sulator, such asa suspension insulator 1.0.for

carrying the wire of the transmission line.

Owing to the proximity 01" the grounded arm or support 9 to the conductor 11 there is a tendency for corona to appear on the conductor in the neighborhood of the arm 9 and in accordance with my invention the irtual diameter of the conductor in the neighborhood of the arm is enlarged to any desired extent by mounting smooth-edged disks or enlargements 12 on the Wire 11 in.

the neighborhood of the insulator 10 and the grounded arm 9. The disks or enlargements 12 exert a shicldingeffect on the charged surface of the longitudinal wire 11 and may be proportioned to enlarge the virtual diameter of the wire to such an extent that the formation of corona in the neighborhood of the tower arm 9 does not occur until after the critical voltage of other parts of the transmission line has been exceeded.

' Fig. 6 shows a similar embodiment of my invention where the wire 11 is secured to a pin type of insulator 13. the enlargements 12 being adjacent the insulator, as shown, and proportioned to render the critical "oltage of the wire 11 as high or higher in the neighborhood of-the insulator as at other points along the wire.

Fig. 7 shows, merely for purposes of illustration, one form of my invention in an embodiment for preventing the appearance 0t till tit

corona at the junction or surface of contact of two dielectrics which are subjected to electrostatic stress but have different characteristics. Such a condition arises, for example, where a conductor forming a portion of the terminal of some piece of electrical apparatus extends through an insulator made of porcelain or some similar solid insulating material. That portion of the conductor which extends through the insulator is surrounded by a solid dielectric having certain characteristics while the remainder of the conductor which extends above the solid insulator is surrounded by air, an insulator having different characteristics from the material of the solid insulator. The surface of contact between the solid insulator and the envelop of air which surrounds the conductor and is subjected to electrostatic stress by potential on the conductor is the point having the lowest critical voltage and is the point at which corona first occurs.

In the device illustrated in Fig. 7, a conductor 14- torming part of a terminal extends from the air into an insulator 15 made of porcelain or other suitable material.

In accordance with my invention, the appearance of corona at the point where the conductor 14 enters the solid insulator 15 is prevented by providing at the surface of contact between the air and the insulator 15 a conducting plate 16 made of metal or other good conducting material, and preferably, though not necessarily, connected to the conductor 14-. The metal plate forms a conductire partition or wall between the two diairman electrics at a point Where they are both subjected to the electrostatic stress due to potential on the conductor, and exerts an equalizing or shielding effect by means of which the electrostatic stress is distributed in such a manner that there is no greater concentration of stress on the air in the neighborhood of the insulator 15 than occurs at other points along the conductor 14, so that the critical voltage of the conductor 14 is rendered substantially the same throughout its length and the appearance of corona at the point where the conductor passes from the air into the insulator 15 is prevented. 1 1x perience has shown that the arrangement disclosed in Fig. 7 is effective in raising the critical voltage of the conductor 14: at the point where it passes from the air into the insulator 15.

While I do not wish to be restricted in any way to any theory of operation of my invention, and while the action of the plate 16 in raising the critical voltage may possibly be explained in various ways, I at the present time consider that the plate 16 probably operates as follows: Let it be assumed that. as shown diagrammatically in Fig. 8, there is stretched a short distance above ground 17 a conductor 18 which may be subjected to high potential. Surrounding the conductor 18 is solid insulation 19 of some material which has higher specific inductive capacity than the air which surrounds the remainder of the conductor 18. On one side of the in sulation 19 there is a metal plate 20, while the other side is directly in contact With the air. When high potential is applied to the conductor 18 there is a certain potential gradient or drop through the air from the conductor 18 to ground, as, from the point a on the conductor to the point Z) and thence to ground at the point c. There will also be from the point of on the conductor 18 through the insulation 19 to the point e and thence to ground at the point f a potential gradient which clifiers from the potential gradient between a and c, for the reason that the potential gradient from cl to 6 through the solid material 19 is different from the potential gradient from a to I) through air. As a result there may be said to exist between the insulating material 19 and the surrounding air which is in con tact with it a transverse electrostatic stress which increases with the distance from the conductor owlng to the continual increasing diderence between the potential gradient through the air and the potential gradient through the solid insulating material.

lln Fig. 8 the arrows 9 represent diagrammatically the transverse electrostatic stress between the solid insulating material 19' and the air in contact With it. Under these con ditions the density of the electrostatic lines of force in the air in contact w ith the surface of the insulating material 19 reaches a point at which the air breaks down and corona appears.

If a metal plate, such as the plate 20, be secured to the radial surface of the insulating material 15) the transverse electrostatic stress due to the difference in the potential gradientthrough the solid insulating material and the potential gradient through air is equalized or distributed and thereby formation of corona is hindered. The plate 20 may be connected directly to the conductor 18 in the same manner that the plate 16 is connected to the conductor 1-l-, in which case the potential of the conductor is distril'aited over the radial surface of the insulating material 19, and the metal plate 20 so hinders the formation of corona that the critical voltage along the radial surface of the solid insulating material 19 may be raised to such a point that corona will appear elsewhere on the conductor 18 before it appears where the conductor 18 enters the insulating material 19.

The various forms of my invention above shown are merely for purposes of illustration and the principles disclosed therein may be used in many other ways and for many other kinds of conductors than those illustrated. I therefore do not wish to be restricted to the precise arrangements disclosed, but aim in the appended claims to cover all modifications within the spirit and scope of my invention.

hat I claim as no and desire to secure by Letters Patent of the l nited States, is,-

1. A conductor comprising a longitudinal conducting element and a plurality of transverse conducting bodies with surfaces and edges curved to prevent corona and charged from said element and spaced along said element and away from one another to exert on the entire length of said element, between said conducting bodies, an electrostatic influence which renders the critical voltage of said conductor higher at all points between said bodies than the critical voltage of said conducting element alone.

2. A conductor comprising a wire having on it a plurality of disks in electrical connection with the wire and spaced along it to cause the electrostatic field produced along said wire by each disk, to overlap the electrostatic field produced along said wire by each adjacent disk and thereby render the critical voltage of said conductor higher than that of said wire.

3. A conductor comprising a cylindrical conducting element having secured to it throughout its length a plurality of flat disks with edges curved on a radius great enough to prevent corona and spaced along said element to distribute the electrostatic stress along the entire surface of said element between disks in such a manner as to renderthe critical voltage of said conductor higher than that of said cylindrical conducting element constituting the minimum sections of said conductor.

r. A high potential conductor comprising a longitudinal portion and a plurality of transverse, smooth edged conducting portions electrically connected to said longitudinal portion and spaced away from one another and projecting from said longitudinal portion at intervals which enable said transverse portions to cooperate and subject all of said longitudinal portion between said transverse portions to the electrostatic influence of said transverse portions and raise the critical voltage of said longitudinal portion.

5. A conductor comprising element having intermediate its ends enlarged portions with smooth surfaces and rounded edges, projecting above the adjacent surface of said element and spaced along said element to modify the distribution of electrostatic stress on said element between said enlarged portions and render the critical voltage of said conductor higher than that of said conducting element.

In witness whereof, I have hereunto set my hand this 22nd day of April, 1911.

GIUSEPPE FACCIOLI.

a conducting Witnesses \VALTER S. MOODY, lV. J. lVooLDnmoE.

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