US3383459A

US3383459A - Anticorona suspension clamp

Info

Publication number: US3383459A
Application number: US590611A
Authority: US
Inventors: Short Herbert Douglass
Original assignee: Lacal Industries Ltd
Current assignee: Lacal Industries Ltd
Priority date: 1965-11-01
Filing date: 1966-10-31
Publication date: 1968-05-14
Anticipated expiration: 1985-05-14

Description

y 14, 1963 H. D. SHORT ANTICIORONA SUSPENSION CLAMP 2 Sheets-Sheet 1 Filed Oct. 51, 1966 INVENTOR. H. 0. SHORT WMay/ fl ATTORNEYS May 14, 1968 H. D. SHORT ANTICORONA SUSPENSION CLAMP 2 Sheets-Sheet 2 Filed 001;. 31, 1966 wwww 6 c F INVENTOR. H. o. s H o R T WWW! FIGS ATTORNEYS United States Patent 3,383,459 ANTICORONA SUSPENSION CLAMP Herbert Douglass Short, Newmarket, Ontario, Canada,

assignor to Lacal Industries Limited, Newmarket, Ontario, Canada Filed Oct. 31, 1966, Ser. No. 590,611 Claims priority, application Canada, Nov. 1, 1965, 944,230 1 Claim. (Cl. 174-144) ABSTRACT OF THE DISCLOSURE The invention is a suspension clamp assembly for an electricity transmitting cable having three integral corona flanges extending outwardly of the body, one at each end and one at the centre of the body. The centre flange terminates in spheroidal formations which extend above the cable receiving channel and which are adapted to receive a pin for connecting the unit to an insulator chain.

This invention relates to a high voltage suspension clamp adapted to support a single conductor of an electrical transmission line.

Clamps of the general type of this invention are suspended from the lower one of a series of line insulators that depend from a transmission tower to support single conductors in spaced relation to other single conductors. Transmission voltages are frequently in the order of 250- 500 kv., and the conductor cables mounted therein commonly have diameters in the order of two inches. The method of using clamps to hold these conductors at the towers is well known.

There are many electrical problems in the operation of transmission lines but an important one is the phenomenon of corona and corona losses. Corona is a manifestation of ionization formed in air at breakdown of the air due to high potential differences. It represents a loss of electrical power from the transmission line and should be eliminated or kept within tolerable limits. At the same time it is desired to transmit as much power as possible over a given line by keeping voltage high.

It is well known that one can reduce the effect of corona by reducing the intensity or concentration of the electric field at the surface of the clamp created by the potential of the conductor and/or increasing the electrostatic capacity of the insulators immediately adjacent to the clamp within which the conductor is mounted, which in turn tends to even out the voltage distribution across the individual insulators of the string that connect the clamp to the tower, and hence their susceptibility to corona formation.

A common, and generally accepted, method of reducing corona with single conductor clamps of the type of this invention is the use of corona rings inounted 'by means of appropriate brackets to the side of the conductor clamp with their principal plane substantially parallel to the longitudinal axis of the conductor in the clamp. These rings can be designed as effective corona prevention devices at a given transmission voltage. They will increase the capacity, and therefore the coupling of the clamp, to the lower insulator in the insulator string that extends from the tower so that the voltage distribution across the line insulators is improved, and the corona ignition voltage and R.I.V. level of the line insulators enhanced. They, in addition, can be designed to provide a large conducting surface to shield the sharper corners of the clamp whereby to reduce the concentration of electrostatic flux at such parts, and prevent corona discharge.

The mounting of corona rings, however, is relatively costly and involves maintenance problems. The rings must be secured to the clamps by means of brackets and. under heavy ice and wind loads the rings tend to distort, and the brackets tend to fail. There is, thus, a service problem.

Flashover from line to ground through the tower in the path of the insulators is also a common fault encountered in transmission line practice. If the flashover occurs across the porcelain it may damage the porcelain of the insulators. It is good practice to provide flashover devices to conduct any such fiashover faults away from the insulator strings. Here again, the devices must be separately attached and. involve installation and maintenance costs.

It is an object of this invention to provide a less costly, and more service-free corona protection than is afforded by the commonly used rings.

It is a further object of this invention to provide a less costly and more service-free fiashover protection device than is afforded by the commonly used devices.

It has been found that effective corona protection capable of improving the coupling of the clamp to the insulator string, and shielding sharp parts of the assembly where there tends to be concentration of electrostatic flux can be achieved by means of flanges cast integrally with the clamp but having their principal planes substantially at right angles to the longitudinal axis of the clamp and, therefore, the conductor. The construction is cheaper in the first instance because there is no mechanical connection of the corona protecting device to the clamp, and there are no service problems of the type encountered with the separately formed corona rings that must be mounted on the side of the clamp.

Generally speaking, a suspension clamp assembly, according to this invention, for a single conductor comprises an elongated clamp having a longitudinally extending conducto-r channel formed therein, means for securing the conductor in the channel with its longitudinal axis aligned with the longitudinal axis of the conductor channel, the clamp having at least one integrally formed corona flange having its planes substantially at right angles to the longitudinal axis of the conductor channel. The invention will 'be cleanly understood after reference to the following detailed specification read in conjunction with the drawings.

In the drawings:

FIGURE 1 is a perspective illustration of a suspension clamp according to this invention;

FIGURE 2 is a sectional view along the line 2-2 of FIGURE 1;

FIGURE 3 is a sectional view along the line 3-3 of FIGURE 1, but showing the socket tongue in position;

FIGURE 4 is an exploded view of an alternative clamp assembly according to this invention;

FIGURE 5 is a longitudinal sectional view of FIGURE 4 but showing the clamp elements in operative position; and

FIGURE 6 is a schematic illustration of a bracket suspended at the bottom of a string of insulators on a transmission line tower.

Referring to the drawings, the numeral 10 generally refers to a single conductor clamp, according to this invention. It comprises two

co-operating sections

12 and 14 having semi-round jaws that together define a longitudinally extending conductor channel 16. The

clamp sections

12 and 14 have bolts 18 that extend therethrough, and that have co-operating nuts 20 adapted to thread onto their free ends to hold the

clamp sections

12 and 14 in clamping arrangement to secure a conductor therein in use.

According to the invention, the

clamp sections

12 and 14 have

flanges

22 and 24 respectively at their ends, the

flange sections

22 and 24 co-operating to form a rounded corona flange or ring at each end of the clamp assembly with its principal plane at right angles to the longitudinal axis of the conductor channel 16. The corona flange has generous rounded proportions to increase the surface area whereby to limit the electrostatic field intensity at the surface of the clamp assembly at the operating conditions to a level that eliminates, or reduces to an acceptable limit, corona effect. It is also designed and serves the purpose, reducing the distance between the clamp and the porcelain dielectric of an insulator to which the clamp is connected in use to increasing the coupling of the clamp assembly to the bottom insulator of the insulator string.

In this latter connection, the numeral 26 refers to a standard socket tongue that joins wit-h the downwardly projecting pin of the lowermost insulator of an insulator string in use. Tongue 26 is connected to the clamp assembly by means of the pin 28 which threads into the clamp section 12, as illustrated in FIGURE 3. The upper end of the tongue 26 is pin-connected to the insulator pin, or ball of the lowest insulator in the insulator string, but depends from the transmission tower in use.

It will be noted that tongue 26 which connects the clamp assembly to an insulator is short and is adapted to keep the porcelain of the insulator close to the body of the clamp. The corona rings are adapted to extend beyond the edge of the insulator porcelain so that they, by their height above the general body of the clamp, achieve a closer coupling to the insulator.

The corona rings lying outwardly as they do, from the edge of the insulator, also function as grading rings; grading rings consisting essentially of a ring, or the like, disposed outwardly and at a higher level than the porcelain of the lowest insulator, are often used for the purpose of conducting a flash-over from the line to the tower and away from the string of insulators. It will be apparent that the integral structure of the flanges of this invention is Well adapted to grading rings.

As is well known in the art, one can improve the voltage distribution across the string of insulators from the conductor in the clamp to ground by increasing the capacity of the bottom insulator and clamp assembly. To do this, one strives to decrease the distance between the metal of the clamp and the porcelain of the first insulator, i.e. achieve a close coupling. The corona flanges of this invention serve this purpose. They also increase the same capacity by presenting an increased surface area.

FIGURES 4 and illustrate a further embodiment of the invention where a third corona flange is provided intermediate two end flanges, and where the end flanges do not extend on the upper side of a conductor in use. In this embodiment, the suspension clamp assembly comprises an elongated clamp having a body 40 that co-operates with a saddle 42 to define a longitudinally extending conductor channel 44. The saddle 42 has upwardly extending minor flanges at its ends and is retained in position to secure a conductor in the conductor channel with its longitudinal axis aligned with the longitudinal axis of the conductor channel by means of a pair of U-shaped clamps 46 that extend over the saddle 42, through the body 40 and have nuts 48 and lock washers 49 at their bifurcated ends to maintain the assembly secured. Cleats S0 bolted to the saddle 42 are provided to maintain the U-shaped clamps 46 in position. In this case, the socket tongue 52 (similar in design to pin 26) that mounts the suspension clamp assembly to an insulator on an insulator string is connected to the clamp assembly by means of pin 54 that passes through the assembly and threads into the shoulder 56. Bolt 54 is maintained in position by means of a locking pin 58 that enters into a channel 60, which in turn communicates with the bearing hole in shoulder 62 of the clamp assembly. Pin 58 has an undulation 64 therein that springs over the bolt 54 between

shoulders

66 and 68 to prevent it from accidentally turning out of its mounting as the straight leg thereof enters a through hole in bolt 54. Y

In use, cable is clamped to the clamp assembly and tightened into position by tightening the U-clamps 46 whereby the cable can be suspended from the lower insulator of an insulator chain.

It will be noted that the body 40 of the suspension clamp is formed with a corona flange 69 at each of its ends. These flanges extend only on the underside of the conductor channel.

In addition, in the case of the clamp 4t) a second corona flange "i0 is provided between the flanges 69. Corona flange 70 terminates at the

sockets

56 and 62 which, it will be noted, are designed with a spheroidal shape. These spheroidal shoulders at the extremeties of the flange 70 serve to improve the close coupling of the clamp to the insulator. The flange, in this particular case, is also specially useful in shielding against corona discharge from the head of bolt 54. It will also be noted that the ends of the saddle 12 are slightly flanged and rounded. In this case, the connecting socket is also short and adapted to achieve close coupling to an insulation.

It will be apparent that modifications of this invention other than those illustrated are possible. The essence of the invention is the elimination of the old separately formed corona rings that were mounted with their planes parallel to the longitudinal axis of the conductor channel of the clamp by the provision of a corona flange that is cast integrally with the clamp members and that has its planes at right angles to the conductor channel. The integrally cast corona rings of this invention function electrically in a similar manner to those of the prior art to improve coupling and provide shielding. It is their novel disposition which permits them to be integrally formed with the clamp. The invention results in very substantial savings in initial cost because the casting of an integral flange is very much less than the cost of providing a separate appliance and attaching it by means of brackets. Moreover, from a maintenance point of view, the invention is to be much preferred over prior practice because it substantially eliminates maintenance of the corona rings.

To refer the use of the clamp, reference will be made to schematic illustration of FIGURE 6 where insulators are indicated as capacitors and the tower is indicated as ground. The clamp is suspended from the insulator pin of the bottom insulator 102 of a string of

insulators

102, 104, 106 and 108 that is, in turn, suspended from the transmission tower 110. In this connection, the insulators are of standard construction and consist essentially of a metal cap and a pin separated by a porcelain insulator. The cap on the top is adapted to receive the pin of a companion and similar insulator. Such insulators can be considered electrically as a capacitor, the metal cap socket being one plate, the porcelain element being the electrolyte, and the pin being the other plate. Insulators are, in practice, connected in series, the pin of one insulator connecting in socket of the cap of the next insulator. As indicated above, the clamp of this invention connects with the pin of the lowermost insulator in a string that depends from the tower.

It is well known that the voltage distribution across a string of insulators depending from a tower with a transmission line secured to a clamp assembly that depends from the lowermost insulator is uneven. It is not uncommon to have as high as 30% of the voltage between the line 112 and the tower 110 across the insulator closest to the line with as little as 3% of the total voltage across the insulator closest to the tower. Transmission line voltages are commonly in the order of 200-500 kv.

It is also known that one can, in effect, increase the combined capacity of the insulator closest to the line and the line clamp by close coupling the line clamp and the lowermost insulator, i.e., putting the clamp and its conductor closer to the porcelain of the insulator that is closest to the line. The combined. capacity of the lowermost insulator and line clamp and line can also be increased by increasing the surface area of the line clamp. These effects are achieved with conventional corona rings. Both of these effects are also achieved with the novel and economical structure of this invention.

The rounded flanges, which increase the surface area of the clamp at critical points and achieve a closer coupling of the clamp to the insulator also have the effect of shielding sharp edges of the clamp, and thereby reducing the electrostatic shield intensity of the clamp. It is well recognized that electrostatic field intensity is very high at sharp edges such as at bolts and corners. By providing a rounded section at the flanges, this can be reduced to provide shielding.

The increasing of the combined capacity of the lower insulator and clamp has the effect of achieving a more even voltage distribution across the various insulators in a string and reduces the corona inception voltage at which the transmission line may be operated. The shielding effect achieved has a similar result.

What I claim as my invention is:

1. A suspension clamp assembly for connecting a conductor to the bottom insulator of a string of insulators comprising, a body, a saddle adapted to overlie said body, said saddle and said body cooperating to define a conductor channel, clamp means for clamping a conductor between said saddle and said body, said body having three corona flanges extending therefrom with their principal planes substantially at right angles to the longitudinal axis of said conductor channel, the first one of said three corona flanges being located at one end of said body, the second one of said three corona flanges being located at the other end of said body, the third one of said corona flanges being located between said first and second corona flanges, each of said corona flanges extending outwardly of said clamp means whereby to eifectively shield said clamp means, said third corona flange terminating on each side of said body in a shoulder having a spheroidal shape at a height above said conductor channel, and means between the shoulders for connecting said suspension clamp assembly to said bottom insulator.

References Cited UNITED STATES PATENTS 1,170,725 2/1916 Austin 174-144 1,630,423 5/1927 Gothberg 174-169 X 1,799,114 3/1931 Miller 24863 2,000,652 5/1935 Snyder 174-169 2,122,988 7/1938 Nelson 24858 X 2,699,462 1/1955 Exner 174-40 X 3,218,009 11/1965 McWhierter.

LARAMIE E. ASKIN, Primary Examiner.