US1847421A - Transmission tower having insulating sections with protecting gaps or resistance - Google Patents

Description

March 1, 1932. A. o. AUSTIN 1.8475421 TRANSMISSION TOWER HAVING INSULATING SECTIONS WITH PROTECTING GAPS OR RESISTANCE Filed June 1; 1926 INVENTOR.

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ATTORNEY! Patented Mar. 1, 1932 UNITED STATES PATENT OFFICE ARTHUR O. AUSTIN, F BARBERTON, OHIO, ASSIGNOR, BY HESNE ASSIGNMENTS, TO THE OHIO BRASS COMPANY, OF MANSFIELD, OHIO, A CORPORATION OF NEW JERSEY TRANSMISSION TOWER HAVING INSULATING SECTIONS WITH PROTECTING GAPS OB RESISTANCE Application filed June 1, 1926. Serial No. 112,748.

This invention relates tothe supports for high tension transmission lines and has for its object the provision of transmission line supports which shall diminish the liability of flash-over or arcing and which shall give improved construction and operation. The specific objects of the invention will appear in the following specification.

The invention is exemplified in the com- ,10 bination and arrangement of parts shown in the accompanying drawings and described in the following specification and it is more particuarly pointed out in the appended .claims. 1

In the drawings- Fig. 1 is an elevation of a transmission tower. showing one embodiment of the present invention.

Fig. 2 is a fragmentary elevation looking 2 from the right in Fig. 1.

Fig. 3 is a fragmentary view showing'a modified detail of construction.

Fig. 4 is a fragmentary elevation showing a modified detail of a different part of the invention.

Fig. 5 is an elevation with parts in section of a detail of the construction.

In a high voltage transmission line it is highly desirable to provide suflicient insula tion at the supports so that an arc will not form over the insulator or from the conductor to ground causing a short circuit. Then an are forms over the insulator or between conductor and ground, it is usually necessary to remove voltage from the line or lower the voltage materially. This tends to afiect synchronous and other apparatus connected to the system even though no serious damage is caused by the power are to ground. Arcs to ground on many systems form a large percentage of the troubles or interruptions on the system. In order to minimize the effect of these interruptions'parallel transmission lines may be necessary and 45 much equipment in the form of circuit breakers and relays required to cut ofi the affected line.

Since the fixed charges on large transmission systems may be a large proportion of the cost of producing and delivering power, any im rovement which tends to reduce the cost 0 the transmission line is an important factor. In many transmission systems at least %0: the fixed charges are those due to cost of the transmission line. Where the reliability of the circuit is poor, multiple circuits may be required and this in turn may require a great increase in the outlay not only for the additional conductors, towers and insulators, but for the additional right of way.

Where the danger of trouble on the trans mission line can be reduced, it may be possible to use a fewer number of circuits. so that any improvement which will tend to eliminate arcs to ground is well worth while as it tends -to lower the cost of delivered power. Arcs to ground tend to increase with the growth or size of the connected transmission system. The increasing amount of trouble tends to ofiset the economic advantage of interconnection of power systems so that in many systems which originally operated with a high degree of reliability it becomes necessary when they are interconnected with other systems to reduce the number of arcs to ground in order to improve or maintain the original standard of operation. Where large amounts of power are available which may be fed into a short circuit, an arc to ground may do considerable damage to the conductor. insulator or supporting structure, necessitating a shut-down for repairs or causing a considerable interruption to service. One of the most serious causes of interruption is an arc to ground started by lightning or by birds.

The present invention is devised to eliminate or. reduce these troubles and is therefore of considerable economic importance in maintaining a high standard of service and reducing the duplication of lines and equipment necessary for the maintenance of a given standard of service. Owing to the fact that lightning may produce very high voltages on the transmission system, it is evident that a large amount of insulation must be provided where it is desired to prevent an are from conductor to ground over the insulator or between conductor or \tower or supporting structure.

Where a large insulator is used, it is necessary to provide corresponding clearance to the supporting structure. This makes it necessary to increase the length of cross arms and the spacing between conductors which not only increases the cost of the supporting structure, but in some cases the regulation of the line is impaired. The present method tends to eliminate flashovers, even where moderate clearances are used and while particularly applicable to new line construction, is readily adapted to improving the operation of existing systems where serious troubles exist due to flash-overs from lightning, electrical surges or from birds. Fig. 1 shows a supporting structure having an upper metallic section 10, projecting arms 11 and insulators 12 supporting conductors 13. A charging, sky or counter E. M. F. wire 14 is attached to the peak of the tower having sectionalizing insulators 15 inserted at intervals along its length. An insulating section 16 is inserted between the conducting sections 10 and 17. The insulating section 16 has screening or discharge members 18 of conducting material a shunting resistance 19 and a shunting condenser 20. The insulating section 16 has insulating braces 21 and cross'ties 22. In the operation of the previous constructions having continuous metal towers a direct stroke of lightning striking the conductor or the release of a bound charge, may so increase the voltage between the conductor and the grounded tower members that a discharge will take place. Where the operating voltage is high the discharge opens up a path permitting the power are to follow, frequently causing an lnterruption to service. It is evident that if the voltage or electrical stress between the conducting member and the grounded supporting structure .is not sufiicient to break down the air space, either over the insulator string or directly to the members of the support,

the abnormal voltage will not open a path for the power are to follow.

The improved construction is designed to reduce the diflerence in potential or voltage between the conductors and supports under operating conditions so that the arc will not take place, and to accomplish this result without undue expense or the creation of additional hazards which would offset the advantages. In operation the release of a bound charge such as a stroke of lightning in the vicinity of the line will tend to produce an increase in potential or voltage between the conductor and the supporting structure in ordinary construction. In the improved arrangement the boundcharge which is released and which tends to raise the potential of the conductor 13 can be used to raise the voltage or potential of the supporting structure providing the bound charge, which affects the supporting structure the same as it affects the conductors, is prevented from flowing to ground. Where the bound charge is prevented from flowing to ground, the difference in potential or voltage between conductors 13 and the supporting structure may be reduced to the point where the arc will not form. It is evident that if the release of the bound charge raises the potential of the tower member in the same degree as it raises the conductors there will be no difierence in potential or voltage between the two other than that. produced by the normal operating voltage. In this case it is evident that lightning would have little or no efiect in causing an arc to ground and it is therefore desirable to approximate this condition as far as economically possible.

If the electrostatic capacity between the insulated section 10 and the ground is so large that the voltage induced by the disturbing condition is not high enough and thereby permits too great a difference in potential or voltage between conductors 13 and section 10, this may be offset by using the sky or counter E. M. F. wire 14 to raise the potential of this section. In order that the bound charge which will tend to raise the potential of the sky wire 14 is not lowered by flowing away to other sections of lower potential, sectionalizing insulators 15 may be used between each tower or occasionally as desired. By regulating the number and size of the sectionalizing insulators 15 the potential of the tower member may be regulated to a considerable extent as the efi'ective length of the counter E. M. F. wire may be controlled. It is evident that if the counter E. M. F. wire is not sec tionalized that it may, in efiect, have the characteristics of a ground wire, particularly where the insulating section is shunted by resistances 19 and electrostatic capacities 20. Where the counter E. M. F. wire 14 is of relatively high resistance, sectionalizing may not be necessary, although the danger of a short circuit produced by bird droppings will be increased. It is evident that where an abnormally high voltage in the form of. a surge exists on the conductors 13 that these conducto s in turn will form an electrostatic condenser with the wire 14 and the upper section 10 of the tower the conductors 13 each constituting one conductor element of a condenser of which the tower section 10 together with the conductor 14 constitutes the other element. Where this electrostatic coupling will tend to lower the voltage between the conductor and the tower member this in turn tends to throw some of the electrical stress on the insulated section.

For very high frequencies such as encountered in service due to surges or lightning, the distribution of electrical stress will be inversely. proportional to the relative electrostatic capacities. It is therefore important that the electrostatic capacity between the upper section and the lower section of the tower or ground be properly related to the electrostatic capacity between the conductors 13 and the upper conducting members of the tower. This is evident by consideration of the following. If the electrostatic capacity of the Section 10 to ground or over the insulating zone of the tower is high which'corresponds This would have the efiect of placing practically all of the potential difference'between the conductors 13 and the tower member 10.

.The path or are established would then tend to throw full stress on the insulated tower section which might cause discharge with the resulting power arc. If on the other hand the relative electrostatic capacities are such that the insulating zone furnishes insulation or counter E. M. F. which will add to that over the insulator string or between conductor 13 and tower members, a higher potential or voltage may be carried by the conductors 13 without producing an are.

In general, the proportions of the average transmission structure are such that an insulating section or zone in the tower similar to that shown in Fig. 1 will be effective without any special means of controlling its electrostatic capacity of the conductors to the zone above the insulating section. Where very heavy conductors are involved, it may be advisable to use the insulated sections to fullest efiiciency so that they may be kept small for mechanical reasons. In this case it may be necessary or advisable to control the electrostatic capacity over the zone by the addition of condenser elements. These may be in the'form of electrostatic condensers such as are used for carrier current systems, by increasing the area eachside of the insulated zone by means of plates or wire screens 23 or by conductors 24 and 25 extending from 25 need not be conductors .strung between towers, but could be projecting members or areas which would increase the electrostatic capacity of the insulating zone. The discharge or screening members 18 may be used to increase the capacity by increasing their length so that they overlap in a vertical plane by maintaining suflicient clearance, but increasing their length and location. By these means the electrostatic capacity of the insulating zone can be easily regulated to suit the conditions of any particu ar installation.

One means of increasing this electrostatic capacity is by means of two overlapping cylindrical conducting members, one connected to each side of the insulating zone. This construction is shown in Fig. 4 in which 26 constitutes one conducting plate of the condenser and 27 the other conducting plate. These may be so spaced that they will also limit the voltage over the insulating zone so as to prevent damage to the members. It is evident that the conducting plates 26 and 27 may have a variety of forms and may be placed inside or outside of the tower or one inside and the other outside.

It has long been recognized that wood poles furnished a considerable amount of insulation which tends to prevent flash-over dur- I ing lightning. Many moderate voltage lines have a higher eflective flash-over voltage between conductor and ground than the highest voltage lines today using steel or grounded supports. In the past, however, difficulty has been encountered in making effective use of a this insulation without serious trouble from other causes. Where the ordinary wood pole is used, lightning tends to shatter the structure in many cases and in districts where the insulators become coated or the insulation becomes defective the leakage and charging current of the insulator frequently burns the wood structure. These disadvantages frequently make it impossible to make use of the advantages of the wood structure in order to prevent flash-overs during surges or due to birds. n

Experiments show that where the discharge path can be kept away from insulating wood members they may be used to advantage. In order to do this it is necessary to shield or screen the wood member by a discharge horn or cap 18. These members are generally in contact with the surface at the start and are spaced further from the insulating members 16 as they approach each other. This ef- -.fects a screening of the ends and ifproperly carried out, a discharge produced by light ning would take place between the ends of the discharge horns away from the surface of the insulating members 16. By proper proportioning this point of discharge may be far enough away from the insulating members so that they will not be carbonized or endangered by the heat of the arc. In general, however, it is desirable to provide sufficient insulation that discharge will not take place. This, however, may not be economically possible or necessary for certain rare conditions in which case the discharge members 18 will protect the insulating members.

The upper discharge or screening members its may be made in the form of a weather shield as shown at 28 in Fig. 3 so formed that they will tend to keep at least a portion of the insulating zone dry so as to maintain a high degree of resistance. In general, however, this is not necessary as the electrostatic capacity issufliciently high for the zone so that under lightning conditions the insulation furnished by the members 16, although wet,

may be as effective as though the members frequency compared to that at normal fre-' quency. In the latter case i. e. at normal frequency, the drop might probably be so low where the members were entirely Wet thata power arc would pick up in case the insulator 12 was actually shorted by birds or otherwise.

It is evident that where the insulating members are shielded so as to keep a portion dry that sufliciently high resistance may be obtained for preventing the power are from forming under normal voltage conditions or where the frequency is comparatively low. In some sections the combined leakage and charging current over the insulators at normal operation voltage is such that any unbalanced current flowing to ground will cause a burning of the structure. This may be prevented by using an insulated zone which will withstand this discharge in the same manner that the insulators have to withstand this discharge. This class of construction usually necessitates the use of porcelain or glass sectionalizing insulators or compound insulators having surfaces which will permit the leakage without carbonization. Many insulators of this kind are available, such as those used in some classes of bus work and for sectionalizing radio towers. In general, however, the use of compound insulator members or ones which will resistsurface leakage is too expensive, as the general results may be obtained by the use of wood or fibre members protected with a shunting resistance 19 which will take care of any unbalanced leakage or voltage to groundproduced by the conductors. In general, this resistance 19 may be very high as the leakage over the insulator is exceedingly small.

Where there is little danger from bird trouble and the relative electrostatic capacities between the conductors and upper secchloride.

tion of the tower and over the insulating zone are large enough a resistance of comparative lv low magnitude may be used as the counter E. M. F. under a surge will be sufficiently high so that the potential or voltage between sistance wire wound in any suitable form,

either encased or in the open, or this resistance may be made up with a high resistance Wire immersed in electrolyte which will form a portion of the resistance, or in an insulating medium, the surrounding mediums being used to prevent flash-over between different sections of the resistance memberand also to cool same and prevent it from being destroyed by a momentarily high discharge.

Another method of forming this resistance is simply to use an insulating tube 19', Fig. 5, filled with a resistance medium such as water to which alcohol or other material is added to prevent freezing. Where there is no (langer of freezing, water itself may be used, the resistance being regulated by the use of any electrolyte such as sodium or calcium If a high resistance is desired to prevent a ground in the case of shorting of the insulator strings by birds, this may be obtained by a small tube filled with water and alcohol or water and glycerin. In general, a resistance of several thousand ohms may be readily obtained in this way which will tend to prevent a short. In case a power are picks up and flows through the resistance, this will usually be cleared automatically as gas will be formed in the resistance tube tending to cause it to act as a fuse.

Discharges are seldom likely to occur successively at the same tower except over long intervals of time so that a cheap form of resistance tube may be used which can be de stroyed or replaced It is evident that for any unbalanced voltage condition between conductors and ground the resistance mem ber must be low enough so that the unbalanced current will be carried to ground without producing a sufiiciently high voltage to burn or start destruction of the insulating members 16 and 21. Where a resistance is used, it is difficult to prevent this from carrying an appreciable current should practically all of the insulation between the conductor and up per section of the tower be eliminated. Cases of this kind are usually of only momentary duration unless the insulator string has been destroyed. Where the upper section of the tower is charged only momentarily the resistance may be used to break the are by the gas By a proper forming the resistance can usually be made of such order that a short due to a conductor grounding on the upper section of the tower will permit the operation of relays.

Wood members are cheap and can be eifectively used for the insulatin section of the tower in most cases, particuIarly where the members are impregnated so as to prevent discharge through their interiors. In general, any of the ordinary means of impregnation are suitable as this tends to keep the water or conducting path out of the inside of the member so that it can be readily shielded or screened at the end by members 18. Inv

many cases the shielding or impregnation is not necessary, but this tends to' eliminate troubles under severe conditions and the impregnation has a further advantage in that it may be used to prolong the life of the wood member so that It will equal or exceed that of the metallic members.

As it is diflicult to make large wood members in a single piece which will not check,-

these members may be built up from comparatively thin members. In general, it is advisable to space the several parts of a member so that they will not hold water in the space between by capillary attraction and thereby tend to induce a discharge between the members. In some cases lowering the surface resistance of the members will take care of any unbalanced leakage. This can be accomplished by slightly charring the surface or by painting with a conducting path of electrolyte. In general, however, where a conducting path of electrolyte is used for painting or impregnating the piece, the resistance changes greatly. with time and it is usually found advisable to .use a shunting resistance which will maintain uniform conditions. If any unbalan ed condition will cause a potential or voltage to exist in the insulated zone this potential or voltage may be dangerous unless the shunting resistance is sufliciently low to discharge same. In case the shunting resistance 19 is not used the zone may be shunted by a conductor or switch provided for that purpose similar to that used in transmission work. This shunting switch, of course, is used only in case of repair or in case the insulating zone 1s of such length that a person desires to bridge it. In addition to preventing arcs to ground. the insulated zone tends to prevent a high voltage at the base of the tower which may endanger life in some cases, articularly where the ground resistance is igh.

I claim 1. In combination a transmission line, an

insulator supporting said line, a structure supporting said insulator, said structure having a wood portion providing insulation for said transmission line in series with said insulator, and a high resistance leakage conductor apart from said wood portion but in parallel therewith and in series with the leakage path over said insulator from said transmission line to ground.

2. In combination a transmission line, an insulator supporting said line, a structure, supporting said insulator, said structure comprising a wood portion roviding insulation between said line and ground in series with said insulator, and means forming an arcing gap in shunt with said wood portion and spaced therefrom and of less length than said wood portion.

3. In combination a transmission line, an insulator supporting said line, a structure supporting said insulator, said structure having a wood portion providing insulation between said transmission line and ground in series with said insulator, a high resistance leakage conductor apart from sald wood portion and in shunt therewith but in series with the leakage path over said insulator from said transmission line to ground, and means forming an arcing gap in shunt with said wood portion and spaced therefrom and of less length than said wood portion.

4. A transmission system having a conductor, a supporting structure for said conductor, said structure having a portion thereof of conducting material disposed ad'acent said conductor and insulated from sai conductor and from ground, and means for charging said portion of said supporting structure with a charge similar to that of the conductor when said conductor is charged abnorject to similar external influences as said transmission line, said counter potential conductor being connected through impedance of more than a thousand ohms to ground.

7. In a transmission system a supporting structure having a portion thereof of conducting material insulated from ground, a

transmission conductor mounted on said insulated portion and insulated'therefrom, a counter potential conductor electrically con-- nected to said insulated portion, said counter potential conductor being connected throughcharging conductor being connected to ground through a conductor subjected to conimpedance to ground, said impedance being of a value to dissipate charges on said insulated structure portion simultaneously with the dissipation of similar charges from the portion of said transmission conductor adj acent said structure, while maintaining a potential in said insulated structure portion commensurate with the induced potential on said transmission conductor portion thus preventing lowering of the flashover voltage between the conductor and ground.

8. A tranmission system comprising a conductor line, a support for said line having a portion thereof of conducting material adjacent said line insulated from ground, said line being insulated from said support, means subject to similar conditions as said line for charging said insulated portion similarly to charges on said line resulting from disturbances affecting said line and for dissipating the charge from said portion concurrently yvith the discharge of the charge from said '9. A transmission system comprising a conductor and a support of conducting material therefor, said conductor being insulated from said support, and means arranged tobe subject to similar influences as said conductor and electrically connected with said support to charge said support similarl to said conductor when said conductor is c arged by external influences, said means'having connection throughrhigh resistance to ground for allowing unbalanced leakage or charging current to escape to ground, said resistance being sufficient to maintain the charge on said support for a time commensurate with the time said conductor retains its charge from the same external influence.

10. In combination a supporthaving a conductor section insulated from round, a transmission line mounted on sai insulated section and insulated therefrom, a charging conductor electrically connected with said insulated section for reducin bound charges in said transmission line an for charging the insulated section of said support, said charging conductor being connected to ground through a conductor subjected to conditions suitable to give approximately the same rate of dissipation of charge from the insulated portion of said support as from the portion of said transmission line adjacent said support.

11. The combination of a support having a conductor section insulated from ground,

a transmission line mounted on said insulated section and insulated therefrom, a charging conductor electrically connected with said insulated section for reducing bound charges in said transmission line and for charging the insulated section of said support, said ditions suitable to give approximately the same rate of dissipation of charge from the insulated portion of said support as from the portion of said transmission line adjacent said support, and means forming a protective discharge gap to ground from said insulated section.

'12. The combination of a wood support having metallic members-mounted thereon and insulated by saidsupport fromground, a transmission line mounted on said support adjacent said metallic membersand insulated therefrom, a charging conductor electrically connected with said metallic members and having connection to ground subject to conditions suitable to give approximately the same rate of dissipation of charges from said metallic members as from the portion of said transmission line adjacent thereto.

13. The combination of a wood support having metallic members mounted thereon and insulated by said support from ground,

a transmission line mounted on said support adjacent said metallic members and insulated therefrom, a charging conductor electrically connected with said metallic members and having connection to ground subject to conditions suitable to give approximately the same rate of dissipation of charges from said metallic members as from the portion of said transmission line adjacent thereto, and spaced arcing horns forming a discharge path to ground spaced from said support.

14. In a high potential transmission line, a supporting structure having a portion thereof insulated from the ground by insulation of an'order suflicient to Withstand a number of kilovolts, a transmission conductor mounted on said insulated portion and insulated therefrom by insulation of an order sufiicient to Withstand a number of kilovolts and a counter potential conductor electrically connected with the insulated portion of said supporting'structure and subject to the same external disturbances as said transmission conductor.

a 15. In a high potential transmission line, a supporting structure having a portion thereof insulated from the ground by insulation sufiicient to withstand several kilovolts without flashover, a transmission conductor supported on said insulated portion and insulated therefrom by insulators sufficient to withstand several kilovolts without flashtrol removal of a bound charge from said insulated section to effect arrate of removal of said charge commensurate with the rate of removal of a similar charge from the portion of the transmission conductor adjacent said insulated section.

16. In combination atransmission line support, an insulator mounted on said support and a transmission line carried by said ini sulator, said supportcomprising a wood portion, metallic supporting means connecting said wood portion with said insulator, said metallic supporting means being insulated from said transmission line by said insulator andfrom ground by said wood portion, and a discharge path extending from said metallic supporting means to ground and comprising a pair of arcing horns forming an arcing gap spaced away from said wood portion, one of said horns being electrically, conductively connected with said metallic supporting means, andthe other of said horns being electrically, conductively connected to ground, the air gap between said arcing horns normally electrically separating said metal? lic supporting means from ground but being shorter than said wood portion to permit arcing across said gap when the voltage between saidmetallic supporting means and ground reaches a predetermined value less than that required to cause a discharge ove said wood portion.

17. In combination a transmission line support, an insulator mounted on said support and a transmission line carried by said insulator, said support comprising a wood portion, metallic supporting means connecting saidwood portion with said insulator, said metallic supporting means being insulated from said transmission line by said insulator and from ground by said wood portion, and

a leakage path for unbalanced leakage current extending from said metallic supporting means to ground and bridging said wood portion, and comprising" a high resistance conductor displaced from said wood portion and of suflicient resistance to retain .an induced charge on said metallic supporting means for a suflicient length of time to prevent discharge from said transmission line to said metallic supporting means when similar charges are induced on said transmission line and said metallic supporting means by a transient disturbance.

18. A support for a high potential transmission line comprising a skeleton tower having an upper metal section, an arm on said section, an insulator string suspended from said arm, a high potential conductor carried by said insulator string, a charging wire electrically connected with said metallic section and having a, sectionalizin insulator interposed therein, a lower meta section, a wood section interposed between said metal sections, insulatingbraces for said wood section, a 'high resistance leakage conductor bridging said wood section, arcing members connected with said metal sections. and diverging outwardly from said. wood section to provide an arcing path over said wood section in spaced relation therewith, andacondenser bridging said wood section.

19. In combination, a skeleton tower having upper and lower metallic portions and an intermediate portion of skeleton construction formed of insulating material, an insulator supported by the upper metallic ortion of said tower, a conductor carrie by said'insulator, and a high resistance member electrically connected conductively with said upper metallic portion and ground and forming a leakage path bridging the portion of said skeleton tower formed of insulating material. 4

20. In combination, a. skeleton tower having upper and lower metal sections and an intermediate section comprising a skeleton wood frame, a high resistance conductor electrically connected conductively with said upper metallic section and connecting the portions of said tower at opposite sides of said wood frame, arcing members for directing a discharge between the metal portions of said tower away from said wood frame, an insulator carried by the upper metal portion of said tower, and a conductor supported by said insulator.

21. In combination, a skeleton tower having upright posts comprising upper and lower metal sections and intermediate sections formed of wood bars connecting the adjacent ends of said metal sections, arcing members for directing discharge between said metal sections away from said wood bars, a con-' section, an insulating tower section, anupper section of conducting material carried by said insulating section, and a transmission line carried by said upper tower section and ,in-

sulated therefrom, said insulating tower section inclilding stress members for withstanding both tensionand-compression spanning the space between said grounded section and said upper tower section, all portions of said stress memberswhich span said space being of insulating material.

23. A high potential transmission system, comprising a tower having a grounded lower section, an intermediate insulating section supported b said lower section, amup r section of con ucting materialv carried y said intermediate section and insulated thereby" from said lower section, all mechanical stress transmitting members of said intermediate section which span .the space between said upper and lower sections being formed of insulating material, a high potential transmis sion line mounted on said upper section and insulated therefrom, arcing horns connected with said upper and lower tower sections respectively for directing discharge between said upper and lower sections away from said intermediate section, the air gap space in the flashover path between said upper and lower sections being commensurate in length with the air gap space between said transmission line and uppersection, and a high resistance leakage shunt bridging said insulating section and forming a leakage path from said upper section to said lower section.

24. The combination with a high potential transmission line, of a support for said line, an insulator carried by said support, said line being mounted on said insulator, a counter potential wire electrically connected conductively with said support and subjected to rture, of means for preventing flash-over from said line to said structure, due to abnormal disturbances, said means comprising a counter potential wire electrically connected conductively with the portion of said supporting structure adjacent said line and extending in the same region as said line, the portion of said supporting structure to which said counter potential wire is connected being "sufficiently insulated from ground to retain a charge induced on said portion and on said counter potential wire for substantially as long a period of time as the charge induced by the same influence is retained on the portion of said transmission line adjacent said supporting structure.

26. In combination a support having a conductor section insulated from ground, a,

transmission line mounted on said insulated section and insulated therefrom, a charging conductor electrically connected conductively with said insulated section for reducing bound charges in said transmission line and for charging the insulated'section of said support, said charging conductor being connected to ground through a conductor path having approximately the same rate of dissipation of a charge from the insulated portion of said support as the rate of dissipation of a like charge from the portion of said transmission line adjacent saidsupport.

27 The combination of a support having a a conductor section insulated from ground,

a transmission line mounted on said insulated section and insulated therefrom, a charging conductor electrically connected conductively with said insulated section for reducing bound charges in said transmission line and for charging the insulated section of said support, said charging conductor being connected to ground through a conductor having approximately the same rate of dissipation of a charge from the insulated portion of said support as the rate of dissipation of a like charge from the portion of said transmission line adjacent said support, and means forming a protective discharge gap to ground from said insulated section.

28. In combination, a transmission line support, an insulator mounted on said support, a transmission line carried by said insulator, said support comprising a portion formed of insulating material and a chargereceiving portion disposed in the vicinity of said transmission line but insulated from said transmission line, said charge-receiving portion being insulated from ground by the insulating portion of said support, and a discharge path extending from said charge-receiving portion to ground, said discharge path having an air gap therein normally electrical ly separating said charge-receiving portion from ground but arranged to be bridged by an are when the potential in said charge-receiving body exceeds a predetermined value, said discharge gap having terminal members for spacing said are away from the insulating portion of said support.

29. In combination, a support for a transmission line, an insulator mounted on said support, a transmission line carried by said insulator, said support having an insulating portion and a charge-receiving portion insulated from ground by said insulating portion, said charge-receivin portion being disposed in the vicinity 0 said transmission line but insulated therefrom, and a leakage path extending from said charge-receiving.

portion to fground and bridging the insulating portion 0 having sufficiently high resistance to retain an induced charge in said charge-receiving portion for a-suflicient length of time'to prevent discharge from said transmission line to said charge-receiving portion when simi lar charges are induced in said transmission line and said charge-receiving portion.

30. In combination, a transmission line support, an insulator mounted on said support, a transmission line carried by said insulator, said support having a portion thereof formed of insulating material and having a charge-receiving portion disposed in the vicinity of said transmission line but insulated therefrom, said charge-receiving portion being insulated from ground by the insulating portion of said support, a conductor forming a leakage path from said charge-receiving portion to ground away from the insulating portion of said support, the resistance of said path being suflicient to retain a said support, said leakage path charge in said charge-receiving portion for a period of time substantially equal to that for which a similar charge is retained by said transmission line adjacent said charge-receiving body, and discharge horns forming an arcing gap across the insulating portion of said support and spaced therefrom to provide a discharge path from said charge-receiving portion to ground when the potential of said charge-receiving portion exceeds a predetermined value.

31. In combination a high potential transmission line and a support on which said line is mounted, said support comprising a section of conducting material at the top thereof, insulating means for supporting said line on said top section and an insulating section interposed between said top section and ground, all mechanical stress transmitting portions of said support that span said insulating section being of insulating material, and a resistance leakage shunt forming a leakage path separated from the material of said insulating section bridging said insulating section and having sufliciently high resistance to maintain the potential induced in said section of conducting material by an external influence, approximately equal to the potential induced in said transmission line by the same influence.

' 32. In combination a transmission line supporting structure having a portion formed of 1 Wood, an insulator carried by said structure and electrically separated from ground by said wood portion, a transmission line carried by said insulator, a metal charge receiving body mounted on said wood portion adjacent said transmission line but insulated therefrom by said insulator,-and a discharge path from said charge receiving body to ground, said discharge path having a gap therein spaced from said wood portion and formed by arcing horns spaced from each other to break the continuity of said path but arranged to be bridged by an are when the potential in said charge receiving body exceeds a predetermined amount.

33. In combination a transmission line conductor, a support for said conductor comprising an upper metallic section, a grounded section, an insulating section interposed between said metallic and said grounded sections, all mechanical stress transmitting means which span the space between said upper section and said grounded section being formed of insulating material, insulating means for supporting said conductor on said metallic section, and discharge members for directing an are between said metallic and said grounded sections in a path away from said insulating section.

34. In combination a high potential transmission line conductor, a support for said conductor comprising metallic sections, said conductor being mounted on the upper one of ually diverging from said insulating section and terminating in the medium adjacent said insulating section, and providing the shortest air discharge gap between said metallic sections.

35. In combination a high potential transmission line conductor, a support for said conductor comprising an upper metallic section, insulating means supporting said conductor on said metallic section, a lower metallic section, an insulating section interposed between said metallic sections and arcing members connected with each of said metallic sections and extending therefrom in overlapping relation with said insulating sections, said members having the ends thereof connected with said metallic sections closely adjacent the surface of said insulating section but arranged to diverge gradually away from the surface of said insulating section, the space between said arcing members constituting the shortest air discharge gap betweensaid metallic sections.

36. In combination a high potential transmission line conductor, a support for said conductor having a port1on of conducting ma terial at the top thereof, an insulator supporting said conductor on said top portion, an insulating section separating said top portion from ground, and a charging wire electrically connected conductively with said top portion.

37. In combination a high potential transmission line conductor, a support for said conductor comprising an upper metallic section,

an insulating section separating said metallic section from ground, insulating means supporting said conductor on said metallic section and insulating said conductor from said metallic section, and a charging wire electrically connected with said metallic section, said charging wire having a sectionalizing insulator interposed therein. 38. In combination a high potential transmission .line conductor, a support for said conductor comprising a tower having upper. and lower metallic support sections, an insulating section interposed between said metal- 'lic sections, an insulator carried by said upper metallic section, said conductor being carried by said insulator, and a high resistance conductor electrically connected conductively with said upper section and bridging said insulating section and spaced away from the material of said insulating section for conducting leakage current between said metallic sections and for preventing such leakage current from causing injury to said insulating section.

39. In combination a high potential transmission line conductor, a support for said conductor comprising a tower having upper and lower metallic support sections, an insulator carried by said upper metallic section, said transmission line conductor being carried by said insulator, a wood section interposed between said metallic sections and a high resistance conductor electrically connected conductively with said upper section and bridging said wood section and separated from the material of said wood section for preventing .injury to said wood section by leakage and charging currents.

40. In combination a high potential transmission line conductor, a support for said conductor comprising a tower having upper and lower metallic sections, a wood section interposed-between said metallic sections, said transmission line conductor being mounted on said upper metallic section and insulated therefrom, and a condenser and a high resistance conductor each having a terminal thereof electrically connected conductively with said upper metallic section and each bridging said wood section said high resistance conductor being distinct from the material of said wood section.

41. In combination a high potential transmission line conductor, a support for said conductor comprising upper and lower metallic sections, a wood section interposed be tween said metallic sections, an insulator supporting said conductor on said upper metallic'section, discharge horns on said metallic sections and directed toward each other across said wood section in spaced relation with said wood section, and a shunt for leakage current bridging said wood section and spaced away.

from the material of said wood section.

42. In combination a high potential transmission line conductor, a support for said conductor comprising upper and lower metallic sections, an insulating section interposed between said metallic sections, a cross arm on said upper metallic sections, an insulator string supported by said cross arm and carrying said high potential conductor, discharge horns connected with said metallic sections adjacent the opposite ends of said insulating section and directed toward each other over said insulating section, said horns being arran ed to diverge gradually away from the sur ace of said insulatingsection, and a high resistance leakage shunt bridging said insulating section and spaced away from the material thereof.

43. A transmission system comprising a supporting structure having a portion thereof of conducting material insulated from ground, a transmission conductor mounted adjacent said insulated portion and insulated therefrom, and a counter-potential conductor electrically connected conductively with said insulated portion and subject to similar external influences as said transmission line, said counter-potential conductor being connected through impedance of more than a thousand ohms to ground.

A. In a transmission system, a supporting structure having a portion thereof of conducting material insulated from ground, a transmission conductor mounted on said insulated portion and insulated therefrom, a counter-potential conductor electrically connected conductively to saidinsulated portion, said counter-potential conductor being connected through impedance to ground, said impedance being of a value to dissipate charges on said insulated structure portion simultaneously with the dissipation of similar charges from the portion of said transmission conductor adjacent said structure while maintaining a potential on said insulated structure portion approximately equal to the induced potential on said transmission conductor to prevent fiashover from said transmission conductor to said supporting structure.

45. A transmission system comprising a conductor line, a support for said line having a portion thereof of conducting material adjacent said line insulated from ground, said line being insulated from said support, means subject to conditions similar to those of said line and electrically connected conductively with said insulated portion for charging said insulated portion similarly to charges on said line resulting from disturbances afi'ecting said line and for dissipating the charge from said insulated portion concurrently with the dissipation of the charge from said line.

&6. In combination a transmission line sup porting structure having a portion formed of wood, an insulator carried by said structure and electrically separated from ground by saidwood portion, a transmission line carried by said insulator, a metallic charge receiving body mounted on said wood portion adjacent said transmission line but insulated from said transmission line by said insulator, a counter-potential conductor electrically connected conductively with said charge receiving body and extending adjacent said transmission line, and a leakage shunt bridging said wood portion but separated therefrom and forming a path from said charge receiving body to ground, said leakage shunt having sufiiciently high impedanceto maintain a charge on said charge receiving body for a period of time approximately the same as the timethat a similar pliarge will be retained by said transmission ine.

47. In combination a transmission line supporting structure having a portion formed of wood, an insulator carried by said structure and electrically separated from ground by said wood portion, a transmission line carried by said insulator, a metal charge receiving body mounted on said wood portion adjacent said transmission line but insulated therefrom by said insulator, a counter-potential conductor electrically connected with said charge receiving body and extending adjacent said transmission line, a discharge path from said charge receiving body to ground, said discharge path having a gap therein spaced from said wood portion and formed by arcing horns spaced from each other to break the continuity of said path but arranged to be bridged by an are when the potential in said charge receiving body exceeds a predetermined amount, and a high resistance shunt spaced from said wood portion and forming a leakage path from said charge receiving body to ground, the im: pedance of said shunt being suflicient to maintain a charge on said charge receiving body induced by an external influence afiectmg said counter-potential conductor and said transmission line for a time approximately the same as the time said transmission line retains its charge induced by the same external influence.

In testimony whereof I have signed 111 name to this specification on this 27th day of May, A. D. 1926.

ARTHUR O. AUSTIN.

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