US 1847460 A
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March 1, 1932. V A.' o. AUSTIN MEANS FOR INCREASING FLASH-OVER VOLTAGE AND RESISTANCE BETWEEN HIGH PENSION CONDUCTORS AND GROUND Filed June 1 192 I L 11 301R; q v r k Patented Mar. 1, 1932 UNITED s ATEs PATENT OFFICE ARTHUR O. AUSTIN, OF NEAR BARBIEZRTON, OHIO, ASSIGNOR, BY MESNE ASSIGNMENTS, TO THE OHIO BRASS COMPANY, OF MANSFIELD, OHIO, A CORPORATION OF NEW JERSEY MEANS FOR INCREASING FLASH-OVER VOLTAGE AND RESISTANCE BETWEEN HIGH TENSION CONDUCTORS AND GROUND Application filed June 1, 1926. Serial No. 112,746.
This invention relates to structural supports for high tension conductors and has for its object the provision of means for increasing the flash-over voltage and resistance between the conductors supported on the structure and ground and at the same time maintaining high resistance between the conductors and ground. A further object 18 to provide a support in the class named which shall be of improved construction and eflicient in operation.
The invention is exemplified in the combination and arrangement of parts shown in the accompanying drawing and described in the following specification and it is more particularly pointed out in the appended claims.
In the drawing- 1 The figure'is an elevation of the top portion of a supporting tower for high potential conductors having one embodimentof the present invention applied thereto.
In the drawing are shown insulator strings 10 and supporting conductors 11. The insulators are supported from cross-arms 12, 13,
14, 15, 16 and 17. The main body of'the tower 18 is metal, whereas the members 12, 13, 14, 15, 16, 17, 19 and 20 are of wood or other high resistance or insulating materlal. While a wood-cross-arm is very effective in increasing the resistance to ground" and in avoiding trouble from birds where bird droppings tend to shunt the insulators they are usually weak -mechanically and require braces. There is also danger tnat the crossarms may burn due to leakage or charging current over the insulators. The improved construction, one arrangement of which is shown in the drawing makes use of the insulation furnished by wood or insulating members and at the same time avoids the usual additional hazards produced by these members.
increased to such an extent that an arc will be established between the conductor and ground over the insulator or from the con- Most flash-overs on transmission lines are produced by surges of high magniductor to the grounded tower structure. The greater the difference in potential between the conductor and tower structure the greater the danger of flash-over.
It is evident that where the potential or voltage necessary to strike an are from the tower conductor to the supporting structure is increased, the probability of an interruption will be decreased. It is also, evident that as the voltage between conductor and grounded structure is lowered, the danger of an are forming will be lessened. It is understood that the path of the arc may be over the insulator or through the air to ground and that a diflerence in voltage or potential is necessary in order to cause the arc to form. If the tower were an insulating member the same as the insulator instead of a conducting member as is the usual practice there would be little tendency for an arc to form between conductor and structure or from the conductor over an insulator.
and add greatly to the reliability of the transmission line. The desired results can best be accomplished by the combination of several factors. It is generally recognized that the use of ground or static wire tends to reduce the maximum voltage imposed by lightning on the conductors. The ound wire, however, tends to lower the resistance to ground and an are striking from the con-- ductor to the tower will usually result in a power are and an interruption in service.
In my improved method, practically all of the general advantages of the static wire are maintained but a new function is added which greatly enhances its value eliminating flashovers.
Static wires 21 and 22 are shown mounted on the structure. With the arrangement shown any number of static wires may be used and they may be either above or below the conductors or'intermediate, depending upon the severity of conditions and results desired. The static wires may serve as a mechanical means for steadying the structure or be in the form of guys providing they include an insulating section in their length. The insulating section may consist of any of the usual forms of tension insulators inserted in the guy wire either at one point or distributed, or the insulator may consist of a wooden section with proper metal attachments for attaching to the guy.
In operation the effect ofthe combination in preventing an are from conductor to ground is as follows. A high resistance element 23 may be used to jumper or shunt the insulating section made of members 19 and 20. The resistance of this member may vary within wide limits and still not cut out the effective insulation of the insulating zone made of members 19 and 20 for surges or potentials produced by lightning. In most cases a resistance of several thousand ohms will prevent burning due to any unbalanced current but the resistance may be as low as fifty or one hundred ohms and still be quite effective in producing a high back E. M. F. during the lightning discharge. Under normal operating conditions with a highly charged cloud over the system, a static wire 21 or 22 will acquire a bound charge, the current for producing the charge flowing up through the resistance 23 over the insulating members 19 or from a portion of the static wire 21 which may be grounded. Since the charge is accumulated slowly, the static wire will assume a ground potential even though the current has to flow over a high resistance. Being at a ground potential it will reduce the bound charge on the conductors 11 in accordance with well known electrostatic laws. When the charged cloud overhead discharges, the bound charge on the conductor as well as the bound charge on the static wire is released simultaneously. Since, however, the bound charge on the static wire and the conductor is of the same polarity the difference in potential will not be very great providing the charges are allowed to flow away on the static wire at approximately the same rate as on the conductor. It is evident that if the static wire is insulated the same as one of the conductors, that this condition would be ap proximated. While these conditions could be set up by using one of the conductors for a static wire, the bound charge might produce'a sufiicient potential between the conductor and a grounded tower to cause an arc to ground. By tying the static wire directly into the conducting tower members adjacent the insulator and providing an insulated zone between the upper section of the conducting tower members and ground it is possible to utilize the bound charge on the static wire to advantage by raising the potential between the body of the tower and the conductor for abnormal potential produced by lightning. By making the impedence of the static wire high it will tend to retain its bound charge where this is too high so that the insulated tower section will not develop too high a potential with respect to the line. This may be controlled by lowering the resistance of the element 23 shunting the resistance zone.
From the above it appears that the static wire is used to obtain a new result, so that the effective flash-over voltage between conductor and tower or ground is raised for the most serious of high voltages produced on transmission lines.
Where insulated arms projecting from the body of the tower are used, it is possible to space conductors more closely together as the tendency to are from the conductor to cross-arm or brace below will be less than where conducting members are used. This permits of a closer vertical spacing of conductors compared to the horizontal spacing to the tower member. Long cross-arms, however are difficult to construct of wood or insulating material without the use of braces. Three methods of bracing the cross-arms are shown.
The cross-arm 12 is braced by a metal member 24. This member is attached to the peak of the tower which is formed with wood or insulating members 25. Where these members have the same equivalent resistance or insulation as the arm 12, the metal brace will not seriously reduce the effective insulation of the arm. If, however, it is desired to develop the full insulation of the arm with rather short members 25, an insulator 26 may be placed in the brace. In some cases it may be desirable to use a wood brace 27. By making up the cross-arms and braces of rather thin wide members and attaching metal plates at the ends, it is possible to make up a very strong structure which will develop a large percentage of the strength of the wood members. In using multiple wood members it is preferable to allow space between the parts so that a low resistance path due to water held by capillary attraction will not be produced. Where leakage over the insulators is sufiicient that there is danger of the wood members burning, a shunting resistance member 28 may be used. This resistance element may be placed along the arm or along the brace as in 29. Where leakage is likely to be very severe over the insulator due to accumulation of dirt or conducting films and fog, the resistance element 28 or 29 must be lower than where the leakage or charging current over the insulator is very small.
While a resistance as low as fifty or one hundred ohms may be quite effective in utilizing the insulation of the arm for lightning disturbances, the resistance can usually be several thousand ohms and still protect the wood members from burning due to leakage current. It is evident that a supporting structure may be provided with one or more insulating zones as desired. In order that these insulating zones be most effective, however, it is necessary that they be well up in the structure so that the bound charge taken up by the tower or by the static wires will raise the potential in the tower sufficiently high so that an arc will not take place between conductor and-the insulated section of the tower. It is evident that the arrangement shown is applicable to either new or old structures. The insulated members 19 and 20 may be protected from a direct stroke of lightning by using a discharge gap-made of members 30. The distance between the members 30 being suflicient that a' discharge will take place at this point at a lower potential than along the members 19 and 20. The shunting resistance 23 as well as the resistances 28 and 29 can be eliminated where the leakage over the insulated sections is suflicient to prevent burning. The resistance elements may be simply formed by use of ordinary high resistance leads or they can consist of a combination of metallic members in an electrolyte or in a bath of oil, or the resistance may be made up of a column of conductin liquid. If this li uid or electrolyte has a high negative coef cient, a heavy leakage maintained for any length of time will heat it up and lower its resistance so that there will be little danger of damage. Where there is no danger of freezing a column of water in a porcelain, fibre or glass tube may be used, the resistance being regulated by the addition of any suitable electrolyte. The resistance may generally be used within wide limits, as the leakage current at normal frequency may produce only a few volts drop while the same resistance may produce a drop in voltage of several hundred thousand volts during a lightning discharge. If a conductor comes in electrical contact with the tower, by dropping on an armor through failure of an insulator, the
resistances may not withstand the load for any great length of time. They usually can be so proportioned that the relays will be operated before they will be destroyed. Where this is not feasible the resistances may be made up of electrolyte which will form gas and clear the short circuit. As the resistance elements are very inexpensive they may be destroyed in the case of a ground without efi'ecting the general efiiciency as a number of grounds on a well built system is relatively small.
I claim-- 1. A transmission line support comprising a metallic mast, a cross arm of insulating material, insulating braces for said cross arm comprising truss members secured to the cross arms adjacent their ends and secured to the mast above the respective cross arms, an insulator supported on said cross arm, and a conductor carried by said insulator.
2. A support for a high potential transmission line comprising a metallic mast having an insulating section therein, all the stress members of said mast which cross said section being formed of insulating material, a wood cross arm carried by said mast above said insulating section, an insulating brace for said cross arm, an insulator carried on said cross arm, and a conductor supported on said insulator.
3. A support for a high tension transmission line comprising a metallic tower or mast having a wood section interposed therein, all the stress members of said mast that cross said section being formed of wood, an insulating cross arm carried by said tower above said wood section, an insulator carried by said cross arm, a conductor supported by said insulator, and a resistance shunt bridging said wood section.
4. A support for a high potential transmission line comprising a metallic mast, an insulating cross arm mounted on said mast, an insulator carried by said cross arm, a conductor supported on said insulator, and a resistance shunt bridging said cross arm but separated from said conductor by said insulator.
'5. A support for a high potential transmission line comprising a metallic mast having an insulating section therein, all the stress members of said mast that cross said section being formed of insulating material, a high resistance conductor bridging said section, an insulating cross arm mounted on said mast above said insulating section, an insulator mounted on said cross arm, a conductor carried by said insulator, and a static wire mountedon said mast above said insulating section and electrically connected with said mast.
6. A support for a high potential conductor comprising a metallic mast, a Wood cross arm mounted on said mast, an insulating section interposed in said mast below said cross arm, all the stress members crossing said section being formed of insulating material, a high resistance conductor shunting said cross arm, and a second high resistance wire shunting said insulating section.
7. A support for a high potential transmission line comprising a metallic mast having a wood section therein, a high resistance conductor shunting said wood section, a wood cross arm mounted on said mast above said wood section, an insulator carried by said cross arm, a conductor supported by said insulator, a high resistance conductor shunting said cross arm, and a static conductor secured to said mast above said inwood section and electrically connected therewith, insulating braces for said cross arms, a resistance shunt bridging said wood section, insulators carried by said cross arms, and conductors mounted on said insulators.
9. A high potential transmission tower having a wood section therein and having metallic portions above and below said wood sections, a resistance shunt bridging said wood. section, discharge horns forming a path for an arc across said wood section and spaced therefrom, a wood cross arm carried by said support above said wood section, an insulator mounted on said cross arm, and a conductor carried by said insulator.
10. A transmission tower comprising upper and lower metallic sections, an interposed Wood section, a leakage current shunt spanning said wood section, an arc gap spanning said wood section in spaced relation therefrom, insulating means for supporting a conductor on the upper metallic section of said tower, and a static wire electrically connected with the upper section of said tower.
11. A high potentialtransmission tower comprising upper and lower metallic sections, a wood section interposed between said metallic sections, a leakage shunt spanning said wood section, a Wood cross arm mounted on said tower above said wood'section, a static wire secured to said tower above said wood section, an insulator carried by said cross arm, and a conductor supported by said insulator,
12. A transmission tower comprising upper and lower metallic sections, a wood section interposed between said metallic sections, a leakage shunt spanning said wood section, an arc gap spanning said wood section and spaced therefrom, wood cross arms secured to the upper metallic section of said tower, insulating bracing members for said cross arms, leakage conductors in parallel with said cross arms, insulators supported by said cross arms, conductors carried by said insulators, and a static wire electrically connected with the upper section of said tower.
13. In combination a transmission line, an insulator for supporting said line, a structure for supporting said insulator, said structure having a wood portion providing insulation supporting said insulator, said structure comprising a wood member providing 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.
In testimony whereof I have signed my name to this specification on this 27th day of May, A. D. 1926.
ARTHUR O. AUSTIN.
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.
14:. In combination a transmission line, an insulator supporting said line, a structure