[Trade Journal]
Publication: Proceedings of the National Electric Light Association 43rd Convention
New York, NY, United States
p. 673-678, col. 1-2
Maintenance of Live Transmission Lines
Sixty companies operating transmission lines replied to the Committee's questionnaire on this subject. Nine of these companies stated that they are maintaining transmission lines while alive. Five companies use the Johnson method, and four use tools and methods concerning which the Committee has no authentic information. An investigation of live line maintenance devices and work was made on the property of the Georgia Railway & Power Company where the Johnson method was developed. A report of this investigation follows:
The Georgia Railway and Power Company makes a regular practice of maintaining transmission lines alive. All of the work done on these is performed in this manner, the lines not being taken out of service for repairs. During the five years that company has been following this practice it has had occasion to change suspension, strain and pin type insulators; change crossarms, replace poles, change dead-ends on strain insulators to both suspension and pin type insulators, reinforce lines, connect and disconnect branch lines, and to do various other kinds of such work.
From a construction standpoint, all of this work is entirely practicable, as equipment consisting of long handled tools has been especially developed with which the conductors and other live parts may be handled. The handles of these tools are made of well seasoned white oak that has been thoroughly dried and varnished. This kind of wood has proved to be the most satisfactory for this work, and it has been stated that hickory and some other species are unsuited to it owing to their higher conductivity.
A brief description of some of the tools used follows, and those described are illustrated in Fig. 8.
These tools are made locally, and great care is taken to use only thoroughly dry wood. All tools in service and all ropes and other equipment used on live lines are kept in a drying room when not in use so that they are in good condition at all times.
The actual methods employed in working on transmission lines were demonstrated by four different jobs. The first job was changing a defective suspension type insulator on a 110,000 volt transmission line, and is illustrated in Fig. 9. The conductor was supported by block and tackle fastened to the top of the tower, and operated from the ground. A strain insulator was used to insulate the tackle from the conductor. One man on the tower, using a clamp stick, held the conductor away from the string of insulators while the other man changed the insulator by hand. After the new insulator was installed, the conductor was again fastened to the string.
The second job was changing a pin type insulator on a 38,000 volt pole line, and is illustrated in Fig. 10. The tie wire holding the conductor was removed, and the conductor was pushed up and out of the way by two men using clamp sticks. The third man then replaced the insulator by hand, after which the conductor was again tied fast, by means of a tie stick. To facilitate this latter operation, the tie wire is made fast to the insulator before the insulator is installed, the two free ends then being wrapped around the conductor, tying it fast to the insulator.
The third job was removing a disc insulator in a string of three insulators holding a dead-end on the same 38,000 volt line, and is illustrated in Fig. 11. Using a come-along, strain insulator, and block and tackle, the strain of the conductor was taken from the insulators, and the conductor was detached and the loose end supported by a clamp stick. The string of insulators was supported with the forked stick, during this operation. The insulators were then passed to the man on the top of the pole, who changed the defective insulator by hand, after which the string was put back in service.
The fourth job was changing a pin type insulator on a 22,000 volt pole line, and is illustrated in Fig. 12. This pole line carried three Circuits, and the insulator on the end pin of the top arm was changed. Since the insulator to be changed was so inaccessible, it was necessary to use the lifting pole to support the conductor. The lifting pole was supported on the bottom crossarm, and is shown in the illustration supporting the conductor. In addition to the lifting pole, one man on the top of the pole also guided the conductor with a clamp stick.
The other man then unscrewed the insulator, using the tie stick for the purpose. The new insulator was installed in a similar manner. This was necessary in this case as the man could not get near enough to the insulator to replace it by hand.
There is an element of danger in connection with this kind of work, just as there is with any line work where live wires are handled, but there is a difference of opinion among operators whether this danger is relatively greater than that incurred in working on 2400 volt lines. In the latter work it is possible to insulate the workmen reasonably well from the conductors by using rubber gloves, shields and other protective devices; whereas on the higher voltages such appliances are not effective, and dependence has to be placed upon the insulation provided by the long handled tools, and by maintaining sufficient clearances so that the tools can be used without danger of the men coming in contact with other wires. The insulation provided by the tools is ample, as similar tools are used in stations for operating knife switches. The danger in doing this kind of work, therefore depends very largely upon the clearances which can be provided.
Generally speaking, the men are safer when working on the higher voltage lines, 60,000 to 150,000 volts, than when working on lower voltages as the clearances are much greater. Furthermore, the work on such lines is as a rule simpler, as suspension type insulators are usually employed on these lines, which type of construction is more easily handled. In general, live line maintenance is particularly applicable to tower line construction where ample clearances are afforded. A study of the text and illustrations describing the four jobs done will emphasize these statements.
It will take a more complete study than has so far been made before specific clearances can be recommended for the various classes of construction and voltages. It is apparent that if such clearances were specified they would be based on the number and arrangement of the circuits on the pole or tower, the spacing of the wires, the length of section, and other variable features.
