Line Insulation of 16,000 Volts

[Trade Journal]

Publication: The Journal of Electricity

San Francisco, CA, United States
vol. 4, no. 6, p. 113-114, col. 2, 1-2




(A paper read before the Santa Cruz Convention of the Pacific Coast Electric Transmission Association. August 17, 1897.)


The problem of long distance transmission of power electrically is, of course, solely a question of high voltage and the satisfactory insulation of copper conductors. We are in this, simply imitating nature's thunderstorm methods and at the same time attempting to avoid her erratic practice of reckless conduction and haphazard discharge. Indeed, the first human inter-meddling in long distance transmission was simply on endeavor, by lightning rods, to attract, restrain and conduct to earth, the sportive thunderbolt, regardless of the solemn declaration of the poet that


"Lightning does the will of God And from its force nor doors nor locks, Can shield you;"


and we are reminded comically of the protest of Abbe Nollet and his set in France, against Benjamin Franklin's proposal to protect buildings front the thunder-storm, which protest was ill effect, that "to ward off Heaven's lightnings was as impious as for a child to shield itself front the chastening rod of a father."

Our commercial currents begin to approximate to the lightning's potential, but we are furnished whit the very hest possible lines of least resistance, and with the fewest and least feasible outlets for escape by the way. Our thunderbolts are arc lights, incandescent lamps and the torque on the shafts of motors. We play .1upii or with results that would have immensely astonished the Roman augurs, and Heaven does not in consequence frown upon our impiety. The problem of high potential has been solved in transformers and high tension generators. Insulation, however, is a less satisfactory field of experiment and experience. To conduct even lightning is easy enough, but to prevent the leakage of a current of only a few thousand volts is difficult.

The following will simply give the solution of the problem of insulation as attempted by the Central California Electric Company, together with experiments accumulated:

The transmission line of the Central California Electric Company extends from Newcastle, in Placer County, in a nearly straight course southwesterly to the City of Sacramento, and is a trifle more than twenty-eight miles long. For the first five miles the poles are of thirty foot sawed redwood and for the remainder of the distance they are of forty foot Washington cedar. The cross arms are five feet long and carry two pins of oak, three and one-half feet apart. A third pin is bolted on to a V-shaped iron strap, which latter is double lag-screwed into the top of the pole and thus the pins form on each pole an equilateral triangle. Three wires form the current and these are spiraled every mile.

The voltage at the power-house is but a little under 16,000 and insulators were selected from the petticoated porcelain variety. They are of the familiar Locke pattern, having enameled surfaces and- three petticoats, the middle of which is longer than the other two, and the wires were fastened in the regulation way on the top groove, except where there was likely to be a lateral strain, in which case they were tied against the off side. At sharp corners there was substituted for the entire iron arrangement of the topmost pin, a block placed out of equilateral on the side of the apex of the pole opposite the strain. In places the high potential wires come within eight inches of each other, but without tendency to arc. Only three annoyances have developed in connection with this arrangement, viz:

First—Some of our petticoats have been shot off by unprincipled, malevolent or thoughtless sportsmen—an evil which was easily remedied by the posting of a reward notice on every fifth pole.

Second—A few insulators (we are not sure of more than seventeen) were seriously defective on surface and split off and broke up under the stress of potential.

Third—A number of poles with defective insulators were burned in whole or in part, owing to the presence of sap, which acted as a conductor to the ground. It will lat well to remark here that our line was erected in two different divisions full a year apart, the first eight miles to Rocklin having preceded the remaining twenty miles to Sacramento by fully a year. The poles of 1896 up to the beginning of the present dry season, were still more or less green. The burning always occurred in these and the defect was invariably in the topmost insulator when the ground was wet. The current escaped through slight cracks in the enamel and crossing the spongy, wet, inner, porcelain, followed the iron of the V-shaped support and penetrated the cedar by the lag screws to find in the sap a good conductor to the moist ground. This thread of current heated, charred and consumed the inflammable wood. Probably a dozen poles were wholly or in part destroyed, but strange to say, this seldom caused serious disarrangement to the wires or interruption to the service. Indeed, we generally learned of the untoward occurrences, not from our switchboard instruments, but from locomotive engineers and freight car conductors, or from telephone messages front villages in the vicinity of the disaster. No pins have been burned or even charred by play of rain-drops or through spider webs, and this is doubtless owing, to the length of the middle petticoat.

We have found that by the assistance of a portable telephone a defective insulator can be exchanged with a shut down on the line of from five to nine minutes. The entire pole line is inspected and every insulator scrutinized each day.

Our firm conviction is that 30,000 volts can be easily restrained with our present insulators, provided the pins are of approved materials or that both arms and pins are boiled in paraffine and then soaked in P. & B. paint. The poles should be of redwood because this will endure a higher degree of heat than cedar without combustion, not to speak of the fact that redwood offers for the same reason greater resistance to stubble and forest fires.

In conclusion we believe that the art of insulation is in its incipiency and we see no reason to doubt that much higher potential than 30,000 volts can and will be used and controlled.


Keywords:Power Transmission : California : Fred Locke : R. Thomas & Sons Company : U-923C
Researcher notes:The porcelain insulator described is Fred Locke's U-923C made for him by R. Thomas & Sons Co. from dry process porcelain.
Supplemental information:Articles: 10508, 10509, 10510
Researcher:Elton Gish
Date completed:December 27, 2009 by: Elton Gish;