Johnson v. Duquesne Light Co.

29 F.2d 784, 1928 U.S. Dist. LEXIS 1640
CourtDistrict Court, W.D. Pennsylvania
DecidedAugust 15, 1928
Docket1206
StatusPublished
Cited by1 cases

This text of 29 F.2d 784 (Johnson v. Duquesne Light Co.) is published on Counsel Stack Legal Research, covering District Court, W.D. Pennsylvania primary law. Counsel Stack provides free access to over 12 million legal documents including statutes, case law, regulations, and constitutions.

Bluebook
Johnson v. Duquesne Light Co., 29 F.2d 784, 1928 U.S. Dist. LEXIS 1640 (W.D. Pa. 1928).

Opinion

SCHOONMAKER, District Judge.

This is a patent suit involving the validity and infringement of Johnson patent, No. 1,366,-078, issued January 18,1921, on application filed March 16, 1918, Serial No. 222,947.

Claims 6 to 11 of the patent are in suit. These all undertake to cover a method of testing of strings of suspension insulators on live transmission lines for the purpose of ascertaining whether or not any of the insulator units is defective.

As applied to electric lines, an insulator is a barrier to prevent the flow of electric current. On telegraph lines and low voltage transmission lines, single insulators are used, but on higher tension lines the number of insulators is increased to care for the increased voltage. These insulators are of porcelain, and, when a number of them are used, they are placed one on top .of the other, being connected either by cement or metal parts, as in the so-called pin type of insulators; or they are connected in a string, forming what is known as suspension insulators. It is to these that the method of testing of the patent applies.

In this string of insulators, each assumes a share of the insulating effect. The voltage distribution to each insulator in the string is not uniform, however, but varies; the insulator next to the line having the greatest voltage across it, and the voltage decreasing with each insulator until the insulator next to the grounded tower is reached. If an insulator is entirely defective, the entire line voltage will have to be withstood by the remaining insulators of the string; if partially defective, it will carry but a part of its normal voltage, easting a greater burden, therefore, upon the remaining good insulators of the string.

The normal distribution of voltage to this string of insulators is known, and was determined, by w.ell-understood electrical principles, befor'e the Johnson patent. If a single insulator did not carry its expected voltage, it was, of course, defective... To ascertain whether a- single, insulator located, in a string of insulators on a live transmission line was carrying its normal share of the *785 voltage or not, you would necessarily corn-. pare its actual condition with its normal and expected condition in a string of good insulators by some voltage determining device. A common device recognized by the standard rules' of the American Institute of Electrical Engineers for the last 20 years is the spark gap.

The patent in suit sets forth a procedure in which ares or sparks are drawn from the metallic parts of the insulators in the string, and the intensities of the arcs drawn from the different parts of the insulators are compared. The lineman making the test must know from experience about what the normal voltage distribution is over the different insulators of the string. If he finds, as indicated by the length of the sparks, that the voltage over each insulator is that which would be normally expected from its position in the string, then the voltage distribution is normal, and the string of insulators is good. If, on the other hand, he finds that there is no arc, or that the arc is shorter than expected from that insulator normally, he knows that the insulator is partially or wholly defective. The procedure of the patents describes two necessary steps in this method of testing: (1) The feeling out of the string insulators by a buzzer to ascertain whether insulator faults be great or small; (2) the short circuiting of each insulator, one at a time, in receding order from the line wire, and noting the sound made and the length of the are drawn. The instrument used in this test is a long wooden stick with a metallic fork at its end, commonly called a buzz stick. No novelty is claimed for this instrument, which was apparently well known before the Johnson patent. In the feeling out procedure, one horn or tine of the metallic fork at the end of the buzz stick is touched to the line wire, and then moved away therefrom to draw an are or spark. The character of the sound is noted. The same procedure is then repeated with relation to the cap of each insulator in its regular order from the line wire; the sound and length of are being noted. If the insulators are good, the are and sound progressively diminishes as the testing recedes from the line wire, except that the cap of the insulator next to the tower gives more sound and a longer, spark than the second one from the tower. If any one of the string is defective, the spark will have the same intensity as that drawn- from the cap of the insulator next below it.

In the short-circuiting process, having first ascertained from the feeling-out process that the string, as a whole, is not perfect throughout, but that only a minority of the insulators are defective, the buzz stick is applied so that one horn or prong touches the hanger of each insulator and the cap thereof, thus short circuiting the hanger of an insulator onto the cap thereof. An arc is drawn from the cap of each insulator and its character noted. If there is a perfect string of insulators, there will be a progressive diminution of sound and the length of the are as you recede in your testing from the line wire. A bad insulator will act as though it were not present.

According to the teachings of the patent, both steps are necessary to this method of test. The patent, lines 22-31, page 1, says:

“In accordance with the invention it is first necessary to feel out the string insulators by an instrument which, because of the noise produced in feeling out, is termed a buzzer, the feeling out proceeding from the line wire toward the end of the string of insulators remote from the line-wire, this procedure avoiding danger of burning out the string of insulators should it transpire that the string is badly at fault.”

Again, lines 53-64, page 2:

“The procedure just described is what is called the feeling out the string of insulators and is needful to prevent the burning out the string should it transpire that, say, only one of the string of insulators is a perfect one and the others are all defective or most of them are defective. Such burning out would occur in the next step of the procedure in which the testing is to ascertain the particular insulators in a string that are defective, especially when such defects occur in the major portion of the number of insulators in the string.”

And again, line 121, page 2, to line 5, page 3:

“The preliminary procedure or feeling out process is needful to prevent a flash-over and a knock-out which Would result if there should be but one good insulator in a string and this insulator was short circuited in the final test locating the particular faulty insulators. Such danger is removed by the feeling out process which does not go to the extent of short circuiting any insulator and it gives a rather clear indication as to whether there are enough good insulators in the string to stand the short circuiting process.”

It will thus be seen that the short-circuiting step cannot be applied until the preliminary feeling-cut process is gone through. Nor can it be applied at all if a majority of the insulators in a string is ascertained in the feeling-out process to be faulty because *786 of the danger of a flash-over or a blow-out in the line.

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Bluebook (online)
29 F.2d 784, 1928 U.S. Dist. LEXIS 1640, Counsel Stack Legal Research, https://law.counselstack.com/opinion/johnson-v-duquesne-light-co-pawd-1928.