US 3324335 A
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June 6, 196? 31mm I 3,324,335
HIGH VOLTAGE PROTECTOR BLOCK Filed Sept. 25, 1963 @NVENTOR MECHAEL Sewn 0 United States Patent 3,324,335 HIGH VOLTAGE PROTECTOR BLOCK Michael Simko, London, Ontario, Canada, assignor to Northern Electric Company Limited, Montreal, Quebec, Canada Filed Sept. 23, 1963, Ser. No. 310,620 5 Claims. (Cl. 313-244) This invention relates to a method of making a high voltage protector block which may be used to safe-guard telephone equipment and persons using such equipment from lightning or other sources of high voltage that could contact the telephone lines connecting such equipment.
In the past, high voltage protector blocks have been made by inserting a carbon rod through a hole in the end of a cup-shaped porcelain insulator having a well so that one end of the rod protrudes beyond the mouth of the well. The rod is then secured in the insulator at the hole by heating and fusing with powdered glass after which the protruding end of the rod is ground flush with the mouth of the well. The whole assembly is then reheated thereby softening the fused glass after which the flush end of the rod is pressed back into the well a predetermined distance. This distance depends upon the voltage which the protector block must withstand without breakdown, as will be explained hereinafter. A fiat carbon plate is then placed over the mouth of the well. Thus, a small air gap is formed between the depressed end of the rod and the adjacent surface of the plate.
To insure an even surface on the adjacent surface of the plate, the plate is ground and lapped prior to assembling it with the insulator. This grinding and lapping operation removes a desirable skin from the surface of the plate.
In use, a protector block is connected in shunt between each side of a telephone line and ground. When a high voltage, due to lightning or high tension wires falling across the lines, strikes the lines .the air in the gap readily ionizes and the high voltage is effectively grounded, thereby protecting any equipment connected to the lines. To be effective, the protector block must be able to discharge the high voltage many times without breaking down.
To do this the width of the air gap must be maintained as wide as possible in order to avoid fusing between the end of the rod and the adjacent surface of the plate. In addition, it must not be allowed to exceed a predetermined maximum or else the desired protection would be lost. Therefore, the width of the air gap must be held within very close tolerances if maximum protection for the connected equipment and life of the block is to be obtained.
In typical protector blocks produced by prior methods, the limits for the width of the air gap between the end of the carbon rod and the adjacent surface of the plate are set at 0.0033 inch (+0.0000, 0.0010). However, in production it has been found very diflicult to stay withing these tolerances using the above-described method of manufacture. When the fusing glass is reheated and the rod depressed into the well to form the required air gap, the rod often cants due to tolerances between the external diameter of the rod and the internal diameter of the mounting hole in the insulator. Consequently, the ground end of the rod is no longer parallel with the mouth of the well. Therefore, at a small point or area on the end surface of the rod, the width of the air gap is less than required. This often results in the carbon rod fusing over to the carbon plate during the initial breakdown tests on the protector blocks thereby rendering it useless and resulting in a large percentage of rejects.
These disadvantages have been overcome in the present invention by substituting an improved method of manufacture. According to the invent-ion, the rod is first inserted through a hole in the end of the porcelain insulator so that the rod protrudes beyond the mouth of the well in the insulator. The rod is then fused in place at the hole using powdered glass, after which the protruding end of .the rod is ground flush with the mouth of the insulator. A carbon plate having a depression is then placed over the mouth of the well. The depression in the plate is located opposite the end of the rod thus forming an air gap. With this method, it is no longer necessary to reseat the rod by reheating the fusing glass and depressing the rod into the well to provide the air gap. Thus, misalignment of .the rod with respect to the plate is avoided. In addition, the depression in the plate and thus the width of the air gap can be readily held within an overall tolerance of 0.0002 inch as opposed to a tolerance of 0.0010 inch obtained by the previous methods of manufacture. This greatly improves the quality of the protector block thereby reducing the number of failures that existed previously.
The step of grinding and lapping the surface of the plate is now obviated since the depression in the plate is formed by pressure from a die having finely polished surfaces. This reduces the cost of producing the plate and avoids removing the skin from the surface of the block. The cost of producing the block is also reduced since the cost of making depressing in the carbon plate is considerably less than the cost of reseating the rod after grinding its end flush with the opening in the porcelain insulator.
An example embodiment of the invention will now be described with reference to the accompanying drawings in which:
FIGURE 1 is a partially exploded and cut away view of a protector block, and
FIGURE 2 is a cross-sectional side elevation of the assembled protector block taken through the line 11-11 of FIGURE 1.
Referring now to the drawings, the protector block comprises a porcelain insulator 10 having a well 11 which opens at a mouth 12. A carbon rod 13 is inserted through a hole 14- in the end of the well 11 opposite the mouth 12 so that one end 15 of .the rod 13 protrudes beyond the mouth 12. The rod 13 is then secured in place in the porcelain insulator 10 by powdered glass 16 which is fused to the rod 13 and the insulator 10 by the application of heat in an induction furnace (not shown). The end 15 of the rod 13 is then ground flush with the mouth 12 of the well 11. A carbon plate 17 in which a shallow depression 18 has been made is placed across the mouth 12 of the well 11. The plate 17 is held against the insulator 10 by an exterior casing (not shown) under a pressure of approximately eight pounds. The width of the depression 18 is approximately the same as the width of the well 11. Thus, a small air gap 19 is formed be- .tween the end 15 of the rod 13 and the adjacent surface of the carbon plate 17. In a typical protector block the depression 18 in the carbon plate 17 is formed by pressing a die (not shown) having a step of 0.0033 inch (+0.0000, -0.0002), into the plate 17. The depth of the step depends upon the desired width of the air gap 19, which is determined by the desired breakdown voltage of the protector block. In production, it has been found expedient to form the depression 18 in both sides of the plate 17. Thus, in a typical protector block, the spacing of the air gap is held within 0.0033 inch t(+0.0000, 0.0002).
Tests over a six month period have shown that the blocks manufactured using the new method lasted an average of 42.6 cycles before breaking down. In comparison, those manufactured by the prior method averaged only 22 cycles. It was found that none of the blocks manufactured by the new method failed under 20 cycles.
What -I claim in my invention is: 1. A high voltage protector block comprising an insulator having at least one side wall forming a well and terminating in a mouth and an end wall opposed to the mouth, a conductive rod located in said end wall so that one end of said rod is flush with the end of said side wall defining the mouth of the well, and a conductive plate located across said mouth of the well, said plate having a depression adjacent said one end of the rod whereby said rod is spaced from said plate.
2. A high voltage protector block as defined in claim 1 in which both the conductive rod and the conductive plate are made of carbon.
3. A high voltage protector block as defined in claim 2 in which the conductive rod is glass fused to the insulator.
4. A high voltage protector block as defined in claim 3 in which said plate fully covers the mouth of the Well. 5. A high voltage protector block as defined in claim 4 in which said rod is concentrically located in said end of the well and the depression is concentrically located in said plate.
References Cited UNITED STATES PATENTS 865,291 9/1907 Bell 313247 1,595,665 8/1926 Kirkm-an 313325 2,145,375 1/1939 Schultz 313-231 2,295,379 9/ 1942 Beck et a1. 313325 2,999,960 9/1961 Cunningham 313--231 3,211,940 10/1965 Hueschen 313325 JOHN W. HUCKERT, Primary Examiner.
A. J. JAMES, Assistant Examiner.