How High-Tension insulators are made at Locke

HIGH-TENSION INSULATORS.

At the works of the Locke Insulator Mfg. Co. at Victor, New York, where the "Victor" insulator is made, the work is on strictly scientific lines, no effort being spared to keep abreast and, if possible, a little in advance of the times. None but the first quality of clay is used in the construction of the modern insulator. From the time the clays are placed in storage bins to the time the finished insulator is shipped from the factory, an expert has a watchful eye upon every process and a daily record of all conditions is accurately kept. Having ascertained, by chemical analysis, the constitution of the various clays, the first concern is to mix them so that a body of maximum electrical and mechanical strength shall result, this being attained only by the utmost nicety of adjustment and constant exercise of engineering judgment. An electrical porcelain pottery is unlike any other kind of works, and unlike even any other pottery, for not only must drying conditions be carefully watched, but the absence of either mechanical or electrical strength in the finished product brings disaster.

Though very finely ground and apparently in the last stage of subdivision, the clays after having been properly mixed as to quantity of each arc placed, together with sufficient water to form a liquid mass, in a ball mill or large iron tub lined with porcelain brick and half filled with quartz pebbles selected from glacial drift in Iceland. The tub is caused to rotate on its supporting axle and the quartz pebbles still further reduce the clays in matter of fineness and thoroughness of mixture. From the ball mill the mixture of clay and water is rim through a lawn or 150-mesh screen to a cistern from which it is drawn by weans of a power pump and forced into filter presses. Filter presses for this class of work are of the type used in many potteries and consist of a series of cast-iron rings separated by sheets of canvas pierced by a 3 in. hole to admit the liquid clay. The canvas sheets so arranged form a series of pockets from which water may readily leak but in which the clay is retained, thus forming "leaves" about 30 in. in diameter. As the pockets become filled with clay the pressure steadily rises until no more can, with safety, be applied. The clay is then ready for working, but to ensure its being homogeneous and thoroughly pliable it is put through a pug mill or large sausage machine which forces it through a die under pressure, whence it emerges as a long "sausage" about 4 in. in diameter. In this state it is delivered to the potter who is thus furnished with a perfectly pliable and reliable clay.

The process of drying and firing of electrical porcelain causes it to shrink about 15 per cent., and accordingly the model of the insulator from which all moulds are made is 15 per cent. larger than the finished piece of ware. Such models are usually turned from blocks of plaster of paris, their surfaces oiled, and the moulds cast from them in one, two or three parts as occasion may require. Having been properly dried, the moulds are tilled with just enough clay by the potter's assistant, and are placed by the potter upon his wheel, where the operation of shaping the inner side of the particular piece under consideration is carried on by the aid of the hands and a properly-shaped former, which is held in place mechanically, and thus produces a perfectly uniform shape inside. The outside, of course, is determined by shape of the mould. The mould with its clay is now set aside for some hours, during which time the plaster performs its function of absorbing the water of the clay immediately adjacent to it. The clay has now become dry enough to handle, and is removed front the mould, carried to the finisher, who by means of a revolving table sets the partially dry ware rotating, a wet sponge and, if necessary, a sharp knife being used to remove any irregularities and produce a smooth exterior. The piece thus finished is now put away and allowed to dry completely, after which it is dipped in a silicate solution, some of which is absorbed by the ware, forming a thin glaze or glass-like surface, whose only function is to produce a smooth finish as well as impart colour to the insulator. At present a dark-brown colour is usually employed, because of its supposed inconspicuousness compared to white; however, it is possible to produce any desired colour by placing in the glaze the proper colouring matter. In some of the smaller-sized insulators the glaze accomplishes a double purpose, for besides covering the surface of the ware it is made to serve as a cement for fastening the parts together, forming a neat and strong joint, for the glaze liquefies at the temperature at which the body vitrifies.

The kilns in which the ware thus prepared is fired are cylindrical, being about 18 ft. in diameter and 16 ft. high, lined with firebrick, and arranged with fire bags around the base, the fire front which is drawn over into the kiln and down through the floor thence to the chimney. In order to protect the insulators during firing they are placed in fireclay receptacles called "saggers," which are piled one on the other until the inside of the kiln is completely filled, after which the entrance to it is bricked up and sealed with timidity mortar. There remains now but to raise gradually the temperature to the required degree, which point is made evident by the fusing-of small porcelain cones placed at regular intervals about the kiln, an opening being left so that ready access may be had to them. Before each opening are placed four cones which fuse at various temperatures, and in firing a kiln the temperature is raised till three of each set of cones are fused and the fourth very nearly so. In watching the cones the heat is so intense that a man cannot face it unprotected and the light is so dazzling that a coloured hand-glass is necessary to soften it so that the eyes can endure it. A thorough knowledge of the exact rate at which the temperature rises has been found very important, and for this purpose a Le Chatelier pyrometer has just been installed. This has a very delicate electric galvanometer which is connected with a platinum-rhodium thermo-couple projected into the kiln. By means of this instrument the temperature can be determined with absolute accuracy. With this knowledge at hand the temperature is raised with such regularity that no unnecessary strains are created in the ware by sudden variations in temperature. The heat within some parts of the kiln is so intense as to fuse the firebrick with which its sides are lined. The proper heat having been attained the tires are allowed to cool down and the annealing process carried on until an insulator absolutely free from internal strains is assured. The door is broken down, and the finished insulators pass from the ceramic to the electrical test and shipping departments.

Insulators designed to carry more than 5,000 volts are subjected to a high-voltage test before leaving the factory. The voltage to which any insulator or part is subjected is usually matte as high as it can be conveniently raised without flashing over. The length of time which such test is applied is usually about one-half to two minutes, according to the purchaser's specifications. Insulators or parts to be tested are inverted in a pan of salt water told a chain front the high-tension wire directly overhead is dropped into the water with which the insulator is partially filled. The pans in which the insulators are inverted are about 35 ft. in length, and enough chains are provided to test as many as 80 large insulators at once on a single rack, additional racks being provided which may be switched on and off by means of a large air-break switch, thus allowing a transformer to be run continuously, eliminating ally waits while loading or testing a rack of insulators. In order to avoid danger of injuring workmen employed about the test, the pans in which the insulators are placed are operated at earth potential, so that all danger is confined to the chains and their supporting conductors.

It is customary to test all parts of the insulator separately before cementing, in order that only perfect parts may be used and also Belt on the final test the failure of a single part may not necessitate the throwing away of a complete insulator, for once the hydraulic cement used for this work becomes set it is impossible to separate the parts without destroying them. The object of the electrical test is to seek out all defects not visible to the eye, such as minute cracks or soft spots in the body of the ware, and to do this with- certainty it has been found necessary to provide a testing equipment with large capacity in order that a moderate draught of current from the secondary shall not reduce its voltage to a low value. At the "Victor" factory the test voltage is supplied by a 200-kw. 300,000-volt transformer, which is capable of working at 500,000 volts and is designed to carry 100 per cent. overload for a considerable time. This transformer is of the core type, with an iron section of approximately 100 sq. in. Normal operation of the transformer at 300,000 volts requires 1,100 volts on the primary, which is made up of four sections to obtain flexibility in connections. The secondary is wound in large flat coils, utilising approximately 42 miles of No. 26 B.&S. wire; the ends of the windings being available, it is a matter of but a few moments' work to change from series to parallel connections. This constitutes by far the largest piece of test apparatus of its kind in the world, and is in constant use for commercial testing as well as experimental work.

There is available for use with the testing equipment 600 volts from a 30-kw. 60-cycle two-phase Stanley alternator, 1,100 volts from a General Electric 60-cycle motor-generator, and 400 volts at 25 cycles directly from the sub-station of the Rochester & Eastern Rapid Railway. Normally the transformer is operated with current from the motor generator set which has a capacity of 200 kw., but for limited periods of time power may be drawn front the railway company to the extent of 500 kw. By this means it is possible to fulfil almost any test requirements.

Adjacent to the commercial test and packing room is the special test and research laboratory, a fireproof building 21 ft. by 48 ft. The floor is of heavy concrete construction so that the vibration of heavy machinery will not be communicated to any delicate measuring instruments. One part is reserved for machinery and transformers, while the other is used as an exhibition and test room, where experiments with the highest voltages may be carried out. The necessary switches and controlling rheostats are located in this room, the high-tension wires entering through large porcelain tubes extending to spark-gap and test rack. As this room may be darkened all experimental work is carried on here so that high-tension phenomena may be more easily observed. For ordinary measurement of high voltages an ordinary spark-gap fitted with sharp needles is employed, but for the sake of a greater facility a simple electrostatic voltmeter has been designed which will measure voltages up to 250,000 without difficulty and with considerable accuracy. It consists merely of it glass jar filled with oil in which are submerged two plates, one being movable and carrying a light vertical plane mirror. The plates are connected so as to be at the same potential, which upon being applied causes the movable plate to swing away from the stationary one, the amount of such deflection being observed by means of a cross-hair telescope and a scale as in an ordinary galvanometer. Any degree of sensitiveness is obtained by varying the distance between the fixed and movable plates. This device greatly facilitates the test of insulators or test plates, as the spark-gap is slow to operate, and is as well subject to considerable error if the needles happen to become burned.

In order to be able at all times to keep a watchful eye upon the ware, plates of ware which dry and are fired much more quickly than the regular insulators are tested several days in advance of the time when the insulators of that particular "mix" enter the kiln. If, then, for any reason, the dielectric strength is low it is known before the clay has been rendered useless. To accomplish this a large porcelain basin filled with oil, supported upon a suitable table, is utilised. In the bottom of the basin a needle-holder is arranged and connection made to one terminal of the testing transformer. Over the basin a small framework supports the other terminal of the transformer which also terminates in a needle point. Needles are used in order that the radius of curvature may be made as important as possible in the various tests. A plate having been inserted the upper terminal is lowered till tile needle touches the surface of the porcelain and the voltage raised till puncture occurs, the voltage being observed by the voltmeter. The plate is then taken out, broken and carefully measured by means of a micrometer. This system of always being forewarned of any fault in the product leads to some very interesting results and yields much positive information regarding the dielectric strength of porcelain and the factors influencing it.

All research on dielectric strength of insulators or similar work is carried on inside the laboratory, but in order to test line insulators under nearly the same conditions to which they will be subjected when in service a cabin has been constructed just outside the laboratory which is fitted with steam and water pipes for humidity and precipitation tests. As this cabin is entirely dark and covers one of the windows of the laboratory, the applied potential may be regulated by the observer, darkness hero as in other high-tension experiments aiding materially in observing the phenomena.

In the machinery room of the laboratory are situated the transformers, generating set and controlling switchboard. All power and lighting circuits are controlled from this point, and by a system of plug connector:4 any combination of circuits may be secured. For power, current and voltage measurements, Thomson inclined-cod instruments are utilised. For very small secondary currents a volt?meter calibrated for current is introduced at the point of earth potential of secondary winding, at which point the current coil of the wattmeter is also introduced, the wattmeter voltage coil being placed across the primary; the fact that primary and secondary voltages are at 180 deg. justifies this method of measurement.

The motor-generator set, which is standard General Electric apparatus, is ordinarily directly connected, but for purposes of special tests at lower or higher frequencies belt and countershaft connections furnish means by which any requirement may be met. In all factory tests it is, of course, possible to make use of the large 200-kw. transformer, but in cases where testing must be done at the point of erection a portable transformer, is very desirable. To meet this demand the engineering department of the company has constructed a 50-kw. 200,000-volt transformer which has been designed to withstand the rough usage incident to a freight traffic. Primary and secondary connections are so made that practically any voltage from 110 to 1,000 may be made to yield the required secondary potential for purposes of test.

Fig. 1 illustrates a typical Locke porcelain insulator of the "Victor" type. It is built up of four pieces and is cemented and glazed. The diameter is 14 in., the height 12 in., the diameter of the top groove 1 in., and of the side groove 4 in. This insulator is tested up to 140,000 volts and is constructed for a line voltage of 60,000. The size of the pin-hole is 1-3/8 in.

Fig. 1 Four Pieces Cemented and Glazed.

Fig. 2 Two Pieces Cemented.

Fig. 2 shows a flint glass insulator made by the same firm, and built up of two separate pieces. Its diameter is 11 in., height 10-1/4 in., diameter of top groove 1-1/8 in., and of side groove 7/8 in. It is intended for use on a 40,000-volt line and the size of the pin-hole is 1-3/8 in.

Messrs. Geipel Lange have been appointed sole European agents to the Locke Insulator Co., and we have received from them a useful catalogue of the company's products, which include telegraph and other insulators as well as those for high-tension heavy-current work.