Cross Arm Research Articles

Development in lightning protection of stations

THE AIEE transformer sub-committee has recently sponsored a paper <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> on the protection of power transformers against lightning surges. The most effective method given combines overhead ground wires, line entrance gaps, and transformer mounted lightning arresters. Such a method does give a high degree of protection, but it is primarily applicable to high voltage, high capacity stations where the overhead ground wire system is justified for both line and station. The conditions noted above are seldom fulfilled on subtransmission systems from 23 kv to 34.5 kv. Effective ground wires and low ground resistances are uneconomical, and the protection provided is usually a more or less modern arrester, not always located and grounded to the best advantage. On the 23-kv subtransmission system of the Duquesne Light Company, the average transmission distance is approximately two miles. This means that most direct strokes will contact the line not more than one mile from some substation. Much of this transmission is now equipped with wood cross arm braces and guy insulators, and at some stations several spans adjacent thereto are carried on unguyed poles.

Development in Lightning Protection of Stations

THE AIEE transformer sub-committee has recently sponsored a paper1 on the protection of power transformers against lightning surges. The most effective method given combines overhead ground wires, line entrance gaps, and transformer mounted lightning arresters. Such a method does give a high degree of protection, but it is primarily applicable to high voltage, high capacity stations where the overhead ground wire system is justified for both line and station. The conditions noted above are seldom fulfilled on subtransmission systems from 23 kv to 34.5 kv. Effective ground wires and low ground resistances are uneconomical, and the protection provided is usually a more or less modern arrester, not always located and grounded to the best advantage. On the 23-kv subtransmission system of the Duquesne Light Company, the average transmission distance is approximately two miles. This means that most direct strokes will contact the line not more than one mile from some substation. Much of this transmission is now equipped with wood cross arm braces and guy insulators, and at some stations several spans adjacent thereto are carried on unguyed poles.

SELF-CLEANING GOGGLES FOR THE BRONCHOSCOPIST

During the course of laryngeal or bronchoscopic examination of patients whose bronchial secretions are profuse, considerable annoyance and loss of time are occasioned by the frequency with which the examiner's protecting goggles become clouded and require cleaning. To obviate this time-consuming difficulty a pair of self-cleaning, or self-replacing, goggles was constructed, description and photographs of which we herewith present: The main feature of the apparatus is a roll of clear, uncoated film support mounted on two rollers so placed in their supporting frame that the film, in winding from one roller to the other, passes across the line of vision. The receiving roller is supplied with a winding and ratchet mechanism actuated by down and up movements of a cross arm, which, in turn, is actuated by opening and closing of the jaw. That portion of the film which has not yet passed before the examining eye (with this instrument,

A Mechanical Analyzer for the Solution of Secular Equations and the Calculation of Molecular Vibration Frequencies

A set of coupled harmonic oscillators has been constructed, so designed that it can be used to solve the numerical secular equations occurring in the theory of the vibration of polyatomic molecules and in other problems. Each oscillator consists of a shaft with cross arms carrying weights to increase the moment of inertia and springs to provide restoring force. The unit is free to rotate about the axis of the shaft, except for the restoring force of the springs. The various units are connected to one another by additional springs. In operation the springs and weights are adjusted to values which represent the coefficients of the secular equation to be solved, the whole device is driven by an eccentric of variable speed, and the frequencies of resonance, representing the roots of the equation, are measured.

Investigation of the Characteristics of the Philips Type of Müller Metalix Tubes as Revealed by the Roentgenogram

THE purpose of the investigation was to determine the class of work in which the Philips type of Muller Metalix tubes will produce better roentgenograms than the Coolidge tubes. Apparatus For the investigation, two Muller Metalix tubes of the Philips type and five Coolidge tubes were used, as listed below, the focal spot sizes being measured by the pinhole method. 1. 3 K.W. Metalix Radiator, focal spot 3.5 × 3.5 mm. 2. 6 K.W. Metalix Water-cooled, focal spot 3.5 × 3.75 mm. 3. 10 milliamperes Coolidge, focal spot 3 × 3 mm. 4. 10 milliamperes Coolidge, focal spot 4 × 4 mm. 5. 30 milliamperes Coolidge, focal spot 4.75 × 5 mm. 6. 100 milliamperes Coolidge, focal spot 8 × 8.5 mm. 7. B. F. Universal, focal spot 7.5 × 11 mm. The energy for the tubes was supplied by a double cross arm rectifying switch type of machine, with all exposure factors controlled and carefully checked. Observation of Detail in Roentgenograms To analyze the detail of structure, wire mesh was used. The distances that the mesh was ra...

An Inexpensive Autoclave for Small Laboratories

The Board of Public Works of this city found it necessary to establish a temporary laboratory for the bacteriological examination of its water supply. An autoclave for the sterilization of culture media was of course needed, but not wishing to purchase an expensive apparatus, the outfit described below was utilized with success. A 25-quart Denver pressure cooker was obtained from a chemical supply house. This cooker is cast in heavy aluminum, is well constructed, of neat appearance, and is easily manipulated. Its cover is equipped with an 1-inch air-cock, a 30 pound pressure gauge and a safety valve designed to blow at 30 pounds gauge pressure. The safety valve is of a familiar type, consisting of a steel ball seated in a brass cup, held in place by a small cross arm fastened by two spiral springs of 30 pound tension. The blow-off pressure of this type of valve is of course not easily regulated. Since it is desirable to maintain a pressure of 15 pounds per square inch for the sterilization of culture media, and to have a means of adjustment to other pressures, if necessary, a small change was made in the safety valve, as described in the following: The springs and cross arm were removed. In place of one spring was put a rigid bar soldered to the spring-holder nearest the cover. A slot was cut in the upper end of this piece, and to this was fastened loosely a cross arm of longer length than the original, making a lever, the union of the two bars being a fulcrum. A sliding weight, about 12 ounces, made from a brass cup filled with lead, was attached to the projecting end of the lever which had been notched. The changes made are shown in figure 1.

The Quebracho Region of Argentina

The quebracho forests of northern Argentina and southern Paraguay have the distinction of being the only forests of their kind in existence. Here and here only, between the 20th and 3ist parallels, quebracho is found in sufficient quantities to permit commercial exploitation. Quebracho as a botanical species is not entirely confined to this particular region, but in no other portion of the globe has it been found to be so abundant and of so desirable quality. The heartwood of the quebracho yields a valuable extract highly desired in the tanning of high-grade leathers and in such demand in both Europe and the United States for the last thirty or more years that this forest product has become of great economical importance. Foreign and domestic companies, principally the former, have invested large sums of money in forest holdings and in the establishment of tannic acid factories. The industry has assumed such dimensions that it is the leading factor in the development and colonization of northern Argentina. Besides being utilized in the manufacture of tannin, the quebracho tree is converted into many other wood products consumed domestically. Chief among these are railroad ties, boards, beams, poles, piles, fence posts, and cross arms. It is also a desirable wood for certain general construction purposes but is limited in these uses because of its heavy weight and short lengths. It is fine-grained and takes a beautiful polish as well as being the hardest, heaviest, and most durable wood known. In fact in Argentina, especially in the quebracho region, this wood is put to almost every use for which wood can be employed. According to official statistics' the total area of forest land in Argentina is 264,0I2,000 acres, which is 36.I per cent of the land surface. This, however, includes some burned-over forest land and also a good deal of woodland, open and scrublike. The great bulk of the forest is located in the northern part of the country. The quebracho region alone is estimated to cover Ioo,ooo,ooo acres, or I3.7 per cent of the total land surface of the republic; but only 45 to 60 per cent of the region is actually timbered. The term quebracho is of Portuguese derivation, literally meaning break Unfortunately, in parts of South America the term has been indiscriminately used, being applied to any wood having sufficient hardness to turn an ax. In the quebracho region, however, quebracho has a definite meaning, for the reason that it is practically the only wood accepted and

110-Kv. transmission line for Oak Grove development of Portland Railway, Light and Power company

This paper covers the design of the 110-kv. transmission line to transmit energy from the new Oak Grove development of the Portland Railway, Light and Power Company to the city of Portland, Oregon, a distance of 54 miles. The company now has three hydroelectric developments aggregating 52,000 kw. supplied from the same general watershed from which energy is transmitted to Portland over five 60-kv. circuits, only one of which is on steel towers. The problem was to design a transmission line to most economically handle the three 30,000-kv-a. units as installed at the new development and to tie in with the existing transmission system. The following factors were considered in determining the design: 1. Transmission voltage 2. Conductor capacity 3. Maximum conductor tension 4. Assumed maximum mechanical loading conditions 5. Type of supporting structures Consideration was also given to the physical characteristics of the country through which the line must be built. For 14.8 miles the line will be located in the United States Government Forest Reserve, which is very heavily timbered, and accordingly cost of clearing will be very high, averaging $15,000 a mile, even after credit for merchantable timber is allowed. This fact, outside of other considerations, required a minimum number of circuits. To reduce clearing costs as much as possible, the line was located along the river gorge necessitating 55 angles, a few as great as 60 deg., and 28 river crossing spans, vearying from 400 to 1800 feet. After considering various types of supporting structures, three types of double circuit, heavy rigid steel towers were decided upon as follows: Type A towers, to be used on tangents up to 800-foot spans, also on curves up to 10 deg., the spans not exceeding 500 feet; suspension insulators to be used. Type B towers, to be used on tangents up to 1700-foot spans, also on curves from 8 to 30 deg., the spans not exceeding 800 feet for the larger curves; suspension insulators to be used. Type C towers, to be used at dead-ends and curves over 30 deg. Towers are designed for 250,000, cir. mil. copper conductors, and maximum loading conditions of one-half inch of ice and eight pounds per square foot wind pressure at 0 deg. fahr. were assumed. Each type of tower was designed to withstand the maximum loading conditions plus 50 per cent without exceeding the elastic limit of the steel, and the towers were subjected to an actual field test. Special steel having an elastic limit of 45,000 pounds per square inch and a minimum elongation of 22 per cent was used in the towers. In order to reduce the number of insulators and deadend positions, use was made of brackets pivoted to the cross arms so that they would be free to swing in the line but rigid across the line. 12-inch brackets are provided for the Type A towers on 8 deg. curves and 24-inch brackets on Type B towers with 30 deg. curves so as to maintain a three-foot clearance between the conductor and steel on that side of the tower where the conductors pull the insulator strings up and toward the cage. The use of these brackes reduced the total cost of the insulators and hardware fully 25 per cent. Tables are included giving resultant simultaneous loading and weights and dimensions for each type of tower.