594
DYNAMOMETERS
Dynamo meters.—If P represent the average give a pressure of 2000 volts, supplied transformers which were situated at considerable distances and spread value of the component of a force in the direction of the over large areas, without an undue amount of copper in displacement, s, of its point of application, the product P.s the transmitting lines. While there was later a tendency measures the work done during the displacement. When to return to the continuous current for central stations, the force acts on a body free to turn about a fixed axis owing to the introduction of better means for economizing only, it is convenient to express the work done by the the weight of copper in the mains, the alternating current transformed product T9, where T is the average turning is again coming into favour in special cases, as rendering it moment or torque acting to produce the displacement 0 possible to place the central station in some convenient site radians. A dynamometer is used in the process of far away from the district which it is to serve. The measuring work to measure the force P, or the torque T. pioneer central station in this direction was the Deptford The factors s or 6 are observed independently. Apparatus station of the London Electric Supply Corporation, which is added to some dynamometers by means of which a furnished current to the heart of London from a distance curve showing the variations of P on a distance base is of 7 miles. In this case, however, the alternators were drawn automatically, the area of the diagram representsingle-phase and gave the high pressure of 10,000 volts ing the work done; with others, integrating apparatus ifc immediately, while more recently the tendency has been combined, from which the work done during a given to employ step-up transformers and a polyphase system.1 interval may be read off directly. It is convenient to The advantage of the latter is that the current, after reach- distinguish between absorption and transmission dynaing the distant sub-stations, can be dealt with by rotary mometers. In the first kind the work done is converted converters, through which it is transformed into a con- into heat; in the second it is transmitted, after measuretinuous current. The alternator is also used for welding, ment, for use. smelting in electric furnaces, and other metallurgical proAbsorption Dynamometers. — Prony’s dynamometer {Ann. cesses where heating effects are alone required; the large Chim. Phys. vol. xix., Paris, 1821), which has been modified various ways, consists in its original form of two symmetriccurrents needed therein can be produced without the dis- in ally-shaped timber beams clamped to the engine-shaft. When advantage of the commutator, and, if necessary, trans- these are held from turning, their frictional resistance may formers can be interposed to lower the voltage and still be adjusted by means of nuts on the screwed bolts which hold further increase the current. The alternating system can them together until the shaft revolves at a given speed. To smoothness of action, the rubbing surfaces are lubricated. thus meet very various needs, and its great recommendation promote A weight is moved along the arm of one of the beams until it may be said to lie in the flexibility with which it can supply just keeps the brake steady, midway between the stops which electrical energy through transformers at any potential, or must be provided to hold it when the weight fails to do so. The general theory of this kind of brake is as follows :—Let F be the through rotary converters in continuous-current form. whole frictional resistance, r the common radius of the rubbing For the farther study of the dynamo, the following may be surfaces, W the force which holds the brake from turning and consulted, in addition to the references already given :—General: whose line of action is at a perpendicular distance R from the —S. P. Thompson. Dynamo-Electric Machinery. London, 1896. axis of the shaft, N the revolutions of the shaft per minute, w —E. Kittler. Handbuch der Elektrotechnik. Stuttgart, 1892.— its angular velocity in radians per second ; then, assuming that G. Kapp. Dynamos, Alternators, and Transformers. London, the adjustments are made so that the engine runs steadily at a 1893 ; Electric Transmission of Energy. London, 1894 ; Dynamo uniform speed, and that the brake is held still, clear of the stops, Construction: Electrical and Mechanical. English trans. Lon- and without oscillation, by W, the torque T exerted by the don, 1899.—H. F. Parshall and H. M. Hobart. Electric engine is equal to the frictional torque Fr acting at the brake Generators, London, 1900; Armature Windings of Electric surfaces, and this is measured by the statical moment of the Machines. London, 1895.—J. A. Montpellier. Les Dynamos. weight W about the axis of revolution ; that is— T = Fr=WR . . . • (1) Paris, 1897.—C. C. Hawkins and F. Wallis. The Dynamo. London, 1896.—A. Wiener. Practical Calculation of Dynamo- Hence WR measures the torque T. Electric Machines. New York, 1898.—C. P. Steinmetz. Elements If more than one force be applied to hold the brake from of Electrical Engineering. New York, 1901. Continuous-Current turning, Fr, and therefore T, are measured by the algebraical sum Dynamos:—J. Fischer-Hinnen. Continuous-Current Dynamos. of their individual moments with respect to the axis. If the London, 1899.—E. Arnold. Die Ankerxoicklungen und Anker- brake is not balanced, its moment about the axis must be konstructionen der Gleichstrom - Dynamo - maschinen. Berlin, included. Therefore, quite generally, = 2WR (2) 1899. —D. C. Jackson. Electromagnetism and the TConstruction of Dynamos. New York, 1893.—H. M. Hobart. “Modern The factor 6 of the product TO is found by means of a revolution Commutating Dynamo Machinery,” Journ. Inst. Elec. Eng. vol. counter. The power of a xxxi. p. 185.—H. J. Ryan. “On the Relation of the Air-Gap motor is measured by the and the Shape of the Poles to the Performance of Dynamo- rate at which it works, Electric Machinery,” Amer. Inst. Elec. Eng., 1891.—W. B. and this is expressed Sayers. “On the Prevention and Control of Sparking,” Journ. T27tN . p A m Inst. Elec. Eng. vol. xxii. p. 377. Alternators :—D. C. Jackson by Tw = —xx— 60 in foot and J. P. Jackson. Alternating Currents and Alternating Current pounds per second, or Machinery. New York, 1896.—J. A. Fleming. The Alternate T27tN r Current Transformer. London, 1899.—C. P. Steinmetz.^ Alter- — „ in horse - power nating Current Phenomena. New York, 1898.—F. Loppe and R. 33,000 units. The latter is Bouquet. Courants Alternatifs Industriels. Paris, 1894.—R. monly referred to ascomthe Ruhlmann. Grundzuge der Wechselstrom-Technik. Leipzig, brake horse-power. The 1897.—S. P. Thompson. Polyphase Electric Currents. London, maintenance of the con1900. —J. Kramer. Der Drehstrom. Jena, im1896.—J. Rodet. of steadiness Distribution de VEnergie par Courants Polyphases. Paris, 1898. ditions plied in equation (1) —W. M. Mordey. “Alternate-Current Working,” Journ. Inst. depends upon the conElec. Eng. vol. xviii. p. 583.—J. Swinburne. “Transformer stancy of F, and thereDistribution,” Journ. Inst. Elec. Eng. vol. xx. pp. 164-181. fore of the coefficient of (c. C. H.) friction g between the rubbing surfaces. The Fig. 1. being 110 miles. Between Eichdorf and Griinberg, energy developed heating at the surfaces, at 225 volts is transmitted after transformation up to 10,000 volts the variations in their smoothness, and the variations of the {Electrician, vol. xxxviii. p. 469, 1897); while in the transmission lubrication make y continuously variable, and necessitate frequent from Paderno to Milan the three-phase current is generated directly at adjustment of AY or of the nuts. Poncelet invented a form ot 13,500 volts (Elettricita, vol. xvii. p. 133, 1898). At Kootenay- Prony brake which automatically adjusted its grip as y change< , Rossland the three-phase current is transformed up from 1100 to 20,000 thereby maintaining F constant. The principle of the Appold compensating brake is shown m volts. 1 Fie. i. A flexible steel band, lined with wood blocks, is As at Chicago, Electrician, vol. xliv. p. 177.
