Morrison's Apparatus for Power Conversion. (West. Electn., vol. xxii., 1898, pp. 277, 278.) The apparatus constitutes a variable speed-gear designed primarily for horseless carriages; the one in question weighs about 200 lbs., and is of 4 HP. A gas- or oil-engine runs at a constant speed of 600 revolutions per minute, and is regulated by a centrifugal governor. To the shaft is fixed a cylinder carrying field-magnets. Mounted upon the shaft, but free to revolve upon it, is a Gramme ring-armature with commutator. When the vehicle is at rest the armature is stationary, and in starting, after the electric circuit is closed, the greatest current is generated. As the speed of the armature increases, the energy exerted diminishes and the speed of the carriage increases. A. S. Belt Driving. J. TULLIS. (Mechanical Engineer, vol. i., 1898, pp. 452-454, 487–490.) The Author discusses the manufacture and care of leather belts for main-driving. High-speed belts running over 4,000 feet per minute should be made of single, pliable, tough thin leather; by compounding such belts, they may be run with advantage up to 9,000 feet per minute. Compound belt-driving is a simple and most trustworthy means of transmitting power without loss from slip. The cost of a narrow pulley is much less than that of a wide pulley; two 20-inch belts, working compound, will transmit more power than one 40-inch belt working from a wide pulley. The Author gives a number of examples in which compound beltdriving has been applied with satisfactory results. To get perfect belt-driving, a great deal depends on the form of the pulleys. Much loss of power and destruction of belting is due to the high convexity with which most pulleys are made. A convexity of 1 inch is sufficient for pulleys 6 inches wide and under; the smaller or driven pulley may be made perfectly flat. The Author discusses belt- versus rope-driving, and expressed his opinion strongly in favour of belts. A. S. Standardizing of Generators, Motors and Transformers. (American Institution of Electrical Engineers, vol. xv., 1898, pp. 71-100.) This is a discussion at the American Institution of Electrical Engineers on the advisability of having all dynamos, transformers, etc., of standard sizes, so as to render pattern-making less laborious, and the manufacture of the machines cheaper. The question was referred to a select committee. W. G. R. Single-phase Induction Motor. C. P. STEINMETZ. (American Institution of Electrical Engineers, vol. xv., 1898, pp. 103-183.) When running at or very near synchronism, the magnetic field of the single-phase induction motor is identical with that of the polyphase motor, since in a turn wound at right angles to the primary winding at synchronism an electromotive force is induced equal to that induced in a turn of the primary winding, but differing therefrom by 90° in phase. The greater portion of this Paper is devoted to starting devices. All starting devices of the commutatorless single-phase induction motor consist in the production of a component of magnetic flux displaced from the axis of polarization of the induced currents, and may be grouped into three classes, viz. :— 1st. Phase splitting Devices, in which the primary system is composed of two or more circuits displaced from each other in position, and combined with impedances of different inductancefactors so as to produce a phase-displacement between them. 2nd. Induction Devices, in which the motor is excited by a combination of two or more circuits which are in inductive relation to each other. This mutual induction between the motor circuits can either take place outside the motor in a separate phase-splitting device, or in the motor proper. 3rd. Monocyclic Starting Device.-An essentially wattless electromotive force of displaced phase is produced outside of the motor, and used to energise a cross-magnetic circuit of the motor, either directly by a special tease-coil on the motor, or indirectly by combining this wattless electromotive force with the main electromotive force, and thereby driving a system of electromotive forces of approximately three-phase or any other relation. Each of these types of starting devices is discussed in detail, the object being to inquire into the starting torques and the acceleration produced. The Author concludes that of all singlephase induction-motor starting devices, the monocyclic device most nearly reproduces in starting and accelerating the conditions of the polyphase motor. In the discussion which followed the reading of the Paper, the question of the legitimacy of the assumption of sine currents and electromotive forces arose. The general opinion was that the results obtained on that assumption agreed so nearly with actual practice as to justify its use. W. G. R. Asynchronous Motors. E. J. BRUNSWICK. (Électricien, vol. xv., 1898, pp. 305–307, 321-324 and 340–344.) The condition that the torque in a polyphase motor should be independent of the speed of the rotor is R = pL; where R is the resistance and L the coefficient of self-induction of each rotor circuit, and p is 27 times the frequency of the induced currents. From this it follows that a uniform torque could be obtained as the rotor runs up to speed by having variable resistances in the rotor circuits, and gradually cutting them out as the speed increases. Such a process involves rubbing contacts and probability of sparking, both of which are undesirable. In the Boucherot system the same end is attained by different means. The stator, instead of being wound in the ordinary fashion, consists of two distinct windings, one of which is fixed, and the other is capable of rotating through an angle representing half a period of the supply current. Thus in a four-pole motor the possible angular rotation is 90°. The movable part of the stator assumes the displaced position at start, and is rotated back again on full speed being attained. The rotor is of special design, but still consists of short-circuited bars without any rubbing contacts whatever. Three types of motors are constructed according as the motor is to be placed in an accessible place or not, or in the case where the conditions require a minimum number of conductors. W. G. R. Thickness of Transformer Plates. W. DITTENBERGER. Loppé has recently given the following formula for the loss per cubic centimetre of iron in the core of a transformer : = € where e is thickness of plates, ‹ that of insulation between them, B' magnetic flux per square centimetre of section of core, and a and B are constants. Using this expression, Loppé graphically determines the value of e, which will render B' a maximum for given values of W and e. The Author solves this problem 1 L'Éclairage Électrique, vol. xi., 1897, p. 548. [THE INST. C.E. VOL. CXXXV.] 2 G analytically, and finds that the required value of e is given by the equation an approximate solution of which may be easily obtained. A. H. Plant of the Ellicott-Square Building, Buffalo, N.Y. F. L. WILSON. (Electrical World, vol. xxxi., 1898, pp. 519–522.) A feature of interest in the electric plant of the Ellicott Building is the system of regulation of the forced draught. The system, due to Mr. John Beckman, depends upon the action of three valves. A regulating valve is placed on the inlet-pipe to the engine which drives the blower. This valve is so arranged as to open and increase the speed of the blower engine as the pressure of the steam in the boiler falls below the desired point, and to close and decrease the speed as the pressure rises. A pressurereducing valve is placed in series with the regulating valve to limit the speed of the fan, and to set the draught pressure in such a manner as to produce the most efficient combustion, and create under the boiler the greatest heat that the water is capable of absorbing. The stack damper is set to hold back this heat, so that the escaping gases do not leave the uptake at more than 100° above the temperature of the steam. When the steam pressure in the boiler has reached the desired point, the regulating-valve cuts off the direct supply of steam to the blower-engine, and the fan would stop but for the introduction of a by-pass consisting of a small pipe supplied with a reducing-valve. By this means steam just sufficient to keep the fan revolving, and at a low pressure of 6 or 8 lbs., is supplied to the engine. The following results of tests on the working of the plant are worthy of notice : Water evaporated per lb. of coal Equivalent from and at 212°. Equivalent water per lb. of combustible from and at 212° Builder's rating Average amount of steam supplied to electric-light engine Average output for 8,760 hours (365 days), kilowatts Average coal per ampere-hour, lbs. (water supplied at 56°) (water supplied at 183°) 6.77 8.18 9.03 250.00 250 00 36.73 77.99 260.00 0.84 0.75 W. G. R. High-Voltage Transmission Lines. S. H. DAILEY. (American Electrician, vol. x., 1898, pp. 194-197.) This is an article on the practical details to be noted in the erection of a high-voltage transmission line. Special attention is paid to safety devices, and the Author recommends that a barb wire should run the entire length of the line, and grounded every half-mile. W. G. R. Protection of Three-Wire System. E. OXLEY. (Electrical Engineer, New York, vol. xxv., 1898, pp. 483-484.) The Author refers to the trouble which may be caused to that side of a three-wire system which has the smaller load due to a sudden and considerable increase in the potential reproduced upon that side, such increase being produced by opening the neutral, or balancing wire, by the blowing of its fuse. The increase in potential from this cause may reach a point where it is almost double the voltage that should normally exist. The injury to incandescent lamps, fan-motors, and enclosed arc-lamps may be considerable. The "over-fusing" of the neutral wire, which has come to be a common practice among wiremen and others, came into existence, and owes its prevalence to the fact that it has hitherto been the only known expedient for avoiding disturbances of this character. This practice of "over-fusing" the neutral wire is directly contrary to the rules of the Board of Fire Underwriters. The Author points out that there is a far greater menace to property, however, in the fact that the abnormal tension on the underloaded side of the system, upon the blowing of the neutral fuse, develops weak spots in the wiring; or if such places already exist, the insulation quickly gives way under the strain, and destructive fires may be the direct result. To remove the possibility of such disturbances occurring, the Author has devised a simple safety attachment for a three-pole switch, of which illustrations are given. The principle of its operation consists in automatically opening the switch by the action of a spring immediately upon the blowing of the neutral fuse, the switch being maintained in its closed position by a latch or catch. This latch is released, or withdrawn from its locking engagement, by the attraction of a small electromagnet having its terminals connected to the ends of the neutral fuse. So long as the fuse remains intact no current flows through the windings of the magnet, as the potential at its terminals is only that due to the drop in voltage in the neutral fuse itself. Upon the blowing of the fuse, however, the potential between the points of connection immediately rises, causing current to flow through the magnet |
