CHAPTER XXIII REVIEW 263. In reviewing the numerous types of apparatus, methods of construction and of operation, discussed in the preceding, an alphabetical list of them is given in the following, comprising name, definition, principal characteristics, advantages and dis- advantages, and the paragraph in which they are discussed. Alexanderson High-frequency Inductor Alternator. — 159. Comprises an inductor disk of very many teeth, revolving at very high speed between two radial armatures. Used for producing very high frequencies, from 20,000 to 200,000 cycles per second. Amortisseur. — Squirrel-cage winding in the pole faces of the synchronous machine, proposed by Leblanc to oppose the hunt- ing tendency, and extensively used. Amplifier. — 161. An apparatus to intensify telephone and radio telephone currents. High-frequency inductor alternator excited by the telephone current, usually by armature reaction through capacity. The generated current is then rectified, be- fore transmission in long-distance telephony, after transmission in radio telephony. Arc Machines. — 138. Constant-current generators, usually direct-current, with rectifying commutators. The last and most extensively used arc machines were: Brush Arc Machine. — 141-144. A quarter-phase constant- current alternator with rectifying commutators. Thomson-Houston Arc Machine. — 141-144. A three-phase F-connected constant-current alternator with rectifying commu- tator. The development of alternating-current series arc lighting by constant-current transformers greatly reduced the importance of the arc machine, and when in the magnetite lamp arc lighting returned to direct current, the development of the mercury-arc rectifier superseded the arc machine. Asynchronous Motor. — Name used for all those types of alternating-current (single-phase or polyphase) motors or motor couples, which approach a definite synchronous speed at no-load, and slip below this speed with increasing load. 459 400 ELECTRICAL APPARATUS Brush Arc Machine. — (Sec1 "Are Machines.'1} Compound Alternator. — 138. Alternator with rectifying com- mutator, connected in Beriea to the armature, either con- ductive!}-, or inductively through transformer, and exciting a scries field winding by the rectified current. The limitation of l he power, which can be rectified, and the need of readjusting the brushes with a change of the inductivity of the load, hasmade njGfl compounding unsuitahie for the modern high-power altcrnu- ton. Condenser Motor. — 77. Single-phase induction motor with condenser in tertiary circuit on stator, for producing shirting torque and high power-factor. The space angle between pri- mary and tertiary stator circuit usually is 45° to 60°, and often a three-phase motor is used, with single-phase supply on one phase. and condenser on a Becond phase. With the small amount of capacity, sufficient for power-factor compensation, usually the starting torque is small, unless a starting resistance is used, Imi the torque efficiency is high. Concatenation. — III, 28. Chain connection, tandem connec- tion, cascade connection. Is the connection o the secondary nl an induction machine with a second machine. The Bttt&d machine may be: 1. An Induction Machine. — The couple then is asynchronous. Hereto belong: The induction frequency converter or genera] aUernai\ transformer, XII, 103. It transforms between alternating-ear- rent systems of different frequency, and has over the indoetiOB- motor generator set the advantage of higher efficiency and lesser capacity, but the disadvantage of not being standard. The' concatenated couple of induction motors, 9, 28, 111. It permits multispeed operation. It has the disadvantage against the multispeed motor, that, two motors are required; but where two or more motors are used, as in induction-motor railroading, it has the advantage of greater simplicity. The internally concatenated motor {Hunt mtttt>r), 36. I' H more efficient than the concatenated couple or the multispeed motor, but limited in design to certain speeds and speed ratios. 2. A Synchronous Machine. — The couple then is synchronous. Hereto belong: The synchronous frequency converter, XII, 103. It has a defi- nite frequency ratio, while that of the induction frequi REVIEW 461 verter slightly changes with the load, by the slip of the induction machine. Induction Motor with Low-frequency Synchronous Exciter. — 47. The synchronous exciter in this case is of small capacity, and gives speed control and power-factor compensation. I nductionGenerator with Low-frequency Exciter. — 110, 121. Syn- chronous induction generator. Stanley induction generator. In this case, the low-frequency exciter may be a synchronous or a commutating machine or any other source of low frequency. The phase rotation of the exciter may be in the reverse direc- tion of the main machine, or in the same direction. In the first case, the couple may be considered as a frequency converter driven backward at many times synchronous speed, the exciter is motor, and the generated frequency less than the speed. In the case of the same phase rotation of exciter and main machine, the generated frequency is higher than the speed, and the exciter also is generator. This synchronous induction generator has peculiar regulation characteristics, as the armature reaction of non-inductive load is absent. 3. A Synchronous Commutating Machine. — 112. The couple is synchronous, and called motor converter. It has the advantage of lower frequency commutation, and permits phase control by the internal reactance of the induction machine. It has higher efficiency and smaller size than a motor-generator set, but is larger and less efficient than the synchronous converter, and therefore has not been able to compete with the latter. 4. A direct-current commutating machine, as exciter, 41. This converts the induction machine into a synchronous machine (Danielson motor). A good induction motor gives a poor syn- chronous motor, but a bad induction motor, of very low power- factor, gives a good synchronous motor, of good power-factor, etc. 5. An alternating-current commutating machine, as low-fre- quency exciter, 52. The couple then is asynchronous. This permits a wide range of power-factor and speed control as motor. As generator it is one form of the Stanley induction generator discussed under (2). 6. A Condenser. — This permits power-factor compensation, 55, and speed control, 11. The power-factor compensation gives good values with very bad induction motors, of low power- factor, but is uneconomical with good motors. Speed control 4(52 ELECTRICAL APPARA TUS usually requires excessive amounts of capacity, and given rather poor constants. The machine is asynchronous. Danielson Motor. — 11. An induction motor converted to a synchronous motor by direct-current excitation. (8ee "COB- catenation (4).") Deep-bar Induction Motor. — 7. Induction motor with deep and narrow rotor bars. At the low frequency near synchronism, the secondary current traverses the entire rotor conductor, and the secondary resistance thus is low. At high slips, u ing, unequal current distribution in the rotor bars concentrates the current in the top of the bars, thus gives a greatly increased effective resistance, and thereby higher torque. However, the high reactance of the deep bar somewhat impairs the power- factor. The effect is very closely the same as in the double squirrel cage. (See "Double Squirrel-cage Induction Motor. "I Double Squirrel-cage Induction Motor.— II, 18. Induction motor having a high-resistance low-reactance squirrel cage, plan to the rotor surface, and a low-resistance high-reactance squirrel cage, embedded in the core. The latter gives torque at good speed regulation near synchronism, but carries little current at lower speeds, due to itst high reactance. The surface squirrel cage gives high torque and good torque efficiency at Ion SpMdfl and standstill, due to its high resistance, but little torque near synchronism. The combination thus gives a uniformly high torque over a wide speed range, but at some sacrifice of power- factor, due to the high reactance of the lower squirrel i get close speed regulation near synchronism, together with high torque over a very wide speed range, for instance, down to full speed in reverse direction (motor brake), a triple sgt may be used, one high resistance low reactance, one medium resistance and reactance, and one very low resistance and high reactance (24). Double Synchronous Machine. — 110, 119. An induction ma- chine, in which the rotor, running at double synchronism, is connected with the stator, either in series or in parallel, but with reverse phase rotation of the rotor, so that the two rotating fields coincide and drop into step at double synchronism. The machine requires a supply of lagging current for excitation, just tike ;itr. induction machine. It may be used as synchronous induction generator, or as synchronous motor. As generator, the armature reaction neutralizes at non-inductive, but not at inductive load, REVIEW 463 and thus gives peculiar regulation characteristics, similar as the Stanley induction generator. It has been proposed for steam- turbine alternators, as it would permit higher turbine speed (3000 revolutions at 25 cycles) but has not yet been used. As motor it has the disadvantage that it is not self-starting. Eickemeyer Inductively Compensated Single-phase Series Motor. — 193. Single-phase commutating machine with series field and inductive compensating winding. Eickemeyer Inductor Alternator. — 160. Inductor alternator with field coils parallel to shaft, so that the magnetic flux disposi- tion is that of a bipolar or multipolar machine, in which the multitooth inductor takes the place of the armature of the stand- ard machine. Voltage induction then takes place in armature coils in the pole faces, and the magnetic flux in the inductor re- verses, with a frequency much lower than that of the induced voltage. This type of inductor machine is specially adopted for moderately high frequencies, 300 to 2000 cycles, and used in in- ductor alternators and inductor converters. In the latter, the in- ductor carries a low-frequency closed circuit armature winding connected to a commutator to receive direct current as motor. Eickemeyer Rotary Terminal Induction Motor. — XI, 101. Single-phase induction motor with closed circuit primary winding connected to commutator. The brushes leading the supply cur- rent into the commutator stand still at full speed, but revolve at lower speeds and in starting. This machine can give full maxi- mum torque at any speed down to standstill, depending on the speed of the brushes, but its disadvantage is sparking at the com- mutator, which requires special consideration. Frequency Converter or General Alternating-current Trans- former.— XII, 103. Transforms a polyphase system into another polyphase system of different frequency and where desired of differ ent voltage and different number of phases. Consists of an induc- tion machine concatenated to a second machine, which may be an induction machine or a synchronous machine, thus giving the induction frequency converter and the synchronous frequency con- verter. (See "Concatenation.") In the synchronous frequency converter the frequency ratio is rigidly constant, in the induction frequency converter it varies slightly with the load, by the slip of the induction machine. When increasing the frequency, the second machine is motor, when decreasing the frequency, it is generator. Above synchronism, both machines are generators I(>l ELECTRICAL Al'l'AHA Tl S and the machine thus a synchronous induction generator. En concatenation, the first machine always nets an Frequency con- verter. The frequency converter has the advantage "I [MM machine capacity than the motor generator, but the disadvantage of not being standard yet. Heyland Motor. — 59, 210. Squirrel-cage induction motor with commutator for power-factor compensation. Hunt Motor. — 30. Internally concatenated induction motor. (See "Concatenation (l).") Hysteresis Motor. — X, 98. Motor with polyphase stain ud laminated rotor of uniform reluctance in all directions, without winding. Gives constant torque at all speeds, by the hystereBM of the rotor, as motor below and as generatoi above HynchroDBSB, while at synchronism it may be either. Poor power-factor and small output make it feasible only in very small BU6S, BUCt H motor meters. Inductor Machines. — XVII, 150. Synchronous machine, gen- erator or motor, in which field and armature coils stand still ami the magnetic field flux is constant, and the voltage is induced b) changing the flux path, that is, admitting and withdrawing the flux from the armature coils by means of a revolving inductor. The inducing Hux in the armature coils thus does not alternate, but pulsates without reversal. For standard freqiirnrM-. tin- inductor machine is less economical and little used, but it offers great constructive advantages at high frequencies and is ll nlv feasible type at extremely high frequencies. Excited by alter- naling currents, the inductor machine may be Used U amplilic: (see "Amplifier"); excited by polyphase currents, ii a (ton inductor frequency converter, 102; with a direct-current wind- ing on the inductor, it is a direct-current kigh-frequi <>> . (See "Eickemeyer Inductor Alternator.") Leading current, power-factor compensation and phase eontn I can be produced by: Condenser. Polarisation cell. Overexcited synchronous motor or synchronous col Induction machine concatenated to condenser, to sj I motor or to low-frequency commutating machine. Alternating-current commutating machine with lagging field excitation. Leblanc'sPanchahuteur. — 145. Synchronous rectifier of many REVIEW 465 phases, fed by polyphase transformer increasing the number of phases, and driven by a synchronous motor having as many cir- cuits as the rectifier has phases, each synchronous motor circuit being connected in shunt to the corresponding rectifier phase to byepass the differential current and thereby reduce inductive sparking. Can rectify materially more power than the standard rectifier, but is inferior to the converter. Magneto Commutation. — 163. Apparatus in which the induc- tion is varied, with stationary inducing (exciting) and induced coils, by shifting or reversing the magnetic flux path by means of a movable part of the magnetic circuit, the inductor. Applied to stationary induction apparatus, as voltage regulators, and to synchronous machines, as inductor alternator. Monocyclic. — 127. A system of polyphase voltages with essen- tially single-phase flow of power. A system of polyphase vol- tages, in which one phase regulates for constant voltage, that is, a voltage which does not materially drop within the range of power considered, while the voltage in quadrature phase thereto is of limited power, that is, rapidly drops with increase of load. Monocyclic systems, as the square or the triangle, are derived from single-phase supply by limited energy storage in inductance or capacity, and used in those cases, as single-phase induction motor starting, where the use of a phase converter would be uneconomical. Motor Converter. — 112. An induction machine concatenated with a synchronous commutating machine. (See " Concatenation (3).") The latter thus receives part of the power mechanically, part electrically, at lower frequency, and thereby offers the ad- vantages incident to a lower frequency in a commutating machine. It permits phase control by the internal reactance of the induc- tion machine. Smaller than a motor-generator set, but larger than a synchronous converter, and the latter therefore preferable where it can be used. Multiple Squirrel-cage Induction Motor. — (See " Double Squirrel-cage Induction Motor.") Multispeed Induction Motor. — 14. Polyphase Induction Motor with the primary windings arranged so that by the opera- tion of a switch, the number of poles of the motor, and thereby its speed can be changed. It is the most convenient method of producing several economical speeds in an induction motor, and therefore is extensively used. At the lower speed, the power- factor necessarily is lower. 30 466 ELECTRICAL APPARATUS Permutator. — 146. Machine to convert polyphase alternating to direct current, consisting of a stationary polyphase tean.-- former with many secondary phases connected to a stationary commutator, with a set of revolving brushes driven by a syn- chronous motor. Thus essentially a synchronous converter with stationary armature and revolving field, but with two armature windings, primary and secondary. The tofMCTl objection is the use of revolving brushes, which do not permit individual observation and adjustment during operation, and thus are liable to sparking. Phase Balancer.— 134. An apparatus producing a. polyphase system of opposite phase rotation for insertion in series to I polyphase system, to restore the voltage balance disturbed by a single-phase load. It may be: A stationary induction-phase balancer, consisting of an induc- tion regulator with reversed phase rotation of the series winding. A synchronous-phase balancer, consisting of a synchronous machine of reversed phase rotation, having two sets of field wind- ings in quadrature. By varying, or reversing the excitation of the latter, any phase relation of the balancer voltage with those of the main polyphase system can be produced. The synchronous phase balancer is mainly used, connected into the neutral of n synchronous phase converter, to control the latter so as to make the latter balance the load and voltage of a polypoM with considerable single-phase load, such as that of a single- phase railway system. Polyphase Commutator Motor. — Such motors may be shunt, 181, or series type, 187, for mtiltispeed, adjustable-speed and varying-speed service. In commutation, they tend to be inferior to single-phase commutator motors, as their rotating field does not leave any neutral direction, in which a commutating field could be produced, such as is used in single-phase oommotttw motors. Therefore, polyphase commutator motors have been built with separate phases and neutral spaces between the phases, for commutating fields: Scherbius motor.. Reaction Machines. — XVI, 147. .Synchronous machine, motor or generator, in which the voltage is induced by pulsation of the magnetic reluctance, that is, by make and break of the magnetic circuit. It thus differs from the inductor machine, in that in the latter the total field flux is constant, but is shifted with re- gards to the armature coils, while in the reaction machine the REVIEW 467 total field flux pulsates. The reaction machine has low output and low power-factor, but the type is useful in small synchronous motors, due to the simplicity resulting from the absence of direct- current field excitation. Rectifiers. — XV, 138. Apparatus to convert alternating into direct current by synchronously changing connections. Rec- tification may occur either by synchronously reversing connec- tions between alternating-current and direct-current circuit: reversing rectifier, or by alternately making contact between the direct-current circuit and the alternating-current circuit, when the latter is of the right direction, and opening contact, when of the reverse direction: contact-making rectifier. Mechanical rectifiers may be of either type. Arc rectifiers, such as the mer- cury-arc rectifier, which use the unidirectional conduction of the arc, necessarily are contact-making rectifiers. Full-wave rectifiers are those in which the direct-current cir- cuit receives both half waves of alternating current; half -wave rectifiers those in which only alternate half waves are rectified, the intermediate or reverse half waves suppressed. The latter type is permissible only in small sizes, as the interrupted pul- sating current traverses both circuits, and produces in the alter- nating-current circuit a unidirectional magnetization, which may give excessive losses and heating in induction apparatus. The foremost objection to the mechanical rectifier is, that the power which can be rectified without injurious inductive spark- ing, is limited, especially in single-phase rectifiers, but for small amounts of power, as for battery charging and constant-current arc lighting they are useful. However, even there the arc recti- fier is usually preferable. The brush arc machine and the Thomson Houston arc machine were polyphase alternators with rectifying commutators. Regulating Pole Converter. — Variable-ratio converter. Split- pole converter, XXI, 230. A synchronous converter, in which the ratio between direct-current voltage and alternating-current voltage can be varied at will, over a considerable range, by shift- ing the direction of the resultant magnetic field flux so that the voltage between the commutator brushes is less than maximum alternating-current voltage, and by changing, at constant im- pressed effective alternating voltage, the maximum alternating- current voltage and with it the direct-current voltage, by the superposition of a third harmonic produced in the converter in 468 ELECTRICAL APPARATUS such a manner, that this harmonic exists only in the local COB- verier circuit. This is done by separating the field pole into two parts, a larger main pole, which has constant excitation, anil a smaller regulating pole, in which the excitation is varied and reversed. A resultant armature reaction exists in the regulating pole converter, proportional to the deviation of the voltage ratio from standard, and requires the use of a series Beld Regulating pole converters are extensively used for adjltataHo voltage service, as direct-current distribution, storaja charging, etc., due to their simplicity and wide voltage range at practically unity power-factor, white for automatic pottage control under fluctuating load, as railway service, phase control of the standard converter is usually preferred. Repulsion Generator. — 217. Repulsion motor operated generator. Repulsion Motor.— 194, 208, 214. Single-phase commutator motor in which the armature is short-circuited and energised fay induction from a stationary con pensa ting winding as primary. Usually of varying speed or series characteristic. Gives betta commutation than the series motor at moderate speeds, Rotary Terminal Single-phase Induction Motor.— XI, 101 (See "Eickemeyer Rotary Terminal Induction Motor.") Shading Coil. — 73. A short-circuited turn surrounding i part of the pole face of a single-phase induction motor with definite poles, for the purpose of giving a phase displacement of I he flux, and therehy a starting torque. It is the simplest ;iml cheap- est single-phase motor-starting device, but gives only low start- ing torque and low torque efficiency, thus is not well suited for larger motors. It thus is very extensively used in small motors. almost exclusively in alternating-current fan motors. Single-phase Commutator Motor. —XX, 189. Commutator motor with alternating-current field excitation, and such modi- fications of design, as result therefrom. Thai is. lamination of the magnetic structure, high ratio of armature reaction to Geld excitation, and compensation for armature reaction and self- induction, etc. Such motor thus comprises three circuits: the armature circuit, the field circuit, and the compensating circuit in quadrature, on the stator, to the field circuit. These cir- cuits may be energized by conduction, from the main current, or by induction, as secondaries with the main current as pri- mary. If the armature receives the main current, the motor is REVIEW 469 a series or shunt motor; if it is closed upon itself, directly or through another circuit, the motor is called a repulsion motor. A combination of both gives the series repulsion motor. Single-phase commutator motors of series characteristic are used for alternating-current railroading, of shunt characteristic as stationary motors, as for instance the induction repuhion motor, either as constant-speed high-starting-torque motors, or as adjustable-speed motors. Lagging the field magnetism, as by shunted resistance, pro- duces a lead of the armature current. This can be used for power-factor compensation, and single-phase commutator motors thereby built with very high power-factors. Or the machine, with lagging quadrature field excitation, can be used as effective capacity. The single-phase commutator motor is the only type which, with series field excitation, gives a varying-speed motor of series-motor characteristics, and with shunt excitation or its equivalent, give speed variation and adjustment like that of the direct-current motor with field control,, and is therefore exten- sively used. Its disadvantage, however, is the difficulty and limitation in design, resulting from the e.m.f . induced in the short- circuited coils under the brush, by the alternation of the main field, which tends toward sparking at the commutator. Single-phase Generation. — 135. Speed Control of Polyphase Induction Motor. — By resistance in the secondary, 8. Gives a speed varying with the load. By pyro-electric resista7ice in the secondary, 10. (lives good speed regulation at any speed, but such pyro-electric conductors tend toward instability. By condenser in the secondary, 11. (lives good speed regula- tion, but rather poor power-factor, and usually requires an un- economically large amount of capacity. By commutator, 58. Gives good speed regulation and per- mits power-factor control, but has the disadvantage and com- plication of an alternating-current commutator. By concatenation with a low-frequency commutating machine as exciter, 52. Has the disadvantage of complication. Stanley Induction Generator. — 117. Induction machine with low-frequency exciter. (See "Concatenation (2).") Stanley Inductor Alternator. — 150. Inductor machine with two armatures and inductors, and a concentric field coil between the same. (See "Inductor Machine.,,) 470 ELECTRICAL APPARATUS Starting Devices. — Polyphase induction motor: Remittance of high temperature coefficient, 2. Gives good torque curve at low speed and good regulation at speed, but requires high temperature in the resistance. Hysteresis device, 4. Gives good speed regulation and good torque at low speed and in starting, but somewhat impairs the power-factor. Eddy-current device, 5; double and triple squirrel-cage, 18. 20, 24; and deep-bar rotor, 7. Give good speed regulation combined with good torque at low speed and in starting, but somewhat impairs I lie power-factor. (See " Double Squirrel-cage Induction Motor" and "Deep-bar Induction Motor."} Single-phase induction motor: Phase-splitting devices, 67. Resistance in one phase, 68. In- ductive devices, 72. Shading coil, 73. (See "Shading CoiL") Monocyclic devices, 76. Resistance-reactance device or mono- cyclic triangle. Condenser motor, 77. (See " Condenser Motor.") Repulsion-motor starting. Series-motor starting. Synchronous-induction Generator.— XIII, 113. Induction machine, in which the secondary is connected so as to Ba a definite speed. This may be done: 1. By connecting the secondary, in reverse phase rotation, in shunt or in series to the primary: double gynehrotUrUi (See "Double Synchronous Machine.") 2. By connecting the secondary in shunt to the primary through a commutator. In this ease, the resultant frequency is fixed by speed antl ratio of primary to secondary turns. 3. By connecting the secondary to a source of constant low frequency; Stanley induction generator. In this case, the low- frequency phase rotation impressed upon the secondary may l>c in the same or in opposite direction to the speed. (See "Con* catenation (2).") Synchronous-induction Motor. — IX, 97. An induction motor with single-phase secondary. Tends to {hop into step as syn- chronoue motor, and then becomes generator when driven by power. Its low power-factor makes it unsuitable except fur small sixes, where the simplicity due to the absence of djreet current excitation may make it convenient as self-starling syn- chronous motor. As reaction machine, 150. Thomson-Houston Arc Machine. — 141-144. Three-phase V- REVIEW 471 connected constant-current alternator with rectifying commu- tator. Thomson Repulsion Motor. — 193. Single-phase compensated commutating machine with armature energized by secondary current, and field coil and compensating coil combined in one coil. Unipolar Machines. — Unipolar or acyclic machine, XXII, 247. Machine in which a continuous voltage is induced by the rotation of a conductor through a constant and uniform magnetic field. Such machines must have as many pairs of collector rings as there are conductors, and the main magnetic flux of the machine must pass through the collector rings, hence current collection occurs from high-speed collector rings. Coil windings are impossible in unipolar machines. Such machines either are of low voltage, or of large size and high speed, thus had no application before the development of the high-speed steam turbine, and now three- phase generation with conversion by synchronous converter has eliminated the demand for very large direct-current generating units. The foremost disadvantage is the high-speed current collection, which is still unsolved, and the liability to excessive losses by eddy currents due to any asymmetry of the magnetic field. Winter-Eichbery-Latour Motor. — 194. Single-phase compen- sated series-type motor with armature excitation, that is, the exciting current, instead of through the field, passes through the armature by a set of auxiliary brushes in quadrature with the main brushes. Its advantage is the higher power-factor, due to the elimination of the field inductance, but its disadvantage the complication of an additional set of alternating-current commu- tator brushes.