The conception of the field of force, or, as we should more correctly say, the field of energy, thus takes the place of the conception of action at a distance and of the ether. The beam of light and the electromagnetic wave (like that of the radio communication station or that surrounding a power transmission line) are therefore periodic alternations of the electromagnetic energy field in space, and the differ- ences are merely those due to the differences of frequency. Thus the electromagnetic field of the 60-cycle transmission line has a wave length of 3 X lO^V^O cm. = 5000 km. Its extent is limited to the space between the conductors and their immediate surroundings, being therefore extremely small compared with the wave length, and under these conditions the part of the electromagnetic energy which is radiated into space is extremely small. It is so small that it may be neglected and that it may be s…
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Section titled “Theme Doors”Highest-Value Candidate Passages
Section titled “Highest-Value Candidate Passages”In using the conception of electric quantity Q, we consider only the terminals of the lines of dielectric flux, that is, deal merely with the effect of the dielectric flux on the electric circuit which produced it. This conception is in many cases more convenient, but it necessarily fails, when the distribution of the dielectric flux in the dielectric field is of importance, such as is the case when dealing with high dielectric field intensities, approach- ing the possibility of disruptive effects in the field of force, or when dealing with the effect produced by the introduction of ma- terials of different permittivity into the dielectric field. There- fore, with the increasing importance of the dielectric field in engineering, the conception of electric quantity, or charge, is gradually being replaced by the conception of the dielectric flux and the dielectric field, analogous to the magnetic field, wh…
A simple harmonic oscillation as a line discharge would require a sinoidal distribution of potential on the transmission line at the instant of discharge, which is not probable, so that probably all lightning discharges of transmission lines or oscillations produced by sudden changes of circuit conditions are complex waves of many harmonics, which in their relative magnitude depend upon the initial charge and its distribution - that is, in the case of the lightning discharge, upon the atmospheric electrostatic field of force.
177. The magnetic circuit of the induction motor at or near synchronism consists of two magnetic fluxes superimposed upon each other in quadrature, in time, and in position. In the polyphase motor these fluxes are produced by e.m.fs. displaced in phase. In the monocyclic motor one of the fluxes is due to the primary power circuit, the other to the primary exciting circuit. In the single-phase motor the one flux is produced by the primary circuit, the other by the currents produced in the secondary or armature, which are carried into quadrature posi- tion by the rotation of the armature. In consequence thereof, while in all these motors the magnetic distribution is the same at or near synchronism, and can be represented by a rotating field of uniform intensity and uniform velocity, it remains such in polyphase and monocyclic motors; but in the single-phase motor, with increasing slip - that is, decreasing…
Consequently, in the polyphase motor running synchronously, that is, doing no work whatever, the secondary becomes current- less, and the primary current is the exciting current of the motor only. In the single-phase induction motor, even when running light, the secondary still carries the exciting current of the mag- netic flux in quadrature with the axis of the primary exciting coil. Since, this flux has essentially the same intensity as the flux in the direction of the axis of the primary exciting coil, the current in the armature of the single-phase induction motor run- ning light, and therefore also the primary current corresponding thereto, has the same m.m.f., that is, the same intensity, as the primary exciting current, and the total primary current of the single-phase induction motor running light is thus twice the exciting current, that is, it is the exciting current of the main magnetic flux p…
In consequence of the relative motion of the primary and secondary, the magnetic circuit of the induction motor must be arranged so that the secondary while revolving does not leave the magnetic field of force. That means, the magnetic field of force must be of constant intensity in all directions, or, in other words, the component of magnetic flux in any direction in space be of the same or approximately the same intensity but differing in phase. Such a magnetic field can either be considered as the superposition of two magnetic fields of equal intensity in quad- rature in time and space, or it can be represented theoretically by a revolving magnetic flux of constant intensity, or rotating
The inductively compensated series motor with secondary ex- citation, or inverted repulsion motor, 3, takes an intermediary position between the series motors and the repulsion motors; it is a series motor in so far as the armature is in the main supply circuit, but magnetically it has repulsion-motor characteristics, that is, contains a lagging quadrature flux. As the field exci- tation consumes considerable voltage, when supplied from the compensating winding as secondary circuit, considerable voltage must he generated in this winding, thus giving a corresponding transformer flux. With increasing speed and therewith decreas- ing current, the voltage consumed by the field coils decreases, and therewith the transformer flux which generates this voltage. Therefore, the inverted repulsion motor contains a transformer flux which has approximately the intensity and the phase re- quired for commutation; it la…
A simple harmonic oscillation as a line discharge would require a sinoidal distribution of potential on the trans- mission line at the instant of discharge, which is not proba- ble, so that probably all lightning discharges of transmission lines or oscillations produced by sudden changes of circuit conditions are complex waves of many harmonics, which in their relative magnitude depend upon the initial charge and its distribution - that is, in the case of the lightning dis- charge, upon the atmospheric electrostatic field of force.
between iron or magnetite terminals, and requiring about 75 volts, is white and very brilliant, that is, has a spectrum with many lines about uniformly distributed over the visible range. We can greatly increase the temperature of the arc by using a high-frequency condenser discharge: in this case very large currents of very short duration exist as oscillations between the terminals, with periods of rest between the oscillations, very long compared with the duration of the current. In this case the duration of the current is too short to feed a large volume of electrode vapor into the arc stream, and as the current is very large during the short moment of the discharge, the vapor between the terminals is very greatly overheated. Oscil- lating condenser discharges thus offer a means of increasing the temperature of the arc stream very greatly beyond the boiling point of the material. When using a condense…
A part of this magnetic flux (lines a in Fig. 111-4) interlinks with the armature circuit only, that is, is true self-inductive or leakage flux. Another part, however, (6) interlinks with the field also, and thus is mutual inductive flux of the armature cir- cuit on the field circuit. In a polyphase machine, the resultant armature flux, that is, the resultant of the fluxes. Fig. Ill, of all phases, revolves synchronously at (approximately) constant in- tensity, as a rotating field of armature reaction, and, therefore, is stationary with regard to the synchronously revolving field, F, Hence, the mutual inductive flux of the armature on the field, though an alternating flux, exerts no induction on the field circuit, is indeed a unidirectional or constant flux with regards to the field circuit. Therefore, under stationary conditions of load, no difference exists between the self-inductive and the mutual in-…
22. Usually in electric circuits; current, voltage, the magnetic field and the dielectric field are proportional to each other, and the transient thus is a simple exponential, if resulting from one form of stored energy, as discussed in the preceding lectures. This, how- ever, is no longer the case if the magnetic field contains iron or other magnetic materials, or if the dielectric field reaches densities beyond the dielectric strength of the carrier of the field, etc.; and the proportionality between current or voltage and their respective fields, the magnetic and the dielectric, thus ceases, or, as it may be expressed, the inductance L is not constant, but varies w^ith the current, or the capacity is not constant, but varies with the voltage.
22. Usually in electric circuits, current, voltage, the magnetic field and the dielectric field are proportional to each other, and the transient thus is a simple exponential, if resulting from one form of stored energy, as discussed in the preceding lectures. This, how- ever, is no longer the case if the magnetic field contains iron or other magnetic materials, or if the dielectric field reaches densities beyond the dielectric strength of the carrier of the field, etc. ; and the proportionality between current or voltage and their respective fields, the magnetic and the dielectric, thus ceases, or, as it may be expressed, the inductance L is not constant, but varies with the current, or the capacity is not constant, but varies with the voltage.
If light is a wave motion, there must be something to move, and this hypothetical carrier of the light wave has been called the ether. Here our troubles begin. The phenomenon of polarization shows that light is a transverse wave; that is, the ether atoms move at right angles to the light beam, and not in its direction as. is the case with sound waves. In such transverse motion a vibrating ether atom neither approaches nor recedes from the next ether atom, and the only way in which in the propagation of the light wave the vibratory motion of each ether atom can be transmitted to the next one is by forces acting between the ether atoms so as to hold them together in their relative positions. Bodies in which the atoms are held together in their relative positions are solid bodies. That is, trans- verse waves can exist only in solid bodies. As the velocity of light is extremely high, the forces between the e…
circuit current during the fraction of the half-wave, which the discharge over the multi-gap arrester lasts, is moderate, due to its very short duration, and can easily be absorbed and radiated by the arrester; so that even if lightning discharges rapidly follow each other for some time, they can be taken care of by the arrester with moderate temperature rise : assuming a vicious thunder storm, in which lightning flashes succeed each other practically continuously, several per second. Each discharge causes a short circuit over the lightning arrester, varying in duration from nearly a half-wave - if the discharge occurs at the beginning of a half-wave - to practically nothing - if the discharge takes place near the end of a half-wave - ^that is, in average, for one-half of one-half wave, or :- • sec, in a 60 cycle system. Therefore from two to three lightning dis- charges per second would still short circ…
110. Artificial light is used for the purpose of seeing and distinguishing objects clearly and comfortably when the day- light fails. The problem of artificial lighting thus comprises con- sideration of the source of light or the illuminant; the flux of light issuing from it; the distribution of the light flux in space, that is, the light flux density in space and more particularly at the illuminated objects; the illumination, that is, the light flux density reflected from the illuminated objects, and the effect produced thereby on the human eye. In the latter, we have left the field of physics and entered the realm of physiology, which is not as amenable to exact experimental determination, and where our knowledge thus is far more limited than in physical science. This then constitutes one of the main difficulties of the art of illuminating engineering: that it embraces the field of two dif- ferent scie…
former, the high-tension switches are opened at the generator end of the transmission line. The energy stored magnetically and dielectrically in line and transformer then dissipates by a transient, as shown in the oscillogram Fig. 41. This gives the oscillation of a circuit consisting of 28 miles of line and 2500-kw. 100-kv. step-up and step-down transformers, and is produced by discon- necting this circuit by low-tension switches. In the transformer, the duration of the transient would be very great, possibly several seconds, as the stored magnetic energy (L) is very large, the dis- sipation of power (r and g) relatively small; in the line, the tran- sient is of fairly short duration, as r (and g) are considerable. Left to themselves, the line oscillations thus would die out much more rapidly, by the dissipation of their stored energy, than the transformer oscillations. Since line and transformer are co…
former, the high-tension switches are opened at the generator end of the transmission line. The energy stored magnetically and dielectrically in line and transformer then dissipates by a transient, as shown in the oscillogram Fig. 41. This gives the oscillation of a circuit consisting of 28 miles of line and 2500-kw. 100-kv. step-up and step-down transformers, and is produced by discon- necting this circuit by low-tension switches. In the transformer, the duration of the transient would be very great, possibly several seconds, as the stored magnetic energy (L) is very large, the dis- sipation of power (r and g) relatively small; in the line, the tran- sient is of fairly short duration, as r (and g) are considerable. Left to themselves, the line oscillations thus would die out much more rapidly, by the dissipation of their stored energy, than the transformer oscillations. Since line and transformer are co…
As the electromagnetic field represents energy storage in space, it cannot extend through space instantaneously, but must propagate through space at a finite velocity, the rate at which the power radiated by the source of the field can fill up the space with the field energy. The field energy is proportional to the energy radiation of the source of the field (transmission line, radio antenna, incandescent body) and to the electromagnetic constants of space (permeability, or specific inductance, and permittivity, or specific capac- ity), and the velocity of propagation of the electromagnetic field - that is, the velocity of light - ^thus is:
giving most of the light flux between the horizontal and 20 deg. below the horizontal; in many cases of indoor illumination a light source giving most of the light between the vertical and an angle of from 30 to 60 deg. from the vertical - depending on the diameter of the area of concentrated illumination and the height of the illuminant above it. It can also be done by modifying or directing the light flux of the illuminant by reflec- tion or diffraction and diffusion, either from walls and ceilings of the illuminated area, or by attachments to the illuminant, as reflectors, diffusing globes, diffracting shades, etc. Further- more, the required flux distribution can be secured by the use of a number of illuminants, and with a larger area this usually is necessary. Frequently the desired flux distribution is pro- duced by using an illuminant giving more light flux than neces- sary, and destroying the exc…
Hence the logical error which led to the ether theory is the assumption that a w^ave must necessarily be a wave motion. A wave may be a wave motion of matter, as the water wave and sound wave, or it may not be a wave motion. Electrical engineering has dealt with alternating- current and voltage waves, calculated their phenomena and applied them industrially, but has never considered that anything material moves in the alternating-current wave and has never felt the need of an ether as the hypothetical carrier of the electric wave. When Maxwell and Hertz proved the identity of the electromagnetic wave and the light wave, the natural conclusion was that light is an electromagnetic wave, that the ether was unnecessary also
Suppose we have a permanent bar magnet M (Fig. 2) and bring a piece of iron / near it. It is attracted, or moved; that is, a force is exerted on it. We bring a piece of copper near the magnet, and nothing happens. We say the space surrounding the magnet is a magnetic field. A field, or field of force, we define as “a condition in space exerting a force on a body susceptible to this field.” Thus, a piece of iron being magnetizable - that is, susceptible to a magnetic field^ - ^will be acted upon; a piece of copper, not being magnetizable, shows no action. A field is completely defined and characterized at any point by its intensity and its direction, and in Faraday’s pictorial representation of the field by the lines of force, the direction of the lines of force represents the direction of the field, and the density of the lines of force represents the intensity of the field. To produce a field of force r…
The alternation of the field flux induces an e.m.f. of self induction in the field winding. In the shunt motor, this causes the field exciting current and with it the magnetic field flux to lag and thereby to be out of phase with the armature current which, to represent work, must essentially be an energy current, and thereby reduces output and efficiency and hence requires some method of compensation, as capacity in series with the field winding or excitation of the field from a quadrature phase of voltage. In the series motor the self-inductance of the field causes the main current to lag behind the impressed voltage and thereby lowers the power-factor of the motor. Thus, to get good power-factor, the field self-inductance must be made low, that is, the field as weak and the armature as strong as possible. With such a strong armature, and weak field, the commutating pole is not sufficient to control ma…
67. In the theoretical investigation of electric circuits the velocity of propagation of the electric field through space is usually not considered, but the electric field assumed as instan- taneous throughout space; that is, the electromagnetic com- ponent of the field is considered as in phase with the current, the electrostatic component as in phase with the voltage. In reality, however, the electric field starts at the conductor and propa- gates from there through space with a finite though very high velocity, the velocity of light; that is, at any point in space the electric field at any moment corresponds not to the condi- tion of the electric energy flow at that moment but to that at a moment earlier by the time of propagation from the conductor to the point under consideration, or, in other words, the electric field lags the more, the greater the distance from the conductor.
dielectric flux, dielectric field intensity, permittivity, as used in dealing with the electrostatic fields of high potential apparatus, as transmission insulators, transformer bushings, etc. The fore- most difference is that in the magnetic field, a line of force must always return into itself in a closed circuit, while in the electro- static or dielectric field, a line of force may terminate in a con- ductor. The terminals of the lines of electrostatic flux, ^ at the conductor, then are represented by the conception of a quantity of electricity or electric charge, Q, being located on the con- ductor. Thus, at the terminal of the line of unit dielectric flux, unit electric quantity is located on the conductor.