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…
Transients, Waves, And Surges Passage Atlas
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Why This Theme Matters
Section titled “Why This Theme Matters”This passage may expose the time-domain behavior hidden by steady-state circuit language.
Candidate Passages
Section titled “Candidate Passages”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.
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…
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…
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…
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
To estimate the current which discharges in the lightning flash, the conductivity of air in the path of the discharge, and the diameter of the discharge are required, and as both are unknown, any estimate must be very approximate only. The specific resistance of gases and vapors decreases with increasing temperature and with decreasing pressure. It is a few ohm centimeters at atmospheric pressure and the high temperature of the magnetite or carbon arc, and is also a few ohm centimeters at the low temperature and low pressure of a high current Geissler tube discharge. The mercury arc stream also gives a specific resistance of a few ohms. The temperature of the air in the lightning discharge probably is moderately high, but the pressure is also not far from atmos- pheric, so that lOO ohm centimeters may not be very far from the true magnitude of the resistance. Estimating one to two feet as the diameter of…
44. Such circuits with distributed series capacity are of great interest in that it is probable that lightning flashes in the clouds are discharges in such circuits. From the distance traversed by lightning flashes in the clouds, their character, and the disruptive strength of air, it appears certain that no potential difference can exist in the clouds of such magnitude as to cause a disruptive discharge across a mile or more of space. It is probable that as the result of condensation of moisture, and the lack of uni- formity of such condensation, due to the gusty nature of air currents, a non-uniform distribution of potential is produced between the rain drops in the cloud; and when the potential gradient somewhere in space exceeds the disruptive value, an oscillatory discharge starts between the rain drops, and grad- ually, in a number of successive discharges, traverses the cloud and equalizes the pot…
When in a circuit, as a transmission line, a disturbance or oscillation occurs while this circuit is connected to other cir- cuits - as the generating system and the receiving apparatus - as is usually the case, the disturbance generally penetrates into the circuits connected to the circuit in which the disturbance originated, that is, the entire system oscillates, and this oscilla- tion usually is a full- wave oscillation; that is, the oscillation of a circuit closed upon itself; occasionally a half- wave oscillation. For instance, if in a transmission system comprising generators, step-up transformers, high-potential lines, step-down trans- formers, and load, a short circuit occurs in the line, the circuit comprising the load, the step-down transformers, and the lines from the step-down transformers to the short circuit is left closed upon itself without power supply, and its stored energy is, therefor…
The phenomenon of interference proves that light is a wave, a periodic phenomenon, just like an alternating current. Thus the wave theory of light and radiation stands today as unshaken as ever. However, when this theory was established, the only waves with which people were familiar were the waves in water and the sound waves, and both are wave motions. As the only known waves were wave motions, it was natural that the light wave also was considered as a wave motion. This led to the question of what moves in the light wave, and thus to the hypothesis of the ether, with all its contradictory and illogical attri- butes. But there is no more reason to assume the light wave to be a wave motion than there is to assume the alternating-current wave to be a motion of matter. We know that nothing material is moving in the alternating- current or voltage wave, and if the wave theory of light had been propounded a…
Assuming a thunder cloud to pass over the line. The ground below the cloud then assumes an electrostatic charge, corresponding to the opposite charge of the cloud. The trans- mission line, as part of the ground, thus also assumes a static charge, higher than that of the ground, since it projects above it. Any equalization of the potential distribution in the cloud by a lightning flash, as discussed in the preceding, requires a change in the electrostatic charge of the line, corresponding to the changed potential difference between ground and cloud above the ground, and the static charge thus set free on the line rushes as an impulse or wave along the line. The wave shape of such impulses induced by cloud discharges is in general not a smooth sine wave, but may be very irregular : during the equalization of the cloud potential by the lightning flash, the potential difference against ground, of the part of…
The wave length of oscillation thus depends on the length of the circuit in which the stored energy readjusts itself. For instance, in the short circuit oscillation of the system, the wave extends over the entire circuit, including generators and trans- formers ; and the entire circuit so represents one wave, or one- half wave, that is, the wave length is very considerable. If the readjustment of stored energy takes place only over a section of the circuit, the wave length is shorter. For instance, if by a thunder cloud a static charge is induced on the trans- mission line, and by a lightning flash in the cloud, the cloud discharges, the electrostatic charge induced by it on the line
Naturally, as soon as determinations of spark voltages became available, attempts were made to estimate the voltage of a lightning flash. Considering, in a lightning flash, the dis- charge as that in an ununiform field, similar to that between needle points, and so requiring about 10,000 volts per inch. In this case, a lightning flash of two miles, or about 10,000 feet length, would require a potential difference of about 1200 million volts. The existence of such voltages in the clouds does not appear possible: a potential difference of 1000 mil- lion volts would produce a brush discharge of about one-half mile in length, before the final lightning flash occurs. In the brush discharge the air is electrically broken down, and becomes conducting. But it is also mechanically and chemically broken down, that is, the molecules are dissociated and recombine after the discharge, in all possible combinations. Th…
and the change of flux, b, thus induces in the field circuit an e.m.f. and causes a current which retards the change of this flux com- ponent, 6. Or, in other words, an increase of armature current tends to increase its mutual magnetic flux, 6, and thereby to de- crease the field flux. This decrease of field flux induces in the field circuit an e.m.f., which adds itself to the voltage impressed upon the field, thereby increases the field current and maintains the field flux against the demagnetizing action of the armature cur- rent, causing it to decrease only gradually. Inversely, a decrease of armature current gives a simultaneous decrease of the self- inductive part of the flux, a in Fig. Ill, but a gradual decrease of the mutual inductive part, 6, and corresponding gradual increase of the resultant field flux, by inducing a transient voltage in the field, in opposition to the exciter voltage, and the…
causes an oscillation in which the lower frequencies predominate, that is, a low-frequency high-power surge. A spark discharge from the line, a sudden high voltage charge entering the line locally, as directly by a lightning stroke, or indirectly by induc- tion during a lightning discharge elsewhere, gives a distribution of potential which momentarily is very non-uniform, changes very abruptly along the line, and thus gives rise mainly to very high harmonics, but as a rule does not contain to any appre- ciable extent the lower frequencies; that is, it causes a high- frequency oscillation, more or less local in extent, and while of high voltage, of rather limited power, and therefore less destruc- tive than a low-frequency surge.
Since the resultant m.m.f. of the machine, which produces the flux, is the difference of the field excitation, Fig. 21 D and the armature reaction, then if the armature reaction shows an initial os- cillation, in Fig. 21 E, the field-exciting current must give the same oscillation, since its m.m.f. minus the armature reaction gives the resultant field excitation corresponding to flux $>. The starting transient of the polyphase armature reaction thus appears in the field current, as shown in Fig. 22(7, as an oscillation of full machine frequency. As the mutual induction between armature and field circuit is not perfect, the transient pulsation of armature reaction appears with reduced amplitude in the field current, and this reduction is the greater, the poorer the mutual inductance, that is, the more distant the field winding is from the armature wind- ing. In Fig. 22(7 a damping of 20 per cent is assume…
Maxwell then has deduced mathematically, and Hertz demonstrated experimentally, that the alternating electro- magnetic field - that is, the electromagnetic wave - has the same speed of propagation as the light wave, and has shown that the electromagnetic wave and the (polarized) light wave are identical in all their properties. Hence light is an electromagnetic wave - that is, an alternating electro- magnetic field of extremely high frequency.
To limit the machine current which followed the light- ning discharge, and so enable the lightning arrester to open the discharge circuit, series resistance was introduced in the arrester. Series resistance, however, also limited the discharge current, and with very heavy discharges, such lightning arresters with series resistance failed to protect the circuits, that is, failed to discharge the abnormal voltage without destructive pressure rise. This difficulty was solved by the introduction of shunted resistances, that is, resistances shunt- ing a part of the spark gaps. All the minor discharges then pass over the resistances and the unshunted spark gaps, the
[[PDF_PAGE:49]] Report of Charles P. Steinmetz 43 Denotations e = nominal induced E. M. F. of alternator or group of alternators. Xii = true self inductive reactance of alternator or group of alter- nators. xn= external reactance of alternator or group of alternators, thus. Xi = xn+Xi2 = total self inductive reactance of alternators or group of alternators. xj = effective reactance of armature reaction of alternator or group of alternators, thus: Xo=xn+x 2 synchronous reactance of alternator or group of alternators. x = reactance (or impedance) between alternators. z = impedance of circuit between alternators. = Vi- 2+(2x!+x) 2 , where r = resistance of circuit between alternators. Or approximately a = phase angle of circuit between alternators, where: tan a = Or approximately : a = 90 degrees. w = phase displacement from mean, of oscillating alternators, thus: 2co = total phase displacement of oscillati…
Similar transient phenomena also occur in space, that is, with space, distance, length, etc., as independent variable. Such transient phenomena then connect the conditions of the electric quantities at one point in space with the electric quantities at another point in space, as, for instance, current and potential difference at the generator end of a transmission line with those at the receiving end of the line, or current density at the surface of a solid conductor carrying alternating current, as the rail return of a single-phase railway, with the current density at the center or in general inside of the conductor, or the distribution of alternating magnetism inside of a solid iron, as a lamina of an alternating-current transformer, etc. In such transient phenom- ena in space, the electric quantities, which appear as functions of space or distance, are not the instantaneous values, as in the preceding…
The frequency of oscillations occurring in electric cir- cuits varies over an enormous range: from low frequencies, very little above alternator frequency, up to hundreds of mil- lions of cycles per second ; and the effect of the oscillations in the system therefore varies accordingly: from the relatively harmless static displays; brush discharges, streamers, sparks, etc., of extremely high frequencies, down to the disastrous high power low frequency short circuit oscillations, in which even in 10,000 volt system*^, currents ^i many thousands of amperes may surge, which voltages approaching 100,000, and with which no protective device can cope, which does not have unlimited discharge capacity, that is, contains no resistance whatever in the discharge path.
that is, the effective value of the discharge current is propor- tional to the condenser potential, e0, proportional to the square root of the capacity, C, and the frequency of charge, fv and inversely proportional to the square root of the resistance, r0, of the discharge circuit; but it does not depend upon the induc- tance L0 of the discharge circuit, and therefore does not depend on the frequency of the discharge oscillation. The power of the discharge is
80. As the result of the phenomena discussed in the preceding chapters, conductors intended to convey currents of very high frequency, as lightning discharges, high frequency oscillations of transmission lines, the currents used in wireless telegraphy, etc., cannot be calculated by the use of the constants derived at low frequency, but effective resistance and inductance, and therewith the power consumed by the conductor, and the voltage drop, may be of an entirely different magnitude from the values which would be found by using the usual values of resistance and induc- tance. In conductors such as are used in the connections and the discharge path of lightning arresters and surge protectors, the unequal current distribution in the conductor (Chapter VII) and the power and voltage consumed by electric radiation, due to the finite velocity of the electric field (Chapter VIII), require con- sideration.
The frequency at the wave length lWo is zero, since at this wave length the phenomenon ceases to be oscillatory ; that is, due to the energy losses in the circuit, by the effective resistance r and effective conductance g, the frequency / of the wave is reduced below the value corresponding to the wave length lw, the more, the greater the wave length, until at the wave length lWo the frequency becomes zero and the phenomenon thereby non-oscillatory. This means that with increasing wave length the velocity of propagation of the phenomenon decreases, and becomes zero at wave length lWo.
outer ones adjustable and set for about ^ in. gap. This lamp is connected across a high voltage 0.2-mf. mica condenser C, which is connected to the high voltage terminal of a small step-up trans- former T giving about 15,000 volts (200 watts, 110 •*- 13,200 volts). The low tension side of the transformer is connected to the 240-volt 60-cycle circuit through a rheostat R to limit the current. The transformer charges the condenser, and when the voltage of the condenser has risen sufficiently high it discharges through the spark gaps I by an oscillation of high frequency (about 500,000 cycles), then charges again from the transformer, discharges through the gap, etc. As several such condenser dis- charges occur during each half wave of alternating supply voltage the light given by the discharge appears continuous.
Since the resultant m.m.f. of the machine, which produces the flux, is the difference of the field excitation. Fig. 2 ID and the armature reaction, then if the armature reaction shows an initial os- cillation, in Fig. 21 E, the field-exciting current must give the same oscillation, since its m.m.f. minus the armature reaction gives the resultant field excitation corresponding to flux $. The starting transient of the polyphase armature reaction thus appears in the j&eld current, as shown in Fig. 22C, as an oscillation of full machine frequency. As the mutual induction between armature and field circuit is not perfect, the transient pulsation of armature reaction appears with reduced amplitude in the field current, and this reduction is the greater, the poorer the mutual inductance, that is, the more distant the field winding is from the armature wind- ing. In Fig. 22(7 a damping of 20 per cent is assumed,…
On the field current, which, due to the single-phase armature reaction, shows a permanent double-frequency pulsation, is now superimposed the transient full-frequency pulsation resultant from the transient armature reaction, as discussed in paragraph 20. Every second peak of the permanent double-frequency pulsation then coincides with a peak of the transient full-frequency pulsa- tion, and is thereby increased, while the intermediate peak of the double-frequency pulsation coincides with a minimum of the full- frequency pulsation, and is thereby reduced. The result is that successive waves of the double-frequency pulsation of the field current are unequal in amplitude, and high and low peaks alter- nate. The difference between successive double-frequency waves is a maximum in the beginning, and gradually decreases, due to the decrease of the transient full-frequency pulsation, and finally the double-frequ…
216. The main causes of a pulsation of reactance are : magnetic saturation and hysteresis, and synchronous motion. Since in an ironclad magnetic circuit the magnetism is not proportional to the M.M.F., the wave of magnetism and thus the wave of E.M.F. will differ from the wave of cur- rent. As far as this distortion is due to the variation of permeability, the distortion is symmetrical and the wave of induced E.M.F. represents no power. The distortion caused by hysteresis, or the lag of the magnetism behind the M.M.F., causes an unsymmetrical distortion of the wave which makes the wave of induced E.M.F. differ by more than 90° from the current wave and thereby represents power, - the power consumed by hysteresis.
237. The main causes of a pulsation of reactance are : magnetic saturation and hysteresis, and synchronous motion. Since in an ironclad magnetic circuit the magnetism is not proportional to the M.M.F., the wave of magnetism and thus the wave of E.M.F. will differ from the wave of cur- rent. As far as this distortion is due to the variation of permeability, the distortion is symmetrical and the wave of induced E.M.F. ‘represents no power. The distortion caused by hysteresis, or the lag of the magnetism behind the M.M.F., causes an unsymmetrical distortion of the wave which makes the wave of induced E.M.F. differ by more than 90° from the current wave and thereby represents power, - the power consumed by hysteresis.
I of the synchronous machine, corresponding to the field excita- tion. The actual magnetic flux of the machine, however, does not correspond to e, and thus to the field excitation, but corre- sponds to the resultant m.m.f. of field excitation and armature reaction, which latter varies in intensity and in phase during the oscillation of 0. Hence, while e is constant, the magnetic flux is not constant, but pulsates with the oscillations of the machine. This pulsation of the magnetic flux lags l>ehind the pulsation of m.m.f., and thereby gives rise to a term in 6 in equation (28). If PB, &, e, eu, Z are such that a retardation of the motor increases the magnetizing, or decreases the demagnetising force of the armature reaction, a negative term, P,, appears, otherwise a positive term. Pi in this case is the energy consumed by the magnetic cycle uf the machine at full frequency, assuming the cycle at full fre…
Assume now that a ground, P, is brought near one of the IjneBi A, to within the striking distance of the voltage, e. A dischaigB then occurs over the conductor, P. Such may occur by the puiu>* ture of a line insulator as not infrequently the case. Let r «■ re- sistance of discharge path, P. While without this discharge path, the voltage between A and C would be ei = e (assuming sini^ phase circuit) with a grounded conductor, P, approaching line A within striking distance of voltage, e, a discharge occurs over P forming an arc, and the circuit of the impressed voltage, 2 s, now comprises the condenser, C2, in series to the multiple circuit of con- denser, Ci, and arc, P, and the condenser, Ci, rapidly discharges^ voltage, eij decreases, and the voltage, 62, increases. With a de- crease of voltage, ei, the discharge current, i, also decreaseSi and the voltage consumed by the discharge arc, e’, increases un…