142 SCIENTIFIC AMERICAN SUPPLEMENT No. 1881 MARCH 2, 1912 Electrical Disturbances and the Nature of Electrical Energy* By Charles P. Steinmetz To all of us who are interested in the use of electric stopped by reactance, the voltage may rise to destructive is inappreciable. With the alternating fields of trans­ energy the nature and characteristics of electric energy values. mission lines, the effect of the velocity of propagation are of importance; as on their understanding depends Disturbances may enter the electric system from of the field is therefore negligible and is always neglected. our success in the economic use of this energy, and the outside, as by lightning; or they may originate Not so with the aiternating field of a wireless tele­ our ability of guarding against the difficulties, troubles in the system, as by switching, synchronizing, etc.; graph station. Using frequencies from one hundred and dangers which it may threaten when out of control. or again, they may originate in the circuit by outside thousand to a million cycles, the wave length is from Electric energy is industrially used as direct current interference, as by an arcing ground, a spark discharge 188,000 188,000 and as alternating current, that is, as steady flow and to an isolated conductor, etc. =1.8 miles =0.188 miles, or about 100,000 as wave motion, usually of 2.5 or cycles. Electric A characteristic of most of these disturbances (which 1,000,000 60 to disturbances are of various character, and, where usually are comprised by the name of transients) is 1,000 feet.. With a wave length of from 1,000 feet to they are periodic or wave motions, are often of very that they easily pass from circuit to circuit across space 2 miles, the electric wave extends over hundreds of high frequencies. by magnetic or static induction, but frequently do cycles within the operative radius of a wireless tele­ It can not well be doubted that electric disturbances not travel along the circuit for any considerable dis­ graph station, which may be hundreds or even thousands in our systems are increasing in number. The reason tance. The cause of this is found in their nature, par­ of miles. It is appreciable also in long distance tele­ therefor is found in the increasing size and energy of ticularly the frequency. phone lines. The average frequency of the sound waves- modern electric systems. Just as in a pail of water When an electric current passes through a circuit, 500 cycles-gives a wave length of 376 miles, and a even a gale will not cause an appreciable disturbance, there is in the space surrounding the conductor which 1,000-mile telephone line thus comprises over 2 Yz or, as a small pond is usually quiet while the ocean is carries the current an electric field; lines of magnetic waves. That is, at the moment when one-half cycle never at rest, but continually traversed by undulations force surround the conductor, and lines of electro­ of telephone current arrives in Chicago from New York, from small ripples to big waves, so in a small isolated static or dielectric force radiate from the conductor. five succeeding half waves have already left the New plant high voltage disturbances are practically unknown; In a direct current circuit, if the current is continuous, York terminal and are on the way. are rare in smaller central stations; while in the huge the field is constant; there is a condition of stress in Abnormal electric waves in industrial electric power modern systems waves continuously traverse the cir­ the space surrounding the conductor, which repre­ circuits vary from a few cycles per second (in the sta­ cuits, from minute high frequency ripples of negligible sents stored energy, magnetic energy and dielectric tionary oscillations of compound electric circuits) up energy to occasional high power surges of destructive energy, just as a compressed spring or a moving to thousands, hundreds of thousands and millions of energy. mass represents stored energy. In an alternating cycles per second. At frequencies of many thousand The nature and form of disturbances met in electric current circuit, the electric field also alternates; that is, cycles per second, the ordinary measuring instruments, systems are as variegated as those of any other form with every half wave of current and of voltage, the the oscillograph, etc., fail to record the wave; but of energy. Single electric waves or impulses may magnetic and the dielectric field start at the conductor, such very high frequency waves can still be observed appear as magnetic discharges, analogous to the snap and run out from the conductor into space with the and measured through their inductive effects by bringing of a whip in acoustics. Oscillations appear as waves velocity of light, or 188,000 miles per second. Where a conductor near them: the electric wave, impinging which start suddenly and gradually die out, like the waves this alternating field of the conductor, this electric on this exploring conductor ("resonator" or "receiving produced by throwing a stone in water; such are the wave, impinges on another conductor, a voltage and a antenna") then induces a current in it, and this is disturbances caused by switching, synchronizing, etc. current are induced therein. The induction is propor­ observed by a sufficiently delicate apparatus. In this Then there are traveling waves, analogous to the ocean tional to the intensity of the field (the current and manner, the telephone disturbances caused by alter­ waves, of various size and wave length; such for in­ voltage in the conductor which produce the field) and nating electric railway circuits have been studied by stance as the disturbances caused by arcing grounds, to the frequency. Thus, where the frequency is ex­ exploring antennae. A very intense wave, at short by lightning, etc. Standing waves or stationary oscil­ tremely high, intense induction occurs; that is, con­ distance from its origin, may be observed by the spark lations, like those of a tuning fork or violin string, siderable energy is transferred from the conductor across a small gap in the exploring antenna. Inversely, may appear; and occasionally also, the most dangerous which produces the electric wave (the primary or at hundreds of miles distance from the wireless sending of all disturbances, cumulative oscillations, like the sending conductor) to any conductor on which the station, the extremely weak wave is still observed in resonance of a tuning fork, namely, oscillations which wave impinges (the secondary or receiving conductor). the receiving antenna by a change of the surface tension gradually build up, increase in intensity until they The result is, that a large part of the energy of the of a platinum hair wire dipped into an electrolyte, finally limit themselves and become stationary, or die primary conductor passes inductively across space the change in resistance of which operates a relay. down again, or increase until something happens. Such into secondary conductors, and the energy decreases By the exploring antenna, electric waves have been for instance are the hunting of synchronous maehines, rapidly along the primary conductor. other words, st.udied and observed up to frequencies of hundreds ID certain internal transformer oscillations, etc. such a high frequency current does not pass for long of millions of cycles per second-so-called "Hertzian Disturbances may affect the system by their quantity, distances along a conductor, but rapidly transfers its waves,"-as they occur in industrial circuits between or by their intensity. Electric power can he resolved energy by induction to adjacent conductors. This the end cylinders of high voltage multi-gap lightning into the product of two terms, quantity (or current) higher induction, resulting from the higher frequency, arresters. There, they are the cause of the high sen­ and inteDsity (or voltage), Just as most other forms is the explanation of the apparent difference in the sitiveness of the arrester for high frequency disturbances. of energy are resolved into the product of two terms. propagation of high frequency disturbances from the We have to realize though, that light and radiant Hydraulic energy is quantity of water times head or propagation of the low frequency power of our alter­ heat, the Hertzian waves, the waves of the wireless pressure; heat energy is entropy times temperature, nating current systems: the higher the frequency, the telegraphy station, the alternating fields of our trans­ etc. Instances of current disturbances are the mo­ more preponderant 'become the inductive effects, which mission and distribution circuits, are one and the same mentary short circuit currents of alternators, the very transfer energy from circuit to circuit across space, phenomenon-electric waves traveling through space high frequency currents of arcing grounds, etc. Voltage and therefore the more rapidly the energy decreases with the same velocity (188,000 miles per second) disturbances appear wherever an electric wave breaks and the current dies out along the circuit, that is, the and exhibiting the same characteristics, but differing at a barrier in a circuit, as at a reactance, or in the more local is the phenomenon. merely by their frequencies. This does not mean that end turns of a tran"former. The flow of electric power thus comprises phenomena electricity and light are the same, but that light 'is A wave in the water, as a big ocean wave, may cause inside of the conductor, viz., the dissipation of electric an extremely high frequency electric wave, an extremely damage by its bulk, by overturning a structure. So energy by the resistance of the conductor through its rapid alternating electric field, while the electric field a current wave may cause damage by its volume: the conversion into heat and phenomena in the space out­ of the direct current is a st.eady stress in space.