Alternating current

“ An alternating current is one which reverses its direction and passes first one way and then the other. It may be represented by a curved line, shown in Figure 88. It starts at zero, and gradually grows stronger and stronger. Then it commences to die away until no current is flowing. ”

“ We observe how the energy of an alternating current traversing the wire manifests itself—not so much in the wire as in the surrounding space—in the most surprising manner, taking the forms of heat, light, mechanical energy, and, most surprising of all, even chemical affinity. ”

“ The alternating current may be regarded as a fluid in which a wave proceeds first in one direction and then in the other, seesaw fashion; and in practice these changes of direction take place as frequently as from fifty to two hundred times per second. Instruments employed for continuous currents may contain iron and permanent magnets, but for the alternating currents the latter must be completely absent, and any iron employed in the construction of the instruments must be very soft and much subdivided, or it will become extremely hot. ”

“ If the current is not so interrupted, it cannot be felt at all, which may be proved by lifting up the spring on the spindle of the ordinary kind. The current is an alternating one, and changes its direction throughout the circuit, however extended it may be, at every half revolution. The current must be commutated. If it is required to have a continuous current, use must be made of what is termed a commutator, and I shall endeavour to explain the manner in which it acts as simply as possible. ”

“ Direct current flows constantly 28 in one direction only, like water down a river or like the passage of time. On the other hand, alternating current changes direction regularly, like the oscillation of the balance wheel in a watch. ”

“ The alternating-current dynamo gives a surging of electricity back and forth in the wires, and this may be distinguished from the direct current by its feeling; when, however, the number of alternations per second is increased very greatly, one may receive through the body considerable quantities of electricity without feeling it. With a very high frequency current one may put himself in circuit and light a 16-candle-power lamp without any disagreeable sensation. ”

“ The alternating current pressure can be kept constant through the full range of direct current voltage by changing the main field so as always to give an equal and opposite flux change to that of the regulating field. ”

“ Whether there is a true time lag, or whether the retardation is due to eddy currents circulating in minute paths, must remain an open question, but the fact is that a coil wound upon an iron core and traversed by an alternating current creates a moving field of force, capable of setting an armature in rotation. ”

“ The almost universal adoption of the alternating current system of distribution of electrical energy for light and power, and the many inherent advantages of the alternating current motor, have created the wide field of application now covered by this type of apparatus. ”

“ After the watch has been placed in position, an alternating current, that is, one whose direction is changing at regular intervals, is sent through the winding, and thus a magnetic field is produced that also changes in direction as the current reverses. ”

“ Alternating current being less efficient in the production of useful light than direct current, the amperage must be greater and this produces a greater loss in voltage, the loss being always proportional to the product of current times resistance. The drop in voltage over a certain resistance is therefore always greater, when an alternating-current arc is used, than it is with direct ”

“ Is the direct current indicated by the sine curve in figs. 174 to 178 continuous?
Ans. No; it is properly described as a pulsating current, or one, constant in direction, but periodically varying in intensity so as to progress in a series of throbbings or pulsations instead of with uniform strength.175
Ques. What is generally understood by the word “continuous” as applied to the current obtained from a dynamo?
Ans. It is usually accepted as meaning a steady or non-pulsating direct current; one that has a uniform pressure and constant direction of flow as opposed to an alternating current. ”

“ It will be observed that if an intermittent counter or opposing force be developed in the branches of the circuit and of higher electromotive force than that of the generator, an alternating current will result in each branch, with the waves of one sign preponderating, while a constantly or uniformly acting opposition in the branches of higher electromotive force than the generator would produce a pulsating current, which conditions would be, under some circumstances, the equivalent of those described. ”

“ Of the various branches of electrical investigation, perhaps the most interesting and immediately the most promising is that dealing with alternating currents. ”

“ Hardly have we become familiar with one fact, when novel experiences are met with and new avenues of research are opened. Even at this hour possibilities not dreamed of before are, by the use of these currents, partly realized. As in nature all is ebb and tide, all is wave motion, so it seems that; in all branches of industry alternating currents--electric wave motion--will have the sway. ”

“ Single or Monophase Current.—This kind of alternating current is generated by an alternator having a single winding on its armature. Two wires, a lead and return, are used as in direct current.
An elementary diagram showing the working principles is illustrated in fig. 1,249, a similar hydraulic cycle being shown in figs. 1,250 to 1,252.
Fig. 1,249.—Elementary one loop alternator and sine curve illustrating single phase alternating current. There are three points during the revolution at which there is no current: at 0° the position shown, 180°, and 360° ”

“ The properties of alternating currents are more complex than those of continuous currents, and their behavior more difficult to predict. This arises from the fact that the magnetic effects are of far more importance than those of steady currents. ”

“ Where the current is to be used chiefly for lighting and there are only a few or no motors to be supplied, the choice between direct current and alternating current will depend greatly upon the size of the installation, direct current being preferable for small installations and alternating current for large installations. ”

“ Thus there are as many
changes of direction of current per rotation as there are coils in the
armature or poles in the field.
Fig. 134. ALTERNATING CURRENT DYNAMO WITH
SEPARATE EXCITER MOUNTED ON MAIN SHAFT.
195 STANDARD ELECTRICAL DICTIONARY.
The field-magnets whose windings may be in series are often excited by a
separate direct current generation. Some are self-exciting, one or more
of the armature coils being separated from the rest, and connected to a
special commutator, which rectifies its current. ”

“ The pressure, or voltage, of an alternating current can be stepped up or stepped down, that is, raised or lowered, by means of a transformer, which is the simplest form of induction coil. The current strength varies proportionately with the charges in pressure so that there can never be any increase in the total amount of energy but there is always a loss of energy due to heating and other causes. The moral again is that an electrically driven perpetual motion machine is a delusion and a snare. Alternating current can be [78] changed into interrupted direct current, see Fig. ”

“ Alternating currents are of interest to us because of their general commercial use. To understand the reason for the extensive application of alternating currents it is necessary to learn the fundamental principles which pertain to them. ”

“ The needle should be parallel to the coil of A G, and if properly done, the needle will be made to vibrate back and forth slightly at each change in the polarity of I C.
443. Direct and Alternating Currents. A current that flows steadily in one direction is said to be a direct current. A cell gives a direct current when the circuit is closed. When the current passes in one direction for an instant, and then reverses immediately and flows in the opposite direction, it is said to alternate. The induced current which flowed through the galvanoscope in Exp. ”

“ The destructive or harmful effects of transients in electrical systems are far more common and more serious than with other forms of energy, and the engineers have therefore been driven by necessity to their careful and extensive study.
4. The simplest form of transient occurs where the effect is directly proportional to the cause. This is generally the case in electric circuits, since voltage, current, magnetic flux, etc., are proportional to each other, and the electrical transients therefore are usually of the simplest nature. ”

“ Now in a conductor, when the field is in a steady state, there is no electromotive intensity, and therefore no motion and no transformation of energy. The energy merely streams round the outside of the conductor, if in motion at all in its neighbourhood. If the field is changing, energy can pass into the conductor, as there may be temporary E.M.I. set up within it, and there will be transformation. But we already know the nature of this transformation, for it constitutes the induced current. ”

“ According to one theory, when we close the primary circuit the surrounding ether is thrown into a peculiar state of strain that we will call magnetic or electrical lines of force. When the ether wave strikes the second wire there is a molecular movement from a state of rest to a state of static strain. During the time that the molecules are moving from the normal to the strained position in sympathy with the ether we have the condition of a dynamic current, which lasts only a moment. ”

“ These results shew clearly that, if the phenomena are due to momentum, the momentum is certainly not that of the electricity in the wire, because the same wire, conveying the same current, exhibits effects which differ according to its form ”

“ Science divides electricity into two kinds—static and dynamic. Static comes from a Greek word, meaning to stand, and refers to electricity as a stationary charge. Dynamic is from the Greek word meaning power, and refers to electricity in motion. When Franklin made his celebrated kite experiment, the electricity came down the string, and from the key on the end of the string he stored it in a Leyden jar. While the electricity was moving down [Pg 47] the string it was dynamic, but as soon as it was stored in the Leyden jar it became static. Current electricity is dynamic. ”

“ Accordingly, the outflow, undifferentiated, of Life and Energy from the Eternal Substantive of Spirit, is never stopped by its own current in any of its differentiated streams; it is impossible for a current to be stopped by its own flow, whether it be a current of electricity, steam, water, or anything else. What then does stop the flow of any sort of current? It is the Resistance or inertia of the channel through which it flows; so that we come back to the formula of Ohm's Law, C = E/R as a general proposition applicable to any conceivable sort of energy. ”

“ The energy of the current in the section of the winding undergoing commutation is wasted in heating the wire during the interval when it is short circuited, and as it passes on, energy must again be spent in starting a current in it in the reverse direction. There is, then, a lagging of the current in the armature coils due to self-induction. ”

“ II Mass Longitudinal and Mass Transversal
We know that electric currents produce the phenomena of induction, in particular self-induction. When a current increases, there develops an electromotive force of self-induction which tends to oppose the current; on the contrary, when the current decreases, the electromotive force of self-induction tends to maintain the current. The self-induction therefore opposes every variation of the intensity of the current, just as in mechanics the inertia of a body opposes every variation of its velocity. ”

“ The considerations just given concern the loss of field or the shortening and apparent disappearance of the magnetic lines or circuits, as giving rise to the self-induction or increased potential on breaking. Where the energizing current is slowly cut off or diminished the energy is gradually transferred to the wire in producing elevation of potential during the decrease ”

“ But as the induction-current close to the wire dies away, a new induction-current is generated in the medium beyond, so that the space occupied by the induction-current is continually becoming wider, while its intensity is continually diminishing. ”

“ A2 and B2 represent the intermittent currents produced, 4 impulses of B2 being made in the same time as 5 impulses of A2. The line A2 + B2 represents the resultant effect upon the main line when the reeds a and a1 are simultaneously caused to make and break the same circuit, and from the illustration you will perceive that the resultant current, whilst retaining a uniform intensity, is less interrupted when both reeds are in operation than when one alone is employed. ”

“ Disturbance of equilibrium and sympathetic equation constitute the dual power that governs all the varied forms of life and motion which exist terrestrially, of which the electric or magnetic is the prime mover and regulator. All electrical action, no matter of what character, has its sympathetic birth by the intervention of that current of the triune flow, which I call the dominant, with the Polar harmonic current ”