Incandescent Electric Lighting/Incandescent
INCANDESCENT
Electric Lighting.
At the time when the first edition of this little volume issued from the press. Electric Lighting by Incandescence, had barely got beyond the stage of a laboratory experiment, and the possibility of lighting large districts from a central station, as successfully as with gas, was doubted by men who now stand high in electrical circles. So great indeed has been the change in this art since that time, that we are rapidly becoming possessed of the indifference consequent upon familiarity, and take the introduction of the electric light into our factories, business places, and dwellings, as a matter of course.
There is however one phase of this industry, which is rapidly placing—even a general knowledge, of the means by which the electric current is generated and distributed beyond the reach of all but those actually connected with it as a business, or the student who proposes to follow it as a profession; this is the tendency to centralize electric lighting and to substitute large central stations, where the machinery for generating the current is located and whence the wires are run for distributing the same, for the numerous small plants now scattered over the country.
While these central stations cheapen the production of the light, and bring it within the reach of those who otherwise could not afford it, it does away with the large number of isolated plants, which formerly afforded the curious an opportunity to inspect the generation, distribution and utilization in light, of this form of energy.
While the opportunities to become informed upon this subject are rapidly growing less, the electric light as factor in our civilization, is becoming daily of more importance.
Millions of capital are being invested in its production, and it is being introduced throughout the world as rapidly as human activity, supplemented by all the agencies of an advanced civilization, can accomplish this end.
It is to meet the want among the intelligent laity, that is now—and will be later on more keenly—felt, for a general knowledge of this subject, superficial perhaps, but yet connected and logically arranged, that the publishers have decided to re-issue this number of their Science Series, with the matter contained therein, thoroughly revised and brought down to date; and trust that the same generous appreciation which attended their first effort, will justify them in this attempt to give to the public a popular exposition of the art of electric lighting by incandescence.
While a system of electric lighting, includes a large number of devices, the greater portion of these are simply designed to control or utilize the current produced by the generator. This latter then is practically the alpha and omega of all systems^ for from it goes forth, and to it returns, the energy which in different parts of the circuit, take the form of light, through the instrumentality of the carbon filament enclosed in the glass bulb of the lamp. The generator acts somewhat like a pump, having a reservoir within it, and which, when in motion, forces the water from the reservoir, through a long loop of pipe, both ends of which terminate in itself.
It is thus, that the circuit may be said to commence and end at the generator, which transforms the mechanical energy imparted to it into electrical energy, and through the medium of electricity, produces effects that would be otherwise unobtainable.
While the laws, upon which the construction and operation of the electric generator depends, are complex, it is yet possible to understand its parts, their relation to, and action upon each other, without entering deeply into their intricacies.
We are all familiar with the common horse-shoe magnet, and have used it as a toy, if not otherwise.
While watching how readily a needle, tack, or other small object of iron or steel, would follow its movements, we have wondered how this motion was produced without the objects coming into actual contact with the magnet, and have rested content with the explanation that the phenomena before us, was the result of a force called magnetism, which resided in the magnet.
This force which stretched forth its invisible fingers to move the tiny needle, is that upon which depends the action of the electric generator; the magnet however, differing in size, and also in the method by which its magnetic powers are excited, as will be explained hereafter. For the present let us confine ourselves to the horse-shoe magnet with which we are so familiar.
If we take such a magnet, and wave it to and fro above a needle resting upon the smooth top of a table, we will find that the needle will follow the magnet energetically or otherwise, according to the proximity of the magnet; that is to say, the farther the magnet is away the less its power over the needle.
It may be well to state here, that, when speaking of the action of the magnet upon any object, we wish it to be under-
Fig. 1.
stood that the object is presented to the ends of the magnet, as it is in its ends that its greatest strength lies. The relative conditions of the different parts of a straight-bar magnet are shown in Fig. 1, the brush-like lines at the ends giving a clear idea by their number and length, of the different degrees of magnetism existing at various points in the magnet; these conditions would remain practically the same were the magnet bent in horse* shoe form.
If we substitute for the needle a loop of copper wire we shall, by the motion before described, induce in the copper wire a current of electricity, and that without actual contact between the magnet and the wire.
Should you hold a horseshoe-magnet a slight distance above a long bar of iron, and then move it forward parallel thereto, you would find that it offered resistance to being moved thus, and that you would be forced to put forth some strength, both to keep it in motion as well as to prevent it being drawn down into contact with the iron; in fact, the sensation would be much the same as that experienced in moving a brush across the surface of a liquid, oil for instance, with the bristles just touching its surface.
These invisible bristle-like projections produce the current of electricity in the wire when the latter cuts through them.
To tell why such results follow the movements we have described we leave to higher authorities; our purpose is to deal with the facts, believing this sufficient for the purpose we have in view.
If you will glance at figure 2 you will see there shown a loop of wire such as has been referred to, mounted upon a shaft having a handle for the purpose of
Fig. 2.
revolving the loop rapidly between the ends of a magnet. This wire is covered with a substance which prevents the electricity passing from it otherwise than through the large pieces of metal, which are arranged about a cylindrical piece of non-conducting material, as a block of wood, in such a manner as not to touch each other; this latter being shown in the cut located near the handle on the forward end of the shaft. Figure 3 shows an end view of this insulating device.
Fig. 3.
If the shaft which supports the loop is rapidly revolved; a current of electricity will be set up in the wire loop by bridging over the space at the ends of the wire between the metal plates with a piece of metal or another loop of copper wire; copper always being used to conduct electricity where it can be, for the reason that it is the best practical conductor of electricity.
Such a device as this would be of little service in producing the large currents needed for the electric light, both because there would be an insufficient amount of wire and, further, because such magnets as have been described—called permanent magnets—cannot be made sufficiently strong for the commercial generation of great currents.
We therefore have to resort to methods which; while they differ somewhat from this arrangement in detail^ are practically the same.
In the first place we must have a large number of these wire loops, and as the wire is soft and easily bent, we must wind it about a core so as to hold it rigidly in place, as it has to be revolved very rapidly. Again, the ends of each wire loop must be brought out and attached to plates or blocks of metal, arranged upon some kind of non-conducting substance at one end of the shaft upon which the whole will turn. Sometimes the ends of the loops are attached to each other in such a manner as to combine all the loops as though they were one wire, and then separate pieces of wire are attached to them where they join each other, and these short wires terminate in plates at the end of the shaft as before described. As each loop of wire (which may be made of one or more coils) comes into the space between the ends of the mag« net, a current is set up in it; this current increasing or subsiding, according to the position of the loop with relation to the ends of the magnet. As the current is generated, it flows toward the pieces of metal arranged on the end of the shaft, and from them into what are called brushes, which are flat pieces of metal that rest against those arranged on the end of the shaft so as to have intimate contact with them without retarding their rotation.
This arrangement is clearly shown in the cut. Fig. 4, in which a is a shaft, to which is fixed a drum or core b, wound with a number of coils of insulated wire c; that is, wire which is carefully covered with a material which practically prevents the passage of electricity through it. These wires are connected together at the front end of the drum, and are also secured to curved pieces of metal d, which for the sake of clearness, are shown with that end of the shaft removed, and as also having the brushes e e resting against them.
These plates, d d, vary in number according to the number of coils of wire wound about the drum, and when arranged in place and secured to a drum or core of insulating material,—that is material which will not conduct electricity,—are
Fig. 4
called the "commutator;" their office being to conduct the impulses of current from each coil as it comes into proper position with relation to the ends of the magnet, into the brushes, from which it passes out through the line wires to the lamps or other electrical devices.
{{center block|
Fig. 5.
The drum with the wire wound about it is called the "Armature."
In the practical machine used in electric lighting, the core of the armature is made of thin discs of soft sheet iron; these discs are prevented from touching the shaft by the interposition of insulating material, and have insulating material, arranged between them so as to prevent their touching each other, they are however so rigidly secured to the shaft as to be in no danger of becoming loose when the shaft is rapidly rotated. Fig. 5 shows a complete armature, with commutator attached ready to be placed in position in the generator.
When the parts of a generator are properly connected to each other, as well as to the outside lamp circuit, the current generated in the armature, is augmented by the presence of the iron core, which attracts the lines of force extending out from the field pieces, and so concentrates them as to cause the wire wound about it to cut through the greatest possible number of these lines in a given time.
And here it becomes necessary to lay aside the permanent horseshoe-magnet, which has served us so well up to this point in our explanation, and substitute in its place the practical electro-magnet.
If we retain the shape of the horseshoe (see fig. 6), and make our magnet of soft iron—instead of steel, the material of which the permanent horseshoe-magnets are made—we shall have a device which will need something to charge it with magnetism whenever it is brought into use; this something is the electric current^ and we supply it to the magnet by winding one or more coils of insulated wire about the legs of the magnet near their ends.
It is necessary that there should be a slight trace of magnetism in these electromagnets, in order that the electric current may have something to act upon to assist it in creating the necessary magnetic condition in the generator; this want is supplied by what is called residual magnetism, the name given to the small
Fig. 6.
quantity of magnetism which always resides in large masses of iron or steel, or remains there after it has once been excited by an electric current.
These horseshoe-magnets are called the "Field Magnets" of a generator, because, between their ends where the armature is located is what is known as the field of force, taking its name from the lines of force, which is the technical term used for designating the power eminating from the poles of a magnet; and finally, in the practical generator the magnet ceases to assume the form of a horseshoe.
In Fig. 7 is shown a generator of the type now commonly used for supplying the current for the incandescent electric light. The ring having the alternate black and white spaces, is the commutator, which you will remember is secured to the same shaft as the armature and is practically the same. The large circle about the commutator is intended to represent the outer surface of the armature, which runs very close to the field pieces, N S, as these enlarged ends of the magnet are called. The heavy lines resting against the commutator are the brushes from which the wires leading to and from the lamps go forth.
Fig. 7.
You will notice that from the upper brush, two wires are led; the larger of these, is supposed to be the wire that carries the current to the lamps^ the location of which is shown by the dotted portion of the heavy line; the direction of the current in the same being indicated by the small arrows as proceeding from the upper to the lower brush.
The fine wire passing from the upper to the lower brush is shown as being coiled about both legs of the magnet, and terminating in the lower brush. The office of this wire is to magnetize the iron in the electro-magnet, and it is made smaller than the lamp wire, because only a small portion of the current generated in the armature is intended to flow through it, the greater portion being utilized in the lamps.
Fig. 8 gives a clear illustration of this, the lamps being shown as they are arranged in practical lighting. Here also is shown, what is termed a resistance box^ which is a box filled with a large number of coils of wire, made of material that will not readily conduct electricity, and so arranged as to be capable of being brought one after another into circuit with the fine wire passing around the field-magnets, so as to regulate the amount of current which passes about
Fig. 8.
them, thus controlling the amount of current generated.
The form of generator shown in this figure, is that need in the Edison system of incandescent electric lighting.
The pole pieces rest upon blocks of zinc, which do not interfere with their magnetized condition; and this zinc is in turn supported upon an iron base, the whole being secured together so as to form a neat and compact machine as shown in Fig. 9.
Before proceeding to discuss the means and devices for utilizing the electric current, let us be quite sure that we fully understand the several parts of the generator, or Dynamo, as it is commonly called, their individual purpose, action upon, and relation to each other. First are the electro-magnets known as "field-magnets" with their ends or "poles" enlarged by the "field-pieces" between which is the space known as the "field Of force" or "magnetic-field," in which revolves the "armature" having its several "coils" of wire connected to the strips of the "commutator," these strips having intimate contact with the "brushes" resting upon them, which 
Fig. 9.—Edison Dynamo Machine. (To face page 26.)
latter are connected together by the "line wires," the outgoing current wire generally passing forth from the upper brush to the locality to be lighted, from which the wire for the incoming current returns to be secured to the under brush, or what is equivalent to that, the line wires are secured in "binding posts" connected directly to the brushes. We thus have a "closed circuit" as it is generally termed, consisting of the wire coiled upon the armature, the strips or plates upon the commutator, the brushes, and the wire leading from and returning to them, between, or in which the lamps are arranged ; so that the current of electricity generated in the armature, passes through all of these, and returns again to the armature, thus completely traversing what is known as the "lamp circuit."
We also have a line of finer wire passing from one of the brushes, coiling about the field-magnets, and returning to the other brush; this is known as the "field circuit."
The lamp circuit is so named, because in it are located the incandescent lamps.
The field circuit takes its name from its office of furnishing the necessary current for the excitation of the field-magnets.
Having located and arranged all the parts of the generator, let us proceed to note how they act upon each other.
Attached to the shaft of the armature, is an iron^ wheel or pulley, about which passes the belt from a steam engine. When the engine is started, this belt transmits its motion to the pulley, rapidly revolving it and the armature upon the shaft with it.
As the armature revolves, the wire round about it is acted upon by the residual magnetism in the field pieces; this excites a slight current in the armature, a part of which passes out to the lamp circuit, the remainder passing through the field circuit and increasing the magnetism in the fields, which act somewhat more strongly upon the armature, increasing and strengthening the current passing from it, which in turn acts upon the magnets, and thus each aids the other, until the magnets have reached their full power, and we have the generator working at its greatest capacity; the major portion of the current flowing out to the lamps, while the remainder keeps the field magnets charged with the magnetism necessary for the generation of the current.