Chapter XV: Electric Light, Heat, and Power

For the use of the cuts in this chapter, the Publishers desire to
acknowledge the courtesy of the General Electric Company, the Thomson
Electric Welding Company, and the Cooper Hewitt Electric Company.

With the discovery of the reversibility of the dynamo, the invention of the telephone, and the improvements in the electric light began the great modern development of electricity which proved that marvellous agent to be a master-workman.

Many of the things electrical that we ordinarily think of as modern inventions are merely modern applications of phenomena that were discovered many years ago. The pioneers in the science of dynamic electricity performed their experiments with the electric light, electro-magnets, etc., by using galvanic batteries. But for practical purposes the consuming of zinc and chemicals in such batteries was too expensive a way to generate electricity, and prevented any commercial use of the results of their experiments until cheaper electricity could be had.

The Work of the Dynamo

The invention of the dynamo, with which we obtain electricity from mechanical power, changed all that. Instead of consuming zinc in primary batteries, men could obtain it by burning coal, which is much cheaper, under the boiler of a steam-engine used to drive the dynamo. Thus it is that modern electricity comes from mechanical power. It is really the energy of a steam-engine or a water-wheel, or some other “prime mover,” working through the medium of electricity, that is transmitted to a distance and distributed over wires. The electricity may then be transmuted into light, heat, or chemical energy as the case may be, to light our electric lamps, develop the intense heat of the electric furnace, and charge storage-batteries.

Moreover, some time after the invention of the dynamo it was found that the mechanical power put into one of these machines could be transmitted electrically and reproduced as mechanical power. In other words, a dynamo could be made to revolve and give out power, as a motor, by supplying it with current from another dynamo. This showed the way to transmute electricity back again into mechanical power, to run our electric cars and trains, and all kinds of machinery in our factories and elsewhere. Nowadays the dynamo is used to generate nearly all the electricity that we need. Even in such comparatively old electrical applications as electro-plating and the telegraph and telephone, primary batteries are being supplanted by motor dynamos, which we shall learn about later.

It is from the invention of the dynamo and the discovery that it was reversible that we date the beginning of what are known as heavy electrical engineering applications, including electric light, heat, and power. In this closing chapter it is purposed to learn a little about these applications, and in so doing to summarize briefly the things that we have already studied.

The Electric Light

In the chapter on Electrical Resistance we learned that an electric current always encounters a resistance in passing through a conductor, and that when the current is strong enough the conductor is heated up. The electric light is produced by the heating of a conductor of one kind or another to incandescence by the electrical friction of the current passing through it.

The first electric light was made by Sir Humphry Davy over a hundred years ago. He discovered that when a current from a great many cells of battery was interrupted the spark did not simply appear for an instant and then go out, as it does when only a few cells are used, but remained playing between the terminals of the circuit. He found by experiment that if pieces of carbon are used as the terminals--or “electrodes,” as they are called--the electricity passes between them in an intensely hot flame, or “arc.” The latter, which is due to the electrical resistance of the vapor of carbon, heats up the carbon-points so that they give a brilliant white light.

Before the dynamo came into use, the electric light was rarely seen, except as a philosophical experiment; but as soon as cheap electricity became available, commercial electric arc-lamps were made by many inventors and have been continually improved. Fig. 1 shows one form of modern arc-lamp, with its case removed to show the interior mechanism. In most arc-lamps the lamp itself consists of a pair of carbon or other electrodes in the form of long rods arranged vertically, with their tips normally in contact. When the current is turned on, the mechanism lifts the upper electrode away from the lower one. The interruption of the circuit thus caused “strikes the arc” between the tips, and the mechanism keeps the arc-distance unchanged as the carbons burn away. Some arc-lamps are made to burn on continuous-current, and others on alternating-current circuits. When continuous current is used, the upper (or positive) carbon burns away about twice as fast as the lower one, forming a cup, or “crater,” from which most of the light comes.

Uses of the Arc-Light

The first commercial use of the arc-light on a large scale was for street-lighting, to replace the old-fashioned gas-lamps. But another important use is in search-lights, in which the arc-lamp is fitted with a powerful reflector for throwing a very bright light to a distance. Fig. 2 is a view of a search-light arranged to go on top of a ship’s pilot-house. In war-time the ships carry search-lights to help them find the enemy’s ships and repel attack; and they are used in the army also, by having a portable dynamo and engine drawn by horses. The arc is also employed in projectors for lecture-rooms, and sometimes for the headlights of steam and electric locomotives and interurban electric cars.

Incandescent and Other Lamps

The arc-lamp came into wide use for lighting large spaces like streets, stores, and public halls, but was found to be too intense for lighting smaller places like private houses. After many experiments, Edison succeeded in subdividing the electric light into the small pear-shaped “incandescent” lamps that we now see everywhere. In this kind of electric lamp the light comes from a thin “filament” of carbon, contained in a glass globe from which all air has been removed. Since there is no oxygen to support combustion, the filament may be heated white-hot by the current without being consumed.

In certain other forms of incandescent lamps that are just coming into use, the filaments are made of rare metals--osmium, tantalum, etc.--that will stand a high temperature without melting. The Nernst lamp has a filament consisting of a mixture of certain materials that has to be heated before it will conduct electricity.

Then there are the so-called “vapor” lamps, consisting of a glass tube full of conducting metallic vapor which gives out light when a current is passed through it. The best-known form is the Cooper Hewitt mercury vapor-lamp shown in Fig. 3, which gives a peculiar greenish light.

From the point of view of efficiency, the electric light, wonderful as it is, leaves much to be desired. The light always comes from a hot resistance; and whether this resistance is a mass of conducting vapor, as in the arc and vapor lamps, or a solid conducting filament, as in the so-called “incandescent” lamps, much more heat than light is produced. A needed improvement, therefore, is in the direction of obtaining a greater percentage of light for a given amount of electrical energy.

Electric Heat

The generation of heat in electrical devices usually means wasted energy--sometimes a very serious waste, as we have just seen. There are certain kinds of electrical apparatus, however, that are designed to transform all of the electrical energy delivered to them into heat, for various industrial and household purposes.

Electric Furnaces

By far the most important application of electric heat, as such, is in electric furnaces, by means of which we attain the highest temperatures known to man. The electric furnace consists of a chamber of “refractory” material, containing the substances to be acted upon by the heat, with a pair of big carbon electrodes thrust into the centre, as shown in Fig. 4, which is a picture of Moissan’s electric furnace for the distillation of metals, and supplied with heavy continuous or alternating currents. The apparatus is therefore a sort of gigantic electric arc-lamp, so enclosed that the whole of the intense heat of the arc is confined and concentrated on the smelting or other work. In many places where cheap electric power is to be had--as in the vicinity of the great Niagara Falls power-plants--electric furnaces are employed in what are known as electrometallurgical and electrochemical manufacturing processes. By their aid many metals and other substances that were formerly scientific curiosities, or entirely unknown, are produced commercially; such as aluminum, certain rare metals, and calcium carbide, from which that wonderful illuminant, acetylene-gas, is obtained.

Welding Metals

Another useful application of electric heat is in the welding of metals. Instead of heating the pieces to be welded in a forge, their ends are simply butted together and the electricity--generally from an alternating-current transformer--turned on. The heat developed by the “contact resistance” between the pieces quickly softens the metal so that the pieces may be forced together, forming a perfect weld in a few minutes without any hammering. Fig. 5 is a view of one form of electric welding-machine in which this is accomplished. The electric process can weld certain metals that cannot be joined securely by ordinary welding methods, and is used in several special arts.

Welding is also performed by the heat of a special electric arc-lamp, which a workman holds in his hand like a blow-pipe or torch. This process is especially useful in joining the edges of sheet-steel, in making tanks for electric “transformers,” etc. The workmen have to wear smoked glasses in order to protect their eyes from the intense glare of the arc.

Electric Car-heaters

Perhaps the simplest and best-known application of electric heat is the electric car-heater, consisting of coils of high-resistance wire--such as iron or German-silver wire--mounted on an insulating, non-combustible frame which is placed under the seats of the car. Part of the current from the trolley wire or third rail passes through the resistance-coils, heating them up and thereby warming the air in the car.

Household Uses

Nowadays electric heat is being more and more widely utilized in what are known as household electric heating-appliances. One of the most useful of these is the electric flat-iron, shown in Fig. 6. This flat-iron is designed to do away with the use of a hot stove of any kind, and is internally heated by means of a resistance-coil of peculiar shape placed in the bottom of the iron close against its working face. The iron is connected to an electric-light socket by means of an attaching plug on the end of a long, flexible cord. It takes only a few minutes to get hot, and its use saves much time and labor.

The list of special heating-appliances that are now made includes curling-iron heaters; heating-pads, for taking the place of hot-water bags in the sick-room; cigar-lighters, in which a little grid “resistance” is made incandescent by pressing a button; foot-warmers; and radiators to dry wet shoes or skirts on rainy days. For industrial use there are glue-pots, for bookbinders and pattern-makers; large flat-irons, for tailor-shops and laundries; and electric ovens, for drying certain parts of electrical machines and for cooking various kinds of “prepared foods.”

Many electric cooking-utensils are made for the household, such as coffee-percolators, egg-boilers, ovens, disk stoves, etc. Each one is equipped with a resistance-coil like that in the electric flat-iron just described, so that it contains its own source of heat, which is under perfect control by means of a switch. An “electric kitchen” consists of a number of these utensils, wired to a convenient table or stand, as shown in Fig. 7.

Electric Power

We have seen that the modern way to generate electricity is from mechanical energy applied through a dynamo, and that the “electric power” thus generated may be transmitted over wires to a distance and there transformed into other forms of energy, such as light, heat, and chemical energy, or reproduced again as mechanical energy. The last mentioned of these transformations is the most important of them all, because it is the one that means the most for the advancement of civilization. Before the invention of the dynamo and the discovery that it was reversible, mechanical power could be employed only in the place where it was generated, so that its use was restricted; whereas nowadays the field of power is broadened and its cost reduced by electrical transmission and distribution.

In the chapter on Dynamos and Motors we learned how to make and use those machines. Let us review, very briefly, just what happens in the double transformation--of mechanical energy into electricity and then back again at the end of a line of wires--that we call electric-power transmission. In the dynamo, the power of the water-wheel, or whatever other prime mover is used, is exerted in generating electricity by forcing the electric conductors of the machine through a magnetic field. The electricity is led away to a distance--a hundred miles, perhaps--by wires and allowed to enter another machine similar to the dynamo, but operating as a motor. Here the first process is reversed: the electricity passing through the conductors of the motor reacts upon its magnetic field, causing the machine to revolve and thus generating mechanical power again. The line-wires carry the power just as positively as though a long shaft ran from the prime mover to the receiving end of the line, and much more economically. The action that goes on is similar to the operation of the telephone--which is indeed a special case of electric-power transmission--as already explained in a former chapter: the sound of the voice being transformed, at the telephone-transmitter, into electrical energy in the form of alternating currents, then carried as such over the line and finally reproduced as sound again at the receiver.

Power from Water-wheels

“Hydro-electric” transmissions--i. e., electric transmissions of power from a water-wheel as prime mover--are the most important because they bring into use cheap water-power that formerly ran to waste. There are many hydro-electric transmissions in this country, Mexico, and Canada, some of them utilizing the power of waterfalls or rapids located in mountainous and inaccessible parts. The alternating current is nearly always used because by it men can much more easily and safely generate, transmit, and receive the high voltages that have to be used than by the continuous current. The machinery at the “main generating station” consists of big alternating-current dynamos, which sometimes have vertical shafts instead of horizontal ones, so that they may be driven directly by turbines. The current is generated at a moderate potential, which is then “stepped-up,” by “static transformers,” to the comparatively high-line voltage that is required in long-distance transmissions.

Transformers

Fig. 8 is a view of a very large transformer of over 2500 electrical horse-power capacity. In the picture the containing-tank is represented as transparent, so as to show the transformer proper inside. The latter is really a special kind of induction-coil, with primary and secondary windings, and a core, weighing many tons, built up of thin sheets of steel. In this kind of transformer, the tank is filled with oil, to keep the transformer cool in operation, and to help insulate it against the high potential to which it is subjected. At the receiving end, or “sub-station,” the high-voltage electric power enters a set of “step-down” transformers, from which it is delivered again, at moderate potential, to the motors.

Sometimes power is distributed from a single great generating station to several sub-stations. In the Necaxa transmission, in Mexico, over 35,000 horse-power is taken from a waterfall in the mountains and transmitted at 60,000 volts potential to Mexico City, 100 miles away, and to the mining town of El Oro, seventy-four miles farther on.

Several kinds of motors are used at the receiving end of electric-power transmission-lines, according to the work that they are called upon to do. For “stationary” work, like driving the machines in mills and factories, two principal kinds of alternating-current motors are employed--synchronous and induction motors. The former are built just like alternating-current dynamos, and when they are running they keep “in step” with the dynamo at the other end of the line; i. e., the motion of their field windings relatively to their armatures keeps exact pace with the same motion at the dynamo, just as though a long shaft ran from one machine to the other instead of the electric wires of the transmission-line. A motor of this type, at work driving an air-compressor, is shown in Fig. 9. The induction-motor is really a sort of transformer, the primary winding of which is the fixed part, or field, and the secondary winding the rotating armature. It does not keep in step with the dynamo, like the synchronous motor, but adapts its speed to the “load,” or amount of work that it is called upon to do, like a continuous-current motor.

Rotary Converters

Sometimes alternating-current electric power is transformed at the sub-station into continuous-current power. This is done by a special kind of transformer called a “rotary converter.” The static transformers of which we have just been speaking are built, like ordinary reduction-coils, with no moving parts, and operate by taking in alternating currents at a given potential and giving out alternating currents at a different potential, higher or lower as the case may be. The rotary converter, however, is built something like a dynamo, with a stationary field and a revolving armature, and ordinarily operates by receiving an alternating current at a given potential and delivering a continuous current of the same or a different potential. This kind of transformation is employed wherever it is desired to obtain any large amount of continuous current from an alternating-current transmission-line; and especially to obtain “500-volt continuous current” for operating street and interurban electric railways, as we shall see under the next heading. Fig. 10 shows one form of rotary converter built for supplying continuous current for trolley service.

Oftentimes the sub-station of a transmission system contains both static transformers and rotary converters, to supply both alternating current and continuous current from the same high-voltage alternating-current line. When the continuous current has to be transformed from one voltage to another, a “motor dynamo” is used, consisting of an electric motor driving a dynamo on a common shaft.

One of the most interesting features of electric-power transmission is the care that is taken to avoid the terrible danger from the high potentials, and at the same time prevent loss of power on the way. The electricity in the machinery and in the line-wires that extend across the country is veritable lightning, and has to be carefully guarded from doing any damage or escaping. To prevent leakage, the insulation of all of the station machinery and apparatus is made extra good, with “high dielectric strength,” so that it will not be punctured by the high voltage; and the line-insulators are made very large, and electrically and mechanically strong--quite unlike the ordinary-sized glass or porcelain insulators that are employed for telegraph and telephone lines. Each insulator before being put up is tested under a “breakdown voltage” much higher than it is to stand in actual service.

Oil-switches

The switching of high-voltage electric power is a knotty problem. The circuit cannot be interrupted by “air-break” switches, such as are used in ordinary electric-light stations, for any attempt to do so would result in a destructive arc many feet long, that could not be extinguished. Therefore “oil-switches” are always used to control the line-circuits at the main generating station and the sub-stations. In these oil-switches--which are designed to be operated from a distance, by hand-levers, or sometimes by electric motors--the circuit is made and broken under the surface of oil, which prevents the formation of an arc. Moreover, the switchboard attendant does not have to come anywhere near the deadly high-voltage wires, but can make the necessary connections at a safe distance.

Electric Traction

The use of the electric motor to propel vehicles of all kinds is called electric traction. It is, of course, a branch of electric power, which we have just been considering; and it is in many respects the most important branch. The wealth of a country is largely built up and maintained by its facilities for transportation, such as its canals, highways, railroads, and street and interurban car-lines.

In this field electric power is playing a most important part, although it was not many years ago that the first experimental electric cars were put in to replace horses on the street-railways of our cities. The change was found to be so successful that the field of the trolley-car was widened and extended very rapidly, until now we have our great suburban and interurban electric railways, with cars almost or quite as big as those on the steam-railroads and running at even higher speeds. During the last few years, also, the sphere of the steam-railroad itself has been invaded by electricity, by the construction of powerful electric locomotives to draw passenger and freight trains.

The Trolley-car

Let us consider just what it is that makes a trolley-car go. Since electric power is only mechanical energy in another form, we know that the motionless copper trolley-wire, suspended over the track in our streets, is the means of propelling the car just as truly--though in a different way--as if it were a moving steel cable to which the car was attached. We must keep in mind the fact that the electricity is not itself the source of power, but only the medium of transmission. The engine in the power-house, by turning a dynamo there, maintains a constant electric pressure, or “constant potential,” as it is termed, in the trolley-wire. This pressure of electricity forces the power through the motors of the car as soon as the motorman makes the connection to them by turning the handle of his “controller.”

The Continuous-current Motor

Fig. 11 is a view of one form of continuous-current motor. There is not much of the motor itself to be seen, because it is entirely enclosed in a cast-iron case. The shaft of the motor has a small “spur gear” fixed on one end, driving a gear-wheel which is fixed on the car axle. By this arrangement more than one revolution of the motor armature is required to make one revolution of the car-wheel, which multiplies the force exerted in turning the wheel.

The Controller

Fig. 12 is a view of a type of controller that is used on the platform of trolley-cars. The cover is removed to show the contacts, inside, by which the electric power is turned on gradually by the controller handle. The trains of electric cars that run on the elevated structures and in the subways of our large cities are supplied with power from a “third rail” placed by the side of the track, on insulating supports, and the motors on all the cars are controlled from a single “master-controller” on the front platform of the forward car. This system of control, known as the “multiple-unit” system, gives electric trains several advantages over the old kind, drawn by steam-locomotives; such as they used to have on the New York elevated roads, for example. For one thing, the train can be started much more quickly, since all the motors begin to turn the car-wheels at the same instant. Then again, the system enables a long train of cars to be controlled as easily as a single car, and better “traction” between wheels and track is obtained.

Electric Locomotives

Several of the great steam-railroads are now adopting the electric locomotive to draw their trains. Fig. 13 is a view of one of the great continuous current electric locomotives that are used by the New York Central Railroad to handle many of its passenger-trains in and out of the Grand Central Station, in New York city. The motors of this powerful electric engine, unlike those of trolley-cars, are “gearless”; that is, their armatures are fixed directly on the locomotive axles so that they revolve at the same speed as the driving-wheels.

All of the railway motors considered thus far have been of the continuous-current type, although the current to operate them is often obtained from alternating current transmission-systems, through rotary converters, as described above. The alternating current is also beginning to be employed to drive cars and trains. One type of alternating current railway motor, designed for “single-phase” operation, is in use on several interurban systems in this country, running on high-voltage alternating current most of the time, but on continuous current when within the city limits.

Other Forms of Electric Traction

Electric traction also includes electric automobiles, supplied by storage-batteries; a slow-speed electric locomotive for drawing canal-boats, and called “the electric mule”; and an ingenious gasolene-electric outfit for driving cars by electric motors without any trolley, third rail, or storage-battery. The last-mentioned arrangement consists of a set of electric car-motors mounted on the trucks in the usual way, but supplied with current by a dynamo mounted on the car itself and driven by a gasolene-engine. Thus the car carries its own power-station about with it, and is independent of any outside source of electricity.

* * * * *

The old alchemists sought to transmute _matter_ from one form to another; and especially lead and other “base metals” into gold, in order that they might grow rich by concentrating the precious metal in their own selfish hands. The modern miracle that electricity works for us, the transmutation of _energy_, is a higher and broader thing, because it multiplies and distributes the world’s good things.