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Nature's Miracles Volume 3: Electricity and Magnetism

<h2>CHAPTER XXIV.</h2> <h3>NIAGARA FALLS POWER—APPLIANCES.</h3> In the last chapter I described some of the appliances used in connection with the power-house. There are many things that are commonplace as electrical appliances when used with currents of low voltage and small quantity, that become extremely interesting when constructed for the purpose of handling such currents as are developed by the dynamos used at Niagara. For instance, it is a very commonplace and simple thing to break and close a circuit carrying such a current as is used for ordinary telegraphic purposes, but it requires quite a complicated and scientifically constructed device to handle currents of large volume and great pressure. If such a current as is generated by a dynamo giving out 5000 horse-power under a pressure of 2200 volts should be broken at a single point in a conductor, there would be a flash and a report, attended with such a degree of heat and such power for disintegration that it would destroy the instrument. The circuit-breakers used at Niagara are constructed with a very large number of contacts made of metal sleeves, or tubes, say one inch in diameter, so constructed that one will slide within the other; the sleeves being slotted so as to give them a little spring that secures a firm contact. These are all connected together electrically, on each half of the switch, as one conductor, so that when the switch is closed the current is divided into as many parts as there are points of contact in the switch. Suppose there are 100 of these contact-points, a one-hundredth part of the current would be flowing through each one of them. If, now, these points are so arranged that they can be all simultaneously separated, the spark that will occur at each break will be very small as compared with what it would be if the whole current were flowing through a single point, and it would be so small that there would be no danger attending the opening of the switch. These switches are carefully guarded, being boxed in and under the control of a single individual. There is another apparatus that is a necessary part of every manufacturing or other kind of plant that uses electricity from this power-house, and this is called the transformer. Many of you are familiar with the box-shaped apparatus that is used in connection with electric lighting when the alternating current is used. Where simply heating effects are required, such as in electric lighting, for instance, the alternating current can be used to greater advantage than the direct current when it has to be carried to some distance, owing to the fact that it may be a current of high voltage. A greater amount can be carried through a small conductor; thus greatly reducing the cost of an electrical plant that distributes power to a distance. A transformer is an apparatus that changes the current from one voltage to another. In the ordinary electric-light plant, such as is used in a small town or village, the current that is sent out from the power-station has a pressure of from 1000 to 1500 volts, according to the distance to which it is sent. It would not do, however, for the current to enter a dwelling at this high pressure, because it is dangerous to handle, and the liability to fires originating from the current would be greatly increased. At some point, therefore, outside of the building, and not a great distance from it, a transformer is inserted which changes the voltage, say, from 1000 down to 50 or 100, according to the kind of lamps used. Some lamps are constructed to be used with a current of fifty volts and others for 100 or more. The lamp must always be adapted to the current or the current to the lamp, as you choose. The human body may be placed in a circuit where such low voltage is used without danger, but it would be exceedingly dangerous to be put in contact with a pressure of 1000 or more volts, such as is used for lighting purposes. In principle the transformer is nothing more or less than an induction-coil on a very large scale. The ordinary induction-coil, such as is used for medical purposes, is ordinarily constructed by winding a coarse wire around an iron core. This core is usually made of a bundle of soft iron wires, because the wires more readily magnetize and demagnetize than a solid iron core would. Around this coil of coarse wire, which we call the primary coil, is wound a secondary coil of finer wire. If now a battery is connected with the primary coil, which is made of the coarse wire, and the circuit is interrupted by some sort of mechanical circuit-breaker, each time the primary or battery circuit is opened there will be a momentary impulse in the secondary circuit of a much higher voltage; and at the moment the primary circuit is closed there will be another impulse in this secondary circuit in the opposite direction. The latter impulse is called the initial and the former the terminal impulse. A current created in this manner is called an induced current. The initial current is not so strong as the terminal in this particular arrangement. If we should take hold of the two wires connected with the two poles of the battery and bring them together so as to close the circuit, and then separate them so as to break it we should scarcely feel any sensation—if there were only one or two cells, such as are ordinarily used with such coils. But if we connect these wires to the coils of the induction apparatus and then take hold of the two ends of the secondary coil and break and close the primary circuit we should feel a painful shock at each break and close, although the actual amount of current flowing through the secondary wire is not as great as that which flows through the primary; but the voltage (or electromotive force) is higher, and thus is able to drive what current there is through a conductor of higher resistance, such as the human body. For this reason there is more current forced through the body, which is a poor conductor, than can be by a direct battery current which has a lower voltage. If now we should take a battery of a number of cells, so as to get a voltage equal to that given off by the secondary coil, and connect it with the fine-wire coil instead of the coarse-wire coil—thus making what was before the secondary coil the primary—by breaking and closing the battery circuit as before we shall get a secondary or induced current in the coarse-wire coil, but it will be a current of low voltage, and will not produce the painful sensation that the secondary coil did. We have now described the principle of a transformer as it is worked out in an ordinary induction-coil. As has been stated, at Niagara Falls the current comes from the dynamos with an electromotive force or pressure of 2200 volts. For some purposes this voltage is not high enough, and for other purposes it is too high; therefore it has to be transformed before it is used! For some purposes this transformation takes place in the power-house, and for others it takes place at the establishment where it is used. For instance, take the current that is sent to Buffalo, a distance of from twenty to thirty miles. The current first runs to a transformer connected with the power-house, where it is "stepped-up" (to use the parlance of the craft) from a voltage of 2200 to 10,000. It is carried to Buffalo through wire conductors that are strung on poles, and is there "stepped-down" again through another transformer to the voltage required for use at that place. The object of raising the voltage from 2200 to 10,000 in this case is to save money in the construction of the line of conductors between the two points. If the voltage were left at 2200—the conductors remaining the same as they are now—the loss in transmission would be very great, owing to the resistance which these wires would offer to a current of such comparatively low voltage as 2200. To overcome this difficulty—if the voltage is not increased—it would be necessary to use conductors that are very much larger in cross-section (thicker) than the present ones are. And as these conductors are made of copper the expense would be too great to admit of any profit to the company. If we go back to an illustration we used in one of the early chapters on electricity we can better explain what takes place by increasing the voltage. If we have a column of water kept at a level say of ten feet above a hole where it discharges, that is one inch in diameter, a certain definite amount of water will discharge there each minute. If now we substitute for the hole that is one inch in diameter one that is only one-half inch in diameter a very much smaller amount of water will discharge each minute, if the head is kept at the same point—namely, ten feet. But if now we raise the column of water we shall in time reach a height which will produce a pressure that will cause as much water to discharge per minute through the one-half-inch hole as before discharged through the one-inch hole with only the pressure of a ten-foot column. This is exactly what takes place when the voltage is "stepped-up," which is equivalent to an increase of pressure. It will be seen from the foregoing that these transformers have to be made with reference to the use the current is to be put to. In general shape they are alike in appearance, the difference being chiefly in the relation the primary sustains to the secondary coils. There is another kind of transformer that is used when it is necessary to have the current always running in the same direction. This transformer, as heretofore explained, does not change the voltage of the current, but simply transforms what was an alternating into a direct current. By alternating current we mean one that is made up of impulses of alternating polarity—first a positive and then a negative. The direct current is one whose impulses are all of one polarity. The direct current is required for all purposes where electrolysis (chemical decomposition by electricity, as of silver for silver-plating, etc.) is a part of the process. The alternating current may be used without transformation in all processes where heat is the chief factor. For motive power either current may be used, only the electromotors have to be constructed with reference to the kind of current that is used. The rotary transformer, which may be driven by any power, consists of a wheel carrying a rotating commutator so arranged with reference to brushes that deliver the current to the commutator and carry it away from the same, that the brushes leading out from the transformer will always have impulses of the same polarity delivered to them. In the parlance of the craft, the transformers that are used to change the voltage from high to low, or vice versa, are called "static transformers," simply because they are stationary, we suppose. The others are called rotary, or moving transformers, to distinguish them from the other forms. The operation of the latter is purely mechanical, while the former is electrical. In some instances where the static transformers are very large they develop a great amount of heat, so much that it is necessary to devise means for dissipating it as fast as created. In some instances this is done by air-currents forced through them, but in others, where they are very large, oil is kept circulating through the transformer from a tank that is elevated above it, the oil being pumped back by a rotary pump into the tank where it is cooled by a coil of pipe located in the oil, through which cold water is continually circulating. By this means cold oil is constantly flowing down through the transformer, where it absorbs the heat, which in turn is pumped back into the tank, where it is cooled. Having now traced the energy from the water-wheel through the various transformations and having described in a very general way the apparatus both for generating electricity and for transforming it to the right voltage necessary for the various uses to which it is put, we will proceed in our next chapter to follow it out to the points where it is delivered, and trace it through its processes, and the part it plays in creating the products of these various commercial establishments. <hr style="width: 65%;" /> <div style="break-after:column;"></div>

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