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ELECTRIC TRANSMISSION OF POWER:

ITS PRESENT POSITION AND ADVANTAGES.

Richard William Henry By, PAGET HIGGOS, LL.D., D.Sc., TILFORD FREEMAN AND ASSOCIATES OF THE INSTITUTION OF CIVIL ENGINEERS; AUTHOR OF 'THE ELECTRIC LIGHTING OF CITIES,' 'ELECTRICAL APPLICATIONS,' "ELECTRIC LIGHTING," "ELECTRICAL FORMULAE" (MILDEWORTH), ETC.

A stylized illustration of an electrical circuit or generator.

LONDON: E. & F. N. SPON, 46, CHARGING CROSS. NEW YORK: 446, BROOME STREET. 1879. Handwritten note "Inq 4098.79" on top left. DEC 14 1880 Boudrel's Fund. - PREFACE.

It is needless to dwell upon the benefits of economical transmission of power. Where distance is involved, none of the existing systems are so nearly perfect as to leave no room for fresh trials; on the contrary, all kinds of manufactures and trades are alive to a simple means of transmitting power.

Extensive experience with dynamo-electric machines and their various uses has shown me that electric transmission has before it a very wide field. For this reason, I have collected into the following pages the most reliable data on this subject, and have added some experimental results from my own working. I hope I have furnished to the inquirer that information which will enable him to form his own opinion. It may be well to point out that I do not propose a system of my own nor advocate specially.

First describing the machines employed, their relative merits and demerits, there is next considered the mechanical ratio of the efficiency of this method of transmission, and its applicability either to short or long vi

PREFACE.

distances. Some objections that have been advanced are met, and in conclusion are given some of the most definite advantages of employing electricity.

I hope that the desire to afford information upon a comparatively novel subject may be taken in palliation of shortcomings in style and arrangement.

PAGET HIGGS. CONTENTS.

CHAPTER I. Dynamo-Electric Machines 1

CHAPTER II. The Gramme Machine 4

CHAPTER III. The Brush Machine 11

CHAPTER IV. The Wallace-Faraday and Siemens Machines 19

CHAPTER V. Efficiency of Dynamo-Electric Machines 24

CHAPTER VI. Practicability of Transmission of Power by Electricity 34 viii CONTENTS.

CHAPTER VII. Efficiency of Coupled Machines ... 57

CHAPTER VIII. Comparative Efficiency of Various Machines... 59

CHAPTER IX. Other Theoretical Considerations ... 78

CHAPTER X. Conclusions ... 85 ELECTRIC TRANSMISSION OF POWER.

CHAPTER I.

DYNAMO-ELECTRIC MACHINES.

Whilst the invention of the dynamo-electric machine, transmission of power by electricity could never have become an accomplished fact. But the growth of electrical invention has been so rapid that it may be desirable to give some idea of the use of a dynamo-electric machine, and advisable briefly to review this branch of electricity.

The principles of magnetic-electricity were elucidated by Faraday, who found that when a bar of iron surrounded by a coil or helix of wire, a current is approached to or drawn from the bar, a current of electricity is induced in the coil. Further, he found that when one pole of the magnet was approached to the bar, the electrical current had a direction opposite to that electrical current produced when the other pole was approached to the bar: also that the opposite poles of the magnet had opposite actions, or, in other words, produced by the same movement currents of opposite directions. His researches proved that the soft iron and the magnets might change places, and that the changes of intensity of a current induced in a coil placed in a magnetic field, either by changes of intensity of this magnetic field, or by the coil being made to cut through magnetic rays of different intensities.

2 2 ELECTRIC TRANSMISSION OF POWER.

The practical application of this important addition to electrical knowledge soon appeared in the first magneto-electric machine, constructed in 1833, by Pixii. In this machine a horse-shoe magnet was caused to revolve with its poles before those of a double electro-magnet. This machine has been much improved, and disadvantages of the heavier part, the permanent magnet being now but one tooth. Clarke improved upon this construction in machine of small dimensions, the magnets in which were fixed, and the coil caused to rotate. Machines virtually on the principle of Clarke's machine but of different form were constructed by Holmes, of London, and the Compagnie d'Alliance, of Paris. All these machines may be classed as magneto-electric, that is to say, the current produced depends upon the action of magnets upon an electrical circuit.

Magneto-electric machines are quite distinct from electro-magnetic machines, in which the electrical current is made to produce movement, being itself generated by source foreign to the motor.

Magneto-electric machines are disadvantageous in use, because their output increases with their dimensions, and machines for the production of powerful currents become cumbersome and costly. The rapid rotation, and consequently rapid reversals of magnetism of the iron core, give rise to great heating of the working parts, and to secondary currents. A considerable step from magneto-electric to dynamo-electric machines was due to Mr. S. Alfred Varley, Sir Charles Wheatstone, and Dr. Werner Siemens, who quite independently discovered and worked upon the same principle of accumulation by mutual action, the priority of this discovery being claimed by his patent. In this construction of machine, induced currents are caused to circulate in the electro-magnet coils that produce them, and are in this way increased. By this mutual action currents are produced, the limit of intensity DYNAMO-ELECTRIC MACHINES. 3

of which is co-equal with the maximum limit of magnetic accumulation.

This principle of accumulation by mutual action is now employed in all machines where currents of great intensity are required.

As all these machines can be made to yield electricity, through rotation imparted to them by the expenditure of mechanical power, they may be used as generators, i.e., by causing the current generated by one machine to be passed into the coils of a second machine. This second machine will then rotate in an opposite direction, about 50 per cent. of the mechanical power expended upon the pulley of the first machine being withdrawn from the pulley of the second. This is the basis of electrical transmission of power.

2 4 ELECTRIC TRANSMISSION OF POWER.

CHAPTER II. THE GRAMME MACHINE.

The machine invented by M. Gramme is essentially the parent of present dynamo-electric machines. To comprehend the principle of the Gramme machine, let Fig. 1

Fig. 1

represent a magnetised bar, A B, and a conducting helix, capable of moving to and fro on the bar. If the helix is brought towards the bar from its position at X, an induced current is produced at each movement. These currents are in the same direction while the helix passes the middle, M, of the bar, A B, until it leaves the opposite pole, B. When the helix is moved back to and from the magnet, two distinct periods are to be distinguished: in the first half of the movement the currents are direct, and in the second they are inverted. If, instead of moving freely from right to left as we have supposed, the movement is from left to right, the phenomena are as before, with the exception that the currents are opposite.

Let two magnets, A B, and B' A' (Fig. 2), be placed end to end, in contact by poles of the same name, B'B'. The whole forms a single magnet with a consequent point at THE GRAMME MACHINE. 5

the centre. If the helix is moved with relation to this system, it is traversed by a positive current during the first movement, between A and B; by a negative current

Fig. 2.

A diagram showing a helix with two poles labeled A' and B', connected to a circuit with terminals M and M'. The diagram also shows the direction of current flow through the circuit. in the second, from B to B'; again by a negative current in the third, from B' to A'; and finally by a positive current, when leaving A'.

Replacing the straight magnets by two semi-circular magnets (Fig. 3), so as to end, the poles of the same name together, there occur the two poles, A', B', B", and the results are the same as in the preceding. MM' being these neutral points.

The essential part of the Gramme machine is a soft-iron ring, furnished with an insulating band which is wound on the whole length of the iron. The extremities of this helix are soldered together, so as to form a continuous wire without issuing or re-entrant end. If the wire is denuded exteriorly, the part bored forms a straight band running round the whole of the circumference. Friction-pieces, M and M', are applied to the bored part of the helix. When the ring is phased before the poles S and N, of a magnet, the soft iron is magnetised

A diagram showing a helix with two poles labeled A and B, connected to a circuit with terminals M and M'. The diagram also shows the direction of current flow through the circuit. M A B B' M A' 6 ELECTRIC TRANSMISSION OF POWER.

by induction, and there occur in the ring two poles, N and S, opposed to the poles S and N. If the ring revolves between the poles of a permanent magnet, the induced poles always keep the ring always in the same relation with respect to the poles N and S, and are subject to displacement in the iron itself with velocity equal, and of contrary direction, to that of the ring. Whatever may be the rapidity of the movement, the poles N S remain fixed, and each part of the copper helix successively will pass before them.

An element of this helix will be the locale of a current

Fig. 4.

of a certain direction when traversing the path M SM' (Fig. 4), and of a current of inverse direction to the first when passing through the path M' NM. And, as all the elements of the helix possess the same property, all parts of the helix above the line MM will be traversed by currents of one direction, and all parts below this line by a current of inverse direction to the preceding.

These two currents are evidently equal and opposite, and balance one another. When two voltaic batteries, composed of several cells, are connected in opposition, it is necessary only to put the extremities of a circuit in communication with the poles common to the THE GRAMME MACHINE. 7

two batteries, and the currents become associated in quantity. M. Gramme collects the currents developed in the ring of his machine by establishing collectors on the line M'M', where the currents in contrary direction encounter each other.

In practice, Gramme does not demute the wire of the ring. Fig. 5 shows the wire and coils. One or two coils

Fig. 5.

(B) are shown in position, and with the iron ring laid bare, and out.

Insulated radial pieces, R, are each attached to the issuing end of a coil, and to the entrant end of the following coil. The currents are collected on the pieces, R, as they weave round on the issuing wire. These pieces, brought parallel with the axle, are carried through and beyond the interior of the ring, and are brought near one another upon a cylinder of small diameter. The friction-brushes on the pieces are in a plane perpendicular to the polar line S and N—that is, at the middle or neutral point M and M'. The intensity of the current 8 ELECTRIC TRANSMISSION OF POWER.

increase with the velocity of rotation; the electro-motive force is proportional to the velocity. Gramme modifies his machine so as to produce effects of tension or of

A detailed diagram of an electrical machine, showing various components such as coils, wires, and mechanical parts.

quantity, by winding the ring with fine or coarse wire. With equal velocities of the ring the electric tension will be proportional to the number of convolutions of the wire. THE GRAMME MACHINE. 9

Figs. 6 and 7 represent a Gramme machine; it consists of two flanks of cast iron, arranged vertically, and connected by four iron bars, serving as cores to electro-magnets. The axle is of steel; its bearings are relatively very long. The central ring has two wires wound parallel.

Fig. 7.

A diagram showing the construction of a Gramme machine. on the soft iron, and connected to two collectors to receive the currents. The poles of the electro-magnet are of large size, and embrace seven-eighths of the total circumference of the central ring. Four brushes collect the currents produced. The electro-magnet is placed in the circuit. The total length of the machine, pulley included,

10 10 ELECTRIC TRANSMISSION OF POWER.

is 31$\frac{1}{2}$ inches, its width 1 foot 9$\frac{1}{4}$ inches, and its height 23 inches. Its weight is 880 lbs.

The double coil is connected to 120 conductors, 60 on each side. Its exterior diameter is 27 inches; the weight of wire wound on it is 31 lbs. The four bobbins have a diameter of 24 inches and a length of 152 inches. The total weight of wire wound on the four bams is 211 lbs. The winding of the wires on the ring is effected as if two complete bobbins were put one beside the other, and these two bobbins may be connected in tension or in quantity. THE BRUSH MACHINE. 11

CHAPTER III.

THE BRUSH MACHINE.

Mr. Burson, the inventor of the machine bearing his name, considers that even the best forms of magneto-electric apparatus are unnecessarily bulky, heavy, and expensive, and are more or less wasteful of mechanical power. The armature of the Brush machine (Figs. 8 to 11) is of

Fig. 8.

iron, in the form of a ring, and is attached to a hub, which is rigidly attached to the shaft C (Fig. 8). The armature, instead of having a uniform cross section, as in the Gramme machine, is provided with grooves, or depressions, in a direction at right angles with its magnetic 12 ELECTRIC TRANSMISSION OF POWER.

axis or length. These grooves are wound full of insulated copper wire, and are of any suitable number. The advan- tage of winding the wire on the armature depressions is twofold. The projecting portion of the armature between the sections of the cylinder is always very close to the poles N' and S' of the magnets, from which the magnetic force is derived, thus utilizing the inductive force of the latter to a much greater extent than is possible in the case of annular armatures entirely covered with wire, which would require a large space to seat the magnets. Owing to the exposure of a very considerable portion of the armature to the atmosphere, the heat, which is always developed by the rapidly succeeding magnetis- tions and demagnetizations, is quickly dissipated. In this case, is rapidly dissipated by radiation and convection. In the case of armatures completely covered with wire, the escape of heat is very slow, so that they must be run at a comparatively low rate of speed, with corresponding effect, in order to prevent injurious heating. Opposite sections on the same shaft are connected together, and their remaining ends connected with two segments of metal of the commutator cylinder E, which is carried by the shaft C, and is of insulating material (Fig. 9).

The two metal segments are placed opposite each other on the cylinder, and are each of a length less than half the circumfer- ence of that of the latter, thus exposing the in- sulating cylinder in two places diametrically opposite one another and alternating with the metal segments. The two segments, say S' and S', cor- A diagram showing a cylindrical commutator with two metal segments attached to it. The diagram also shows a shaft labeled C and a cylinder labeled E. Fig. 9 THE BRUSH MACHINE.

responding to sections 3 and 7 of wire, hold a position on the cylinder in advance of those of the preceding sections $8^{\mathrm{th}}$ and $8^{\mathrm{th}}$ to the same angular extent that the sections 3 and 7 in question are in advance of sections 2 and 6. In this arrangement the number of segments is equal to the number of sections, each segment being connected with one section by means of a short lead. Each of each section can, however, be attached to two opposite segments, the commutator cylinder, in that case, being constructed with double the number of segments as in the former case, thus making the number of segments double that of the sections. The brushes are flat plates or brushes, insulated from each other, pressed lightly upon the cylinder E at opposite points, so selected that while each section of wire on the armature is passing from one neutral point to the other, the corresponding segment on the commutator is passing from one brush to another. These plates or brushes collect the currents of electricity generated by the revolution of the armature, one being positive and the other negative. When the section of wire is passing the neutral points on the armature, the brushes are in contact with the conducting material of the cylinder between the corresponding segments, thus cutting the section, which is at the time useless, out of the circuit altogether. The necessity for thus insulating each section from the plates during the time it is passing from one neutral point to another is observed that, if this were not done, the idle section would afford a passage for the current generated in the active sections. During this time a section or bobbin is passing from one neutral point of the armature to the next one, an electric impulse, which is called an electro-motive force, is induced in it. This electro-motive force, starting from nothing at the neutral point, quickly increases to nearly its maximum, and remains almost constant until the section is near the next neutral point,

13 14 ELECTRIC TRANSMISSION OF POWER.

when it rapidly falls to zero as the neutral point is reached.

The insulating spaces are made of such a length that a section or bobbin is cut out of the circuit, not only when it is at the neutral points, but also during the time when its electro-motive force is rising and falling at the beginning and end of an impulse.

If the insulating space is too short, so as to keep or bring a section in the circuit, while its electro-motive force is low, then the current from the other sections, being of opposite polarity, will tend to overcome this weak contact and discharge through this insulation. If the insulating spaces are a little longer than necessary, no material inconvenience results. A suitable length for practical purposes is easily determined experimentally.

It is found that the neutral points of the armature motion are considerably in advance of their theoretical position, this circumstance being attributed to the time required to saturate any point of the armature with magnetism, so that the given point is carried beyond the point of greatest magnetism, or of the field before recovering its maximum charge. M. Gouy believes it is due to the reaction, by induction, of the armature cells upon the core and coils of the electro-magnet.

It is necessary to adjust the commutator cylinder on the revolving shaft of the machine with special reference to the direction of rotation of the armature motion, in order that its insulating space may correspond with the neutral points. This adjustment is made experimentally as follows: The commutator cylinder having been placed approximately in its proper position, the machine is started and a spark is observed at each point of contact between the plates and commutator cylinder is noted. If sparks occur, the commutator cylinder is turned slightly forward or backward on its axis, until the sparks disappear. THE BRUSH MACHINE.

The presence of sparks when the commutator is even slightly out of its proper position is easily explained. If a break between a pair of segments and the plates occurs while the corresponding section of wire on the armature is still active, a spark is produced by the interruption of the current through this passage. As soon as the section in question will have become neutral, and then commenced to conduct the current from the active sections, and the interruption of this passage causes a spark in this instance. If the commutator is much removed from its proper position, the sparking may be so great as to very rapidly destroy both the commutator and the brushes, while the current from the machine is correspondingly diminished.

With the arrangement, where the first and last ends of each of two adjacent segments are attached to two opposite segments the intensity of the induced electrical current will be that due to the length of wire in a single section only, while the quantity will be directly as the number of sections. By doubling the size of each bobbin, and diminishing the number of sections, we can increase indefinitely the intensity and one half the quantity of the former will be obtained. This effect, however, can be secured in another manner, by connecting the first and last ends of the two opposite sections together, and joining the remaining ends to two opposite segments, as illustrated in Fig. 10. This arrangement is found most convenient in practice.

The arrangement of the cylinder for two segments S (Fig. 8) is usually replaced by another, in which the last end of one section and the first end of the succeeding may be connected with a strip of metal.

A diagram showing an arrangement for two segments with one segment's ends connected to another segment's ends. Fig. 10. 16 ELECTRIC TRANSMISSION OF POWER.

attached to the cylinder, parallel with its axis, as in the Siemens and Gramme machines. These metallic stripes or conductors are equal in number to the sections of wire on the armature, and are insulated from each other. The plates press upon the cylinder, in this case, at points corresponding to the neutral points of the armature, thus being at right angles with their position in the first consequent. This plan, which is the one commonly used with annular armatures, gives fair results, but is subject to a serious disadvantage from which the first is free. The difficulty is, that the current of wire passing near the neutral points of the armature distribute little or no useful effect, but the current from the other sections must pass through these in order to reach the plates, thus experiencing a considerable and entirely useless resistance; and, owing to the opposite direction of the currents through the active sections on opposite sides of the neutral point, these currents, by passing through the idle sections, tend strongly to produce "consequent" points in the armature where the neutral points should be, thus interfering seriously with the theoretical distribution of magnetism of the armature. The electromagnets H are driven by the whole or a portion of the electric current derived from the revolving armature, as is usual in apparatus of this kind, the novel feature of this part of the machine consists in the manner in which these magnets are presented to the armature. This arrangement is such that a very large proportion of the entire surface of the armature is constantly presented to the poles of the magnets, thus securing uniformity of magnetisation, as well as maximum amount. The iron segments, constituting the poles of this part of the machine, are connected to the armature. The pieces N or S may be connected at their outer edges, thus forming one piece, and enclosing the armature still more. In the other dynamo-electric machines no magnetic field is maintained when the ex- THE BRUSH MACHINE. 17

ternal circuit is opened, except that due to residual mag- netism; hence the electro-motive force developed by the machine in this condition is very feeble. It is only when the external circuit is closed through a resistance

A diagram showing a circuit with various components labeled (D), (E), (F), (G), (H), (I), (J), (K), (L), (M), (N), (O), (P), (Q), (R), (S), (T), (U), (V), (W), (X), (Y), (Z).

not too large that powerful currents are developed, owing to the strong magnetic field produced by the circulation of the current themselves around the field magnets.

By diverting from external work a portion of the 18

ELECTRIC TRANSMISSION OF POWER.

current of the machine, and using it either alone, or in connection with the rest of the current for working the field magnet, a permanent field may be obtained.

Mr. H. Brunn winds the cores of the field magnets with a quantity of wire which has a high resistance in comparison with that of the external circuit, and the rest of the wire in the machine. The ends of this wire are so connected with other parts of the machine that when the latter is running, a current of electricity constantly flows through them, and it is only by closing the external circuit be closed or not. The high resistance of this wire prevents the passage through it of more than a small proportion of the whole current capable of being evolved by the machine, provided that the external circuit is not materially lessened. When this device, called a "teaser," is used in connection with field magnet, also wound with coarse wire (Fig. 11), for the purpose of still further increasing the magnetic field by employing the main current for this purpose, then the "teaser" may be so arranged that the current which passes through it will also circulate in the coarse wire, thus increasing efficiency THE WALLACE-FARMER AND SIEMENS MACHINES. 19

CHAPTER IV.

THE WALLACE-FARMER AND SIEMENS MACHINES.

In the Wallace-Farmer machine (Fig. 12) the magnetic field is produced by two horse-shoe electro-magnets, but with poles of opposite character facing each other.

Fig. 12

Between the arms of the magnets, and passing through the uprights supporting them, is the shaft, carrying at its centre the rotating armature. This consists of a disc of cast iron, near the periphery of which, and at right angles to either faces, are iron cores, wound with insulated wire, thus constituting a double series of coils. The armature c 2 20 ELECTRIC TRANSMISSION OF POWER.

coils (Figs. 13 and 14) being connected end to end, the loops so formed are connected in the same manner, and to a commutator of the same construction as that of the Gramme. As the armature rotates, the cores pass between the opposed north and south poles of the field magnets, and the current generated depends on the change of

Fig. 13. A diagram showing two parallel bars with a central core, labeled 'n' and 's'. The core is shown in cross-section. Fig. 14. A diagram showing a circular core with a central hole, labeled 'n' and 's'. The core is shown in cross-section.

polarity of the cores. It will be seen that this constitutes a double machine, each series of coils, with its commutator, being capable of use independently of the other; but in practice the electrical connections are so made that the currents generated in the two series of armature coils pass through the field magnet coils, and are joined in one external circuit.

This form of armature also presents considerable uncovered surface of iron to the cooling effect of the air, but, like that of the Brush, presents considerable resistance to rotation.

In the Wallace-Farmer machine there is considerable heating of the armature, the temperature being sometimes sufficiently high to melt sealing-wax.

In the Siemens machine, the conductor of insulated copper wire is coiled in several lengths and convolutions THE WALLACE-FARMER AND SIEMENS MACHINES, 21

upon a cylinder shown in transverse (Fig. 15), and in end view by Fig. 16. Each convolution is parallel to the

Fig. 15.

A diagram showing a cylindrical machine with multiple convolutions around its perimeter.

longitudinal axis of the cylinder, and the whole surface of the cylinder is covered with wire, laid on in six sections.

Fig. 16.

A diagram showing a cylindrical machine with multiple convolutions around its perimeter, with surrounding iron bars.

Surrounding the wire cylinder for about two-thirds of its surface are curved iron bars, the space between these 22 ELECTRIC TRANSMISSION OF POWER.

curved bars and the wire cylinder being as small as is consistent with the free rotation of the cylinder. The curved bars are themselves the prolongations of the cores of large flat electro-magnets; the coils of these electro-magnets and the wire of the cylinder form (from brush to brush) four continuous electrical circuits. Upon revolu- tion of the wire cylinder, a current is generated upon a longitudinal axis at proper bearings, the axis carrying a pulley, a current is generated in it, and this current, initially weak, is directed into the coil of the electro-magnet, magnetizing the core, which induces still stronger currents in its own circuit, and so on until mutual action continues until the magnetic limit of the iron is attained. At every revolution of the wire cylinder, the maximum magnetic power acting upon each convolution is attained when the convolution passes through the middle of the coil. This current is then reduced to zero when the convolution is perpendicular to that position. Each convolution is therefore subject to a neutral position, and by Lenz's law a convolution starting from that position on one side of the axis towards the north pole will be traversed by a current tending to a direct induced current, and that portion of the convolution on the opposite side of the axis will be traversed by a current of opposite direction, as regards a given point, but of the same direction as regards circuits. Each of these convolutions consists upon the cylinder consist of two separate coils, the whole having twenty-four ends; two of these ends are brought to each of the segments of a circular commutator in such a manner that the whole six double sections form a continuous circuit, which is shown in Fig. 3.

In order that the segments may be properly presented to the collecting brushes, the connections are arranged according to their relative momentary position. The electric currents are collected upon two wire brushes THE WALLACE-FARMER AND SIEMENS MACHINES, 23

tangential to the segments of the commutator, and these brushes form, through the electro-magnets, the two elec- trodes of the machine. The electro-magnet coils are connected the conducting wires leading to the system where the current is to be utilised.

The dimensions, weights, number of revolutions made by the cylinder, and HP. required for driving, are for three sizes of the machine, as under—

Dimension in Inches.			Weight in lbs.	Revolutions per Minute.	HP.
Length.	Width.	Height		Cylinders.
25	21-0	8-9	298	1,100	11 to 2
29	26-0	9-5	419	850	3 ,, 54
44	28-3	12-6	1,379	480	9 ,, 10

24 ELECTRIC TRANSMISSION OF POWER.

CHAPTER V. EFFICIENCY OF DYNAMO-ELECTRIC MACHINES.

When two machines are coupled in circuit for the trans- mission of the power of a prime mover, we may consider two causes of loss of power in each machine, viz., (1) that of a current generator, and (2) that of the two machines con- sidered together as a transmitting system. In a paper read before the Institution of Mechanical Engineers, by Dr. Hopkinsin, it has been pointed out that it is desirable to know the amount of power absorbed in each case with varied speed and known resistances in the circuit and with varied speeds of rotation; and what amount of power is absorbed in each case.

The mechanical energy communicated by the steam- engine or other motor is not immediately converted into the energy of heat, but is first converted into the energy of an electric current in a conducting circuit. The whole of what is needed to be known may be more easily acer- taind and expressed if the subject of inquiry is stated as: what current can be produced under given conditions of circuits; and at what expenditure of mechanical power. The subject has been treated more or less by Edlund (Pogg. Annal., 1867 and 1868), Houston and Thomas in America, Macart (Journal de Physique, March 1870), Thomas (Phil. Trans. Roy. Soc. London, March 1879), Schwendier (? Report on Electric Light Experiments). Dr. Hopkinsin limits his inquiry to an account of some experiments on the production of currents by a Siemens medium-sized machine, the machine which EFFICIENCY OF DYNAMO-ELECTRIC MACHINES. 25

is said to produce a light of 6000 candle, by an expenditure of 38 HP. The intensity of the magnetic field in such machines, and the Simons' law on which Gramme machines may be regarded as a function of the current passing; to learn what this function is for the machine in question, we may construct a curve in which the absolute representative current passing, and the ordinates the electro-motive force for one second, are plotted against the power of a current, that is its energy per second, is the product of the electro-motive force and its intensity; this is in all cases less than the power required to drive the machine, and the ratio between the two may fairly be called the efficiency of the machine. Thus, when a pump forcing water through a pipe against friction ; then electric current corresponds to the water passing per second, and electro-motive force to the difference of pressure on the two sides of the pump; and just as the product of electro-motive force and current is power, so the product of electro-motive force and current is power; which is directly comparable with the power expended in driving the machine or the pump, as the case may be.

The peculiarity of the so-called dynamo-electric machine lies in the fact that the product of pressure (the electro-motive force) depends directly on what corresponds to the volume passed (the current). Each experiment requires the determination of the speed, the driving power, the resistances in circuit, and the current passing.

In Dr. Hopkinson's measurements, the speed of the steam engine was maintained very constant by means of a governor specially arranged for great sensitiveness. The speed was varied by means of a weight and a spring, attached to a lever connected with a pulley. The power was transmitted from the engine to a counter- shaft by means of a strap, and by a second strap from the counter- shaft to the pulley of the machine. On this second 26

ELECTRIC TRANSMISSION OF POWER.

The strap was the dynamometer (Fig. 17), arranged as used by the Author, and described in a paper read before the Institution of Civil Engineers, 1877-8.

Fig. 17.

The tension difference in the two parts of the strap of the dynamometer and the velocity of rotation of the machine being known, the power received was EFFICIENCY OF DYNAMO-ELECTRIC MACHINES. 27

obtained, expressed in gram-centimètres per second. Multiplying by 981, the value of gravity in centimètres and seconds, the power is then expressed in ergs* per second, and is ready for comparison with the results of the electrical experiments.

The dynamo-electric machine in these trials was a fissure machine, and the armature coil had fifty-six divisions, and the brushes are single, not divided—that is, each brush is in connection with one segment of the commutator at each instant. The leading wire was 100 yards of seven copper wires, insulated with tape and inda- rubber, and having a diameter of about 6½ millimetres. The current was measured by means of a galvanometer, or by measuring the difference of potential at the extremities of a resistance, all the resistances of the circuit being known. The resistance coil comprised ten coils of common brass wire, each, wound round a couple of wooden cylinders, which were fixed to the frame of the set; each wire was about 60 metres long, and of No. 17 Birmingham wire gauge, weighing about 14-6 grammes per metre. Each terminal was connected to a cup of mercury excavated in the baseboard, so that the coils could be immersed in mercury without loss of pressure. The resistance of each coil being about 5 ohms, this set could be arranged to give resistance varying from 0-3 to 30 ohms. The commutator was a double copper vessel, a resistance coil of uncovered German-silver wire nearly 2 metres long, 1-5 millimetres in diameter, and having a resistance of about ½ ohm, was suspended within it from an ebenite cover,

The dyne is the force which will in one second impart to one gramme a velocity of one centimetre per second, and an erg is the work done by a dyne working through a centimetre; a horse-power may be taken as equal to 72000 dyne-centimetre per second, or 72000 ergs per second. See Report of Brit. Assoc. 1873, and Eucton, "On the Centimètre-Gramme Second System of Units."

28 ELECTRIC TRANSMISSION OF POWER.

which also carried a little brass stirrer; and the calorimeter was filled with water to the level determined by the mark of a scriber. It was, of course, necessary to know the capacity of the calorimeter for heat. It was filled with warm water up to the mark, and the coil placed in position; 130 grams of ice were then withdrawn, and the temperature of the calorimeter was found to be 58°8' centigrade; after the lapse of one minute it was 58°3' centigrade; after a second minute, 57°9' centigrade. 120 grammes of cold water, temperature 13°' centigrade, were then introduced into the calorimeter; a hour later, at the reading of 57°9' centigrade, the temperature was 50°0' centigrade; hence it was inferred that the capacity of the calorimeter is equal to that of 750 grammes of water.

The resistance of the wire used in the binary scale, from 1 ohm to 1024 ohms, was determined by a single element of Daniell's battery, in which the sulphate of zinc solution floats on a sulphate of copper; its electromotive force is assumed to be $\frac{1}{2}$ volt. The resistances added in series with this circuit, and similar lines of glass, such as are described in the "Philosophical Magazine," February, 1879. Preliminary to experiments on the current, determinations of resistances were made. When the ends of the cable were connected, the resistance was found to be 0-125 ohm. The resistances in the machines were determined by the following apparatus: armature coil, 0-166 and 0-162 respectively; armature coil, 0-324 total, 0-632. Direct examination was made of the whole machine in eight positions of the commutator, giving 0-648 ohm with a maximum variation from the mean of 0-0 per cent. At another time, when no current flowed through the machine for some time, the resistance was found to be 0-683, an increase which would be accounted for by a rise of temperature of $12^{\circ}$ centigrade, or thenceforth. The resistance of the calorimeter is 0-20, without its leading wire, which may be EFFICIENCY OF DYNAMO-ELECTRIC MACHINES. 29

taken as 0-01. There were thus three leading resistances which must be considered: (1), the resistance of the machine and leading wire, assumed throughout as 0-81, denoted by $q_1$; (2), the resistance of the brass coils, $C$, calculated from the several determinations, with the addition of the resistance of the leading wire, 0-02, and denoted by $q_2$; (3), the resistance of the calomelimeter and leading wire denoted by $c_p$.

Two approximate corrections were employed, and should be detailed. The first is the correction for the considerable heating of the resistance coil. These were arranged in two series, one each side being in parallel circuit, and two sets in series. The current from the machine, being about 7-4 wels in each wire, was passed for three or four minutes; the circuit was then broken, and the resistance $c_1$ was determined within one second of breaking circuit, when it was found to be about 5 per cent greater than when cold; this resistance was falling, the following was adopted as a rule of correction : square the current in a single wire, and increase the resistance by $\frac{1}{y_0}$ per cent, for every unit in the square. This correction is based on the fact that the calorimeter was losing heat all the time it was being used. It was assumed that it loses 0-01 centigrade per minute for every 1° centigrade, by which the temperature of the calorimeter exceeds that of the air; this correction is, of course, based on the experiment already mentioned.

The method of calculation may now be explained:

R is the total resistance of the circuit, equal to $q_1 + q_2 + c_1$

Q is the heat passing in wels;

E is the electro-motive force round the circuit in volts;

$W_1$ is the work per second converted into heat in the circuit, as determined by the galvanometer, measured in ergs per second; 30 ELECTRIC TRANSMISSION OF POWER.

$W_2$ is the work per second as determined by the calorimeter; $W_3$ is the work per second as determined by the dynamometer, less the power required to drive the machine when the switch is open. $H P$ is the equivalent of $W_2$, i.e., $HP = W_2 \times 720$, $n$ is the number of revolutions per minute of the armature. Then:

$Q = 961 \times \frac{a - b}{b} \times \frac{1}{n}$

$E = Q R$

$W_{3} = E Q$

also $W_2 = R$ multiplied by the mechanical equivalent of the heat generated per second in the calorimeter.

The accompanying table gives the results of the experiments. In each case, a current of 1 ampere was passed through a resistance of 1 ohm, and 961 watts, or 1.28 HP, was required to drive the machine at 720 revolutions on open circuit. An examination of the table shows that the efficiency of the machine is about 90 per cent exclusive of friction. Comparing experiments 11 and 13, and also the last two experiments with those preceding them, it will be seen that the electro-motive force is proportional to the speed of rotation within the errors of observation. Experiments 14, 15, and 16 were intended to ascertain the effect of displacing the commutator brushes.

The principal object of the experiments was to ascertain how far the electro-motive force depended on the current. This relation is represented by a curve (Fig. 18) in which the abscissae represent the currents flowing, or the values of $Q$ in the table, and the ordinates the electro-motive forces, or the values of $E$ reduced to a speed of 720 revolutions per minute. The curve shows that there is a point of inflection in the curve near the origin. The experiments 1 to 5 indicate that this is the true form of the curve, and it is confirmed in a remarkable manner by a EFFICIENCY OF DYNAMO-ELECTRIC MACHINES. 31

special experiment. A resistance intermediate between 54 and 4 was used in circuit, and E and Q were determined in two different ways; first, by starting with an open circuit, which was then closed; secondly, by starting with a portion of the resistance short circuited, and a very powerful current being passed through the machine to short circuit. It was found that E and Q were four times as great in the latter case as in the former. The curve (Fig. 18) will also determine what current will flow at any given speed of rotation of the machine, and under any conditions whatever, whether due to attraction or of opposed electro-motive forces. It will also give very approximate indications of the corresponding curve for other machines of the same configuration, but in which the number of times the wires passes round the electro-magnet is increased.

It will be well to compare these results with those obtained by others. M. Mascart worked on a Gramme machine with comparatively low currents; he represents his results approximately by the formula,

$E = n (a + b Q),$

where (a) and (b) are constants. This corresponds to the rapidly-rising part of the above curve. Mr. Trowbridge with a Siemens machine obtained a maximum efficiency of 76 per cent., and this is about where it was running below its normal velocity. Dr. Schwendler states that the loss of power with a Siemens machine in producing currents of over 20 webers is 12 per cent. Now, taking Dr. Hopkinsin's experiments, to 18, the mean value of (W_p) is 2-888, and to 12, the mean value is 2-021, the power required to drive the machine when no current passes, it appears that 13 per cent. of the power applied is wasted. Again, taking experiments 4, 6, 8, 10, and 12, the mean value of (W_p) is 2-888 and of (W_p), 3-076, indicating a waste of power amounting to 32 ELECTRIC TRANSMISSION OF POWER.

12 per cent. Of the loss, 0-28 HP., is accounted for by fric- tion of the journals and commutator brush; the remainder

A graph showing the relation between current and voltage for a generator with brushes. The x-axis represents current (in amperes), ranging from 0 to 10 amperes. The y-axis represents voltage (in volts), ranging from 0 to 15 volts. The curve shows a decreasing trend as current increases. Key: - A dot at (0, 15) indicates the starting point. - A series of dots along the curve represent different points at various currents. - The curve starts at (0, 15) and decreases as current increases. - The curve is labeled "Current vs. Voltage" and "Generator with Brushes." - The graph is labeled "Fig. 18."

is expended in local currents, or by loss of kinetic energy of current when sparks occur at the commutator. EFFICIENCY OF DYNAMO-ELECTRIC MACHINES. 33

System

Rural.

Urban.

Current, A.

Voltage, V.

Efficiency, %

Position of Commutator Brush.

Current, A.

Voltage, V.

Current, A.

Voltage, V.

Efficiency, %

500

0.0001

87.5

0.0012

1.140

0.016

1.098

1.00

500

0.0001

87.5

0.0012

1.140

0.016

1.098

1.00

500

0.0001

87.5

0.0012

1.140

0.016

1.098

1.00

500

0.0001

87.5

0.0012

1.140

0.016

1.098

1.00

500

0.0001

87.5

0.0012

1.140

0.016

1.098

1.00

553.333333333333366666666666666666666666666666666666666666666666666666666666666666666666666666777777777777777777777777777777777777777777777777777777777777777777777888888888888888888888888888888888888888888888888889999999999999999999999999999999999999999999999999999999999999999999999999999999999999999... (Repeating sequence)

Extra load at brush.

Extra load at brush.CHAPTER VI. PRACTICABILITY OF TRANSMISSION OF POWER BY ELECTRICITY.

To deal with objections first, we may regard the trans- mission of large electric currents as considered by Mr. J. T. Sprague, in his lecture delivered at Glasgow, March 14, 1878, and since published, Mr. Siemens says, "The principal objec- tion that has been raised by electricians to the conveyance of power to this distance of miles, is on account of the ap- parently great increase of internal resistance encountered with increase of distance. In order that the magnetoelectric machine may work under the most favourable conditions, it should have an internal resistance depending in a great measure upon the nature of the work to be performed. The internal resistance is usually expressed in ohms or unit of resistance. If the resistance is greater, a notable proportion of the power expended will be converted into heat in the conductors, causing both loss of effect and great inconvenience. By another law the electrical re- sistance of any conductor must be such that it would be somewhat, but not much, larger than the internal resistance, say 1-0' unit. The external resistance is composed of two elements, namely, the conductor, and the resistance of the electric lamp or electro-magnetic engine, which latter may be taken as equal to one-tenth of the internal resistance or half a unit available for the conductor. These conditions deter- mine really the size of the conductor for any distance to which the current has to be conveyed.

"Suppose the distance to be half a mile, a copper wire of ·25-inch diameter will produce the half-unit resistance,

A page from a book showing text about electric transmission. PRACTICABILITY OF ELECTRIC TRANSMISSION. 35

which is already a wire of considerable dimensions, for the purpose of working a single lamp. If the distance he doubled wire of the same thickness will give twice the electrical resistance, and in order to reduce it again to half a unit its sectional area must be doubled, so that a conductor of 30 mile length would require to be 60% = 8,600 times as thick as the original wire, and this enormous increase in weight would certainly be required if the object to be accomplished was the working of one electric lamp by a dynamo-electric machine. My critics have, however, fallen into the error of overlooking the fact that the resistance of a circuit capable of working one lamp as it is for working 100 or 1000 lamps.

Electricity is not conducted upon the conditions pertaining to a pipe conveying a passable fluid, the resistance of which increases with the square of the velocity of flow; it is, on the contrary, a matter of indifference what amount of energy is transmitted through an electric conductor; the only limit is imposed by the fact that in transmitting electric energy, the heat itself re- takes a certain quantity of energy, owing to that transmitted, which makes its appearance therein in the form of heat."

This heat, as Mr. Siemens goes on to explain, would increase the resistance of the conductor; but to simplify the problem that heat and its effects are not taken into account in the following remarks, Mr. Sprague assumes that the heat is radiated away or got rid of, so as to keep the conductor at a uniform temperature. According to Mr. Sprague, there are two ways of regarding "resistance."

In Ohm's formula it is constant for all currents. So is the diameter of a pipe transmitting water. The same pipe will deliver any variable quantity or current of water corresponding to the pressure; so the same wire d 2

36 ELECTRIC TRANSMISSION OF POWER.

will deliver any variable quantity or current of electricity corresponding to the electro-motive force. This aspect of resistance then is a mathematical one, existing only in calculations.

True, or practical resistance, is measurable by the energy expended to overcome it. The energy expended by a current in passing a given conductor (resistance in the mathematical sense being simply the reciprocal of the conducting power under unit condition) varies as the square of the current or velocity of flow.

Therefore, the resistance is properly estimated under precisely the "conditional appertaining to a pipe conveying a pendentable fluid."

The resistance in a circuit are of several orders:

That of the conductor itself, which is constant.
Any work effected by the current. This may in some cases be expressed as a counter electro-motive force, in others simply as a resistance, but in either case it can be represented in ohms, or as a reduced length; but the expression of it is variable, because it depends upon the energy expended per moment to move it, and must be expressed by the square root of the energy involved in Ohm's formulae.

When all forms of energy expended are thus expressed as resistance in ohms, the ratio of useful work done, to the inevitable expenditure in developing that resisting the energy to the work, is exactly proportional to the resistance of each part of the circuit.

There is a difficulty, continue Mr.Sydney, in applying these principles to the illustrations employed by Mr. Steiner, in that he does not mean by "the resistance of 1 ohm at the point of work done." If by that is meant simply the wire resistance of an electro- motor or of a lamp, they belong to the side of energy lost or expended; if the work to be done is not included in the 1 ohm, then it would seem that, as it would act as an PRACTICABILITY OF ELECTRIC TRANSMISSION. 37

additional resistance, the internal resistance of the generator machine must be increased in order to develop the requisite electro-motive force.

For the present purpose, then, which is to indicate the nature of the problem and the difficulties to be met, rather than how to overcome them, Mr. Siemens' actual figures may be taken, though they do not show the exact mean ratio of the lamp or motor engine. Here we meet at once the problem, what is the work done in, or the mechanical equivalent of an electric light of, say, 1000 candles? Does any one know? The problem involves these simultaneous requirements--light, illumination, and current. With batteries of known electro-motive force this can replace the latter data required. We have all sorts of statements, from 5 to 6 ohm for resistance, to the figures given by Messrs. Ayrton and Perry, which come out as follows:

Grosses in E. R. T. I. 1/4	Total	Resistance.	Current.	Energy in Foot-lights.
	Volts.	Volts.	Amp.	Total.	Volts.	Amp.	Total.
60	188-0	12-0	12-0	24-0	5-33	15-05
80	144-0	15-0	20-0	30-0	4-07	14-157
120	319-0	34-4	39-4	54-4	6-64	21-617

Unfortunately there is no measure of the light produced in these three cases. Taking the common statement that such a light consumes 1 HP. of an engine (though Mr. Siemens states that his smaller size converts 2 HP., and gives 1250 candles) and take the resistance as 1 ohm in the arc and 1/2 in the machine and condenser; this

As far as regards the conductor, it is immaterial whether the current conveyed is utilised to produce light or motor-power. Hence the words of the argument have been retained.

38 ELECTRIC TRANSMISSION OF POWER.

gives $33,000 \div 9.5 = 13,200$ feet pounds expended in the arc, a very singular approximation (considering by how different a road it has been reached) to the figures above. The mechanical equivalent of the webber-ohm current per second is 787 foot pound, or 44-24 per minute. $\frac{13,200}{44.24} = 298.37,$ the square root of which, 17-273, represents the current developing 13,200 foot pounds per minute in the ohm resistance, a useful effect of 0-4 of the power expended.

If, now, 100 such lights were to be applied to the same circuit conditions, it would be necessary to put in circuit ten times as much current as before, in order to main- tain their total joint resistance = 1, and the current would have to be 17,273 $\times$ 10 = 172-73, developing 100 times as much heat in machine and conductor, and still expending 0-6 of the power in transmission. This also supposes that there is no loss of energy due to friction, etc., a con- dition of things not likely to be attained in practice. In converting the current again into mechanical power, the 0-4 of power sent would be reduced by the effective ratio of the transformer machine.

In reply to Mr. Smith's proposal to convey 100 HP, a distance of 30 miles through a conductor 3 inches in diameter, he says, "The electrical resistance of the con- ductor would be 0-18 unit, and supposing that the total resistance in circuit was made 2-5 units, which, as I before stated, gives a favourable working condition, it follows that $0.18 \times 100 = 72$ HP." would be expanded in heating the conductor. This would represent about 15 lbs. of coal per hour, a quantity quite insufficient to raise a mass of 1800 tons of copper, with a surface of 132,000 square feet to a sensibly-heated condition."

A diagram showing the relationship between current, resistance, and power. PRACTICABILITY OF ELECTRIC TRANSMISSION, 39

It seems from this, the proposal is not to convey 1000 HP. but only so much as is possible out of that original power. Then, giving machine 1 and conductor 0-18 ohm resistance, we have 1-32 left for useful work; so we divide it:—

1 Dynamo machine 400 HP.
0-18 Conductor	72
1-32 Engine or lights	528

This latter figure being reduced in actual work to prob- ably 300 HP.

To obtain the 300 HP., then, we have to provide:—

Machines for converting the electricity into 300 HP.
1900 tons of best copper rod carefully insulated.
Machines capable of converting 1000 HP. into electrici- ty.

Appleson's process for getting rid of 400 HP. worth of heat in this latter machinery.

Mr. Siemens says he is convinced that the sectional area of the conductor might safely be reduced to 2 inches, giving half the weight of the conductor; but as the con- verting engine is to be worked by steam, and gas engines of equal power, the question resolves itself into this, is it better worth while to lay down even 950 tons of copper, and fit up the 1000 H.P. engines, or to pur- chase the fuel needed to work the 300 H.P. engines where they are placed? The answer will depend on what weight receive different answers in the mountains of Chili, and where coal is to be obtained at even the most extreme English prices.

Mr. Sprague's views are practically answered by the able papers presented to the Franklin Institute by Professors Thomson and Houston; the statements made as to the size and cost of the cable that would be needed to convey the power of Niagara Falls to a distance of several hundred miles by electricity, having induced with 40 ELECTRIC TRANSMISSION OF POWER.

the Authors the hope that they may throw light upon this interesting subject.

As an example of some of the statements alluded to, the following are cited, viz.:—That made by a certain electrician, who asserts that the thickness of the cable required to convey the current that could be produced by the power of Niagara Falls would be greater than exists in the enormous deposits in the region of Lake Superior. Another statement estimates the cost of the cable at about 212 per linear foot.

As a matter of fact, however, the thickness of the cable required to convey such power at any particular moment, and the Professor's state that it is possible, should it be deemed desirable, to convey the total power of Niagara a distance of 500 miles or more by a copper cable not exceeding one-half" of an inch in diameter, is an extreme case, and the exigencies of practical working would not require such restrictions as to size. The following considerations will elucidate this matter.—Suppose two machines connected by a cable of, say, 1 mile in length. One machine, A, is used as an example. It is producing power by the expenditure of energy. The other machine, B, used as an electrical motor, is producing power by the current transmitted to it from A by the cable C. The other terminals, a and y are either put to earth or connected by a separate conductor.

Let us suppose that the electro-motive force of the current which flows is unity, since, by the revolution of R, a counter electro-motive force is produced to that of A, the electro-motive force of the current that flows is manifestly the difference of the two. Let the resistance of A and B be equalized, so that we have two units of cable and connections between them the 0-01 of this unit.

Then the current which flows will be $C = \frac{E}{R} = \frac{1}{1 - 0.01}$

If, now, an additional machine A' and an additional motor PRACTICABILITY OF ELECTRIC TRANSMISSION.

B', and an additional mile of cable be introduced into the above circuit, the electro-motive force will be doubled, and the resistances will be doubled, the current strength remaining the same as $C = \frac{1}{E} = \frac{1+1}{1+0.01+0.01} = 2$.

Here it will be seen that the introduction of the two additional machines A'B' has permitted the length of the cable, C, to be doubled without increasing the strength of the current which flows, and yet allowing the expenditure of double the power at A'A', and a double recovery at B'B' of power, or, in other words, a double transmission of power without increase of current.

Increase now the number of machines at A to, say, one thousand, and one of those at B in like proportion, and the distance between them, or the length of the cable, one thousand times, or in the case we have supposed make it one thousand times greater than before. Then, although the same current will flow, yet, we have a thousand times the expenditure of power at one end of the cable and a thousand-fold recovery at the other end, without increase of current. And the same will be true for any other proportion.

Since the electro-motive force is increased in proportion to the increase of power transmission, the insulation of the cable and machines would require to be proportionally increased.

As an example it may be mentioned that a dynamo-electric machine used for A may have a resistance of, say, 40 ohms and produce an electro-motive force of, say, 400 volts. Such a machine might require from three to five horse-power when used in connection with a suitable motor B for recovering its energy.

If the resistance of the motor B be, say, 60 ohms, and the cable transmitting the current a distance of 1 mile be 1 ohm, then the current $C = \frac{400}{60 + 40 + 1} = 101$ 42 ELECTRIC TRANSMISSION OF POWER.

If, now, 1000 machines and 1000 motors and 1000 miles of cable, each of the same relative resistances, be used the current $C = \frac{1000 \times 400}{1000 \times 101}$ which has maxi- mally the same value as before. If the supposition of the power being to drive one machine be correct, from 5000 to 2000 HP. would be expended driving the machines, and possibly about 50 per cent. of this amount recovered. Then we have from 1500 to 2000 HP. con- veyed a distance of 1000 miles. What diameter of copper cable will be required for such transmission? Since the thin cable is subject to the law of the resistance of 1 ohm to the mile, calculation would place the requisite thickness at about 4 inch. If, however, the distance be only 500 miles, then the resistance per mile may be doubled, and the section of the cable reduced by one half, or its diameter will be less than one-fifth of an inch.

For the consumption of 1,000,000 HP., a cable of about 3 inches in diameter would suffice under the same condi- tions. However, by producing a much higher electro- motive force, the consumption of the cable could be propor- tionally increased until the theoretical estimate given in the preceding lines might be fulfilled. The enormous electro-motive force required in the above calculation would, however, necessitate such perfect insulation of the cable that the practical limit might soon be reached. The amount of power that could be transferred in any one direction would, of course, be dependent upon the uses that could be found for it, and it is hardly conceivable that any one locality could advantageously use the enormous supply of power we have referred to.

Stripping all these considerations from their importance fact still remains, that with a cable of very limited size an enormous quantity of power may be transferred to considerable distances. The burning of coal in the mines, and the consequence of the power generated by the flow PRACTICABILITY OF ELECTRIC TRANSMISSION. 43

of rivers, may therefore be regarded as practicable, always, however, remembering that a loss of about 50 per cent. will be almost unavoidable.

In a subsequent series of experiments, details of which are unpublished, the Professors Thomson and Houston have succeeded in transmitting considerable power through a wire only 1/10th of an inch in diameter. Mr. Siemens has made statements that are in general accordance with these views. Mr. Siemens has remarked that the electrical transmission of power, although new and untried, is one of considerable interest, and the amount of from 40 to 60 per cent. of the power lost at the central station is allowable. By putting one machine to work with an expenditure of, say, 3 HP., a power could be produced and utilised at a distance not exceeding half a mile or a mile, according to the size and length of the conductor, equal to nearly one-half that amount of power which would be required if so exerted, it would be possible to distribute over a town power which would be exceedingly convenient and free from the dangers and troubles attending electric motors, and with an expenditure of power actually greater than, because, on account of the only 40 per cent. of the power exerted at the central station was actually obtained at the further station, it was nevertheless obtained at a very low rate. A 100-HP. engine, economically constructed, would produce 1 HP. with less than 3 lbs. of coal, whereas a small motor consuming 1 HP. would require 6 to 8 lbs. of coal per hour. Bearing that difference in mind, the magneto-electric machine would be an economical one. How far the principle would be applicable ultimately for the utilisation of such natural forces as water-power from a distance is difficult to determine, but it appears to depend upon the length of the electrical conductor. Its resistance increased in the ratio of its length; and as the increased resistance would mean loss of useful effect in the same proportion, it would be necessary to double the area of 44 ELECTRIC TRANSMISSION OF POWER.

the electric conductor in doubling its length, in order to maintain the same ratio of efficiency; but, if that were done, the resistance might be increased to many miles, and, he believed, profitably, without further loss of power. Professors Houston and Thomson have, however, shown so noted in the preceding lines how this loss is to be avoided.

In order to get the best effect out of a dynamo-electric machine, there should be an external resistance not exceeding the resistance of the wire in the machine. Otherwise, it would be uneconomical to increase the resistance in the machine to zero more than 1 ohm, otherwise there was a loss of current through the heating of the coil. If, therefore, there was a machine with 1 ohm resistance, there ought to be a conductor of double the area of power. For instance, a dynamo-magnetic engine not exceeding 1 ohm, if, instead of passing 1 mile, it was desired to go 2 miles, it would be necessary first of all to employ a conductor twice the length; but that conductor would give 2 ohms resistance, and would therefore destroy one half of the current by bringing it up to 1 ohm resistance. It would be necessary then to double the second wire, or to double the area of the first, and in that case there would be a wire of twice the length and twice the cost. That point is to be looked into in the weight and in the weight of the conductor in proportion to the distance. Having twice the area to deal with, a second generator could be put on, and electricity enough to work two machines could be sent through the double area to a double distance. But when that was done, the conductor was increased for the power was increased only in the proportion of the increase of length; but that was not enough. The electric conductor did not resist the motion of electricity in the same manner as a pipe resisted the flow of liquid through it, but an ohm's RESISTANCE was an ohm's resistance for a larger as well as for a smaller current flowing through it, which resistance was only increased by a rise of temperature in the con- ductor. This rise of temperature was kept down by dissipation of heat from the conductor; or, considering that the longer and doubled conductor would possess four times the surface area of the shorter one, and that the single and short conductor, it would be capable of trans- mitting four times the amount of electric current. It might, therefore, be said that it was no dearer to transmit electro-motive force to the greater than to the smaller distance, but that it was more expensive to do so, a result which seemed startling, but which he nevertheless ventured to put forward with considerable confidence. In uniting the two longer conductors into one, the surface would, however, be increased only in the ratio of $\sqrt{2}:1$; therefore, if the current transmitted were doubled, the longer and shorter conductor would, strictly speaking, be increased in the ratio of $1:2/\sqrt{2}$, or $1:2:83$, and the longer conductor would be dearer than the shorter per unit of electro-motive force transmitted in the proportion of 4:2:83.

Sir William Thomson has remarked that the question of the heat developed in the wire was the fundamental question with reference to the quantity of metal required to communicate the effect to a distance. The most prac- tical way of doing this is to have a copper tube in the wire in the shape of a copper tube. Having a copper tube, with a moderate amount of copper in its sectional area, and a current of water flowing through it with occasional places to let it off, and places to allow water to be admitted into the tube at intervals. With- out any injury to the insulation, a power of carrying off heat practically unlimited. He believed that with an ex- ceedingly moderate amount of copper, it would be possible to carry the electric energy to a distance of several

PRACTICABILITY OF ELECTRIC TRANSMISSION. 45 46 ELECTRIC TRANSMISSION OF POWER.

hundred miles. The economical and engineering moral of the theory appeared to be that towns heneeforth would be lighted by coals burned at the pit's mouth, where it was cheapest. The carriage expense of electricity was nothing, while that of coal was sometimes the greater part of its cost. The dress at the pit's mouth, which was formerly wasted, could be used for working dynamo engines of the most economical kind. Nothing could exceed the practical importance of this fact. The power transmissible by these machines was not simply sufficient for working sewing-machines, but turned out to be sufficient for purposes other than those of sewing-machines. Whether a sufficient number of any amount of HP. might not be developed. Taking the case of the machines required to develop 1000 HP., he believed it would be found comparable with the cost of a 1000 HP. engine; and he need not point out the vast economy to be obtained by the use of such a fall as that at Niagara, or the employment of waste coal at the pit's mouth. EFFICIENCY OF COUPLED MACHINES. 47

CHAPTER VII. EFFICIENCY OF COUPLED MACHINES.

As regards the efficiency of the system comprising two machines, the following quotation from a paper read by the Author before the Institution of Civil Engineers, 1870 (of which the Silver Medal was awarded), will fully elucidate this point:

The means at present employed for the transmission of power to a distance are well known. In adding to the list it may be well to point out that besides the use of electric current obtained by voltaic battery, and conveyed to an electro-magnetic motor by conducting wires, and the employment of dynamo-machines, there is just the difference that results in obtaining the electric light by a Grove or a Burnham battery, and in taking the light from a lamp by a Grove or a Burnham machine. In the one case an expensive mechanical action is converted into force; in the other, the force produced by a steam or other economical motor is transmitted. With the electro-magnetic motor the system is generative; with the Dynamo-electric machine it is consumptive; inasmuch as transmitting power produced by an independent motor. In point of fact, this independent motor may be a natural source of power, such as the fall of water, the utilisation of the product of oil wells, with prime-movers situated at these works.

The limit set by distance to the transmission of power, by means at present adopted, has been comparatively narrow. Hydraulic power has been the most adaptable, with, however, several important disadvantages. Although 48

ELECTRIC TRANSMISSION OF POWER.

electricity as a means of transmission is also limited by the distance to be traversed, the limit is in this case much more extensible, and under favourable instances practically disappears. The limit is dependent upon the quantity of electricity that can be conveyed by the conductor, since mechanical power is required to convey the energy.

For the transmission of power, may from a steam or water motor initially, the following system is adopted: First, a strap or belt from the motor is carried to the pulley of the driving dynamo-electric machine which generates the current necessary for the required length, the electrical current generated in the first machine is conveyed to the terminals of a second and precisely similar machine. Thus the first machine generates the current which is utilised in imparting motion to the motor, while the second reviews the probable efficiency of such a system. This subject has been treated in its mathematical relations by M. Mauroir in the Journal de Physique.

It is well known that all magneto-electric machines, when set in motion, induce currents themselves, as electrical systems, currents opposing the motive current. For example, when a current from some source is directed into the coils of a dynamo-machine, the coil commences to revolve. Immediately it commences to revolve, it also begins to generate a current in its own coils, which is opposite in direction to the motive current, and subtractive from the strength of the latter. The current-strength from the source is, therefore, at a maximum when the second machine, or that driven by the current, is at rest. From this it follows easily that the greatest work is to be yielded by the second machine when the strength of the current given by the first machine, or source, has been reduced to one-half by the induced current from the second machine. With these machines it has been generally found that the current- EFFICIENCY OF COUPLED MACHINES. 49

strength is proportional to the velocity or number of revolutions of the cylinder; so that, supposing two equal

Fig. 19.

A graph showing the efficiency of two machines. The x-axis represents the percentage of work unloaded, ranging from 0% to 100%. The y-axis represents the efficiency, also ranging from 0% to 100%. The curve starts at 100% efficiency at 0% unloaded work, drops to around 50% efficiency at about 30% unloaded work, then rises again to around 75% efficiency at about 60% unloaded work, and finally drops back to around 50% efficiency at about 80% unloaded work.

Fig. 20.

A graph showing the efficiency of two machines. The x-axis represents the percentage of work unloaded, ranging from 0% to 100%. The y-axis represents the efficiency, also ranging from 0% to 100%. The curve starts at 100% efficiency at 0% unloaded work, drops to around 75% efficiency at about 30% unloaded work, then rises again to around 50% efficiency at about 60% unloaded work, and finally drops back to around 25% efficiency at about 80% unloaded work.

machines arranged for the transmission of power, the amount of work reclaimable from the second machine will 50 ELECTRIC TRANSMISSION OF POWER.

be 50 per cent. of that employed upon the first, and the number of revolutions of the armature of the second machine corresponding to the maximum of work reclaimed will be half the number made by the first.

Figs. 19 to 21 show curves drawn through six points from results actually obtained. The revolutions of the cylinder of the second machine are represented as abscissas

A graph showing the relationship between revolutions and work reclaimed. The x-axis represents revolutions, ranging from 0 to 360. The y-axis represents work reclaimed, ranging from 0 to 1100. The curve shows that as revolutions increase, so does work reclaimed. Fig. 21.

and the work reclaimed as ordinates. The numerical values are given in the following table:

RESULT OF EXPERIMENTS WITH DYNAMOMETERS FOR THE TRANSMISSION OF POWER BY THE ELECTRIC CURRENT.

Machine A (for Reversing Driving C.)	Machine B (for Reversing Driving B.)	Machine C (for Reversing Driving B.)
Revolutions of C.	Per cent. of C. claimed.	Revolutions of B.	Per cent. of B. claimed.	Revolutions of B.	Per cent. of B. claimed.
1,008	77	884	34	1,199	39
750	88	834	44	926	44
584	38	767	44	963	48
561	38	675	45	963	48
480	37	675	45	963	48
358	--	385	--	500	--

EFFICIENCY OF COUPLED MACHINES. 51

The departures from the theoretical values are somewhat marked, but are within the limits of error that occur with this class of measurements, made with no great attempt at accuracy.

In order to ascertain the effects of resistance in the circuit connecting the driving and driven engines, two machines were connected by leading wires, having resistance of $\frac{3}{4}$ unit, 1 unit, and 1$\frac{1}{4}$ unit respectively. The machine having $\frac{3}{4}$ unit resistance gave without inserted resistance an efficiency of 44 per cent.; with $\frac{4}{3}$ unit resistance added to the circuit the efficiency was reduced to 38 per cent., giving a loss of 6 per cent.; with 1 unit resistance added the efficiency was 32 per cent., giving a loss of 12 per cent.; and with 1$\frac{1}{4}$ unit added resistance the efficiency was 26 per cent., giving a loss of 18 per cent. The experiments clearly proved that the loss of efficiency is proportional to the added resistance.

With a machine having $\frac{3}{4}$ unit resistance, a current of 5 watts through the circuit was maintained, with an expenditure of 2 HP. This gave a current of which the mechanical value, when the machine was connected to a precisely similar machine, was 56,000 foot-lbs., with the secondary machine at rest, and a remainder of 29,000 foot-lbs. with the second machine in motion, the HP. expended being maintained constant. The work re- claimed, measured on the dynamometer, was 48 per cent., closely agreeing with the efficiency of one-half. As to the effect of circuit resistance on the transmission of power in the case of two equal and similar machines, it was found that increased resistance reduced the efficiency to 26 per cent. with all particular machines employed; but if convolutions of wire were added to the cylinder of the machine the efficiency would again approach that given by theory. It must be noted that the theoretical efficiency of 50 per cent. is referred to the use of two equal and similar machines, one used as the driving, the other as the driven machine. It is quite probable e 2 52 ELECTRIC TRANSMISSION OF POWER.

that a larger percentage of work realised might be attained by some other arrangement of machines. By driving one machine by two others coupled in series, the results of three readings gave: speed of small machine, 1060 revolutions; speed of medium machine, 1820 revolutions. The medium machine driven by one small machine gave: speed of small machine, taken from three readings, 1060 revolutions; speed of medium machine, 780 revolutions. It would thus be seen that the speed of the medium machine had been rather more than doubled by driving it from two machines coupled in series. The best conditions for work admitted of direct proportion between the speeds of the two machines, and a galvanometer put in circuit between them, the deflections showed that when the second machine was at rest, the current was of twice the intensity that occurred when the second machine was giving its best work. M. Massart has shown that if the number of revolutions of the first machine were kept constant, the greatest efficiency would be attained when the number of the revolutions of the second machine were nearly equal to unity. But he also proved that when the greater amount of power was given by the first machine, it was half the number of revolutions of the first machine, and then the first machine would require half the power to drive it which was required when the second machine was standing, and this power could only be transmitted by the second machine. This is a very different thing from the conclusion that the maximum efficiency was one half.

In some experimental researches on magneto-electric machines, M. Massart and Angot, in 'Le Journal de Physique', vol. I., p. 395, investigated the relation of the magnitude of the electromotive force produced in connexion with a conductor moving through a magnetic field. Some considerations in a former article* by these authors, give only a first ap

Vide Minutes of Proceedings Inst. C.E., vol. I., p. 902.

EFFICIENCY OF COUPLED MACHINES. 53

proximation to the action of machines containing magnets or electro-magnets. It has been supposed that the mag- netism of the magnets is proportional to the intensity of the currents by which they are surrounded; but there exist between the magnets and the currents reactions that may greatly modify the results. Electro-dynamic machines do not include neither the magnetism nor the soft iron give rise to no more current than the time necessary for the manifestation of the electro-dynamic forces being inappreciable.

In magnetic machines of the second type the effective magnetism of the permanent magnets is changed in a complex manner by the influence of the bobbin. If it be admitted that the variation of the magnetism of the magnets is proportional to the magnetic power of the bobbin, which is in direct ratio to the intensity of the current, it is to be expected that magnetism of the magnets will be increased when they exert an attraction between the two systems, and that it will be diminished in the case of repulsion. The diminution of repulsive force will be greater than the increase of attractive force, since the magnets are attracted by each other, according upon saturation; there will result from this fact a slight diminution of work, and this may be represented by a term proportional to the square of the intensity of the current. The equation* then become for the motor machine,

$E = N H = N (I (A - B)$ $$E = N(A - B) = N\left(A_i - B\right)\frac{E_0 - E}{R}$$

I and $i$ are current intensities; $E_0$ primary electro-motive force; $A$ secondary electro-motive force; $B$ total resistance; $N$ and $n$ number of revolutions in the stator and rotor respectively; $dW$ mechanical work in time $dt$. The other relations are explained in the text.

54 ELECTRIC TRANSMISSION OF POWER.

Whence is deduced,

$E = N \cdot A \cdot B$

$I = N \cdot E$

instead of $E = N \cdot A$. The electro-motive force of induction, for a given velocity, is as much weaker than that of the battery, the stronger. The machine left to itself has still a velocity, the limit of which is given by the condition $I = 0$, which is

$N_3 = \frac{E_0}{A}$

as if the reaction had not been taken into account. The efficiency is diminished, because it has for expression,

$r = \frac{E - N \cdot A \cdot I - A \cdot R}{E_0 - N_3 \cdot I - N_3 \cdot B}$

To calculate the coefficients $A$ and $B$ the limit of velocity $N_3$ of the motor machine must be determined, whence is deduced

$A = \frac{E_0}{N_3}$

as measure for the efficiency for a given velocity; thus the equation

$r = \frac{N \cdot I - N_3 \cdot B}{N_3 \cdot I - N_3 \cdot B}$

obtains, whence is deduced

$B = R \cdot \frac{N - r}{N(1-r)}.$ EFFICIENCY OF COUPLED MACHINES. 55

The limit of velocity $N_4$ is easily obtained by experiment, since it is proportional to the electro-motive force of the battery employed, which may be chosen as work as desired.

When the machine is employed as electro-motor, the condition of production $\frac{K}{i} > R$ is always realised for a very weak current, and equilibrium exists when

$\frac{A}{B - B} = R,$

$i = \frac{A}{R + B} = \frac{A}{R + B} = \frac{A}{R + B} = \frac{I + A}{R}.$

The apparatus behaves as a battery, the electro-motive force of which is proportional to the velocity, with the conditions of adding to the actual resistance a fictitious resistance itself proportional to the velocity. The intensity will then have a limiting value given by the equation,

$i = \frac{A}{B}.$

In magneto-electric machines, that is to say with fixed and moving electro-magnets, the influence of the wires of a system of bolting on the opposed electro-magnets gives, as in the case of the electro-motor, a diminution of attraction and a greater diminution of repulsive forces, which again introduce into the work a negative variation proportional to the magnetism and to the intensity of the current that may be considered comprised in the term $C_1M^2P$. On the other hand, the action of the electro-magnet on the magnet gives also a diminution of work, which is sensibly proportional to the square of the magnetisation, and may be comprehended in the term $C_2M^2P$, so that there will be 56 ELECTRIC TRANSMISSION OF POWER.

nothing to modify the theory. The reaction which is weak in the machines of the second type, plays on the contrary an important part in composite machines consisting of magnets and electro-magnets. If it be considered that the magnetism of fixed magnets is modified by a quantity proportional to their area, and that of the electro-magnets, there results a diminution of work proportional to the square of magnetisation, or to $M^2$.

The efficiency is

$r = \frac{E}{E_0} = \frac{N(A + A_1 M)}{E_0} = \frac{A + A_1 M}{R}$

If the current is sufficiently weak, so that the coefficient $M$ has the constant value $M_0$, it becomes

$r = \frac{N - N_0}{N - N_0} = \frac{A + A_1 M_0}{R}$

an expression of the same form as for machines of the second type of magneto-electric machines. The greater number of electric motors enter into this category, because they are made up of a form of two systems of electro-magnets—or what is the same thing, of fixed electro-magnets, and of movable pieces of soft iron. In these machines work has for expression,

$K = N H = N P (C + C_{1} M + C_{2} M P)$

If the intensity is feeble the parenthesis may be represented by a constant $A$, and

$K = N A P,$

and the electro-motive force of induction is

$E = N A .$ EFFICIENCY OF COUPLED MACHINES. 57

For the other part,

$I\ R = E_0 - E = R I_q - N A I,$

whence is deduced

$N A = R \left(\frac{I_q}{I} - 1\right)$

The Gramme machine with electro-magnets enters into the same type in theory, but entirely differs from the preceding in construction. This machine the Authors have studied as an electro-motor only. The resistance of the magnet is so great that the current which the brush communicates successively with the different bobbins of the ring, but does not vary more than 3 per cent; the mean is 1'104 ohms. The Authors have added successively exterior resistances to the amount of 200 ohms, and have varied the speed from a quarter of a revolution to fifteen revolutions per second. It has been remarked that this enormous speed can be obtained on very resistant circuits only, because the intensity increases so rapidly that with a shorter circuit all the disposable power of the motor, which otherwise would be wasted, is used up; the quantities are reduced into absolute units (webers), and the resistance expressed in ohms. The phenomena are regular when the resistance does not exceed 10 ohms, nor the speed of the machine ten revolutions per second. Thus, if the quantity is inferior to 0'05 weber, it is proportional to its square root; if it is inferior to 0'1 weber, total resistance of the circuit. For larger quantities the constant has for expression $R$ $\frac{I}{n}$ which depends only upon the intensity of the current. This result accords with theory.

$n i (C + C_{i} M + C_{q} M_{p}),$ 58 ELECTRIC TRANSMISSION OF POWER.

which gives

$i = n \left( \frac{C + C_1 M + C_2 M_2}{R} \right) \text{ or } i = i(C + C_1 M + C_2 M_2).$

The values of $\frac{i R}{n}$ increasing nearly proportionally to the quantity, calculations can be effected by the following empirical formula,

$\frac{i R}{n} = 0.286 + 0.44,$

where $i$ is the quantity of current, $R$ the resistance of the whole circuit, and $n$ the number of revolutions of the Gramme-armature. COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 59

CHAPTER VIII. COMPARATIVE EFFICIENCY OF VARIOUS MACHINES.

NOTHING can be done in the inter-comparison of any natural force until accurate measurements have been made. For those measurements we are indebted to a great extent to the experiments on the conversion of elec- tric machines formed by the Franklin Institute, and to Professors Houston and Thomson's report as to the ratio of efficiency in the conversion of motive-power into electricity.

In entering this comparatively new field of research, peculiar difficulties occurred, owing to conditions that do not exist in the various forms of batteries used as sources of electrical power. In many battery circuits a high external resistance may be employed, and the electro- motive force of the battery will then be practically zero; while in dynamo-electric machines, in which the reaction principle is employed, the introduction of a very high external resistance into the circuit must be necessarily attended by decided variations in the electro-motive force due to changes in the resistance of the machine through which the currents have their origin. Moreover, a considerable difficulty is experienced in the great variations in the behaviour of these machines when the resistance of the external work is changed. Changes due to loss of con- ductivity, changes due to wear, and changes in the machine itself. Those variations are also attended by change in the power required to drive the machine, and in the speed of running, which again react on the current generated. These are certain normal conditions in the running of 60 ELECTRIC TRANSMISSION OF POWER. dynamo-electric machines under which all measurements can be made, viz.—

The circuit must be closed, since, on opening, all electric manifestations cease.

The speed of the machine must be, as nearly as possible, constant.

The power required to maintain a given rate of speed must be, as nearly as possible, constant.

The machines submitted to the Committee for determination were as follows, viz.—

Two machines of different size, and of somewhat different degree of construction, built according to the invention of Mr. C. F. Wallace and styled respectively in the same report as A', the larger of the two machines, and A", the smaller.
Two machines, known as the Wallace-Farmer machines, differing in size and in minor details of construction, but designated respectively as B', the larger of the two, and B", the smaller. In the case of the machine B', the experiments were discontinued after the measurement of the resistances was made, insufficient power being at disposal to maintain the machine at its proper rate of speed.
A Gramme machine of the ordinary construction.

All the above machines are constructed so that the whole current traverses the coils of the field magnets, being simple current machines, in which the reaction principle is employed. The commutators are designated A', the commutators are so arranged as to permit the use of two separate circuits when desired.

For the purpose of preserving a ready measure of the current produced by each machine under normal conditions, a machine was constructed by which a considerable but definite proportion of the current was caused to traverse the coils of a galvanometer, thus giving with each machine a convenient deflection, which could at any COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 61

time be reproduced. As the interposition of this shunt in the circuit did not appreciably increase its resistance, the normal conditions of running were preserved.

As indicating the preservation of normal conditions in any case, the speed of running and the resistance being the same, the current produced was indicated by the dynamometer, the current produced, as indicated by the galvanometer, was in each case the same.

Certain of the machines experimented with heated coal-balls, and certain of those without, the tests, therefore, were made when the machines were as nearly as possible at about the temperature of the surrounding air.

It is evident that no other standard could be well adopted, as under a prolonged run the temperature of the different parts of the machine would increase very unequally; and, moreover, it would be impossible to make any reliable measurements of the temperatures of many such parts.

In measuring the resistance of the machines, a Wheatstone's bridge, with a sliding contact, was used in connection with a galvanometer and a suitable voltaic battery. In taking the resistance of the machines, several measurements were made with the armatures in different positions, and the mean of these measurements taken as the true resistance.

To determine the value of the current, two methods were selected, one based on the production of heat in a circuit of known resistance, and the other upon the proportion of heat to current with that of a Daniell's battery.

In the application of the first method, eight litres of water, at a known temperature, were taken and placed in a suitable non-conducting vessel. In this was immersed a German-silver wire, and a sliding contact adjusted to 62 ELECTRIC TRANSMISSION OF POWER.

afford a resistance equal to that of the exterior resistance under consideration. This was now introduced into the circuit of the machine. All these arrangements having been made, the temperature of the water was accurately obtained by a delicate thermometer, the current passing through the machine running under normal conditions being allowed to flow for some time, through the calorimeter so provided. From the data thus obtained, after making the necessary corrections as to the weight of the water employed, the total heating effect in the external circuit, as given in Table II, was calculated. Since the heat produced in any part of an electrical circuit is directly proportional to the resistance of those portions, the total heat of the circuit was easily calculated, and is given in Table III, in English heat units. For ease of reference, this constant has been given for conversion of these units into the now commonly accepted units of heat. Having thus obtained the heating effect, the electrical current is—

$C = \frac{\sqrt{W}A \times 772}{Rt}$

where C = the current per ohm; W, the weight of water in pounds; A, the increase of temperature in degrees Fahr.; t, the time in hours; B, the number of times ; t, the time in seconds; and c, the constant 0-787355, the equivalent in foot-lb. of one weber per ohm per second. The currents so deduced for the different machines are given in Table IV.

The other method employed for measuring the current, viz. the comparison of a definite portion thereof with the current from a Daniell's battery, was as follows:—

A shunt was constructed, of which one division of the circuit was 0-12 ohm and the other 3000 ohms. In this latter division of the circuit was placed a low-resistance COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 63

galvanometer, on which convenient deflections were obtained. This shunt being placed in the circuit of the machine, the galvanometer deflections were carefully noted. These substituted resistances were immersed in water, in order to maintain an equal temperature.

Three Daniell's cells were carefully set up in circuit with the galvanometer, each with a set of standard resistance coils. Resistances were unplugged sufficient to produce the same deflections as those noted with the shunt above mentioned.

The shunt ratio, as nearly as could conveniently be obtained, was $\frac{1}{70}$ . The above formula

$C = \frac{a \times 1-072}{B}$

where C equals the Weber current ; a, the reciprocal of the shunt ratio; $s$, the number of cells employed; 1-072, the assumed normal value of the electro-motive force of a Daniell's cell, and B, the resistances in the circuit with the battery, gives at once the current. In comparison with the theoretical value of this current, the internal resistance of the battery was so small as to be neglected.

The results obtained were as follows:

Name of Machine.	Shunt Ratio.	Number of Daniell's Cells.	Resistance (ohms).	Speed of Machine.
Largo Brush	• • •	• • •	8	5 ohms	1,100
Small Brush	• • •	• • •	• • •	3,700	1,400
Wallace-Farmer	• • •	• • •	• • •	8,320	844
Graeme	• • •	• • •	• • •	6,980	1,040
				4,800	800

The Weber currents, as calculated from the above data, are given in Table IV. 64 ELECTRIC TRANSMISSION OF POWER.

From the results thus derived, the electro-motive force was deduced by the general formula,

$E = C \times R.$

The electro-motive force thus calculated will be found in Table IV.

TABLE IV.—SHOWING WEIGHTS, POWER ABSORBED, ETC., BY DYNAMO-ELECTRIC MACHINES, TESTED BY A COMMITTEE OF THE FRANKLIN INSTITUTE, 1877-78.

Sense of Machine

Copper wire in—

Weight

Armature

Field Magneto

Weight

Large Brush Small

Large Wall Small

Gramme

475 300 600 300 600 300 600 300 600 300 600 300 600 300 600 300 600 300 600 300 600 300 600 300 600 300 600 300 600 300 600 300 600

1/242/48

1/242/48Statements are frequently made, when speaking of certain dynamo-electric machines, that they are equal to a given number of Daniell's cells, or some known battery cells. It is evident, however, that no such comparison can properly be made, since the electro-motive force of a dynamo-electric machine, in which the reaction principle is employed, changes considerably with any change in the relative position of the circuit, while the internal resistance, while that of any good form of battery, disregarding polarization, remains approximately constant. The internal

These reports have been condensed to show merely the power expended and returnable by dynamo-electric machines.

COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 65

resistance of dynamo-electric machines is, as a rule, very much lower than that of any ordinary series of battery cells, as generally constructed, and therefore, to obtain with a battery conditions equivalent to those in a dynamo-electric machine, a sufficient number of cells in series would have to be employed to give the same electro-motive force; while, at the same time, the internal resistance of each of their number in multiple are, would require to be such that the internal resistance should equal that of the machine.

Suppose, for example, that it be desired to replace the large Brush machine by a battery whose electro-motive force and internal resistance shall be equal respectively to that of the machine, and that we adopt as a standard a Daniell's cell, of an internal resistance of, say, one ohm.

Referring to Table IV., the electro-motive force of this machine is about 39 volts, to produce which about 39 cells, or multiples thereof, must be employed. In Fig. II., the internal resistance of this machine is about 0-49 ohm.

To reduce the resistance of our standard cells to this figure, when 37 cells are employed in series, 76 cells in multiple are required would be necessary. Therefore, the total number of cells required for this purpose would equal $37 \times 76$ or 2812 cells, working over the same external resistance. It must be borne in mind, however, that although the machine is equal to 2812 of the cells taken, that no other arrangement of these cells than that mentioned above can be made so as to reproduce the same conditions, and, moreover, the external resistances must be the same. The same principles applied to other machines would, when the internal resistance was great, require a large number of cells, but arranged in different ways. This difference arises from by far the greater portion of the work being done in overcoming the resistance of the battery itself.

The true comparative measure of the efficiency of dynamo-electric machines as means for converting motive- 66 ELECTRIC TRANSMISSION OF POWER.

power into work derived from electrical currents, is found by comparing the units of work consumed with the equivalent unit of work appearing in the circuit external to the machine. In Table V, the comparative data are given.

The heat due to local circuits in the conducting masses of metal in the machine, irrespective of the wire, consumes force in proportion to the resistance of the wire, and is the least action of the machine, and is manifestly comparable to the well-known local action of the voltaic battery, since in each case it not only acts to diminish the effective current produced but also adds to the cost.

No device can be devised to alter unknown or abnormal external resistance can be of any value, since the proportion of work done, in the several portions of an electrical circuit, depends upon and varies with the resistances they offer to its passage. If, therefore, in separate determinations which are particularly made for each part of that part of a circuit the work of which is measured, be in one instance large in proportion to the remainder of the circuit, and in another small, the two measurements thus made would give widely different results, since in the case where the resistance was great, a large part of the circuit, the percentage of the total work appearing there would be greater than if the small resistance had been used. Wherever an attempt has been made to determine the efficiency of a single machine, or of the relative efficiency of two machines, by measuring the quantity of gas evolved in a voltameter, or by the electrolysis of copper sulphate in a decomposing cell, when the resistance of the voltameter or decomposing cell did not represent the normal working resistance, it is manifest that these methods cannot properly be taken as a measure of the actual efficiency.

During any continued run, the heating of the wire of the machine, either directly by the current, or indirectly from conduction from those parts of the machine heated COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 67

by local action, as explained in a former part of this report, produces an increased resistance, and a consequent falling off in the efficiency of the machine. In Table II., at the temperature of 73° Fahr., At, the small Irish machine, had a resistance of 0-485 ohms, whilst at 88° Fahr., at the armature coil, it was 0-495 ohms. These differences were still more marked in the case of B.

In A', the small Irish machine will be noticed that two separate resistances are set up for the resistance of the machine. These correspond to different connections, viz. the resistance, 1-230 ohms, being the connection at the commutator for low resistance, the double conducting wires representing the resistance of 0-485 ohms, and 0-495 ohms represent the resistance when the sections of the double conductor are coupled at the commutator in series.

Referring to Table III., the numbers given in the column headed "Heat in external circuit" are the measures of the total heating power in that portion of the circuit external to the machine.

In the column headed "Total heat of circuit" are given the quantities of heat developed in the whole circuit, which numbers, compared with those in the preceding column, furnish us with the relative proportions of the work of the circuit, which appear in the external circuit.

The column headed "Heat per ohm per second" gives the relative work per ohm of resistance in each case, and these numbers, multiplied by the total resistance, give the total energy of the current expressed in heat units per second.

In Table IV. are given the results of calculation and measurement as to the electrical work of each machine. It is evident from these results that according to principles of electrical science, that in the Weber current and the unit electro-motive force, we have the data for comparing the work of these machines with that of any other machine or r 2 68 ELECTRIC TRANSMISSION OF POWER.

Table II.--Resistance of Iron-Frame Machines. Derived from Determinations by
Name of Machine	Resistance of Frame	Resistance of Core	Resistance of Wires	Resistance of External.	Resistance of Total Core and Frame.	Resistance of Total Core and Frame.	Resistance of Total Core and Frame.	Remarks.
A1, Large Brush	732	9.96	0.57	0.010	9.97	1.00	A1 beginning of run.
A' = A1	80	0.96	0.86	0.010	1.018	1.018	After running for 5 minutes.
A'' = A'	74	1.226	1.70	0.010	2.923	Average for five revolutions.
B', Large Winder	74	4.62	4.62	1.98	0.010	6.58	Mechanically high.
B'' = B'	138	2.23	2.23

COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 69

TABLE III—TERMINAL EFFICIENCY OF DYNAMIC ELECTRIC MACHINES. DIFFERENCE IN PERCENTAGE BETWEEN THE EFFICIENCY OF THE MACHINE AND THE TURBINE.

Machine Efficiency

Power Output (kW)

Efficiency (%)

A1 large Brush

512

19-84

25-25

0.82

49-328

69-19

0.881

1,340

107,000

A1 small Brush

18-63

9-09

0.82

35-87

58-97

0.832

1,717-700

127,700

B small Turbine

524

19-63

11-55

0.82

49-45

75-97

0.858

1,439

134,940

JP small Turbine

524

19-63

9-92

0.82

49-45

75-97

0.858

1,439

134,940

For conversion to mechanical heat unit, 1 lb. water = 1 Fahr. = 290-15 grams of water = 1° centigrade.

Gross Efficiency.

Power Output (kW)

Efficiency (%)

A1 large Brush - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1 small Brush - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - m - mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:mm:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:MM:

Water & Fuel Consumption (g)

Power Output (kW)

Efficiency (%)

A1 large Brush · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · A1 small Brush·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m·m············································································································································································································..JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turbine JJP small Turine JJP smla... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .......................................................................................................................................................................................

Water & Fuel Consumption (g)

Power Output (kW)

Efficiency (%)

A1 large Brush • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • A1 smal lBrush•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbin e B smal lTurbine Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmall Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsmalt Gsma I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i ii ii iii iv v vi vii viii ix x xi xii xiiixiv xv xvi xvii xviii xix xx xxx xxxi xxxii xxxiii xxxiv xxxv xxxvi xxxvii xxxviii xxxix xxxx xxxxix xxxxii xxxxiii xxxxiv xxxxv xxxxvi xxxxvii xxxxviii xxxxix xxxxx xxxxxi xxxxii xxxxiii xxxxiv xxxxv xxxxvi xxxxvii xxxxviii xxxxixxxxxx xxxxxixxxxxiixxxxxiiixxxxxivxxxxvxxxxvixxxxviixxxxviiixxxxixxxxxxixxxxxxiixxxxxxixxxxxxxiixxxxxxxiiixxxxxivxxxxvxxxxvixxxxviixxxxviiixxxxixxxxxxixxxxxxiixxxxxxixxxxxxxiixxxxxxxiiixxxxxivxxxxvxxxxvixxxxviixxxxviiixxxxixxxxxxixxxxxxiixxxxxxiXXXXXIIXXXXIIIXXXXIVXXXXVXXXXVIXXXXVIIXXXXVIIIXXXXIXXXXXXIXXXXXXIIXXXXXXIXXXXXXXIIXXXXXXXIIIXXXXIVXXXXVXXXXVIXXXXVIIXXXXVIIIXXXXIXXXXXXIXXXXXXIIXXXXXXIXXXXXXXIIXXXXXXXIIIXXXXIVXXXXVXXXXVIXXXXVIIXXXXVIIIXXXXIXXXXXXIXXXXXXIIXXXXXXIXXXXXXXIIXXXXXXXIIIXXXXIVXXXXVXXXXVIXXXXVIIXXXXVIIIXXXXIXXXXXXIXXXXXXIIXXXXXXIXXXXXXXIIXXXXXXXIIIXXXXIVXXXXVXXXXVIXXXXVIIXXXXVIIIXXXXIXXXXXXIXXXXXXIIXXXXXXIXXXXXXXIIXXXXXXXIIIXXXXIVXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 70 ELECTRIC TRANSMISSION OF POWER.

TABLE IV—CUMBER AND REVERSE-MINUTE FORCE OF DYNAMIC ELECTRIC MACHINES. DRAWINGS FROM THE WATER POWER JOURNAL.

Number of Machine

Value of Power per Unit

A large Brush.

30-57

20-87

55-66

30-28

60-06

187-066

Signed 1,240 revolutions.

A small Brush.

n - n

19-69

21-72

55-66

61-63

50-21

117-700

n - n

A small Wheel.

n - n

10-42

9-75

70-88

30-38

75-068

n - n

Jr. small Wheel.

n - n

9-63

10-42

70-88

n - n

9/22 COMPARATIVE EFFICIENCY OF VARIOUS MACHINES. 71

battery, whether used for light, heat, or electrolysis, or any other form of electrical work.

The value of the Weber current, as deduced from the heat developed by it, in comparison with that of a Daniell's cell, do not exactly agree; nor could this have been expected, when the difficulty of minutely reproducing the conditions as to speed, resistance, etc., is considered.

By comparison of the electro-motive force of the different machines, it appears that no definite unit seems to have been assigned to all the forms.

Table VI. is designed especially to permit a legitimate comparison of the relative efficiency in converting motive-power into current. The actual dynamometer reading is given in the first column. In order to allow for differences of construction and differences in speed of running, the friction and resistance of the air very greatly, being least with the Gramme, as might be expected, since the form of the revolving armature and the speed of the machine conduce to this result. This is, of course, a point greatly in favour of the Gramme machine.

That portion of the power expended available for producing current is given in the third column, being the remainder, after deducting the friction, as above men- tioned; i. e., that which is left over and can be used in the normal circuit. This is found to be the case by com- paring calculations of the total work of the circuit in foot-lbs. expended in producing such current as given in the appropriate column.

For instance, in the case of A', the large Brush machine, the available force for producing current is 89,656 foot-lbs. per minute, of which only 53,846 reappear as heat in the circuit. The balance is most probably expended in the production of local currents in the various conducting masses constituting the machine. The whole amount thus expended in local action is given in the column designated "F. P.", unaccounted for in the circuit."

Table VI.	Designated especially to permit a legitimate comparison of the relative efficiency in converting motive-power into current.
The actual dynamometer reading is given in the first column.	In order to allow for differences of construction and differences in speed of running, the friction and resistance of the air very greatly, being least with the Gramme, as might be expected, since the form of the revolving armature and the speed of the machine conduce to this result.
This is found to be the case by comparing calculations of the total work of the circuit in foot-lbs. expended in producing such current as given in the appropriate column.	For instance, in the case of A', the large Brush machine, the available force for producing current is 89,656 foot-lbs. per minute, of which only 53,846 reappear as heat in the circuit. The balance is most probably expended in the production of local currents in the various conducting masses constituting the machine. The whole amount thus expended in local action is given in the column designated "F. P.", unaccounted for in the circuit."

72 ELECTRIC TRANSMISSION OF POWER.

A*	* n*	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'	n*n'
Table V. --Draws of Electric-Driven Machines at Various Points on Network. Drawings show
Distribution of Power at Various Points on Network.	Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings of Drawings.	For conversion table Grammermatical mistakes - A Box penal = 120 Grammatical mistakes, equal to
A* large Brush	177,006	177,006	80,006	80,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006	50,006
A* small Brush