fc UNIVERSITY OF CALIFORNIA ANDREW SMITH HALLIDIL: ARMATURE WINDINGS OF DIRECT CURRENT DYNAMOS EXTENSION AND APPLICATION OF A GENERAL WINDING RULE BY E. ARNOLD .1 ENGINEER, ASSISTANT PROFESSOR IN ELECTROTECHNICS AND MACHINE DESIGN AT THE RIGA POLYTECHNIC SCHOOL TRANSLATED FROM THE ORIGINAL GERMAN BY FRANCIS B. DE GRESS, M. E. CHIEF OF TESTING DEPARTMENT, CROCKER-WHEELER COMPANY WITH 146 ILLUSTRATIONS NEW YORK: D. VAN NOSTRAND COMPANY 23 MURRAY AND 27 WARREN STS. 1902 HALLIDIE COPYRIGHT, 1902, BY D. VAN NOSTRAND COMPANY TYPOGRAPHY BY C. J. PETERS & SON, BOSTON, MASS. U.S. A. PBEFACE. WHILE lecturing upon electrotechnics at the Polytechnic in Riga, I experienced the difficulty of presenting to the students in a brief and simple manner the various methods of winding armatures for direct current machines, so as to enable them to solve independently any assumed problem in winding. In consequence of this, I endeavored to establish rules for the various windings, and found that all so called closed-coil wind- ings with either a series or parallel arrangement of the in- ductors could be embraced under a general rule which applied equally well to ring, drum, and disk armatures. The common as well as the peculiar properties of the various windings can be accurately observed with the aid of this rule. The relationship between ring, drum, and disk armature wind- ings, is brought into prominence, and the transition from one winding to another can be accomplished without difficulty. This rule not only embraces all known windings, but accom- plishes even more, a general solution of the winding problem. By the aid of this rule, and in conjunction with the various methods of connecting inductors treated in the first section, it is possible to design other windings. In the later sections I have shown several designs for connections, which to my knowledge have never been published before. The results which I have obtained appear to be of sufficient interest to be made public, the more so because even in the best text books on electrotech- nics, armature windings, especially those of multipolar machines, have been treated somewhat unsatisfactorily. (SIGNED) E. ARNOLD. RIGA, March 5, 1891. iii TRANSLATOR'S PREFACE. Professor Arnold's " Ankerwicklungen," in which is given his general formula for the design of direct current armatiire windings, has been considered of sufficient importance to be translated and published in the present form. Many of the designs shown by him are of historic interest only, but the principle expressed is fundamental, and of value to the enigneer or designer, and no attempt has been made to go beyond the subject as treated in his book. The translator's thanks are due to Messrs. A. W. K. Peirce and W. F. Crawford, for valuable assistance in preparing the work. F. B. DE GEESS. NEW YOKE, March 5th, 1902. CONTENTS. PAGE METHODS or CONNECTING INDUCTORS . . . '. . 1 A. CLOSED-COIL WINDINGS -.. , 16 RING ARMATURE WINDINGS 1. BIPOLAR RING ARMATURES . . . ... . . . . . . 20 2. MULTIPOLAR RING ARMATURES WITH PARALLEL WINDING . 24 3. MULTIPOLAR RING AMATURES WITH SERIES WINDING . . 32 4. MULTIPOLAR RING ARMATURES WITH MIXED WINDINGS . . 44 DRUM WINDINGS 1. BIPOLAR DRUM ARMATURES 47 2. MULTIPOLAR DRUM ARMATURES WITH PARALLEL WINDING . 62 3. MULTIPOLAR DRUM ARMATURES WITH SERIES WINDING . . 70 4. MULTIPOLAR ARMATURES WITH MIXED WINDINGS .... 78 DISK ARMATURE WINDINGS 89 THE HopKiNSON-MuiRHEAD DISK ARMATURE ... .. , . 93 SIEMENS-HALSKE DISK ARMATURE .......... 93 W. THOMSON AND POLESCHKO DISK ARMATURE ...... 97 PACINOTTI'S DISK ARMATURE . . 98 EDISON'S DISK ARMATURE 99 EDISON'S MULTIPOLAR DISK AR'MATURE WITH PARALLEL WIND- ING . . . , . * . . . , . . . . . 101 APPLICATION OF THE ANDREWS-PERRY WINDING TO DISK ARMA- TURES . . . . . 102 DESROZIERS' DISK ARMATURE 104 FANTA'S DISK ARMATURE 107 JEHL AND RUPP DISK ARMATURES 109 W. FRITSCHE'S DISK ARMATURE 112 v VI CONTENTS. PAGE B. OPEN-COIL WINDINGS ..".,, . . . . 115 1. RING ARMATURE WINDINGS . . .... .... . 115 2. DRUM ARMATURES, THOMSON-HOUSTON WINDING .... 117 3. DISK ARMATURE WINDINGS, WILDE'S DISK ARMATURE . . 120 FERRANTI-THOMSON DISK ARMATURE 121 BOLLMAN DISK ARMATURE . 122 ARMATURE WINDINGS, METHODS OF CONNECTING INDUCTORS FOR OBTAINING DIRECT CURRENTS. IF an inductor be moved in a magnetic field in such a manner as to cut the lines of force, an electromotive force will be induced in the inductor. If the inductor belongs to a closed circuit, maintains its position relative to the direction of the lines of force, and be moved with a constant velocity, a constant electromotive force will be induced, and a current of constant strength will be ob- tained. The electromotive force is in- duced as shown in Fig. 1, per- pendicularly to the lines of force and perpendicularly to the direc- tion of motion. Let Fig. 2 represent a mag- netic field produced by two poles of opposite sign; let the North pole stand over the paper so that the lines of force pass into the paper from the North to the South pole. If an inductor be moved in the direction of the double arrow through the given field, an electromotive force will be induced in it in the direction of the single arrow. To produce a closed circuit, it is assumed that the con- ductor slides upon two fixed rails, A B and (7 Z>, whose ends are joined by the conductors AmO and BnD. Under these 1 Fig. 1. ARMATURE WINDINGS. conditions a current will then flow in the direction shown by the arrows. A continuous current could only be maintained in this manner if the field were infinitely large ; for as soon as the Fig. 2. inductor leaves the magnetic field the induction ceases, and if the direction of motion be reversed, the direction of the floAv of current is also reversed. A continuous magnetic field, from which a continuous cur- Fig. 3. Fig. 4, rent can be obtained, will be made if the field be transferred to the surface of a cylinder, and the inductor be moved in a circu- lar path as shown by Figs. 3 and 4. METHODS OF CONNECTING INDUCTORS. This arrangement involves the principle of a unipolar machine. The magnitude of the electromotive force depends on the intensity of the magnetic field, on the length of the inductor, and on its velocity. The intensity of the field and the velocity of the inductor cannot be increased indefinitely ; therefore, beyond a certain point an increase of the electro- motive force can only be obtained by increasing the length of the inductor. But even here certain complications arise. Single straight inductors, as ab in Fig. 4, can only be used to obtain small E. M. F.'s ; higher E. M. F.'s must be obtained by collecting the impulses induced in several inductors and putting them in series. The uni- polar induction, as shown in Figs. 2, 3, and 4, does not permit of series connection; for if several inductors, a &, c d, e /", g A, be connected by the cross con- nectors, be, de, fg, as in Fig. 5, the cross connectors by their motion through the magnetic field would also have E. M. F.'s generated in them, which oppose the E. M. F.'s of the inductors ; so that after subtracting these opposite E. M. F.'s, there would remain that of one inductor, gh ; therefore every attempt to construct unipolar machines with inductors in series, even with the most ingenious connections and devices, must fail. For series grouping, successive poles must be of opposite sign. If an inductor be moved in a straight line or rotated in a Fig. 5. 4 ARMATURE WINDINGS. magnetic field of alternating polarity, at each change of polarity a change in the direction of the E. M. F. takes place, and a direct current can only be obtained by the use of a commutator. The arrangement of these inductors and their connection with the commutator must be carried out in such a manner I Fig. 6. that the E. M. F.'s in all the inductors have the same relative direction, and also that the change in the direction of the current takes place at the right time. In the following figures, the magnetic poles are considered as being arranged in a circle at equal distances apart and of m mm alternate polarity. For convenience in representation, the cir- cular path of the inductors is developed into a straight line, and the circular arrangement of the poles is likewise represented. Some simple ways of connecting several inductors in series are thus shown in Figs. 6 and 7. The inductors a >, c d. e /, y ^, are connected in METHODS OF CONNECTING INDUCTORS. D such a manner by the inactive connectors 5 J, c e, f h that their E. M. F.'s, as shown by the arrows, are additive. In Fig. 6 the distance between the inductors is equal to twice the distance between the poles, while in Fig. 7 it is the same as the distance between the poles. The dotted lines show the position of the inductors at commutation. The use of con- nectors can be overcome by placing the inductors in an oblique position, as shown in Fig. 8. With this method of connection, it is necessary that the pole pieces be lozenge-shaped, in order m Fig. 9. that an inductor should not be in two magnetic fields and have opposing E. M. F.'s induced in it. The dotted lines again show the position of the inductors at commutation. If the inductors a >, and c d, in Fig. 7, be connected, not direct, but as shown in Fig. 9, through bg hi Jed so that the magnetic field be passed through twice, then the inductors a b and g ^, also c d and i Jc, are alternately under induction. G ARMATURE WINDINGS. It follows therefore, that the distance between these inductors must at least equal the width of the pole ; for if both inductors should corne within the same magnetic field, the E. M. F.'s in- duced in them would be opposed. Fig. 10 agrees with Fig. 9, except in the circular form which has been given to the induc- Fig. 10. tors in place of the rectilinear form heretofore used. The inductors in Fig. 10 are in the position of commutation, while Fig. 9 shows the point of maximum induction. Figs. 9 and 1 represent a form of winding, which will be spoken of as " loop- winding." This " loop- winding " may also be obtained by joining together inductors that are moving under poles of the same sign as in Fig. 6, or by connecting, in Fig. 9, h to e direct, which gives the arrangement shown in Fig. 11. It is evident that we cannot obtain a direct current of a constant intensity from the arrangements heretofore shown, because the commutation of all the inductors takes' place at the same moment and when they are all inoperative. In order to obtain a direct current of constant intensity, a large number of inductors must be used, so arranged in METHODS OF CONNECTING INDUCTORS. different parts of the field, that in a certain number of them the maximum induction takes place, in others a lesser amount, and in some none at all. Then the inductors may be con- nected with one another as follows : 1. In such a manner that they constitute a closed or end- less winding, and so that between the points of commutation no opposing E. M. F.'s will be induced at any time. The con- nection with the exterior circuit must be made in such a manner that a reversal of the current in the inductors can take place in those only which at the time are not under induction. This form of winding will be spoken of as a closed-coil winding. 2. The inductors may be connected in groups, in which all the members of each group are in a magnetic field of the same intensity, and only that group which is subject to the maximum, or nearly the maximum, induction is connected to the exterior circuit, while all the other groups are entirely cut out. This form of winding will be called an Open-Coil Winding. Closed-coil windings will be considered first. In Fig. 12 there are two poles, of opposite sign, and the inductors are placed at equal distances apart. If we assume that the lines of force ^ Q o pass from the North to the adjacent South pole, then the series winding can be so ar- ranged that the oppo- site ends of adjacent inductors are connected together by inactive Fig. 12. conductors, i.e., by conductors so arranged as not to cut lines of force. These are shown in the figure by dotted lines ; their position in space must be imagined to be somewhat as shown in elevation by Fig. 13. If the cross connections are drawn 8 ARMATURE WINDINGS. in for all the inductors, and the direction of the current flowing is indicated by arrows, supposing the inductors to move to the right, it will be found that they are divided into two groups, B fig. 13. Fig. 14. in which all the E. M. F.'s of positive sign and all of negative sign are additive. If the scheme of Fig. 12 be arranged in a circle, and A be joined to .5, an endless spiral is obtained with the permanent points of commutation, -j- and . The reversal of the current does not take place in all the inductors at once, but only in those which are at the point of m Fig. 15. commutation, therefore by using a sufficiently large number of inductors the variations in the intensity of the current are not noticeable. The current divides itself at the point into two branches which reunite at the + point : this branching of the current always takes place in a closed-coil winding, and therefore only half of the total number of inductors can be in series with each other. Fig. 14 shows this branching of the circuit in which METHODS OF CONNECTING INDUCTORS. 9 B> B. ywvww\ ywww\ A. A K- B represents the exterior circuit. Fig. 15 represents a 4-pole arrangement, which is obtained by doubling the arrange- ment shown in Fig. 12. Here a double branching of the circuit takes place as shown in Fig. 16. The inductors are divided into 4 equal groups, the inductors of each group being in series, while the groups themselves are in parallel. Under similar conditions, the E. M. F. obtained is equal to that of Fig. 12. The inductors can also be con- nected in a closed-coil winding, so that only a single branching takes place ; that is, half of the inductors are connected in series whereby double the E. M. F. is obtained. This is rep- resented in Fig. 17; the joining of the successive inductors agrees with the arrangements of Fig. 6, and Fig. 17 may be regarded as an extension of Fig. 6. The distance between these inductors is either greater or less than the distance be- Fig. 16. Fig. 17. tween poles, but the sum of them is 110 longer optional. The whole winding develops into several angular figures of the form 1 6 6, which figure can be considered as the element of the winding containing only one inductor subject to induc- tion. If this scheme be considered as wound either upon a cylinder or disk, so that the inductor AB coincides with A'B', 10 ARMATURE WINDINGS. then the number of inductors must be so chosen that the cross connections shall always embrace an equal number of divisions, and in following out the winding through every inductor the last inductor considered will be found connected to the first. The inductors must, of course, be taken in their natural succes- sion; that is, starting with 6, after going through the whole scheme once, we should come to the adjacent inductor 5 on the left, or 7 on the right. The proof that this method of winding is correct, and gives a single branching, according to Fig. 14, can be shown by indicating the direction of the current, and following it out in the drawing. Starting from the point of commutation 8, and going either in the direction 8, 3, 4, etc., or in the direction 8, 3, 3, 7, etc., in either case, by following the direction of the current through half the inductors, the second point of commutation ( + ) will be reached. At any instant the reversal of current takes placq only in the two inductors which are at the points of commutation, at which time they pass from one branch of the circuit to the other. A new scheme of the utmost importance in the design of multipolar machines may be deduced from Fig. 17, if, instead of connecting together those inductors which pass under poles of the same sign, as in Fig. 6, we connect those inductors which, as in Figs. 7 and 8, pass under all poles successively. The number of inductors and the number of divisions between two inductors which are to be connected together must be so chosen, that an uninterrupted circuit may be traced out, which, after passing through each point of division, returns to the starting- point. Figs. 18 and 19 show Figs. 7 and 8 changed to meet these conditions. In each element of the winding there are two inductors, which are shown by heavy lines in Figs. 18 and 19. If the direction of the current be again followed out, there will be found only two points where the current apparently runs in opposite directions. These are the points at which the current for the exterior circuit is collected. We can now solve the METHODS OF CONNECTING INDUCTORS. 11 problem for series winding in general for any number of pairs of poles, by multiplying the number of inductors in Figs. 17, 18, and 19. It will always be found that by this arrangement Fig. 18. one-half of the inductors can be connected in series with each other, therefore only two points of commutation are required. It is evident that the last three schemes can be used in the design of direct current windings if every element which passes through a magnetic field of alternate sign has induced in it E. M. F.'s which are additive. To obtain a complete plan of a winding of this character, it is only necessary to join together several elements in a closed circuit, and to observe that no vari- ation from the assumed form of the element shall take place. Many schemes in addition to those shown in Figs. 9, 10, and 11 can be devised to meet the conditions outlined above. 12 AKMATUHE WINDINGS. Fig. 20. Figs. 20 and 21 show the elements of two windings of this character. The element shown in Fig. 20 may be obtained Fig. 21. from Fig. 9, and that in Fig. 21 by uniting Figs. 6 and 12. Fig. 22 is a scheme elaborated from Fig. 9, and Fig. 23 from Fig. 11. One element of Fig. 22 contains 4 inductors. Fig. 22. A scheme differing radically from those mentioned above is shown in Fig. 24. While the windings in Figs. 17, 18, and 19 METHODS OF CONNECTING INDUCTORS. 13 always advance through the successive fields in zigzag form ; that shown in Fig. 24, alternates back and forth. The in- ductor is bent along the broken line 1, 2, 3, 4, 5, 6, 7, making a hexagonal or rectangular element, which ends at the adjacent Fig. 23. points 1 and 7. If new elements of the same shape be added, continuing from number 7 on through all the points of division, the last element must end at point 1, which gives the scheme developed in Fig. 25. As may be seen from the figures, each element is subject to the action of two poles o*f opposite sign; by following out the direction of the current the points of collection (-f) and ( ) may be found. This winding may be spoken of as " loop winding," and that of Figs. 17, 18 and 19 as "wave wind- ing." l Fig. 22 is a mixed wave and loop winding, but as it has the pecu- liarities of a wave winding it will be classed under that head. The characteristic difference be- tween these windings appears imme- diately upon comparing schemes like that of Fig. 25 with others similar to Fig. 18. While the wave winding has only 1 See W. Fritsche. Die Gleichstrom-Dynamomaschinen. Berlin, 1889. 7 Fig. 24. 14 ARMATURE WINDINGS. two neutral points independent of the number of magnetic fields, the loop winding has as many neutral points as magnetic fields. The wave winding in Fig. 25 gives for multipolar machines a series winding, while the loop winding gives a mul- (+> Fig. 25. tiple winding. Fig. 15 is therefore to be regarded as a loop winding (spiral winding). Let z be the total number of inductors moved in the field, and n the number of poles. Then with the wave winding the number of inductors connected in series is equal to - , but with the loop winding it will be equal to - Under equal conditions the E. M. F. in the first case will be times that of the second. 2 In the series winding, the inductors are arranged in two groups, corresponding to the single branching of the circuit, while in the loop winding it is divided into n groups having branches. The inductors of the single groups are in series, but the groups themselves are in parallel. As will be shown later, the wave winding may also be used for parallel winding, but the loop winding cannot be used for series winding. The system of winding given in Fig. 25 can be further developed. W. Fritsche suggests that the vertical parts of the elements, indicated by the numbers 1, 2, 3, 4, etc., be elimi- METHODS OF CONNECTING INDUCTORS. 15 nated, thereby giving the elements a rhombic form as shown in Fig. 26. To avoid generating opposing E. M. F.'s, the pole pieces also must be given a rhombic shape. The element of a loop winding may be so formed that it will lie within the influence of two poles of the same sign as shown in Fig 27. The peculiar feature of this scheme is, that it is only good for 4, 8, 12, etc., poles, and in this case inductors are -joined in series and not - inductors as in the first loop windings considered. In a four pole scheme (w = 4), there will be but two neutral points, as in the wave winding. The cross-connectors in this figure can be so arranged that N Fig. 27. they will not cross each other, which gives a wave winding similar to that of Fig. 17. These general schemes outlined above will now be applied to the windings of. armatures for direct current machines. Noth- ing further will be said here about open-coil armatures, they being treated in a separate chapter. A. CLOSED-COIL WINDINGS. GENERAL FORMULA FOR WINDING DIRECT CURRENT ARMATURES. FKOM an examination of the windings of armatures for bipolar and multipolar machines with parallel or series grouping applied to ring, drum, or disk armatures, it appears at the first glance, that owing to the great variety of them, it would be impossible to make a general formula for winding, which would cover all these conditions. A thorough examination will show that in reality a simple formula will cover all windings ; that is, for parallel or series groupings, for bipolar or multipolar machines, for ring, drum, or disk armatures, and one which will show the necessary connec- tions of the armature inductors for obtaining the desired results. From the observations in the first chapter, it is evident that a correct winding will be obtained when those inductors lying at the same distance apart in the magnetic field are joined together in such a manner that an equal number of inductors or divis- ions are always included between two inductors that are con- nected together, and after tracing the connections through all the inductors, in which, in the separate branchings of the cir- cuit the impulses are additive, the last inductor is connected to the starting-point. The distance between the poles determines which inductors are to be connected together. From Figs. 17, 18, and 19, it is clear that in following out the schemes, we move alternately from the division points on a line AA', to those on a line BB f . If, for example, Fig. 19 be redrawn so that the points on the 16 CLOSED-COIL WINDINGS. 17 imaginary lines AA' and BB r become two concentric circles of which BB' is the inner, the development of winding becomes identical with the following geometrical problem : Let the circumferences of tivo concentric circles be divided into - equal parts. Between the z points of division a line is to be 2t drawn so that either one continuous line or several lines result, ivhich will be closed on themselves. This will depend on the as- sumptions made, and each line in passing once around the circle will give a variable number of points of intersection or bending, which will also depend on the assumptions made. The problem is solved when y, the number of spaces on either circumference between successive points of intersection on that circumference, satisfies the equation, y -(j a\ where Jc and a are whole numbers. b = the number of inductors lying between two successive points of intersection of the broken line on the circle. z = sum of the inductors or the sum of the points on both circles. In Fig. 28, where z = 20, k = 3, a = 1, b = 2, we have and a broken line of this character is represented. Let the division points of the outer circle be numbered suc- cessively from 1 to 10 ; now if y, the number of divisions which should lie between two points, equals 3, then 1 should be joined with (1 + 3) = 4, 4 with (4 -f 3) = 7, etc. On the inner circle we observe the same rule. The 20th inductor, 7d, returns to the starting-point. Since 5 = 2 there are between two successive points in the same circle, for instance 1 and 4, two inductors, \a, and a4. 18 ARMATURE WINDINGS. If 1 be joined direct to 4, then b will equal 1, and z will then denote the number of divisions on the outer circle, the inner circle being no longer necessary for the construction. Starting at 1, by going once around along the broken line, the points 4, dl, #10, are obtained. If z and b are given, the sum of the broken lines closed on themselves (or loops), or the number of points, depends on the as- sumed values of k and a. Returning to the winding, let k = -= equal half the num- ber of poles, and there- fore n equals the num- ber of poles. Let z = number of inductors on the circumference of the armature ; y any whole number chosen with reference to the number of poles and number of inductors ; a a constant which when a = 1 gives a single branching, when a = 2 a double branching, \vhen a = 3 a triple branching, etc. ; b equal the number of inductors in an element lr of the winding- a; any element. We have then generally, ,/ \ z = M-7T-2/ and Fig. 28. In regard to the value of z and 6, it should be noticed that if the inductor consists of several" strands lying alongside of or above one another, they are to be considered as a single inductor. CLOSED-COIL WINDINGS. 19 The general rule is ; The end (beginning) of the jrth element shall be joined to the beginning (end) of the (x-\-y) element. The sum y gives the number of inductors over which it is necessary to advance to reach that inductor whose beginning shall be joined to the end of the inductor started from, y may be called the " spacing " of the winding. With the aid of the formula, z = b the winding of bipolar and multipolar machines can be classified as follows : 1. SERIES WINDING. For this a = 1. In the special case when n = 2, parallel and series windings are identical, and the winding can be a wave winding as well as a loop winding. ryi This is also the case where = 2. (Compare Figs. 44 and n 45.) When - > 2 a wave winding always results. 2. PARALLEL WINDINGS. Windings with - branchings can be classified : A. Parallel winding with loop or spiral winding. In this case a multipolar armature is considered as being built up from several bipolar armatures and independent of the number of poles ; the values n = 2, a = 1 are always substituted in the formula. B. Parallel connection in wave winding. Here a = - If a single winding, closed on itself, is desired, y and -must be num- bers prime to each other. 3. MIXED WINDINGS. Here a >1 and a ^ - This case results in either several windings closed on themselves with special points of collection on the commutator, or a single winding closed on itself with a branchings. The number of closed windings or elements can be deter- 20 ARMATURE WINDINGS. mined generally, if it is noted that all the elements can be joined in a single winding, only when y and - are numbers prime to each other. If they have a common factor, as - = o i x p, and y = i x #, where p and q are two numbers prime to each other, i closed windings or i independent circuits result. The total number of branchings still remains equal to #, and the points of collection equal to 2a. In the following pages we shall consider ring, drum, and disk armatures, and prove the correctness of the above formulae. We will see at the same time that the formula will always give a correct scheme of winding, and that the laying out of a scheme for winding by means of the formula is very much simplified. The methods of representation vary ; in most schemes the circular form is retained and the commutator end of the arma- ture is shown. The connectors on the front end are shown as full lines, those on the back as dotted lines, or they are omitted. This method has the advantage over others, that the practical development of the winding can be shown, and that the transition from ring to drum and disk windings can be best observed. Where it is desirable to show the relationship of various windings, Fritsche's method is used. This gives a developed scheme, as shown in the first chapter. RING ARMATURE WINDINGS. 1. BIPOLAR RING ARMATURES. The first winding to be considered will be a simple bipolar scheme of the Pacinotti-Gramme type of armature, and in this case, with twelve coils. All the coils are so connected that they constitute an end- less spiral. At each point where two coils are joined, a con- nection is made to one of the twelve segments of which the CLOSED-COIL WINDINGS. 21 commutator is composed. This commutator rotates, of course, with the armature. With the given position of the poles and the given direction of rotation of the armature, a current is induced in the inductors whose positive direction is shown by arrows. The stationary Fig 29. brushes which carry the current to the exterior circuit, bear on the commutator at D L and _Z) 2 , and a direct current is obtained, which, if the number of coils be sufficient, is of a constant intensity. A shortcircuit of the armature coils in the neutral zone occurs when the brushes are resting upon the two commutator segments to which each coil is connected. This shortcircuit is followed by a reversal of current in these coils. If the brush D l should rest upon the segments a and m, and at the same time D 2 should rest upon / and ^, coils 10 and 4, respectively, 22 AEMATUKE WINDINGS. are shortcircuited through the brushes. While thus short- circuited they are inactive; but as they pass beyond the point of commutation the direction of the current in them is reversed. The Gramme winding agrees with the scheme given in Figs. 12 and 14. In Fig. 30 it is shown again how the current branches into the two parallel halves of the armature, J> t SJ). 2 and D } ND f> . This style of armature winding for even, sparkless operation requires that the two branches of the armature circuit be subjected to an equal induction; therefore both halves must have an equal resistance, an equal length of wire, and must induce equal electromotive forces that is, equal lengths of wire must move with equal mean velocities in a field of equal intensity. For ring windings, the number of coils which is denoted by *, must always equal the number of inductors, z ; and the gen- eral formula gives 5 = 1, where a = 1, n = 2, z = s = 12, and y = s I = 13 or 11. The beginning of the xth coil is, where y 11, to be joined with the end of the x -f llth, and therefore the beginning of 1 with the end of 12. When y = 13, it follows that 1 shall be joined to 14 (12 -f- 2), or with No. 2, which agrees with our rule. When a 2 and y = s 2 = 10, coil 1 must be joined with 1 4- 10 = 11, and correspondingly, when y = s + 2 = 14, with (1 4- 14) = 12 4- 3, or with coil 3. In this manner two inde- pendent windings would be obtained, each with one commu- tator. To the one would belong coils with odd, to the other those with even, numbers. The bipolar windings, according to Wodicka* and Swin- burne,! can be so developed that the number of commutator bars should be equal to half the sum of the coils. Fig. 31 * La Lum. Elec., 1887, Vol. xxv., p. 44. t Ibid., Vol. xxvi., p. 157. CLOSED-COIL WINDINGS. 23 shows Wodicka's scheme worked out for 16 coils. The oppo- site coils are so joined that their impulses are additive. An element of this winding consists now of two coils. The beginning of the eight elements or pairs of coils will be denoted Fig. 31. by 123 ... 8, and the ends, respectively, by I 1 2 1 3 l . . . 8 1 . The general formula is applicable also in this case : Here z = s = 16, b = 2, n = 2, y =| - 1 = 7. The beginning of pair number 1 is to be connected with the end of the pair 1+7 = 8; that is, with 8 l , etc. The difference between the Gramme winding and that of Wodicka becomes 24 ARMATURE WINDINGS. more noticeable if the Wodicka ring with its winding is devel- oped as heretofore. (See Fig. 32.) By comparison with the Fig. 32. scheme of Fig. 71, which shows the Hefner-Alteneck drum winding, it will be seen that they are identical. 2. MULTIPOLAR RING ARMATURES WITH PARALLEL WINDING. The connections of the single coils for parallel winding can be carried out in the same manner for multipolar as for bipolar armatures. The winding consists then, independent of the number of poles, of a continuous spiral divided up into a num- ber of equal sections, at the junctions of which connections are made to the commutator. The branchings of the circuit corre- spond to Fig. 16. The coils of each branch follow each other successively in the ring, and lie in the same magnetic field. The number of brushes and the number of circuits is equal to the number of poles. Fig. 33 shows this arrangement for a 4-pole ring armature. Observing that this arrangement agrees with the bipolar arrangement of Fig. 29, and that each coil is to be regarded as a single element, the general formula applies as follows : CLOSED-COIL WINDINGS. 25 where n = 2, b = 1. If a = 1 and s = 16, then ?/ = 15. The formula requires that the beginning and the end of the adjacent coils be joined together. If it be desired to retain - branchings H of the circuit, by inserting the value a = -, another scheme re- sults. The coils belonging to the same branching are no longer adjacent, but lie at the same time in two or more magnetic fields. When n = 4, and a = - = 2, the number of coils s remaining a 16, then y = 9. Now the end V should be joined to the begin- ning of 1 + 9 = 10, etc., as represented by Fig. 34 (compare also Figs. 81, 82). Developing this circular arrangement, Fig. 35 is obtained, in which each coil is represented by a straight line, and may be more easily followed. 26 ARMATURE WINDINGS. To obtain the points of commutation, denote the direction of the current in the inductors by arrows , and in following these Fig. 34. out it will be seen that there must be 4 brushes, located at the points marked -f and , in order that there shall be no oppos- ing E. M. F.'s in the branches. 1 ^ fl *- 4 , , c > 7 - fi _ $ ) 1 i 2 3 S 1 & i >' '-'-' --'' '-''' '-''' ''-'' -_*! *.**' -''' '..-"' '"-; .-'* 1 ;'***' .--^ **''. '.'-'' 1 y ^ .--'] ^ | ,** ' 3' 7' 8' 9* 10' II' 12' 13 K' JS' 16' ! Fig. 35. To observe the shortcircuiting of the coils the positive and negative brushes respectively must be considered as connected CLOSED-COIL WINDINGS. 27 together by connectors within the commutator, which is shown in Fig. 34. At the moment when the coils are in the position shown, 15 and 7 are cut out by the negative brashes, and 11 and 3 by the positive brushes. The great number of brushes which is required for the mul- tipolar parallel winding can be avoided, if desirable, by the use Fig. 36. of a winding advanced by Mordey for this purpose. The seg- ments of the commutator which are symmetrically disposed relative to the fields, are connected together. Then, inde- pendent of the number of poles, only two brushes are required, as shown in Fig. 36. The Mordey winding can be more easily arranged if the con- nectors shown in Fig. 36 be joined, as shown in Fig. 37.* The * W. Fritsche, Die Gleichstrom-Dynamomaschinen, page 4. 28 ARMATURE WINDINGS. number of segments will then be - - and to each segment ~ connectors are attached. The winding of Wodicka, shown in Fig. 31, can also be used for multipolar armatures. Let w be the number of winding spaces * on the armature, n the number of poles, then those coils which lie between 1 winding spaces should be connected together as one pair. In Fig. 38, s = w = 16, n = 4, and between each pair of coils, for example, 1 ni\ and 1', there are +1=5, winding spaces. The ends of the coils are connected together according to the scheme shown in Fig. 33 ; that is, V with 2, 2' with 3, etc. In this case b = 2 ? * " Wickungsfelder " = winding spaces, divisions for winding. CLOSED-COIL WINDINGS. 29 Fig. 38. 30 ABMATURE WINDINGS. a = 1, and the value n = 2 must always be substituted in the general formula, independent of the number of poles. Fig. 39 shows the development of this scheme. Wodicka's method of procedure can be expanded by uniting in series n coils, if there Fig. 40. be n poles. There must be a segment of the commutator for each of these groups, the total number being - . The number of winding spaces lying between two coils of a group is again - 1. Fig. 40 shows such an arrangement, where * = iv = 32, and n = 4. Denoting the coils by successive numbers, and ad- iv vancing each time, - +1 = 9 winding spaces, the armature CLOSED-COIL WINDINGS. 31 coils to be joined together will be found to be according to the following table : - , . 28. . 32. , 31. 29. 1. The formula gives this winding by inserting the values 1 . . . 10 . . . 19 5 . . . 14 . . . 23 9 . . . 18 . . . 27 4 . . . 13 . .. . 22 8 . . . 17 . . . 26 3 . . . 12 . . . 21 7 . . . 16 . . . 25 2 . . . 11 . . . 20 6 . 15 . , 24 Fig. 41, a development of this winding, shows that the scheme of connections is identical with that of a wave winding. Preserving the same method of winding, it is evident, from 32 ARMATURE WINDINGS. Fig. 41, that the number of commutator segments can be doubled by leading to the commutator the connectors coming together at a 1 , b l , 3. MULTIPOLAR RING ARMATURES WITH SERIES WINDING. In the parallel winding of multipolar armatures, there are as many branchings in the circuits as poles. In the series windings, there being but two branches, only two brushes are required. The scheme for bipolar armatures given in Fig. 30 is there- fore also applicable to multipolar armatures with series winding. All the coils, starting from the brushes, form two groups in which the direction of the current is opposite. Both groups must have an equal inductive value. OLOSED-rCOIL WINDINGS. 33 Under similar conditions, with the same number of turns on the armature, the E. M. F. induced by a series winding 7? would be ~ times that of a parallel winding, while the current L would be reduced in the same ratio. Series windings should, therefore, be used for high E.M. F.'s, or where a low peripheral speed of the armature is desired or necessary. As a series winding allows a more simple con- Fig. 43. struction of the commutator and brush connections, it is also useful in certain cases where a parallel winding might be used. A scheme for series winding can be deduced from a parallel winding in a very simple manner. In the case of an even number of coils, those lying symmetrically and in the same parts of the field are joined so that they may be regarded as' a single coil, and therefore require a single commutator bar. 34 AKMATURE WINDINGS. As the number of equivalent coils is equal to ^ , then the o ^ number of commutator segments, 1 and ^ - in the general f orm- / n \ > ^ 1 ula8=i =h a > The possible number of these windings, if developed for parallel or multiple windings, would be large. It is not the intention to investigate here their usefulness or significance, but to present a few typical cases. In Fig. 56 the values n = 6, b = 1. a = 2, y = 4, are assumed, then s = 14, and the scheme gives two independent series windings which require the brush po- sitions J?j, B^ B^ B^. If the number of coils be odd, for in- CLOSED-COIL WINDINGS. 45 stance, y = 5 and s = ~L7, a simple winding closed on itself would result, requiring 4 brushes. Fig. 57 represents this case where w = 8, # = 2, 6 = 1, y 5, s = 22. All the coils are joined into a closed spiral. If the assumption is made that n = 6, = 4, 6 = 1, y = 10, s = 34, the interesting winding shown in Fig. 58 Fig. 57. results. This arrangement has two independent windings for each set of 17 coils, with the brush positions a, and that those at an angle of - - degrees apart be connected together. Fig. 91 gives a scheme employing 9 coils and 18 segments with four poles. The cross-connections are shown within the commutator, similar to the Mordey winding. In the given position 2 2' is shortcircuited, 9 9' having just passed that point, and 4 4' is approaching it. CLOSED-COIL WINDINGS. 77 n A drum winding of Alioth & Co. shows that where ~ is even, a series winding can be obtained with an even number of coils, which winding is shown in Figs. 92 and 93, and agrees with the scheme of Fig. 54. The Alioth winding can be better understood from Fig. 93. The heavy lines show the front of Fig. 93. the armature and the connectors to the commutator. The developed scheme, Fig. 94, is interesting from the fact that it shows a mixture of loop and wave winding. Each element has four inductors (6 = 4) shown in Fig. 94 by heavy lines. There are five elements altogether. The numbers la, Ila, Ilia, IVa, Va, denote the beginnings, and the ends are denoted by le, lie, Hie, IVe, Ve. 78 ARMATURE WINDINGS. 2/20 From the formula, y = -7 1 - = 3. Therefore, le is to be connected to le, + 3 = IVa, and IVe with IVe, + 3 = 7 = 5 + 2, therefore with Ila, etc. 4. MULTIPOLAR ARMATURES WITH MIXED WINDINGS. The schemes given for ring armatures are easily applied to drums, and no new examples need be given. REMARKS UPON THE CONSTRUCTION OF DRUM ARMATURES. The practical construction of a winding, especially with a drum armature, differs considerably from the schemes given. It is therefore important to call attention to a few salient points. Fig. 94. The methods used to wind the coils upon the armature may vary. Fig. 95 gives a commutator end view of a bipolar arma- ture. The number of coils is assumed to be 14 ; the number CLOSED-COIL WINDINGS. 79 of winding spaces 28. Corresponding with the schemes in Figs. 60 and 61, the coils must cross the rear end on a chord of the circle. Beginning with the winding at a, the conductor is first taken to the point b on the front end, then carried along the surface of the drum to the back end, then carried across along Fig. 95 a chord, arid brought forward again to the point c. The opera- tion is repeated until the desired number of turns is obtained. In this figure each coil has only two turns. If 2 3 4 6, or more conductors of smaller sections be substituted for one of the large conductors previously considered, they may all be wound as one conductor or as several. If coil A be obtained in this manner, and taking each time alternate winding spaces, the coils B, (7, D be wound, when the last coil is finished, all the winding spaces will be occupied ; and on joining together the free ends as specified, the 80 ARMATURE WINDINGS. fourteen points of connection to the commutator segments will be obtained. If the number of winding spaces be equal to the number of coils, Fig. 67, the coils must be wound in successive spaces. When half the number of coils have been thus wound, all the winding spaces will be occupied, and the remainder of the coils must be wound over the first half, each two adjacent ends being joined to one commutator bar. If the connections to the commutator are to follow the schemes given in Figs. 62, 63, 68, 69, it is better not to bring out both ends, a and , on the same side of the drum, but to start the winding at , then one-half of the projecting ends are bent to the right, and the rest to the left, and joined to the commutator according ,to the scheme selected. A better arrangement of the mass of wires on the ends of the drum, and a winding of better appearance, can be obtained if, instead of the connections being invariably carried across to the right of the shaft they be divided between the two sides. This has the disadvantage, however, of taking up more room on the ends. With large conductors this becomes particularly noticeable, but may be obviated by the use of several smaller wires wound as a single conductor. For example, given a drum whose circumference is divided into 24 winding spaces in which 24 coils are to be wound, each coil to consist of two convolutions of four wires each whose diameter is about 1.5 mm. The connections are to be carried out according to the scheme given in Fig. 68. In Fig. 96, the position of the first four coils is given. These are wound in the succession I, II, III, IV. Beginning with 4 wires at a, they are carried to position 1, thence along the surface of the drum to the rear end, then across to the opposite winding space, and along the surface of the drum to 2 ; across the front end to 3 ; from here to the rear face again ; then across on the other side of the shaft to 4 ; and along the surface of the drum to the front end, which completes the first coil. After winding twelve CLOSED-COIL AVINDINGS. 81 coils in this manner twelve more are wound outside of them. One of these outside coils is shown in the figure, 1' and 4' being the ends. -The method of connecting the 24 coils with each other is obtained from Figs. 68 and 69. If the conditions given were, to wind twelve coils of two turns each, consisting of 8 wires wound as one conductor, the winding would have been carried out in the same manner. In this case the ends at a and 4' are joined together and to a com- Fig. 96. mutator segment, also the ends at 4 and V. A symmetrical arrangement of the mass of wires and a winding of neat appear- ance can be obtained by using the method shown in Fig. 97 for a bipolar winding. The coils are wound in pairs, and two suc- cessive pairs are at an angle of 90, or nearly 90, with each other. It is assumed in this figure that the ends a and e of a coil are upon the same side of the drum as in Fig. 95. Begin- ning with the pair 1, observe that the ends a and e of the first coil lie upon one side of the drum and the ends a and e 82 ARMATURE WINDINGS. of the second coil lie upon the opposite side. The position of all the pairs of coils as indicated in the figure by II, III, . . . VII, are obtained in the same manner. The shaft lies between the two coils of each pair. If there be 28 winding spaces, and the number of coils remains 28, it would become necessary, after having wound the first seven coils, to wind a second series of coils in the same Fig. 97. succession over the first, in such a manner that the ends of the coil wound over I, should be brought out at bd. If, however, it is the intention to use 14 coils, each occupy- ing two winding spaces, the first pair of the second set is wound over 1 in such a manner that the free ends, ae, ae, of both pairs coincide in position, for they are in this case connected in parallel. To properly connect these ends to the commutator, the begin- nings and ends of adjacent coils are connected to one bar. CLOSED-COIL WINDINGS. 83 In this winding it is preferable to substitute a conductor of several strands for a solid wire. To illustrate the difference of potential between successive coils, the coils in Figs. 95 and 97 are numbered from 1 to 7 ? starting at the negative brush, the numbers indicating approxi- mately the difference of potential between the coils. In the case where two coils cross at some point, the difference of Fig. 98. potential between the two crossing coils is proportional to the difference between the numbers which represent them. A winding of this description is best arranged when the least difference of potential exists between coils which cross. In Fig. 95 as well as 97, it is shown that the greatest differ- ence of potential exists between coils which cross; there being a cross between 1 and 7, 7 and 2, and between 6 and 1. These windings are therefore equivalent in this respect. 84 ARMATURE WINDINGS. The exact position of the winding and the number of cross- ings cannot be previously determined. With careful work- manship both schemes, Figs. 95 and 97, will give good results. The same remarks which have been made upon bipolar arma- tures can also be applied to multipolar windings. The coils may be wound in either manner with equally good results. To obtain a better and more permanent position for the wire, a number of pins, made either entirely of insulating mate- rial or of metal insulated from the winding, may be let into Fig. 99. ends of the drum to act as points of support for the coil. Fig. 98 represents a 4-pole winding with 12 coils. The succession in which the coils are wound is as follows : 1 1', 4 4', 7 V, 10 10', 3 3', 6 6', 9 9', 12 12', 2 2', 5 5', 8 8', 11 11' ; if the winding be carried out in this order, the coils will be symmetrical, the mass of wire on the ends of the drum will be well distributed and of neat appearance. The winding is begun at a (see coil 1 1') ; carried across the front end embracing two insulated dividing pins qq, to 6, CLOSED-COIL WINDINGS. 85 then along the surface of the drum to the rear end, then again embracing two dividing pins to the second winding space of the coil, then carried along the sur- face of the drum to c. This is repeated until the desired number of turns is obtained. Especial care should be taken in bring- ing out the ends a and e. If they be connected as shown in the figure, the points of connection to the commutator segments, A, J9, (7, are obtained. After the winding is completed, a disk having holes corresponding in po- sition with the retaining pins may be fastened over the winding, serving to secure the pins in their position. Alioth & Co. (see Fig. 92) wind their armatures with "formed" coils, which were previously given a trapezoidal shape by being bent over a wooden form. Owing to their method of construction the insulation can be practically perfect. Differing radically 86 ARMATURE WINDINGS. from the methods of winding described are those in which the connectors do not touch each other in crossing. The first winding of this description was introduced by the Siemens Company,* and used for arma- tures of low potentials with heavy currents. Fig. 99 shows one of these armatures. In this armature, copper rods of large cross- section are used. These are joined to the commutator, ac- cording to Fig. 62, by copper strips bent in such a manner as to lie in two parallel planes with air insulation between. Crompton and Swinburne f used this winding for machines of higher electromotive force, using flat copper bars laid edgewise on the drum, with the ends joined by copper strips bent spirally and lying in different planes. The author uses this bar winding for d fc 4-pole and other rnultipolar lighting generators using notched armatures. (This method of winding with copper bars and bent cross connectors has been used extensively in this country. TRANSLATOR.) Figs. 100, 1-01, 102, show the winding of a 4-pole Fig. 102. armature. To prevent confusion, only 21 coils are shown, con- sisting of flat copper bars. There are in all 42 copper bars necessary, 21 having the length J/, and 21 the length L 2 . These are laid alternately around the periphery of the drum. Of the bars, those having the length Z., are connected to the commutator. Around the surface of the drum there are 42 narrow slots into which the insulation and the copper bars are * Elektrot. Zeitschr., vol. 2, p. 54 ; S. P. Thompson, Dy. Elect. Mach., p. 2G6. t S. P. Thompson, Dy. Elect. Mach., 3d ed., p. 167. CLOSED-COIL WINDINGS. 87 let. The cross connectors are made of sheet copper of the shape shown in Fig. 102, having two arms a and 6 ? and the lug c. These are bent on a form to the right shape, a c b, and Fig. 103. Fig. 104. the ends a and b each connected to a bar. The adjacent con- nectors are separated by a piece of insulating material of the same form (or wrapped with silk tape and shellacked. TRANS.). After all these con- nectors have been put in place, a ring of insulating materials is slipped over the projecting lugs are connected together. Desroziers makes - odd in his ma- A chines, actually n = 6. The number of inductors, 2, is always divisible by 4, and every four inductors with their connectors Fig. 124. constitute an element. In this manner the number of commu- tator segments is reduced one-half, c = - x -^ In Fig. < 2 o 124 Desroziers' winding is represented assuming n = 6, z = 2 (3 X 5 + 1) = 32, y = 5, and c = 24. This winding con- sists of straight radial conductors which are moved in the magnetic field, and are joined together on the exterior and the interior of the disk by spirally bent wires. Crossings of the connectors are entirely avoided by this method. A coil, 106 ARMATURE WINDINGS. as considered in the formula, consists of two radial parts (b = 2) and two connecting parts ; for example, a a^ b l be. An element, according to Desroziers, consists of four radial parts and four connecting pieces, for example, aa x ^ bc^ d^ de. From the junction of two elements, connections are carried to , - 2 x 360 three segments, at an angle 01 6 = 120 C The complete scheme obtained in this manner is shown in Fig. 125. To prevent crossings (in the diagram) the dotted Fig. 125. parts of the inductors are supposed to lie on the rear face of the disk, and the parts shown by full lines lie on the front face. The necessary rigidity is given to the armature by a wheel-like supporting disk made of German silver 2 mm. thick, which is fastened by means of bolts to a hub on the shaft of the machine, and insulated on both sides with sheets of papier-mache fastened to the disk with pins. One-half of the armature winding is fastened outside of each papier-mache disk before it is put in place on the German silver disk, so that two workmen can be em- CLOSED-COIL WINDINGS. 107 ployed on a winding, working independently of each other. After the complete halves of the winding have been put in position on the supporting disk, the proper connections are made between the windings and the commutator. Fig. 126. FANTA'S DISK ARMATURE.* Fanta's method of construction requires that the parts of the armature subject to induction be made as thin as possible. Owing to this fact he obtains an intense field with a small magnetizing force. The armature consists of a metallic supporting disk, R, in Fig., 127, having an insulating disk on each side. These insu- lating disks are each divided into 3 concentric parts, A,B,C, of which the middle one (.) can be removed after the armature has been wound. The other two remain permanently fastened in position to the supporting disk R. Before fastening the insulating disks to the core they are wound with wire. The plan of winding, which is illustrated in Figs. 128 and 129, is similar to that of Desroziers'. The path of the element on the core is as follows : starting from , it passes along the rear side to the hole I ; passing through this hole, it follows an eccentric curve from c to d; passes * German Patent, No. 46240, March 25, 1888. Fig. 127. 108 ARMATURE WINDINGS. through the disk A again, and on the other side is carried radially from e to /. At / it passes through the ring (7, follows the eccentric curve #, h on the front side of the disk ; at h again through a hole to ?', and is then brought out radi- Fig. 128. ally to Tc. An element of this winding is shown in Fig. 129. On each of the side plates, ABC A^B^C^ a certain number of these elements are wound. The parts of the winding which are radial in their direction are all on one side of the disk, lying closely along- side of each other. This side of the wound disks is placed next to the supporting disk, and the rings AA l and CC^ are fastened to it. The central rings, B and B^ may be taken away, which allows the air gap to be materially reduced. The elements are con- nected to each other according to the results desired, either in series or in parallel. CLOSED-COIL WINDINGS. 109 JEHL AND RUPP DISK ARMATURES.* One of the greatest improvements in disk armatures was made by F. Jehl, who in 1887 patented a method of construct- ing disk armatures. It is a well-known fact that the cross connections on the rear face of a drum armature, can be so arranged as to avoid crossings. In Desroziers' and Fanta's winding the method by which crossings are obviated, is to build up the windings in two Fig. 130. Fig. 131. separate planes. This is the case in the Jehl and Rupp arma- ture, the halves of the armature being in two parallel planes. Here the elements do not require any support, being so shaped and proportioned as to give the necessary rigidity. The elements for parallel winding are bent to shape from blanks of the form shown in Fig. 130 ; and it may be seen from Fig. 131, that the elements a v and b l lie in different planes. The left end t is connected to the right end b Q of the preceding element, and the right end, 5 p to the left end, 2 , of the succeeding element. If all the elements be joined, as shown, a closed circuit winding is obtained, one-half on each side of the armature. * German Patent, 43298 ; Kittler, Handb., Vol. ii., p. 39. 110 ARMATURE WINDINGS. The scheme of this winding is shown in Fig. 132, and it will be readily seen that it is a loop winding'. For the sake of clearness a winding with a small number of coils has been selected. The parts of the winding ajb^afi^ajbp etc., belong each to one bent strip. The conductors lying upon the front of the armature are shown by heavy lines. In order to obtain the greatest number of coils in an arma- ture, the inner parts of the coils can be replaced by a thinner Fig. 132. metallic band which must be increased in width to retain the original cross-section. With this change the coils may be brought closer together. The number of commutator segments can be equal to half the number of inductors, or several inductors of a group may be joined together, and the ends brought to the commu- tator. If the number of inductors z = b (y 1), and they be CLOSED-COIL WINDINGS. Ill joined together according to the general rule, a wave winding is obtained. In Fig. 133, z = 14, y = 3, n = 4. If connected, as shown, the number of elements will be 7. Jehl and Rupp also connect the winding as shown in Fig. 134. Here b = 4,2 = 4 (y^ l) or z = 4(3 x 2 - 1) = 20, y = 3. Each element consists of four radial arms, the begin- nings of which are numbered 1, 2, 3, etc., the ends 1', 2', 3', etc. 1 ' is joined to 1 + y = 4, etc. Fig. 133. In the same manner as in the ring armature shown in Fig. 52, the number of commutator bars may be reduced one-half, but if a commutator bar be inserted diametrically opposite each of the present bars the number will again become ^ . i A difference which exists between the disk armatures of Desroziers and Fanta and that of Jehl and Rupp is that in the first the radial inductors belonging to one coil are in different 112 ARMATURE WINDINGS. magnetic fields and are both active, while in the latter only one side of a coil is active. The width of the coil is somewhat greater than that of the pole-piece. If the width of the coil were the same as that of the field, the neutral space would Fig. 134. disappear; it is therefore imperative that the coils be wider. The construction of armature coils from metallic strips lying in two planes may be advantageously employed in other windings. W. FRITSCHE'S DISK ARMATURE.* To W. Fritsche belongs the credit of having united the Jehl and Rupp construction with the Andrews,! Perry and Desroziers windings, and of having evolved a practical method of carrying it out. The fundamental difference between Frit- sche's disk armature and those of Desroziers and Jehl is that * German patent, No. 45808, June 19, 1887. t Kittler, Handb., Vol. i., Stuttgart, 1886, p. 532. CLOSED-COIL WINDINGS. 113 Fritsche used straight rods bent to lie in two planes. The con- nection is according to the general rule. Fritsche's winding is ^ given in Fig. 135, where n = 8, z = 42, - = 21 (elements) y = 5. a Inductor 1 is to be connected to 1 -f y = 6. The angle between 1 and 6 is bisected by the line OM. This inter- cepts the circumference of the interior limit of the winding at a. 1 a and 6 a show the positions of the inductors. The Fritsche winding may be derived from that given in Fig. 120 18 by substituting a triangular shape for the polygonal one there given, and by shaping of the pole shoes so as to prevent oppos- ing E. M. F.'s being generated in the inductors. The same winding would be obtained if the scheme given in 87 were developed circularly. A comparison of the Fritsche disk arma- ture with the ring armature of Andrews, Fig. 49, will show that if in the latter figure, 1 and 1', 2 and 2', etc., coincide, the 114 AKMATUKE WINDINGS. cross connectors themselves will give a correct scheme for a Fritsche disk armature, when n = 6, z = 32, y = 5. For a col- lector, Fritsche uses the connection pieces at the junctions of -the elements on the circumference. The position of the brushes on the circumference of the armature is shown in the figure. The inductors themselves are made of bent sheet iron, the inner and outer ends soldered to the connection pieces ; the entire system of inductors is fastened to the shaft. OPEN-COIL WINDINGS. 115 B. OPEN-COIL WINDINGS. Open-coil windings, whose elements were spoken of on page 7, have become prominent through the Brush and Thomson- Houston machines. Their peculiarities and their methods of operation will not be entered upon here. They have been fully discussed in S. P. Thompson's book, and also in Professor E. Kittler's. The principle of the windings will be shown in the following pages. i. RING ARMATURE WINDINGS. BRUSH RING ARMATURE. (Fio. 136.) There are in all, 8 coils wound in the same direction. The rear ends of two diametrically opposite coils are connected together, that is, 1 to 1, 2 to 2, 3 to 3, 4 to 4 ; these connec- tions are indicated by dotted lines. The front ends of these pairs of coils are connected to the commutator. The commu- tator consists of four rings lying alongside of each other on the shaft, each ring consisting of two segments, each segment em- bracing | of the circumference. In the figure these rings are shown as lying in the plane of the paper, and therefore of dif- ferent diameters. In the two inner rings, having the common brushes P l P 2 , the corresponding sections are shifted 90, and are connected to the pairs of coils 1-1, 3-3, which also lie at right angles to each other. The outer rings with the common brushes, Q l and Q^ are connected to the remaining coils, 2-2 and 4-4, and the segments are at an angle of 45 with the first pair. In the position shown in the drawing, and with the given 116 ARMATURE WINDINGS. direction of rotation, the E. M. F. in 11 has attained its maxi- mum, that in 4-4 is increasing, that in 2-2 is decreasing, while 3-3 lies in the neutral space. The current enters the armature at Pp passes through the coils 1-1 to the brush P 2 , thence to the brush Q^ then to the coils 2-2 and 4-4, which are in parallel, to Q 9 , and returns to P 1? through the external circuit. The coils 3-3 are cut out entirely. If the coils change position, a cor- responding change takes place in the path of the current through Fig. 136, them. Each coil is cut out of circuit twice for i of a revolution, and at that time when its E. M. F. is approaching or receding from 0. Those coils which are either approaching or receding from the point of maximum induction, are always in parallel. The number of coils may be increased if desired, still adhering to the Brush winding. Each pair of coils requires a col- lector ring, and every four coils lying at an angle of 90 require a common pair of brushes. These are connected successively in series. The armature of the largest Brush machine has but 12 OPEN-COIL WINDINGS. 117 coils. Fig. 137 shows its arrangement. While the armature is in the position shown in the figure, the coils 4-4 are in the neutral zone and are cut out of the circuit. The path of the current through the armature is as follows : P,-!- Q,-P,< I > Q,-P 3 < I > 2 to the others. The distance between two segments of one circuit = - = the circumference. In Fig. 146 a developed view of the collector is given, which shows that the segments lie in a position 124 ARMATURE WINDINGS. oblique to the axis, so the brushes must rest on at least two, and at times three segments. Thus, of the armature coils, at least two, and sometimes three, are in circuit. There is always at least one coil that is cut out, and at the time when its E. M. F. is zero, and about to reverse. The 4- and signs of Fig. 146 refer to the points between which the direction of the current in the armature cir- cuits reverses, hence the brushes may be either 1 3 5 7 9 or 11 twelfths of the circumference apart. LIST OF WORKS ON ELECTRICAL SCIENCE PUBLISHED AND FOR SALE BY D. VAN NOSTRAND COMPANY, 23 Murray and 27 Warren Streets, New York. ABBOTT, A. V. The Electrical Transmission of Energy. A Manual for the Design of Electrical Circuits. Third Edition, revised. Illustrations and 9 folding plates. 8vo, cloth. $4.50. ARNOLD, E. Armature Windings of Direct Current Dynamos. Extension and application of a general winding rule. Translated from the original German by Francis B. DeGress, M.E. {In press.} ATKINSON, PHILIP. Elements of Static Electricity, with full description of the Holtz and Topler Machines, and their mode of operating. Second Edition. Illustrated. 12mo, cloth. $1.50. The Elements of Dynamic Electricity and Magnetism. Third Edition. Illus- trated. 12mo, cloth. $2.00. Elements of Electric Lighting, including Electric Generation, Measurement, Storage, and Distribution. Tenth Edition. Fully revised and new matter added. Illustrated. 8vo, cloth. $1.50. Power Transmitted by Electricity and Applied by the Electric Motor, including Electric Railway Construction. Illustrated. Second Edition, Fully Revised, and New Matter added, I2mo, cloth, $2.00. BADT, F. B. New Dynamo Tender's Handbook. 70 Illustrations. 16mo, cloth. $1.00. Electric Transmission Handbook. Illustrations and Tables. 16mo, cloth, $1.00. Incandescent Wiring Handbook. Fourth Edition. Illustrations and Tables. 12mo, cloth. $1.00. Bell Hanger's Handbook. Third Edition. Illustrated. 12mo, cloth. $1.00. BIGGS, C. H. W. First Principles of Electricity and Magnetism. Illustrated. 12mo, cloth. $2.00. BLAKESLEY, T. H. Papers on Alternating Currents of Electricity. For the use of Students and Engineers. Third Edition, enlarged, 12mo, cloth. $1.50. NOSTk AMD'S LIST OF WORKS BOTTONE, S. R. Electrical Instrument-Making for Amateurs. A Practical Handbook. Sixth Edition. Enlarged by a chapter on "The Telephone." With 48 Illustrations. 12mo, cloth. 50 cents. Electric Bells, and All about Them. A Practical Book for Practical Men. With over 100 Illustrations. Fifth Edition. 12mo, cloth. 50 cents. The Dynamo: How Made and How Used. A Book for Amateurs. Eighth Edition. 100 Illustrations. 12mo, cloth. $1.00. Electro-Motors : How Made and How Used. A Handbook for Amateurs and Practical Men. Illustrated. 12mo, cloth. 75 cents. CLARK, D. K. Tramways : Their Construction and Working. Embracing a Comprehensive History of the System, with Accounts of the Various Modes of Traction, a Description of the Varieties of Rolling Stock, and Ample Details of Cost and Working Expenses; with Special Reference to the Tramways of the United Kingdom. Second Edition. Revised and rewritten. With over 400 Illustrations. Contains a section on Electric Traction. 8vo, cloth. $9.00. CROCKER, F. B., and WHEELER, S. S. The Practical Management of Dyna- mos and Motors. Eighth Edition. Illustrated. 12mo, cloth. $1.00. CROCKER, F. B. Electric Lighting. A Practical Exposition of the Art for the Use of Electricians, Students, and Others interested in the Installation or Opera- tion of Electric Lighting Plants. Volume I. : The Generating Plant. Vol. II. : Distributing System and Lamps. 8vo, cloth, each, $3.00. CUMMING, LINN^US, M.A. Electricity Treated Experimentally. For the Use of Schools and Students. Third Edition. 12mo, cloth. $1.50. DESMOND, CHAS. Electricity for Engineers. Part I.: Constant Current. Part II.: Alternate Current. Revised Edition. Illustrated. 12mo, cloth. $2.50. DU MONCEL, Count TH. Electro-Magnets : The Determination of the Elements of their Construction. 16mo, cloth. (No. 64 Van Nostrand's Science Series.) 50 cents. DYNAMIC ELECTRICITY. Its Modern Use and Measurement, chiefly in its appli- cation to Electric Lighting and Telegraphy, including: 1. Some Points in Electric Lighting, by Dr. John Hopkinson. 2. On the Treatment of Elec- tricity for Commercial Purposes, by J. N. Schoolbred. 3. Electric-Light Arithmetic, by R. E. Day, M.E. 18mo, boards. (No. 71 Van Nostrand's Science Series.) 50 cents. EMMETT, WM. L. Alternating Current Wiring and Distribution. 16mo, cloth. Illustrated. $1.00. EWING, J. A. Magnetic Induction in Iron and other Metals. Third edition, revised. Illustrated. 8vo, cloth. $4.00. FISKE, Lieut. BRADLEY A., U.S.N. Electricity in Theory and Practice ; or, The Elements of Electrical Engineering. Tenth Edition. 8vo, cloth. $2.50. FLEMING, Prof. J. A. The Alternate-Current Transformer in Theory and Prac- tice. Vol. L: The Induction of Electric Currents. 500 pp. Fifth Issue. Illustrated. 8vo, cloth. $5.00. Vol. II. : The Utilization of Induced Cur- rents. Third Issue. 594 pp. Illustrated. 8vo, cloth. $5.00. Electric Lamps and Electric Lighting. 8vo, cloth. $3.00. ON ELECTRICAL SCIENCE. FOSTER, HORATIO A. Electrical Engineer's Pocket-Book. (In press.) GORDON, J. E. H. School Electricity. 12mo, cloth. $2.00. GORE, Dr. GEORGE. The Art of Electrolytic Separation of Metals (Theoret- ical and Practical). Illustrated. 8vo, cloth. $3.50. GUILLEMIN, AMEDEE. Electricity and Magnetism. Translated, revised, and edited by Prof. Silvanus P. Thompson. 600 Illustrations and several Plates. Large 8vo, cloth. $0.00. GUY, ARTHUR F. Electric Light and Power, giving the result of practical expe- rience in Central-Station Work. Svo, cloth. Illustrated. $2.50. HASKINS, C. H. The Galvanometer and its Uses. A Manual for Electricians and Students. Fourth Edition, revised. 12mo, morocco. $1.50. Transformers : Their Theory, Construction and Application Simplified. Illus- trated. 12mo, cloth. $1.25. HAWKINS, C. C., and WALLIS, F. The Dynamo: Its Theory, Design, and Manufacture. 190 Illustrations. Svo, cloth. $3.00. HOBBS, W. R. P. The Arithmetic of Electrical Measurements. With numerous examples, fully worked. Seventh Edition. 12mo, cloth. 50 cents. HOSPITALIER, E. Polyphased Alternating Currents. Illustrated. Svo, cloth, $1.40. HOUSTON, Prof. E. J. A Dictionary of Electrical Words, Terms, and Phrases. Fourth Edition, Rewritten and greatly enlarged. Large Svo, 570 illustrations, cloth. $7.00. INCANDESCENT ELECTRIC LIGHTING. A Practical Description of the Edison System, by H. Latimer. To which is added: The Design and Operation of Incandescent Stations, by C. J. Field; A Description of the Edison Electro- lyte Meter, by A. E. Kennelly; and a Paper on the Maximum Efficiency of Inrandescent Lamps, by T. W. Howells. Illustrated. 16mo, cloth. (No. 57 Van Nostrand's Science Series.) 50 cents. INDUCTION COILS: How Made and How Used. Third Edition. 16mo, cloth. (No. 53 Van Nostrand's Science Series.) 50 cents. KAPP, GISBERT, C.E. Electric Transmission of Energy and its Transforma- tion, Subdivision, and Distribution. A Practical Handbook. Fourth Edi- tion, thoroughly revised. 12mo, cloth. $3.50. Alternate-Current Machinery. 190 pp. Illustrated. (No. 96 Van Nostrand's Science Series.) 50 cents. Dynamos, Alternators, and Transformers. Illustrated. Svo, cloth. $4.00. KEMPE, H. R. The Electrical Engineer's Pocket-Book: Modern Rules, For- mulae, Tables, and Data. Second Edition, with additions. 32mo, leather. $1.75. A Handbook of Electrical Testing. Fifth Edition. 200 Illustrations. Svo. cloth. $6.00. KENNELLY, A. E. Theoretical Elements of Electro-Dynamic Machinery. Vol. I. Illustrated. Svo, cloth. $1.50. KILGOUR, M. H., and SWAN, H., and BIGGS, C. H. W. Electrical Distribu- tion : Its Theory and Practice. Illustrated. Svo, cloth. $4.00. VAN NOSTRAND'S LIST OF WORKS LOCKWOOD, T. D. Electricity, Magnetism, and Electro-Telegraphy. A Prac- tical Guide and Handbook of General Information for Electrical Students, Operators, and Inspectors. Fourth Edition. Illustrated. Svo, cloth. $2.50. LORING, A. E. A Handbook of the Electro-Magnetic Telegraph. 16mo, cloth. (No. 39 Van Nostrand's Science Series.) 50 cents. MARTIN, T. C., and WETZLER, J. The Electro-Motor and its Applications. Fourth Edition. With an Appendix on the Development of the Electric Motor since 1888, by Dr. L. Bell. 300 Illustrations. 4to, cloth. $3.00. MAVER, WM., Jr. American Telegraphy : Systems, Apparatus, Operations. 450 Illustrations. Svo, cloth. 575 Pages. $3.50. MORROW, J. T., and REID, T. Arithmetic of Magnetism and Electricity. 12mo, cloth. $1.00. MUNRO, JOHN, C.E., and JAMIESON, ANDREW, C.E. A Pocket-Book of Electrical Rules and Tables. For the use of Electricians and Engineers. Twelfth Edition. Revised and enlarged. With numerous diagrams. Pocket size, leather. $2.50. NIPHER, FRANCIS E., A.M. Theory of Magnetic Measurements. With an Appendix on the Method of Least Squares. 12mo, cloth. $1.00. NOLL, AUGUSTUS. How to Wire Buildings. A Manual of the Art of Interior Wiring. Fourth Edition. 8vo, cloth. Illustrated. $1.50. OHM, Dr. G. S. The Galvanic Circuit Investigated Mathematically. Berlin, 1827. Translated by William Francis. With Preface and Notes by the Editor, Thos. D. Lockwood. 12mo, cloth. (No. 102 Van Nostrand's Science Series.) 50 cents. OUDIN, MAURICE A. M. S. Standard Polyphase Apparatus and Systems. Il- lustrated with many photo-reproductions, diagrams and tables. Second Edition, revised. Svo, cloth. $3.00. 'the excuse for this little book, is the demand for information, in a convenient form, on the characteristics and uses of the various types of Polyphase Apparatus, and on the actual working of the several Polyphase Systems now sanctioned by the best practice. Preface. PALAZ, A. Treatise on Industrial Photometry. Specially applied to Electric Lighting. Translated from the French by G. W. Patterson, Jr., Assistant Professor of Physics in the University of Michigan, and M. R. Patterson, B.A. Second Edition. Fully Illustrated. Svo, cloth. $4.00. PARSHALL, H. F., and HOBART, H. M. Armature Windings of Electric Machines. With 140 full-page plates, 65 tables and descriptive letter-press. 4to, cloth. $7.50. PERRY, NELSON W. Electric Railway Motors. Their Construction, Operation, and Maintenance. An Elementary Practical Handbook for those engaged in the management and operation of Electric Railway Apparatus, with Rules and Instructions for Motormen. 12mo, cloth. $1.00. PLANTE, GASTON. The Storage of Electrical Energy, and Researches in the Effects created by Currents combining Quantity with High Tension. Trans- lated from the French by Paul B. Elwell. 89 Illustrations. Svo. $4.00. POPE, F. L. Modern Practice of the Electric Telegraph. A Handbook for Electricians and Operators. An entirely new work, revised and enlarged, and brought up to date throughout. Illustrations. Svo, cloth. $1.50. OiV ELECTRICAL SCIENCE PREECE, W. H., and STUBBS, A. J. Manual of Telephony. Illustrated. 12mo, cloth. $4.50. RECKENZAUN, A. Electric Traction. Illustrated. 8vo, cloth. $4.00. RUSSELL, STUART A. Electric-Light Cables and the Distribution of Elec- tricity. 107 Illustrations. 8vo, cloth. $2.25. SALOMONS, Sir DAVID, M.A. Electric-Light Installations. A Practical Hand- book. Seventh Edition, revised and enlarged. Vol. I. : Management of Accumulators. Illustrated. 12mo, cloth. $1.50. Vol. II. : Apparatus. Illustrated. 12mo, cloth. $2.25. Vol. III.: Application. Illustrated. 12mo, cloth. $1.50. SCHELLEN, Dr. H. Magneto-Electric and Dynamo-Electric Machines. Their Construction and Practical Application to Electric Lighting and the Trans- mission of Power. Translated from the third .German edition by N. S. Keith and Percy Neymann, Ph.D. With very large Additions and Notes relating to American Machines, by N. S. Keith. Vol. I. with 353 Illus- trations. Third Edition. $5.00. SLOANE, Prof. T. O'CONOR. Standard Electrical Dictionary. 300 Illustra- tions. 8vo, cloth. $3.00. SNELL, ALBION T. Electric Motive Power. The Transmission and Distribution of Electric Power by Continuous and Alternate Currents. With a Section on the Applications of Electricity to Mining Work. Illustrated. Svo, cloth. $4.00. SWINBURNE, JAS., and WORDINGHAM, C. H. The Measurement of Elec- tric Currents. Electrical Measuring Instruments. Meters for Electrical Energy. Edited, with Preface, by T. Commerford Martin. Folding Plate and numerous Illustrations. 16mo, cloth. 50 cents. THOM, C., and JONES, W. H. Telegraphic Connections, embracing recent meth- ods in Quadruplex Telegraphy. Twenty colored plates. 8vo, cloth. $1.50. THOMPSON, EDWARD P. How to Make Inventions; or, Inventing as a Science and an Art. An Inventor's Guide. Second Edition. Revised and Enlarged. Illustrated. Svo, paper. $1.00. THOMPSON, Prof. S. P. Dynamo-Electric Machinery. With an Introduction and Notes by Frank L. Pope and H. R. Butler. Fully Illustrated. (No. 66 Van Nostrand's Science Series.) 50 cents. Recent Progress in Dynamo-Electric Machines. Being a Supplement to "Dynamo-Electric Machinery." Illustrated. 12mo, cloth. (No. 75 Van Nostrand's Science Series.) 50 cents. The Electro-Magnet and Electro-Magnetic Mechanism. Second Edition, revised. 213 Illustrations. Svo, cloth. $6.00. TREVERT, E. Practical Directions for Armature and Field-Magnet Winding. Illustrated., 12mo, cloth. $1.50. How to Build Dynamo-Electric Machinery. Embracing the Theory, Designing, and Construction of Dynamos and Motors. With , Appendices on Field- Magnet and Armature Winding, Management of Dynamos and Motors, and useful Tables of Wire Gauges. Illustrated. Svo, cloth. $2.50. TUMLIRZ, Dr. Potential, and its Application to the Explanation of Electri- cal Phenomena. Translated by D. Robertson, M.D. 12mo, cloth. $1.25, LIST OF WORKS ON ELECTRICAL SCIENCE. TUWZELMANN, G. W. de. Electricity in Modern Life. Illustrated. 12mo, cloth. $1.25. URQUHART, J. W. Dynamo Construction. A Practical Handbook for the Use of Engineer Constructors and Electricians in Charge. Illustrated. 12mo, cloth. $3.00. Electric Ship-Lighting. A Hand-book on the Practical Fitting and Running of Ships' Electrical Plant, for the Use of Ship Owners and Builders, Marine Elec- tricians and Sea-going Engineers in Charge. 88 Illustrations. 12mo, cloth. $3.00. Electric Light Fitting. A Hand-bopk for Working Electrical Engineers, Em- bodying Practical Notes on Installation Management. Second Edition, with additional chapters. With numerous Illustrations. 12mo, cloth. $2.00. WALKER, FREDERICK. Practical Dynamo-Building for Amateurs. How to Wind for any Output. Illustrated. 16mo, cloth. (No. 98 Van Nostrand's Science Series.) 50 cents. WALMSLEY, R. M. The Electric Current. How Produced and How Used. With 379 Illustrations. 12mo, cloth. $2.50. WEBB, H. L. A Practical Guide to the Testing of Insulated Wires and Cables. Illustrated. 12mo, cloth. 1,00. WORMELL, R. Electricity in the Service of Man. A Popular and Practical Treatise on the Application of Electricity in Modern Life. From the Ger- man, and edited, with copious additions, by R. Wormell, and an Introduc- tion by Prof. J. Perry. With nearly 850 Illustrations. Royal 8vo, cloth. $5.00. WEYMOUTH, F. MARTEN. Drum Armatures and Commutators. (Theory and Practice.) A complete treatise on the theory and construction of drum- winding, and of commutators for closed-coil armatures, together with a full resume of some of the principal points involved in their design ; and an exposition of armature reactions and sparking. Illustrated. Svo, cloth, $3.00, THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO 5O CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. OCT 17 19: QCT 18 19 1933 LD 21- H