UNIVERSITY OF CALIFORNIA

ANDREW

SMITH

HALLIDIL:

ARMATURE WINDINGS

DIRECT CURRENT DYNAMOS

EXTENSION AND APPLICATION
OF A GENERAL WINDING RULE

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

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

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

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

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

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

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.

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

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,

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

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.

ywvww\

ywww\

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.

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.

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.

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.

Fig. 24.

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.

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.

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

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

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

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.

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

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 - =

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.

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

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.

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

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

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.

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 ^

, c

> 7

- fi

_ $

) 1

S 1

& i

'-'-'

--''

'-'''

''-''

-_*!

*.**'

-'''

'..-"'

'"-;

.-'*

;'***'

.--^

**''.

'.'-''

.--']

,**

' 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.

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.

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.

Fig. 38.

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.

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

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.

Under similar conditions, with the same number of turns
on the armature, the E. M. F. induced by a series winding

would be ~ times that of a parallel winding, while the current

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, <?, will be c = 2 - .

Fig. 42 shows a scheme where n = 4, s = 12, c = 6.

f/g 44.

Starting from segment a, and regarding the diametrically
opposite coils 1 and V as a single coil, the end V is joined to the
segment 5, adjacent to a, and with the beginning of the coil 2
lying next to 1 ; 22' will be the next coil, etc. In this man-

Fig. 45.

ner the multipolar scheme is practically reduced to a bipolar
arrangement and the general formula applies.

In each coil the direction of the current is reversed four
times in a revolution, therefore there are 4 x 12 = 48, or
generally speaking n x s current reversals per revolution.
When the commutator segments c = 6, and with two

brushes, each brush shortcircuits -- = =4 coils. As seen

CLOSED-COIL WINDINGS.

from the scheme of winding, only two coils are shortcircuited
at the same time, therefore the scheme cannot be used in this
form. This difficulty can be overcome by doubling the number
of commutator bars, as shown in Fig. 43.* To the segments

Fig, 46.

a, 6, , d, e, f, in Fig. 42, must be added a y , b^ c^ d,, e j9 jf, which
lie diametrically opposite (where n = 4), and to which they are
joined.

Generally if the number of coils s is a multiple of - , when
n represents any even number of poles, the number -of commuta-
tor bars will equal , and each ~ segments lying - degrees

*j M

n
apart are connected together. Then through each brush ~ coils

* La Lumiere Elec., 1887, page 514 ; The Electrician, 1889, page 139.

AKMATURE WINDINGS.

will be shortcircuited at the same time. Figs. 44 and 45 show
the developments of 42 and 43. The connectors or dead
wires are so drawn in Fig. 44 as to give a wave winding, and
in Fig. 45 a loop winding.

In these figures the joining of 6' with 1 makes the wind-

t,'

Fig. 47.

ing unsymmetrical, owing to the even number of coils. As
b = 1 and z = *, if the number of coils be selected according
to the formula,

the cross connectors will be perfectly symmetrical.

If ~ be odd, s can still be an even number. In Fig. 46

s=^x7 + l =15 and y 1. Numbering the coils succes-

sively, and considering 1, 2, 3, etc., as the beginning and
I/ 2/ 3', as the ends of the coils, then according to the
general formula V is to be joined to 1 + 7 = 8, and 8' with
8 + 7 = 15, etc.

The commutator bars must be joined together according to
the rule given ; but having an odd number, one segment, 5,
cannot be so connected. According to the development there
are always two coils between two segments, and through each
brush two coils are shortcircuited, except between the seg-

/y\

ments a and &, where there is a single coil. If - be odd
and s even, this unevenness disappears. The developed scheme

CLOSED-COIL WINDINGS.

is shown in Fig. 47, where a zigzag wave winding with non-
inductive connectors is obtained.

From Fig. 46 a new winding can be developed, if, instead of

Cn\
or generally -) coils together without branching off,
/

the beginning or ending of each coil be connected to a commu-
tator segment. That is, if in Fig. 46 segment b be connected

Fig. 48.

to the coil 1 1', V be joined not only with 8 but also with
segment <?, but 8' only with segment d, and 15, etc. This wind-
ing was first used by Andrews.* Perry gave this winding in
1882. f S. P. Thompson J is of the opinion that this winding is
only applicable to an odd number of coils. This view is only

correct when - is even. The number of coils must be generally

* G. Kapp, The Engineer, 60 p. 62, 1885. Kippler, Handbuch, Vol. i., page 533.
t S. P. Thompson : Dynamo Electric Machinery, 3d ed., p. 163.
t Ibid.

ARMATURE WINDINGS.

s -^ y 1. A winding of this character, when the values are

p = 4, s = 13, y = 6, c = 13, is given in Fig. 48. Numbering as
usual, and applying the general formula, it is found that the end
of the first coil, 1', is to be joined with the beginning of the y 4- 1

Fig. 49.

coil, or of No. 7, etc. By following the direction of the current

the position of the brushes is found to be 45 apart. When -

is odd this winding can be used for an even number of coils.
In Fig. 49, this is shown, using the values, n = 6, y = 5, s = jj-
X 5 + 1 = 16. Here the peculiarity exists that the brushes are
180 apart. If s be odd, which would be the case if y = 8, then
8 = 3x81= 23, and the position of the brushes would be
60 apart.

In Fig. 48, as well as 49, the connections with the commu-
tator can be made in two planes ; that is, in Fig. 48 the connec-

CLOSED-COIL WINDINGS.

tions aV, 52', <?3', are in one plane and a7, 58, and c9,
in the other, by means of which good insulation is more
easily maintained. The number of coils which are short-
circuited by one brush in Figs. 48 and 49 equals - . In the
latter figure six coils are cut out of the circuit at the same

time. Under such conditions, to obtain a steady current and to
prevent sparking at the commutator, the number of commutator
bars should be made as large as possible.

A greater number of commutator bars can be secured, either
by increasing the number of coils in the armature, or, while still
conforming to the scheme of Fig. 43, by inserting more seg-
ments. Using this latter method, and making the number of

OF THE

'UNIVERSITY

ARMATURE WINDINGS.

segments c = s - , then each brush will shortcircuit == = 1
2 2c sn

coil. Desroziers * has applied this winding to a disk arma-
ture shown in Fig. 124. The number of commutator segments

n n 2 x 360

is generally s -, and - segments which are - - apart are

joined together, and the number of coils is again s = -^ y 1.

Fig. 51.

Fig. 50 shows a Desroziers winding applied to a ring arma-
turef where n = 4, s = 9, y = 5. Here V is joined to 1 + 5 = 6,
and 6' with 6' + 5 == 9 -f 2, therefore with number 2.

The extra bars necessary are shown in section; omitting
these, the winding of Andrews and Perry results. If it be desira-
ble, the number of collector bars can be decreased by applying
the scheme of the drum winding to the ring. If the number of

* Electrotech. Zeitschr., Vol. x., p. 200, 1889.

t Reclmiewski, La Lum. Elec., Vol. xxiv., p. 516, 1887.

CLOSED-COIL WINDINGS.

coils bes=:~{-^l], then the winding can be so arranged

2s ^
that c = Fig. 51 shows this winding, using the values

^ = 4, s ~ 2 x 13, <? = 13, ^/ = 6. The pairs of coils belonging
together are shown by the same numbers, and the connections
are carried out according to the general formula.

Fig. 52.

Instead of joining in pairs coils lying in magnetic fields of
opposite polarity, as shown in Fig. 51, adjacent coils may be so

joined. The number of segments would then be generally -,
assuming 6 = 2 and = 2( yl). In Fig. 52 the values

assumed are n = 4, s = 9, y = 5, and the beginning and ends
of pairs of coils are indicated by the same numbers.

To obtain a series winding according to the general formula V
is joined with 6, and 6' with 2, etc., and to each junction a com-
mutator bar is connected. If the points #, 5, e, d, e,f, g, h, i on the

42 ARMATURE WINDINGS.

cross connectors be connected to the commutator, the resultant
winding will be the same as that given by Andrews and Perry.
This winding can also be carried out if the number of coils be
a multiple of the number of poles ; but the winding will no longer
be symmetrical, as in Fig. 52, but unsymmetrical, as in Fig. 53.

Fig. 53.

The number of segments becomes c = y 1. As there are 12

coils altogether, 10 of which are joined to form 5 pairs, the two
remaining must be connected independently so that 7 collector
bars are necessary; therefore y = 4. The number of coils that are

shortcircuited in Fig. 52 by one brush, is equal to = =4.

This number can be decreased for any number of poles, n to 2,
by using the methods in Figs. 43 and 50, and by making the

number of commutator bars c equal to A scheme result-

CLOSED-COIL WINDINGS.

Fig. 54.

ing from this arrangement is shown in Fig. 54.* An element
of this winding contains two inductors, so that if b = 2,

y = -(- l)orv = - ( . 1 ) = 4, and 1 is joined to 5' or 1' to
n \b / 4 \ z /

5. Omitting the segments shown in cross-section, the scheme
shown in Fig. 52 again results.

Alioth & Co. use this scheme for drum windings, and Jehl and
Rupp use it for disk armatures. (Compare Figs. 91 and 131.)

8 :

_
i

^ t
-

.^ \

" ~*\

Fig. 55-
* La Lum. Elect., Vol. xxiv., p. 515.

ARMATURE WINDINGS.

Fig. 55 is the development of Fig. 54, and shows a wave
winding, with alternate long and short waves.

VZ4

Fig. 56,

4. MULTIPOLAR RING ARMATURES WITH MIXED WINDINGS.
The term " mixed windings " is applied to those which

result when a has the value a > 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.

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, <?, e, g and 6, c?,
/, A, which fall together in pairs. So that although the coils are
joined in eight parallel groups, only four brushes of double
width are required, therefore, for a six-pole machine, an eight-
branch-winding with four sets of brushes results. Fig. 59
shows the arrangement for a six-pole machine if the number of
coils is odd, which would be the case if y = 9, a = 4, s = 31.
All the coils belong to one winding. Of the eight brush
positions in two places two of them fall on adjacent commu-
tator bars, so that six brushes are sufficient.

ARMATURE WINDINGS.

Fig. 59.

CLOSED-COIL WINDINGS.

DRUM WINDINGS.
1. BIPOLAR DRUM ARMATURES.

From the Siemens double- 1 7 inductor and two-part commu-
tator, Von Hefner Alteneck, in 1872, developed an armature
winding which for direct-current use was fully equal to the
ring winding of Paccinotti.

Fig. 60.

Von Hefner Alteneck wound the coils upon a drum parallel
to its axis, so that by rotating the drum in a magnetic field the
two sides of a coil on the surface of the drum were subject to
induction. In this form of winding, it is evident that the num-
ber of inductors z is equal to double the number of coils S.
There are as many commutator segments as coils, and each
segment is connected with two coils in such a manner that the

ARMATURE WINDINGS.

whole forms a closed winding which is divided in two parallel
branches between the brushes.

For simplicity in representing this form of winding, a
scheme employing eight coils, and therefore eight commutator
bars, a, b, c, d, e,f, g, li, will be selected as in Fig. 60, which
represents this armature viewed from the commutator end. The
inductors around the circumference of the drum are therefore

represented by points, while the connectors across the back are
shown by dotted lines, or entirely omitted. Assuming that the
inductors lie at equal distances apart, as each element has two
inductors, 16 winding spaces are required. The circumference
of the cylinder is therefore divided into 16 equal parts, and
alternate divisions are numbered 1 2 ... 8. Space number 5
is diametrically opposite to space number 1. In order that the
second inductor V of the coil 1 V shall not fall upon space

CLOSED-COIL WINDINGS. 49

number 5, it must be carried either to the right or to the left
of that space. In Fig. 60, 1' lies to the right of 5. Start-
ing from 1' and following out the numbering, clockwise, in
the same direction and manner as before, the remaining divis-
ions will be numbered successively 2' 3' . . . 8'. The numbers
1 to 8 will represent the beginnings, and V to 8' the ends of
the corresponding coils. For instance, to obtain the coil 1 1',

starting at 1, the conductor is carried along the surface of
the cylinder to the rear end, then at right angles along the
dotted line V 1 across the rear end, and brought to the front
again, then along 1 V to the point of departure. This is
repeated until the coil has the desired number of turns. The
end of the last turn is not carried back to 1, but is left of
sufficient length at 1' to be connected to its segment of the
commutator.

ARMATURE WINDINGS.

In this manner 16 sections, 1 to 8, 1' to 8', are obtained,
whose connections to the commutator are absolutely determined
by the general formula. Observing the rule that every cross
connector must be connected to a commutator segment, it is

evident that the number of commutator segments must be
equal to the number of coils or sections.

It is immaterial from which section the start is made, that
is, which commutator segment is connected with 1 ; but it is
necessary that the remaining sections be connected in succession,
advancing either to the right or to the left. The first is spoken
of as a clockwise, the latter is an anti-clockwise direction of
winding.* Fig. 60 represents the development of a Von Hefner
Alteneck winding with a clockwise, and Fig. 61 with an anti-
clockwise advance. In both figures, 6 = 2, a = 1, n = 2,

* Compare Dr. A. Von Waltenhofen, Zeitschrift fur Electrotech., 1887, p. 316.

CLOSED-COIL WINDINGS.

z = 2 * = 16, y = - 1 7 1 ) = 7. Therefore the beginning of

any coil x is to be joined to the end of the xth -}- 7th coil;
that is, 1 with 8, etc.

Following out the direction of the current, which is shown
by arrows, the position of the brushes can be easily determined.

It will be observed that on rotating the armature clockwise the
negative brush will be to the right of the line joining the north
with the south pole if the advance is also clockwise, and to the
left if the advance be anti-clockwise. Both brushes are upon
the diameter mm^ which, if there be a large number of coils, is
nearly perpendicular to the line joining the north to the south
pole. In Figs. 60 and 61, which have only eight coils, the
brushes are noticeably advanced in the direction of the wind-
ing, so that the angle mOS departs considerably from 90.

ARMATURE WINDINGS.

Starting from the negative brush the current divides into the
two branches,

B,d 4 4' e 5 5'/ 6 6' # 7 l'B z and

B t d % 3 c 2' 2 b V 1 a 8' 8 hB 2 .

It will be observed that two adjacent coils are shortcircuited
as soon as they lie in a plane perpendicular to the pole line N.S.,
for example, 3 3' and 7 7', Figs. 60 and 61.

The only distinction between the Edison winding and that
of Von Hefner Alteneck is, that the connections with the com-
mutator in the former case are so carried out that the position
of the brushes coincides with the pole line N.S.

Figs. 62 and 63 show two schemes with this change, and
with clockwise and anti-clockwise advance. The change con-
sists in turning the commutator and connections through the
angle m' 08 (Fig. 61), in the direction of the winding. The

CLOSED-COIL WINDINGS.

position of the negative brush becomes independent of the
direction of the winding. Its change of position with the posi-
tive brush depends only on the change of direction of rotation.
As already stated, in the old Edison and Von Hefner Alteneck
method of winding, two adjacent coils are shortcircuited at the
same time. With high potentials it is difficult to maintain a
good insulation between the coils, and Breguet found it advan-

tageous to develop the winding in such a manner as to prevent
the shortcircuiting of two adjacent coils. Figs. 64 and 65 show
this method for the same number of sections. The difference
between this and the previous schemes is that inductor V of
the section 1 1', does not lie immediately to the right or to the
left of number 5, but, as in Fig. 64, is carried to the left of 6,
or as in Fig. 65 to the right of number 4. The two coils
which are shortcircuited in this case, would be 1 1' and 5 5',

or 3 3' and 7

ARMATURE WINDINGS.

each pair being separated by two winding
spaces.

The drum windings which have been so far considered have
had an even number of sections, and further the winding spaces
of all the coils have been side by side upon the surface of the
drum. To accomplish this, it has been necessary to make the
rear connection follow a chord.

Fig. 67.

They can be wound along a diameter providing :

1. An uneven number of coils be employed, and

2. Superimposed winding spaces be used with an even
number of coils.

Fig. 66 represents the winding with an uneven number of
sections, in this case s = 9. In the position shown, while the
negative brush lies upon the segment d, the positive brush is
shortcircuiting coil 8 8', and lies upon two segments h and i.

CLOSED-COIL WINDINGS.

Two coils are never shortcircuited at the same time, and there-
fore, as in the Breguet winding, two adjacent coils are never
shortcircuited. The circuit through the armature is through
the remaining eight coils in the two directions ;

d 3 3' c 2' 2 b V 1 a 9' 9 i,

each having equal lengths of conductor. As there is not
always room enough to place the winding spaces side by side,

it is at times necessary to superimpose the winding spaces of
two adjacent coils. Fig. 67 shows this arrangement for a Von
Hefner Alteneck winding, advancing clockwise, and Fig. 68
for an Edison winding, advancing anti-clockwise. In both these
schemes the number of coils is eight, and the number of wind-
ing spaces also eight. If the coils a 1 1', b 2 2', c 3 3", d 4 Ve

ARMATURE WINDINGS.

be put on first, the eight winding spaces will be occupied and
four commutator segments, a, b, c, d, used. In order to use the
other four commutator segments e,f,g, h, the remaining four
coils may be wound over those already put on; that is, 5 5' over
1 I/ 6 6' over 2 2', 7 T over 3 3', 8 8' over 4 4', and 8 returns
to the starting-point. The two coils 3 3' and 7 1' which lie

upon a diameter perpendicular to the diameter N. S., and
therefore in the neutral zone, are the coils which are short-
circuited by the brushes, thus determining their position.

The connections of the coils and the position of the brushes
follow the rules previously given. Although the schemes
described are frequently employed, they have a slight disadvan-
tage in that the two parallel circuits of the armature have not
an equal inductive value, which increases the tendency to spark

CLOSED-COIL WINDINGS.

at the commutator. To balance the two circuits of an armature
it is necessary that they be of equal resistance, which implies
an equal length of conductor in each, and that the inductors of
each half have an equal mean velocity. In the schemes where
the sections are wound alongside each other these conditions
are obtained, neglecting the small mechanical difficulties in

crossing at the ends, but not in the schemes with coils super-
imposed in pairs. If the armature in Figs. 67 and 68 be
turned through an angle so that segments a and e are under
the brushes, the two branches of the armature are as fol-
lows: a I 1', b 2 2', c 3 3', d 4 4'e, a 8' 8, h T 7, gV 6,/ 5' 5 e.
One consists of all the interior, the other of all the exterior
coils. The induction in each half, and also the resistance, is
equal only at that time when the brushes lie upon c and g

ARMATURE WINDINGS.

Fig. 71.

Fig. 72.

as there are then in each half two exterior and two interior
coils.

The evils arising from this inequality in the two branches of

CLOSED-COIL WINDINGS.

the armature can be easily overcome by properly connecting the
coils. An absolute balance in the induction for every part of
the revolution can only be obtained when half the sum of the
coils is odd. Fig. 69 shows such an arrangement having 14
coils.

Fig. 73.

In laying out this diagram the winding spaces are numbered
1, 2, 3, etc., alternating between the exterior and interior circle,
and the coils are connected according to the general formula.
The successive sections will then lie alternately upon the outer
and inner cylinder, and the halves will balance.

If half the number of coils be even, as in Fig. 70, the
scheme no longer gives a symmetrical winding, and the num-
bers do not alternate successively from the outer to the inner
cylinder, but in one place two winding spaces on the outer and

ARMATURE WINDINGS.

two on the inner cylinder are adjacent. In Fig. 70, / 6 6'
g 1 l r h, and b V 1 a 12' 12 m, are the coils referred to. This
variation of the Siemens winding, which was proposed by
Weston, has the disadvantage that the difference of potential
between the superimposed coils is as great as that between the
adjacent coils of the Siemens scheme. The use of heavier insu-

Fig. 74.

lation, which higher differences of potential necessitate, in-
creases in the Weston armature the depth of the winding and
consequently the distance of the core from the pole pieces.

Fritschie's method of representation is especially applicable
to drum armatures. The development of one of the given
schemes with eight sections or 16 inductors is shown in Figs.
71 or 72.

The poles are shown in cross-section, and the connectors are

CLOSED-COIL WINDINGS.

indicated by the broken lines as heretofore. The point of
commutation can be obtained by following the direction of the
currents as indicated by the arrow points. The cross connec-
tions are such that in Fig. 71 a loop winding results, while in
Fig. 72 they give a wave winding.

Fig. 75.

This method of representation led Fritschie to another style
of drum winding. Consider the scheme of either Fig. 71 or 72
in unchanged form as being wrapped around a cylinder, then
the faces of the cylinder remain free from cross-connectors, the
whole winding being carried on the surface of the cylinder.
A peculiar application of the Von Hefner Alteneck winding
is shown in the armature of the Immisch motor, Fig. 73.*

This has two commutators, each with segmeats. These

commutators are so placed that the middle of a segment of one
is opposite the space between two segments of the other.
Each brush consists of two parts joined together and resting

* La Lum. Electr. 1887, vol. 24, p. 261 ; Elektrotechn. Zeitschr., 1887, p. 531.

ARMATURE WINDINGS.

upon both commutators. In Fig. 73 these commutators are
represented as concentric circles. The circuit is the same as
in a Von Hefner Alteneck dram, and both windings would be
identical if the segments of one commutator (in the Immisch
armature) were inserted between those of the other, for ex-
ample, c between a and b. The double commutator gives the
same result as the ordinary form, except that the coils remain
shortcircuited longer.

Fig. 76.

2. MULTIPOLAR DRUM ARMATURES WITH PARALLEL
WINDING.

In designing an armature winding of this character the
method of procedure is the same as before. The core is
divided into the desired number of winding spaces, the ends of

CLOSED-COIL WINDINGS.

the coils numbered 1, 2, 3, etc., and 1', 2', 3', etc., and the gen-
eral formula applied. If the parallel branchings of the arma-
ture are to have equal lengths of conductor it is necessary that
the number of coils be made a multiple of half the number of

poles .

If ~ be even, then the number of coils must be even, but
if ~ be odd, then the number of coils may be either odd or

even. If the number of coils be a multiple of w, then n coils
will be shortcircuited at the same moment by the n brushes ;

but if s be only a multiple of ~ , then theoretically, only ~ coils
will be shortcircuited, but practically n coils wilj. still be

Fig. 77.

ARMATURE WINDINGS.

shortcircuited at the same time, owing to the width of the
brushes.

This may be observed in Fig. 74, where n = 4, z = 2s == 24.

2/2 \

In the general formula, y = - ( y- a\ , the values a = 1, n = 2,
are substituted to obtain a parallel winding, and y = j 1 =

S 1 = 11. Therefore 1' is to be joined to 1 + 11 = 12, and
to one commutator bar, etc. If this be reversed, and 1 be

Fig. 78.

joined to 12', an equally correct scheme will result, the only
difference being that the positive and negative brushes change
places. In Fig. 74, 4 coils are simultaneously shortcircuited,
for example, 3 3', 6 6', 9 9', 12 12'. Fig. 75 represents the
developed scheme of a multipolar loop winding.

If the position of one inductor of a coil, e.g., 1, be assumed,

CLOSED-COIL WINDINGS.

then the position occupied by the second inductor 1' will be
the same as that in a bipolar armature. In Fig. 74, V can lie
as well to the right as to the left of 4, or following Breguet
two additional winding spaces can be inserted between 4 and V,
V may also be wound over 3 or 4. The conditions which govern
the number of coils in this case are similar to those of a bipolar

Fig. 79.

armature with an odd number of coils. This number must be

ryi tyi

a multiple of , but not of n, and only - coils are simultane-

ously shortcircuited, as can be seen from Fig. 76.

If the coils are wound side by side, each coil can be so
placed that its inductors lie symmetrically in the field ; that is,

each coil embraces the -^ part of the circumference of the

drum. This angle of embrasure can be greater, or preferably,
smaller; for the smaller the angle the fewer the number of
crossings of the coils, but at the same time the surface
embraced lay each coil is so much less.

ARMATURE WINDINGS.

This can be observed in Fig. 77 with n 6, and an odd
number of coils, s = 21, y = s 1 = 20. In the position
shown in Fig. 76, coils 10 10', and 3 3', are shortcircuited, and
in Fig. 77 coils 7 7', 14 14', 21 21', are likewise shortcircuited.
On rotating the armature to the right, the next coils to be
shortcircuited are : in Fig. 76, 13 13', and 6 6', and in Fig. 77,

Fig. 80.

3 3', 10 10', 17 17'. The number of winding spaces in Figs.
74 and 76, which lie between the inductors of two coils, for
example, 1 1', are counted in the direction of the numbering ;
for example, 1' lies to the right of 1. If 1 be considered as
lying the same number of winding spaces to the left as it was
previously to the right, retaining the same system of numbering,
a scheme will be obtained which has been used by Thury for
multipolar drum winding. In this scheme of Thury's, which

CLOSED-COIL WINDINGS.

is shown in Figs. 78 and 79, there are not so many crossings
of coils, having a considerable difference of potential between
them, as in the drum windings previously given. This can be
observed by comparing Fig. 79 with Fig. 75.

n 2/z \

If a be given the value ^ in the general formula, y = - ( -7 a),

another scheme of parallel winding (wave winding) can be

Fig. 81.

obtained. The scheme shown in Fig. 80 is obtained by assum-

1 /32 \
ing the values n = 4, z = 2, s = 32, y = ^ f - 2J = 7.

All the coils are joined together in a single closed winding.
This winding is peculiar in the fact that the coils are short-
circuited by two brushes, either the two positive or the two
negative ; for example, if the two brushes lie upon the seg-
ments ah and cd, then 15 15' and 7 7" are shortcircuited, and
when they lie upon ef and gh, then 11 11' and 3 3' are short-
circuited. It is understood that the brushes of the same sign
are connected together, or else that the corresponding segments
are joined as in a Mordey winding. Comparison of the scheme
of Fig. 81 with that given in Fig. 41, shows that both windings
are of the same character.

ARMATURE WINDINGS.

If y and s have a common factor, then this winding scheme
no longer gives a single circuit, but several circuits closed on

s 2

themselves. If n = 4, s = 14, y = 2 - - = 6, two inter-

laced windings would result, each being a series winding with
two brushes. In Fig. 82 the full lines represent one of these

Fig. 82.

windings, the dotted lines the other, and the coils 13 13', and
fi 6' are shortcircuited. The construction of machines using
multipolar windings with parallel branching requires great care,
not only with regard to the symmetry of the winding itself,
but also with regard to the intensity of the magnetic field.
The effect of different intensities in the several fields are over-
come in the winding schemes shown in Figs. 81, 82, as the

LOSED-COIL WINDINGS.

coils lying between two brushes are distributed through all the
magnet fields.

If the coils be superimposed as assumed in Fig. 83, a sym-
metrical arrangement of the same can be attained by connecting
alternate inside and outside coils with one another. (Compare
with Fig. 69.)

^^^^^

Fig. 83.

In this figure, with the position given, the four branchings
of the circuit are :

*, 14' 14, d, 15' 15, <?, 16' 16, b, V 1, a,
e, 13 13', /, 12 12', g, 11 11', 7i, 10 10', a,
* 6' 6, d fl T 7, <? 8' 8, 5,, 9' 9, a,
e,, 55',/,,44', y , 33', A y , 2 2', a.

To each of these branchings belong two inside and two
outside coils. The Mordey winding for ring armatures, as

ARMATURE WINDINGS.

shown in Figs. 36 and 37, can be carried out in the same
manner for drum armatures.

A four-pole drum armature of Alioth & Co., in which each
commutator bar is connected to the bar directly opposite, is
shown in Fig. 84 ; of the ten coils there given, 10 and are in
the neutral zone and are shortcircuited.

Fig. 84.

3. MULTIPOLAR DRUM ARMATURES WITH SERIES WINDING.

As no radical differences exist between series windings for
ring and drum armatures, the same conditions apply to both.
(See page 33 et seq.) Observing that 6 = 2 and z = 2s the

general formula gives s = y-^ 1, and the number of coils

** st^

shortcircuited by each brush simultaneously is ~ , c being the

CLOSED-COIL WINDINGS.

Fig. 85.

^'l

2'
\/

t \

5'
\/

/ \

<\
R

1
I

^. A 1

Fig. 86.

ARMATURE WINDINGS.

2 3 <r S 6 '? 8 9 10 11 12

Fig. 87.

Fig. 88.

CLOSED-COIL WINDINGS.

number of commutator bars. Assuming n = 4, y = 6, s = 13,
Figs. 85 and 86 give a scheme complying with these assump-
tions and agreeing with the Andrews-Perry winding, shown in
Fig. 40. This winding can be easily carried out on the surface

Fig. 89.

of the drum as the development shows. In order to increase
the effective length of inductor the poles are given the shape
shown in Fig. 86.

If the rectangle A l A 2 B^ B l be eliminated, and the remain-
ing parts drawn together, the scheme shown in Fig. 87 is
obtained, which method is given by W. Fritschie.* The single

* German patent, No. 45808.

ARMATURE WINDINGS.

inductors are laid on the surface of the drum without double
bending.* With a large number of poles the inductors have
only a slight bend.

This variation can also be introduced into the parallel
winding scheme of Fig. 81. The general formula becomes

Fig. 90.

especially valuable in the case of superimposed winding
spaces.

Let n = 4, = y^ + 1 = 10 x 2 + 1 = 21, y = 10, and

that inductors from two coils shall be superimposed on the cir-
cumference of the drum. In Fig. 88 the coils are laid out in
their natural succession, 1 1', 2 2', 3 3', etc., and connected to-

* Krapfung,

CLOSED-COIL WINDINGS.

gether according to the formula, i.e., V with 1 -f 10 = 11,
2' with 2 + 10 = 12, etc. The position of the coils and
their connections are extremely unsymmetrical, and without a
winding rule it would be very difficult to connect the coils
properly. The coils 1 1' to 5 5' lie only on the inner sur-

Fig. 91. .

face, and coils 6 6' to 16 16' on both the inner and outer
surface.

The completed winding may be better represented if the
coils be indicated in succession, and distributed around the
circumference as equally as possible.

In Fig. 89 the following succession is observed: 1 1', 5 5',
11 11', 15 15', 18 18', 8 8', 9 9', 19 19', 17 17', 4 4', 12 12',
7 7', 2 2', 21 21', 10 10', 20 20', 16 16', 6 6', 13 13', 3 3'.

ARMATURE WINDINGS.

With an even number of coils the brushes are 180 apart, as
in a ring winding. In Fig. 90 a winding of this character is

fi~i

shown, the assumption being n = 6, # = 5, s = 5~-f-l = 16.
This winding is only applicable where ~ is odd. If it be desired
that only one coil be shortcircuited by each brush at the same

Fig. 92.

time, it is necessary that the number of commutator segments
be s> 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.

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.

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.

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.

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

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.

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.

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.

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

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.

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 <?, and fastened with a
nut m. If the W. Fritsche
winding given in Figs. 81,
86, 88, be represented as on
the surface of a drum, and
each coil consist of only one
turn, the winding can be car-
ried out in the same manner as the Siemens method so that
the connectors can cross each other without touching.

Fig. 103 gives a side view, and Fig. 104 the section of a
winding according to the scheme given in Fig. 88. The mutu-
ally parallel bars 1, 2, 3, .... etc., are placed upon the cylin-

Fig. 105.

ARMATURE WINDINGS.

der whose diameter is d, and the bars, I/, 2', 3', which cross the
other bars 1, 2, 3, are situated on the surface of a cylinder of

Fig. 106.

larger diameter, D. The points of apparent intersection of the
rods lying in the two planes are joined together, but are insu-
lated from the adjacent points of apparent intersection. Be-
tween the two cylinders d and

D sheets of insulating material
are inserted.

The idea of making use of
the advantages of the Siemens
bar winding for armatures
whose coils must consist of
several turns, was carried out

practically by R. Eikmeyer.*
The shaped wire coils, of Eik-
meyer, and the bar winding of
Siemens, have the same form.
Fig. 106 gives a side view of a bipolar drum having 36 coils of
the previously mentioned form. Fig. 105 gives an end view
of the same with the commutator removed. Fig. 107 gives a
plan view of a single coil, A B being the axis of the drum.
The coils are all of the same shape. On one side of the axis

* German Patent, 54413, Feb. 14, 1888.

CLOSED-COIL WINDINGS. 89

A B, the coil is of less outside width than the inside width of
the other half. This peculiarity of form is carried out regard-
less of the number of turns in the coil, and of the changes in
the shape of the core.

In Fig. 107, b b ] represent the part lying upon the surface
of the drum, and c ^ the part lying on the face ; c 2 c s are the
windings, and d d { the ends leading to the commutator. The
side b of the coil is longer than the side 5 p so that when the
coils are in position on the drum, the side 6 T of each coil clears
the side b of the other coils. On the circumference of the
drum, the long and short sides alternate, and the pins a prevent
the coils moving on the drum. The figure shows that the form
of the connector across the face of the drum is a spiral, passing
from the periphery of the drum toward the center, then along
a line nearly parallel to the axis of the drum, and along another
similar spiral to the opposite side of the drum.

During this cycle the wires change their position, so that
while on the surface of the drum they lie alongside each other,
on the ends they are superimposed. This winding of Eik-
meyer's, and that of Alioth & Co., have the good feature of
equal lengths of wire, therefore equal resistance in the branch-
ings of the circuit, and the additional feature that damaged
coils can be readily replaced.

DISK ARMATURE WINDINGS.

The coils of Ring and Drum armatures turn about an axis
which is perpendicular to the direction of the lines of force in
the magnetic field. From this it follows that the plane of the
coil is at one time parallel and at another time perpendicular
to the direction of the lines of force.

On account of this arrangement, the lines of force pass for
a considerable distance through the armature core. The core
is therefore made of iron, and for mechanical reasons, revolves
with the inductors. This introduces a number of evils which
in multipolar machines are especially noticeable. The repeated

90 ABMATUKE WINDINGS.

magnetization and demagnetization of the core causes losses
from eddy currents and hysteresis, which losses amount to seve-
ral per cent in the best apparatus. Besides this, the heating of
the core from these losses limits the allowable heating in the
conductors and consequently the total output of the machine ;
and finally, the inducing coils, which are distributed in various
parts of the magnetic flux, cause a cross-magnetization, which
weakens and distorts the magnetic field.

In disk armatures, the inductors move in a plane, perpen-
dicular to the direction of the lines of force, about an axis par-
allel tp them. The space which the inductors require in the
magnetic field, in the direction of the lines of force, is limited
to the thickness of the coils, and the iron core can be omitted,
the lines of force passing from pole to pole directly through the
armature windings.

These features render it possible to make a disk armature
of comparatively little weight, even when a large diameter is
employed ; it is therefore possible to obtain a high peripheral
velocity with a low number of revolutions. Owing to the
complete ventilation which may be obtained by this form of
construction, it is possible to increase the current density in the
armature, and hence increase the output of the machine. As
no iron is used in the core, in order to produce an intense mag-
netic field in the space between the poles in which the armature
revolves without excessive magnetizing force, it is necessary
that this space be made as short as possible. Therefore the
coils, subject to induction, should occupy as small a space as
possible in the direction of their axes. This requirement, as
well as the connection of the inductors with each other and
with the commutator, has prevented the more general adoption
of this form of armature, and it is only within the last few
years that their difficulties have been satisfactorily overcome.

Disk armatures are generally used for multipolar, but may
also be designed for bipolar machines.

Series winding is especially applicable to multipolar disk

CLOSED-COIL WINDINGS. 91

armatures, as the desired E. M. F. can be obtained with few
turns in each coil, and is also free from the difficulty which
arises in multipolar armatures with parallel winding; that
is, that the various branches are not all subject to exactly
equal inductions, hence have unequal E. M. F.'s induced in
them.

In the following pages several forms of disk armatures
having only historical interest will be mentioned. The first

Fig, 108.

considered is the disk armature of Niaudet.* This armature
can be regarded as a Gramme ring armature, having the coils
turned through an angle of 90, so that all the coils lie in a
plane perpendicular to the axis of rotation. The connections
of the coils with each other and with the commutator remain
the same, the beginning and the end of two adjacent coils
leading to a common commutator bar.

Tire magnetic field is obtained by the use of two horse-shoe

* Kittler, Handbucli, Vol. ii., p. 23.

ARMATURE AVINDINGS.

magnets, so arranged as to present the north pole of one to the
south pole of the other, and vice versa.

In Fig. 108, which is a diagrammatic representation of this
armature, one of these horse-shoe magnets is considered as
above the paper, the other below. If this armature be rotated
through the magnetic field as shown, a reversal of current

takes place in each coil, when it is in such a position that one
of its diameters coincides with the pole-line, N/S.

If the brushes be set so as to shortcircuit the coils that are
in this position, the armature will be divided into two branch-
ings, the current flowing in an opposite direction in each, and
a direct current will flow in the exterior circuit. The same
construction was also adopted by Wallace-Farmer, and Soren
Hjorth.

CLOSED-COIL WINDINGS. 93

THE HOPKINSON-MUIRHEAD DISK ARMATURE.* (FiG. 109.)

The connection of the coils with each other and to the
commutator in this type of armature agrees with that of the
Niaudet. A peculiar feature is, that the coils lie in two planes,
the coils in one plane being advanced half the width of a coil
beyond those in the other.

These coils are fastened to the sides of a core built up of
strips of iron, and are held in position by radial bolts. The
number of magnetic fields is equal to or less than one-half the
number of coils, and they are otherwise arranged in the same
manner as Niaudet's.

In the diagram, Fig. 109, the position of the coils in the
plane lying to the rear is shown by dotted lines.

SIEMENS & HALSKE DISK ARMATURE.f

VON HEFNER-ALTENECK DESIGN.

A very ingenious method of constructing a multipolar disk
armature, with a series winding, was designed by Von Hefner-
Alteneck ; in this winding, only one coil is shortcircuited at a
time by each brush, the same as in bipolar machines. The
successive magnetic fields are of alternate polarity. The num-
ber of coils in the armature is less than the number of fields,
in fact, s = (n 2).

In Fig. 110, 6 coils are represented, rotating between 8
magnetic fields. Of these 6 coils, but two opposite coils are
wholly in a magnetic field, the others being at a greater or less
distance from a field. The rotation of the armature, therefore,
does not produce a maximum induction in all the coils at the
same time, but in successive coils in successive parts of the revo-
lution.

Considering the armature at any part of a revolution, it is

* English patent, 4886, of 1880.

t German patent, 15389. 1881. Kittler, Handbuch, Vol. ii., p. 29.

94 ARMATURE WINDINGS.

evident that it may be divided into two halves, by a line
passing through its axis, such that the direction of the flow of
the currents in the halves is opposite, while the impulses are
additive. This division line continually changes its position
during the rotation of the armature, but always intersects the
points of the circuit formed by the coils which are connected to

Fig. 110.

the particular commutator segments upon which the brushes
rest. The commutator consists of

n
c = - x segments,

n . . . , - 2 x 360 ,

and every ~ segments which are at an angle of - - degrees

2 ti

apart, are connected together, and are also connected to the
connectors of two adjacent coils. In the Fig. the commutator

has 24 bars, and = 4 segments belong to each group. The

connection of the segments in each group (for example, 1,1,1,1,

CLOSED-COIL WINDINGS.

2, 2, 2, 2,) to each other and to the windings is accomplished by
means of insulated rings carried by the shaft. If the successive
segments of the 6 groups be numbered from 1 ... 6, and the
corresponding connecting wires between the coils be also num-
bered 1 ... 6, then the shortcircuited coils will be those which
are included between the points on the connecting wires, whose
numbers correspond to the numbers of the commutator seg-

Fig. 111.

ments on which the brushes rest; for example, if one brush
rest on segments 5 and 6, and the other upon 2 and 3, the coils
lying between the connection wires 5 and 6 are shortcircuited,
likewise those between 2 and 3.

Instead of having more magnetic fields than coils the number
may be less, and need not be exactly two less. The number of
coils may be increased, for example, to double the number.
The coils may be located in two planes, as in Fig. 109, for the

ARMATURE WINDINGS.

Hopkinson-Muirhead disk armatures, not necessarily with the
centers of the coils in one plane midway between the centers
of the coils in the other. Fig. Ill shows the inter-connections
of the coils for a machine with eight fields and twelve coils.
The coils which are subject to the induction of the field succes-
sively are not connected successively, but at regular intervals,
as shown in the diagram, and are correspondingly cut into
circuit. The number of commutator sections with this scheme
is 48, arranged in 12 groups of 4 segments each.

=4p-

Fig. 112.

The disk armatures which have been described have no prac-
tical importance. By application of the schemes developed for
ring and drum armatures, practical direct-current disk arma-
tures may be evolved. In conclusion, Faraday's disk may be
mentioned. This well-known apparatus is illustrated in Fig.
112, which shows a copper disk rotated in a magnetic field in
such a manner that lines of force are continually cut by the
disk, and by means of brushes bearing on the axis and periphery
of the disk an uninterrupted current is obtained in the exterior
circuit.

CLOSED-COIL WINDINGS.

DISK ARMATURES OF W. THOMSON * AND POLESCHKO.t

If the copper disk (of Faraday) be slit into radial arms
fastened to a common axis, but insulated from each other
toward the periphery, and if this disk be rotated in magnetic
fields of opposite sign as in Fig. 113, Poleschko's arrangement
will be obtained. It is assumed that there is above the plane
of the figure a north pole opposite to the south pole, and a

Fig. 113.

south pole opposite the north pole. The brushes bear on
the periphery of the disk on a line with the poles ($. ^V!),
and as the E. M. F.'s induced in the arms of the disk on which
the brushes rest are additive, the E. M. F. obtained will be
double that of a Faraday disk. The radial slitting of the disk
prevents wasteful eddy currents. W. Thomson joins the outer
ends of the radial arms with copper strips, and insulates the

* S. P. Thompson, Dyn. Mach. Third ed., p. 233.
t La Luin. Elec. Vol. xxxv., 1889, p. G10.

ARMATURE WINDINGS.

inner ends which are joined to the segments of an ordinary
commutator with two brushes.

These are open-coil armatures, and are mentioned here as
they illustrate the origin of disk armatures.

PACINOTTI'S DISK ARMATURE.*

In 1881 a machine was shown at the Paris Exposition
which had been invented by Pacinotti in 1875. His armature
also consisted of radial arms rotating between magnetic poles of

Fig. 114.

opposite sign, but the arms were connected so as to constitute
a closed winding. This method of construction is given in
Fig. 114. The surface of the poles is very much increased in
comparison with those shown in Fig. 113, so that in all the con-
ductors in one-half of the armature the current flows radially

* S. P. Thompson, Dyn. Mach., p. 206.

CLOSED-COIL WINDINGS.

inward, and in the other half radially outward. The manner
of connecting the conductors follows the general rule, here as
well as in the Pacinotti Ring armature.

In the scheme given, s = 10, y = s 4- 1 = 11, therefore 1
must be connected to 1 4- 11 = 12 or 2. The commutator
segments are shown on the periphery for the sake of clearness.
The circuit is as follows ; from the brush B l through the exterior
circuit to B. into the armature, where it divides itself as follows :

B 2 , 8', 8, 7', 7, 6', 6, 5', 5, 4', 4, B r

EDISON'S DISK ARMATURE.

In 1881 Edison patented a machine in which the armature
is nearly the same as that of Pacinotti.

By transferring the commutator connections from the con-
nections of the radial arms which lie 011 the periphery, to

100

AKMATURE AVINDINGS.

Fig. 116.

Fig. 117.

those which are in the inner part of the disk, Edison's scheme,
shown in Fig. 115, results. The actual construction of this
arrangement is shown in plan in Fig. 116 and in section in
Fig. 117.

The sixteen radial conductors consist of copper strips
(/v, a . . .) well insulated from one another. Their connec-

Fig. 118.

CLOSED-COIL WINDINGS.

101

tion with each other on the periphery is effected by eight con-
centric copper bands insulated from each other. The disk is
mounted on a wooden hub, and the radial arms are connected
to the commutator by means of eight insulated copper rings
carried by this hub. The development of both these schemes
is shown in Fig. 118.

A comparison of this with Fig. 71 shows the identity of the
scheme of connecting with the Von Hefner-Alteneck drum
winding. If the development-of the scheme given in Fig. 118
be made circular, so that the side A A forms the outer circle,
Pacinotti's scheme results ; if this side be made the inner circle,
Edison's scheme is obtained.

Fig. 179.

EDISON'S* MULTIPOLAR DISK ARMATURE WITH PARALLEL

WINDING.

Fig. 119 shows the scheme of connection given in Fig. 115,
extended to cover a multipolar field. This is identical with
the drum armature winding shown in Fig. 75.

* The Electrician, December, 1889.

102

ARMATURE WINDINGS.

APPLICATION OF THE ANDREWS-PERRY WINDING TO DISK
ARMATURES.

A new group of disk armature windings may be arranged
by applying the Andrews-Perry winding for ring armatures to
disk armatures.

The most simple form in which this may be done is to
change to a circular form the scheme given in Fig. 86 for
drum armatures in such a manner that the parallel conductors

Fig. 120.

1 ... 13 and V . . . 13' become radii. Fig. 120 shows a
scheme developed in this manner, designed for eight poles.
According to the formula, the number of inductors must be

z =

For series connection a = 1. In Fig. 120, 6 = 2,

y = 5, therefore z = 2 (4 x 5 4- 1) = 42 = 2 s. Every two
inductors are joined in one pair, forming one coil, indicated by
the same numbers. V is to be joined to 1 4- 5 = 6, 2' with 7,

CLOSED-COIL WINDINGS.

103

3' with 8, etc. The number of commutator segments is 21.

There are ~ = 4 coils shortcircuited by each brush at the same

time, and for the position of the armature shown in the
drawing, the coils shortcircuited by the negative brush are
[21, 21'] [55'] [10, 10'] [15, 15'], and by the positive brush
[18', 18] [13', 13] [8', 8] and [3', 3]. The shape of the pole
piece is determined by the shape of the coil. To prevent
opposing E. M. F.'s, the poles must be cut off at an angle on
the outside, and the edges made radial.

The practical construction of a disk armature according to
this scheme presents many difficulties, which have been over-
come in various ways.

The first method to be considered is a disk armature with
an oblique winding. The over-lapping coils in this armature
stand at an angle to the plane of rotation. The angular width

W//7A P^

8'- J JET

I 3 ' J- 4 ' JA J6 I' J8' 19' ?i

Fig. 121.

is such that when one side of the coil is
in one magnetic field, the other side lies
in a field of opposite sign. Fig. 121
gives the position of the coils relative to
the magnetic field. The development
shown gives a view of the circumference
of the armature.

The shape of a single coil for 8 poles is shown in Fig. 122.
The ends of the coils can be joined, according to Fig. 120,
for high E. M. F.'s, or as in Fig. 77. in parallel for low
E. M. F.'s.

Windings employing oblique coils have been devised

Fig. 122.

104

ARMATURE WINDINGS.

by Ayrton and Perry,* by Elphiristone- Vincent * and by
Desroziers f The method of connection employed is not
known to the author. If each coil consist of one turn, and the
entire winding be arranged on a thin disk in an oblique position
and connected according to the general formula, the scheme
given in Fig. 123 will result. This represents a development of

Fig. 123.

the circumference of the armature. The radial inductors are
shown as points, the cross connectors on the circumference as
full lines, the interior connectors as dotted lines. The winding
is carried out as follows : From V along the inner surface to
11, then radially outward, then from 11 obliquely across the
exterior surface to 11', then radially inward, and from 11' on
the inner surface obliquely to 21 and continuing to 21', 10,
10', 20, 20', 9, etc., returning to i'. No crossing takes place,
and the position of the brushes is given in the diagram.

DESROZIERS' DISK ARMATURE. J

Desroziers' method of winding disk armatures agrees with
the scheme given in Fig. 121, which is a wave winding, except
that he employs a greater number of commutator bars than is
there given. This he did with drum armatures, as shown in
Fig. 91, and with ring armatures, as shown in Fig. 50, so that
a brush shortcircuits but one coil, that is, one element, at a
time. In this armature the number of radial inductors is

* S. P. Thompson, Dyn. Mach., 3d ed., p. 206.
t La Lum. Elec., Vol. xxiv., 1887, p. 293,

t Elektrotechnic. Zeitsch., Vol. x., 1889, p. 200. La Lum. Elec., Vol. xxiv., 7 May, 1887,
p. 294.

CLOSED-COIL WINDINGS.

105

2 = b (y - - 1 ). The number of commutator segments, <? = -,

n , ,2x360,

and every - segments lying at an angle of - degrees apart
A w>

are connected together. Desroziers makes - odd in his ma-

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

= 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 ^ .

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.

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

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 > <? 3

through the external circuit back to P^

Fig. 137.

2. DRUM ARMATURES, THOMSON-HOUSTON WINDING.

This armature is shown in Figs. 138-141. The core is com-
posed of iron wire wound on two cast-iron supporting spiders,
the whole forming an oblate spheroid. Pins are inserted in the
edges of the cast-iron spiders for the purpose of properly spa-
cing and guiding the three coils, which are wound on the core
at an angle of 120.

The coils are wound in as follow: first, half of the first
coil, then half of the second coil, then all of the third coil, then

118

ARMATURE WINDINGS.

the other half of the second, and finally the remaining half of
the first coil. This method of procedure gives an equal length
of wire in each coil, and the mean distance of the coils from the
poles is the same. The beginnings of each of the three coils
are connected together, and the ends are connected to the three-
part commutator, The armature when completely wound is
nearly spherical. The developed scheme shown in Fig. 138
represents this winding. The starting ends a 1? 5 1? c 1? are con-

Fig. 138.

nected together, and the ends 1, 2, 3 are connected to the seg-
ments a, 5, c. Coil number 2 is in the neutral position in the
figure, and is cut out of the circuit.

The position of the coils relative to the commutator and to
the brushes is shown in Fig. 139. The coils 1, 2, 3, are indi-
cated by radial lines drawn from the segments #, 6, c, of the

OPEN-COIL WINDINGS.

119

commutator to the center ; N. S. is the pole line. If the arma-
ture be revolved through 30 from the position shown, number
1 will be in the position of maximum induction, number 2

Fig. 140.

approaching this position, and number 3 will be in the neutral
position. (See Fig. 140.)

Coils 2 and 3 are connected in parallel, by the brush resting
upon both I and c. On revolving the armature further, number
3 is cut out of circuit, and number 2 takes its place. The time
during which two coils
are in parallel is there-
fore very short. To in-
crease this time, and to
more advantageously
employ the full field flux,
the commutator seg-
ments might be .length-
ned so as to overlap, as
in the Brush machine.
Thomson-Houston attain
the same end by using Fig - 141 -

a second pair of brushes set at an angle of 60 with the first
pair, and connected to them, as shown in Fig. 141.

120 ARMATURE WINDINGS.

3. DISK ARMATURE WINDINGS, WILDE'S DISK ARMATURE.

In 1867 H. Wilcle patented an alternating dynamo, the
armature of which was so connected as to allow a part of the
current to be rectified to excite the field magnets ; in Fig. 142
an arrangement of this same character is shown.

An armature with eight coils revolves in eight magnetic
fields of alternate sign. The coils in the armature are con-

nected so that a reversal of current takes place in all of them
simultaneously. The commutator is shown in the figure as two
interlocking tooth disks ; actually they consist of two toothed
cylinders mounted on the shaft. Each cylinder has as many
projections as there are fields. One of these cylinders is con-
nected to the beginning of the winding, the other to the end.

A unidirectional pulsating current will be obtained if two
brushes be used on adjacent segments of the rectifier.

The coils may also be arranged in parallel, by connecting
the beginning and the end of each coil with the rectifier.

OPEN-COIL WINDINGS.

121

FERRANTI-THOMSON DISK ARMATURE.

In this case, as in the previous one, the field magnets are
arranged circularly, and of alternate polarity. The armature
consists of copper strips bent into a wave-like shape ; the num-
ber of layers is optional. In the diagram of this winding, Fig.
143, but two layers are shown. The distance between the
radial parts of the coils is the same as the distance between the
centers of the fields. The E. M. F.'s induced in the copper

Fig. 143.

strip are additive, and the total E. M. F. can be made available
at the ends of a break made between any two adjacent coils of
the winding.

When the coils are in the position shown in the drawing,
they are in the position of maximum induction. By connecting
the armature coils in the same manner as is shown in Fig. 142
a rectified current may be obtained, Instead of brushes, Fer-
ranti uses grooved metal disks.*

* Kittler, Handbuch, Vol. ii., p. 136.

122

ARMATURE WINDINGS

BOLLMAN DISK ARMATURE.*

The Bollman winding resembles that of Ferranti-Thomson,
the difference being that in the Bollman armature there are sev-
eral circuits, and the coils of the various circuits overlap. If
a single circuit be taken from the armature it will be found
to agree with the Ferranti-Thomson winding. The scheme of

Fig. 744.

Bollman's winding is shown in Fig. 144, in which there are
twelve magnetic fields arranged in a circle and of alternate
polarity. There are altogether 24 armature coils, divided into
four circuits of 6 coils each. The coils are built up of copper
strip, and no iron is used in the construction of the armature.
Each coil contains several turns, two turns being shown in
the diagram, which consist of radial strips, and are con-
nected at the ends by short circular pieces in such a man-
ner that air may circulate through the winding. The coils

* German patent, 35186, Nov. 18, 1884, Kittler, Handbuch, Vol. ii., p. 37.

OPEN-COIL WINDINGS.

123

are all connected in series. The angular distance between
coils is equal to that between the poles, therefore each coil is
in two fields at the same time.

In the drawing only one circuit is shown, a second being
partially indicated by dotted lines. In order that the air-gap
may be as small as possible, the radial strips lie in one plane.
The connecting strips do not lie in the same plane as the radial
strips, but are bent out to one side to prevent crossings, as
shown in perspective in Fig. 145. In that figure ,5, i,k, o,n,
f,e are the radial inductors, and bcde, fghi, Jclmn are the con-
necting strips. The corresponding position of the other circuit
is shown by the line pq. The connecting strips of two of the

Fig. 145.

Fig. 146.

circuits are bent to the right, and of the other two to the left.
The collector is identical with the rectifier used by Wilde, but
with the separate parts multiplied to cover the increased num-
ber of armature circuits (in this case 4 times), having in all
2 8 = 48 segments. The two ends of each circuit are con-

nected to each - = 6 segments. The segments for the arma-
ture circuits are represented in Fig. 144. The end, e^ is
connected to the shaded segments, and <? >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.

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