Improvements in Dynamo Electric Machines and in Electro-motors.
Year: 1885

page_text: Improvements in Dynamo Electric Machines and in
Electro-motors.
I, GEORGE HOOKHAм of New Bartholomew Street, Birmingham, in the County
of Warwick, Manufacturer, do hereby declare the nature of said invention for
"IMPROVEMENTS IN DYNAMO ELECTRIC MACHINES AND IN ELECTRO-MOTORS to
be as follows :—.
"
In a Cylindrical Armature similar to that described in my Specification N° 7533,
1884 having longitudinal grooves or slots in which the Conductor is wound, so
arranged that the sum of the sectional areas of the ribs or ridges at one time under
a pole-piece of the field Magnets is equal or nearly equal to the Magnetic Section
of the rest of the Armature I find that a slot with parallel sides or walls, i,e, once
of the same width throughout is not always the best form-It is clear, for instance,
that the slots may be wider at the top, where they cut the surface of the cylinder,
than at the bottom; and so long as this difference is not so great as to make the
ribs narrower (or thinner) at the top than they are at the bottom, their effective
magnetic section is not appreciably lessened-I accordingly sometimes inake the
slots of this form, especially when I intend the armature to be wound with a great
many turns of small wire-I generally make the depth of the slots to from one
tenth to one eighth of the diameter of the Armature-It will be found that in a
slot widening out in the manner and to the extent above described and in depth
bearing this proportion to the diameter of the armature, the width of the slot at
the top will bear to its width at the bottom about the proportion of three to
two-Hence if the bottom of the slot will take two wires of a given diameter side
by side the top will take three of the same wires-It is often much more
convenient for winding that the sides of the slot should not be slanting, as the
turns of wire keep their places better in grooves with parallel sides-Therefore in
the case instanced I should widen out the top of the slot to the extent indicated
to a depth sufficient to take one or two layers of wire, still keeping the walls of
the widened portion parallel and forming a shoulder on each wall of the slot-It is
clear that this may be done without lessening the effective magnetic section of the
ribs-Sometimes, when I use slots with straight sides (ie, not shouldered in the
manner just described) after I have filled the slots with wire I wind a layer of

page_text: wire over the entire cylinder as in the ordinary Siemens armature-In this case
the magnets must be longer than when the iron of the armature passes as closely
as possible to the pole-pieces-Each linib of the magnet or magnets must be from
one and a half times to twice the diameter of the armature, whereas with the other
forms of my armature a length of from one to one and a half diameter is sufficient
-When I wind an outside layer of wire as last described, if the slots are wound
with thick wire, I prefer to wind the outside layer with wire of such diameter
that two (or more) stands laid parallel have a total sectional area equal to or
slightly greater than that of the larger wire in the slots-In very large machines,
or in those in which only a low E. M. F. is required as e.g. for electro plating,
instead of making slots in the armature I bore holes from end to end at such
distances apart and in such positions as the slots would have been; the outer side
of such holes being from a thirty-second to a sixteenth of an inch from the surface
of the cyndrical armature-Insulated wires rods of copper are passed into these
holes, and their ends connected either in the usual way or in a manner hereinafter
to be described, by means of insulated strips or sheets or wires of copper-In
practice the holes are punched in the discs of sheet iron of which the armature is
composed at accurate distances, so that when the dists are placed on the spindle
the holes in one disc come exactly opposite those on another-There is sufficient
solid iron left between the holes to give the requisite magnetic section to this part
of the armature.
All these forms of armature may be wound according to known methods such of
those of Siemens, Edison and others-But I have discovered a special mode of
winding applicable to them which I will now proceed to describe-I take an
armature with an even number of slots and a commutator with the same number
of plates or segments-In any slot and that opposite to it I wind as many turns of
the conductor as I find from experience will at a given speed give me the E. M. F,
I desire The two ends of this coil are connected, one to the nearest commutator
plate; the other to that immediately opposite to this plate-I treat every opposite
pair of slots in the same way and connect the ends of their coils similarly and in
order to opposite pairs of commutator plates; each coil being so far independent
of every other coil-In my armature practically the whole of the lines of force
due to the field magnets pass through the arcs at any one time opposite the pole-
pieces It is obvious that any one of the independent coils while passing a
pole-piece is cutting lines of force and has an E. M. F. and that it has little or none
as soon as it is clear of the pole-piece-Suppose there are 30 slots and therefore
fifteen coils, and that ten coils are always cutting the lines of force directly
between the two pole-pieces-As each coil comes under the pole-piece an E. M. F.
rises in it, and as each passes from under, its E. M. F. falls-It is clearly possible
to place a brush opposite one pole-piece and another brush opposite the other of
just such width (i,e, touching just so many commutator plates) that they shall tap
the current from all the coils that have a useful E. M. F being generated in them
If the brushes entered too far to the sides from which the coils come under the
pole-pieces they will touch coils having too little or no E. M. F. and the more active
coils will be short-circuited through them: the same will happen if the brushes
extend too far in the other direction-On the other hand if the brushes do not
extend far enough in either direction coils will come into circuit or go out of
circuit when they are in a position to have, or while they are having a high E. M. F.
generated in them-In the latter case sparking will result; and in either case
there is loss; since the greater the number of coils active together, the less is the
resistance of the armature. It is clear that there must be a point between the two
extremes (i.e. a certain breadth of brush) where neither bad result occurs, and at
which the whole effectual current is utilized in the external circuit without
sparking. This is easily found by trial-The sparking is slight and not injurious
so long as the brushes err on the side of being too narrow rather than too broad
i.e. touching too few rather than too many commutator plates-All other coils
not under the brushes are on open circuit.
i

page_text: The number of independent coils should be as great as possible in order that the
resistance of each may be relatively high, and that each may carry but a small
portion of the whole current.
Both the ill effects above mentioned are thereby reduced to a minimum. More
than one coil may be wound in one pair of slots. The practical limit to the
number of coils is the number of segments into which it is possible or advisable
to divide the commutator. In order still further to increase the resistance of the
coil going out of or coming into action I may insert a resistance between each end
of the brush and the general body of the brush.
It will be seen that one of the brushes may touch as many as, but never more
than, half the commutator plates minus one. If the other brush touches the right
number, only the right number of coils will be in circuit. If the wider brush is
fixed the necessary lead or other adjustment can be given to the other-The movable
brush may be split into two halves by a plane at right angles to the axis of the
commutator. These two halves are to be capable of moving together or inde-
pendently in either direction round the axis. This arrangement will give
adjustment for breadth as well as for position relatively to the field. Each balf
should cover about two thirds of the arc under the pole-piece.
I do not confine myself to the use of the above method of winding and con-
necting to the commutator, with armatures of the special kind herein described.
They are applicable to the ordinary Siemens (or drum) armature on which the
conductor is wound so as to occupy the annular space surrounding the iron of the
armature. and not in slots as above described. In applying my winding to a
Gramme Ring (either with or without slots) it is necessary that the number of
distinct coils (sets of turns) of wire should be even. I take two opposite coils and
connect them together either parallel or in series, and then join the two terminals
so obtained to opposite plates of the commutator.
In my winding it is very important that the resistance of all the coils should be
as nearly equal as possible. In order to ensure this I proceed as follows. Suppose
there are to be 20 coils on the armature and 12 turns in each coil-I wind 6 turns
on 1, 2, 3 ... 19 coils and then wind the 20th coil full. I then finish winding in
the inverse order viz;-19, 18, 17... 2, 1.
'
It will be seen that the first balf of N° 1 has the shortest turns and the second
half the longest turns on the armature; and that all coils (sets of turns) will
average about the same. This method is also applicable to other forms of winding.
Doted this eleventh day of March 1985

page_text: Improvements in Dynamo Electric Machines and in
Electro Motors.
I, GEORGE HOOKнAм of New Bartholomew Street Birmingham, in the County
of Warwick Manufacturer, do hereby declare the nature of said invention for
"IMPROVEMENTS IN DYNAMO ELECTRIC MACHINES AND IN ELECTRO MOTORS,"
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:—
In a cylindrical armature similar to that described in my Specification No 7533
year 1884 having longitudinal grooves or slots in which the conductor is wound, so
arranged that the sum of the sectional areas of the ribs or ridges at one time under
a pole piece of the field magnets is equal or nearly equal to the magnetic section of
the rest of the armature, I find that a slot with parallel sides or walls, i,e. one of the
same width throughout is not always the best form. It is clear, for instance, that
the slots may be wider at the top, where they cut the surface of the cylinder, than
at the bottom; and so long as this difference is not so great as to inake the ribs
narrower (or thinner) at the top than they are at the bottom, their effective
maguetic section is not appreciably lessened. I accordingly sometimes make the
slots of this form, especially when I intend the armature to be wound with a great
many turns of small wire-I generally make the depth of the slots equal to from
one tenth to one eighth of the diameter of the armature-It will be found that in
a slot widening out in the manner and to the extent above described and in depth
bearing this proportion to the diameter of the armature, the width of the slot at
the top may be made so as to bear to its width at the buttom about the proportion
of three to two-Hence if the bottom of the slot will take two wires of a given
diameter side by side, the top will take three of the same wires-It is often much
more convenient for winding that the sides of the slot should not be slanting, as
the turns of wire keep their places better in grooves with parallel sides-Therefore
in the case instanced I should widen out the top of the slot to the extent indicated
to a depth sufficient to take one or two layers of wire, still keeping the walls of the
widened portion parallel, and forming a shoulder on each wall of the slot-It is
clear that this may be done without lessening the effective magnetic section of the
ribs Sometimes, when I use slots with straight sides (i.e. not shouldered in the
manner just described), after I have filled the slots with wire I wind a layer of wire
over the entire cylinder as in the ordinary Siemens armature-In this case the
maguets must be longer than when the iron of the armature passes as closely as
possible to the pole pieces-Each limb of the magnet or magnets must be from one
and a half times to twice the diameter of the armature, whereas with the other
forms of my armature a length of from one to one and a half diameters is sufficient―
When I wind an outside layer of wire as last described, if the slots are wound with
thick wire, I prefer to wind the outside layer with wire of such diameter that two
(or more) strands laid parallel have a total sectional area equal to or slightly greater
than that of the larger wire in the slots-In very large machines, or in those in

page_text: which only a low EM F is required as e.g. for electro-plating, instead of making
slots in the armature I bore holes from end to end at such distances apart and in
such positions as the slots would have been in the outer sides of such holes being
from a thirty second to a sixteenth of an inch from the surface of the cylindrical
armature-Insulated wires or rods of copper are passed into these holes, and their
ends connected either in the usual way or in a manner hereinafter to be described,
by means of insulated strips or sheets or wires of copper. In practice the holes are
punched in the discs of sheet iron of which the armature is composed at accurate
distances, so that when the discs are placed on the spindle the holes in one disc
come exactly opposite those on another. There is sufficient solid iron left between
the holes to give the requisite magnetic section to this part of the armature.
All these forms of armature may be wound according to known methods such as
those of Siemens Edison & others. But I have discovered a special mode of winding
applicable to them which I will now proceed to describe. I take an armature with
an even number of slots and a commutator with the same number of plates or
segments. In any slot and that opposite to it I wind as many turns of the conductor
as I find from experience will at a given speed give me the EMF I desire. The
two ends of this coil are connected, one to the nearest commutator plate, the other
to that immediately opposite to this plate. I treat every opposite pair of slots in
the same way and connect the ends of their coils similarly and in order to opposite
pairs of commutator plates; each coil being, so far, independent of every other
coil-In my armature practically the whole of the lines of force due to the field
magnets pass through the arcs at any one time opposite the pole pieces. It is
obvious that any one of the independent coils while passing a pole piece is cutting
lines of force and has an E. M. F. and that it has little or none as soon as it is clear
of the pole piece. Suppose there are 30 slots and therefore 15 coils, and that 10 coils
are always cutting the lines of force directly between the two pole-pieces. As each
coil comes under the pole piece an E. M. F. rises in it and as each passes from under,
its E. M. F. falls. It is clearly possible to place a brush opposite one pole-piece and
another brush opposite the other of just such width (ie, touching just so many
commutator plates) that they shall tap the current from all the coils that have
a useful E M F being generated in them. If the brushes extend too far to the sides
from which the coils come under the pole pieces they will touch coils having too
little or no E. M. F. and the more active coils will be short-circuited through them.
The same will happen if the brushes extend too far in the other direction. On the
other band if the brushes do not extend far enough in either direction coils will
come into circuit or go out of circuit when they are in a position to have, or while
they are having a high E M F generated in them. In the latter case sparking will
result; and in either case there is loss; since the greater the number of coils active
together, the less is the resistance of the armature. It is clear that there must be
a point between the two extremes (i.e. a certain breadth of brush) where neither
bad result occurs, and at which the whole effectual current is utilized in the external
circuit without sparking-This is easily found by trial. The sparking is slight and
not injurious so long as the brushes err on the side of being too narrow rather than
too broad i.e. touching too few rather than too many commutator plates.
All other coils not under the brushes are on open circuit.
The number of independent coils should be as great as possible in order that the
resistance of each may be relatively high and that each may carry but a small
portion of the whole current. Both the ill effects above mentioned are thereby
reduced to a minimum. More than one coil may be wound in one pair of slots.
The practical limit to the number of coils is the number of segments into which it
is possible or advisable to divide the commutator.
It will be seen that one of the brushes may touch as many as, but never more
than, half the commutator plates minus one. If the other brush touches the right
number, only the right number of coils will be in circuit. If the wider brush is
fixed the necessary lead or other adjustment can be given to the other.

page_text: I do not confine myself to the use of the above methods of winding and connecting
to the commutator, with armatures of the special kind herein described. They are
applicable to the ordinary Siemens (or drum) armature on which the conductor is
wound so as to occupy the annular space surrounding the iron of the armature and
not in slots as above described. In applying my winding to a Gramme or Pacinotti
ring (either with or without slots) it is necessary that the number of distinct coils
(sets of turns) of wire shall be even. I take two opposite coils and connect them
together either parallel or in series, and then join the two terminals so obtained to
opposite plates of the commutator.
In my winding it is very important that the resistance of all the coils should be
as nearly equal as possible. In order to ensure this I proceed as follows. Suppose
there are to be 20 coils on the armature and 12 turns in each coil. I wind 6 turns
on 1, 2, 3 ... 19 coils and then wind the 20th coil full. I then finish winding in
the inverse order viz:-19, 18, 17. . . 2, 1. It will be seen that the first half of
No 1 has the shortest turns and the second half the longest turns on the armature;
and that all the coils (sets of turns) will average about the same. This method is
also applicable to other forms of winding.
Figure 1 shows a section of an armature with a slot widening from bottom to top,
with slanting sides.
Figure 2 similarly shows a section of an armature, with a slot widening from
bottom to top; but with sides maintained parallel with one another, by means of
steps or shoulders.
Figure 3 shows a section of an armature with the conductor wound partly in the
slots, and partly on the general surface of the armature.
Figure 4 shows also a section of an armature in which the slots are replaced or
substituted by holes or tunnels extending lengthwise from end to end of the
armature, the said holes or tunnels being situated as near as practicable to the
peripheral surface of the said armature.
In Figure 5 N, S, represent the poles of a dynamo. a, b, a¹, b¹, are radial lines
drawn from the axis of the spindle to the extremities of the poles; the points at
which these lines cut the commutator indicate the number of sections that will at
one time be exactly opposite the pole pieces respectively. The sections numbered
from 1 to 30 represent the sections of the commutator; for clearness the armature
is omitted. In practice I slide place brushes, all in electrical connection with one
another, touching the sections numbered from 14 to 27 inclusive (=}n →≈) on the
underside of the commutator, and another similar set of brushes on the upper side,
which when the current in the external circuit is considerable would probably
touch the sections numbered 2 to 11 inclusive; but, as I have said, the exact
number and positions of these brushes I find by trial. I connect one main lead to
one set of brushes and the other to the other.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
First. In a dynamo electric machine slots, the armature, for receiving the
conductor, the same being wider at the top than the bottom, the sides being either
slanting or maintained parallel in the manner and for the purpose substantially as
described and illustrated in figures 1 and 2 of the accompanying drawing.
Secondly. In a dynamo electric machine, in place of slots, holes or tunnels
extend lengthwise, from end to end of the armature, in the manner and for the
purpose substantially as described and illustrated in figure 4.
Thirdly. The winding of the conductor on the armature, partly in slots, and
partly around the whole surface of the armature, after the slots have been filled
substantially as described and illustrated in figure 3 of the accompanying drawing.
Fourthly. The method of winding upon the armature a series of independent
coils, each of which has a sufficient number of turns to give the E M. F. required in

page_text: the machine, and so arranged in connexion with a series of brushes that all those
coils which are at one time cutting the principal part of the field, are connected in
parallel are with the terminals of the external circuit, in the manner fully described
but not illustrated.
Fifthly. The method of winding coils on an armature, by which the length of
wire in each coil is on the average made very nearly equal, by dividing them (all
except the middle coil or coils) into two parts, of which one part consists of shorter,
and the other of longer turns of wire, the shorter turns being wound on first, and
afterwards a joint being made and the coil finished by the addition of the longer
turns, in the manner fully described herein but not illustrated.