Year: 1886

page_text: Date of Application, 31st Dec., 1886
Complete Left, 6th Sept., 1887
Complete Accepted, 27th Dec., 1887
We ROOKES EVELYN BELL CROMPTON of the Arc Works Chelmsford, in the
County of Essex, Electrical Engineer, and JAMES SWINBURNE of the Arc Works
Chelmsford aforesaid, Electrical Engineer, do hereby declare the nature of this
invention to be as follows:-
In dynamo electric machines as at present constructed a large proportion of the
magnetising force due to the wiro on the field magnets is spent on overcoming the
air resistance between the poles of the field magnets, and the armature. This air
space has been generally necessary to allow the armature wire to be wound on.
Where it has been reduced by using projections, as for instance in the Pacinotti ring,
heating of the poles and the field magnets is caused, but according to our invention
dynamo electric machines may be made which have a very small clearance between
the armature and the field magnets so that a very small magnetising force on the
field magnets is necessary to magnetise the armature nearly to saturation.
Take for instance the case of a ring or as it is sometimes called a cylinder armature.
such as that used in the well known "Crompton dynamo." A space is here allowed
between the outside of the armature and the pole pieces sufficient to admit of the
requisite amount of wire being wound on. According to our present invention the
wire is not wound on the outside of the armature but passes through holes which are
punched through the discs near the outer edges. Only enough clearance is then
allowed for the armature to turn round freely. These holes in the discs are punched
at such distances apart that there is enough section of iron between them to admit
of the induction due to the field magnets. In small machines they may be made
round for convenience of drilling or punching, but in larger machines they are
preferably made rectangular, or with their sides radial. The iron left on the outside
of these holes is thick enough to make the field between the field magnets and the
armature practically uniform so that no Foucault currents are generated. But it is
also kept thin enough not to waste too much induction round the sides of the
armature, because the induction that goes down this part of the iron is wasted as far
as producing E.M.F. If these holes were not covered over but were simply
external grooves the area of the outside of the armature that was close to the field
would be small. In addition to this Foucault currents would be formed. Instead of
୮

page_text: making the holes rectangular, we sometimes make the outer end of them pointed so as
to reduce the thickness of the iron outside at one point thus lessening the waste of
induction.
The armature thus resembles the Pacinotti armature with iron arranged outside
over the tops of the teeth. Such a machine as this takes generally about 5th of
the magnetising force round the fields.
In a drum armature, the outside is made practically the same except that more space
is allowed between the holes, as the radial depth of the iron is then greater, because
there is no wire going between the inside of the discs and the spindle.
The iron discs are brought close to the axle, just allowing sufficient air space to
admit of the ventilation of the armature. The wires or sets of wires, or coils may be
wound right over the ends as usual in drum armatures or it may be wound over a
chord of the circle or end plates may be used such as are described in the specification
lodged at the Patent Office in pursuance of an application for Letters Patent
No. 15484 made by me the said James Swinburne on the 17th day of December
1885.
Our invention is really applicable to a very large number of types of armatures.
For instance we can take an armature such as used in the old Wallace machine. This
machine had very little clearance between the armature and the fields, but of course
the Foucault currents in such an arrangement were very great. By bridging the
ends of the armature chords over with iron, we not only avoid these Foucault
currents, but we get a larger available polar area. We should not actually make an
armature like this. It is simply explained now as a typical form to give a clear idea
of what our invention really is.
Another form of machine made according to our invention is a ring armature of
square section. The field magnets take the form of thick slabs which cross the sides
of the ring so that the axle goes through the centre of the magnets. The magnets are
magnetised so that the north end of one comes opposite the south end of the other, so
that the induction is through the ring axially, not round the sides of the ring as is
the case in the ordinary ring armature. The wire of the armature is then passed
through holes bored radially in the ring. The wire which comes out at one hole
passes round the periphery of the ring, say 3rd of the circumference and then
passes in at another hole, crossing over inside to the first hole again and so on.
an armature is not made up of discs but of flat iron wound concentrically. As the
field magnets of these machines made according to our invention require very small
magnetising force, very little space is necessary for the wire, they therefore become
very much smaller than those in ordinary use.
Such
Machines made according to our invention have also another great advantage. The
driving of the wire is not dependent on friction, or on strong insulating material, as
it leans against the sides of the holes, and cannot slip.
Dated the 31st day of December 1886
WM. BROOKES & SON,
55 & 56, Chancery Lane, London,
Agents for the Applicants.

page_text: We, ROOKES EVELYN BELL CROMPTON, & JAMES SWINBURNE, of Arc Works
Chelmsford, Electrical engineers, do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
In a dynamo, as at present usually constructed a large proportion of the magnetising
force due to the wire on the field magnets is spent in overcoming the air resistance
between the poles of the field magnets and the armature. This air space has been
generally necessary to allow the armature wire to be wound on. Where it has been
reduced by using projections, as for instance in the Pacinotti ring, heating of the
field magnet poles is caused, but according to our invention dynamo machines may be
made which have a very small clearance between the armature and field magnet poles,
so that a very small magnetising force on the field magnets is sufficient to magnetise
the armature nearly to saturation.
Take for instance, the case of a ring, or as it is sometimes called, a cylinder
armature, such as that used in the well known Crompton dynamo. A space is here
arranged between the outside of the armature and the pole pieces to admit of the
requisite amount of wire being wound on. According to our present invention the
wire is not wound on the outside of the armature, but passes through holes which are
punched through the discs near the outer edges. Only enough clearance is then
allowed for the armature to turn freely. These holes in the discs are punched at such
distances apart that there is enough iron between them to admit of the induction duo
to the field magnets. In small machines they may be made round for convenience in
drilling or punching, but in larger machines they are preferably made rectangular or
with their sides radial, or nearly radial. The iron left outside these holes is thick
enough to make the field between the field magnets & the armature practically
uniform, so that no Foucault currents are generated in the pole pieces; but it is at the
same time kept thin enough not to waste too much induction round the sides of the
armature, because the induction round this part of the armature is wasted as far as
producing electromotive force is concerned. If instead of holes, grooves were used
the armature would resemble the Pacinotti form, & Foucault currents would be
produced in the poles; the surface of iron exposed to the fields would also be loss,
which is of some consequence, as there must always be some clearance, so that there
must always be some magnetising force spent on the air space. Instead of making
the holes rectangular we sometimes make the outside pointed so as to reduce the iron
as much as possible without interfering with the uniformity of induction in the pole
pieces. Instead of using holes we sometimes make an armature like the Pacinotti &
wind iron wire outside after the copper is in place. A light cut may be taken off in
the lathe to make the surface true. This method give greater case in winding.
Fig. 1 of the accompanying drawings is a diagrammatic view of a direct current
dynamo according to our invention. a a is the armature built up of discs in the usual
way. bb are holes for the active wire. A few only are shown. The wire is wound

page_text: through the spaces ee if the armature is wound as in a Gramme machine, or over the
ends if the drum winding is used. ccare the field magnets & d d the field magnet
coils wound round the field magnets. It will be obvious that the whole machine is
very much lighter than those generally constructed, because the field magnets are so
small in proportion to the armature. The machine is also more efficient because less
power is spent on the field excitation. The ampère turns on each field magnet should
be greater than the ampere turns on the part of the armature included between the
points, by an amount which will more than produce the necessary induction when
there is no armature coruent. If the corners of the pole picces ff are brought closer
together the ampere turns needed will be less, but this leads to difficulties in construction.
The machine here shown has what are known as double magnets. Single magnets
might have been used but they would have been much heavier and the machine would
be more liable to spark. The saving in power spent in the field-magnets would
have been very small. Instead of winding the wire round the field magnets it might
have been wound round the armature, but, unless the armature is very long, there is
no saving in doing so.
The pole pieces 9 g. are made just large enough not to be saturated by the induction
due to the field magnets and they are thinned down as shown to reduce the cross
induction as much as possible otherwise the lead of the brushes would be excessive or
the machine would spark. For the same reason the area of iron between the holes is
so proportioned that that part of the magnetic circuit is saturated first by the fields.
We call the induction due to the armature current round such circuits as that shewn
dotted at y the cross induction. The induction due to the armature current which
opposes the field induction & with an unexcited field would be round such a circuit as
that shewn dotted at z interlinked with the field wire we call the back induction.
Theoretical investigations of the action of the armature currents in machines have
led us to the conclusion that such means as these will not be quite effective in large
machines as the difficulties are much increased by the absence of the air space. The
results of our investigations are embodied in another application for Letters Patent
but they apply to this form of machine as well as to others. In Fig. 2 is shewn
what we call reversing pole pieces h h. These are so arranged that in spite of the
action of the armature current, they produce a field which reverses the current in
the sections of wire short-circuited under them by the brushes. The reversing pole
pieces h. h may have coils wound round them, or they may have the field coils wound
more on one side of them than the other, as shewn in the figuro. The excitation
of the field is less in this form of machine as there is no back induction. The arrow
in Fig. 2 shews the direction of rotation of the armature as a dynamo. As a motor
it runs in the opposite direction or else the large & small magnets coils are exchanged.
Fig. 3 shews a machine with no magnet coils proper. The brushes are given a
negative lead so as to be under the reversing pole pieces shewn at h h. These pole
pieces are wound with coils of wire i i. The arrow shows the direction of rotation as
a dynamo, as a motor it is reversed. This is most suitable for large machines. We
are aware that it has been proposed to give brushes a negative lead to make dynamos
compound" without series field winding, but the sparking was to be reduced, or is
reduced by resistance arrangements.
66
According to our arrangement the field has no wire round it & the machine
behaves as a series dynamo, & there is no sparking at the brushes. The coils h h
are preferably in series with the armature though they may be in shunt. If the
reversing poles have a small lead the fields may have a shunt winding & the dynamo
may then be made to compound without series field wire & without sparking.
Fig. 4 show a four pole machine. There are two polar faces to cach pole piece &
they are made substantially as shown so that there may be little cross induction
& little lead of the brushes. A four pole machine might of course be made with
two magnets only each of the horseshoes being wound with one coil of wire but as
four pole machines are used when lightness or large out-puts are desired such an
arrangement would be had. The holes & perforations in the armatures are not
shown in Figs. 2, 3 or 4.

page_text: They are like those in Fig. 1.
Six or more poles may be used.
For alternating current machines our invention is specially applicable. Fig. 5
shews an eight pole machine. There are eight holes in the armature. These are
shaped substantially as shewn so that when the armature is rotated there is the same
induction through the field magnets whatever the position of the armature holes.
This overcomes one of the chief difficulties in alternating current machines, as it
admits of iron in the armature without heating of the field magnets. Instead of
a-a. being the arinature that is to say the part wound with wire in which the alternating
current is generated the parts shewn as field magnets may be used. The field magnets are
then rotated inside the armature. The parts cc should then be laminated. The field
magnets or rotating part may be made of a solid piece of wrought or even cast-iron.
Fig. 6 shews another disposition of the stationary part. If is not so efficient
electrically but has certain mechanical advantages. The stationary parts in Figs. 5 & 6,
may be built up of punched pieces of sheet iron when they form the armature. Even
when they form the field magnets it may perhaps be advisable to laminate them in
large machines as the cross induction varies.
The wire may be wound through the holes & back through the large central hole
but we prefer to wind its backwards and forwards through the holes a a so that each
neck of iron between neighbouring holes is surrounded by a coil of wire whose section
occupies half the area of one hole. Instead of this arrangement the whole of the
wire may be wound round alternate necks so that with an eight pole machine as shewn
in Fig. 5 there are four coils of wire on the moving part.
Fig. 7 shews a machine with the holes in the outer part.
The outer part then forms the field magnets preferably, as the rotating internal part
can be easily punched from thin discs. The wire is wound through the holes b. b as
before. The wire on the rotating part is wound as in an armature of the Pacinnotti
type, except that it gives alternating currents as there are as many field magnet poles
as armature coils. The stationary part may be made of cast iron.
There is difficulty in starting alternating current motors as at present constructed.
To overcome this difficulty we laminate both the armature and field magnets. The
armature is provided with a commutor, as if it were intended to give intermittent
direct currents when excited separately as a dynamo. Thus an eight pole machine
such as that shewn in Fig. 4 has the two ends of its armature circuit connected to
eight sections, of which four are connected to cach. In some cases we use an exciter
also. The motor is run light with its fields excited by the alternating current till it
has reached a high enough speed. A switch then alters the connections and throws
the exciter into circuit.
The exciter itself may be made with laminated field magnets. To start the motor
When
the exciter is fed with the alternating current & drives the motor proper.
sufficient speed is attained switch is moved altering the connections.
In designing such alternating current motors with laminated field magnets to be
shunt wound care must be taken that the armature and field magnets have their self
induction properly proportioned. This demands more cross induction than can easily
be got in machines as now generally constructed, but in machines with almost no air
space there is no difficulty.
Fig. 8 shews a direct current machine with internal rotating field magnet on the
cc is the rotating
same principle. a a is the armature, and 6 6 the holes for the wire.
field magnet, with one exciting coil, and two poles. The armature is wound as in the
Gramme ring, and is formed of thin discs of soft iron. The brushes rotate with the
field magnets. Such a machine as this tends to spark badly; reversing. poles may
therefore be arranged on the revolving field magnets, though not shewn in the
diagram. The output of such a machine can be made enormous in proportion to the
weight of the moving part. The machine may be made with four or more poles, but
we prefer two as shewn.
Even in machines in which the armature is revolved, and in which weight is not of
primary importance, we often use what are known as single magnets, and we provide
them with reversing pole pieces. With a drum armature one reversing pole piece is

page_text: sufficient. With a ring armature it is generally more convenient to use two with
negative lead, so that they are easily arranged on the field magnets.
Since filing our application for provisional protection our notice has been called to
the previous publication of a description of a dynamo with the armature wiro wound
through holes near the periphery. Though this arrangement was probably made with
the view of reducing the air space, no attempt was made at reducing the size of the
magnets, or the power spent in them by this means. The magnets were apparently
designed with the view of surrounding the field magnet coils with iron as completely
as possible, with the idea that by such an arrangement each ampère turn would
somehow have greater magnetising force. This is a common fallacy among dynamo
makers.
We may also state that we are aware that machines with internal revolving magnets
have been made, but not with the wire through holes. They have probably been made
with the object of surrounding the field magnet wire with iron, but they are apt to
give trouble by sparking, and Foucault currents, or to demand considerable magnetising
force on the field magnets.
Having now particularly described and ascertained the nature of our said invention,
and in what manner the same is to be performed, we declare that what we claim is:
In a direct current dynamo or motor:
1. The combination of an armature with the conductors wound through holes ; small
air space; and relatively small field magnets.
2. The combination of an armature with the conductors wound in holes substantially
as described; and field magnet coils of comparatively few ampère turns.
In a direct current dynamo or motor with the armature wire wound through holes :
3. The field magnet poles so formed as to reduce the cross induction, substantially
as described and set forth.
.
4. A Reversing pole piece, or reversing pole pieces.
5. Reversing pole pieces with negative lead.
6. A field magnet or magnets which rotate.
7. A field magnet or field magnets which rotate inside the armature, substantially
as described.
In an alternating current machine:
8. An armature with the conductor wound through holes, substantially as described.
9. An armature with the conductor wound through holes so proportioned that the
induction in the field magnets is constant, or almost constant, substantially as
described.
10. The combination of a stationary part with its conductor wound through holes,
and a rotating part, either being the armature, substantially as described.
Dated this Fifth day of September 1887.
JAMES SWINBURNE.
R. E. B. CROMPTON.