IMPROVEMENTS IN MACHINES FOR GENERATING ELECTRO MOTIVE POWER
Year: 1885

page_text: I, ALPHONSE ISIDORE GRAVIER of Paris in the Republic of France, Engineer do
hereby declare the nature of my invention for IMPROVEMENTS IN MACHINES FOR
GENERATING ELECTRO MOTIVE POWER to be as follows:-
:-
The object of this invention is to increase, to a considerable extent, the
productive power of dynamo-electric or magneto-electric machines, of any
construction, for a given weight of material, (iron and copper) employed.
This invention consists in,-
1st The arrangement and development of the polar extensions and
2nd The employment of masses of iron in the armature, in determined proportions,
and under determined conditions.
•
Field Magnets. In the field magnets of all machines, as heretofore constructed,
large polar extensions have been employed; this may be proved to be a funda-
mental error.
It is now proposed to make the distance between the extremities of the polar
extensions equal to the length of the extensions themselves. The polar extensions
may be arranged either unsymmetrically or symmetrically, care being taken that
the distance between the extremities of the polar extensions is equal to the
development of these extensions.
The first improvement consists, therefore, in reducing the development of the
polar extensions, and making the distance which separates them, equal to, or more
than equal to, their length.
Every dynamo-electric machine composed of two parts, the one fixed, the other
movable, constitutes a complete magnetic circuit.
To obtain from this machine, of given weight, the maximum of useful effect, the
magnetic circuit formed by the two parts, should be completely closed, and for this
purpose the armature should be in contact with the field.
Now this perfect magnetic contact is not possible in actual machines, for
between the iron of the polar extensions of the field magnets, and the iron of the
armature, besides the play necessary for the movement of the armature, there
is always a certain thickness of wire which has to traverse the magnetic lines
of force.

page_text: But that which cannot be obtained by the action of contact, may be obtained
by increasing the sectional area of the armature core, by adding at the same time
to its two dimensions, breadth and thickness, doubling, trebling, quadrupling the
sectional area of the armature core in relation to that of the field, and the limit of
this enlargement is attained when the magnetic circuit it is intended to close, shows
no trace of exterior magnetism.
The minimum section of an armature is, then, that of the field magnets, and the
maximum depends on the distance which separates the iron of the field magnets
from the iron of the armature.
In the generation of electro motive force by dynamo electric machines, the
electro motive force is proportional :-
-
1 To the length of the armature wire;
2nd To the speed of displacement of this wire in the magnetic field;
3rd To the intensity of the magnetic field.
The mode of construction admits of the length of the wire being varied, at will,
for a given mass of wire.
The speed also, within certain limits, can be varied as desired.
To realise the third condition in a given machine, that is to say, to bring its
magnetic field up to a maximum of intensity, the armature should, as above stated,
completely close the magnetic circuit of the armature and the field magnets.
The second part of this invention consists, therefore, in giving to the armatures
of dynamo electric, or magneto-electric machines, sectional arcas equal, or even
superior, to those of the field magnets, in order to close the magnetic circuit as
completely as possible.

page_text: improvements in Machines for Generating Electro
Motive Power.
I ALPHONSE ISIDORE GRAVIER of Paris in the Republic of France, Engineer,
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 :-
The object of this invention is to increase, to a considerable extent, the productive
power of dynamo-electric or magneto-electric machines, of any construction, for a
given weight of material (iron and copper) employed.
This invention consists in,-
1st The arrangement and development of the polar extensions; and
2nd The employment of masses of iron in the armature in determined proportions,
and under determined conditions.
In the field magnets of all machines as heretofore constructed, large polar
extensions have been employed; this can be proved to be a fundamental error;
Figs. 1, 2, and 3 will render this error palpable.
Fig. 1 is a diagram shewing the lines of magnetic force of a system of excited
field magnets A and B, the armature a, b, being in a neutral condition. Here all
is regular and symmetrical; the lines of force emitted by the field A, in order to
penetrate into the field B, enter perpendicularly into the iron of the ring b, a, and
come out of it also perpendicularly after having traversed the two halves of the
ring. The ring thus becomes an electro-magnet with two consequent poles.
Fig. 2 is a diagram shewing the lines of force when the ring is traversed by a
current which enters by means of a brush placed at the point b¹, and goes out by a
second brush placed at the point a¹, the field magnets A and B being in this case
in a neutral condition. This diagram shews clearly the way in which the field
magnets A and B are influenced by the electro magnetic ring a, b, and it will be
readily seen that these field magnets cannot act like the electro magnets of Fig. 1,
since each of them possesses two opposed poles.
Fig. 3 shews a diagram of the lines of magnetic force resulting from the passage
of a current through the field magnets and armature at the same time. The
distribution of the magnetism, in this case, is considerably modified; the symmetry
of Fig. 1, as also that of Fig. 2, is entirely destroyed. It will be seen that the lines
of force of the field magnets, and the armature respectively, are added together in
the part of the field magnets between A A¹ and B B¹, and, on the contrary, repel
each other in the parts between A A² and B B². In the two parts A A', B B¹
where these actions are in accordance, and are added together, the lines of force
will traverse the wires of the armature perpendicularly; on the contrary, in the
two other parts, they will traverse the wires very nearly parallel.
If an armature is caused to rotate under these conditions, it will be found that
the induction is very strong in those parts where the lines of force of the field and
armature combine, and very feeble, or nil, or even of opposite sign, in the parts
where they meet in opposition, and nullify each other.

page_text: As the parts A A and B B2 of the field magnets are thus obviously detrimental'
they may be suppressed, and we thus arrive at the form shewn in Figs. 4 and 5.
These figures show the polar extensions reduced one half, the distance between
the extremities of the polar extensions being equal to the length of the extensions
themselves. The polar extensions may be arranged unsymmetrically, as shewn in
the figures, or symmetrically, as shewn in Fig. 7, care being always taken that the
distance between the extremities of the polar extensions A and B is equal to the
development of these extensions.
The first improvement consists, therefore, in reducing the development of the
polar extensions, and making the distance which separates them equal, or more
than equal, to their length.
The cores of the armature are generally formed of iron wire, or of plates of sheet
iron, and are usually regarded as screens for impeding the action of the field
magnets upon the inner layers of wire of the armature. They are made of various
thickness and sectional form. If the sectional areas of the armature cores are
compared with the sectional areas of the field magnets, it will be found that they
usually vary from th to the smaller.
There is no settled agreement as to the proportion of iron that should be used for
the core of the armature. It is generally admitted that it is requisite to employ
but little of it, and special arrangements have even been made in which iron is
absolutely excluded from the armature.
By analysing the working of a dynamo, it will be seen that its armature core
acts as a magnet, and without this core, the induction in the enveloping wire
would be insignificant. On the contrary, if the core is there, the wire which
covers it is the seat of an electro-motive force which becomes greater and greater
in proportion as the sectional area of the core is increased.
In a Gramme machine, for example, if the thickness of the armature core be
doubled, the electro-motive force will be doubled (all the other conditions of the
machine remaining the same). If the thickness of the iron be trebled, the electro
motive force created will be trebled also; by increasing yet more the thickness of
the core, the electro-motive force will also be increased, but not in the same
proportion as the thickness of the core is increased.
The following is the explanation of this:-
When a given current of electricity circulates in a given mass of wire, around a
given mass of iron, the resulting magnetic circuit in the iron has its maximum of
force when the circuit is completely closed.
This particular condition of an electro-magnet, or closed magnetic circuit, is
shown in Figs. 8 and 9 of the drawings. The dotted line in Fig. 8 represents the
lines of magnetic force developed in the iron by the passage of the electric
current, that is to say, entirely within the interior, and having no exterior
manifestation.
If the magnetic circuit be cut at A. and B, as indicated in Fig. 9, a magnetic
circuit would be formed in the air. For a given current, the mass of copper and
the mass of iron remaining the same,-the magnetic circuit would be reduced to a
minimum strength.
Between these two extreme states, a series of intermediate states may be found,
the value of which depends only upon the quantity of iron employed to close the
magnetic circuit.
With an equal sectional area, the armature A, B can only close the magnetic
circuit, and thereby create a maximum, when there is perfect contact between it
and the electro magnet; the maximum can only be otherwise obtained by increasing
the two dimensions (breadth and thickness) of the armature.
It will now be shown how these principles are applied to various constructions
of dynamo-electric machines.
In every dynamo-electric machine which is composed two parts, the one being
fixed and the other movable; a complete magnetic circuit is established.

page_text: To obtain from a machine, of given weight, the maximum of useful effect, the
inagnetic circuit formed by the two parts should be completely closed, and for this
purpose the armature should be in contact with the field.
This perfect magnetic contact is of course not possible in actual machines, as
there is always a certain thickness of wire which has to traverse the magnetic
lines of force between the iron of the polar extensions of the field magnets, and
the iron of the armature, besides the play necessary for the movement of the
armature.
But that result which cannot be obtained by actual contact, may be obtained
by increasing the sectional area of the armature core, by adding to its two
dimensions (breadth and thickness), doubling, trebling or quadrupling the sectional
area of the armature core in relation to that of the field, the limit of this enlarge-
ment being attained when the magnetic circuit it is intended to close, shows no
trace of exterior magnetisın.
The minimum sectional area of an armature is therefore that of the field
magnets, the maximum area depending on the distance which separates the iron
core of the field magnets from the iron core of the armature.
In the generation of electro motive force by dynamo-electro machines, the
clectro motive force is proportional :-
1st To the length of the armature wire;
2nd To the speed of displacement of this wire in the magnetic field; :
3rd To the intensity of the magnetic field.
The mode of construction admits of the length of the wire being varied, at will,
for a given mass of iron.
The speed also within certain limits can be varied as desired.
To realise the third condition in a given machine, that is to say, to bring its
magnetic field up to a maximum of intensity, the armature should, as above stated,
completely close the magnetic circuit of the armature and the field magnets.
The second part of this invention consists, therefore, in giving to the armatures
of electrical generating machines, sectional areas equal or even superior to those of
the field magnets, in order to close the magnetic circuit as completely as possible.
The combination of these two conditions will now be described, with details of
construction which will permit of a machine of given weight producing an electro
motive force, four or five times greater that it would otherwise produce.
It will also be understood that these machines, being, like other dynamo or
magneto-electric machines, reversible, the principles above enunciated are equally
applicable to electro motors.
The following is a description of a machine in which the improvements above
set forth will be found carried out in a practical manner, it being understood that
the principles above enunciated are applicable to other kinds of dynamo or magneto-
electrical generators.
In the accompanying drawings, Fig. 10 is a front elevation of the machine,
Fig. 11 is a section taken in the line 1. 2 of Fig. 10, and Fig. 12 is a plan view.
This machine is shown as it has actually been constructed, and some of the
results of experiments with it will hereafter be described. The machine is composed
of field electro-magnets and a ring armature.
The field magnets comprise two cylindrical electro magnet cores A, B, having a
diameter of 100/m, and consequently a sectional area of 7854/m².
The cores are enlarged in the middle to 180/m, and are bored out transversely
and thinned, as shown at Fig. 10, the enlarged and bored out part in the middle
forming the polar extension which is intended to act upon the armature ring; its
proportions are such that the distance apart of the points a, b and a¹, b' is the
same as the distance apart of the extremities a a and b b¹ of the polar extensions.
The cores of the field magnets A, B are connected together by two cast iron
standards C C mounted upon the bed plate so as to admit of the ready removal of
the armature ring, should that be found necessary.

page_text: The armature ring is shown in front view, and in place, in Fig. 10.-It is formed
of plates of soft sheet iron arranged perpendicularly to the axis. The sectional
area of this core is 18564/m², so that the ratio between the sectional area of the
armature and that of the field magnets
18564
7854
= 2.35.
93
=
The complete machine weighs about 800 K, and furnishes, at 600 revolutions,
800 = 8 60
93 horses, which gives
129.6 volts and 530 ampères; its work therefore =
of material per horse; if the machine had been constructed in the usual way, it
would have only been equal to 18 horses. Now the lightest machine known
requires, in order to produce 18 horses exteriorly, at least the same weight of
800
matter, 43* per horse.
It is therefore evident, by comparison of the results furnished by the machine
above described, and by machines of ordinary construction, that the theory
generally admitted of electrical generating apparatus, is not applicable to machines
furnished with these improvements, such theory ignoring the enormous influence
exercised upon the distribution of the magnetism in the apparatus by the
armature ring, when that ring is of considerable dimensions.
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
1. The employment of symmetrical or unsymmetrical polar extensions so
arranged that the distance between their extremities shall be equal to their extent,
as explained.
2. The employment, in armatures of electric generators, of cores formed of iron
wire, or of discs of sheet iron, of a sectional area equal or superior to that of the
field magnets, as above described.