Improvements in Dynamo Electric Machines.
Year: 1889

page_text: Date of Application, 2nd Jan., 1889
Complete Specification Left, 28th Sept., 1889-Accepted, 9th Nov., 1889
PROVISIONAL SPECIFICATION.
Improvements in Dynamo Electric Machines.
I ARCADIUS POLESCHKO of Zakhariewvkaya Street St. Petersburg in the Empire
of Russia Gentleman do hereby declare the nature of this invention to be as
follows:-
This Invention has for its object improvements in dynamo electric machines.
The improved machine consists of an iron disc cut up in the direction of its radii
into a large number of narrow sections.
It revolves between pole pieces having the form of narrow sectors on the sides
turned towards the disc which sectors so to speak compress the magnetic flux along
the radius of the disc.
A collector consisting of two brushes side by side rubs on the periphery of the disc
and these can be adjusted to make and break contact with the radii of the disc as
they approach to and recede from the pole pieces either sooner or later as may be
required, this adjustment can be made independently in front of and behind the
pole pieces.
Another brush collector makes contact with the radii at their inner ends adjacent
to the axis.
CARPMAEL & Co.
COMPLETE SPECIFICATION.
Improvements in Dynamo Electric Machines.
I, ARCADIUS POLESOHKO, of Zakhariewvkaya'Street, St. Petersburg, in the
Empire of Russia, Gentleman, 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 :-
By arranging the experiment known by the name of Faradey's Disc in the manner
shown in Figure 1, it is known that the current generated in the disc will be directed
from the centre to the circumference.
The object of my invention is, (1st) to obtain in the radius of the disc subjected
to reduction as great an electromotive force as possible and (2ndly) to utilise in
the outer circuit the whole of the current generated in the said radius, so that
the difference of the potentials at the collectors (brushes) shall differ little from the
electromotive force and that no injurious or parasitic currents shall circulate in the
disc itself.
In order to attain the first part of this object, I proceed in the following manner:
It is known that if the directions of the passage of the current and of the lines of
magnetic force are perpendicular to each other (this condition is strictly fulfilled in
my machine), the electromotive force is in general given by the formula E = 1. V. H.
unities (C. g. s) = 1. V. 10 volts
(1), in which 1 and V respectively
P
8?
express the length and lineal velocity in centimetres-seconds, and H is the density or
tension of the uniform magnetic field. Now H = where P represents the entirety
of the magnetic flux circulating in the closed circuit of the electro-magnet and 8 is
the surface (in square centimetres) of the magnetic field in which this flux is
uniformly distributed.
In the ordinary machines with copper wire armature, the valve of H is incon-
siderable, and as the velocity V is limited, a sufficient electro-motive force is obtained
by increasing the length 1. But it is evident that, inversely, while leaving V with

page_text: the same value, a considerable electro-motive force could be obtained with a com-
paratively small length 1, by increasing the magnetic density H. For this it would
be necessary: 1stly, to generate in the core of the electromagnet a sufficiently strong
magnet flux. P, and, 2ndly, to concentrate. this, flux upon a small surface in the
magnetic field that is to say,, in the space between the opposite poles, or else between
a given pole and the iron core of a moveable armature, as occurs in most of the
existing machines. Designating by the transverse section of the core of the
electro-magnet (in. square centimetres), we shall. get h where h is the magnetic
density in the iron core of the electro-magnet; it is known that h cannot exceed 2000
to 2700 unities c:.g. s. (see G. Kapp "Electric Transmission of Energy" 1888
page 95), while H, i.e., the magnetic density, in air,, can, beyond all doubt, have a
much greater value.
Hence we must have > 8.
=
P
In order to obtain a very great magnetic flux (P), though the magnetising force be
somewhat feeble, I adopt the following means:
According to Kapp (ibidem, page 129) we have:
where is the air space between the iron pole and the iron core of the moveable
(rotating) armature. L' and L designate the mean lengths of the iron cores of the
armature and of the electro-magnet.
The coefficients of the second and third terms of the denominator are only correct
for small magnetic densities. They increase with the increase of the magnetising
force, and for high densities they become 15 to 25 times greater (according to
Shelford-Bidwell.), See also Hospitalier "Electrician's. Formulary" 1888 p. 179.
In employing a disc (Figure 1), '= 8; L' must be equal to about 15 millimetres
and may be equal to
millimetre.
If the disc is of copper, the second term of expression (2) vanishes, but in the first
term + L' must be put instead of 8. Under these. circumstances, the value of the
denominator will depend chiefly on the first term, and it will be pretty large.
If on
L'
the contrary the disc is of iron, the value becomes very small,, and by making
millimetre, the first term is also inconsiderable; the value of the denominator
will depend' upon the third term, which may become very small by making large
enough. Thus it will be seen that in order to obtain a considerable magnetic flux by
means of a feeble electromotive force, the disc must be of iron.
To determine the form to be given to the poles, in order to obtain the greatest
value of H, and to distribute this density in the magnetic field in the most
advantageous manner, I have had recourse to the following considerations:
Designating by a and a the radii of the axis and of the disc (in centimetres) and
by n the number of revolutions per second' (Figure 1) we get:
-
E=(a+a) 2n (a¹·— a) H=π (a¹³ — a²) n. H= S. n. H. unities c..g.,s..=
S. n. H. 10 volts (J.. Joubert, "Elementary Treatise on Electricity" 1889 page 295)
where S is the surface of the disc.
It is easy to see that the different radii of the disc constitute parallel derivations
from the circuit,, and that the value of the electromotive force depends upon the
length of one alone of these radii (or more strictly, the difference (a¹ - a). Hence,
in order to obtain the most favourable action, the magnetic flux P must be directed
upon the disc in such a way, that the radius which is between the collectors or

page_text: brushes (this radius is immoveable as regards space; as regards time, it will be
consecutively all the radii of the disc) traverses the greatest number of lines of force,
that is to say, the magnetic flux must be condensed in the direction of the radius; or
in other words, it must be directed upon the disc in the form of a narrow sector
and in the form of a very strong (dense) jet. Thus, on the side turned towards
the disc, the poles must have the form of a narrow sector, and the surface & of this
sector must be less than the surface
.
When these conditions are fulfilled, the electromotive force generated in the radius
will be very great.
The next essential question is how to collect this electromotive force..
Designating by
the internal resistance of the disc, we have as the difference of
the potentials at the collectors:
e = E-r. I.
As, of all the radii, only those are subject to, induction which are under, the polar
sectors, it follows that all the other radii are, with reference to the induced radii,,
merely simple external conductors, or, in other words, the induced (interpolar) part
of the disc would always be in two parallel and closed circuits, and notably (1st),
the exterior (useful) circuit R and (2nd) all the remainder of the body of the disc.
It is evident that the useful current would in that, case only form a very small part
of I, the product I would be large, and the difference of the potentials e would
only be an insignificant part of the electro-motive force E. There will result
therefrom in the outer circuit very few volts and few ampères; hence the electric
energy collected in the outer circuit would only form an insignificant, part of the
mechanical energy suspended in setting, the machine.in.motion.
The aspect of all this is entirely changed if the disc is cut radially, from the
circumference to the shaft, into a great number (from 60 to 100), of, thin sectors;
these sectors being insulated from each other by layers of air, can no longer
constitute the injurious circuit (2nd) and there will only remain the useful
circuit R.
Thus, to render the fall of the potential in the interior of the disc insignificant,.
and to avoid the diversion of the current in the interior of, the disc. (the injurious or
parasitic currents) the iron, disc must be cut radially, into a great number of narrow
sectors.
The lower collector (brush) must rest (slide) on a copper: (bronze) or iron, ring,
attached to the iron disc and insulated (as well as the disc) from the shaft ;. this
collector must be constructed in the same way, as in the ordinary machines with.
alternating currents.
The upper collector, resting upon. the circumference, of the disc, must, be in the
form of a comb and must touch every part of the circumference of the disc between
the poles, in order to collect the current from all the sectors, which are in the uniform
magnetic field (Figures 2 and 3). The action of the lower collector, opposed to the
disc cut into narrow sections; is the same as in the case of the ordinary Faradey's.
disc, but the upper collector will be differently circumstanced.
In the uniform magnetic field, there will always be 3 or 4 sectors of the disc, and
all the current will be distributed between them. At the moment when the first
sector leaves the upper collector, one of the 3 or 4 parallel circuits becomes open,
which is generally accompanied by a spark, and the latter will be all the larger in
proportion as the current is great in the circuit which has just been opened. In the
machine hereinafter described, the length of the upper collector is from 200 to
300 millimetres; hence, supposing that the sector, at the moment when it leaves the
collector, is not traversed by parasitic currents (when these currents can occur, they
sometimes become extremely powerful) but only by a. portion of the current generated
in the machine, it is evident that at the moment when the sector leaves the collector,
only a. very small part of the current (200, 300, 400.etc:) can pass across the edge of
the collector, so that, for that reason alone, the spark cannot be considerable.. But it.
is possible to avoid sparks altogether..

page_text: .
In point of fact, during the movement of the sector across the uniform magnetic
field, the sector is traversed by the current (useful) directed from the centre to the
circumference; but when this sector altogether leaves the magnetic field, it will offer
an external conduit, parallel to the outer (or working) circuit, and the current in that
sector will have the opposite direction, from the circumference to the centre (this
current is injurious or parasitic). Consequently there must be a moment when the
current in the sector is absolutely null.
Designating the electromotive force of the machine by E and the local electromotive
force engendered in the sector leaving the circuit by E¹, the total external resistance
between the collectors by R, and the internal resistance of the disc (the resistance
of the 3 or 4 sectors of the disc which are in the uniform magnetic field) by ra,
we can easily deduce from Kirchhof's equations that at the moment when
R
E' E
=
(3) the current in the sector leaving the circuit will be null.
R+
It is easy to seize this moment mechanically by varying the position of the upper
brush, by hand, along the circumference of the disc.
...
The entrance of the last sector (of the 3 or 4 sectors subject to induction) into the
circuit does not produce a spark. If this sector were introduced into the circuit not
at the moment determined by the equation (3), but a little later, it would have the
effect of increasing the internal resistance of the machine, and the machine would lose
for some moments a portion of the energy which it is capable of producing (this loss
would however be insignificant, and I only mention it for the purpose of giving a
more complete analysis of the phenomena which may arise); but if, on the other
band, the said sector is introduced into the circuit before the moment indicated, the
consequences will be very awkward, for the sector will then create the effect of a
short outer circuit and the current in it will be directed from the circumference to
the centre. It will therefore be seen that it is essential to introduce the sector into
the circuit, at the moment when the sector is deprived of current. This moment can,
just as well as in the preceding case, be seized mechanically by hand. The upper
brush must therefore be made in the form of two combs, placed side by side and able
to slide one on the other forwards and backwards from the line midway between the
poles (Figures 2, 3, 8 and 9).
By reason of electric inertia, the front end of the double upper brush must always
be advanced further than the back end; it will be seen therefore that the brushes
must have movement independently of each other.
Thus in order to avoid the spark upon the first sector leaving the circuit and to
obviate the injurious loss in the last sector introduced into the circuit, the upper
brush must be constructed in the form of two combs, moveable one upon the other,
in such a way that the common length of the double brush can be varied at either
end, independently of the other.
The construction of the machine. The electro-magnet is in the form of a horse
shoe. Its core A is cast out of soft steel in a single piece. The centre (indifferent or
neutral) part of the electro-magnet forms at the same time the support or foundation
plate of the machine, and the arms of the electro magnet at the same time take the
place of pedestals for the shaft B. This shaft rotates in steel bearings b, surrounded
by bronze or copper rings a a; the shaft B is of aluminous bronze.
The object of this construction is as follows: The shaft B traverses the poles of
the electro-magnet, and by making this shaft of bronze instead of steel, one avoids the
diversion of the 'lines of magnetic force in this shaft. The object of the bronze or
copper rings a a is to separate the shaft from the magnetic centre of the poles of the
electro-magnet. The steel bearings reduce the friction of the bronze shaft ; at
the same time they serve as a magnetic barrier or screen for the shaft, which they
protect against the magnetic forces in the event of a portion of the latter getting into
the space occupied by the bronze rings or collars. By this means, although the
shaft B traverses the poles, it cannot contribute to the diversion of the magnetic
forces and will not be traversed by lines of force; hence there is no fear of the
formation of Foucault currents in this shaft and of its heating.

page_text: The two poles or polar pieces C Care of the same form and are cast of soft steel;
they are fixed upon the corresponding arms of the electro-magnet by means of two
bolts cc each; (Figure 3). The form, in transverse section, of the pieces CC is the
same (as far as the line p. p Figure 2) as that of the core of the electro-magnet;
above the line p p, this form narrows gradually from bottom to top, remaining
always wider on the outside than on the inside (Figures 3, 4 and 5). The polar
pieces C at the same time take the place of caps to the pedestals (Figure 3).
The iron disc D, of small thickness, according to the number of ampères to be
obtained, is made in a single piece (it may be cast, wrought or hammered) and
electrically soldered (by the Benardos process) to the bronze nave d. The disc with
the nave d may equally as well be made, in one piece, of cast soft steel or of wrought
iron and a bronze ring then placed on the nave for the collectors. The complete disc
is then cut, by a suitable tool on the shaping machine or by means of a saw, in the
direction of its radii, into a large number (from 60 to 100) of narrow sectors, as
shown in Figures 3 and 6, and the outer circumference of the disc so cut out is
strengthened by means of a steel hoop e, perfectly insulated from the disc by layers of
asbestos paper. These details are clearly indicated in Figures 7, 8 and 9.
The bronze or steel nave d with the disc D, is fixed upon the aluminous bronze
shaft B, and carefully insulated from the shaft by layers of asbestos paper or other
insulating material. The nave d serves at the same time as a ring, on the cir-
cumference of which the lower collector rubs. The mode of construction of the upper.
collector is shown in Figures 2, 3, 8 and 9.
I reserve to myself the right of altering the details of the construction of the
machine above described, according to the suggestions of practical experience, without
in any way changing the nature of the invention.
Having now particularly described and ascertained the nature of my said Inven-
tion and in what manner the same is to be performed I declare that what I
claim is
1. The rotary induced piece of machinery or armature exclusively of iron, in the
form of an iron disc, cut up, in the direction of its radii, into a large number of
narrow sectors.
2. The polar pieces having the form of narrow sectors on the inner side turned
towards the disc and condensing, so to speak, the magnetic flux along the radius of
the disc; towards the outer side, these polar pieces widen out, so that they present
throughout a sufficient transverse section for the magnetic flux.
3. The system of the upper collector or brush in the form of two combs, side by
side and able to move independently of each other on the circumference of the disc;
for the purpose of introducing into the circuit and excluding therefrom the sectors
of the disc, at the precise moment of the absence of current in the corresponding
sectors, as is explained in the specification.
Dated th: 50th 1.
1000
CARPMAEL & Co.,
Agents for the Applicant.