Improvements in Alternating Current Electric Motors.
Year: 1894

page_text: Date of Application, 11th Apr., 1894-Accepted, 9th June, 1894
COMPLETE SPECIFICATION.
Improvements in Alternating Current Electric Motors.
I, CARL COERPER, of Cologne-Ehrenfeld, in the Empire of Germany, Director,
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 :-
My invention relates to alternating current electric motors.
It is well known that a rotary iron disc will move under the action of
alternating magnet poles if the latter are suitably arranged. The iron disc has
however but a small tractive power and has no synchronous movement; it often
revolves somewhat more rapidly, but as a rule more slowly than corresponds to the
synchronous movement.
By a synchronous movement is understood exactly the speed or half the speed of
rotation which corresponds to the number of the changes of pole. If for instance
the current generator has 60 poles and makes 100 revolutions a minute the current
receiver with 20 poles must perform 300 or 150 revolutions if it is to exert tractive
power. As is well known, this is not so in the case of current receivers with
alternating phases; in fact, when they are loaded a reduction takes place in the
speed of rotation so that perfect synchronism is not obtained.
These inconveniences are obviated by my invention.
In the accompanying drawings Figures 1 and 2 are diagrams showing two
arrangements of my improved electric motor.
A star-shaped mass of iron or armature a composed of a number of iron plates is
arranged to rotate. Two neighbouring arms of the armature, Figure 1, are
subjected to the action of alternating magnet poles. As soon as the armature
attains synchronous movement it exerts a considerable tractive power and maintains
an exactly uniform rotation corresponding to the changes of pole.
The arrangement may also be as illustrated in Figure 2. In this case all the
arms of the star-shaped armature are subjected to the action of alternating magnet
poles. Of course the form of the magnet poles and of the field magnet must be
adapted to the object in view. Use may be made of a closed or an open magnetic
field, and also one with shaped pole pieces. The field magnet may also be arranged
inside and the star-shaped armature outside.
This phenomenon need not be ascribed to the known occurrences in the
alternation of the phases, in fact it is explained simply by the following con-
siderations. When the poles of the field magnet, Figure 2, are changing opposite
poles are induced in the arms of the star-shaped armature. When the changes of
pole succeed each other slowly in the field magnet the polarity of the armature has
time to follow changes and the armature will not therefore rotate. But as soon as
the changes of pole succeed each other so rapidly that the magnetism produced in
the armature is still active when other poles have already been produced by the
current round the field magnet, a repulsion must take place between the magnetism
produced by the action of the current in the magnetic field and the inagnetism of
the same name which is still active in the armature, whilst at the same time the
neighbouring opposite pole of the field magnet exerts a tractive power. If the
current receiver is now rotating at a synchronous or half synchronous speed
the armature will always pass with full power from the polar field of the same name
into the polar field of the opposite name. It therefore depends on the number of
changes of pole, the strength of the magnetic field and the mass of iron of

page_text: the armature whether the conditions of working are
synchronism.
best with full or half
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 :-
An alternating current motor having a bare star-shaped iron armature, in which
two neighbouring arms of the star are subjected to the action of alternating
.magnetic poles.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.