Improvements in Alternating Current Machines.
Year: 1895

page_text: Date of Application, 15th June, 1895
Complete Specification Left, 14th Mar., 1896-Accepted, 18th Apr.,
18:6
PROVISIONAL SPECIFICATION.
Improvements in Alternating Current Machines.
We WALTER CLAUDE JOHNSON of 14 Union Court, Old Broad Street in the
City of London, and Louis JOHN STEELE of 14 Clarendon Road, Holland Park,
in the County of London, Electrical Engineers, do hereby declare the nature of
this invention to be as follows:-
:
This invention relates chiefly to that class of alternators which has a stationary
armature and rotating field magnets or inductors. When the armature contains
iron it is usual to build it up of sectors on which the coils are wound, thus obtaining
the advantage of the easy withdrawal or replacement of any coil. The joints
between these sectors are in some cases faced butt joints, and in others en actual
air gap is left, thus forming a discontinuity in the iron path for the magnetic
field.
The effect of this butt-joint or discontinuity is to produce variations in the
magnetic induction through the magnets which will have the effect of producing a
loss of power due to eddy currents and hystereisis in the magnets themselves unless
they be thoroughly laminated.
For the purpose of preventing this fluctuation of the magnetic field, we so
construct the sectors that the air gap between the field magnet poles and the
armature is not the same at different points, these gaps being so adjusted that the
magnetic resistance at each point is constant thus ensuring a constant magnetic
field through the magnets. According to one arrangement for this purpose, we
make the inner surface of the combined sectors polygonal, instead of circular, or of
such shape that at the joints between the sectors, a greater gap exists between these
and the field magnet poles, than the gap existing between these parts when the
poles are opposite the iniddle of the sectors.
Dated this 15th day of June 1895.
ABEL & IMRAY,
Agents for the Applicants.
COMPLETE SPECIFICATION.
Improvements in Alternating Current Machines.
We, WALTER CLAUDE JOHNSON, of 14 Union Court, Old Broad Street, in
the City of London, and LOUIS JOHN STEELE of 14 Clarendon Road, Holland
Park, in the County of London, 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 :-
This invention relates chiefly to that class of alternators which has a stationary
When the armature contains
armature and rotating field magnets or inductors.
iron it is convenient to build it up of sectors on which the coils are wound, thus
obtaining the advantage of the easy withdrawal or replacement of any coil. The
joints between these sectors are in some cases faced butt joints, and in others an
actual air gap is left, thus forming a discontinuity in the iron path for the magnetic
[Price 8d.1

page_text: field. Such a construction is described in the Specification. to Kapps Patent
No. 17341 of 1893.
The effect of this butt-joint or discontinuity is to produce variations in the
magnetic induction through the magnets which will have the effect of producing
a loss of power due to eddy currents and hystereisis in the magnets themselves,
unless they be thoroughly laminated.
For the purpose of preventing this fluctuation of the magnetic field, we so
construct the scetors that the air gap between the field magnet poles and the
armature is not equal at different points, these gaps being so adjusted that the
magnetic resistance at each position of the pole is constant or nearly so, thus
ensuring a constant magnetic field through the magnets.
According to one arrangement for this purpose, we make the inner surface of the
combined sectors polygonal, instead of circular, or we make it of any other shape
whereby, at the joints between the sectors, a greater gap is made to exist between
tbese and the field magnet poles than the gap existing between these parts when
the poles are opposite the middle of the sectors.
Fig. of the accompanying drawing shews by way of example a vertical section
of part of an alternating current machine constructed according to this invention,
in which a stationary armature is built up of sectors A A, the inner faces a a of
which are formed so as to produce a polygonal shape for the inner surface of the
armature so that as the field magnets B B revolve, a greater gap b will exist
between their end surfaces and the inuer face of the armature when they arrive at
the angles of the polygon, where the butt joints between the sectors are situated,
than the gap between them when in the other positions, as shewn more clearly
by the full and dotted positions of the field magnets in the enlarged view at
Fig. 2.
Although we have described our invention as applied more particularly to
machines with external armatures and internal field magnets, yet it is obvious that
it is equally applicable to machines with reversed arrangement of these parts, in
which case it would be the external surface of the armature built up of separate
sectors that would be formed so as to provide a greater gap between it and the
field magnet poles at the butt joints of the sectors than at the other parts.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
In alternating current machines having an annular armature built up of separate
sectors, so constructing the surfaces of such sectors that are presented to the field
magnet poles that at the joints of the sectors a greater gap is made to exist between
such surfaces and the field magnet poles when these are opposite the joints than
the gap existing beteen these parts when the field magnets are in other positions,
substantially as described.
Dated this 14th day of March 1906
ABEL & IMRAY,
Agents for the Applicants.