Improvements in Means for Adjusting the Reluctance of Magnetic Circuits.
Year: 1898

page_text: Date of Application, 20th Oct., 1898-Accepted, 23rd Dec., 1898
COMPLETE SPECIFICATION.
Improvements in Means for Adjusting the Reluctance of Magnetic
Circuits.
We, THE BRITISH THOMSON-HOUSTON COMPANY LIMITED, of 83, Cannon Street, in
the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by Elihu Thomson,
residing at Swampscott, in the County of Essex, State of Massachusetts, United
States of America, Electrician,) and in what manner the same is to be per-
formed to be particularly described and ascertained in and by the following
statement:-
The present invention comprises broadly the idea of interposing in any magnetic
circuit a body of laminated magnetic material so arranged that the laminae may be
placed either parallel with, or at any desired angle to, the lines of force of the
circuit. By placing the laminae parallel to the lines of force, or in the line of
magnetic induction, the reluctance is least, while if placed at an angle the reluctance
is increased and becomes a maximum when the angle is ninety degrees.
The invention is capable of many embodiments, and in the drawings forming part
of this application there is shown by way of example, three modes of applying the
same.
Fig. 1 illustrates the use of the invention in connection with a reactance
coil.
Fig. 2 shows an application of the invention for the purpose of balancing up the
field magnets of dynamo electric machines.
Fig. 3 shows another mode of applying the invention.
In many cases it is desirable to have an adjustable reactance coil. Fig. 1 is a con-
ventional representation of such a device. The core consists of a laminated structure
of any suitable form as 1. This core either has an opening formed therein, as in
Fig. 2, or is entirely interrupted as shown in the drawing, Fig. 1. The openings or
cuts made in the core are such as to intercept the lines of force produced by current
in the exciting coil 2. A body of laminated magnetic material 3, is arranged so as
to be capable of assuming different angular relations to the lines of force or lines of
magnetic induction in the core. By varying the position of the core the reluctance
of the magnetic circuit will be correspondingly varied, as is evident. The body of
magnetic material may be in the form shown in Fig. 1, or it may be any regular
sided prism, as, for instance, square in cross section, as shown in Fig. 3. If the plug
is cylindrical, it may be mounted in various ways so as to turn. If desired, the
walls of the opening itself may form the bearing, in which case the plug may be
provided with a squared or other angular projection 4, by which it may be turned in
its bearings for purposes of adjustment. If desired, however, the laminated magnetic
material may be mounted on a shaft carried in suitable bearings, in a manner
analogous to that of the armature of a dynamo-electric machine. The construction
is so obvious that no illustration is deemed necessary.
In many cases difficulty is experienced in setting up a multipolar dynamo-electric
machine, so that the electro-motive forces generated between the different sets of
brushes shall be the same. Owing to some accidental difference in the quality of iron

page_text: used, or to a slightly eccentric placing of the armature with respect to the pole pieces,
or to various other causes, it may happen that the flux due to one set of poles may
differ from that due to another. In such a case, if the machine is a generator, one
circuit may furnish more current than another, and in exaggerated cases the current
may even be reversed in some of the circuits. In the case of a motor, under similar
circumstances, the counter electromotive force of the different circuits would be
different, whereby some circuits would take an excessive current and others but very
little. To obviate these difficulties openings are provided in some suitable portion
of each of the magnetic circuits of the machine. The openings are preferably circular
in cross section, as shown in Fig. 2, and may be located at the base of each pole
piece, as shown at 5, or, if desired, the openings may be made in the yoke between
the pole pieces, as indicated, for example, at 6. Into these openings are inserted
plugs of laminated magnetic material, with the laminae arranged longitudinally of the
openings, so as to intercept the lines of force. An end view of the laminae is shown
at 5. By turning the plug by any suitable means, such as shown at Fig. 1, for
example, or by withdrawing the plug and inserting it at a different angle, the
magnetic reluctance of the circuit is changed, and, consequently the flux. By
suitable adjustment, in the manner described, the flux per pole in a multipolar machine
may be equalized or otherwise altered or adjusted.
Fig. 3 shows a slightly different application of the invention. In this case the
pole-pieces of a dynamo-electric machine are provided with openings transverse
thereto and, preferably, square. By inserting a square plug 7, of laminated material,
so that the laminae are either parallel to or lie across, the lines of force, or by
omitting the plug entirely, an effect is obtained equivalent to inserting an air-gap
of different lengths into the magnetic circuit. The air-gap becomes operative when
the reduced section of the pole piece becomed saturated. A bend in the saturation
curve is produced at the point where the air gap becomes operative. Above the
bend in the curve the magnetization is no longer proportional to the magneto-motive
force, and the operation of the machine is thus rendered less sensitive to the change
in the current in the field winding. In this latter application of the invention, it is
preferred to make the laminations of, soft iron and separate them by paper or other
non-magnetic material of suitable thickness.
Generally speaking the laminae may all be formed of the same material, and
suitably separated from each other by sheets of non-magnetic material; or they may
be formed of material of different permeability, such as soft iron and hard steel, and
suitably intermingled. If desired, the use of sheets of non-inagnetic material may be
omitted, the unavoidable air spaces between the laminae being in many cases
sufficient to secure the desired.lack of symmetry in permeability of the laminated
body.
Having now particularly described and ascertained the nature of our said
invention (as communicated to us from abroad) and in what manner the same is to
be performed, we declare that what we claim is:-
1. The method of adjusting the flux in one or more of the magnetic circuits of a
multipolar dynamo-electric machine, which consists in adjusting the reluctance of
the magnetic circuits of the machine.
2. The combination, with a multipolar dynamo-electro machine, of, means for
adjusting the reluctance of one or more of, the magnetic circuits of the
machine.
3. A reluctance adjusting device consisting of intermingled plates of magnetic
material of different permeability.
4. A reluctance adjusting device composed of laminated magnetic material in the
form of a solid of revolution, with laminae arranged parallel to the axis.
5. The combination of a body of magnetic material forming part of a magnetic,
circuit and having an opening therein, and a body of laminated. magnetic material
adapted to assume different positions in said.openings and. with the laminae arranged
longitudinally of the opening for each position.

page_text: 6. The combination of a body of laminated magnetic material having the
configuration of a surface of revolution with the laminae parallel to the axis, and
a body of magnetic material with an opening therein to receive said laminated
body.
7. The combination of a body of magnetic material forming part of a magnetic
circuit and having an opening therein, and a body of laminated magnetic material
adapted to fill said opening and assume different positions therein, thereby varying
the reluctance of the magnetic circuit.