IMPROVEMENTS IN MAGNETO-ELECTRIC AND DYNAMO-ELECTRIC MACHINES
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by George Hookham at the Office of the
Commissioners of Patents on the 16th November 1883.
GEORGE HOOKHAM of Birmingham in the County of Warwick Manufacturer.
"IMPROVEMENTS IN MAGNETO-ELECTRIC AND DYNAMO-ELECTRIC MACHINES
"
My invention consists mainly of improvements in or modifications of an invention
for which Letters Patent were granted to me dated 21 April 1883 No 2042 and
I will describe my present invention with reference to the patented invention
referred to.
Instead of employing only one series of steel or permanent V shaped or bar
magnets arranged radially on a rotating shaft I employ two series of the said
magnets on the same shaft and at a short distance apart the magnets of the two
series being so arranged on their common shaft that the arms or poles of each
magnet of one series are opposite to arms or poles of different polarity on the other
series. In other words the north pole of each magnet of one series
opposite the
south pole of a magnet of the other series. There is thus formed a powerful
magnetic field between the poles of the magnets of the two series the lines of force
in which magnetic field will pass through an armature connecting or nearly
connecting the two opposite magnets and induce an electrical current in a coil on
the said armature.
The armatures are fixed in a circular frame within which the two series of
magnets rotate the coils on the armatures occupying only the middle of the
armatures and ordinarily having a length somewhat less than the breadth of the
space between the two series of magnets so that as the magnets rotate they are free
of the said coils. The armatures are of such a length as to extend over the whole
face of the ends of the magnets.
By the arrangement of parts described a number of armatures double that of
the opposed magnetic poles may be employed or in machines of large size three or
four times as many armatures as pairs of magnetic poles may be employed the
armatures not affecting each other sensibly unless they are close together. Or a
number of armatures equal to a higher multiple of the number of pairs of magnetic
poles may be employed The said armatures being practically independent of each
other may be separately employed to work incandescent electric lamps any one or
more of which may be turned on or off without materially affecting the others
°

page_text: The construction of the armatures may be modified in the following way.
Instead of employing fixed armatures extending over the ends of the opposed
magnets I divide each armature into three parts consisting respectively of the parts
immediately over the ends of the magnets and the intermediate part on which the
coil is situated. The former I attach to their respective magnetic poles and they
consequently rotate with them and constitute keepers or soft iron poles to the
permanent steel magnets. By this arrangement the heating which occurs in those
portions of the armatures not covered by the coils is for the most part prevented
as the attached keepers described never change their polarity. The keepers or
fixed portions of the armatures may be made hollow and fixed as caps on the ends
of the magnets.
The last described arrangement may be modified by dispensing with the soft
iron keepers on the ends of the permanent steel magnets.
In this case the ring of short armatures is so far diminished in diameter as to
bring the short armatures immediately between the ends of the arms of the opposed
magnets.
In all cases I prefer so to arrange the armatures and magnets with respect to
each other that when an armature is situated between the opposed poles of two
magnets another armature shall at the same time be situated between the other
two opposed poles of the same magnets. The magnetic circuit is thus alternately
completely closed and opened during the motion of the armatures or magnets and
a maximum magnetic intensity produced.
Those parts of my invention which relate to armatures are applicable to
dynamo-electric machines