Improvements in Exciting Electro-magnets and Electro-magnetic Machinery.
Year: 1890

page_text: Date of Application, 22nd Aug., 1890-Accepted, 22nd Nov. 1890
COMPLETE SPECIFICATION.
Improvements in Exciting Electro-magnets and Electro-magnetic
Machinery.
I, RANKIN KENNEDY Electrical Engineer 10 India Street, Kilmarnock, Scotland
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 to improvements in the art of exciting magnetism in electro-
magnets and maintaining magnetic fields in electromagnetic machinery such as
dynamos and electromotors and other machines in which magnetic fields are required
and produced particularly applicable to alternating current generators and motors for
the purpose of my invention the field magnets and armatures in the dynamos and
motors made according to this invention are compound wound; that is wound with
two separate circuits, and the field magnets are excited by two separate currents
pulsating in different places; these two pulsating currents are unidirection currents,
derived from two alternating currents, alternating at a difference of phase equal to
a quarter of a complete period of alternation.
The armatures are also double wound, one series of coils being wound in between
the coils of the other series; and there are altogether twice as many coils on the
armature as there are of poles on the field magnet; a commutator is connected to each
series of coils ou the armature, for the purpose of rectifying a portion or the whole
of the alternating currents flowing from them; and the same commutators directs a
portion or the whole of the rectified alternating currents, through the two windings on
the field magnet; the current from the commutator connected to the one series of
armature coils being directed into one circuit of the field, and the current from the
other commutator being directed into the other circuit of the field magnet.
When two alternating currents alternating at a quarter of a complete period
difference in phase are rectified, they are converted into two pulsating unidirection
currents the pulsation of the one being at a maximum when the pulsation of the other
is at a minimum ; and when two such rectified currents are passed one through one
circuit, and the other through the other circuit, of a double wound field magnet, their
combined effect, is magnetically the same as one continuous current, and the resultant
magnetism is very nearly steady.
This invention is equally applicable to motors and generators for alternating currents.
According to this invention when only one alternating current is supplied, the
other current alternating at a difference of phase equal to a quarter of a complete period
is generated within the dynamo or motor in or to which this invention is applied.
In order that my invention may be better understood I append drawings.
Fig. 1 is an ordinary form of motor shown diagrammatically, having a two part com-
mutator C, and a field magnet B, mounted together on a spindle, free to rotate; the
armature with its two coils A. A encloses the field, and is fixed. This motor is driven
by an alternating electric current supplied through main wires M R the current
divides at O and P, part going through contact brushes F F and commutator C to
field magnet coil and part direct to armature coils A A. On starting this motor it will
run up to a speed at which the contact springs F F change contact from one part of
the commutator to the other at the same moment that the alternating current reverses
in direction, so that the current in the field magnet coil shall be a unidirection
current, but pulsating. This speed is called the synchronising speed, and is found by
dividing the number of alternations per second by the half of the number of parts
in the commutator; at the synchronising speed the currents are said to be rectified
into unidirection currents.
The motors made according to this invention are started in the manner described in

page_text: the foregoing, by turning on one alternating current dividing between field coils and
armature coils and running the speed up to the synchronising speed, when the second
current is turned on through the second commutator into the second field magnet
coils.
Figure 2 is a motor made according to this invention driven by two alternating
currents rectified by two commutators C C¹. These two alternating currents alter-
nating at a difference of phase equal, to a quarter of a complete alternation are supplied
through main wires M M' and have a common return wire R. The field magnet N.S.
is wound with two coils G and K and is mounted on a spindle together with two
commutators CC₁ freely rotating.
This motor is started in the same way as that described for that in (Figure 1) the
ordinary motor using the single winding
The second circuit being opened by switch S while the circuit through the com-
mutator C is closed through switch S₁ exciting the field coil K and armature coils of
A A¹ the motor runs up to synchronism, at which speed the other current is closed
through switch S into commutator C¹ and into coil on field magnet G. The field
magnet will now be excited by two pulsating currents one pulsating at its maximum
while the other pulsating at its minimum and the magnetism will be nearly steady
in value, both currents being unidirection currents. When only one current is supplied
the other one alternating at a quarter of a period difference in phase is generated in
coils wound on the armature between the motor coils A A¹ in Fig. 4 and are con-
nected to commutator C¹ to supply the second current to field coil G instead of
taking that current from main wire M. This is shown in Figure 4 which shows a motor
constructed similarly to that shown in Figure 2 having the two additional coils / h¹ for
generating the second current required to excite the coil G. The two coils are
shown connected to commutator C'in Figure 4. This motor is started in the same
way as the aforedescribed motor by turning on current, first from main wires M.R.
to run it up to synchronism and then the current is turned on from the two exciting
coils rectified by commutator (" and passed into coil G on field magnet B.
Figure 3 is an elevation of Figure 2 showing connections to commutators.
Figure 5 is an elevation of Figure 4 showing connections to commutators.
The commutators employed are the ordinary split tube forms so well known to
electricians for redirecting currents.
The motors described have only two poled fields being the simplest but in practice
multipolar field magnets are used as shown in Figures 6 and 7. The coils on the
field magnets are double wound as shown at e e in Figures 6 and 7, and the coils for
generating the second current when only one is supplied are shown at EEE in
Figure 6 and at E E' in Figure 7 on the armatures.
In motors both field magnets and armatures are constructed with laminated iron
cores. The field magnets in Figures 6 and 7 are mounted to rotate inside the armatures
and their poles are marked NS NS. In Figures 8 and 9 are illustrations of a motor
constructed according to this invention at D in Figure 8 driving a pair of rectifying
commutators rectifying two alternating electric currents entering by brushes Fi
F2 F3 alternating at a quarter difference of phase and leaving brushes F* F5 F6 F7
as two rectified pulsating currents when motor D runs at synchronising speed
these currents are used to excite steadily any electro magnetic devices such as a motor
Figure 9 having double windings.
Dynamos according to this invention are wound the same as the motors having two
windings on the field magnets and two windings on the armatures each winding on
the armature having a separate commutator connected, and collecting brushes on
contact therewith for the purpose of collecting the alternating currents and collecting
the rectified alternating currents.
The coils of the one winding on the armature are placed between the coils of the
other winding so that the coils of the one are in a position of maximum induction in
the field when the coils of the other winding are in a position of minimum induction
in the field. In these positions the alternating currents produced are in difference of
phase equal to a quarter of a complete period of alternations. As in the motors the

page_text: ield magnet is excited by these two alternating currents rectified and passed each
through separate windings on the field magnet. Fig. 10 shows a simple dynamo con-
structed according to this invention. B B is the field magnet with two windings G. K.
mounted on a spindle free to rotate together with two commutators CC with
contact brushes F F F2 F3 to take off the rectified alternating currents and pass one
current into G. coil on field magnet and the other into K coil in whole or in part.
The armature is of ring form enclosing the field magnet and carries four generating
coils A Ahh, A A¹ forming one series h h another series. The current generated
in the one series differs in phase from that in the other series by a quarter of a period
of alternation and a portion of the one current is rectified by commutator C and a
portion of the other by C' commutator into two pulsating unidirection currents the
one passing into coil G on field magnet and the other into coil K for the purpose
of exciting the said field magnet steadily or approximately steadily.
Any electromagnet wound with two separate coils is according to this invention very
nearly steadily excited by energising or exciting the two separate windings of the
coils by two pulsating unidirection currents the one current pulsating at a inaximum
at the same instant at which the other is at a minimum as described.
Having now particularly described and ascertained the nature of my said invention
and in what manner the same is to be performed I declare that what I claim is
1st. In electric generators and motors exciting the fieldmagnets by a combination of
two windings thereon with two pulsating unidirection electric currents derived from
two alternating electric currents the one alternating at a difference of phase from the
other equal to one quarter of a complete period of alternation the one pulsating cur-
rent exciting the one winding the other pulsating current exciting the other winding
on the field magnet.
2nd. The combination of an electromagnet having two windings with two
unidirection pulsating currents pulsating in different phases so that the one current
reaches its highest value in the one winding at the same instant that the other current
reaches its lowest value in the other winding on the field magnet for the purpose of
maintaining a steady magnetic field.
3rd. In an electromotor having a double wound field magnet exciting the one
winding by a current from a main supply of alternating current rectified by a com-
mutator into a pulsating unidirection current and exciting the other winding by a
current generated in the motor alternating at a difference of phase with the main
supply equal to a quarter of a complete period of alternation and rectified by a com-
mutator into a pulsating unidirection current.
Dated this Twanty first day of August 1890