Improvements in and connected with Alternating Current Electric Motors.
Year: 1892

page_text: Date of Application, 22nd Sept., 1892
Complete Specification Left, 22nd June, 1893-Accepted, 22nd Sept., 1893
PROVISIONAL SPECIFICATION.
Improvements in and connected with Alternating Current Electric
Motors.
I, JAMES SWINBURNE, of Broom Hall Works, Teddington, Middlesex,
Electrical Engineer, do hereby declare the nature of this invention to be as
follows:-
My invention has reference to alternating current electric motors of the
synchronising type, for use with single or simple alternating currents.
Motors with a redressed field exciting current taken off in shunt to the armature
circuit, that is to say connected across the supply mains, have already been
described by me in my Specification No. 17120 of 1886, and these motors have
come into use to some extent in Germany. There is a difficulty, with regard to
the sparking at the commutators. If the segments & brushes are arranged so as
to short-circuit the mains, even at the moments of low electromotive force, a large
current starts, & sparking results when it is broken. If, on the other hand the
brushes & sections are arranged so as not to short-circuit the mains, the field
circuit must be broken, and this also gives rise to sparks. These evils have been
to some extent mitigated by using double brushes with resistances between them.
The arrangement has a further drawback, in that the full available pressure is
needed to overcome the resistance of the field magnet circuit, so that at starting,
when the self-induction of the fields comes into play, the field may not be excited
strongly enough. My invention has for its object, the avoidance of these draw-
backs; & this is accomplished by exciting the fields with very low pressures, such
as 5 or 10 volts. The excitation is provided by a special transformer, or the
armature of the motor is itself made to act partly as a transformer.
A motor according to my invention is constructed like an alternating current
generator, the field magnet being laminated. The field magnets are not, however,
separately excited, as in the case of most generators, but are excited by means of a
redressed current of low pressure obtained from a special circuit on the armature,
or by other suitable means.
As for example, a motor may be taken with a stationary armature & a rotating
internal field magnet. The armature wire may be wound through holes as
described in my Specification 17120 of 1886, and the field magnet may consist of
a star-shaped mass of laminated iron with copper coils, affording suitable poles.
The field magnets are wound with few turns of thick copper wire, so that they
demand a very low electromotive force to excite them. Thus, if the motor has
to run on 1000 or even 100 volts, the exciting pressure is kept down to say 10 or
even 5 volts. The excitation is supplied by a special circuit consisting of a few
turns wound on the armature. Instead of employing a special circuit, the field may
be excited in shunt to a few turns of the main armature circuit. The rotating field
magnet carries a commutator for redressing the exciting current.
To start the motor the main circuit is completed, a resistance being employed
if necessary to prevent the current being too great at first.
Some motors, especially small machines will start without further trouble.
Others require a stronger field. If the field is excited in shunt to a few of the
armature turns, more may be put in circuit for starting. This can be easily affected
by a switch where the armature is stationary. Another method is to open the
part of the armature circuit which is shunted by the fields, this puts the fields in
series with the rest of the armature, & gives more torque. If the low pressure
excitation is provided by a special transformer, the number of turus in one circuit

page_text: may be altered, it is also advisable to wind the transformer for constant current
rather than constant pressure.
Sometimes the field is wound with two circuits & provided with two commutators.
One circuit is then in series with the main armature circuit, or in the case of high
pressure machines has a current proportional to the main currents provided by a
transformer. This series circuit will then help to magnetise them if the shunt
circuit is opened. The machine can thus be started as series wound, and when
it is up to speed, the shunt circuit may be put into use too. The series circuit may
then be left to strengthen or weaken the field, as necessary. There is still another
way of starting the motor, which has been suggested to me by C. E. L. Brown of
Baden, Switzerland. The exciting current is not completed at starting.
One or both brushes however must be put down. The armature current then
induces currents in the field magnets when they are in such positions that the
brushes short circuit the commutator sections. The field currents are thus pro-
duced in certain positions only, & by placing the brushes in the right place the
machine will start, & increase its velocity till full speed is reached. The exciting
circuit is then completed, & the machine takes little current, & is capable of giving
a large output. Some forms of machine will start with the exciting circuit
complete from the beginning, others start best with the brushes acting as short-
circuiters only.
In all cases it important to use few turns of wire on the fields & to excite with
very low pressures, as the pressure induced in the field magnets by the armature
current is otherwise so great that the sparking is serious on starting.
The armature may be wound with two circuits so that a double current may be
used for starting the motor. The double current is produced by putting self-
induction in one circuit & capacity in the other to produce the necessary difference
of phase. Self-induction alone seldom produces enough lag. In some cases I
provide a sort of compound excitation by means of an open circuit transformer.
One circuit of this is in series with the field magnets, the transformer & magnets
being in shunt to the mains or in series with the armature circuit or in shunt to the
part of the armature circuit mentioned. The other circuit of the transformer is
in series with the main armature circuit. The transformer is so designed that the
field magnets are properly magnetised at no load, the magnetising current being
the magnetising current of the transformer also. As the load increases, the field
current is thus increased or decreased as desired, by the main current in the other
circuit of the transformer.
Dated this 21st day of September 1892.
COMPLETE SPECIFICATION.
Improvements in and connected with Alternating Current Electric
Motors.
I, JAMES SWINBURNE, of Broom Hall Works, Teddington, Electrical Engineer
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 has reference to alternating current electric motors of the
synchronising type, for use with single or simple alternating currents.
Motors with a redressed field exciting current taken off in shunt to the armature
circuit, that is to say connected across the supply mains, have already been
described by me in my Specification No. 17120 of 1886, and these motors have
come into use to some extent in Germany. There is a difficulty, however, with
regard to the sparking at the commutators. If the segments and brushes are
arranged so as to short-circuit the mains, even at the moments of low electromotive

page_text: force, a large current starts, and sparking results when it is broken. If, on the
other hand the brushes and sections are arranged so as not to short-circuit the
mains, the field circuit must be broken, and this also gives rise to sparks. These
evils have been to some extent mitigated by using double brushes with resistances
between them. The arrangement has a further drawback, in that the full available
pressure is needed to overcome the resistance of the field magnet circuit, so that
at starting, when the self-induction of the fields comes into play, the field may not
be excited strongly enough. My invention has for its object, the avoidance of
these drawbacks; and this is accomplished by exciting the fields with very low
pressures, such as 5 or 10 volts The excitation is provided by a special trans-
former, or the armature of the motor is itself made to act partly as a transformer
at the moment of starting.
A motor according to my invention is constructed like an alternating current
generator, the field magnet being laminated. The field magnets are not, however,
separately excited, as in the case of most generators, but are excited by means of a
redressed current of low pressure obtained from a special circuit on the armature,
or by other suitable means.
As for example, a motor may be taken with a stationary armature and a rotating
internal field magnet. The armature wire may be wound through holes as described
in my Specification 17120 of 1886, and the field magnet may consist of a star-
shaped mass of laminated iron with copper coils, affording suitable poles. The field
magnets are wound with few turns of thick copper wire, so that they demand a very
low electromotive force to excite them. Thus, if the motor has to run on 1000 or
volts. The
even 100 volts, the exciting pressure is kept down to say 10 or even
excitation is supplied by a special circuit consisting of a few turns wound on the
armature. Instead of employing a special circuit, the field may be excited in shunt
to a few turns of the main armature circuit. The rotating field magnet carries a
commutator for redressing the exciting current.
To start the motor the main circuit is completed, a resistance being employed if
necessary to prevent the current being too great at first.
Some motors, especially small machines, will start without further trouble.
Others require a stronger field. If the field is excited in shunt to a few of the
armature turns, more may be put in circuit for starting. This can be easily affected
by a switch where the armature is stationary. Another method is to open the part
of the armature circuit which is shunted by the fields, this puts the fields in series
with the rest of the armature, and gives more torque. If the low pressure excitation
is provided by a special transformer, the number of turns in one circuit may be
altered, it is also advisable to wind the transformer for constant current rather than
constant pressure.
Sometimes the field is wound with two circuits and provided with two commu-
tators. One circuit is then in series with the main armature circuit, or in the case
of high pressure machines has a current proportional to the main currents provided
by a transformer. This series circuit will then help to magnetise the fields if the
shunt circuit is opened. The machine can thus be started as series wound, and
when it is up to speed, the shunt circuit may be put into use too. The series
There is
circuit may then be left to strengthen or weaken the field, as necessary.
still another way of starting the motor, which has been suggested to me by
C. E. L. Brown of Baden, Switzerland. The exciting current is not completed at
starting. One or both brushes however must be put down. The armature current
then induces currents in the field magnets when they are in such positions that the
brushes short-circuit the commutator sections. The field currents are thus produced
in certain positions only, and by placing the brushes in the right place the machine
will start, and increase its velocity till full speed is reached. The exciting circuit
is then completed, and the machine takes little current, and is capable of giving a
large output. Some forms of machine will start with the exciting circuit complete
from the beginning, others start best with the brushes acting as short circuits only.
In all cases it is important to use few turns of wire on the fields and to excite

page_text: with very low pressures, as the pressure induced in the field magnets by the armature
current is otherwise so great that the sparking is serious on starting.
The armature may be wound with two circuits so that the double current may be
used for starting the motor. The double current is produced by putting self-
induction in one circuit and capacity in the other to produce the necessary difference
of phase. Self-induction alone seldom produces enough lag.
In some cases I provide a sort of compound excitation by means of an open
circuit transformer. One circuit of this is in series with the field magnets, the
transformer and magnets being in shunt to the mains or in series with the armature
circuit or in shunt to the part of the armature circuit mentioned. The other circuit
of the transformer is in series with the main armature circuit. The transformer is
so designed that the field magnets are properly magnetised at no load, the magne-
tising current being the magnetising current of the transformer also. As the load
increases, the field current is thus increased or decreased as desired, by the main
current in the other circuit of the transformer.
DESCRIPTION OF THE DRAWINGS.
Fig. 1 is a diagram of a motor according to my invention with a separate
excitation circuit. A & B are the terminals, & C, C, C, C, the armature coils, the
armature being stationary, consisting of discs with coils wound on them. The
armature coils proper do not cover the whole of the armature. The field magnets,
which revolve, consist of cross shape stampings wound with ordinary low pressure
exciting coils. There is a four part commutator. The part of the armature not
occupied by the main armature coils has four small low pressure coils F F F F,
which excite the field.
Fig. 2 shows the field not excited by separate coils, but in shunt to part of the
main armature circuit. If the switch H is opened, the fields are put in series with
the armature, so that a higher pressure on them is available for starting. On the
other band if H is closed, and if I is opened, the field is open circuited, and the
motor is started by the Thomson method, that is to say by the currents induced in
the field magnets by the armature when the brushes are in such positions that they
short circuit the field coils.
Fig. 3 shows the armature as before. The field is now excited by a step down
transformer with its primary between A & B. Its secondary has several contacts
so that the exciting pressure can be raised on starting.
Fig. 4 shows double or compound transformer excitation. G is a transformer for
transforming down, as in Fig. 3. There is a second little transformer N, one of
whose circuits is in series with the armature, and the other with the low pressure
exciting circuit.
Fig. 5 shows a motor with condenser for starting. On starting the switch I is
put on the upper contact, so as to short circuit the field magnets. The switch K on
being closed makes the circuit through the coils L L L L which have a condenser M
in series with them. The apparatus is then a double current motor. On putting
the switch I on the other contact it becomes self exciting.
Having now particularly described & ascertained the nature of my said inven-
tion, & in what manner the same is to be performed, I declare that what I
claim is :
1. An alternating current motor with its fields excited by a redressed current of
very low pressure.
2. An alternating current motor with its fields excited in shunt to a portion of its
armature circuit, substantially as described.
3. An alternating current motor with its fields excited by a special low pressure
armature circuit.
4. An alternating current motor with its fields excited partly by a shunt circuit
of low pressure, and partly by a series circuit of low pressure.

page_text: 5. An alternating current motor with an open circuit transformer arranged
substantially in the manner and for the purpose explained.
6. A self exciting alternating motor started by means of a double current
produced as described.
Dated thie 22nd day of June 1893
JAMES SWINBURNE.