An Improvement in Electric Motors Worked by Alternating Currents.
Year: 1888

page_text: Date of Application, 20th Dec., 1888
Complete Specification Left, 14th Sept., 1889-Accepted, 26th Oct., 1889
PROVISIONAL SPECIFICATION.
[Communicated from abroad by ALFRED MILES TAYLOR, at present in Baroda, India,
Electrical Engineer.]
An Improvement in Electric Motors Worked by Alternating
Currents.
We, SIEMENS BROS. & Co. Limited, of 12 Queen Annes Gate, Westminster, in
the County of Middlesex, do hereby declare the nature of this invention to be as
follows:-
When an electric motor is worked by alternating currents it is necessary that its
armature should revolve at such speed that the successive passages of the armature
coils through the polar fields should correspond with the alternations of current
Consequently it is generally necessary to start such a machine and work it to its
normal speed by extraneous power before the working circuit is closed.
This invention relates to means of starting such a machine by the working current
itself, without having recourse to any extraneous power.
For this purpose, the coils of the field magnets are connected to two brushes which
bear against a commutator having twice as many insulated plates as there are coils
in the armature.
These brushes are so situated or are of such length that while the one is in contact
with a plate of the commutator, the other is in contact with a plate next to it or
the 3rd 5th or odd number distant from it.
Half the number of the plates, say the 1st 3rd 5th &c. are connected to an insu-
lated ring, and the other plates say the 2nd 4th 6th &c. are connected to another
ring, the first ring being in connection with the one end of the wires constituting
the armature coils, and the other ring with the other end of these wires. Against
the two rings bear a pair of brushes, which present two terminals; the commutator
These terminals
brushes previously mentioned also presenting two terminals.
are subject to a double switch having its two contact arms connected respectively
to the two main leads. On moving both arms of the switch simultaneously to the
one hand they connect the ring brushes to the main leads, on moving them to the
other hand they connect the commutator brushes to the main leads. In order to start
the machine, the first movement of the switch arms is made whereby both the armature
coils and those of the field magnets are subjected to the alternations of the current,
and the armature is thus caused to rotate. When suitable speed is attained the
switch arms are moved to the other hand so as to connect only the commutator brushes
to the main leads. The current is then alternated in the armature coils but retains
constant direction in the field coils.
Obviously in machines where the armature is stationary and the field magnets
revolve, the connections to the commutator and the rings have to be inverted.
Dated this 90th day of December 1888.
ABEL & IMKAI,
Agents for the Applicants.

page_text: COMPLETE SPECIFICATION.
An Improvement in Electric Motors Worked by Alternating
Currents.
We, SIEMENS BROS. & Co. Limited, of 12 Queen Annes Gate, Westminster, in the
County of Middlesex, 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:-
When an electric motor is worked by alternating currents it is necessary that -its
armature should revolve at such speed that the successive passages of the armature
coils through the polar fields should correspond with the alternations of current.
Consequently it is generally necessary to start such a machine and work it to its normal
speed by extraneous power before the working circuit is closed.
This invention relates to means of starting such a machine by the working current
itself without having recourse to any extraneous power. For this purpose, the coils
of the field magnets are connected to two brushes which bear against a commutator
having twice as many insulated plates as there are coils in the armature.
These brushes are so situated or are of such length that while the one is in contact
with a plate of the commutator, the other is in contact with a plate next to it or
the 3rd 5th or odd number distant from it. Half the number of the plates, say
the 1st 3rd 5th &c. are connected to an insulated ring, and the other plates say the 2nd,
4th, 6th, &c. are connected to another ring, the first ring being in connection with the
one end of the wires constituting the armature coils, and the other ring with the
other end of these wires.
Against the two rings bear a pair of brushes which present two terminals, the
commutator brushes previously mentioned also presenting two terminals. These
terminals are subject to a double switch having its two contact arius connected
respectively to the two main leads.
On moving both arms of the switch simultaneously to the one hand they connect
the ring brushes to the main leads, on moving them to the other hand they connect
the commutator brushes to the main leads. In order to start the machine, the first
movement of the switch arms is made whereby both the commutator and the field
magnet coils are connected to the leads the armature being thus caused to rotate.
When suitable speed is attained the switch arms are moved to the other hand so as to
connect only the ring brushes to the main leads.
The current is then alternated in the armature coils but retains constant direction
in the field coils.
Obviously in machines where the armature is stationary and the field magnets
revolve, the connections to the commutator and the rings have to be inverted.
The accompanying drawing shews diagrammatically the arrangement according to
this invention for starting an alternate current electric motor, assumed to be of the
kind which has stationary field magnets indicated by the coil M and a revolving
armature having its coils connected to the plates of a commutator Con which bear
the two brushes B B' which are connected to the field magnet coils M.
On the revolving shaft of the machine are placed two insulated rings R R', the one
ring R being electrically connected to the 1st 3rd 5th and other odd plates of the
commutator C, and the other ring R¹ being connected to the 2nd 4th and other even
plates of the commutator C.
On the rings R R¹ bear respectively two brushes D D. These brushes and the
brushes B B are connected respectively to four terminals d, d¹, b, b¹, presenting
contacts for a double switch S S connected to the main leads L L for the alternate
currents. For starting the motor, the switch arms S S¹ are moved simultaneously
so as to make contact with b b¹, thus exciting the field magnets by the alternating
current, while the current for the armature coils is rendered constant in direction by
the commutator. Thus a strong starting force is obtained which shortly brings the
motor up to speed.

page_text: When the desired speed is attained, the switches S S¹ are moved simultaneously
to contact with d d thus sending the alternating current by the brushes D D¹ and
rings R R¹ to the plates of the commutator Cand thence partly to the armature coils and
partly by the brushes B B', to the field magnet coils. The armature coils are now excited
by the alternating currents, but owing to the action of the commutator C the field
magnets M receive a commuted current of constant direction and the motor is thus
maintained in action.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, we declare that what we
claim is
For starting an electric motor worked by alternating currents, connecting the
commutator brushes to the field magnet coils and to a pair of terminals, connecting
the alternate plates of the commutator to two rings furnished with brushes connected
to another pair of terminals, and providing a double switch whereby the main leads
can be connected to either pair of the terminals, substantially as described.
Dated this · day of September 1889.
ABEL & IMRAY,
Agents for the Applicants.