Improvement in Regulation of Rotary Transformer Direct Current Electromotive Force.
Year: 1898

page_text: PROVISIONAL SPECIFICATION.
PROVISIONAL SPECIFICATION.
Improvement in Regulation of Rotary Transformer Direct Current
Electromotive Force.
I, BENJAMIN GARVER LAMME, of 230, Stratford Avenue, Pittsburg, in the
County of Allegheny and State of Pennsylvania, U.S.A., Electrical Engineer, do
hereby declare the nature of this invention to be as follows:-
My invention relates to the transformation of alternating currents into direct
currents by means of rotary transformers, and has for its object to provide
improved means for regulating the potential at the direct current terminals of
the transformer.
According to my invention I interpose between the alternating current side of
the rotary transformer a stationary transformer which is so arranged that the
electromotive force supplied to the rotary transformer can be varied within
certain limits, and I further arrange that the excitation of the field magnet of the
rotary transformer can also be varied, and by the combination of these two devices
the electromotive force of the direct current side of the rotary transtormer can
be regulated within very wide limits.
The improved system will be best understood by the aid of the accompanying
drawing in which,
Figure 1 is a diagram of the apparatus and circuits suitable for practising the
invention, and Fig. 2 illustrating a modification.
In Figure 1, 1 is a two-phase alternating current generator, and 2 and 2º are
stationary transformers for the respective out of phase circuits, the secondary
windings 3 and 3 of which are respectively provided with leads 5, 6, 7 and 8,
5, 6, 7 and 8, at intervals, in order that a greater or less length of each
secondary may be included in circuit according to the electromotive force desired.
9 is a rotary transformer provided with a shunt field-magnet winding 10.
11 is a
rheostat connected in series with the field-magnet winding 10 and provided with
means for including more or less of it in circuit, as may be desired. 12 and 12*
are choke coils connected respectively in the circuits of the secondaries 3 and 3ª
of the stationary transformers 2 and 2", which supply the rotary transformer 9
with alternating current.

page_text: The free end of choke coil 12 is provided with a switch arm 13+ by means of
which any desired number of section in the secondary winding 3 may be included
in circuit with rotary transformer 9, and the free end of choke coil 12" is pro-
vided with a similar switch arm 13 which co-operates in the same manner with
the secondary 3*. 13 and 14 are direct current motors connected across the
circuit supplied by the direct current end of the rotary transformer 9.
If the motors are to be used for propelling a railway vehicle, means may
obviously be provided, if desired, whereby they may be connected either in series
or in parallel, such construction and arrangement being well understood in the art.
For convenience of illustration, I have shewn a single-phase circuit in Figure 2,
but it will be understood that the invention is not limited in any case as regards
the number of phases of current.
The apparatus and circuits illustrated in Figure 2 also differ from what is
illustrated in Figure 1, as regards the number and arrangement of the choke
coils. It will be seen that in Figure 2, I employ a series of choke coils 12, 12",
12b, and 12, one for each division of the secondary winding, in lieu of the single
coil of Figure 1. Either arrangement is suitable for practical use; but inasmuch
as the electromotive force and the torque vary with the length of the transformer
secondary included in circuit, it may in some cases be desirable to employ a
series of choke coils of different capacity, as is indicated in Figure 2.
The system is operated as follows. Assuming that a slow speed for the
motors 13 and 14 is desired, if the rheostat 11, and the switch arms 13+ and 13* or
the switch arm 13+ as the case may be, be in the position shewn, it is obvious that
the transformer 2 will be supplying its lowest electromotive force, and the field
of the rotary transformer will be as weak as it is possible to make
it with the apparatus shewn. With this arrangement of parts,
the lagging current in the alternating current circuit will generate in the choke
coils counter electromotive forces which lower the alternating current electro-
motive force of the rotary transformer, and thus lower the direct current electro-
motive force to the minimum point.
In order to increase the direct current electro-motive force, and consequently
the speed of the direct currents motors, the field-magnet of the rotary trans-
former may be gradually strengthened by cutting out step by step the resistance
of the rheostat 11, until the field is strong enough to produce a current in the
alternating current circuit that leads the electro-motive force in which condition
a component of the electromotive force generated in the choke coil will be added
to that supplied by the length of transformer secondary included in the circuit,
so that the electro motive force supplied by the rotary transformer is higher than
that supplied by the stationary transformer. If a still greater speed of motors
is desired, another length of the stationary transformer may be included in
circuit, and the entire resistance of the rheostat simultaneously inserted in the
field circuit of the machine, after which the operation above described may be
repeated. This operation may be continued until the entire secondary of the
transformer is included in circuit and all of the resistance is cut out of the rotary
transformer field circuit, when the maximum direct current electro-motive force,
and consequently the maximum speed of the motors 13, 14, will be obtained.
In order to decrease the speed of the motors, the operation above described will
obviously be reversed.
It will be understood that by this method a very wide range of electro-
motive force and consequently a very wide range of speed of the motors may be
obtained without the use of a regulating rheostat in the circuit of the motors.
Dated this 28th day of June 1898
W. P. THOMPSON & Co.,
322, High Holborn, London, W.C., Patent Agents for the Applicant.

page_text: Improvement in Regulation of Rotary Transformer Direct Current
Electromotive Force.
I. BENJAMIN GARVER LAMME. of 230, Stratford Avenue, Pittsburgh, in the
County of Allegheny and State of Pennsylvania, U.S.A.. 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 relates to systems of electrical distribution in which single phase
or polyphase alternating currents are converted by means of a rotary transformer
into direct currents which operate the translating devices.
The object of my invention is to provide for regulating the potential difference
of the direct current given out by a rotary transformer, and by the accomplish-
ment of this object I am furthermore enabled to operate direct current motors
at variable speeds from an alternating current circuit.
According to my invention I include in the alternating current circuit which
supplies the rotary transformer an inductance coil, and I also arrange that the
excitation of the field-magnet of the rotary transformer shall be able to be varied;
such variation of the field strength would not by itself materially alter the electro-
motive force supplied to the rotary transformer, but the addition of an inductive
resistance in the supply circuit increases the alteration of the electro-motive force
very considerably. In order to increase the range through which the electro-
motive force of supply can be varied, I furthermore interpose a stationary trans-
former between the alternating current side of the rotary transformer and the
alternating current mains, said transformer being so arranged that the electro-
motive force at the terminals of the secondary coil can be varied. By employing
these two devices so as to obtain variations in both of the ways mentioned, the
electro-motive force supplied to the rotary transformer and thereby the direct
current electro-motive force given out by the same can be regulated very
gradually within wide limits.
My invention will be clearly understood by the aid of the accompanying dia-
grams in which Figure 1 shews my improved arrangements for gradually varying
the electro-motive force of the direct current side of a rotary transformer,
Figure 2 illustrating a modification of the system.
Referring now to Figure 1, 1 is a two-phase alternating current generator,
and 2 and 3 are stationary transformers for the two respective circuits in quad-
rature, the secondary windings 4 and 5 of which are respectively provided with
leads 6, 7, 8, 9, 10, 11, 12, and 13, at intervals, in order that a greater or less
length of each secondary may be included in circuit according to the electro-
motive force desired. 14 is a rotary transformer provided with a shunt field-
magnet winding 15. 16 is a rheostat connected in series with the fi-magnet
winding 15 and provided with means for including more or less of it in circuit,
as may be desired.
17 and 18 are choke coils connected respectively in the
circuits of the secondaries 4 and 5 of the stationary transformers 2 and 3, which
supply the rotary transformer 14 with alternating current.
The free end of choke coil 17 is provided with a switch arm 19 by means of which
any desired number of sections in the secondary winding 4 may be included in
circuit with the rotary transformer 14, and the free end of choke coil 18 is pro-
vided with a similar switch arm 20 which co-operates in the same manner with
the secondary 5. 21 and 22 are direct current motors connected across the circuit
supplied by the direct current end of the rotary transformer 14.

page_text: For convenience of illustration, I have shewn a single-phase circuit in Figure 2,
but it will be understood that the invention is not limited in any case as regards
the number of phases of current.
The apparatus and circuits illustrated in Figure 2 also differ from what is
illustrated in Figure 1, as regards the number and arrangement of the choke
coils. It will be seen that in Figure 2, 1 employ a series of choke coils 23, 24,
25 and 26, one for each division of the secondary winding, in lieu of the single
coil of Figure 1. Either arrangement is suitable for ractical use; but inasmuch
as the electro-motive force and the torque vary with the length of the transformer
secondary included in circuit, it may in some cases be desirable to employ a
series of different choke coils as is indicated in Figure 2.
The system is operated as follows:-Assuming that a slow speed for the
motors 21 and 22 is desired, if the rheostat 16 and the switch arms 19 and 20
(Figure 1) or the switch arm 19 (Figure 2) be in the position shewn, it is obvious
that the transformers or transformer will be supplying the lowest electro-motive
force, and the field of the rotary transformer will be as weak as it is possible to
make it with the apparatus shewn. With this arrangement of parts the lagging
current in the alternating current circuit will generate in the choke coils counter
electro-motive forces which lower the alternating current electro-motive force of
the rotary transformer, and thus lower the direct current electro-motive force to the
minimum point.
In order to increase the direct current electro-motive force, and consequently
the speed of the direct current motors, the field-magnet of the rotary trans-
former may be gradually strengthened by cutting out step by step the resistance
of the rheostat 16, until the field is strong enough to produce in the alternating
current circuit a current which leads the electro-motive force in which condition
a component of the electro-motive force generated in the choke coil will be added
to that supplied by the length of transformer secondary included in the circuit,
so that the electro-motive force supplied to the rotary transformer is relatively
higher than that supplied by the stationary transformer. If a still greater speed
of motors is required, another length of the stationary transformer may be included
in circuit and the entire resistance of the rheostat 16 simultaneously inserted in
the field circuit of the machine, after which the operation above described may
be repeated. This operation may be so continued until the entire secondary of
the transformer is included in circuit and all of the resistance is cut out of the
rotary transformer field circuit, when the maximum direct current electro-motive
force, and consequently the maximum speed of the motors 21, 22, will be obtained.
In order to decrease the speed of the motors, the operation above described will
obviously be reversed.
The lengths of the various sections of the secondary windings and the total
resistance of the rheostat 16 are so arranged relatively to each other and to the
remaining portion of the circuit that the electro-motive force supplied to the rotary
transformer when all the resistance 16 is cut out of circuit closely approximates
that which is supplied when all the resistance 16 is in circuit and another section
of the transformer winding is included: by this means I ensure a gradual
variation of the electro-motive force throughout the whole range of supply.
In lieu of a stationary transformer having a separate primary and secondary
winding an auto-transformer or resistance placed across the alternate current
mains may be employed, the number of coils of such resistance included between
the leads supplying current to the rotary transformer being varied as required.
Furthermore, instead of varying the number of coils of the secondary of the
transformer the number of coils of the primary may be varied, or the magnetic
relations of the two coils may be varied, or other means may be used so as to
vary the electro-motive force supplied to the rotary transformer. Said rotary
transformer may be of any suitable type, and I do not restrict myself to the
precise form indicated.

page_text: 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;-
1. A system of electrical distribution wherein a rotary transformer is employed
for converting alternating currents of one or more phases into direct currents for
operating translating devices, and having an inductance coil included in the
alternating current circuit for the purpose of increasing the variation of the
electro-motive force supplied by the rotary transformer when the excitation of
its field-magnet is varied.
2. In a system of electrical distribution of the kind described, the provision of
means for varying the excitation of the field-magnet of the rotary transformer as
well as for varying the electro-motive force impressed on the alternating current
leads supplying said transformer, whereby a gradual variation of the electro-
motive force is obtained, substantially as described.
3. The various systems of regulating the electro-motive force of the direct
current delivered from a rotary transformer, substantially as herein described
with reference to the accompanying drawing.
Dated the 27th day of March 1899.
W. P. THOMPSON & Co.,
Of London, Liverpool, Manchester and Birmingham.