Improvements in Systems of Electrical Distribution.
Year: 1898

page_text: Date of Application, 28th June, 1898
Complete Specification Left, 27th Mar., 1899-Accepted, 29th Apr., 1899
[Communicated from abroad by CILARLES FELTON SCOTT, of East Pittsburg, Penn-
sylvania, U.S.A., and BENJAMIN (ARVER LAMME, of 230, Stratford Avenue,
Pittsburg, U.S.A., Electrical Engineers.]
Improvements in Systems of Electrical Distribution.
I, REGINALD BELFIELD, of 32, Victoria Street, in the City of Westminster,
Electrician, do hereby declare the nature of this invention to be as follows;-
-
This invention relates to systems of electrical distribution, and has for its
object to provide a system by means of which direct current motors can be operated
at variable speeds from an alternating current circuit.
The improved system is particularly applicable for use in connection with
electric railways, though it is not specially restricted to such use.
The employment of alternating currents where energy is to be transmitted over
long distances possesses many and well known advantages, when, however, varia-
tion in speed is required it is not desirable to use alternating current motors,
since they can only be run efficiently at synchronism, and furthermore, in electric
rai.way work such motors are particularly unsuitable because they are not selt-
starting Multiphase motors are also impracticable, because they cannot be
operated efficiently except at or near synchronous speed. Neither of these objec-
tions apply to direct current motors but hitherto the necessary variations in speed
have been obtained by varying the resistance in circuit; a method, however,
which is wasteful owing to the losses in the resistances when these are inserted.
According to the present invention the advantages of line transmission by
alternating currents, and also variation of speed in the motors with little loss is
obtained by employing a rotary transformer to receive current from the alternat-
ing circuit and transmit direct current to the motors, the speed being varied by
vaiving the electromotive force applied to the alternating current side of the rotary
transformer, and thereby varying the electromotive force of the direct current side
of the same.
As the potential difference of the alternating current mains will in general be
considerably in excess of the maximum difference of potential required for operat-
ing motors, a step-down transformer will be advantageously interposed between the
alternating current mains and the rotary transformer, and in such case the voltage
applied to the rotary transformer may be readily varied by altering the length of
either the primary or secondary winding of the transformer, or the mutual relation
of the two windings. Where an auto-converter having a single coil is employed,
loops may be brought out from such coil to which connection may be made in
order to vary the voltage required.
The accompanying drawing is a diagram illustrating the invention applied
for the purpose of propelling a railway vehicle, the alternating current mains
consisting of an overhead conductor 1, and the rails 2, the current being conveyed
by a trolley arm 5, through the primary 3 of a stationary transformer 4, and a
wire to the wheels of the vehicle, and thence through the wheels to the rails.
Or the wire 6 may be connected to another trolley conveying the current to a

page_text: a
second trolley wire. The secondary 7 of the transformer 4 is shewn as pro-
vided with a plurality of loops brought out to contact points 8, with which a
movable switch arm 9 engages. One end of the secondary 7 is connected to a
brush bearing on one of the collecting rings 10 of the rotary transformer 11, and
the switch arm 9 is connected to the brush bearing on the other collecting ring 12.
It will be seen from this construction that as the switch arm 9 is moved from
one contact point 8 to another, the active length of the secondary of the trans-
former will be varied and consequently the electromotive force applied to the
rotary transformer 11 will be varied, the number of contact points & depending
upon the variation of voltage desired. The leads from the commutator 13 of the
rotary transformer extend directly to the brushes of the railway motors 14. These
motors are shewn as connected in parallel, but it is obvious that they may be
connected in series, if desired. The particular type of rotary transformer employed
is not material, but I prefer to employ a transformer in which the armature has
single winding and the field magnet of which has a shunt winding 15, as
indicated. The motors 14 are shewn as provided with series field magnet wind-
ings 16, but the invention is not limited in this regard. If series wound field
magnets are employed, the speed of the motors will be dependent both upon the
load and upon the voltage applied, and consequently the speed with any load
may be varied over a wide range by means of changes in the electro-
motive force applied. If shunt-wound motors are employed, the field windings
may be supplied with current either from a second rotary transformer supplying
current at a constant electromotive force or from an independent source, in which
case the speed will depend within close limits upon the electromotive force applied.
If shunt wound motors are employed and the energizing current is derived from
the rotary transformer 11 which gives a variable electromotive force, a rheostat
will be necessary in the field circuit. The rotary transformer 11 may, under
certain conditions, be run without the application of other power, but in cases
where the electromotive force is varied over a very wide range, it will probably
be necessary, in order to secure a constant synchronous speed, to provide a driving
means for such transformer the speed of which will not be in any way dependent
upon such variable electromotive force. I have shewn as such means a small
synchronous motor 17, the armature of which is coupled directly to the armature
of the rotary transformer 11, and the winding of which is supplied with current
from the secondary 7 of the stationary transformer 4, the leads 18 and 19 being
connected to points in said secondary which give a constant electromotive force.
The field winding 20 of the synchronous motor 17 may be excited from any suitable
source. In the present instance I have shewn the machine as self-excited, a com-
mutator 21 being provided with which the terminals of the winding 20 are
connected. As the motor 17 is not self-starting, I have shewn a small secondary
battery 22 for providing the necessary energy for starting the motor, and a
switch 23 for cutting the battery out of circuit when the motor has attained
synchronous speed. Any other suitable starting means may be employed.
The system above described is especially applicable to railway work, where it is
desirable to employ an alternating current transmission circuit of high voltage,
and at the same time to employ direct current motors of standard type which
will operate efficiently at all speeds. In this system the current required for
starting and accelerating the speed will be in approximate proportion to the
actual power expended. The system also applicable to the operation of hoists
in which considerable speed variations are required.
While I have shewn a singlephase alternating current circuit, it will be under-
stood that the system is also applicable to and intended for multiphase circuits.
Dated this 28th day of June 1898.
W. P. THOMPSON & Co.,
322. High Holborn, London, W.C.,
Patent Agents for the Applicant.

page_text: I, REGINALD BELFIELD, of 32, Victoria Street, in the City of Westminster,
Electrician, 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 systems of electrical distribution, and has for its
object to provide a system by means of which direct current motors can be operated
at variable speeds from an alternating current circuit.
The improved system is particularly applicable for use in connection with
electric railways, though it is not specially restricted to such use.
The employment of alternating currents where energy is to be transmitted over
long distances possesses many and well-known advantages, when, however, it is
required to transform the electrical energy into mechanical energy it is not
desirable to use alternating current motors where variation in speed is wanted,
as for example in railway work, since they can only be run efficiently at syn-
chronism, and furthermore, in electric railway work such motors are particularly
unsuitable because they are not self-starting. Multiphase motors are also imprac-
ticable, because they cannot be operated emciently except at or near synchronous
speed. Neither of these objections applies to direct current motors but hitherto
the necessary variations in speed have been obtained by varying the resistance
in circuit; a method, however, which is wasteful owing to the losses in the
resistances when these are inserted.
According to the present invention the advantages of line transmission by
alternating currents, and also variation of speed in the motors with little loss is
obtained by employing a rotary transformer to receive current from the alternat-
ing circuit and transmit direct current to the motors, the speed being varied by
varying the electro-motive force applied to the alternating current side of the rotary
transformer, and thereby varying the electro-motive force of the direct current side
of the same.
As the potential difference of the alternating current mains will in general be
considerably in excess of the maximum difference of potential required for operat-
ing motors, a step-down transformer will be advantageously interposed between the
alternating current mains and the rotary transformer, and in such case the voltage
applied to the rotary transformer may be readily varied by altering the length of
either the primary or secondary winding of the transformer, or the mutual relation
of the two windings. Where an auto-converter having a single coil is employed,
branches or loops may be brought out at intervals from such coil to which con-
nection may be made so as to include various lengths of the coil in circuit and
thereby vary the voltage required.
The accompanying drawing is a diagram illustrating the invention applied
for the purpose of propelling a railway vehicle, the alternating current mains
consisting of an overhead conductor 1, and the rails 2, the current being conveyed
by a trolley arm 5, through the primary 3 of a stationary transformer 4, and a
wire 6 to the wheels of the vehicle, and thence through the wheels to the rails,
or the wire 6 may be connected to another trolley conveying the current to a
second trolley wire. The secondary of the transformer 4 is shewn as pro-
vided with a plurality of loops brought out to contact points S, with which a
movable switch arm 9 engages. One end of the secondary 7 is connected to a
brush bearing on one of the collecting rings 10 of the rotary transformer 11, and
the switch arm 9 is connected to the brush bearing on the other collecting ring 12.
It will be seen from this construction that as the switch arm 9 is moved from

page_text: one contact point 8 to another, the active length of the secondary of the trans-
former will be varied and consequently the electro-motive force applied to the
rotary transformer 11 will be varied, the number of contact points depending
upon the variation of voltage desired. The leads from the commutator 13 of the
rotary transformer extend directly to the brushes of the railway motors 14. These
motors are shewn as connected in parallel, but it is obvious that they may be
connected in series, if desired. The particular type of rotary transtormer employed
is not material, but I prefer to employ a transiormer in which the armature nas
a single winding and the field-magnet of which has a shunt-wanding 15, as
indicated. The motors 14 are shewn as provided with series field-magnet wind-
ings 16, but the invention is not limited in this regard. If series-wound held
magnets are employed, the speed of the motors will be dependent both upon the
load and upon the voltage applied, and consequently the speed with any load
may be varied over a wide range by means of changes in the electro-
motive force applied. If shunt-wound motors are employed, the field windings
may be supplied with current either from a second rotary transformer supplying
current at a constant electro-motive force or from an independent source, in which
case the speed wilt depend within close limits upon the electro-motive force applied.
If shunt wound motors are employed and the energising current is derived from.
the rotary transformer 11 which gives a variable electro-motive force, a rheostat
will be necessary in the field circuit. The rotary transformer 11 may, under
certain conditions, be run without the application of other power, but in cases
where the electro-motive force is varied over a very wide range, it will probably
be necessary, in order to secure a constant synchronous speed, to provide a driving
means for such transformer the speed of which will not be in any way dependent
upon such variable electro-motive force. I have shewn as such means a small
synchronous motor 17, the armature of which is coupled directly to the armature
of the rotary transformer 11, and the winding of which is supplied with current
from the secondary 7 of the stationary transformer 4, the leads 18 and 19 being
connected to points in said secondary which give a constant electro-motive force.
The field winding 20 of the synchronous motor 17 may be excited from any suitable
source. In the present instance I have shewn the machine as self-excited, a com-
mutator 21 being provided with which the terminals of the winding 20 are
connected. As the motor 17 is not self-starting, I have shewn a small secondary
battery 22 for providing the necessary energy for starting the motor, and a
switch 23 for cutting the battery out of circuit when the motor has attained
synchronous speed. Any other suitable starting means may be employed.
The system above described is especially applicable to railway work, where it is
desirable to employ an alternating current transmission circuit of high voltage,
and at the same time to employ direct current motors of standard type which
will operate efficiently at all speeds. In this system the current required for
starting and accelerating the speed will be in approximate proportion to the
actual power expended. The system is also applicable to the operation of hoists
in which considerable speed variations are required.
While I have shown a single-phase alternating current circuit, it will be under-
stood that the system is also applicable to and intended for multi-phase circuits.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, as communicated to me
by my foreign correspondent, I declare that what I claim ist-
1. A system of electrical distribution, comprising an alternating current supply
circuit, one or more direct current motors, a rotary transformer taking alternating
current from said supply circuit and supplying direct current to said motor or
motors, and means for varying the alternating current electro-motive force sup-
plied to the rotary transformer and thereby varying the direct current electro-
motive force and consequently the speed of the motors.
2. In a system of electrical distribution of the kind described, the provision of

page_text: means such as a moter mechanically coupled to the rotary transformer for starting,
rotating and maintaining the same in synchronism.
3. The arrangements for operating direct current electric railway motors or
alternating current motors substantially as described with reference to the
accompanying drawings.
Dated the 27th day of March 1899.
W. P. THOMPSON & Co.,
Of London, Liverpool, Manchester and Birmingham.