Year: 1898

page_text: I, BENJAMIN GARVER LAMME, of 230, Stratford Avenue, Pittsburg, County of
Allegheny and State of Pennsylvania, United States of America, Electrical
Engineer, do hereby declare the nature of this invention to be as follows:
:-
My invention relates to the transformation of direct currents to alternating
currents, and has for its object to provide a method and a means whereby the
speed of the rotary transformer employed may be maintained substantially
constant irrespective of changes in the amount of inductive load on the alternat-
ing current circuit.
It is well known that a rotary transformer employed in transforming alternat-
ing to direct currents has a certain definite speed which is determined by the
rate of alternations of the current supplied to its alternating current terminals.
The speed, therefore, remains constant even though the electromotive force be
varied, provided the rate of alternations is not changed.
This transformation from alternating currents to direct currents is the one
most usually practised, but it sometimes occurs that a demand is made for alter-
nating current for driving induction motors or for other purposes, where the
only readily available source of current is a direct current generator or a plant
embodying several such generators. Under such conditions, it becomes necessary,
in order to utilize the existing plant, to transform some or all of the direct
current to alternating current. It is, of course, desirable to employ a rotary
transformer for this purpose, but with such reversed operation of the rotary
transformer, the rate of alternations of the current obviously depends upon the
speed of the armature, and this in turn is dependent upon the field magnet
strength and the direct current electromotive force supplied to the armature.
If the rotary transformer is delivering an alternating current that is in step
with its electro-motive force, the armature reactions of the direct current are
opposed to, and practically neutralize, those of the alternating current. Under
this condition, the rate of alternations of the alternating current will remain
practically constant notwithstanding variations in the load, provided the field

page_text: charge and the applied direct current electromotive force remains constant; but
if the alternating current is not in step with its electromotive force, there will
be two components, one of which is in step with the electromotive force and is
represented by the direct current supplied to the transformer, and the other of
which is at right angles to the electromotive force and is not represented by any
corresponding direct current. This right-angled component may be either a lead-
ing or a lagging current and will react upon the field magnet so as to magnetize
or demagnetize it, as the case may be. If it exerts a magnetizing effect, it
strengthens the field magnet and the speed of the rotary transformer decreases.
If it demagnetizes the field magnet, the speed of the transformer will increase.
Therefore, if the alternating current circuit carries an inductive load, such, for
example, as induction motors, which changes from time to time, the variations
in the amount of inductive load will cause variations in the speed of the trans-
former which will in turn vary the speed of the motors driven by it.
In order to obviate this variation in speed with changes in the amount of
inductive load, according to my invention I employ a small direct current
generator for exciting the field magnet of the rotary transformer. Said generator
may have either a shunt, series or a compound winding, but it is normally
operated to produce an electromotive force which corresponds to a degree of field
magnet excitation very much below saturation. The speed of the exciting
generator is automatically varied in accordance with the changes in the amount
of inductive load on the alternating current side of the rotary transformer, for
example, it may be driven either by an alternating current motor which is in
turn driven by current supplied by the rotary transformer, or it is belted directly
to the said rotary transformer.
If the amount of the alternating current inductive load on a rotary trans-
former changes so that the rate of alternations decreases, for example, then the
exciting generator and the motor driving the same will also decrease in speed.
This action will also decrease the exciting electromotive force of the rotary trans-
former, and as the exciter is unsaturated, a small drop in speed will produce a
relatively large drop in the electromotive force. This lowering of the exciting
electromotive force will thus weaken the field of the rotary transformer and
effect an increase of its armature speed up to near the normal; on the other
hand, an increase in speed of the rotary transformer will be accompanied by an
increase in the exciting electromotive forces which will act immediately to
lower the speed of the transformer.
In the accompanying drawing, Figure 1 is a diagram of a system embodying
my invention, and Figure 2 is a similar diagram of a modification.
Referring particularly to Figure 1, 1 is a direct current generator which may
have any suitable type of field magnet winding, that shewn being of the com-
pound variety. 2 is a rotary transformer receiving direct current from a gene-
rator 1 and supplying alternating current to the mains 3, 4, 5 and 6. 7 is a two-
phase motor, which represents the inductive load upon the alternating current
circuit. The field-magnet winding 8 of the rotary transformer 2 is shewn as
excited by a direct current generator 9 having a series of field-magnet winding 10,
this probably being the most desirable winding for this system, although the
invention is not limited in this respect. The armature of the generator 9 is shewn
as belted to a small two-phase motor 11 which receives its driving current from
the mains 3, 4, 5 and 6.
The operation of this system effects a substantially constant speed of the
rotary transformer notwithstanding changes in the amount of inductive load on
the alternating current circuits supplied by it as has been already set forth.
In Figure 2 the main direct current generator 1ª is shewn as a shunt-wound
machine, also the exciting generator 9 is belted directly to the rotary trans-
former instead of being driven by a separate motor, as in the arrangement shewn
in Figure 1.
It has been found in practice that this method gives very satisfactory results

page_text: and that the variations in speed of the rotary transformer are less than one-
tenth as great as they are when the transformer is operated as a shunt-wound
machine in the ordinary way.
A
ام
1000
W. P. THOMPSON & Co.,
322, High Holborn, London, W.C., Patent Agents for the Applicant.
Improvement in Systems of Electrical Distribution and Regulation.
I, BENJAMIN GARVER LAMME, of 230, Stratford Avenue, Pittsburgh, County of
Allegheny and State of Pennsylvania, United States of America, 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 the transformation of direct currents to alternating
currents, and has for its object to provide a method and a means whereby the
speed of the rotary transformer employed may be maintained substantially
constant irrespective of changes in the amount of inductive load on the alternat-
ing current circuit.
It is well known that a rotary transformer employed in transforming alternat-
ing to direct currents has a certain definite speed which is determined by the
rate of alternations of the current supplied to its alternating current terminals.
The speed, therefore, remains constant even though the electromotive force be
varied, provided the rate of alternations is not changed.
This transformation from alternating currents to direct currents is the one
most usually practised, but it sometimes occurs that a demand is made for alter-
nating current for driving induction motors or for other purposes, where the
only readily available source of current is a direct current generator or a plant
embodying several such generators. Under such conditions, it becomes necessary,
in order to utilize the existing plant, to transform some or all of the direct
current to alternating current. It is, of course, desirable to employ a rotary
transformer for this purpose, but with such reversed operation of the rotary
transformer, the rate of alternations of the current obviously depends upon the
speed of the armature, and this in turn is dependent upon the field-magnet
strength and the direct current electromotive force supplied to the armature.
If the rotary transformer is delivering an alternating current that is in step
with its electromotive force, the armature reactions of the direct current are
opposed to, and practically neutralize, those of the alternating current. Under
this condition, the rate of alternations of the alternating current will remain
practically, constant notwithstanding variations in the load, provided the field
charge and the applied direct current electromotive force remain constant; but
if the alternating current is not in step with its electromotive force, there will
be two components, one of which is in step with the electromotive force and is
represented by the direct current supplied to the transformer, and the other of
which is at right angles to the electromotive force and is not represented by any
corresponding direct current. This right-angled component may be either a lead-
ing or a lagging current and will react upon the field-magnet so as to megnetise
or demagnetize it, as the case may be. If it exerts a magnetizing effect, it
strengthens the field-magnet and the speed of the rotary transformer decreases.

page_text: If it demagnetizes the field-magnet, the speed of the transformer will increase.
Therefore, if the alternating current circuit carries an inductive load, such, for
example, as induction motors, which changes from time to time, the variations
in the amount of inductive load will cause variations in the speed of the trans-
former which will in turn vary the speed of the motors driven by it.
In order to obviate this variation in speed with changes in the amount of
inductive load, according to my invention I employ a small direct current
generator for exciting the field-magnet of the rotary transformer. Said generator
may have either a shunt, series or a compound winding, but it is normally
operated to produce an electromotive force which corresponds to a degree of field-
magnet excitation very much below saturation. The speed of the exciting
generator is automatically varied in accordance with the changes in the amount
of inductive load on the alternating current side of the rotary transformer, for
example, it may be driven either by an alternating current motor which is in
turn driven by current supplied by the rotary transformer, or it is belted directly
to the said rotary transformer.
If the amount of the alternating current inductive load on a rotary trans-
former changes so that the rate of alternations decreases, for example, then the
exciting generator and the motor driving the same will also decrease in speed.
This action will also decrease the exciting electromotive force of the rotary trans-
former, and as the exciter is unsaturated, a small drop in speed will produce a
relatively large drop in the electromotive force. This lowering of the exciting
electromotive force will thus weaken the field of the rotary transformer and
effect an increase of its armature speed up to near the normal; on the other
hand, an increase in speed of the rotary transformer will be accompanied by an
increase in the exciting electromotive forces which will act immediately to
lower the speed of the transformer.
In the drawing filed with my Provisional Specification, Figure 1 is a diagram
of a system embodying my invention, and Figure 2 is a similar diagram of a
modification.
Referring particularly to Figure 1, 1 is a direct current generator which may
have any suitable type of field-magnet winding, that shewn being of the com-
pound variety. 2 is a rotary transformer receiving direct current from the gene-
rator 1 and supplying alternating current to the mains 3, 4, 5 and 6. 7 is a two-
phase motor, which represents the inductive load upon the alternative current
circuit. The field-magnet winding S of the rotary transformer 2 is shewn as
excited by a direct current generator 9 having a series field-magnet winding 10,
this probably being the most desirable winding for this system, although the
invention is not limited in this respect. The armature of the generator 9 is shewn
as belted to a small two-phase motor 11. which receives its driving current from
the mains 3, 4, 5, and 6.
The operation of this system effects a substantially constant speed of the
rotary transformer notwithstanding changes in the amount of inductive load on
the alternating current circuits supplied by it as has been already set forth.
In Figure 2 the main direct current generator 1" is shewn as a shunt-wound
machine, also the exciting generator 9 is belted directly to the rotary trans-
former instead of being driven by a separate motor, as in the arrangement shewn
in Figure 1.
It has been found in practice that this method gives very satisfactory results
and that the variations in speed of the rotary transformer are less than one-
tenth as great as they are when the transformer is operated as a shunt-wound
machine in the ordinary way.
Although the drawings illustrate the invention as applied to a system wherein
two-phase alternating currents are employed it is clear from the considerations
herein before stated that the invention is applicable to rotary transformers
delivering alternating currents irrespective of the number of phases in the alter-
nating current circuit.

page_text: Having now particulary 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) The method of maintaining approximately constant the number of alter-
nations of the alternating current given out by a rotary transformer used for
transforming direct currents into alternating currents, which consists in causing
the excitation of the transformer field-magnet to vary in accordance with the
change of the inductive load in the alternating current circuit, or in accordance
with the change of speed of the rotary transformer.
2) For exciting the field-magnet of a rotary transformer which is transforming
direct currents into alternating currents, a direct current generator the current
supplied by which varies in accordance with the variation in inductive load in
the alternating current circuit.
3) The improved systems of electrical distribution substantially as described
with reference to Figures 1 and 2 of the drawings.
Dated this Oth day of Tunn 1900.
W. P. THOMPSON & Co.,
Of London, Liverpool, Manchester and Birmingham.