Method of Regulating the Electric Current Produced by Electric Generators Driven by a Motor Having an Irregular or Variable Speed.
Year: 1889

page_text: Date of Application, 15th Apr., 1889
Complete Specification Left, 15th Jan., 1890-Accepted, 14th June, 1890
PROVISIONAL SPECIFICATION.
Method of Regulating the Electric Current Produced by Electric
Generators Driven by a Motor Having an Irregular or Variable
Speed.
I, PAUL HOHо of rue Verte, Brussels, in the Kingdom of Belgium, Engineer, do
hereby declare the nature of this invention to be as follows:-
The object of the present invention is to produce a current of a predetermined
strength, either constant or variable in a predetermined manner, in an electric machine
the speed of which varies within certain limits; by operating on the intensity of the
field magnets as described hereafter.
Before describing the general principle serving as a basis to the present invention
it is advisable, for the sake of easier understanding to describe an example of applying
the invention.
Supposing for instance it is desired to obtain from a dynamo electric machine, the
speed of which varies between 750 and 1250 revolutions, constant electro motive force
equal to 100 volts;
Fig. 1 represents the diagrams (characteristics) taken with this machine for
different speeds ranging between 750 and 1250 revolutions. These diagrams show
the values of the ampere-turns necessary at these different speeds for the production
of 100 volts and expressing these values in ordinates I'obtain in the curve abg
(Fig. 2) a graphic representation of the amperè-turns necessary to obtain 100 volts at
the speed from 750 to 1250 revolutions.
It suffices therefore to give the dynamo an excitement varying with the speed in
accordance with the law laid down by the curve abg of Fig. 2, and this is the
problem solved by the present invention. This excitement can for instance be
produced by means of two small auxiliary machines.
To facilitate the understanding of this system we will suppose that the work of
these auxiliary machines is known and represented by the curves I and II Fig. 3
which give the volts produced by each machine individually. By means of these
auxiliary machines the principal machine may be excited in the following manner for
instance ;
A first exciting circuit wound round the field magnet of the principal machine is
fed by the auxiliary machine I. A second exciting circuit is fed by a current
resulting from the difference of the electro-motive forces produced by the two auxiliary
machines; i.e. the second circuit is arranged in series with the armatures of the two
auxiliary machines, the homonymous poles of which correspond. As indicated in
Fig. 3 the difference of the electro-motive force of the two auxiliary machines
at 1000 revolutions is equal to zero.
At a speed of a 1000 revolutions therefore the current in the 2nd circuit will be zero
and the total excitement at 1000 revolutions must be furnished by the first circuit
only i.e. the first circuit must be so calculated that the electromotive force q m fig. 3
produced by the first auxiliary machine at 1000 revolutions gives the excitement
indicated as b b¹ fig. 2.
For the other speeds the excitement produced by the first current will be in
proportion with the electro-motive force which feeds this current i.e. the electro-motive
forces represented by the curve I fig. 3.
This excitement produced in the first circuit is represented by the line cbf fig. 2.
It remains now to produce an excitement represented by the algebraical differences of
the ordinates of the curves ab g and c bf fig. 2, which differences are represented by
the ordinates first positive, then negative of the curve d b' f¹ fig. 2. As said above
these excitements must be produced by the second circuit by the differences of the
electromotive forces of the two auxiliary machines.

page_text: At 750 revolutions the difference between the electro-motive forces is pl p' fig. 3,
and this must produce an excitation of d d¹ fig. 2, this permits of the constants of the
second exciting circuit being calculated.
In this manner the proper excitement is obtained for 1000 and for 750 revolutions.
This proper excitement can always be obtained for any two different speeds no
matter what the results of the auxiliary machines are, always provided that these
results are different.
There remain now the other speeds; for these the excitements to be produced by
the second circuit are given by the ordinates of the curve d b' f¹ fig. 2.
It being understood that p¹ p³ fig. 3 gives an excitement d d¹ fig. 2, the
curve p* m n³ fig. 3 (in which p³ p is equal to pl p² and the ordinates of which
are in proportion to the ordinates of d b¹ f¹ fig. 2) represents the electro-motive forces
in the second exciting circuit for the purpose of obtaining the proper excitement for
all speeds ranging from 750 to 1250 revolutions.
If the ordinates of the curve p* m n³ are subtracted algebraically from the ordinates
of the curve I fig. 3, the curve p³ q n2 is obtained which represents the result the
second auxiliary machine must give for obtaining the proper excitement for all speeds
ranging between 750 and 1250 revolutions.
In the foregoing example the curve p³ m n² conforms exactly with that of the
second auxiliary machine because the two machines were properly chosen beforehand.
The more the real curve of the second machine is like the one indicated above, the
more perfect will be the regularity in the speeds between 750 and 1250 revolutions.
It will be remarked that the regulating influence will be produced before a speed
of 750 revolutions is reached and will persist after 1250 and that to a degree
depending upon the results of the auxiliary machines.
Now for regulating the results of the two auxiliary machines it will be observed
that besides the means presented by the selection and construction of each individual
machine, new elements are here at disposal, in fact here are two machines each of
which can be excited either by itself or by the other or by both.
In the above example the same result would have been arrived at if the two
auxiliary machines had acted separately in two distinct circuits arranged so as to
produce excitements in contrary directions.
It is easy to understand that proceeding in a similar manner to that described above
the principal dynamo machine instead of producing a constant electro-motive force
could have been made to produce an electro-motive force varying in predetermined
manner according to the speed.
In the above described example two auxiliary machines have been used; if however
the electro-motive force of the principal machine is used for the exciting, it suffices
to use one single auxiliary machine. In this case the calculations will be analogous
to the above but care must be taken of the fact that this source of excitement is
itself submitted to the effects of regulation.
Instead of producing the excitement hy means of two or more separate circuits, it
may be produced by a single exciting circuit provided that the electro-motive force of
the current passing through this circuit has a proportionally similar result to that of
the exciting which is to be produced.
An electro-motive force having such a result may emanate from a single dynamo
which has been regulated to this effect or it may result from a combination of
electro-motive forces emanating from divers sources and the combined results of which
give the desired result.
In a general manner I have proved mathematically that if a machine to be regulated
is excited by two or more exciting circuits which receive their current from two or
more sources of electricity the results of which however are different and independent
for each circuit, excitings equal to those desired for so many different speeds as there
are exciting circuits, can be obtained.
It must be observed that each of the said exciting circuits can be fed by a single
source or by a combination of several sources.
In other words a curve being given representing the diagram which the result of

page_text: the excitement should follow or describe when the speed of the machine varies within
certain limits, it will always be possible to obtain with mathematical exactness the
necessary excitings for as many different speeds as there are exciting currents
provided that the results of the latter are different and independent; or in other
words to produce an exciting curve having so many points as desired in common with
the desired result curve.
Each of the dynamos employed as auxiliary sources can be excited by itself or by
one or more others and as mentioned above the principal dynamo can always itself
furnish one of the auxiliary sources.
As different electric currents giving different results can be obtained from the same
machine, whether the principal or the auxiliaries, by placing the brushes at different
points of the commutator different currents coming from the same armature can be
used for the exciting in the same way as before.
Two commutators one on each side of the armature may be used.
The result of the electro-motive force of these currents when the speed of the
machine varies, depends essentially upon the magnetic field corresponding to the part
of the armature enclosed between the two brushes.
To obtain thus electro-motive forces giving different results from the same armature
the field magnets can be so constructed as to exert different magnetic actions on the
different parts of the armature, and these differences may lie in the field magnet
itself, in the pole pieces or other parts, in their nature, manner, and degree of exciting,
in their form and dimensions, in their magnetic resistances, in their position, in
their distance from the armature or in any other element having an influence on
the magnetism.
The intensity of the magnetic field depends further upon the nature of the
armature. Electro-motive forces of different results may therefore be obtained by
means of different armatures submitted to the magnetising action of the same
inducing system.
When several armatures are employed the inducing system acting on these armatures
may also be partially combined or mixed and this applies as well to the machine to be
regulated as to the auxiliary machines.
The above described method of regulating can be employed as well with machines
having alternating currents as with those having continuous currents. In the
practical employment of this method I do not restrict myself to any special mechanical
arrangement.
Dated this 15th day of April 1889.
W. P. THOMPSON & BOULT,
Agents.
COMPLETE SPECIFICATION.
Method of Regulating the Electric Current Produced by Electric
Generators Driven by a Motor Having an Irregular or Variable
Speed.
I, PAUL HOHо of rue Verte, Brussels, in the Kingdom of Belgium, Engineer,
do hereby declare the nature of this invention and in what manner the same is to be
to be performed, to be particularly described and ascertained in and by the following
statement:
The object of the present invention is to produce a current of a predetermined strength,
either constant or variable in a predetermined manner, in an electric machine the
speed of which varies within certain limits, by operating on the intensity of the field
magnets as described hereafter.
Before describing the general principle serving as a basis to the present invention,
it is advisable, for the sake of easier understanding, to describe an example of applying
the invention.

page_text: Supposing for instance it is desired to obtain from a dynamo electric machine, the
speed of which varies between 750 and 1250 revolutions, a constant electro-motive
force equal to 100 volts;
The curves in figure 1 show the characteristics of the dynamio for 750, 875, 1000
and 1250 revolutions. If on the characteristic corresponding to 750 revolutions the
point be taken at which 100 volts are obtained the abscissae of this point will indicate
the number of ampere-windings which are required to excite the inductors of the
dynamo so that it should produce 100 volts by making 750 revolutions.
Corresponding points may be similarly taken on the other characteristics corre-
sponding to 875, 1000 and 1250 revolutions.
In Fig. 2 the different rates of speed are indicated by abscissae. Upon the axis of
these abscissae ordinates may be constructed corresponding respectively to 750, 875,
1000 and 1250 revolutions, representing the value or number of ampere-windings
required in order to obtain 100 volts by means of a dynamo running respectively at
these different rates of speed. There will then be obtained point g for 1250 revolutions,
b for 1000 revolutions, a for 750 revolutions; and by connecting those points a
curve a bg is obtained. Thus each point of this curve represents through its ordinate
the number of ampere-windings that are required for the dynamo to produce 100 volts
while moving at the rate of speed indicated by the corresponding absciss.
The purpose to attain therefore is, to obtain upon the inductors an amount of
excitation varying in function to the speed according to the law graphically represented
by the said curve a b g.
I will now proceed to show that it is possible to obtain the required amount of
excitation at any two different rates of speed, viz. by means of two exciting circuits
fed from two different sources of electricity. Such arrangement is shown in Figure 4.
The first circuit is fed by a small separate and given dynamo I, the electro-motive
power of which varies according to the speed in the manner represented by curve I,
Figure 3.
The second circuit is fed by the same dynamo I and by a second small dynamo II
arranged in series with the exciting circuit (as illustrated by Figure 4) but in such a
manner that both dynamos act in opposite directions to each other; they being for
the purpose connected by their poles of the same sign. The current passing through
the second circuit will therefore be equal to the difference between the electro-motive
force of the two dynamos I and II divided by the resistance of the circuit.
The curve II (Fig. 3) indicates the manner in which the electro-motive power of
dynamo II varies with the rate of speed of that dynamo.
It will be seen that the electro-motive power of either dynamo, corresponding to
1000 revolutions, is equal, the difference therefore being zero. Thus at 1000 revo-
lutions there is no current in the second exciting circuit, and it is the first circuit
alone which has to produce the necessary excitation as represented by the ordinate b b 1
(Fig. 2); that is the e.m.f. q m (Fig. 3) has to produce the excitation bb' (Fig. 2).
This permits the constants of the first exciting circuit to be calculated and so the
proper excitation will be obtained when the dynamo is running at 1000 revolutions
per minute.
For all other rates of speed the excitation caused by the first circuit will vary
proportionately to the ordinates of curve 1 (Fig. 3) as represented by the ordinates of
the curve cbf (Fig. 2).
For 750 revolutions for instance, the first exciting circuit will generate an excitation
equal to the ordinate of point c. And as for 750 revolutions it is necessary that the
excitation should equal the ordinate of point a, what is required is to obtain a supple-
mentary excitation equal to a c. Now this is obtained by means of the second exciting
circuit.
It will indeed be seen by reference to Figure 3 that at 750 revolutions a difference
arises in the electro-motive power between the two dynamos equal to p¹ p¹¹; and it
is this difference p₁ p" that should now produce the excitation a c (Fig. 2) in the
second circuit. This permits the constants of the second circuit to be calculated.

page_text: Suitable excitations are thus obtained both for 1000 and 750 revolutions
respectively. This is what I desired to demonstrate. It might further be shown
how excitations behave for any other speed, but the foregoing is sufficient for the
comprehension of the principle.
The system can be understood so that two circuits which are fed by two different
sources of electricity, and which excite a main dynamo may produce a resulting
excitation-effect that increases when speed decreases, and vice-versa; and so the
main dynamo may produce a constant e.m.f. Therefore it is required only that the
constants of the two exciting circuits be calculated on a suitable manner, as is shown
in the example, or that they be experimentally determined.
It will now be observed that it is possible to influence the results of the two
auxiliary machines; besides the means presented by the selection and construction of
each individual machine, new elements are here at disposal; in fact here are two
machines each of which can be excited either by itself or by the other or by both.
In the above described example two auxiliary machines have been used; if
however the electro-motive force of the principal machine is used for the exciting, it
suffices to use one single auxiliary machine, as is shown in Fig. 5. In this case
the calculations will be analogous to the above, but care must be taken of the fact
that this source of excitement is itself submitted to the effects of regulation.
In the above example the same result would have been arrived at, if the two
exciting machines had acted separately in two distinct exciting circuits, arranged so
as to produce excitements in contrary directions.
It is easy to understand that, proceeding in a similar manner to that described
above, the principal dynamo machine, instead of producing a constant electro-motive
force, could have been regulated so as to produce an electro-motive force varying in
a predetermined manner according to the speed.
In a general way the following facts have been ascertained :-With a given
dynamo it is possible to determine either by calculation or experiment the number
of ampere-windings necessary for exciting the magnetic field of such dynamo so that
the latter should when running at a given rate of speed produce a given electro-
motive force. If thus the numbers of ampere-windings are found, which are necessary
at several different rates of speed, they will enable a general law to be laid down, either
by a mathematical expression or graphically by a curve, according to which magnetic
excitation (expressed in ampere-windings) should vary "in function" of the speed, so
that in acting upon the inductors of an electric machine it should cause the latter to
generate an electro-motive force which remains constant, whereas the speed varies, or
which varies in an arbitrarily predetermined manner. It is obvious that the machine
to be used for this purpose should be so arranged that its magnetic field is not liable to
become saturated by its maximum excitation.
Let B
ho the various rates of snood arhitmanile calcatal

page_text: To obtain the given magnetic excitations upon the inductor it is necessary
that ;-
At nanuod
"2
(e1\
L
1
Pm (omla
"m
are not proportionate, that is to say that the electromotive forces °1 *2
vary in different proportions whenever the speed varies. It follows that if an
electrical machine is excited by two or more circuits any desired excitations may be
obtained therein, while it runs at as many different and arbitrarily determined rates
of speed as there are exciting circuits fed by different sources of electricity, which
may be of any kind whatsoever provided their electromotive forces do not vary
proportionately when the rate of speed varies; whereupon currents may be generated
in this machine at those arbitrarily determined rates of speed, the electromotive
forces of which represent predetermined quantities or indeed one constant
quantity.
The result obtained may be substantially described as follows;-It is possible to
construct the curve being the expression of the rate of variation of the magnetic
excitement, to which are to be submitted the inductors of the dynamo in proportion
to speed so that the electro motive power continues either constant or variable
according to a given law. A curve of excitement may now be obtained which will
coincide with the first curve in as many points as may be desirable with mathematical
precision.
-
REMARKS.
1. It will be observed that to obtain the result just mentioned the sources of
electricity supplying the exciting currents are required to fulfil no other condition
except that their electromotive forces should vary in accordance with different
functions of speed.
2. It will also be seen that the rates of speed in regard to which a perfect
coincidence is obtained between a given curve of excitement and the curve of
excitement obtained may be determined in a perfectly arbitrary manner.
3. It must be observed that each of the said exciting circuits can be fed by one
single source or by a combination of several sources of electricity.
4. Each of the dynamos employed as auxiliary sources can be excited by itself,
or by one or more others, and as mentioned formerly, the principal dynamo can
always itself furnish one of the auxiliary sources.

page_text: 5. For this purpose any desirable sources of electricity may be used such as
dynamos, primary or secondary cells &c.
Instead of producing the excitement by means of two or more separate circuits,
it may be produced by a single exciting circuit, provided that the electro-motive
force of the current passing through this circuit has a proportionately similar result
to that of the excitement which is to be produced.
An electro-motive force having such a result may emanate from a single dynamo
which has been regulated to this effect, or it may result from a combination of
electro-motive forces emanating from divers sources, and the combined results of
which give the desired result.
The only objection that might be made to the controlling system such as I have
described is that it is necessary that at least one accessory source of electricity
should be available for excitation, this however is no serious objection and it
will be seen that an accessory source of electricity may, if need be, be dispensed
with.
In all electrical machines the electro-motive force collected between the two
brushes is the result of the algebraic sum of all electro-motive forces induced
into the coils of the armature interposed between the brushes. The armature of
an electric machine may therefore be considered as constituting a certain
number of distinct sources of electricity; different currents may be collected upon
such an armature by means of several brushes arranged in different points of the
collector.
The electro-motive forces in use in the different parts of the armature may or
may not be equal (that is to say may or may not vary according to speed).
These variations mainly depend on the distribution of the magnetic field in the
different portions of the armature.
When these rates of variation are different the principles set forth above may
be applied for feeding two or more of the exciting circuits of the machine just as
in the case of different sources of electricity.
Such currents may be collected even in an armature of an ordinary dynamo.
This however immediately suggests the idea of creating special dynamos for
this purpose adapted to distribute the magnetic field differently in the different
portions of the armature and to form a number of neutral points in the latter
so that the currents to be used for excitation may be readily collected on these
points.
Among many combinations that might be devised for this purpose those which
form what I bave termed dynamo electric machines with compound magnetic fields
are calculated to fulfil the desired object most thoroughly.
An instance of this is shown in Fig. 6 where a small dynamo of this description
produces exciting currents for an ordinary dynamo which it is desired to regulate.
The inducing system comprises four pole pieces N, S, and N' S' the two former
differing from the two latter in intensity of the magnetic action produced upon the
armature and the system being formed in all other respects in any suitable manner
such for instance as is indicated in dotted lines in the said figure.
Four brushes are arranged upon the collector in the points a b b c so that they
may separately collect the currents produced in the armature by the four individual
pole pieces. The points 6 and b¹ have the same electric potential, the brushes band 6¹
may therefore be connected in series; the electro-motive forces induced by the pole
pieces N and S between a-b and between a-b' are different from those induced by
the pole pieces N' and S¹ between bc and b¹-c and the current collected between
a-bb is different from the current collected between b b'—c.
To come more nearly within the scope of the instance mentioned above let us
suppose that the pole pieces N and S, which are larger than the pieces N' and S¹ and
can therefore supply a more intense magnetic fluid than N¹ S¹, are however less
saturated than these pole pieces N¹ S¹.
By constructing in this case the curves representing the methol of variation of

page_text: the electro-motive forces of the two currents in proportion to speed and by comparing
the curves to those given in the preceding example and corresponding to two ordinary
machines viz. the curves I and II of figure 3 it will be seen that the inflection of
these curves are analogous and that the current collected between a-b b' more
nearly approaches the curve No. II than the current collected between bbc
approaches the curve No. I.
Now these currents may be dealt with in the same way as was the case in the
instance illustrated by figures 4 and 5 that is both currents may be employed for
exciting the main machine it is desired to regulate just as if these currents were
supplied by two separate machines a condition of things represented in Figure 6.
The first circuit is fed by either of the two currents say by the current 6 6¹-c;
the second circuit is fed by the difference between the two, that is to say the difference
between the electro-motive force created between c-b ¹ on the one hand and the
electro-motive force induced between a-b¹ on the other hand. To effect this it is
sufficient to collect the second current between the brushes a and c (as the poles N
and S¹ act in contrary directions).
The action of these currents is exactly the same as that referred to in regard to
figures 4 and 5 and the preceding remarks will equally well apply here.
In some cases it may be advantageous to use two commutators one on each side of
the armature.
The result of the electro-motive force of a dynamo when the speed varies,
depends essentially upon the magnetic field corresponding to the part of the armature
enclosed between the two brushes.
To obtain thus electro-motive forces giving different results from the same armature,
the field magnets can be so constructed as to exert different magnetic actions on the
different parts of the armature and these differences may lie in the field magnet itself,
in the pole pieces or other parts, in their nature, manner, and degree of exciting,
in their form and dimensions, in their magnetic resistances, in their position, in
their distance from the armature, or in any other element having an influence on
the magnetism.
Different currents thus collected from the armature of the dynamo may be utilized
for exciting and regulating a second dynamo see Fig. 6, but they may also be made
use of for exciting and regulating the same dynamo.
The intensity of the magnetic field depends further upon the nature of the armature.
Electro-motive forces of different results may therefore be obtained by means of
different armatures, submitted to the magnetising action of the same inducing
system.
When several armatures are employed, the inducing systems acting on these
armatures may also be partially combined or mixed, and this applies as well to the
machine to be regulated as to the auxiliary machines.
The above described method of regulating can be employed as well with
machines having alternating currents as with those having continuous currents.
In the practical employment of this method I do not restrict myself to any special
mechanical arrangement.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The controlling forces for dynamo electric machines operated by means of motors
of variable speed consist in an arrangement in which the whole or part of the
inductors of the dynamo are excited by one or more dynamos liable to the same
variations of speed one or more exciting circuits being combined in such a manner
that a total exciting effect takes place in accordance with a predetermined law in
a certain proportion to the speed for the purpose of enabling the intensity of the
magnetic field to be controlled as required according to the variations of speed.
2. For the purpose of producing in an electric machine, working at a speed
.

page_text: rying within certain limits, a current whose electro-motive force varies in the desired
nstant or variable ratio to the speed, the arrangements adapted to excite the
agnetic field of the dynamo as follows:
(A) by two or more exciting circuits supplied, (a) by two or more auxiliary electric
machines either combined with each other or not; (b) by the main machine
and one or more auxiliary machines; (c) by one
or more auxiliary
machines and one or more batteries of accumulators with, or without, the
addition of the main machine.
Or (B) by two exciting circuits supplied respectively (d) one by a battery of
accumulators, and the other by the dynamo itself, or by the combination of
the dynamo and the said battery.
Or (C) by one exciting circuit supplied, (e) by an electric machine provided
with arrangements enabling it to produce currents whose strength varies in
the desired ratio to the speed; or (ƒ) by a combination of several electric
machines.
3. For the purpose specified in the preceding claim the arrangements for exciting
e magnetic field of the dynamo by means of two or more exciting circuits, fed
currents supplied by one and the same armature, although by different portions of
ch armature.
4. For the purpose indicated above, and in order to assist the proper working of
e arrangements mentioned in the preceding claim, the devices for influencing the
agnetism or magnetization differently in different portions of the armature.
5. For the purpose set forth in claim 2 the arrangements for exciting the magnetic
ld of a dynamo by means of two or more exciting circuits, fed by currents generated
two or more armatures, which armatures are submitted to the magnetizing
tion of induction devices which are partly or totally combined; it being under-
od that such inductors may, or may not similarly combine with those of the main
chine.
Dated this 15th day of January 1890
W. P. THOMPSON & BOULT,
Agents for the Applicant.