Improved Method of Regulating Dynamo Electric Machines.
Year: 1899

page_text: Date of Application, 30th Dec., 1899-Accepted, 7th Apr.,
1900
COMPLETE SPECIFICATION.
Improved Method of Regulating Dynamo Electric Machines.
We, THE BRITISHI THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of our
said invention (which has been communicated to us from abroad by Charles P.
Steinmetz, of Schenectady, in the County of Schenectady, State of New York,
United States of America, Electrical Engineer), and in what manner the same is
to be performed, to be particularly described and ascertained in and by the follow-
ing statement:-
The magnetic characteristic or saturation curve of a dynamo electric machine
is always to a certain extent curved, for the reason that the magnetization does
not increase at the same rate as the increase of magnetizing or exciting current.
Since the external characteristic or load curve of a dynamo electric machine
is always to a certain extent dependent for its shape upon the mag-
netic characteristic ΟΙ saturation curve of the magnetic circuit of the
on external characteristic is corre-
machine, it follows that the load curve
spondingly curved. Thus, when compounding a self exciting direct current
generator for constant potential, the voltage at half load will be higher than at
no load and at full load. In a similar manner, when over compounding such a
machine by the use of a series field, the ampere turns of which are proportional
to the load, the voltage does not rise proportionally to the increase in foad, but
rises at a decreasing rate, corresponding to the decreasing rate of increase of
flux in the magnetic circuit. The voltage thus rises more from no load to half
load, than from half load to full load.
It is for the purpose of our invention to compensate for this variation in volt-
age due to the variation in permeability of the magnetic circuit, and we accom-
plish the result by varying the field magneto motive force or forces at a rate
greater than the rate of variation of load. We believe ourselves to be the first
to accomplish the result described, and although the various means devised by
us and disclosed in this application operate without the aid of moving parts
we, nevertheless, deem our invention a generic one and broad enough to include
the use of automatically actuated moving parts, for the purpose described.
We have described in the specification, and illustrated in the accompanying
drawings, several modes of carrying out our invention, but do not wish to be
understood as limiting ourselves specifically to any one of the means described,
but consider our invention to cover broadly the idea of varying the exciting power
of a magnetizing coil or coils of a dynamo electric machine at a rate greater
than the rate of change of load.
Fig. 1 illustrates one mode of carrying out our invention, and Figs. 2 and 3
show modified forms of the same.
In Fig. 1 we have shown our invention as applied to a self exciting direct
In order to
current dynamo electric machine having series and shunt coils.
straighten the external.characteristic of the machine, it is necessary to increase
the ampere turns of the series winding at a rate greater than the increase of load

page_text: on the machine. This result we accomplish in the present instance, by shunting
the series coil with a resistance having a temperature coefficient greater then that
of the series coil, in other words, by a device the resistance of which increases
with increase of current faster than the resistance of the series coil increases.
under similar conditions. If, as is usually the case, the series coil is formed of
copper, we may employ iron as the material of which to form the shunt about
the series coil, though it is obvious that the use of any other material is equally
within the scope of our invention. In the drawings, 1 represents the armature of
the direct current dynamo electric machine. Connected in series therewith in
the usual manner is the series exciting coil 2. Shunted around the series coil is
the variable resistance coil 3 of the character described, that is to say, having a
temperature coefficient higher than that of the series coil. This resistance is
arranged to be varied simply for the purpose of initial adjustment and it is not
in general intended to be altered during the normal operation of the machine,
although, if desired, such use is not prohibited.
For this purpose a switch arm 9 with co-operating contacts may be employed.
In shunt with the brushes, in the usual manner, is the shunt exciting coil 4
having in series therewith the usual variable regulating resistanco 5.
In the operation of the form of our invention described, it will be obvious that
as the current supplied either to or from the machine increases, the current
through the series coil and the resistance in shunt thereto will divide in certain
proportions. As the current through the machine increases the branch currents
through the series coil 2, and its shunted resistance 3, increase. Owing to the
fact however that the resistance of the shunt 3 increases with increase of current
faster than the resistance of series coil 2, it follows that a greater proportion of
current will pass through the series coil at higher values of load than at lower.
By suitably adjusting the resistance of the shunt 3, a value may be found such
that the current passing through the series coil 2 increases faster than the load
by an amount just sufficient to compensate for the drop in voltage due to the
decreasing permeability of the magnetic circuit. The load curve thus becomes
a straight line.
In Fig. 2 is shown a somewhat different arrangement for accomplishing the
same purpose. As before, 1 denotes the armature of a dynamo electric machine
around the brushes of which is connected the shunt winding 4. In series with the
armature is a series exciting coil 2. In order to increase the ampere turns of the
series field faster than the increase of load, we place in series with said coil a
counter electro-motive force device 6, the counter electro-motive force of which
increases at a rate less then proportional to the current passing through said
device. For this purpose we preferably employ polarization cells or a suitable
number of elements of a storage battery.
The electro-motive force consumed in passing current through a device of this
character is composed of two quantities. One is the counter electromotive force
proper of the device and is sensibly constant through considerable variations of
current. The other is the electromotive force consumed by the resistance of the
device, and this is proportional to the current. It consequently follows that the
electromotive force consumed in the counter electromotive force device is less
than proportional to the current passing through the same.
Referring again to Fig. 2, it will be noted that the series coil 2 and the counter
electro-motive force device 6 are shunted by the resistance 7. For the present
purpose this resistance may preferably have as low a temperature coefficient as
possible so as to remain practically constant with changes of current. The mode
of operation will be apparent from what has been said. The current passing
either to or from the machine will divide, part going through the series coil and
the counter electro-motive force device, the other part going through the shunt
about the same. Since the resistance of the shunt 7 is nearly constant the drop
of potential across the same will be almost exactly proportional to the current
passing.

page_text: With respect to the series coil, however, the state of affairs is different. The
electromotive force lost in passing the current through the same varies with the
current, being less in proportion when the current is large than when it is small.
It will be seen, therefore, that the ratio in which current will divide between the
series coil and the shunt 7 will vary with the load. A greater proportion of the
current will pass through the series coil at heavy loads than at light ones and
thus compensate for the drop in potential due to the curving magnetic character-
istic of the machine.
In Fig. 3 is shown another modification in the embodiment of our invention.
In this case, as in the others, 1 represents the armature of a dynamo electric
machine shunted around the brushes of which is the shunt exciting coil 4.
The series magnetizing coil is shown at 2 and this coil has in series therewith
a resistance 8 having a negative temperature coefficient, that is, a resistance which
decreases in value with increase in temperature, or what amounts to the same
thing, with increase of current passing through it. The resistance 7 is shunted
around the series coil 2 and the resistance 8. The shunt resistance 7 should have
as low a temperature coefficient as possible so as to vary but little in resistance
with the varying value of current passing through it.
In the operation of the machine, as thus arranged, current will divide between
the two branch circuits described, in inverse proportion to their respective resist-
ances. Owing to the fact that the resistance decreases with increase of current,
while the resistance of the shunt 7 remains sensibly constant, it follows that a
greater proportion of current will pass through the series field coil at heavy loada
than at light loads and thus obtain the same result accomplished by the two
mcdifications of our invention already described. We preferably employ carbon
as the material from which to construct the resistance 8. It will be evident
that instead of employing a resistance 8 having a negative temperature coefficient,
it will be sufficient if we employ materials having temperature coefficient such
that the ratio between the resistance 7 and the combined resistance of the series
coil and its resistance 8 becomes greater as the load increases.
We find it convenient to construct the shunt resistance 7 of German silver.
Although in connection with Figs. 2 and 3 of the drawings, we have described
certain modifications of our invention, in which the regulating shunt resistance 7
has a low temperature coefficient, it is evident that the same result may be pro-
duced, but in a greater degree, by making the regulating resistance 7 of material
having a high temperature coefficient, since the conditions requisite to carrying
out our invention are effected so long as the current through the series coil is
caused to vary at a ratio greater than the variation of load on the machine.
Our invention is to be sharply distinguished from the commonly used structure,
in which a German silver shunt is placed about the series winding of a compound
machine in order to initially adjust its magnetizing power. In this case the mode
of action is radically different from that of our invention, since a smaller instead
of a larger, proportion of the total current will pass through the series coil at
heavy loads than at light loads, thus tending to destroy rather than help the
regulation.
Instead of relying upon any particular one of the instrumentalities described,
we, may, if deemed expedient, employ them in conjunction, as illustrated in Fig. 4.
In this figure, 1 designates as before, the armature of a dynamo electric machine
having the shunt field winding 4 and series compounding coil 2. A resistance 8
of negative temperature coefficient and polarization cells 6 are included in series
with each other and with the series coil 2. A resistance of iron or other material
of high temperature coefficient forms a derived circuit in parallel with the circuit
including the series coil 2, resistance 8, and polarization cells 6. From what has
already been said in connection with the other figures of the drawings, it will
readily be seen that as the load on the machine increases, the current, through
the series compounding coil, will also increase, but at a rate greater than the rate
of increase of load.

page_text: Still another application of our invention is found in the case where a shunt
wound generator is used as a constant current fachine, to supply translating
devices in series, in which case the machine is worked within the range included
by the bend in its characteristic curve. With machines specially designed to be
operated in this manner, the voltage may be varied through a considerable range
without varying the current to any great extent. So long as saturation is not
reached, or closely approached the voltage at the terminals of the machine is pro-
portional to the excitation, and the excitation is approximately proportional to
the resistance of the work circuit. As the load increases, however, the magneti-
zation of the field approaches saturation so that the voltage of the machine does
not increase in proportion to the current through the shunt field, and the current
in the work circuit therefore decreases instead of remaining constant as desired
To compensate for the effect of saturation in the case described, we insert in the
shunt field a resistance having a high negative temperature coefficient, the effect
of which is to cause an increase of current through the shunt winding more than
proportional to the increase of electromotive force at the terminals of the machine.
By a suitable proportioning of parts, the effect of changing permeability of the
magnetic circuit of the machine may thus be compensated for.
Fig. 5 is a diagrammatic illustration of the form of the invention just described,
in which 1 represents the armature of a shunt wound generator having the field
winding 12. În series with said winding is a resistance 10 having a negative tem-
perature coefficient. This resistance is preferably formed of carbon.
external circuit contains lamps or other translating devices 11 in series.
current through the translating devices 11 is maintained constant in the manner
described.
The
The
It will be evident to those skilled in the art, that our invention is not limited
to dynamo-electric generators but is equally applicable in connection with the
speed regulation of electric motors. It will therefore be understood that when
we speak of a load on a dynamo electric machine, the term is intended to include
both the electrical load, when the machine is used as a generator, and the
mechanical load when the machine is used as a motor.
Having now particularly described and ascertained the nature of our said inven-
tion (as communicated to us from abroad) and in what manner the same is to be
performed, we declare that what we claim is :--
1-The method of regulating a dynamo electric machine which consists in com-
pensating for the variation in voltage due to variation in permeability of the
magnetic circuit.
2 The method of regulating a dynamo electric machine which consists in arti-
ficially compensating for the effect due to variation in permeability of the
magnetic circuit.
The method of regulating a dynamo electric machine, which consists in
diverting current from a field coil of the machine in such proportions that the
ratio between the current diverted and that passing in the coil is less when the
load on the machine is heavy than when it is light.
4 The method of varying the magnetizing power of a coil, which consists in
shunting the same by a resistance having a higher temperature coefficient than
that of the coil.
5 The method of regulating a dynamo electric machine, which consists in
conducting current passing through the machine, through two parallel circuits,
one of which includes a coil on the machine; and varying the current passing
through the branch containing the coil at a rate greater than the rate of variation
of current in the other branch.
6 The method of compounding a direct current dynamo electric machine, which
consists in exciting the field of the machine by the combined action of two
magneto-motive forces one of which is substantially constant, while the other has
a rate of variation greater than the rate of change of load on the machine.

page_text: 7-The method of exciting the field of a dynamo electric machine, which con-
sists in passing current through a field coil on the machine, and controlling the
flow of said current in such a manner that its rate of variation is greater than
the rate of variation of load on, the machine.
8 The method of shaping the external characteristic of a dynamo electric
machine, which consists in compensating for the variation in voltage due to varia-
tion in permeability of the magnetic circuit.
9-In a dynamo electric, machine, the combination of a winding on the field
magnet, and a shunt about said winding having a higher temperature coefficient
than said winding.
10 In a dynamo electric machine, a divided circuit including in one of its
branches a winding on the field of the machine, and so constituted that with vari-
ation of load on the machine the rate of change of current in the branch including
the winding is greater than the rate of change of current in the other branch.
11 In a dynamo electric machine, a divided circuit traversed by the main cur-
rent of the machine, and including in one of its branches a winding on the field
of the machine, the divided circuit being so constituted that with variations of
load on the machine, the rate of change of current in the branch including the
winding is greater than the rate of change of current in the other branch.
12 A dynamo electric machine having a field exciting coil and means for
diverting current therefrom at a rate less than the rate of variation of load on
the machine.
13 A dynamo electric machine having series and shunt field exciting coils, and
means for varying the current passing through the series coil at a rate greater
than the rate of change of load on the machine.
14 The combination of a compound wound dynamo electric machine and a
resistance of iron in shunt about the series coil.
15 The combination of a compound wound dynamo electric machine and a
shunt about the series coil having a higher temperature coefficient than that of
the coil.
16 In a dynamo electric machine, the combination of a field exciting coil
having in series therewith a resistance of negative temperature coefficient.
17 In a dynamo electric machine, the combination of a field exciting coil, a
carbon resistance in series therewith and a shunt about said coil and resistance
18 In a dvnamo electric machine, the combination of a field exciting coil, a
polarization cell in series with said coil, and a shunt about said coil and polariza-
tion cell.
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