Improvements in connection with Dynamo-electric Generators for Regulating the Circuit Currents to Arc Lamps.
Year: 1890

page_text: Date of Application, 15th July, 1890-Accepted, 23rd Aug., 1890
COMI DEIE DI POLICATION
Improvements in connection with Dynamo-electric Generators for
Regulating the Circuit Currents to Arc Lamps.
1 JAMES YATE JOHNSON of 47 Lincoln's Inn Fields in the County of Middlesex
Gentleman do hereby declare the nature of this Invention which has been
communicated to me from abroad by Higham Patent Right Co. of Rockland
Maine in the United States of America 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 the regulation of arc light dynamos and its object is
to so provide for the regulation that this class of dynamos can be made much cheaper
and at the same time more efficient than has been heretofore permissible.
All are light dynamos now known are constructed with a large amount of armature
and field magnet windings to a small amount of iron in the armature and field
magnet cores that is they are so designed that by working up to the degree of
magnetic saturation an increase of current above the normal will either drop or
else not increase the potential at the terminals of the dynamo; this of course is
independent of any movement of a regulator.
It is well known in the art, however, that such dynamos will cost more to
manufacture and be much lower in efficiency than dynamos constructed with a
small amount of wire windings to a relatively large amount of iron in the magnetic
circuit; but nevertheless such dynamos are purposely so designed and for no other
reason than to ensure stability of current in the working circuit.
The necessity of this design is due, firstly to the peculiar properties of an arc light
secondly to the nature of a series wonnd dynamo and thirdly to the action of the
regulator itself.
Whenever attempts have been made to run are light dynamos with unsaturated
magnets they have always met with most discouraging results due to the instability of
the current. In order that this shall be made more apparent, it will be well to point
out some of the peculiarities referred to. In the first place the resistance of an arc
will fall when the current rises, and rise when the current falls, which, as will be
understood, is just the reverse action to what would be desired for the stability of
current.
This change of resistance in the arc is no small variation it falling more than half
when the current is doubled and rising more than double when the current is halved.
Not even when the feeding mechanism in the lamp is extremely sensitive can the
resistance be kept from varying. In fact the feeding mechanism is generally so far
behind in its movement as to make the variation even more than would be the case if
the arc was kept at a fixed length.
It will be obvious from the above, that in order to ensure stability of current the
potential at the terminals of an arc light dynamo should drop when the current rises
and it is to accomplish this that these dynamos are worked up to the dip of the curve,
that is to the degree of magnetic saturation where the potential at the terminals of the
dynamo will either drop or not increase by an increase of current..
From this the failure to work dynamos with unsaturated magnets may be under-
stood. For if the dynamo were a series wound machine (which is the only successful
winding for high tension dynamos) and had unsaturated magnets an increase of current
would raise the intensity of the magnetic field thereby increasing the voltage which
as will be understood is also the reverse of what would be desired for the stability
of current.
When an arc light dynamo is provided with any of the regulators known to the art
the notential at the terminals of the dynamos will of course dron when the current

page_text: °
increases but this is of no avail for the stability of current, for while the regulator will
drop the potential when the current rises, it will always (when regulating an
unsaturated machine) drop it too far, as shall be presently described. No matter how
little this may be beyond the conditions of stability it will be added to each oscillation
of the regulator finally multiplying up until there is a great "surging" of current.
The lamps will first drop down the carbons and then draw them apart while the
regulator will work from one extreme to the other first raising up the current and then
cutting it down.
This phenomenon which always comes with an increase of iron in the dynamo
beyond a certain limit has too often been met with to need further description
here.
It is the object of this Invention however to produce a regulator which will effect
the conditions of stability without resorting to the over saturation of the magnets or
in other words to the costly and inefficient design of machine which has heretofore
been compulsory,
Fig. 1. of the drawings represents partly in diagram a slightly modified but well
known form of regulator. A is a controlling electro-magnet the windings of which
are connected in the working circuit; B is an electro-magnet to move an arm L
according as the magnet A opens or closes the short circuit around the magnet B as
will be understood. The movement of the arm L of course may effect the regulation
in various ways, as by shifting the commutator brushes or varying the excitation of
the field magnet or by controlling the power of the motive engine to vary the speed of
the dynamo armature. In Figure 1 there is shown a valve O as connected to the arm L
to represent this last method of regulation while to represent the two former methods
of regulation the arm L is shewn in Figures 9 and 10 as connected to commutator
brushes (Figure 9) and as controlling a variable resistance (Figure 10) in a shunt
around the field magnot coils.
Figures 2, 3 and 4 are diagrams showing curves to illustrate the variation of current
and potentials at the terminals of the dynamo when a change of resistance takes place.
Such a curve will be herein called the "regulation curve." The horizontal lines in
the diagram represent the intensity of the current in ampères while the vertical lines
represent the potential in volts.
Imagine a dynamo provided with the regulator shewn in Figure 1, to be supplying
a current to a circuit of are lights and the system to be running steadily at ten ampères
and 2,100 volts. If under these conditions two are lights of 50 volts each should be
cut out of the circuit it will be known mathematically that the potential will have to
drop to 2000 volts to keep the current at ten ampères. Such a mathematical point in
the adjustment will be herein called the "theoretical adjustment." This adjustinent
however is never accomplished by any of the arc circuit regulators now in use.
can be better understood by referring to Figure 2 which represents the regulation
curve of a saturated machine.
This
Imagine the whole to be running steadily under the condition indicated at c in the
diagram and suppose the two are lights be then cut out of the circuit. Of course the
current will rise and if the regulator is sensitive enough to operate within one per cent.
variation of current, the potential will at this point start to drop, but the current will
rise above this before the potential will have dropped to 2000 volts. If at this point
the current has started to fall, as shewn in the diagram the conditions of stability will
have been accomplished notwithstanding the fact that the potential will have to keep
on dropping until the current falls below normal before the magnet A can open the
short circuit around the magnet B to move the regulating mechanism (valve of the
steam engine or commutator brushes &c.) to check the fall of potential.
From the curve in the diagram it will be seen that by the time the current has
dropped to normal the potential has dropped to about 1950 volts which altho' beyond
the theoretical adjustment which is indicated at c¹ is within the conditions of stability.
For instance when the dynamo was running at 2100 volts and the two lamps of
50 volts each were cut out there was left a five per cent. surplus of volts over the
theoretical adjustment, while after the movement of the regulator there was only about

page_text: 2 per cent. of volts less than the theoretical a ljustinent and as the 2 per cent. below
is nearer the theoretical adjustment than the 5 per cent. above, the regulator is
operating within the conditions of stability. The dotted curve below the normal line
represents the reverse movement of the regulator which of course is still nearer to the
theoretical adjustment.
These are the conditions of stability of all are light dynamos now in use, namely the
use of saturated magnets and sufficient resistance in the windings to drop the potential
when the current rises in order that the current shall start to drop before the theoretical
adjustment takes place.
These conditions of stability will probably be better understood by describing the
conditions of unstability of an unsaturated dynamo.
Figure 3 represents the regulation curve of an unsaturated dynamo. Supposing as
before the whole to be running under the conditions indicated at c in the diagram and
then the two are lights of 50 volts each to be cut out, the first effect will be as
before, a rise of current and the regulator will move to drop the potential. In this
case however there will not be sufficient electrical resistance in the dynamo to drop
the potential; but the rise of current will increase the potential for if the magnets are
unsaturated the intensity of the magnetic field will be increased by an increase of
current thereby increasing the voltage. If therefore, when the regulator shall have
dropped the potential to 2000 volts, the current shall be (say for clearness of illustra-
tion) 5 per cent. above normal the potential then in order to compensate for the
increased intensity of the magnetic field will have to be dropped 5 per cent. more or to
1900 volts before the current will be only checked from rising further. At this point
the potential will continue to drop until the current falls to normal when the potential
will have dropped, as shewn in the diagram to about 1800 volts which is beyond the
conditions of stability. In other words the 5 per cent, surplus of volts left by cutting
out the two lamps has been reduced by the regulator to 10 per cent. of volts below the
theoretical adjustment which of course is further from the theoretical adjustment than
before the regulator moved at all. The dotted curve represents the reverse-movement
of the regulator from which the phenomenon of unstability will be apparent.
Diagram Figure 4 represents the regulation curve that should be made by a
regulator of an unsaturated dynamo when subjected to the same conditions as above,
in order to ensure stability of current. From this it will be seen that the rise of
current has been checked, as before, by a drop of potential to 1900 volts but as
distinguished from the curve in the diagram, Figure 3 almost as soon as the current
has started to drop the potential has started to rise and when the current has fallen to
normal the potential has reached 2000 volts or the theoretical adjustment, which is
the maximum condition of stability, as will now be understood.
In Figure 5 is shewn a regulator for carrying out this method of regulating and
stabling the current for unsaturated dynamos or in other words as graphically repre-
sented in the diagram, Figure 4. This regulator has been shewn, for the sake of
clearness precisely the same as that illustrated in Figure 1 with the exception of
certain additional and distinguishing features namely a moveable contact S a spring H
and a dash pot P.
The function of the spring H will be to keep the contact S somewhere near the
normal position which is the position shown in Figure 5, while the dash pot P which
should be just strong enough to yield very slowly under the action of the spring H
will be to keep the contact S in any position it may be placed for an appréciable
time.
The operation of this regulator is as follows:-
Referring to the diagram Figure 4 suppose the dynamo to be running steadily
under the conditions indicated at c and the regulator to be working at the P sition
shown at Figure 5 and that then two are lamps are cut out as before. The first rise
of current will cause the magnet A to open the short circuit around the magnet B as
was the case with the regulator shown in Figure 1 bat as distinguished from, the
regulator shown in Figure 1 the rise of current after the short circuit has been opened
(which is represented in the diagram to have risen to about 5 per cent. above normal)

page_text: will pull up
the contact S as shewn in Figure 6 where it will be held by means of the
dash pot P, so that the short circuit around the magnet B will be closed almost as
soon as the current starts to return to normal whereby the potential can be raised to
the theoretical adjustment by the time the current reaches normal as illustrated by
the curve shewn in the diagram 4.
This adjustment of the regulator which would be the ideal one could be accomplished
yet it should be 'understood that it is not necessary for the regulator to effect a
theoretical adjustment at the first oscillation. So long as every oscillation of the
regulator will effect an adjustment nearer to the theoretical adjustment than the
preceding one the conditions of stability will be obtained as explained above.
By the word "normal as used in this Specification in connection with the
current is meant that intensity of current at which the regulator is intended to
maintain it constant.
Figure 7 shews the contact S as pulled down which will be the case when a fall of
current, occurs whereby the short circuit can be opened without the current having to
rise to normal as will be understood.
To make this device more effective the piston of the dash pot should be provided
with a small relief valve as shewn for instance at w in Figure 8. Such a valve
should be just strong enough, not to open by the action of the spring H yet delicate
enough to open by the action of the magnet A in order that the contact S can be
readily pulled up or down.
This Invention is not limited to any one form of device to accomplish this method
of stabling the current of unsaturated dynamos for other forms conld be easily devised
by anyone skilled in the art by the aid of the foregoing explanation of the Invention.
This Invention or discovery lies in the method herein disclosed for stabling are
circuit currents that is to say dropping the potential when the current rises above
normal and then raising it while the current is still above normal as illustrated in
diagram 4 which is the condition of stability of an unsaturated dynamo as clearly
set forth.
In all methods of regulating are circuit currents now in use when the regulator is
adjusted to give a practically constant current throughout the working limits the
regulator will not raise the potential when the current is above normal until the current
falls below normal as illustrated in diagram 3 which is the condition of unstability as
above explained, of an unsaturated dynamo.
The Invention has for the sake of illustration been described as effecting the
conditions of stability for the current only when the lamps are cut out of the circuit
but it should be understood that the current will have to be also stable when a fixed
number of lamps are kept burning.
Under such conditions the current will take an oscillating or wave like motion of
about 2 or 3 per cent. variation according to the sensitiveness of the regulator and on
the rise and fall of each of these little waves of current the regulator will by this
Invention raise the potential while the current in any of these oscillating movements
is above normal and drop the potential while the current is below normal.
It may sound somewhat inaccurate or obscure to speak of saturated magnets in
dynamos where the regulation is accomplished by varying the intensity of the magnetic
field, for it would seem that in order to vary the magnetic intensity the magnets must
necessarily be below saturation. It may be well to mention, therefore that in all
dynamos of this type the magnets are always saturated when working at full load and
the range of regulation is restricted, when supplying are lights, purely to variations
along the bend of the "Saturation curve." In cases where the range of. regulation
extends below the bend of the curve the armature and line resistance is either
extremely high or else incandescent lamps or other devices not possessing the
peculiarities of an arc light are supplied in the circuit. In other cases the regulation
.is not adjusted to give a constant current throughout the range of regulation but is
adjusted to give 10 or 15 per cent. more current under light load than under full load
whereby stability will be more or less effected at a sacrifice of regulation.
With this method of regulating and stabling the current however a purely arc light

page_text: circuit can be supplied from an unsaturated dynamo and the current kept at a constant
intensity throughout the whole range of regulation.
It may also be confusing to speak of raising and dropping the potential in reference
to the current when it is known that in almost all arc circuits the E.M.F. (electro
motive force) for various reasons is continually jumping up and down. For instance
dynamos with open coil armatures and a small number of commutator segments will
keep up a continual fluctuation of the E.M.F. in the circuit. Again there are
regulators that when regulating raise and lower the potential step by step as it were.
In such cases (say for illustration) if the dynamo were an unsaturated dynamo and
were subjected to the same conditions for regulation as herein mentioned a curve
would then be drawn similar to the arc indicated by dotted lines in Figure 11.
Now it will be seen from this curve that while the potential will be both raised and
dropped when the current is above or below normal respectively the mean potential
will be precisely as shewn in Figure 3. It should therefore be understood that by all
the curves herein shown and in the references made to them as to variations of potential
is meant the variation of mean potential.
While the potential may fluctuate more or less with different regulators now known
to the art, with no regulator has the potential, (that is the true or mean potential)
been lowered to check a rise of current and then raised again while the current is
above normal, as herein disclosed, for the purpose of regulating or stabling the current
of an unsaturated dynamo.
Having now particularly described and ascertained the nature of this Inven-
tion and in what manner the same is to be performed it is declared that what
I claim is :-
:-
1. The mode herein disclosed for regulating and stabling are circuit currents at a
constant intensity said mode consisting when the current rises above normal in first
dropping the potential to check the rise of current and then raising the potential
while the current is still above normal or when a fall of current occurs in first raising
the potential but dropping it again while the current is below normal, all substantially
as described.
2. The combination of a dynamo electric generator and an arc light circuit supplied
with current from the said generator a regulator controlling the current at a constant
intensity and means substantially as described to drop the potential when the current
rises above normal and then raise the potential again while the current is above normal
or when the current falls below normal to raise the potential and then drop it again
while the current is below normal all substantially as described.
Dated this 15th day of July 1800
J. H. JOHNSON & Co.,
47, Lincoln's Inn Fields, London, Agents.