Improvements in the Regulation of Alternating Dynamo-electric Generators.
Year: 1890

page_text: Date of Application, 11th Mar., 1890-Accepted, 19th Apr., 1890
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Improvements in the Regulation of Alternating Dynamo-electric
Generators.
I, STANLEY CHARLES CUTHBERT CURRIE, Electrician, a Subject of the Queen of
Great Britain, now residing in Philadelphia, Pennsylvania, U.S.A., 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:
The object of the invention is to provide means whereby, in the case of an
alternating current dynamo supplying lamps or other translating devices, either
through a transformer or otherwise, the mechanical load upon the prime motor-for
instance. the steam engine driving the dynamo-may be kept practically constant,
notwithstanding the fact that the load upon the dynamo is variable, depending
as it does upon the numbor of translating devices in use. In electric light systems,
the load upon the dynamo, and consequently upon the engine, is a varying one.
This fact, coupled with the necessity of having the engine and boiler power (except
in the case of a direct storage system) sufficient to carry the maximum load, causes of
necessity a very much larger consumption of coal than would be the case were it
possible to run the engine with a constant mean load.
Where direct current machines supply lamps, the load upon the engine can be
maintained practically constant by use of storage batteries as regulators, such
batteries being of sufficient capacity to meet the maximum variation, and placed in
parallel with the dynamo and lamp circuit. Where alternating current machines are
used, however, the storage batteries cannot be charged and consequently the system
just mentioned. cannot be used.
By using storage batteries, in combination with an alternating current machine,
the load upon the engine can be maintained at a constant; and, in the event of the
engine breaking down, current will still be supplied to the system by means of the
storage battery. My invention will be understood from the following specification
and accompanying drawings, which latter illustrate, diagrammatically, two ways of
embodying or carrying out my idea.
Figures 1 and 2 are similar diagram views illustrating organizations differing
somewhat in detail.
:
A G represents any suitable alternating electric generator, and D a direct current
exciter therefor, mounted upon the same shaft. F, F, are the field magnets of the
alternating generator, and are excited by the direct current from the exciter D,
through the coils f. M, M, represent the coils of the revolving armature of the
alternating. generator from which wires W run to a distribution circuit. In the
present instance, transformers are shown connected in multiple between the leads
of the generator, in the usual manner. The exciter D is of larger dimensions and
greater power than would be required merely for the usual excitation of the field
magnets F, F, and is so made for a purpose presently described. A, A, represent
a storage battery of a size and capacity adapted to the circumstances. Any other form
of alternating generator may, of course, be used. That illustrated being selected
merely for the purpose of illustration.
The exciting coils f, of the field-magnets F, of the alternating generator, are
connected in a circuit between the + and - terminals C, C², of the exciter D, and
are of comparatively fine wire.
"The field magnets B, of the exciter, are shunt wound with relatively fine wire, as
shown in the drawings. In Figure 1, these magnets are also compound wound, as I
will now describe. Thick wires a', a are lead from the terminals of the storage
battery A, the.circuit being completed in the following manner :

page_text: The wire a passes around each of the field poles F, of the alternating generator,
being wound successively upon said poles in alternate directions,, the same as the
exciting coils, and then passes around one field 'magnet of the exciter D to the
brush, thence through brush C around the other field magnet of the exciter, and
from thence the wire a loads to the other terminal of the storage battery A..
Of course the size of the wires a¹, a², the number of turns around the field
magnets F, and around the field magnets of the exciter D, as well as the direction of
the winding, must be in accordance with the special requirements of each case, and
the objects to be attained; which are as follows: Suppose the load in the dynamo
is one half it's total capacity, or, in other words, that half the total number of lamps
are lighted, and also assume that this condition represents the mean load. The
number of cells in the storage battery should be so regulated that in this case
the E.M.F. of the exciter balances that of the battery, and no current flows therefore
in the circuit a³, a³.
Suppose now that the lamp load falls below the mean, then the load on the engine
being lighter, the E.M.F. of the exciter D will rise, and, if the winding of the
circuit a, a be properly arranged, a current will pass from the exciter to the
battery A, which will be charged thereby.
The speed of the engine being now slightly increased, the effect of the coarse wire
coils around the field magnets F will, in this instance, tend to neutralize the effect of
the smaller coils, and thus lower the magnetic intensity.
On the other hand, suppose the lamp-load is greater than usual, the tendency
of the engine will be to slow down, and the battery A will discharge through the
circuit a, a, and-increase the magnetic intensity of the field magnets F, as well
as the magnetic intensity of the exciter D, which will now run as a motor, and
assist the engine in driving the shaft of the alternating generator.
By properly proportioning the size and number of windings of the field coils,
the variation in load can be proportionally compensated for by the variation of
field intensity. Also by properly proportioning the capacity and size of the
battery, and of the exciter D, the current discharge of the former into the latter
could be made to take the maximum load, in the event of a break-down of the
engine.
a³,
In Figure 2, the organization is the same, with the exception that the wires a¹,
run direct to the brushes of the exciter. The operation is practically the same as that
above described.
A switch S, shown in both figures, may be employed to short circuit the
wires a¹, a³, around the coils F. in which case the variation of field excitation will be
within smaller limits.
Various modifications can, of course, be made by those skilled in this art,
according to the requirements in particular cases; that is to say, the direction of
winding of the circuit a¹, a³, on the field magnets F, or the field magnets of the
exciter, or both may be reversed from that illustrated and described. This, how-
ever, of course depends upon whether it is desired to maintain a constant speed
for the engine, and consequently a constant number of alternations: or whether
the E.M.F. of the distribution circuit W is to be maintained at a constant
and the current be variable; or the current constant and the E.M.F. variable.
I have shown rheostats Rh, both in the exciting circuit from the dynamo D. to the
field coils of the alternating generator, in the circuit a', a³, and in the shunt field
coil circuit of the exciter D, by which the circuit conditions may be varied.
The E.M.F. of the exciter D, may thus be raised or lowered according to whether
the battery is to be charged or not.
The arrangement shown in Figure 2 is more especially applicable to an alternating
distribution system in which a variable potential and constant current are required.
The rheostat in the field circuit of the exciter may be manipulated manually, or
actuated electro-magnetically by the current of the lamp circuit, as is perfectly
well understood, so that, when the lamp load is light, the E.M.F. of the exciter
may be raised and current passed through a¹, a², such current acting against the

page_text: current in the exciting coils f, and tending to reduce the magnetic intensity of the
fields of the generator. By this means the speed of the engine can be maintained at
a constant.
•
In all cases, the primary object is to run the exciter as a dynamo to charge
the storage battery and excite the field magnets F, F, of the generator, when the
lamp load is light; and when the lamp load is heavy the discharge from the storage
battery runs the oxciter as a motor, which drives or assists in driving the shaft of the
alternating generator.
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 combination with, an alternating generator and a constant current exciter
mounted upon or connected with the same shaft, of a storage battery included in a
circuit with the exciter, for the purpose set forth.
2. The combination, substantially as set forth, of an alternating generator, a
constant current exciter mounted upon or connected with the same shaft, a storage
battery and a circuit including the excitor and storage battery and field coils of
the alternating generator.
3. The combination, substantially as set forth, of an alternating generator and
its exciter, a distribution circuit W leading from the alternating generator, and a
storage battery connected in circuit with the exciter, and circuit connections
whereby, when the lamp load is light, the exciter is run as a dynamo to charge
the storage battery, and, when the load is heavy, the discharge from the storage
battery drives or assists in driving the shaft of the generator.
4. The combination, substantially as set forth, of an alternating generator, an
exciter mounted upon or connected with the same shaft, a storage battery, and a
circuit including the storage battery, the field coils of the alternating generator, and
the field coils of the exciter, for the purposes described.
Dated this 25th day of January 1890.
STANLEY CHARLES CUTHBERT CURRIE.