Improvements in Regulating Electric Alternators.
Year: 1899

page_text: Date of Application, 28th Nov., 1899-Accepted, 7th Apr., 1900
COMPLETE SPECIFICATION.
Improvements in Regulating Electric Alternators.
We, THE BRITISH 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, residing at 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 following statement:-
Our present invention aims to provide a suitable method and means of regu-
lating the electromotive force of alternating-current dynamo-electric machines,
so as to compound the machines, as for constant potential either at the brushes
or at any desired point in the distribution system, irrespective of any changes
in load or in the phase relation between current and electromotive force.
A method and apparatus accomplishing these results was disclosed in British
Patent No. 29,585 of 1897.
Our present invention consists in certain improvements upon the method and
apparatus disclosed in the said patent, designed particularly to avoid the large
exciter of somewhat unusual design which is required by the said invention.
In the drawings attached to this specification, Fig. 1 is a diagrammatic view
of one embodiment of our present invention; Fig. 2 is a similar view of a
slightly modified form; Fig. 3 is an illustrative diagram explaining the prin-
ciples of the invention, and Fig. 4 is a diagram of a further modification applic-
able to polyphase machines.
Referring more particularly to Fig. 1, A is the armature of the main alter-
nator, whose electromotive force is to be regulated, while B is its field magnet
winding. The alternator, in the form shown, feeds current through the rings
and brushes to the mains a, b, which mains are supposed to lead to the distribu-
tion system. The field-magnet coils B are supplied with current from the main
exciter E, driven in any suitable way, as, for example, by the belt G.
The field-magnet windings 12 of the exciter E, are fed from the commu-
tator F, and controlled by the resistance R as usual. But interposed in series
with the field magnet circuit is the armature A¹ of an auxiliary exciter, which
is so arranged as to be driven in synchronism with the main alternator. For
example, the two machines, the main generator and the auxiliary exciter, may
have the same number of poles, and may be placed upon the same shafts, or
upon shafts mechanically connected by the coupling C, or any other arrange-
ment may be used by which the two machines will be maintained in rigid
synchronism, speaking from an electrical point of view. The armature wind-
ing A¹ of the auxiliary exciter is connected in series with the armature A,
of the main machine, and with the mains a, b, so that the current of the main
machine passes through the armature of the auxiliary exciter. The connections
are so made that the electromotive force, or potential difference, created in
the armature A¹, by the passage of the main alternating current therethrough,
shall be slightly in advance of the electromotive force induced in the arma-
ture A by its relative rotation with the fields B'.

page_text: It will be seen that when no current passes through the mains a, b, that is
to say, when there is no load on the main alternator, the electromotive force of
the current supplied to the field, windings B2, 12, of the main exciter will be
the sum of the electromotive force due to its armature E and the electromotive
force induced by the rotation of the armature A¹ of the auxiliary exciter within
its field magnets 11.
The current due to this electromotive force' may be adjusted by means of the
resistance R, to bring the field excitation of the main exciter to such a value
as to generate a current in the circuit d, leading to the field magnet coils B, B,
of the main alternator, sufficient to bring the electromotive force of the arma-
ture A of the alternator to the point desired. This is the -no-load-excitation.
If, now, a non-inductive load is thrown on the main alternator, alternating
current will pass from the armature A through the armature A¹ of the auxiliary
exciter, which will have the effect of increasing the electromotive force upon
the direct current side of the auxiliary exciter. This will, in turn, if the
machines are properly designed, increase the electromotive force of the main
exciter E, and, finally, increase the electromotive force of the main alternator,
sufficient to compensate for the drop in its armature. If the machine is to be
over-compounded, the design will be such that the rise in potential will be suffi-
cient to compensate, not only for the drop in the armature but also for the drop
in the feeders up to a certain chosen point in the distribution system.
Referring now to Fig. 3, in which the armature A¹ of the auxiliary exciter
is shown furnishing the sole current for the field magnets B2 of the main exciter,
m may be supposed to be the polar line of the field magnets B', which field
magnets are preferably unsupplied with any exciting winding but excited
simply by the armature re-action. It will then be evident that the line 'of
maximum electromotive force, when no current flows in the mains a, b, will be
the linen, nearly at right angles with the motor m.
It will thus be seen that the mains a, b, connect through the rings and brushes
with two diametrically opposite points in the armature winding A¹. These
two points are upon the line n2, which line is slightly in advance in the direc-
tion of rotation, of the line n¹.
It, appears therefore, that any increase in the lag of the current in the main
circuit will cause the maximum electromotive force created by the passage of
the main current through the auxiliary armature, to occur more nearly in phase
with the electromotive force induced by the mere rotation of the auxiliary
armature, within its field magnets, that is to say, on or about the line 12
It thus appears that any increase in the lag of the main current, will cause
a corresponding increase in the excitation of the alternator. On the other
hand, any lead of the current in the main circuit will cause the maximum point
of electromotive force n² to come to some such point as ", tending to reduce the
excitation of the main machine.
The machine is thus automatically regulated, not only for changes of load,
but also for changes of lag or lead in the main circuit.
Though we have shown the auxiliary exciter as a small generator with un-
wound field magnets, it will be obvious that any dynamic source of electromotive
force may be adopted to perform its functions.
In the form shown in Fig. 2, the field magnets of the main exciter are excited,
by two separate coils or sets of coils, B2, B2 and B3, B³. The coils 133 are excited
in shunt to the armature E, and regulated by the resistance R³, and furnish
what may be termed the initial excitation. The coils B2 are excited directly
from the armature A¹ of the auxiliary exciter through the resistance R, and
furnish the additional or regulating excitation.
Fig. 4 is a diagram showing the application of our invention to polyphase
machines. In this figure the transformer T has its primary coils in series
with the mains a, b, c, supposed to be the mains leading from the three-phase
generator to be regulated, while its secondaries, shown here as Y-connected
65

page_text: feed the armature A¹ of the auxiliary exciter through rings and brushes. The
armature A¹ feeds the field magnet windings B2, as in the form shown in Figs. 2
and 3. The operation of this device will be obvious, from what has already been
said. It will be noticed that the electrical connection between the main arma-
ture A and the auxiliary armature A¹ may, in any case, be either direct or
inductive.
Our invention is particularly important in connection with existing installa-
tions, as it enables voltage regulations for phase displacement to be obtained
without the necessity of purchasing new and expensive main exciters.
It will be obvious that various changes in form and arrangement may be
made without departing from the spirit of our invention, and it will be seen
that our invention may also be applied to the regulation of synchronous and
other alternating motors.
Having now particularly described and ascertained the nature of our said in-
vention (which has been communicated to us from abroad) and in what manner
the same is to be performed, we declare that what we claim is;-
1 The combination with a dynamo-electric machine, of the alternating cur-
rent type, of means for furnishing thereto a normal field excitation, and an
auxiliary exciter acting to modify the field excitation in accordance with changes
in the volume and in the phase relation of the current in the main circuit.
2 In combination, a dynamo, a main exciter for the dynamo, an auxiliary
exciter supplying current to the field magnets of the main exciter, and con-
nections from the armature of the dynamo to that of the auxiliary exciter by
which an alternating current from the main machine passes through the arma-
ture of the auxiliary exciter, substantially as described.
3-In combination, a dynamo, a main exciter, an auxiliary exciter controll-
ing the fields of the main exciter, and having field magnets excited by its own
armature reaction and connections from the main dynamo by which an alter-
nating current from the armature is passed through that of the auxiliary exciter,
substantially as described.
4 In combination, an alternating current dynamo having a main exciter,
an auxiliary exciter controlling the fields of the main exciter, the auxiliary
exciter having an unwound field magnet, and a connection by which the alter-
nating current of the main dynamo is passed through the armature of the
auxiliary exciter so as to produce an electromotive force in advance of that due
to rotation; the auxiliary exciter and the main dynamo being driven in syn-
chronism, substantially as described.
THE BRITISH THOMSON-HOUSTON CO., LTD.,
ALFRED CLEMENTS,
Assistant Secretary.
W. MARTINDALE,
T. R. THOMPSON,
Directors.