Improvements connected with Dynamo Electric Machines.
Year: 1896

page_text: Date of Application, 29th Sept., 1896-Accepted, 24th Dec., 1896
Improvements connected with Dynamo Electric Machines.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 38, Parliament
Street, Westminster, in the County of London, Electrical Engineers, do hereby
declare the nature of this invention (which has been communicated to us from
abroad by Charles P. Steinmetz, of Schenectady, County of Schenectady, State
of New York, 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:-
Our invention relates to dynamo electric machines, and more particularly to the
large generators used for alternating current work, either for long distance
transmission or for central station plants; and has for its object to provide a
convenient means of compounding such generators, capable of easy regulation
and accurately providing for all loads to which the generating capacity of the
machines is adapted.
To the ends pointed out, we provide, as is usual with such machines, a separate
exciter for the field-magnets, and we also provide a commutator in one of the series
leads of the machine, by which the current is rectified while passing around the
field magnet of a third machine, presently to be referred to; the third machine, to
which reference is made, has also a winding upon its field magnet in shunt across
the mains from the exciter to the field magnets of the large generator. The third
machine is a counter electro-motive force generator in series with the exciter.
The arrangement indicated allows us to oppose the two electro-motive forces to one
another, and get a very close and accurate compounding effect by varying their
ratio so that the electro-motive force of the exciter is controlled by the resultant
effect of the two opposing electro-motive forces.
The accompanying drawing shows in diagram the arrangement just described.
Therein A indicates diagrammatically the main generator, of which A' is the field-
magnet winding, A2 the armature winding, B, B₁ the collector rings, and C the
commutator in the lead to the collector ring B'. 1 and 2 are the mains leading to the
work. E is the exciting machine, shunt wound, as is customary, its armature being
connected by the leads 3, 4, to the field magnet coil A¹ of the main machine. F is
the third machine already alluded to, its field-magnets being energized by a coil fin
shunt to the mains 3, 4, through the leads 5, 6, and having a regulating resistance D¹
in circuit therewith. From the commutator C a series circuit to the main machine
passes by the leads 2, 2, through the differential series winding upon the field
magnet of the machine F, the armature of which is in series in the lead 4 between
the main exciter E and the field magnet of the main generator A¹. D is a resistance
in shunt between the leads 2, 2b, serving to prevent sparking at the commutator.
The operation of our improved method and means of compounding is as follows:
During the normal working of the machine, the counter electro-motive force of the
machine F is so proportioned to the direct electro-motive force of the exciter E,
by means of the regulating resistance D', that the field magnet winding A¹ is
sufficiently energized to maintain the potential of the current delivered by the
armature A³. When however the load increases, and with the load the current,
and the drop of potential incident thereto takes place, the same increase of current
increases the effect of the differential series winding f, diminishing the counter

page_text: electro-motive force of the third machine F, thus allowing an increased excitation
of the field magnet A' and increasing the potential of the delivered current; while
on a decrease of load in the main circuit, the reverse of this operation takes place.
The machine F may be driven in any desired manner, as for example, by being
mechanically connected with the engine or other prime mover driving the main
alternator.
We may also change this differentiation of the two forces so far as to make them
assisting instead of opposing electro-motive forces, as where the capacity of the
machine. would be so taxed that the differential winding f¹ upon the field magnet
of the motor or counter electro-motive force machine would become so highly
energized as to reverse the polarity of the machine and thus cause it to. generate
additional electro-motive force acting to assist that of the exciter and still more
highly energize the field magnets of the main alternator. Such an arrangement
however we do not contemplate employing in practice unless for a few moments
when a sudden load is thrown upon the machine which it is not adapted to carry
consecutively. Under such circumstances the regulation is not so effective, and the
machine varies somewhat in electro-motive force and output.
Although we have described our improved method in its relation to an alternating
current machine, in which it is of greatest efficacy as compared with other systems,
we do not intend to limit ourselves to its use in that relation only, but we intend
to embrace in the scope of the claims continuous current machinery, as this requires
no modification in the principle of invention and no practical modification in the
apparatus embodying the principle, the substitution of a commutator for a collecting
ring being an immaterial change in the practice of our invention.
We find a material advantage in the use of the special apparatus herein set out,
inasmuch as the saturation curve of the counter electro-motive force machine
modifies that of the field-magnets of the main generator, so that the current rises
in potential slowly at first, and as the limit of load is reached, faster and faster,
thus maintaining the proper electro-motive force of the machine under its extreme
capacity; whereas, with ordinary means of exciting, the characteristic rises most
rapidly at about half load, and after that, falls slightly.
Having now particularly described and ascertained the nature of this inven
tion as communicated to us from abroad and the manner in which the same is to
be performed we declare that what we claim is :-
1. The combination of a dynamo electric generator, having its field excited by
the resultant action of a main exciter source, and a regulating dynamo machine in
series therewith, and a field coil on the regulating machine whose excitation is
varied proportionally to the current flowing in the circuit of the main machine,
as set forth.
2. The combination of an alternator, an exciter therefor and a regulating dynamo
in the exciter circuit, whose field in energized by current from the exciter and by
the commuted or rectified current of the alternator, as set forth.
3. The combination of an alternator, an exciter, a regulating machine in the
exciter circuit, and a field coil on the regulating machine energized by the
commutated or rectified current of the alternator, as set forth.
4. The combination with an alternating current dynamo electric machine, of a
separate exciter and a counter electro-motive force machine, having a differential series
coil upon its field magnets, the exciter and counter electro-motive force machine
being in the circuit with the field-magnet winding of the main machine; whereby the
increase of current incident to additional load on the alternator acts to cut down
the counter electro-motive force, and vary the excitation of the field magnets.
5, The combination of an alternating current dynamo electric machine, a separate
exciter furnishing electro-motive force for the field magnets thereof, a counter
electro-motive force machine in the same field magnet circuit, a differential series
coil upon the field magnet of the counter electro-motive force machine, and a

page_text: commutator in the lead from the main machine to the differential series coil; all
arranged, as herein described and set out, to vary the effect of the counter
electro-motive force armature inversely to changes in the load.
Dated this 29th day of September 1896.
han the Anglicenta
J. C. CHAPMAN,
70 Chancery Lane, London, W.C., Chartered Patent Agent.