Improvements in Apparatus for Rectifying Alternating Electric Currents.
Year: 1899

page_text: Date of Application, 25th Apr., 1899-Accepted, 20th Jan., 1900
COMPLETE SPECIFICATION.
Improvements in Apparatus for Rectifying Alternating Electric
Currents.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by Elihu Thomson.
residing at Swampscott, in the County of Essex, State of Massachusetts, United
State 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:
-
In order to obviate or to reduce to a minimum the amount of sparking which
may take place in the operation of rectifying devices for changing an alternating
current of any particular character to a uni-directional current, it is necessary
that the commutation or periodic disconnection of the alternating mains from the
work circuit carrying the uni-directional current should take place at such points
in the wave of the alternating current or currents as will result in the smallest
value of unbalanced electromotive force acting between the terminals of the
respective circuits as they are being separated. If the relative positions of the
commutator and brushes of the rectifying device at the instant of commutation
bear a fixed relation in point of time to some particular phase value of the
impressed alternating electromotive force, it will be evident that as the load
changes in the work circuit the instant at which commutation takes place will
occur at different points or values in the current wave, owing to the fact that the
change in impressed electro-motive force or effective resistance of the work
circuit produces a change in the phase relations between the impressed alter-
nating electromotive force and current, wherefrom it follows that if the brush
adjustment in the rectifying device be suitable for one particular load it becomes
unsuitable for a different load or loads. We have discovered that by automa-
tically varying the times at which commutation takes place, in accordance with
varying load, such relations may be maintained between the electromotive forces
acting at the instant of commutation as will result in a minimum amount of
sparking of the rectifying device through its entire range of operation. We
consider ourselves to be the first to devise means for accomplishing this result
and intend hereafter to lay claim to the same broadly.
Although in the following description and accompanying drawings there is
set forth an arrangement of apparatus suitable for carrying out this invention,
it will be evident that the invention in its broader aspects is not in any sense
limited to the employment of the particular apparatus shown, but may be
embodied in and its beneficial results obtained from the employment of many
similar arrangements whether the same be in their action electrical or largely
mechanical. In short, the invention comprises the broad idea of causing the
operation of commutation in a rectifying device to be automatically made at
such instants with respect to the phase of the impressed electromotive force as

page_text: may be necessary to secure a minimum amount of sparking with changes
of load.
The brushes and commutator of a rectifying device such as those employed
are relatively movable with respect to each other, but so far as this invention is
concerned, either of them may be fixed in space and the other movable with
respect thereto, the adjustment between the same being performed in any desired
manner, one method of doing which is hereinafter shown.
In the drawings Fig. 1, illustrates in diagram a rectifying device supplied with
constant current and operating in accordance with the invention the constant
current being derived from the secondaries of two-phase constant current trans-
formers. Fig. 2 illustrates a similar arrangement applied in connection with
three-phase apparatus. Fig. 3 shows a system in which a plurality of rectifying
devices are operated from the same distributing mains. Figs. 4 and 5 represent
a plurality of commutating devices mechanically geared together so as to main-
tain a constant ratio between their relative rates of rotation. Fig. 6 illustrates
diagrammatically a switching-over apparatus for putting a work circuit in con-
nection with any one of a plurality of rectifying circuits, and Fig. 7 illustrates
one form of brush actuating mechanism which may be employed in carrying
out this invention.
The alternating currents to be rectified may be derived from any suitable
source whether single phase or multiphase and whether generated in that form
directly or converted into that character by suitable transforming apparatus.
In Fig. 1 there is illustrated a two-phase generator A from which the current
to be rectified is derived. So far as this invention is concerned the construction
of the generator is immaterial, but it is preferably of the direct driven slow-
speed multipolar type now commonly employed. The generator has the usual
revolving field F connected through collector rings with the exciter E for fur-
nishing current thereto. The stationary member of the generator carries two sets
of angularly displaced windings in which currents differing in phase by 90°
are induced. These windings are interconnected in the ordinary manner and
mains m are connected thereto and lead to a distribution system from which
current may be derived for any desired purpose, such as operating motors, lights
or other translating devices. From the distributing mains m, m connections are
made to the primary coils P1, P2 of a constant current transformer of the type
operating by mutual repulsion of the primaries and secondaries of the same.
The relative motion between the primary and secondary windings of a trans-
former of this type incident to changes of load in the circuit supplied by the
secondary windings of the same is utilized to suitably shift the brushes which
operate in connection with the rectifying device for changing the secondary
alternating current into a uni-directional current. The movable secondary coils
of the transformer are shown at S1, S2. The core of the transformer is indicated
in dotted lines. The secondary coils, as before stated, are relatively movable
with respect to their respective primary coils, and in order to make the move-
ment of each coil even as well as dependent upon the movement of the other,
the said secondary coils are mounted in connection with some suitable system of
mechanical devices whereby the movement of one secondary coil toward its
primary is communicated to the other secondary coil in such manner as to pro-
duce a similar movement of the latter coil.
In Fig. 1 there is shown one arrangement of apparatus for accomplishing this
purpose the same consisting of balancing levers L, L1, L2, to which the secondary
coils are connected by flexible or link connections as shown. The levers L, L,
L³, referred to are separately mounted so as to turn about the rod as a fulcrum,
or they may, if desired, be arranged on knife edges, as may be preferred, the
particular construction being a mere matter of mechanical detail. One end of
the lever L supports one side of the secondary coil S1, while its opposite end
supports one side of the other secondary coil S². The other ends of the respective
zecondary coils S¹, S³, are supported through suitable connections from the

page_text: opposing ends of the two levers L1, L2, as shown. These connections are so made
and adjusted that the weight of the secondary coil S2 over-balances that of the
secondary coil S, with the result that when there is no current flowing the
respective secondaries S1, S2 are brought closely adjacent to their respective
primaries. It will be observed that the downward pull due to the secondary S
acts through the chain C and the lever L to raise one end of the secondary coil St,
while the downward pull exerted by the secondary S2 on its supporting chains C¹,
Cacts through the levers L1, L2 to raise the opposite end of the secondary S¹.
As regards the operation of this transformer it will suffice for the present purpose
to state that as the resistance in the secondary circuit increases the current
supplied thereto consequently tends to decrease with the result that the secondary
coils approach their respective primary coils being no longer repelled by the same
force as before. By this action the flux through the secondary coils is increased,
thus causing an increase in secondary electromotive force, and so tending to
preserve a constant current in the secondary.
The currents in the transformer secondaries are conducted by suitable leads to
a rectifying device K. The rectifying device may be directly mounted on the
shaft of the prime mover, or it may be suitably geared thereto as shown, or it
Suitable contact
may be driven by a synchronous motor, as may be desired.
rings R carried upon the shaft of the commutating device and insulated there-
from and from each other are connected to the respective terminals of the
secondary windings as shown. Each ring in its turn is connected to the corre-
sponding segments of a two phase commutator similar to the commutator in the
brush arc-lighting machine. One set of commutator segments is connected
through the corresponding rings R with one of the secondary coils of the trans-
former. Another set of commutator segments angularly displaced on the same
shaft carrying the first set is connected through other rings with the other
secondary coil. The breaks in one commutator come opposite the middle points
in the conducting portions of the other commutator. As the present invention
has no special reference to the particular form of commutator employed a more
detailed description of the same is unnecessary.
Brushes B, B carried by a yoke Y, bear upon the commutators, each brush
making contact simultaneously with each commutator as shown. The yoke Y
is arranged to be rotated through a limited are about the axis of rotation of the
commutator in order to secure the proper adjustment necessary to a sparkless
operation of the same, as has been explained. In order to render this adjust-
ment automatic with changes of load in the work circuit, suitable mechanical
connections are made between the yoke Y and the moving secondaries of the
transformer, the currents from which are to be rectified. Many suitable devices
for accomplishing this purpose may be produced, and in Fig. 1 there is shown
one arrangement which has been found to be desirable. This arrangement con-
sists of the lever L3 fulcrumed at some fixed point as and connected
from an intermediate point of the same to the yoke Y by the link L. The freo
end of the lever L3 is connected by the link L with some one of the oscillating
levers L, L, L2, as for example, the lever L. In the operation of these
mechanical connections, it will readily be seen that the reciprocating motion of
the secondary coils S1, S2 of the transformer consequent upon changes of load in
the circuit supplied thereby, is transformed into an oscillating motion and is
communicated to the yoke Y carrying the brushes B. By proper attention to
the mechanical design of this structure, the motion communicated to the
yoke may be made such as to shift the brushes B backward and forward as
the load changes, in such a manner as will result in a minimum amount of
sparking at the commutator. It is obvious that the motion of the secondary
coils may be communicated to the brushes B and in any other manner than that
shown either directly or indirectly as found most convenient.
In Fig. 2 there is shown an apparatus for rectifying three phase currents,
the device for performing this function being somewhat different from the

page_text: arrangement of apparatus shown in Fig. 1. A three-phase generator A', or any
other source of three-phase current, is used to supply energy to the three-phase
constant current transformer, such as shown in Fig. 2. Three primary coils P¹,
P2, P3, are inter-connected in the usual manner and receive their energy through
leads me of the three-phase system. It is evident of course, that the three-
phase currents in the mains m may be supplied to any other translating devices
desired without involving any departure from the invention. Associated with
the primary coils of the transformer are corresponding secondary coils S4, S5, S6
mounted upon a suitable framework G and movable relatively to the primary
coils. Both primary and secondary coils encircle suitable legs or branches of
the transformier core, shown in dotted lines. The frame G is connected through
suitable cross-bars and uprights with one end of the lever L, the connections
with the lever being made by means of the shaft H movable within an opening
in said lever. The lever L is fulcrumed in a suitable manner at p and the
weight of the secondary coils of the transformer is nearly but not quite balanced
by the weight W arranged to slide on one arm of the lever L.
Currents from the secondary coils are transmitted through suitable conductors
to brushes bearing upon the collector rings R of the rectifying device K, which
may be driven in any well known manner. The rings are respectively con-
nected to the segments of the commutator for rectifying the three-phase current.
The rectified current is collected by brushes B and transmitted to the work
circuit supplying arc lamps or the like. The brushes B, similarly to the con-
struction shown in Fig. 1, are carried by a yoke Y, the latter being
connected as shown, by a link L to some convenient point in the
length of the lever L. The repulsion of the secondary coils of the
transformer by the primaries acts as in the form shown in Fig. 1, to communi-
cate motion through the lever L to the yoke Y and so to adjust the position of
the brushes B. By suitable proportioning and adjustment of parts the brushes B
may be maintained in the position of minimum sparking throughout the limits
of load variation of the apparatus. It is obvious that the arrangement of levers
shown might be radically varied without in any way departing from the prin-
ciple of the invention.
Fig. 3 illustrates diagrammatically a plurality of rectifying commutators
having a fixed ratio of rotation such as would be obtained for example, by mount-
ing them upon the same shaft. The brush carrying yokes Y and Y2 are actuated
in the manner previously described, the movements of the secondary coils St S
actuating the yoke Y of one commutator and the movements of the set of
secondary coils S3, S actuating the yoke Y2 of the other commutating device
the primaries corresponding to those secondary coils being excited from the
same distribution system, as shown.
Instead of mounting the respective rectifying sets on the same shaft, it is
equally feasable to mount each set upon a separate shaft, the individual shafts
being connected by suitable gearing, such as spur-wheels or other positively
actuating devices of an appropriate nature for maintaining a fixed ratio of
rotation between the individual rectifying commutators as shown in Fig. 5.
Where rectifying apparatus is to be operated continuously or at least through-
out long intervals, as in commercial practice, it is advisable, from motives of
prudence, to follow the common engineering practice of providing reserve sets
of apparatus to take the place of the apparatus in use in the event of injury or
accident to the same, thus obviating otherwise vexatious and annoying delays
in service. In the employment of reserve apparatus it is desirable to provide
changeover switches for substituting the connections of the reserve apparatus
for those of the apparatus to be cut out of circuit. In Fig. 6 there is illustrated
an arrangement of switches and circuits for accomplishing this result. The
mains supplying the alternating current to be rectified are shown at m¹ and two
sets of connections are taken therefrom, one set of which may be put in circuit with
the mains m³ through the switch X, while the other set of connections may, in

page_text: similar manner, be put in circuit with the mains m² through the switch Z. The
circuit m is intended to supply the primary of the transformer, the secondary
of which supplies current to the rectifying device K. In similar manner the
circuit m supplies the primary of the transformer the secondary of which fur-
nishes current to the rectifying device K³. The switch Z is intended to connect
either one of the two commutating devices K, K³, with the work circuit supply-
ing lamps L. The switch X Z, Zare mechanically connected in some suitable
manner so as to be operated simultaneously, as for example by the connecting
bar B.
As the connections are shown in Fig. 6 the rectifying device K is connected
through its transformer, not shown, with the mains m³ and through the switch X
with the distributing conductors m. The commutator of the rectifying device K
is connected through the switch Z with the work circuit as shown. In case of
accident to the set of apparatus thus in circuit the switches X, Z, Z, may be
thrown, thus cutting out this apparatus and putting in circuit the rectifying
device X3 with its similar set of supply devices, as will be readily understood.
Instead of shifting or adjusting the brushes of the rectifying apparatus through
motion derived from the repulsion of the windings of the main supply trans-
former we sometimes prefer to employ a device the purpose of which is primarily
to operate the brush shifting mechanism and not to operate as a transformer, as
in the cases above described. In Fig. 7 we have illustrated such an arrange-
ment of apparatus. The primary and secondary of a supply transformer are
shown at P and S and may be either relatively movable or fixed with respect to
each other as may be desired. If the coils are movably related to each other the
weight of one of the coils may be partially counterbalanced by means of a lever
and suitable connections with the weight W, as diagrammatically indicated.
At is illustrated the actuating mechanism for adjusting the brushes of the
rectifying device K. This device consists of two relatively moving coils, the
force exerted between which is communicated through suitable levers and links
with the brush carrying yoke Y. Through one of the coils the current from
the secondary S of the main transformer passes, while through the other coil
is passed the current from the primary P of the main transformer. It will
thus be seen that the force exerted between the relatively moving coils of the
actuating device is dependent upon the load supplied by the main transformer.
By suitable proportioning and arrangement of parts, the relative motion of the
coils of the brush shifting device may be so transmitted to the brushes of the
rectifying commutator K as always to maintain the same in a position of
minimum sparking. If found desirable the coils of the brush actuating device
may be associated with a core of magnetic material indicated in dotted lines.
Although in the apparatus above described constant current transformers have
been illustrated because of the desirability of obtaining a rectified current of
constant volume suitable for use in supplying are lights or the like, it will be
evident that this invention is not to be limited to the employment of such trans-
formers, for if found desirable, any other type of transformer may be employed,
or, indeed, the use of transformers may be dispensed with altogether. In cases
where we do not make use of constant current transformers of the type described
we may substitute for their function as brush-shifting devices, any other
mechanism suitable therefor, since it will be understood that this invention in
its broader aspects is not dependent upon the particular means employed for
maintaining a sparkless relation between the parts of the rectifying device when
in operation.
Having now particularly described and ascertained the nature of our said
invention (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 rectifying an alternating current of variable power, which

page_text: consists in automatically causing the rectification to take place at such phase
values of the alternating current as will result in a minimum amount of sparking.
2-The method which consists in generating an alternating current of constant
volume passing the same to a rectifying commutator and shifting the position
of brushes on said commutator as the power of said current varies.
3-The method which consists in transmitting an alternating current of con-
stant volume to a rectifying commutator and automatically shifting the brushes
on said commutator as the power of said current varies.
4 The method which consists in passing an alternating current to a rectifying
commutator and automatically causing the times of commutation to vary with
respect to the phase of the impressed alternating electro-motive force.
5 The method which consists in passing an alternating current to a rectifying
commutator, and automatically causing a given relative position of commutator
and brushes to occur at non-corresponding points in succeeding waves of the
impressed electro-motive force.
6-The method which consists in passing an alternating current to a rectifying
commutator and automatically shifting the position of brushes on said commutator
as the power of said current varies.
The method which consists in supplying an alternating current to a
rectifying commutator and automatically shifting the position of the brushes on
said commutator, as the power of said current varies.
S The method of rectifying an alternating current which consists in auto-
matically causing the rectification to take place at time corresponding to varying
phase values of the impressed alternating electro-motive force.
9 The method which consists in generating an alternating current of sub-
stantially constant potential, transmitting the same, generating therefrom an
alternating current of substantially constant volume, passing the same through
a rectifying commutator, and automatically causing the times of commutation
to vary with respect to the phase of the alternating electro-motive-force impressed
on the commutator.
10 The combination of conductors carrying alternating currents, a rectifying
commutator and brushes, and means for automatically causing a given relative
position of commutator and brushes to occur at non-corresponding points in
succeeding waves of the impressed electro-motive force.
11 The combination of mains carrying alternating curients, a rectifying
device for changing the alternating currents into uni-directional currents and
means for automatically causing the times of commutation to vary with respect
to the phase of the impressed alternating electro-motive force.
12 The combination of conductors carrying alternating currents, a rectifying
device for changing the alternating currents into uni-directional currents, and
means for automatically causing the rectification to take place corresponding to
varying phase values of the impressed alternating electro-motive force.
13 The combination of mains connected to a distribution system and carrying
alternating currents, a rectifying device for changing the alternating currents
into uni-directional currents, and automatically controlled means for maintaining
such a relation between the phase of the current to be rectified and the instants
when rectification takes place as will result in a substantially non-sparking
operation of the rectifier.
14-The combination of mains connected to a distribution system and carrying
alternating currents, a rectifying device for changing the alternating currents
into uni-directional currents, and automatically controlled means for maintained
brushes of said rectifying device in the position of minimum sparking.
15 The combination of a circuft carrying alternating current, a rectifying
device for changing the alternating currents into uni-directional currents and
means for automatically shifting the brushes of said rectifying device.
16 The combination of a transformer having coils relatively movable with
respect to each other, a rectifying device receiving current from one or more of

page_text: said coils, and means controlled by the relative movement of said coils for vary-
ing the times at which rectification takes place.
17-The combination of a transformer having coils relatively movable with
respect to each other, a rectifying commutator and brushes, and means operated
by relative movement between said coils to shift the position of the brushes on
the commutator.
16 The combination of a transformer having coils movable relatively to each
other, a commutator, a yoke carrying brushes bearing on said commutator and a
system of link and lever connections between said yoke and one of said coils.
19 The combination of a transformer having coils movable relatively to
each other, a commutator, brushes bearing thereon, and mechanical connections
between said brushes and one of said coils.
The combination of a plurality of transforming devices adapted to receive
current of one character and the deliver said current in an altered condition,
mains for supplying current to said devices and simultaneously operated switches
with suitable connections for cutting one of said devices out of circuit and re-
placing it by another of said devices.
1000
THE BRITISH THOMSON-HOUSTON (O., LTD..
A R. MONKS,
W. MARTINDALE,
ALFRED CLEMENTS,
}
Directors.
Assistant Secretary.