An Apparatus for Converting Alternating Currents of Electricity into Direct Currents.
Year: 1892

page_text: Date of Application, 11th Aug., 1892
Complete Specification Left, 9th May, 1893-Accepted, 11th Aug., 1893
PROVISIONAL SPECIFICATION.
An Apparatus for Converting Alternating Currents of Electricity
into Direct Currents.
We RICHARD NORMAN LUCAS of No. 8 Featherstone Buildings High Holborn
in the County of London Translator of Languages and ANTHONY GEORGE NEW
of Palace Chambers Bridge Street Electrical Engineer do hereby declare the
nature of this invention to be as follows:-
The object which it is desired to attain is to provide a means of automatically
converting alternating currents of electricity into direct currents of constant
direction.
The means hitherto adopted for effecting conversion by employing a revolving
commutator in connection with some form of alternating current transformer
present very considerable practical disadvantages.
In the first place in these forms of apparatus the revolving commutator is usually
driven by a so-called synchronizing motor in order that the velocity of rotation of
the commutator may preserve a proper relation to the frequency of alternation of
the current to be converted. But these motors will not start of themselves, and
various devices for starting them by means of separate mechanisms or self starting
motors coupled with them have been designed. These starting appliances must
however be thrown into and out of gear, and hence necessitate the employment of
a workman or attendant and they consequently cannot be employed where automatic
action is indispensable.
Methods which have been proposed of overcoming this difficulty by the use of
motors so wound as to be self-starting and yet to synchronize or maintain a velocity
proportional to the number of alternations of the current actuating them, have
only been practically successful in the case of multiphase motors i.e. motors driven
by two or more alternating currents arranged in quadrature (or otherwise) with
each other. But such motors cannot well be employed with ordinary single-phase
alternating currents, such as are at present used for lighting purposes.
A further inconvenience attaching to the above methods of conversion is that if
the commutator revolve slightly too slowly or too fast the direct current obtained
will be liable to periodic reversal of direction the disadvantages whereof are
obvious.
It will be seen that the system of appliances constituting the present invention
enables these difficulties to be satisfactorily overcome and the conversion of
alternating into direct currents to be effected with as little supervision and as
automatically as in the case of the transformations from high to low tension, which
take place in ordinary alternating current transformers while in addition the system
presents the further advantage that the direction of the currents so obtained is
constant.
The general arrangement of the apparatus is as follows:-
The terminals of the secondary coil of any suitable ordinary alternating current
transformer are connected to two brushes similar in construction to those employed
for collecting the current from dynamo electro machines. An ordinary com-
mutator, composed by preference of the same number of sections as the current it
is intended to convert has alternations in any given period of time is mounted in
bearings on centres or generally in such a manner that it may be capable of rapid
revolution about its axis. Adjacent to this commutator are situated two metal
rings insulated from one another and so arranged as to be capable of revolving
with it, or they may be rigidly secured to it. Every alternate section of the
commutator is connected up to one of these rings and the other sections are

page_text: connected up to the other. A second pair of collecting brushes presses upon this
commutator in the ordinary manner the brushes being separated by such an angle,
as will cause them to be always in electrical connection with a different ring.
The brushes which are connected with the terminals of the secondary coil of
the transformer press upon and make sliding contract with the two mettalic rings
mentioned above. Suppose now that we have to deal with a current which has
100 alternations per second, then if the commutator and the rings connected with
it are made to revolve at such a pace that each of the collecting brushes which
press upon it passes from one section of the commutator to the next in Thoth of a
second, we shall be able on connecting the brushes by a conductor or any desired
circuit to obtain a direct current through the said conductor or circuit.
It is obvious that the best way of effecting this in the case in question is to
cause the commutator to revolve once per second. But it is essential that absolute
synchronism between the alternations of the current and the passage of two
adjacent sections of the commutator under the brushes should be preserved. Thus
supposing the number of alternations in the current to be converted increases then
the commutator must revolve correspondingly faster and vice-versa.
This is effected by the employment of an ordinary or synchronizing alternate
current motor driven by a shunt off the secondary coil of the transformer (or other
suitable means) to drive the revolving commutator for it is a well known property
of these motors that their velocity may be made to vary according to the rapidity
of alternation of the current by which they are actuated.
To start this motor (and with it the revolving commutator) and to bring it up to
the velocity at which it synchronizes and will work independently a second motor
coupled with it is employed. This motor is constructed with 6 or by preference 8
magnetic fields and with an armature in which the coils are open-circuited and
connected to opposite sections of a suitable commutator on which press brushes in
the ordinary manner.
The result is that each of the coils of the armature is excited in such a manner
as to be attracted by the magnetic field in front of it and the motor will con-
sequently start in all positions. The commutator may also be arranged to commute
the magnetic fields instead of the armature coils with the same result. But other
types of self-starting motors may of course be also employed.
An essential feature of the invention is formed by the clutch which couples
these two motors together. It may in general outline be said to consist of two
collars one being connected with each of the motors and ribbed or toothed and
working one inside the other and further capable of movement backwards and
forwards along the axles together with which they revolve. They are further
connected to a lever attached to two ordinary governor halls in such a way that
when the governor balls revolve they tend to separate the two collars. This they
are unable to do, as long as the synchronizing motor forms a load on the starting
motor, for the collar with which it is connected then presses upon the collar con-
nected with the starting motor and the resulting friction prevents separation. As
soon however as the synchronizing motor works of itself, i.e. synchronizes the load
and consequently the friction. between the collars is removed: they become
separated by the action of the governor and in this way the starting motor is
thrown out of gear. The electric connection with the starting motor is made either
through the clutch or through the governor and hence when thrown out of gear it
comes to rest, springs out upon the clutch in such a way that when both the motors
stop, they are again thrown into gear with one another and electric connection
with the starting motor is re-established.
The action of the apparatus is thus perfectly automatic and supervision in
consequence unnecessary.
By rocking the brushes through an angle corresponding to one section of the
commutator, the direction of the current may at any moment be reversed. This
fact is made use of to prevent the reversal of the current in the circuit which
would occur if the commutator revolved too fast or too slowly. The brushes are

page_text: kept in one position by a spring or permanent magnet. An electromagnet or
magnets excited by the converted current (or a part of it) acts against this spring
or permanent magnet whenever the current flows along its coils in the opposite
direction to that required. The electro magnet is more powerful than the spring
or permanent magnet and will in this case immediately rock the brushes over
through the angle necessary for bringing the current back to its original direction.
The relative strengths of spring and magnets are so arranged that where the
current, though not reversed, weakened by a similar cause the brushes will be
revolved until the current is restored to its full strength.
The brushes may be revolved instead of or as well as the commutator without
altering the essential principle of the invention. And it is not necessary that the
commutator should consist of any precise number of segments or sections as
difference in their number can be compensated for by varying the velocity at which
the said commutator is caused to revolve.
Dated L
C A
1900
RICHARD NORMAN LUCAS.
ANTHONY GEORGE NEW.
COMPLETE SPECIFICATION.
An Apparatus for Converting Alternating Currents of Electricity
into Direct Currents.
RICHARD NORMAN LUCAS of 8 Featherstone Buildings High Holborn W.C.
Translator of Languages, and ANTHONY GEORGE NEW of Palace Chambers
Westminster Electrical Engineer 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 which it is desired to attain is to provide a means of automatically
converting alternating currents of electricity into direct currents of constant
direction.
The means hitherto adopted for effecting conversion by employing a revolving
commutator in connection with some form of alternating current transformer present
very considerable practical disadvantages.
In the first place in these forms of apparatus the revolving commutator is usually
driven by a so-called synchronizing motor in order that the velocity of rotation of
the commutator may preserve a proper relation to the frequency of alternation of
the current to be converted. But these motors will not start of themselves, and
various devices for starting them by means of separate mechanisms or self-starting
motors coupled with them have been designed. These starting appliances, inust
however, be thrown into and out of gear and hence necessitate the employment of
a workman or attendant, and they consequently cannot be adopted where automatic
action is indispensible.
Methods which have been proposed of overcoming this difficulty by the use of
motors so wound as to be self-starting and yet to synchronize or maintain a velocity
proportional to the number of alternations of the current actuating them, have only
been practically successful in the case of multiphase motors, i.e. motors driven by
two or more alternating currents arranged in quadrature (or otherwise) with each
other. But such motors cannot well be employed with ordinary single-phase
alternating currents such as are at present used for lighting purposes.
A further inconvenience attaching to the above methods of conversion is that if
the commutator revolve slightly too slow or too fast the direct current obtained
will be liable to periodic reversal of direction the disadvantages whereof are
obvious.
It will be seen that the system of appliances constituting the present invention
enables these difficulties to be satisfactorily overcome, and the conversion if alter-

page_text: nating into direct currents to be effected with as little supervision and as auto-
matically as in the case of the transformations from high to low tension which take
place in ordinary alternating current transformers; while in addition the system
presents the further advantage that the direction of the currents so obtained is
constant.
The general arrangement of the apparatus is as follows:-
The terminals of the secondary coil of any suitable ordinary alternating current
transformer are connected to two brushes similar in construction to those employed
for collecting the currents in dynamo electric machines. An ordinary commutator,
composed by preference of the same number of sections as the current it is intended
to convert has alternations in any given period of time is mounted in bearings, on
centres, or generally in such a manner that it may be capable of rapid revolution
about its axis. Adjacent to this commutator are situated two metal rings insulated
from one another and so arranged as to be capable of revolving with it, or they
may be rigidly secured to it. Every alternate section of the commutator is con-
nected up to one of these rings, and the other sections are connected up to the
other. A second pair of collecting brushes presses upon this commutator in the
ordinary manner, the brushes being separated by such an angle as will cause them
to be always in electrical connection. with a different ring. The brushes which are
connected with the terminals of the secondary coil of the transformer press upon
and make sliding contact with the two metallic rings mentioned above. Suppose
now that we have to deal with a current which has 100 alternations per second
then, if the commutator and the rings connected with it are made to revolve at
such a speed that each of the collecting brushes which press upon it passes from
one section of the commutator to the next in both of a second we shall be able
on connecting the brushes by a conductor or any desired circuit to obtain a direct
current through the said conductor or circuit. It is obvious that the best way of
effecting this in the case in question is to cause the commutator to revolve once
per second. But it is essential that absolute synchronism between the alternations
of the current and the passage of two adjacent sections of the commutator under
the brushes should be preserved. Thus supposing the number of alternations
in the current to be converted increases then the commutator must revolve
correspondingly faster and nice-versa.
This is effected by the employment of an ordinary or synchronizing alternate
current motor driven by a shunt off the secondary coil of the transformer (or other
suitable means) to drive the revolving commutator; for it is a well known property
.of these motors that their velocity may be made to vary according to the rapidity
of alternation of the current by which they are actuated.
To start this motor (and with it the revolving commutator) and to bring it up to the
velocity at which it synchronizes and will work independently a second motor coupled
with it is employed. This motor is constructed with magnetic fields and with an
.armature in which the coils are open circuited and connected to opposite section
of a suitable commutator on which press brushes in the ordinary manner.
The result is that each of the coils of the armature is excited in such a manner
as to be attracted by the magnetic field in front of it and the motor will conse-
quently start in all positions. The commutator may also be arranged to commute
the magnetic fields instead of the armature coils with the same result. But other
types of self starting motors may of course also be employed.
An essential feature of the invention is formed by the clutch which couples these
two motors together.
This consists of two collars one being connected with each of the motors and
ribbed or toothed and working one inside the other, and further capable of move-
ment backwards and forwards along the axles together with which they revolve.
They are further connected to a lever attached to two ordinary governor balls in
such a way that when the governor balls revolve they tend to separate the two
collars. This they are unable to do as long as the synchronizing motor forms a
load on the starting motor, 'for the collar with which it is connected then presses

page_text: upon the collar connected with the starting motor and the resulting friction prevents
separation. As soon however as the synchronizing motor works of itself i.e.
synchronizes, the load, and consequently the friction between the collars is removed,
they become separated by the action of the governor, and in this way the starting
motor is thrown out of gear. The electric connection with the starting motor is
made either through the clutch or through the governor and hence when thrown
out of gear it comes to rest. Springs act upon the clutch in such a way that when
both the motors stop, they are again thrown into gear with one another and electric
connection with the starting motor is re-established. The action of the apparatus
is thus perfectly automatic and supervision in consequence unnecessary.
By rocking the brushes through an angle corresponding to one section of the
commutator the direction of the current may at any moment be reversed. This
fact is made use of to prevent the reversal of the current in the circuit which would
occur if the commutator revolved too fast or too slowly. The brushes are kept in
one position by a spring permanent magnet or equivalent device. An electro-
maguet or magnets excited by the converted current (or a part of it) acts against
this spring or permanent magnet whenever the current flows along its coils in the
opposite direction to that required. The electro magnet is more powerful than the
spring or permanent magnet and will in this case immediately rock the brushes
over though the angle necessary for bringing the current back to its original
direction. The relative strengths of spring and magnets are so arranged that
where the current though not reversed is weakened by a similar cause the brushes
will be rocked until the current is restored to its full strength.
Without altering the essential principle of the invention the brushes may be
revolved instead of or as well as the commutator. And it is not necessary that the
commutator should consist of any precise number of segments or sections as
difference in the number thereof can be compensated for by varying the velocity by
suitable gearing.
One of the methods in which we carry out our invention is shewn in the
accompanying drawings in which :-
Fig. is a general drawing of the apparatus, partly in view and partly in
section.
Fig. 2 is a section through A. B and C. D. shewing the arrangement for
automatically moving the brushes.
Fig. 3 is a detailed drawing of a portion of the same.
Fig. 4 is a diagram of the electrical connections.
In the abovementioned drawings E and E' are the terminals of the secondary
coil of any suitable alternating current transformer or generator and are con-
nected to the two brush holders and brushes e and e¹: F is a commutator
composed of 50 segments which is mounted on a spindle G which revolves in
bearings g and g; connected to this commutator but insulated from one another
are two metal rings H and H each of which is connected to alternate segments
of the commutator F: a pair of brush-holders and collecting brushes and h
press upon this commutator F in the ordinary manner as shewn. The brushes e
and before mentioned press upon the rings H and H' and form a sliding contact
with them.
These four brushes are mounted upon a rocking bar 1 from which they are
insulated.
K is an ordinary synchronous motor which is driven by the alternating current
i.e. is connected in parallel with the brushes e and e: the armature of this motor
is attached rigidly to the spindle G: this motor has 50 fields and thus when
working for every impulse forward revolves the commutator F through an angle
of 7.2° K is a self starting alternating current motor which is connected across
the brushes e and e' (in parallel with K) through the clutch L: the armature of K'
is mounted on a spindle G₁ which runs in bearings 91 and 91. The clutch Lis
composed of two toothed discs and P which are mounted respectively on the
spindles G and G₁: the disc slides along the spindle G but being fitted with a

page_text: feather key is otherwise securely attached the disc is firmly keyed to the
spindle G which is in line with the spindle G: these discs when pressed together
by the spring compel G to be revolved when G¹ revolves: electrical contact to
the motor K is made through these discs: attaching the sliding disc to a firmly
secured (to the spindle G) disc 13 are links which also carry governing balls L¹
(as shewn in Fig. 1).
M is a permanent horse shoe magnet which is mounted about the spindle G and
is capable of a rocking movement: fixed to this magnet as shewn (Fig. 3) are
two pawls m and m which when M rocks in one direction engage with the fifty-
toothed ratchet-wheel m' which is rigidly secured to the rocking bar I moving it
forward one tooth and when M rocks in the other direction moves back over one
tooth of m' without engaging it fixed about the poles of the magnet M are two
helices N and N' through the coils of which pass the converted current (direct) in
such a direction as to form like poles at their upper ends thereby imparting a
turning moment to the permanent magnet M by attraction and repulsion. By this
means when the current flows in the desired direction the magnet M becomes
(or is) rocked over in the direction of revolution and if the current is reversed
from any cause the coils N and N¹ changing their polarity the magnet M becomes
rocked over in the opposite direction and carries with it by means of the pawls m
and ratchet wheel m the brushes and h¹ thus rectifying the direction of the
current.
P and P are the converted (direct) current terminals.
We are aware that revolving commutators have been proposed as a means for
converting alternating-currents into direct currents, and also that it has been
proposed to drive them by synchronous motors for use with which various forms of
starting appliances (which however are thrown in and out of gear by hand and are
consequently not automatic in their action) have been devised.
But what we claim is :-
1. The employment in connection with a revolving commutator of a self-starting
and of a synchronizing motor geared to one another by means of the special clutch
or device described (through which also electrical contact is made with the self-
starting motor) in such a manner that when the revolving commutator is brought
to revolve at the required velocity the self-starting motor is thrown out of gear
and also out of electrical connection with the source from which it is supplied with
electricity and consequently comes to rest, while when the synchronizing motor and
with it the revolving commutator cease or tend to cease to revolve the self-starting
motor is thrown into gear and into contact with its source of electricity and the
apparatus is in a position to start again and act as before thus becoming com-
pletely automatic in its operation essentially in the manner and for the purpose
described.
2. The electro-magnetic mechanism for maintaining the direction of the converted
current constant by rocking the collecting brushes through the requisite angle as
described.
Dated this 9th day of Mar 1902
RICHARD NORMAN LUCAS.. 4
ANTHONY GEORGE NEW.