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April 20, 1948.
Original Filed Deo. 21., 1939
Patented Apr. 20, 1948
Moron nmvE srs'rEM
Edward W. Kellogg, Indianapolis, Ind., miglior
to Radio Corporation of America, a corporation
of Delaware
Original application December 21, 1939, Serial
No. 310,385, now Patent No. 2,295,664, dated
September 15, 1942. Divided and this applica
tion April 30, 1942, Serial No. 441,149
8 Claims. (Cl. 318-41)
This invention relates to motor drive systems
such as are useful in correlating the speeds of
a plurality of separate motors under diilîerent
conditions of operation, and has for its principal
object the provision of an improved drive system
and method of operation whereby variation in
the relation between the speeds of such motors
is obviated or minimized.
This application is a, division of U. S. Patent
ings as the primary Ito which the A'.-C. voltage
is applied and to interconnect the stators which
then act as secondary.
An important example of the application oi’
Selsyn motors is in recording sound for motion
pictures. In this work it is necessary to thread
film records into a number of reproducing ma
chines in such positions that the contribution of
each original record to the nnal recording in
2,295,664, which issued September 15, 1942, on my 10 which these various original records are com
bined will occur at exactly the right time. The
only practical Way to preserve this synchronism
Where it is necessary to drive several mecha
is to have the machines so arranged that they
nisms which cannot be mechanically intercon
will all come up to speed together, run together
nected but which must run in strict synchro 15 and slow down together.
nism, it is in most applications satisfactory to
Although Selsyn motors have been fairly satis
operate the several mechanisms by means of syn
factory for this purpose, they are not above re
chronous motors all supplied from the same power
proach. In certain applications, of which record
system. In other applications, it is necessary
ing sound is a striking example, a degree of speed
that the synchronism be preserved throughout 20 constancy is required far in excess of that which
the operations of bringing the machines up to
is needed for most other purposes. Synchronous
speed or stopping them. In other words, the
driving systems, whether employing ordinary syn
several mechanisms are locked together as if me
chronous motors or Selsyn motors, are subject
chanically interconnected, and this interconnec
to hunting or an oscillatory action superimposed
application, Serial No. 310,365, filed December 2l,
tion is not broken at any time. Where this is re
quired, it is usual to employ Selsyn motors. These
have been used for many years and their princi
ple of operation is well known. Briefly stated, a
Selsyn motor is essentially the same as a wound
25 on their continuous rotation. This phenomenon
has been recognized for years in synchronous mo
tors and is well understood. 'I'he oscillations in
many cases are not continuous and, after a dis
turbance, persist for only a few cycles, but they
rotor induction motor. Both the rotor and sta 30 are started again by any little disturbance in
tor windings are preferably polyphase, but one
power supply or load. The cure for hunting lies
or the other Imay be single phase and the system
in endowing the motors with the property of
still works. If the rotors of the several machines
damping out oscillations. Synchronous motors
are connected together but not connected to any
can be given very powerful damping properties
external source of power, and the stators are all 35 by use of pole face grids. The same expedient is
supplied with alternating current from a common
not applicable to Selsyn motors and these are
source, the rotors will seek a position at which
inherently more subject to oscillations and do not
the secondary or rotor winding voltages are sub
give as high an order of speed constancy as the
stantially balanced and little cross current flows.
synchronous motors. Builders of Selsyn motors
If one of the rotors is forcibly turned, all of the 40 have resorted to such expedients as coupling me
other rotors seek a new position of equilibrium,
chanical damping devices to the motors which
and this following of one by the others continues
absorb energy from any oscillatory movement.
for all speeds up to synchronism, although the
This method is helpful but heavy and cumber
torque by which the several motors are held in
some, and not as satisfactory as the damping
step or synchronism becomes weak as the rotor
that is obtained in synchronous motors. It is
speed approaches the synchronous speed of the
the purpose of my invention to provide Selsyn
stator field. The frequency of the cross currents
motor systems with the superior damping which
which hold the machines together approaches
characterizes synchronous motor systems, which
zero as synchronous speed is approached and like
at the same time preserving the indispensable
wise the voltage which -drives the currents through 50 features of the Selsyn system of being able to
the windings approaches zero. Therefore, it is
maintain _absolute synchronism from start to stop
not practical to operate Selsyn motors close to
of a run. For this purpose, I employ Selsyn mo
synchronous speed. It is common _to operate them
tors and a main driving motor exactly as in pres
at from one-half to two-thirds of synchronous
ent Selsyn motor systems. As in present Selsyn
speed. It is equally possible to use the rotor wind 55 systems. the driving motor drives a Selsyn unit I
phonographs, cameras and recorders which are
chronous speed. Since the rotor also revolves at
synchronous speed, there is no relative motion
between the stator iield and the grids in the rotor.`
t0 be operated in synchronlsm. `
In the case of the Selsyn, there is a rotating iield
which is called the master Selsyn, and is some-what larger than the units attached‘to the nlm
The several motors are locked together by ap
plying a polyphase voltage to all oi' the primary
windings, which are here assumed to be the sta
tors, all of the rotors or secondarles being con
nected together, but no voltage being applied to
the secondaries. When the machines are thus
locked together, the main motor is started, driv
ing its master Selsyn,y and all of the other mo
tors >respond by rotating at their appropriate rel
ative speeds. There are cross currents between
the secondary windings _of the machines, and
which is moving with respect tothe primary at
synchronous speed and `with respect to the sec
ondary at one-third synchronous speed. Pole
face grids would have excessive currents induced
in them and would destroy the effect of the ro
tating iield, as well as produce a powerful torque
tending to make the motor pull up to substan
tially full synchronous speed, acting as an induc
tion motor. An effect exactly equivalent to the
pole-face grids can be obtained in a synchronous
motor by providing, in addition to the field wind
ing (normally excited by direct current), a scc
ond winding placed at 90 electrical degrees from
the main ileld winding and short-circuited upon
itself. The spatial relationship between these
these cross currents iiowing through the wind
ings react with the rotating iields produced by
the primary windings to supply the torques re
quired by the several motors. If the'chosen op
erating speed is two-thirds of synchronous speed, 20 two windings is the same as that between two
windings of a polyphase alternating current wind
a four-pole Selsyn motor will run» 1200 R. P. M.
ing. Thus, the polyphase primary winding of
(instead of 1800 R. P. M., which is the speed at
which a four-pole synchronous motor would run) .
the Selsyn motor or generator may be made to
Under these conditions, the secondary currents
serve as a direct current field winding and a short
have a frequency of 20 cycles per second.
Up to the point oi' reaching running speed, my
system operates exactly as an ordinary Selsyn
driving system. From this point on, I provide
the driven machines with the superior steadiness
and freedom from hunting characteristic of the 80
circuited damping Winding. If the primary wind
ing is two-phase, this means simply supplying
direct current to one of the polyphase windings
and short-circuiting the other. In the case of
a three-phase winding, the identical eiîect may
be obtained by connecting two of the .three ter
minals together and using this as one terminal
true synchronous motor, and this may be accom
for the direct current, the third terminal serv
plished in the following manner:
ing as the other direct current connection. I
The polyphase power supply is removed from
have operated Selsyn motors in this manner and
the primary winding and a direct current con
nection substituted. This change is accomplished 85 have demonstrated the superior damping which
may be obtained by thus operating them as syn
so rapidly that none of the machines has an op
chronous motors. The direct current required is
portunity to drop out of step or slip a pole dur
substantially the same as the maximum value
ing the moment of no power supply. The change
of the alternating current, but since the only im
can be made, for example, in about one-tenth
pedance to be overcome is the ohmic resistance
second.l When direct current' instead oi 60-cycle
of the conductors, a low voltage direct current
alternating current ñows through the primary
supply, such as may be conveniently obtained
winding of the master Selsyn generator, the sec
from batteries, sufûces.
ondary current suddenly changes >from. 20 cycles
For certain applications, it is important not
to 40 cycles. The magnetic :fields of the several
only to prevent the slipping of a pole by any of
motors, instead of rotating in space at synchro
the motors during a period oi.’ acceleration, but
nous speed, become stationary. The ¿l0-cycle cur
to provide an exact adjustment of phase position
rent now produced by the main generator re
ci’ the several machines within a small number
acts with this stationary ñeld in the motors to
of degrees of arc. This, for example, is the case
provide the required driving torque. Fortunately,
in what is known as the background projœtion
no appreciable shift in phase takes place in the
system employed in making motion pictures. The
course of this transition. The generator voltage
camera and the projector must be held insyn
and the counter electromotive forces of the mo
chronism to within a very small angle of toler
tors were approximately balanced for the 20-cycle
ance and it may be desirable to make adjust
circulating current and they are now also ap
proximately balanced for the láiO-cycle current. 55 ments of this angle. It is possible to produce
variations in the angle at which the machines
The entire system now operates no longer as a
are locked together by slightly altering the dis
Selsyn system but as a true synchronous genera
tribution of direct current in the windings. This
tor and motors. The entire transfer of power ls
may be done by small series resistors in the
now accomplished by the ‘iO-cycle current.
direct current supply.. `The exact running posi
At the end of the run, the reverse operation
tion may then be controlled by setting these re
is performed. The direct current supplied to the
sistances at the proper values. This adjustment
primary winding is removed and the polyphase
might be necessary to compensate for the eiîect
alternating current restored. The machines then
of the load on the motor so that, if the machines
come to rest together in accordance with the
standard Selsyn operation. Since the machines 65 are set with certain relations at standstill, the
exact relation may be preserved during running.
which I employ mustserve during part oi the
These resistancesneed not be so large as to ma
time as Selsyn motors, they may not be provided
terially impair the damping which depends on
with pole-face grids for damping. The reason
a virtually short-circuited winding. They only
for this is well understood by electrical engineers.
The grids must have very little motion with re 70 need to be comparable in magnitude with the re
sistance of thewindings themselves in order to
spect to the magnetic ileld produced by the wind
control the current distribution.
ing in the other member of the motor. In a syn
Figures 1 to 3 illustrate a motor system involv
chronous motor, the poles are commonly in the
ing the use .ora plurality of rotary converters,
rotor which is provided with pole-»face grids, while
the stator produces a ñeld which rotates at Syn“ 75 one of which is operated to control the others. -. i
2,440, 176
It is well known that rotary converters can be
operated in parallel on both the A. C. and D. C.
sides. This has been made the basis of the so
called “A. C.-D. C. interlock motor system,” which
has been commercially applied to motion pic
ture production, where it is desired to run several
machines in strict synchronism. The A. C.-D. C.
interlock system has not been commercially ap
plied to cases where it is desired to lock the ma
chines together electrically at standstill and to
bring them up in step. For this purpose, as has
normal operation, depending on the load, being of
the order of from one-half to one-third of the
voltage which this normal operation ratio would
If the slip rings of a machine, to winch voltage
has been applied on the D. ‘C. side as :lust de
scribed, are connected to the polyphase terminals
of a second machine, currents will flow between
the two machines and these currents, flowing
through the windings of the second machine, will
react with the field thereof to lock the armature
into a certain position. If the first machine is at
standstill, the second machine will rotate to a
point of their synchronization are simply syn 15 suitable position and remain there even though
considerable force is exerted to move it. If the
chronous A. C.“ machines, have not been used
armature of the first machine is rotated through
for interlocking from start is that neither they,
a small angle, the distribution of currents in both
nor any other synchronous generators, when they
changes, and the second machine
are turning over at very low speed as during start
moves to a new position. If the motion is con
ing, put out enough A. C. voltage to provide the 20 tinuous, the second machine rotates at the same
necessary interchange of power to hold the ma
speed at the first. Although the currents in the
chines together. For example, a generator which
second machine will, in general, be much weaker
could supply 100 volts across the A. C. terminals
than those in the first machine, the latter may
at full speed would develop only one volt when
be made several times full load current, under
it is just starting and the speed is only 1% of full 25 which conditions the currents in the second
speed. The A. C.-D. C. machine or rotary con
machine will be abundantly adequate to cause the
verter, however, can be made to perform the func
armature to start up under load and rotate in
tion of a switching device whereby it can supply
synchronism with the first machine. This syn
an appreciable voltage across its A. C. terminals
chronous operation is maintained all the way
at standstill as well as at extremely low speeds. 30 from standstill to full speed. As soon as the
If enough voltage is applied to the direct cur
speed has reached a point where the induced
rent brushes, for example, to send several times
voltage in the windings of the first machine be
normal full load current through the armature '
comes considerable in comparison with the ap
windings, the slip rings will assume voltages de
plied D. C. voltage, the excessive current in the
pendent on the positions of the taps in the wind 35 windings of the first machine drops to a moderate
ings to which they _are connected. Thus, if the
value and the machines are thereafter locked
tap corresponding to slip ring A is connected to
together by normal synchronous motor action.
the commutator bar directly under the positive
This transition from control of the current by
already been explained, Selsyn generators and
motors have been employed. The reason that
the A. C.-D. C. motors, which from the stand
brush, this ring will have substantially the same
resistance only, to control by electromagnetically
>potential as the brush. If the tar is half-way 40 induced voltages, takes place at about the speed
between brushes, the ring will be at mid-poten
at which reactance in the motor windings begins
tial, or, if the tap is connected to the bar under
to predominate over ohmic resistance.
the negative brush, the ring will be at full nega
If the D. C. voltage applied to the `brushes of
tive potential. The windings serve as a double
the first machine is frorn‘a low voltage, low re
path potentiometer and the slip rings are con
sistance source, the machine will not come up to
nected to this potentiometer at points which vary
full speed, but will continue to run at a low speed.
relative to the brushes. Thus, at standstill, the
three rings, if the machine is wound for three
phase, ‘will assume certain potentials dependent
on the position of the armature and slip ring taps. 50
If the armature is now rotated, no matter how
slowly, the positions of the slip ring taps will shift
from one brush to the other along the poten
If the D. C. voltage is from a source having a
voltage suitable for full speed operation, but if
there is a suitable amount of resistance in the
leads to prevent excessive current at standstill,
then the D. C. voltage will continue to rise as the
machine comes up to speed, while the input cur
rent falls. During the entire acceleration, the
output voltage isboosted somewhat by the re~
rise and fall and reversal of slip ring potential. 55 sistance effect which at very low speed was
entirely responsible for the A. C~ voltage.
In the absence of load, this slip ring potential
would be essentially a triangular or sharp peaked
It has been proposed by others to start several
wave. If some load is drawn from the slip rings,
A. C.-D. C. motors together and bring them up in
complete interlock by impressing a suitable D. C.
the wave shape will be changed, but it will still
be alternating in character, and, although con 60 voltage across the brushes of each machine and
taining overtones or harmonics, the voltage will
depending on the cross currents through the A. C.
have a large component of the fundamental' fre
leads to hold the several machines in step. This
l quency. The relative phase of the voltages at the
method differs from the method of my invention
three rings will depend on the positions of the
in that I supply most of the D. C. to one machine
taps to which they are connected. If the taps are 65 only. The cross currents which serve to tie 'the y
120 electrical degrees apart, the voltages will con
machines together are not reduced in effective
stitute a true three-phase system. Although
ness by impressing D. C. across both machines.
movement of the armature conductors through
The actual current may be less but the current
the magnetic field of the machine may be so slow
change which tends to retard whichever machine
that the induced voltage from this cause is negli 70 is ahead or to accelerate whichever machine is
gible, the machine can still supply a polyphase
behind is increased by applying D. C. voltage to
alternating voltage by pure resistance potenti
the second machine. In other words, the
ometer effect. The ratio of A. C. to D. C. volt
strength of the interlock effect at low speeds is
age under these conditions of operation will be
increased by applying D. C, voltage to 'both ma
substantially less than the ratio at full speed or 75 chines. The dimculty with this method of bring
tiometer paths in such a manner as to cause a
ing machines up to speed together lies in the fact
expedients.' namely, limiting the direct current
that the direct current which flows in the
windings of both machines exerts so powerful an
supplied to the armatures of the machines which
are to be held in synchronism with the ñrst or
accelerating torque that the interlock eifect is
almost negligible in comparison. The result is
master m-achine and reducing the rate of ac
celeration of the system, minimizes the require
ments for interlocking torque and vthereby insures
that, when several machines are started up in
the adequacy of the torque developed bythe poly
phase currents between the machines.
For some purposes, it is sufficient to insure that
direct current is kept to moderately small values, 10 the machines- be locked together at standstill,
during acceleration and during the period of full
the entire system accelerates> with great rapidity
speed operation. If this is all that is required.
with the result that any differences in the inertia
the arrangements already described will suñlce,
characteristics of the loads becomes magniñed,
except that on cutting off the power supply the
tending to make the machine which must over
interlock in this manner, the amount of direct
current which is supplied to each machine must
be carefully adiusted to its load and, unless the
come the greater inertia, fall behind the machine 16 machine chosen as a master and provided with
a large flywheel would coast excessively. It is
which has less inertia load. In other words, both
therefore desirable that a brake be applied to
the friction load and the inertia loads need to
this machine which will bring it to rest in a rea
be balanced. This results in an extremely criti
» sonable time. This brake can be automatically
cal system.
AIn accordance with my invention, I sacrifice 20 applied when the power is cut ou. There are,
the slight increase in interlocking torque which
on the other hand, numerous applications in
.might be obtained from supplying a _large amount
which it is `desirable notv only to accelerate the
several machines to full speed from standstill, in
of direct current to all of the machines, and de
complete interlock, but to bring them to rest
pend for` my interlocking polyphase current sub
stantially entirely on the currents supplied from 25 again in interlock and hold them so during prep
the slip rings of one machine, a relatively large
arations for another run. In, order to accom
direct current being supplied to its brushes. The
plish this, I reverse the operation of starting.
Instead ci’ cutting oiï the D. C. power supply
other machines then operate essentially' as syn
when the system is stopped, I permit the D. C.
chronous motors, depending on the A. C. to sup
ply an accelerating torque rather than on direct 30 through the armature of the first machine to
current supplied directly to their brushes. I « continue to flow, and to rise as the machine slows
may, however, supply a limited value of D. C. to
down to its original excessive value. Dependence
the brushes of the other motors, sufficient only
must then be placed entirely on the brake to
lto overcome their frictional loads. By so doing,
bring the machines to rest. As soon as the ma
I reduce the amount of torque which must be
chines have come to rest, the D. C. supply to the
supplied from the A. C. side `but do not permit
master machine may be cut 01T.
the torque developed bythe D. C. in the windings
The arrangement so far described will accom
to produce such a powerful forward torque as to
plish the requirements as set forth, namely, to
require the A. C. interlock to exert an appreciable
lock the machines together at standstill, bring ‘
retarding torque. In order to produce enough
them up to speed, operate at full speed and slow
. A. C. output from the first machine which serves
all machines down together in interlock. If it is
as a master for the group, I may supply its
desired to hold the machines in interlock over
brushes for a short period with from three to
an appreciable period of time at standstill, it is
six times normal full-load current. This results
desirable to provide a change of connections
in a corresponding increase in the A. C. voltage 45 whereby the currents which hold the machines in
and current available to fbe supplied to the other
fixed relation will be supplied directly to the
machines. This excessive D. C. in the winding of
polyphase or slip ring conductors rather than to
the first machine results in the development of
the brushes of any machine. This eliminates any
a very powerful accelerating torque. Since, at
tendency for any of the machines to try to run.
the very low speeds, dependence is placed on the 50 The fields> of all machines are maintained at full
potentiometer eiîect for producing A. C. voltage,
value, and D. C. voltage is applied to the conduc
and electromagnetically induced voltage plays a
tors -of the polyphase connections. This D. C.
negligible part, it `would be possible to prevent
voltage may be applied between any two of the
the excessive torque by temporarily weakening the
three conductors _or between one conductor and
field of the master machine, the other fields being 55 the other two, which may be connected together.
,provided with full excitation from the start.
expedient, however, is undesirable for the
, reasonf that it is desirable to develop the induced
When the stationary locking current is applied
in this manner, each machine receives its due
proportion of the current, which, in the arrange
voltage as early as possible in the course of ac
ment I have shown in Figure 1, can be inde
celeration. It might even be desirable to over 60 pendently adjusted. When the switches are
excit’ei'thefñelds of all of the machines during
closed which apply D. C. to the A. C. leads, the
acceleration. _I therefore permitv the lexcessive
machines will, in general, execute a small rota
_torque >tube-developed in the first machine but
tion, since the position at which they came to
prevent it from accelerating toorapidly by some
rest will be random, whereas the application of
, - mechanical means, as, for example, mounting a 65 D. C. to the A. C. conductors will force them to
- large-flywheel on the motor shaft. The moment
assume a specific position. This shift, however,
- of' inertia of the flywheel is sufilcient to prolong
will be less than 180 electric degrees and will not
the period of acceleration to such’a point that
result in any slipping of poles. If desirable, an
the inertia eifects to be overcome by the other
auxiliary commutator, not illustrated, may be
machines ¿ play a negligible part. v In other words, 70 employed, which will lock the machines at what
they'jneed develop very little more torque .than
that- required by their friction load. This makes
ever position they have stopped, thus eliminating
any possibility of their being caught on "dead
center” and, therefore, not all executing identi
cal‘movements. Alternatively, the brake may be
Y machine during acceleration as it is after full
'speedis reached. The combination of the two 75 arranged to bring the master machine to final
it as easy for them to stay in step with the master
rest in a specified position of its revolution. In
general, these reiinements will not be required.
Figure 2 illustrates in schematic form two
A. C.-D. C. motors, one driving a sound recorder
|0| and the other a camera |02.
The master
|00 to overcome load Iriction. The motors will
now come up to speed in the manner already
described. When full speed is reached, it may
be desirable to synchronize all oi’ the machines
with a main (iO-cycle polyphase power supply,
the frequency of which is accurately maintained
motor |03v is provided with input conductors |04
connected to a D. C. supply |05 through the
from the power house. For this purpose, switch
-switch box |06. The camera motor |01 is like
|6| is shown. Synchronization would be per
wise supplied with D. C. input conductors and
formed in the manner that is common when large
switch, designated respectively |08 and |09. The 10 synchronous motors or alternators are brought
A. C. conductors ||0 pass through a switch box
up to speed by some auxiliary power and then
||| by which they may be connected either to
synchronized with others. As one method of
the D. C. supply |05 or to a polyphase A. C. sup
indicating the time to close switch ISI, the syn
ply ||2. The flywheel is shown at ||3 with an
chronizing lamps |52 are indicated. There are
electrically operated brake ||4 to bring the mas
well-known devices for automatically synchro
ter motor to rest.
nizing machines with the line and any such
If a comparatively ylarge number of machines
automatic system may be employed. For stop
is to be operated in this manner. it is desirable
ping the system, switch |6| would be opened.
to make the master motor larger than the others,
The brake would be applied to the motor
in order that the resistance of its windings may
not too greatly limit the current distributed to
the cher machines. Such an arrangement is il
lustrated in Figure 1, where the master motor
|20 is not shown as driving any of the machines,
but it might do so if this appears to be desirable.
Figure 3 shows another motor at |2| driving a
recorder |0| and other motors |22, |22, driving
ñlrn phonographs |24, |24. The connections
shown at |25 represent multi-conductor cables
|20 and, as soon as it has been brought
to rest, switches |4| to |45 inclusive would- be
thrown to the upper position whereby the ma
chines are locked together for standstill. Re
sistances |51 are shown as variable, whereby the
speed of the entire system may be controlled, as
for example, to facilitate synchronizing with the
polyphase supply. The. current'l limiting resist
ances |51, |51 and |58, |58 are shown as divided
substantially equally between the positive and
or groups of cables through which each of the
negative connections. If either the positive or
motors |2I, |22 is connected individually on both 80 the » negative brushes are connected together
its A C. and D. C. sides to switch box |30, where
through'a low resistance connection, the master
suitable switches are provided to accomplish the
motor |20 will transfer a combination of D. C.
several switching operations already described.
and A. C. to the other machines, and the D. C.
Typical switching arrangements are shown in 35. may produce too much forward torque. More
Fig. 1 except that some obviously desirable
over, the D. C. which thus flows between the
switches are omitted for the sake of simplicity;
machine robs the A. C. power transfer and thus
as, for example, switches through which the
weakens the interlock.
ñelds are excited. A number of switches are
I claim as my invention:
shown in the drawing and it is to be understood 40
1. In a drive system for the synchronous oper
that these would normally be operated as a unit,
ation from standstill to full speed of a. plurality
either by mechanically connecting the various
switch blades together or by providing a suitable
group of relays, which operate from a main con
of electrodynamic machines each provided with
polyphase alternating current terminals and with
direct current terminals, the combination of
trol and perform the switching operations.
means for supplying direct current to said alter
For putting the system into operation, the 45 nating
current terminals for interlocking said
master D. C. switch |40 is closed, thereby ex
machines at standstill, means for interconnect
y citing the iields of all of the machines. In order
ing said alternating current terminals, means
to lock all of the machines together at stand
for supplying a relatively large direct current to
still, the group of switches indicated at |4|, |42, 50 the direct current terminals of one of said ma
|43, |44 and |45 would all be thrown to the
chines and a relatively small direct current to
upper position. This, it will be noted, does not
direct current terminals of the other of said
apply any D. C. to the brushes of any of the
machines for starting said machines, and means
machines, but supplies D. C. to the polyphase
for sychronizing said machines with an alternat
conductors |41, |48, |49 and to the correspond
ing current supply source.
ing slip ring conductors of the several motors.
2. In a drive system for the synchronous oper
This D. C. for locking the machine together is
ation from standstill to full speed 0f a plurality
supplied through resistors |52 _to |55 inclusive,
of electrodynamic machines each provided with
these resistors having been adjusted to send cur
alternating current terminals and with
rent of suitable magnitude through each machine.
direct current terminals, the combination of
When- the system is to be started, switches |4|
switching means for supplying direct current to
to |45 inclusive are thrown to the lower posi
said polyphase terminals for locking said ma
tion which removes the D. C. voltage from the
chines together at standstill and for intercon
A. C. conductors |41, |48, |49 and establishes a
necting said polyphase terminals during the ac
through connection of these conductors from
of said machines, and means for sup
each machine to all of the others. Switch |44
plying relatively large and small values of direct
connects the brushes of the master motor |20
current to said direct current terminals during
to the D. C. supply, through the comparatively
said acceleration.
low resistance |51 which permit a large current to
3. In a drive system for the synchronous oper
iiow when the machines are at standstill. Switch ‘
ation from standstill to full speed of a plurality
|45 connects the motor |60, which may represent 70 of electrodynamic -machines each provided with
motor |01, |2| or |22 of the other figures, to
polyphase alternating current terminals and with
the D. C. supply through resistances |58 which
direct current terminals, the combination of
are of relatively high value and permit only
enough D. C. to iiow through the brushes of motor 75 switching means for supplying direct current to
said polyphase terminals for locking said ma
2,440,170 '
ll ‘
chines together at standstill and ior intercon
necting said polyphase terminals during acceler
ation of said machines, means for supplying rel
atively large and small values or direct current
to said direct current terminals during said ac
celeration, alternating current supply terminals,
and means for connecting said alternating cur
rapid acceleration of said machine, and mechan
ical means for bringing said machine to rest.
'1. In the operation of a drive ysystem for the
synchronous operation from standstill to full
speed of a plurality oi electrodynamic machines,
each provided with polyphase alternating cur
rent terminals and with direct current terminals,
the method which includes supplying a direct
rent supply terminals to the alternating current
current to one of said machines large in com
terminals of said machines for normal operation
10 parison with the normal operating current ci
0i said machines.
said machine, retarding acceleration oi said
4. In a drive system ior the synchronous
machine, and decelerating said machine to
operation from standstill to full speed oi` a plu
standstill while continuing to supply direct cur
rality of electrodynamic machines each provided
with polyphase alternating current lterminals
rent to said machine.
8. In the operation of a. drive system for the
and with direct current terminals, the combina
synchronous operation from standstill to full
tion oi switching means for supplying direct cur
speed of a plurality of electrodynamic machines
rent to said polyphase terminals for locking said
each including a winding provided with poly
machines together at standstill and for inter
phase alternating current terminals and with
connecting said polyphase terminals during ac
direct current terminals, the method which in
celeration o! said machines, means for supplying
relatively large and small values of direct cur 20. cludes 'supplying direct current to said polyphase
terminals for interlocking said machines, inter
rent to said direct current terminals for acceler
connecting said polyphase terminals for acceler
ating said machines, and braking means for de
` ating said machines, supplying to the direct cur
celerating said machines.
5. In a drive system for the synchronous 25 rent terminals of one of said machines a direct
current greater than that applied to the corre
operation from standstill to full speed of a plu
sponding direct current terminals of the other oi
rality of electrodynamic machines each includ
said machines, and applying a retarding force to
ing a winding provided with polyphase alternatà
the machine supplied with said greater direct
ing current terminals and with direct current
supply terminals, the combination ot means ior 30 current.
interconnecting the alternating terminals of a
plurality oi.' said machines, means for supplying
ssrmnhcns man
direct current to the direct current terminals
oi’ one oi said machines. and means for pre
The following references are of record in the
, venting rapid acceleration o! said machine.
35 ille of this patent:
6. In a drive system for the synchronous oper
[email protected] STA'I'ES PATENTS
ation from standstill to full speed of a plurality
of electrodynamic machines eachv including a
Number '
winding provided with polyphase alternating cur
Alchele __, ........ __ Feb. 26, 1907
rent terminals and with direct current supply 4f, 2,132,630
Kengon ___________ __ Dec. 5, 1939
terminals, the combination of means for inter- _
connecting the alternating terminals oi a plu
rality oi' said machines, means for supplying direct current to the direct current terminals
of one oi said machines, means for preventing 45
Great Britain ..... .__ Feb. 26, 1923
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