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Патент USA US2408218

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' Sept 24», W466
Filed June 27, 1944
5 W099‘.
C, a~
Patented Sept. 24, 1946
George E. King, Swissvale, Pa., assignor to ‘West
inghouse ElectrrcyCorporation,
East‘ Pittsburgh,
Pa., in corporation of Pennsylvania
Application June 27, 1944, Serial No. 542,402
3Claims. (Cl. 172-479)
The present invention relates; to variable volt
age control systems and more particularly to-elec
tri'c motor control systems for automatically con
trolling the operation‘ of motors used to drivema
chine-tool elements, paper mills and the: like, ele
vators, electrically operated shovels. and so on.
' Thisainvention provides certain improvements
in variable voltage control systems inwhich- ro~
toting regulators are employed to regulatea given
quantity, and the invention as, hereinafter de
scribed and as illustrated in the drawing is- spe
ci?cally directed to. the regulation of the speed
of rotation of a direct-current motor. However,
it will be apparent to‘ one skilled in the art that
the invention. is not limited to speed‘ regulation
alone since various- modi?cations of the system
‘may be made to control the motor torque or
power. It will further be apparent that the in
vention is not necessarily limited to motor control
since automatic regulation of the voltage current
or electrical power supplied to an electrical load
of substantially any type susceptible of. regula
tion may be had.
The improvements provided by the present in- N
vention insofar as increased e?iciency and speed
of operation are concerned in motor control sys—
tems, for example of the type disclosed in ap
plicant’s Patent No. 2,205,204, are readily ap
parent. In general, such systems comprise a di-.
rect~current motor, a main generator connected ’
in series circuit relation with the motor, a. regu
lating generator for controlling’ the electrical out
put of the main generator, in response to a
changing motor characteristic which it is de
sired to regulate and an exciter for supplying‘
electrical energy to the electrical system‘, or some
portion thereof, depending upon the arrangement
the output terminals of t he bridge. The input
terminals of the bridge ci rcuit are connected to
a suitable source of direct current which may
be varied to controlthe excitation of the main
generator control ?elds and in view of the series
connection of the two regulating generator ?elds
with the two main generator control- ?elds the
same exciting current fro in the external source
?ows therethrough. The differential magnetoe
motive force of the voltage and current energized
regulating generator ?elds are opposed to the
magnetomotive force resulting from the external
excitation of the two regulating generator ?elds
in the bridge circuit. Thus when the motor is
operating at a proper spe ed as indicated by the
excitation of the main generator control ?elds the
total ?ux in the regulating generator is zero.
The regulating generator armature winding by
reason of its connection in the bridge circuit is
in such circuit relation with its two ?eld wind
ings in‘ the bridge circuit that the generator is
substantially self energizing and may therefore
have an electrical output independent of the ex
ternal excitation of its two windings in the bridge
circuit,v or of its voltage and current energized
windings, Thus upon a departure in balance of
the mentioned differential magnetomotive force
against the magnetomotive force of the two regu
lating generator bridge circuit windings, an out
put of the regulating generator is fed into the
bridge circuit in a direction to correct the exist
ing unbalance. When a balance in the regulating
generator windings is ag ain reached this gen
erator maintains: the corre ctive current necessary
to keep such balance until a further disturbance
While this practice of connecting ?eld wind
of the component parts.
ings of the‘ regulating ge nerator in series with
The regulating generators used in such sys-.
terns are generally provided with a ?eld winding 40 the generator control ?elds provides an accurate
measurement of the generator control ?eld cur
energized proportionally to the motor current, a
rent, it has been found that the system during
?eld winding energized proportionally to the mo
tor armature terminal voltage and differentially
related to the current energized ?eld, the differ
ential magnetomotive force of the voltage and
reversing cycles tended slightly vto be sluggish.
This sluggishness of op'er atio-n resulted because
the currents in the regulating generator ?eld
windings could change no faster than those‘ in the
generator control ?eld windings, by reason of
their series connection. While the generator
control ?eld windings are designed to have a fair
ly low impedance, the impedance of these wind
current energized ?elds is indicative of the coun.-'
ter emf of the motor and hence indicates the
speed ofv the motor, and two ?eld windings each
connected in series with. a control ?eld winding
for the main‘ generator. The series connected 50
in'gs is, none the less,‘ considerably higher than
regulating generator and main generator ?eld
that ‘required for the regu lating generator ?elds.
windings are usually arranged in opposite legs
Thus,v even- though the ?eld windings of‘ the regu
of a conventional bridge circuit having resistors
Ilating generator ' are :of a
character that permits
in the remaining two opposite legs and the regu-:
a faster'change of current than those of the. main
lating generator armature is connected across
generator,‘ the series conn ection of the windings
of these two machines prevented such a condition.
It is highly desirable that machine tools have
a high production capacity. On such machines,
for example as metal planers, as the machine is
being operated with fairly short strokes, the re
versing cycle of the motor may comprise a sub
stantial portion of the time required for a com
plete operating cycle. For this reason, it is neces»
sary that the motor be decelerated, stopped and 10
controller which provides certain desirable auto
matic control features and which comprises the
cut and return directional contactors C and R, a
control relay CR, an automatic relay AR, a break
relay BR, a voltage relay VR, 3. ?eld weakening
relay FR. and a ?eld weakening contactor FW;
and (6) The limit switches which comprise the cut
and return limit switches CLS and RLS and the
cut and return slowdown limit switches CSD and
accelerated in a reverse direction in as little time
as the electrical and mechanical characteristics '
of the equipment will permit. This has been
accomplished in part, in the past, by designing
faster control ?elds for the main generator and
also by controlling the resistance of the discharge
circuits for these generator ?elds so that the flux
The motor and the main generator in Fig. 1 are
connected with their armatures in series circuit
decay in the generator ?elds may be as rapid as
can be attained without producing current peaks
on deceleration near or above the maximum
limits that the motor energized by the generator
can commutate.
With the present scheme of control, a forcing
action of the generator control ?elds is obtained
by removing the regulating generator ?elds from
their series circuit relationship with the generator
relationship. As will be seen more conveniently
from Fig. 2, the ?eld windings GFI and GF2 of
the main generator are connected in opposite legs
of a conventional Wheatstone bridge circuit, hav
ing for its other two opposite legs, the bridge
balancing resistors RESI and RESZ. The input
terminals of this bridge circuit are identi?ed as
3 and 4 and the output terminals of the bridge
are identi?ed :as I and 2. The armature winding
of the regulator generator and the winding RSF
in series therewith, are connected in series with
the resistor elements RESE' and RESI l which are
of predetermined ?xed value and the resistor
RESB which is varied by means of the contacts
control ?elds and placing a single ?eld elsewhere
ARI and ARZ across the galvanometer terminals
in the system that it may yet be energized by
i and 2 of the bridge circuit. The control ?eld
currents proportional, if not equal, to those ?ow
winding RCF is connected in series with the sen
ing through the generator shunt ?eld windings.
sitivity adjusting resistor RES9 across the con
With such an arrangement, the current ?ow 30 ductors supplying the bridge circuit. The dif
through the newly located ?eld of the regulating
ferential ?eld winding RDF is connected with its
generator may change as rapidly as the imped
series sensitivity adjusting resistor RESB across
ance of the ?eld will permit and produce correc
the motor armature as will be seen from Fig. 1
tive currents far in advance of those which were
and the separately excited ?eld winding RF is
attainable with the system of control previously
connected in shunt relationship with the main
A principal object of this invention is to in
crease the speed of regulation of a generator em
generator series ?eld winding GSF and, hence,
is excited in proportion to the current ?owing
ployed in a variable voltage control system.
The regulating generator RG is preferably
Another object of this invention is to provide a 40 provided with operating characteristics which,
variable voltage control system in which the rate
while unfavorable vfrom an operating point of
of change of currents in the main generator sup
view insofar as a machine such as the main
plying the system is increased.
generator G is concerned, are most favorable
Other objects and advantages will become ap
for the regulating generator. Normally stable
parent upon a study of the following disclosure
operation of a direct-current generator is ob
when considered in conjunction with the accom
tained only if the slope of the resistance line
panying drawing in which:
of the ?eld circuit is less than that of a line
Figure 1 is a schematic diagram of a complete
tangent to the initial substantially straight line
system of control for a reversible motor operat
portion of the no-load saturation curve of the
ing a planer platen or other tool actuating ma 50 machine. If the resistance is less, the generator
chine embodying the novel features of this inven
can have an open circuit voltage which is de
termined by the intersection of the resistance
Fig. 2 is an elemental diagram of a portion of
line with the saturation curve. If the resistance
the system of Fig. 1 and illustrates the novel fea
55 is higher, and, consequently, the slope of the re
tures of this invention.
sistance line higher than the initial straight line
Referring now to Fig. 1 of the drawing, the
portion of the saturation curve, the generator
speci?c system illustrated therein is for control
voltage cannot build up. If the slope of the
ling a direct-current motor of the type used, for
resistance line just equals the slope of the in
example, in operating a planer platten. This sys
itial portion of the saturation curve, that is, is
tem comprises generally: (1) A direct-current
tangent to this portion of the saturation curve,
motor M having a separately excited ?eld wind
the generator can theoretically have an open
ing MF; (2) A variable voltage direct-current
circuit voltage’ equal to any of the points of
generator G having a series connected ?eld Wind
tangency. It is the latter of the three mentioned
ing GSF, two separately excited control ?eld
conditions for which the regulating generator is
windings GFI and GFZ, and a shunt connected 65 preferably adjusted. The action of the ?eld
differential or suicide field winding GDF; (3) A
windings RDF and RF together with that of
regulating generator RG provided with a series
the control ?eld winding RCF select the proper
connected ?eld winding RSF, a separately excited
control ?eld winding RCF, a separately excited,
operating point of this generator along the
tangent curve and maintain this operating point
differentially connected ?eld winding RDF and a 70 constant for any ‘setting of the generator rheo
separately excited ?eld winding RF; (4) An ex
citer E which supplies the direct-current potential
As previously noted, the ‘armature winding of
of a constant value to the system and which has
the regulating generator, the series ?eld winding
a ?eld winding EF connected in shunt relation
75 RSF and a group of resistors RES5, RESB, and
stat GR.
ship with .the armature thereof ; (5)‘ A magnetic
RES“ are connected in series across the gal
ation of the cut and return limit switches CLS
and RLS.
The control relay CR, during periods when the
vanometer terminals I and 2 of the Wheatstone
bridge circuit. Normally, the resistor RESB is
substantially entirely shunted from the series
circuit by the contact AR! of the automatic relay
AR. The value of the resistance in this series
motor generator system is being started and dur-.
ing periods when the planer platen is desired to
be stopped with the generator system still oper
ating, provides circuits to control the break relay
circuit is preferably such, that when adjusted to
obtain the desired tangent relationship of the
BR to connect the differential or suicide ?eld
resistance line of the regulating generator ?eld
circuit with the no-load saturation curve, that 10 GDF of‘the main generator across the armature
thereof to prevent creeping of the motor, and
the total voltage across the galvanometer circuit
provides a circuit for the coil of the ?eld weaken
ing contact FW' across the positive and negative
conductors 3+ and B- to close the contacts FWI
of this contactor and short the motor rheostat
MR from the circuit of the motor ?eld winding
is zero for a predetermined operating condition.
Since in the present system of control it is
desired to regulate the speed of the motor M,
an indication of the counter voltage of the motor
is desired. rFhis is obtained by connecting the
MF, thus applying full ?eld excitation to this
differential ?eld winding RDF across the motor
armature terminals and by connecting the ?eld
?eld winding GSF. In this manner, the differ
the ?eld circuit of the motor and ‘when open,
removes the shunt circuit and thus connects this
ential ?eld Winding is excited by a voltage pro
portional to the motor armature terminal volt~
age, and the ?eld winding RF has a voltage ap
rheostat in the circuit.
— eration beyond predetermined speeds of the motor
position, the differential magnetomotive force
produced by these ?elds is an indication of the
speed of the motor. The control ?eld winding
RCF, by reason of its connection across the input 30
terminals to the bridge circuit, is energized by
a- voltage proportional to the voltage applied to
the ?eld windings GFl and GF2 of the main
generator and, hence, produces a magnetomotive
force which is an indication of the selected speed 35
of operation of the motor. The magnetomotive
forces produced by the control ?eld winding RCF
and the electrically opposed ?eld windings RDF
and RF are in opposition and the differential of
these magnetomotive forces is an indication of
the departure of the motor speed from the
selected speed of operation, as determined by
the setting of either of the out or return leads
GCL or GRL of the generator rheostat GR.
The differential magnetomotive force of the three
regulator generator ?eld windings causes a cor
rective current, produced ‘by the regulator gen
erator, to ?ow in the Wheatstone bridge circuit
in such a direction as to produce the necessary
change in excitation in the main generator ?eld '
windings GF! and GFZ, that the motor speed
may be brought to its selected value.
Before proceeding with a discussion of the
operation of the system as shown in Fig. l, a
description of the various contactors and relays
comprising the magnetic controller will prob
ably be desirable.
The cut and return directional relays C and
R are provided primarily to establish the proper
polarity of the Wheatstone bridge circuit and,
hence, the main generator by controlling the di
The ?eld weakening relay FR is provided with
the contacts FR! which during periods of accel
plied thereacross proportional to the load current
of the series motor generator circuit. Since the
?eld windings RDF' and RF are in electrical op
The ?eld weakening contactor FW when closed,
as just explained, shunts the motor rheostat from
winding" RF across the main generator series
are open, thereby permitting the ?eld weakening
contactor to drop out and weaken the motor ?eld
winding. This relay is provided with two coils
FRCI and FRC2. The coil FRCZ, as will be seen
more clearly from Fig. 2, is energized by the ex
citer voltage and the coil FRCi, as will be seen
l, is energized by a voltage proportional
to the voltage applied across the motor armature.
Both coils of this relay must be energized before
this relay picks up. The coil FRCZ, immediately
upon operation of either of the contactors C and
R, has the exciter voltage applied thereacross.
The coil F‘RCI during periods of acceleration is
energized by the increasing voltage across the
motor generator series circuit. Thus, a slight
time delay is obtained during acceleration, as
well as deceleration, before this relay picks up
or drops out.
The voltage relay VR together with the CR
contactor controls the energization of the coil
of the break relay BR through its contacts VRl.
This relay, in a manner similar to the ?eld weak
ening relay m, is provided with two coils VRCI
and VRCZ, the coil VRCS being responsive to the
voltage across the motor generator series circuit
and the coil VRC2. responding to the exciter volt—
age. The coil VRCZ of this relay when energized
causes the relay to pick up. Coil VRC! alone will
hold the relay up.
The automatic relay AR varies the resistance
of the discharge circuit for the generator ?elds
GFl and GFZ and for the regulating generator
?eld RSF. As previously explained, the purpose
of changing this resistance in the ?eld discharge
circuit is to obtain a more rapid rate of decay of
the generator ?eld ?ux. This automatic relay
rection of flow through the ?eld windings GF!
has two coils. The main coil ARC?! is connected
and GF2 thereof, and to establish portions of
across the exciter and responds to eXcit'er voltage.
the control circuits for the ?eld weakening con
The‘ other coil or holding coil ARC! responds to
tactor W, the ?eld weakening relay FR and the
the voltage across the motor generator series cir
voltage relay VR. These contactors also control
cuit.‘v This relay picks up immediately upon the
the degree of excitation of the generator and
energization of the coil ARC?! when either of the
motor ?eld winding through the medium of the
contact-ore C or R operate, and it is held in by
generator ?eld winding rheostat GR and the
motor ?eld winding rheostat MR. Each of these 70 the holding coil ARC! during reverse cycles until
the generator voltage has declined to a suf?cient
contactors is provided with a single coil which
value to permit the insertion of more resistance
is interlocked with the other contactor and which
in the ?eld discharge circuits, thus tending to
are each selectively connected across the eX
force the deceleration and acceleration at the
citer busses B+ and B— through operation of
and the beginning of each direction of move
either the cut and return push buttons or oper 75 end
ment of the planer platen.
' _
It will be understood that the generator system
of Fig. l is to be driven by a constant speed prime
mover connected to the common shaft indicated
by the dotted line intersecting the axes of the
three generators.
Such prime mover together
with its control circuits have not been shown for
the purpose of simplifying the illustration of the
invention. Similarly, it will be understood that
inching operation of the planer platen may be
obtained by installing suitable inching push but
tons in the control system in the manner shown,
for example, in the applicant's Patent No.
2,205,204. These have also been omitted from
the system in an effort to simplify the illustra
tion of the invention.
To operate the system the prime mover (not
accelerated under the influence of a high torque.
The voltage relay VR picks up immediately when
the main generator shunt ?elds are energized,
thus opening the contacts VRI and open circuit
ing the coil of the break relay BR‘. Thus the
differential or suicide ?eld is instantly removed
from the generator circuit. When the main gen
erator voltage builds up to a predetermined value,
the ?eld weakening relay picks up opening‘its
10 contacts FRI thereby opening the circuit to the
?eld weakening contactor FW, This contactor
immediately drops out, opening its contacts FWI
and inserting the motor rheostat in the circuit of
the motor ?eld MF.
The resistance now in the
15 motor ?eld circuit is determined by the setting
of the motor rheostat cut lead MCL. The motor
thus accelerates to the speed determined by, the
rheostat setting. Immediately upon closing of
the contacts C4 of the contactor C, the coil ARCZ
shown) driving the system of generators is
brought up to speed. A voltage is thus applied
by the exciter across the conductors B+ and B—~.
of the automatic relay is energized and this relay
The BR relay thus picks up, since the coil thereof 20 picks up, closing its contacts ARI and decreasing
is connected across the busses 13+ and 13
the resistance across the galvanometer terminals
through the now closed contacts VRI and CR1
of the bridge circuit to the predetermined value
and closes its contact BRI to connect the differ
for normal operation.
ential ?eld winding GDF of the main generator
Near the end of the cut stroke, the cut slow
across this generator. Thus, any voltage which
down limit switch CSD is operated, This opens
tends to build up in the generator due to residual
its contacts CSDZ and closes its contacts CSDI.
magnetism. is opposed by the action of the differ
Closing of the contacts CSDI establishes a circuit
ential ?eld winding and hence, no voltage or at
through the contacts R5 and the contacts CSDI
least insufficient voltage to cause operation of
for the coil of the ?eldvweakening relay. This
the motor is applied across the motor armature 30 relay immediately picks up and shunts the motor
terminals. At the same time the ?eld weakening
rheostat MR from the circuit and thus near the
contactor FW is connected across the positive
end of the cut stroke causes the planer motor
and negative busses through a circuit which in
separately excited ?eld MF to build up to full
cludes the now closed contact CR2. This closes
strength. The motor now slows down to full ?eld
the contacts FW! and shunts the
speed. At the same time, the coil FRCZ of the
MR thereby applying that portion of the exciter
?eld weakening relay FR is deenergized and this
voltage to the generator ?eld winding MF as
relay drops out closing its contacts FRI, As the
determined by the value of the permanent resistor
planer platen reaches the extreme limit of its
RP2, The initial direction of the planer platen
out stroke, the cut limit switch is operated. This
can be selected by the cut and return push but
deenergizes the coil of the cut relay C which drops
tons, provided the planer table or platen is be
out and closes its contacts C1 causing the return
tween the limits of its travel.
contactor R to pick up. This closes the contacts
Pressing the out push button closes the back
RI and R3 and reverses the polarity of the bridge
contacts thereof and connects the coil of the con
circuit. At the same time, the excitation of the
trol relay CR through the stop push button across " bridge
circuit is increased since the current sup
the exciter busses 13+ and B—. This relay im
plied to the bridge circuit is now controlled by
mediately picks up, closing its contacts CR3,
the setting of the return lead GRL of the gen
CR5, CR6 and CR1, and opening its contacts
erator rheostat and less resistance is in series
CRI, CR2 and CR4. An instant thereafter. while
with the bridge circuit. Also a circuit is estab
the cut push button is yet depressed and the cir
lished to prevent the ?eld weakening contactor
cuit through the contacts CR1, now closed to the
FW from dropping out. This circuit includes the
coil of the return contactor R, open, the cut con
contacts R3, generator return lead GRL, a por
tactor C picks up since its coil is energized
tion of the generator rheostat GR, the generator
through a circuit across the positive and nega
cut lead GCL, contact members R4, contact
tive busses which includes the return push but
members RSD2 of the return slowdown limit
ton, the now closed contact CR6. back contact
switch, contact members FRI and a coil of the
R1 and the return limit switch RLS, This opens
?eld weakening contact FW. The motor is thus
the circuit for the coil of the return contactor R
accelerated in the reverse direction at full ?eld
at contacts C1 thus preventing this contactor
speed and when the generator voltage builds up
from picking up and at the same time establishes
sufficiently, the contact members FRI open and
a second circuit for the coil of the ?eld weaken
the planer platen is ‘driven in the return direc
ing contact FW to hold this contactor in. which
tion at a speed determined by the setting of the
includes the contacts C3, C4. contacts CSD2 for
rheostat leads GRL and GCL.
the cut slowdown limit switch CSD and the con
With the system just described, when the
tacts FRI of the ?eld weakening relay FR which 5 speed of the planer motor is correct for the set
are yet closed. Since the contacts CI and C3 of
ting of the rheostat, the three sets of regulator
the contactor C are now closed and the contactors
generator ?elds balance each other and no volt
CR3 of the control relay are closed, a voltage is
age is generated in the generator by the action
applied across the Wheatstone bridge circuit and
of these ?eld windings. The voltage across the
this voltage is determined by the setting of the
output terminals of the bridge circuit is there
lead GCL for the generator rheostat. The ?eld
fore zero. Should the motor speed attempt to
windings of the main generator are thus ener
change, the regulator generator ?elds become un
gized and current begins to flow through the
balanced and the regulator generator generates a
motor armature. The speed of the motor thus
voltage causing current to ?ow through the
builds up to its full ?eld speed and the motor is 75
Wheatstone bridge circuit in the direction re
quired to hold the planer motor speed constant
and in accordance with the setting of the rheo
Because the main generator is separately ex
cited, variable voltage is easily obtained by means
of a rheostat such as GR in series with the main
in an amount proportional to the motor armature
terminal voltage, and the third separately excited
?eld Winding being connected in a circuit dis
posed across the input terminals of said bridge
2. In a system of control for a motor, the com
bination of, a generator having a pair of ?eld
generator control ?eld circuits. Part of the speed
a motor directly connected to be ener
range is obtained by varying the main generator
gized :by the generator, an electrical bridge cir
voltage and maintaining full ?eld on the planer
cuit including said generator ?eld windings in
motor, and the rest of the speed range is obtained
opposite legs thereof and having electrical bridge
by weakening the planer motor ?eld and main
balancing elements in the remaining two opposite
taining full voltage on the main generator.
legs, a source of electrical energy for energizing
Tests made with a system according to this
invention indicated that measurable increases in 15 the bridge circuit, a regulating generator includ
ing a series connected ?eld winding and three
the speed of reversing the motor could be ob
separately excited ?eld windings, said regulating
tained. With a system connected according to
generator including the series ?eld winding being
that mentioned in the preceding pages, in which
connected across the output terminals of said
the control ?eld windings of the regulating gen
bridge circuit, two of said separately excited ?eld
erator were connected in series with the control
windings being differentially connected to the
?eld windings of the main generator, it was found
motor-generator circuit one winding being con
that the motor required 1.76 seconds to accelerate
nected to be energized in an amount proportional
to ‘765 R. P. M. or 90 per cent of the full testing
to the current in the motor-generator circuit and
speed of 850 R. P. M. With the system provided
the other winding being connected to be ener
by this invention, the: motor accelerated to 765
gized by a voltage proportional to the motor ar
R. P. M. in 1.25 seconds or 71 per cent of the time
mature terminal voltage, and the third separately
required with the standard connections. With
excited ?eld winding being connected to be ener
the connections according to this invention, it
was found that the regulating generator was ac
gized in an amount proportional to the Voltage ~
applied across said bridge circuit by said source
of electrical energy.
connections of the previously described prior art 30
3. In a system of control for a direct current
system, the regulating generator current was neg
motor, the combination of, a direct current motor
ative for a large portion of the reverse cycle thus
having an armature winding and a ?eld winding,
tending to retard if not actually retarding the
a main generator having an armature winding
and a pair of ?eld windings, circuit means elec
Further comparative tests made with the for
connecting the armature winding of said
mer system and the system according to this
generator and the armature winding of said motor
invention, while reversing the motor from 1,200
in series circuit relationship, an electrical bridge
R. P. M. in one direction to 1,080 R. P. M. in the
circuit, said pair of generator ?eld windings being
opposite direction, indicated that with the system
connected, in opposite legs of the electrical bridge
according to this invention, the motor accelerates
circuit, a pair of electrical bridge balancing ele
from rest to 1,080 R. P. M. in 77 per cent of the
ments connected in the remaining opposite legs
time required with the former system and re
of the bridge circuit, a regulating generator hav
verses within the speed limits mentioned in 81
ing an armature winding, a ?eld Winding in series
per cent of the time required with the former
with the regulating generator armature winding
and three separately excited ?eld windings; cir
The foregoing disclosure and the showings made
cuit means connecting the armature winding and
in the drawing are merely illustrative of the prin
series ?eld winding of the regulating generator
ciples of this invention and are not to be inter
preted in a limiting sense. The only limitations 50 across the output terminals of said electrical
bridge circuit, means for adjusting the resistance
are to be determined from the scope of the ap
of the series ?eld circuit of the regulating gen
pended claims.
erator such that the resistance line thereof is
I claim as my invention:
tangent to the initial straight line portion of the
1. In a system of control for a motor, the com
no-load saturation curve of the regulating gen
bination of, a generator having a pair of ?eld
erator, circuit means connecting one of said sepa
windings, a motor directly connected to be ener
rately excited ?eld windings of the regulating
gized by the generator, an electrical bridge cir
generator to the motor-generator armature cir
cuit including said generator ?eld windings in
cuit to be energized in an amount proportional to
opposite legs thereof and having electrical bridge
the current ?owing in said circuit, circuit means
balancing elements in the remaining two opposite
differentially connecting another separately ex
legs, a source of electrical energy for energizing -60 cited ?eld winding of the regulating generator
the bridge circuit, a regulating generator includ
with respect to the current energized ?eld wind
ing a series connected ?eld winding and three
ing, to the motor-generator armature circuit to be
separately excited ?eld windings, said regulating
energized in an amount proportional to the motor
generator including the series ?eld winding being
armature terminal voltage, circuit means conconnected across the output terminals of said
necting the third separately excited ?eld winding
bridge circuit, two of said separately excited ?eld
of the regulating generator across the input ter
windings being differentially connected to the
minals of the electrical bridge circuit, and means
motor-generator circuit, one winding being con
for supplying direct current to said bridge circuit
nected to be energized in an amount proportional
and said motor ?eld winding.
to the current in the motor-generator circuit and
tually forcing the acceleration, whereas with the
the other winding being connected to be energized
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