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Патент USA US2406424

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2,406,424
Patented Aug. 27, 1946
UNITED STATES PATENT OFFICE
2,406,424.
CONTROL SYSTEM
George E. King, Swissvale, Pa. assignor to West
inghouse Electric Corporation, East Pittsburgh,
Pa., a corporation of Pennsylvania
Application Gotober 17, 1944, Serial No. 559,065
10 Claims. (01. 172—-179)
1
The present invention relates to variable volt
age control systems and, more particularly, to
electric motor control systems for operating or
automatically controlling the operation of mo
tors connected to various types of mechanical
loads. In certain of its aspects this invention
is related to a copending application of G. E.
King and W. H. Formhalls, Serial No. 559,068,
?led on the same date as this application and
.
2
of the motor, driving the casting machine. Thus,
speed regulation at this normal running speed by
means of a rotating regulator is not essential.
Current limiting control by means of a rotating
regulator is, however, provided to limit the ac
celerating and braking current. This current
limiting rotating regulator is so connected that
it circulates current through the field windings
of the main generator, supplying the motor when
entitled. Control systems (W. E. Case 23,453) and 10 ever the main motor armature current approaches
the preselected maximum value. This current
also
SerialtoNo.
a copending
559,066, ?led
application
on the same
of G.
dateE. as this
is circulated in such a direction with respect
to the normal supply currents circulating in these
application and entitled Control systems (W. E.
?elds, that the main generator output current is
Case 23,417).
This invention provides certain improvements 15 limited within the preselected maximum value.
The creeping speed is very slow and may, for
in variable voltage control systems in which ro
example, be about 1.2% of the full ?eld speed
tating regulators are employed to regulate cer
of the main drive motor. Speed regulation of the
tain electric quantities of the system, and the
motor at this slow speed by ordinary adjust
invention as hereinafter described and as illus
trated in the drawing is speci?cally directed. to 20 ments of the excitation of the main ?elds of the
generator, is not practicable. To obtain this slow
the regulation of the speed of rotation of a di
constant speed, a rotating regulator is used to
rect-current motor together with provisions for
control a separate generator ?eld. When this
limiting the motor current whether the motor is
control is utilized for creeping speeds, the ?eld
operating normally as a motor or during regen
erative periods when the motor is being over ‘15125 windings of the main generator which control
the running speed are disconnected from the cir
hauled by its mechanical load and driven as a
cuit. The rotating regulator used to limit the
generator. It will be apparent to one skilled in
current in the motor functions in this capacity
the art that the invention is not limited to speed’
during acceleration and braking at both creeping
regulation alone since various modi?cations of
and running speeds.
the systems may be made to control the motor
On some applications it is desirable to operate
torque or power in conjunction with the current
over a wide speed range with good speed regula
limiting features mentioned. It will further be
tion and at the same time limit the accelerating
apparent that the invention is riot necessarily
and braking current. The second form of the
limited to motor control since automatic regula~
invention illustrated in the drawing shows a vari
tion of the voltage, current or electric power sup
able voltage control system of this type. In this
plied to an electrical load of substantially any
second form of the invention the speed regulat
type susceptible of regulation may be had.
ing generator, unlike that of the ?rst-mentioned
In one form of the invention illustrated, the
form of the invention, functions throughout the
variable voltage control system is particularly
entire speed range to control the speed of the
adapted for controlling the speed of a motor used
motor. It, further unlike the speed regulating
to drive a centrifugal casting machine. Such a
generator of the ?rst form of the invention, sup
machine usually has ?xed running and creeping
plies only the corrective current to the main
speeds. After the metal is poured into the mould
generator ?eld windings with which it is con
to be rotated. the machine is accelerated, by way
of example, in 15 minutes to the running speed, 4:5 nected rather than the total current necessary
for exciting and regulating the main generator
at which speed it may operate for 50 minutes.
?elds. In this second form of the invention the
The machine is then decelerated and brought to
rest in approximately a 10~minute interval of
current limiting features, as previously described,
are obtained. The current limiting rotating reg
time. It is then again started and brought up
to creeping speed where it is operated for about 50 ulator, however, regulates directly the speed reg
ulating generator and indirectly the main gen
100 minutes, after which it is again brought to
erator rather than directly as in the ?rst form
rest, and in due course of time the completed
of the invention. In this second form of the
casting is removed.
invention, the two rotating regulators, that is, the
The running speed of the centrifugal casting
machine is constant and at the full ?eld speed 55 speed and the current limiting rotating regula
2,406,424
3
4
tors, are connected in effective series circuit rela
tionship. By means of this expedient there is
considerable ampli?cation of the regulating quan
tities thus effecting a quick response. During
is connected in series circuit relationship with
reversing facilities. Reversing may be obtained
by simply adding reversing contactors. Such
regulating generator
the armature winding of a main generator G.
A current limiting regulating generator RCL is
utilized to limit the currents circulating in the
braking periods the main generator current is
series motor generator armature circuit within
reversed. Thus, the action of the regulating gen
preselected maximum values. A speed regulating
erators is to tend to maintain the generator ?eld
generator R5 is utilized to control the electrical
current and prevent this ?eld current from col~
output of the main generator G when it is desired
lapsing too fast.
to operate the drive motor M at very slow or
In order to simplify the drawing and the ac 10 creeping speeds. An exciter E‘ is provided to
companying descriptive disclosure, the two forms
supply a constant electrical quantity to various
of the invention illustrated are shown without
elements of the system. The exciter
the speed
the current limiting
regulator RCL and the main generator G are
expedients are well known in the art and any 15 driven at a constant speed by any suitable con—
suitable form of reversing equipment may be
stant speed prime mover or system of prime
utilized without departing from the spirit and
movers. As shown by way of illustration but not
scope of the teachings of this invention.
limitation they are connected to a common shaft
A principal object of this invention is to pro
to be driven by a single prime mover. The con
vide a variable voltage drive including a motor 20 stant speed prime mover, however, is not shown
in which automatic speed regulation of the motor
in an effort to simplify the illustration of the
is provided in conjunction with automatic regu
invention.
lation of the motor current.
The main motor M is provided with a single
Another object of this invention is to provide
separately excited ?eld winding MF which re
a variable voltage drive providing two selectively 25 ceives its excitation directly from the exciter.
obtained constant running speeds for a motor
The main generator G is provided with a differ
in conjunction with current limiting protection
ential ?eld winding GDF which is utilized at the
for the motor.
end of braking periods of the motor to buck-down
Still another object of this invention is to pro
or neutralize the residual voltage of the main
vide a variable voltage drive of the character 30 generator. It is further provided with control
referred to which provides a wide range of speed
?eld windings GSFi, GSFZ and GSF3. The
regulation for a motor in conjunction with pro
windings GSFI and GSFIZ are connected (see
tection against excessive motor currents.
Fig. 3) in opposite legs of a conventional Wheat
A speci?c object of this invention is to provide
stone bridge circuit which has as its other two
a variable voltage drive utilizing rotating regu 35 opposite legs the bridge balancing resistors RI
lators for regulating the speed of a motor and
and
This bridge circuit is connected at its
limiting the motor current in which the rotating
input terminals l and 2 across the exciter buses
regulator controlling the motor currents requires
B! and 32. Thus the ?eld windings of the main
a certain value of excitation of its ?eld windings
generator are excited in accordance with the
before a corrective output thereof is obtained.
40 exciter voltage at some constant value depending
Other objects and advantages will become ap
upon the value of the resistor R3. As shown in
parent upon a study of the following disclosure
Fig. 2, the ?eld winding GSF3 of the main gen
when considered in conjunction with the accom
erator is connected in series with the armature
panying drawing, in which:
circuit of the speed regulating generator RS,
Figure 1 schematically illustrates a variable 45 which series circuit includes the series ?eld wind
voltage drive providing protection against exces
sive currents, in which constant speeds of the
motor controlled by the variable voltage system.
ing R5! for the speed regulating generator, which
by reason of its series connection with the arma
ture of generator BS is excited by the armature
are selectively obtained;
current thereof, and a resistor SR! which is
Fig. 2 diagrammatically illustrates a detail of 60 utilized to adjust the resistance of the ?eld cir
the invention illustrated in Fig. 1;
cuit RS! for the speed regulating generator to
Fig. 3 diagrammatically illustrates another
impart self-energizing properties to the speed
detail of the invention illustrated in Fig. 1;
regulating generator. This series circuit also
Fig. 4 is a modi?cation of the invention pro
includes the contact members CGF2 of the creep
viding a wide range of speed control for the motor 55 contactor CGF which functions alternately with
in conjunction with protection against excessive
the running contactor RGF to selectively control
the main generator at running or creeping speeds.
Fig. 5 diagrammatically illustrates a detail of
A discharge resistor DR shunts the main gen
the invention of Fig. 4;
erator ?eld GSFB to provide a discharge path
Fig. 6 is a detail of one of the rotating regu 60 therefor upon opening of the contact members
lators utilized in the variable voltage drives illus
CGFZ.
trated in the drawing;
The current limiting regulating generator RCL
Fig. '7 is a curve graphically illustrating the
is provided with a series connected armature cur
operating characteristics of one of the rotating
rent excited ?eld ‘Winding RCLI and a control ?eld
65 winding RCLZ. The control ?eld winding RCL2 is
regulators utilized in this invention: and
Fig. 8 is a curve graphically illustrating the
energized by the drop across the resistor R4 con
operating characteristics of the other rotating
nected in series in the main motor generator ar
regulator utilized in this invention.
mature circuit. and thus has a voltage applied
Referring now to Fig. 1 of the drawing, the
thereacross proportional to the currents ?owing
invention illustrated therein corresponds to the 70 in the circuit and of a polarity depending upon
?rst form of the invention hereinbefore generally
the direction of the current flow. The series ?eld
described. It comprises a main drive motor M
winding RCLl has a resistor SR2 connected in
which is mechanically connected to drive the
series therewith for adjusting the resistance of
mentioned centrifugal casting machine (not illus
this ?eld circuit, and this assembly, in conjunc
trated). The armature winding of this motor 75 tion with the armature member I4 of the current
current in the system;
I
2,406,424
5
6
limiting generator, is connected across the output
with three sets of contact members DFI, DF2 and
terminals 3 and 4 of the previously mentioned
Wheatstone bridge circuit.
The speed regulating generator RS is provided
with two di?erentially connected ?eld windings
RS2 and RS4 which are respectively connected
DF3. The contact members DFI when closed
complete the ?eld circuit for the di?erential ?eld
winding GDF of the main generator. The con
tact members DFZ, which are back contacts,
function in conjunction with either the contact
across the resistor R4 in the motor generator se
ries armature circuit and the motor armature ter
members RRZ or CR2 to energize either the CGF
or RGF relays depending upon whether the CR
minals. Pattern ?eld winding RS3 provides the
or RR relay is picked up. The contact members
control pattern voltage for the speed regulating 10 DF3 when closed function in conjunction with the
generator. It is connected across the exciter
Stop push button, the contacts CB2, either the
buses BI and B2 by the contact members CGFI of
Creep or Run push buttons depending upon
the creep generator ?eld contactor CGF. The
which is depressed and the CR4 or RR4 contacts,
winding RSI for the speed regulating generator,
also ‘depending upon which of the Creep or Run
as previously described, is series connected and
push buttons are depressed, to deenergize either
the generator is of the self-energizing type,
the RR or CR relays. The run generator ?eld
The exciter E, as illustrated, is provided merely
relay RGF is provided with a single contact RGFI
with a shunt ?eld winding EF. Any suitable ?eld
which, as previously described, when closed'en
winding system for this machine may be utilized
ergizes the Wheatstone bridge circuit and as fol
since per se it forms no part of this invention.
20 lows energizes the main generator ?eld windings
The control equipment, which cooperatively
GSFZ and GSFI to operate the motor at its run
functions to provide selectively obtained opera
ning speed: The creep relay CR is provided with a
tions of the system as well as functioning in part
plurality of contacts CR! to CR4. Contacts CRI
to protect the system, comprises a main circuit
when closed provide an energizing circuit for the
breaker CB of the single-pole type for opening “a timing relay TR across the exciter buses BI and
the main motor armature circuit on power failure,
B2; the contact members CR2 when closed pro
overload and loss of motor shunt ?eld. Creep
vide, in conjunction with the back contact mem
relay CR. and run relay RR are provided for se
bers DFZ, an energizingr circuit for the creep gen
lecting the creeping or running speeds. Creep
erator ?eld contactor CGF across the exciter
generator ?eld contactor CGF and run generator 3 i) buses 13! and B2; the contact members CR3 when
?eld contactor RGF are provided respectively for
closed complete, in conjunction with the contact
energizing the circuits for the main generator
members CB2 of the main circuit breaker CB, the
?elds GSF3, GSFI and GSF2 for obtaining the
creeping and running speeds of the motor. Dif
ferential ?eld relay DF is provided for closing the
Stop push button and the contact members RRII,
a holding circuit for the operating coil of the
creep relay CR; and ?nally the contact members
?eld circuit for the ?eld winding GDF of the
main generator G to neutralize the generator
CR4 which function in a similar capacity to the
contact members RR4. The run relay RR is pro
residual voltage and prevent the motor from
vided with a similar group of contacts as the relay
creeping. A time relay TR is provided to time the
CR.
These contacts are numbered RRI to RR4
operation of the DF relay. A voltage relay VR 40 and function in a capacity similar to that of the
is provided to prevent the operation of the relays
contacts of the creep relay. The creep generator
TR and DF until the generator voltage has
?eld contactor CGF is provided with the con
dropped to a low value. A ?eld loss relay FL has
tact members CGFI and CGF2. The contact
its coil connected in series in the bus B2 and thus
members CGFI connect the pattern ?eld winding
senses a loss of exciting current for the motor ?eld
RS3 of the speed regulating generator RS across
winding MF. Creep and Run push buttons, so
the exciter buses Bi and B2. The contact mem
designated in the drawing, respectively control
the energization of the CR and RR relays to effect
creeping and running speeds of the motor. ' A. Stop
push. button, so designated in the drawing, is pro 50
vided to deenergize either of the creep or run re
lays depending upon which is energized at the in
stant the Stop button is depressed.
The relay FL has one set of contact members
bers CGFZ, as hereinbefore described, complete
the circuit for the creep generator ?eld winding
GSF3 across the speed regulating generator RS.
Before proceeding with the discussion of the
operation of the control system, an understand-
ing of the function and characteristics of the
regulating generators RCL and RS should be
had.
Both of these generators as illustrated are
FL! which control the energization of the operat 55 series generators. The following discussion is
ing coil of the main circuit breaker CB. The
directed to the generator RS. In Fig. 7 of the
main circuit breaker CB has a set of main con
tacts CBI which, when closed, complete the series
motor generator armature circuit. It also is pro
drawing the saturation curve of a series gener
ator is drawn. Stable operation of a series gen~
erator is obtainable only if the resistance of the
vided with an auxiliary contact CB2 which when 60 ?eld circuit is less than that of a line tangent to
closed, in conjunction with the Stop push but
the saturation curve, that is, tangent to the in
ton and either the contact members RR3 or
itial substantially straight line portion of the
CR3, establishes holding circuits for either the
saturation curve. If the resistance is higher the
RR or CR relays. The voltage relay VR is pro~
generator voltage cannot build up. If the re
vided with one set of contact members VRI
sistance is lower the generator open circuit volt
which when closed establish a holding circuit
age will be that determined by the intersection of
for the timing relay TR. This circuit is effective
the line with the saturation curve. If the resist~
only during running speeds of the motor since
ance line of the field circuit is as designated by RL
when the motor is operating at creeping speeds
in Fig. '7 the generator can theoretically have an
the voltage across the motor armature terminals m open circuit voltage equal to the ordinate of any
is of such a low value that this relay does not pick
of the points of tangency, for example, the points
up. The relay TR is provided with one set of con
PI and P2.
'
tact members TR! which, when closed, connect
While this would be undesirable in a standard
the operating coil of the relay DF across the ex
generator, it is an ideal characteristic for a reg~
citer buses BI and B2. The relay DF is provided 75 ulating generator since then the purpose of the
2,406,424
7
8
control ?eld windings, that is, the pattern ?eld
RS3 and the di?erentially connected windings
netomotive forces of the pattern and differen
tially connected ?elds thereof are neutralized.
If the speed of the motor rises, the converse of
RS2 and RS4, becomes that of locating the
the above-discussed function
proper operating point of a series generator in
cluding a series armature current excited held U! place.
and armature, keeping this operating point con
obviously takes
The current limiting regulating generator RCL
has self-energizing properties similar to those of
stant and supplying the required amount of
the speed regulating generator. In addition, this
power to the connected ?eld windings of the main
regulating generator requires a certain value, of
generator. With the resistor R8 in the pattern
?eld circuit selected to provide the desired ex 10 excitation of its ?eld circuit before an electrical
output thereof occurs. In Fig. 6 a single field
citing current in the pattern ?eld RS3, and the
pole of the machine is illustrated to show the
circuit closed, voltage in the regulating gener
manner in which this function is obtained. As
ator armature rises rapidly because the excita~
Will be apparent from Fig. 1, this generator- has
tion of the pattern ?eld RS3 is added to the ef
fect of the series ?eld. This voltage excites the 15 but a. single control ?eld winding for the reason
that such a single control ?eld winding is all
generator ?eld GSFS causing voltages to appear
that is required in the instant application. It
across the differentially connected ?elds RS2
will, however, be apparent that any suitable num
and RS4 which, if the selected speed of the mo
ber of ?eld windings functioning, for example, in
tor is correct, a resulting differential voltage neu
the manner of those of the speed regulating gen
tralizes the pattern. ?eld. The regulating gen
erator RS may be provided for different applica
erator thus reaches a steady point of operation
tions. In order to provide current limiting con-1
because there is no forcing of the ?elds and due
trol for the motor some means must be employed
to the self-energizing properties of this gener
to eifect operation of the current limiting regu-v
ator the series ?eld can just maintain this steady
state condition.
25 lating generator RCL only when the load current
exceeds a safe maximum value. To accomplish
As previously noted, the speed of the motor is
this the regulating generator RCL is given spe
to be regulated at creeping speed, thus, an indi
cial characteristics such as illustrated graphical
sired,
cation since,
of thethe
counter
counter
voltage
voltage
of indicates
the motorthe de
ly in Fig. 8. This characteristic differs from that
parture in speed of the motor from the desired 30 of the speed regulating generator RS by having
an extended low voltage or zero voltage interval
value. This is obtained by connecting the ?eld
which extends equally on both sides of the ordi
winding RS4 across the motor armature termi
nate designated generator volts. A character
nals to ‘be energized by the voltage drop across
istic of this type can be obtained by providing the
these terminals, and by connecting the ?eld
?eld poles of the generator with a magnetic shunt
winding RS2 across the resistor Rllv in series in
such as l2 in Fig. 6 which saturates at a smaller
the motor generator armature circuit. In this
flux density than the main ?eld pole l6. Numeral
manner the ?eld winding RS4; has applied there
M designates a portion of the rotor spaced from
across a voltage proportional to the motor arma
the ?eld pole by a small arcuate air gap, and
ture terminal voltage and the ?eld winding RS2
numeral Iii designates a non-magnetic insert in
has applied thereacross a voltage proportional
the circuit of the ?eld pole which, in effect, pro
to the load current of the motor armature.
vides a small air gap. The pole structure com
When the motor is operating at normal speed the
prises a base portion in good magnetic contact
excitation of the ?eld Winding RS4 is greater
with the stator l8 and a pole shoe portion 20 ad
than the excitation of the ?eld, winding RS2. By
having the ?eld winding RS4 differentially con 45 jacent to the armature. The windings of the
generator are arranged on the main pole 16. The
nected with respect to the ?eld winding RS2, the
air gap formed by the non-magnetic insert [0
differential voltage resulting from the differen~
carries both the pole and the shunt magnetic
tial action of the ?eld windings
and RS4
neutralizes the action of the ?eld winding RS3.
?ux, and hence does not in?uence the division
Thus the excitation of the main generator ?eld 50 of the flux. It primarily determines the low or
winding GSFS, which
utilized for operating
zero voltage interval previously mentioned, and
the slope of the characteristic curve beyond the
the motor at creeping speeds, is maintained at
low voltage interval. Because of this gap, sub
a constant value.
stantially all the ?ux flows through the magnetic
Considering now an increase in load of the
motor M causing its speed to drop, it will be ap 55 shunt since the reluctance of this path is low
parent that the motor armature terminal volt
and almost none of it is forced across the motor
generator armature circuit to generate a voltage
age will drop ‘while at the same time the motor
armature current will rise.
This causes the e:.~
as long as the field excitation of RCLZ is in
citation of the ?eld winding RS2 connected
sufficient to saturate the magnetic shunt. The
across the resistor Rd to increase, while at the 60 magnetic shunt I2 is so proportioned that it
same time the excitation of the ?eld winding
saturates at an excitation corresponding to the
RS4 is decreasing. The differential voltage thus
termination of the low or zero voltage interval
obtained is smaller than the pattern voltage. As
and then becomes unable to carry more ?ux.
a result the excitation of the speed regulating
Consequently, after the saturation of the mag
generator is increased to increase the excitation 65 netic shunt, an increasing ?eld excitation forces
of the generator ?eld winding GSFS to bring the
flux across the air gap to the armature so that
motor up to a speed indicated by the pattern
now a. voltage is generated. The action after the
voltage. The speed thus increases until the ao
magnetic shunt has saturated is similar to that
tion of the differentially connected ?elds again
of the speed regulating generator RS.
neutralizes the pattern ?eld and generator RS 70
By connecting the series connected armature
due .to the self~energizing properties thereof
I4, the self-energizing ?eld winding RCLI and
the tuning resistor SR2 across the output termi
again maintains this new condition. At this
nals 3 and 4 of the conventional Wheatstone
time the speed is exactly the same as before the
bridge circuit it is possible to control the excita
load on the motor changed because the regulat
ing generator can be at balance only if the mag 75 tion of the main generator ?eld windings GSFI
2,406,424
10
and GSFZ in such a manner that the current
circulating in the series motor generator arma
ture circuit never exceeds a preselected maximum
For example, if the current in the motor
‘ value.
generator series circuit should rise beyond the
a voltage having an electrical current which cir
culates in the bridge circuit in such a direction
as to decrease the excitation of the generator
?elds GSFI and GSFZ thus controlling the max
preselected maximum value, the drop across the
resistor R4 and, consequently, the voltage across
circuit. As the motor approaches the running
speed the accelerating current diminishes and the
current limiting regulating generator ceases to
function.
the control ?eld Winding RCL2 for the current
limiting regulating generator, is su?icient to pro
imum value of current in the motor generator
Pressing the Stop push button drops out relay
duce an electrical output of this machine. By 10
RR and as a consequence, the relay RGF, thus
properly determining the polarity of the various
disconnecting the bridge circuit from the exciter
elements connected in the conventional bridge
and deenergizing the generator ?eld windings
circuit, the output current of this generator is
GSF: and GSFE. The generator Voltage de
circulated through each of the ?eld windings
GSFI and GSFZ of the main generator in a 15 creases until it is less than the counter voltage
of the motor. The motor then generates a cur
direction opposite to that supplied by the exciter
rent in the reverse direction through the gen
E. As a result the excitation of these ?elds is
erator trying to drive it as a motor and speed
reduced, and the voltage output, and consequently
up the motor generator set. When the regen
the current in the motor generator armature cir
cuit is reduced to a safe value.
20 erative current approaches the preset maximum
The operation of the system may be described
as follows. Upon starting of the prime motor
(not shown) the various generators of the system
are rotated at a constant speed. Rotation of the
armature of the exciter E causes a voltage to be
applied across the exciter buses BI and B2. As
a consequence the motor ?eld winding MB‘ is
energized. When the exciter voltage builds up
the ?eld loss relay FL closes closing the circuit
to the circuit breaker CB under voltage release
coil. The circuit breaker now closes connecting
the motor armature to the main generator arma
ture. With building up of the exciter voltage
the differential ?eld relay DF, connected across
the exciter buses through the contact members
T'Ri, picks up and connects the generator differ
ential ?eld across the generator armature to neu
tralize the residual generator voltage.
Pressing the Run push’ button completes a cir
cuit from the exciter bus B2 through the contact
members CB2 of the main circuit breaker, the
Stop push button, the contact members DF3,
the back contact members of the Run push but
ton, the normally closed contact members of
the Creep push button, the contact members CR4
value, the current limiting regulating generator
again circulates a current in the bridge circuit
through the generator ?elds which this time
tends to maintain the generator voltage and
prevent it from collapsing too rapidly and thus
limits the maximum regenerative current. As
the motor approaches zero speed the voltage re
lay VR drops out deenergizing the operating coil
of the TR relay. After a time delay the TR relay
drops out and energizes through its contact mem
bers TRI the differential ?eld relay DF, thus
connecting the generator differential ?eld across
the generator armature bringing the generator
voltage doWn near zero and causing the motor
to stop.
Pressing the Creep button causes the creep
relay CR, time relay TR, differential ?eld relay
DF and creep generator ?eld contactor CGF to
operate in their sequence. These circuits are
substantially the same as those traced in con
nection with the running operation of the vari
able voltage drive and hence are not again
traced. The contactor CGF when closed ener
giZes the pattern ?eld RS3 of the speed regulat
ing generator through its contact members CGFI
and completes the circuit for the ?eld winding of
of the creep relay CR and the coil of the run
the main generator GSF3 to the armature of the
relay RR, to the exciter bus Bl. The run relay
speed regulating generator RS. The speed regu
thus picks up, closing its contact members RRI,
lating generator armature circulates a current
RRZ, RR3 and opening its contact members RRA.
through the connected generator ?eld GSF3 and
Closing of the contact members RRI causes the
the generator voltage builds up starting the mo
TR relay to pick up, opening its back contact
tor. It should be noted that the current limit
members TR! which drops out the di?erential
ing regulating generator is free to limit the ac
_ relay DF. When the differential relay DF drops
celerating and regenerative current by means of
out its contact members DFZ close, establishing
a circuit through these contact members and the 55 the bridge-type circuit, as previously described.
If the creeping speed is very low there Will not
contact members RR2 for the coil of the relay
be sufficient generator voltage to pick up the
RGF across the exciter buses BI and B2. Ener
VR relay. Thus the timing relay is held in only
gization of the relay RGF closes the contact
through the contact members CR! which e?ect
members RGFI thereof which complete the con
nection of the input terminals l and 2 of the 60 its energization. Thus when the Stop push but
ton is depressed to bring the motor to rest, the
Wheatstone bridge circuit across the exciter buses
timing relay after a short time delay drops out
BI and B2 and energizes the run generator ?elds
and applies the differential ?eld GDF by means
GSFI and GSF2. The generator voltage builds
of the DF relay to neutralize the residual voltage
up circulating a current through the motor ar
or the main generator G.
mature circuit, the motor starts, and the cur
The embodiment of the invention illustrated
rent increases in value until it approaches the
in Fig. 4 corresponds to the second form of the
maximum set by the current limiting regulating
invention generally discussed in the opening par
generator RCL. As the generator voltage in
agraphs of this speci?cation. This embodiment
creases, the voltage relay VR picks up forming
again utilizes the speed controlling and current
with its contact members VRI, now closed, a
limiting regulating generators discussed in con
holding circuit for the timing relay TR. If dur
nection with Fig. 1 of the drawing. Hence a
ing this interval, the current builds up in the
further description of these machines and their
motor generator armature circuit to a value
above the preset maximum value, the current
characteristics is believed unnecessary in con
limiting regulating generator RCL will produce 75 nection with Fig. 4.
11
£2,406,424
The variable voltage drive of Fig. 4 is, as previ
ously mentioned, adapted to provide a wide range
of speed control for the motor.
This is accom
plished by utilizing the electrical output of the
speed regulating generator for regulating pur
poses only. That is, only corrective current is
supplied to the control ?eld windings GSFI and
GSFZ of the main generator by this speed regu
lating generator. Thus the speed may be varied
12
windings GSFI and GSFZ and starts the motor.
The motor then begins to accelerate to a speed
determined by the setting of the rheostat R.
During this accelerating period the motor arma
ture currents are high and the armature terminal
voltage relatively low. As a result, the differen
tial voltage resulting from the di?erential action
of the differentially connected ?elds RS2 and
RS4 is insu?icient to neutralize the pattern volt
age. An electrical output of the generator RS
over a considerably wider range before satura
tion of this relatively small machine occurs.
thus follows, which is circulated in such a direc
Referring now to Figs. 4 and 5, the main gen
tion through the fields GSFI and GSFZ as to
erator G now is provided with but two control
increase their excitation. In other words, the
?eld windings GSFI and GSFZ. The current
generator RS forces the ?elds of the main gen
limiting regulating generator RCL, like that of 15 erator G to rapidly accelerate the motor. If the
Fig. 1, again has the series armature current ex
motor is driving a substantial mechanical load,
the armature currents will in all probability, at
cited ?eld RCLI and the control ?eld RCL2. The
speed regulating generator RS, like that of Fig. 1,
has the differentially connected voltage and cur
rent responsive ?eld windings RS4 and RS2, re
spectively, and a pattern ?eld RS3. ‘Unlike Fig. 1
this generator is provided with two series arma~
ture current excited ?elds RSla and RSIb which
least during the early portions of the accelerat
ing period, rise above the maximum value deter
mined by the characteristics of the current limit
ing regulating generator RCL. This machine
thus generates a voltage having a current ‘which
is circulated in the second electrical bridge cir
function as does the single ?eld of the RS gen
cuit in a direction to reduce the excitation of
erator of Fig. 1 to impart self-energizing proper 25 the series armature current excited ?elds RSla
and RSlb or the generator RS to thus reduce
ties to the machine.
7
The manner in which the regulating generators
this generator’s amplifying characteristics and
‘are connected in the system is readily observed
consequently, its electrical output.
As follows,
in Fig. 5. Here the main generator ?eld windits forcing action on the generator ?elds GSFI
ings are again connected in the opposite legs of 30 and GSF? decreases and the main generator
the Wheatstone bridge circuit with the resistors
voltage drops. This continues until the arma—
RI and R2 forming the other two legs. The pat
ture currents of the motor are within permissible
tern ?eld winding RS3 is connected in series with
values and thereafter the current is maintained
a speed controlling rheostat R from the positive
substantially at this constant level throughout
jexciter bus Bl to the input terminal l of this 35 the accelerating period. Thus a heavily loaded
bridge circuit. It thus, upon pressing of the Start
motor may be accelerated in the minimum pos
push button and closing of the contacts CI of
sible time without the possibility of overloading
the contactor C which is held in at the contacts
the system elements.
. C2, is energized by a current indicative of the
‘W hen the Stop button is pressed, the energizing
current ?owing in the bridge circuit which cur—
circuit for the bridge network is opened at con
rent is indicative of the selected speed of opera
tacts Ci, thereby deenergizing the pattern ?eld
tion of the motor M. Thus the pattern excita
R’ and also removing this source of excitation
tion of the speed regulating generator is estab
for the main generator ?eld windings GSFI and
' lished. ‘Each of the self-energizing ?eld windings
If under these conditions the motor is
RSla and RSIb arevconnected in opposite legs r overhauled by the load to which ‘it is connected,
of 'asecond Wheatstone bridge circuit which has
the motor functions as a generator and tends to
‘for its other two legs the resistors R6 and R1.
drive the generator as a motor. Since the pat
One armature terminal of the speed regulating
tern ?eld
has been deenergized, the excita
generator RS is connected to the input terminal
tion resulting from the yet energized ?elds RS2
5 of the second bridge circuit, and the other 50 vand RS4 now acting cumulatively reverses the
armature terminal is connected to the output
electrical output of the regulating generator RS
terminal 3 of the ?rst bridge circuit. The re
to rev‘ersely excite the main ?eld windings GSFI
sistor SRl, which establishes the desired resist—
and
As follows the main generator volt
ance of the self-energizing ?eld circuit, is con
age rapidly drops and tendsto build up in the
nected between the other input terminal 6 of
opposite direction to thus in e?ect aid the regen
the“ second bridge circuit and the other output
erative action‘of the motor. The current limit
terminal 4 of the ?rst bridge circuit. The arma
ing generator RCL again functions to produce an
ture of the current limiting regulating generator
electrical output in such a direction as to oppose
RCL, its series connected armature current ex
cited ?eld winding RCLI and the series resistor
SR2 for this circuit are connected across the
the currents circulating in the self-excited ?elds
RSia and RSlb. With increasing currents the
electrical currents of the RCL generator are
greater in magnitude than those of the RS gen
circuit. Thus in a manner similar to the speed
erator. Thus the current in the series ?elds RS‘la
regulating generator the current limiting regu
and RSlb reverses and consequently the current
lating generator supplies only corrective current 65 in the ?elds GSFl and GSFZ is reversed. The
output terminals ‘land 8 of the second bridge
to the series ?eld RSIa and RSlb of the speed
regulating generator.
excitation of the generator ?elds is now there
fore'in a direction to maintain the generator volt
The operation of this system is as follows.
Depressing the Start push button energizes the
age thereby preventing regenerative currents in
excess of the preset maximum value.
contactor C which then closes its contacts Cl and 70
The variable voltage drives of this ‘invention
provide automatic overload current protection
C2. Closure of contact members C2 provides a
holding circuit for this contactor until the Stop
push button is operated. Closure of the contact
'members Cl completes the energizing circuit for
the bridge network containing the generator ?eld
which results not in'aitime wasting shutdown of
the system but which limits thecurr'erits'within
permissible values, providing maximum ‘accelera
tion of the motor for the given mechanical load
2,406,424
13
14
it is driving. Further, this automatic overload
said main generator for limiting the electrical
protection is provided by means of a simple, small
rotating regulator which requires a minimum of
maintenance e?ort and which, for the most part,
eliminates the complications of relay or contactor
output thereof to a predetermined Value.
4. In a variable voltage drive, the combination
of, a drive motor, a main generator for energizing
the drive motor, ?eld winding means for the main
systems which function in this capacity.
generator, means for supplying a constant elec
The foregoing disclosure and the showings
trical current to a ?rst portion of the ?eld wind
made in the drawing are merely illustrative of the
ing means, a regulating generator having an elec
principles of this invention and are not to be in
trical output controlled in accordance with cer
terpreted in a limiting sense. Numerous modi? 10 tain electrical quantities of the motor for ener
cations of the variable voltage drives as well as
gizing a second portion of the ?eld winding means,
the system elements are possible, the results of
and means for selectively utilizing the regulating
which may be predicted from the teachings of
generator and the means for supplying a constant
this disclosure. The only limitations are to be
electrical current to control said main generator.
determined from the scope of the appended 15
5. In a variable voltage drive, the combination
claims.
of, a drive motor, a main generator for energizing
I claim as my invention:
the drive motor, ?eld winding means for the main
1. In a variable voltage drive, the combination
generator, means for supplying a constant elec
of, a motor, a main generator for energizing said
trical current to a ?rst portion of the ?eld wind
motor, ?eld windings for said generator, an elec 20 ing means, a ?rst regulating generator having an
trical bridge circuit, means for supplying elec
electrical output controlled in dependence of cer
trical energy to the electrical bridge circuit, two
tain electrical quantities of the motor for ener
of the ?eld windings for said main generator
gizing a second portion of the ?eld winding means,
being connected in opposite legs of the bridge cir~
means for selectively utilizing the ?rst regulating
cuit, a ?rst regulating generator responsive to
generator and the means for supplying a constant
electrical quantities of said motor for regulating
electrical current to control said main generator,
the electrical output of said main generator, a
a second regulating generator including at least
second regulating generator responsive to the
one control ?eld winding, means for providing
electrical current supplied to said motor by said
electrical properties in the second regulating gen
main generator for controlling the excitation of
erator such that said ?eld winding must be ex
said ?eld windings in said bridge circuit to pre
cited above a predetermined minimum value be
vent excessive motor currents, and means for ren
fore an electrical quantity is generated, means for
dering said regulating generator ineffective to
energizing the control ?eld winding in depend
regulate said current until a predetermined max
ence of an electrical quantity of the motor, and
imum current value is reached,
2. In a variable voltage drive the combination
of, a motor, a main generator for energizing the
motor, ?eld windings for the main generator, an
circuit means connecting said second regulating
generator with said ?rst portion of the ?eld
winding means for the main generator.
6. In a variable voltage drive, the combination
electrical bridge circuit, means for supplying elec
of, a motor, an armature winding and a ?eld
trical energy to the electrical bridge circuit, cer~ 40 winding for the motor, a main generator, an
tain of the ?eld windings of the main generator
armature winding and a plurality of control ?eld
being connected in opposite legs of the electrical
windings for the main generator, circuit means
bridge circuit such that the ampere turns in each
connecting the armature winding of the main
leg are equal, a ?rst regulating generator respon
generator and the armature winding of the motor
sive to electrical quantities of the motor for con
in series circuit relationship, an electrical bridge
trolling the excitation of said certain of the ?eld
circuit, two of said plurality of control ?eld wind
windings, a second regulating generator responsive
ings for the main generator being connected in
to the motor armature currents for controlling the
opposite legs of the electrical bridge circuit, a
?rst regulating generator, and means for render
?rst regulating generator, an armature current
ing the second regulating generator ine?ective to
excited voltage sustaining ?eld winding and a plu
control the ?rst regulating generator until a max 50 rality of control ?eld windings for the ?rst regu
imum motor armature current is reached.
lating generator, circuit means connecting two of
3. In a variable voltage drive, the combination
the control ?eld windings of the ?rst regulating
of, a motor, a main generator for energizing said
generator in the series armature circuit of the
motor, ?eld windings for said main generator,
main generator and motor to be energized in ac
an electrical bridge circuit, two of the ?eld wind
cordance with di?erent electrical quantities there
ings for said main generator being connected in
of, a second regulating generator, an armature
opposite legs of said bridge circuit, means for
current excited voltage sustaining ?eld winding
supplying electrical energy to said bridge circuit,
and a control ?eld winding for the second regulat
a ?rst regulating generator responsive to selected
ing generator, ?eld poles for the windings of the
electrical quantities of said motor for controlling
second regulating generator, magnetic shunts of
the electrical output of said main generator, a
lesser cross-sectional dimension than the ?eld
second regulating generator having ?eld poles
poles, shunting said ?eld poles; circuit means
and magnetic shunts shunting the ?eld poles
connecting the control ?eld winding of the second
which magnetic shunts saturate at lesser flux
regulating generator in the series armature cir
densities than the ?eld poles, ?eld windings asso
cuit of the main generator and motor to be ener
ciated with said ?eld poles, said second regulating
gized in accordance with an electrical quantity
generator having the characteristic of producing
thereof, circuit means for electrically connecting
abruptly increasing electrical outputs upon satu
said ?rst regulating generator to energize a third
ration of the magnetic shunt, means for energiz
control ?eld winding of the main generator, cir
ing the ?eld windings of the second regulating
cuit means connecting the second regulating gen
generator in dependence of the magnitude of the
erator across the output terminals of the elec
electrical current supplied to said motor by said
trical bridge circuit, means for supplying electri
main generator, and circuit means connecting said
cal energy to a third control ?eld winding of the
second regulating generator to effect a control of 75 ?rst regulating generator, to the electrical bridge
2,406,424
15
16
circuit and to the ?eld winding of the motor; and
means for selectively connecting said ?rst regu
lating generator ‘and said electrical bridge cir~
circuit, and means for controlling the second
‘regulating generator in dependence of an elec
trical quantity of the motor.
‘
9. In a variable voltage drive, the combination
cuit to said means for supplying electrical energy.
of, a motor, a main generator for energizing the
'7. In a variable voltage drive, the combination
motor, a pair of control ?eld windings for the
of, a motor, an armature winding and a ?eld
main generator, a ?rst electrical bridge circuit,
winding for the motor, a main generator, an
said pair of control ?eld windings for the reg
armature winding and a plurality of control ?eld
ulating generator'b'eing connected in opposite legs
windings for the main generator, circuit means
connecting the armature winding of the main 10 of the electrical bridge circuit, a ?rst regulating
generator, said ?rst regulating generator being
generator and the armature winding of the motor
controlled in dependence of electrical quantities
in series circuit relationship, an electrical bridge
of said motor, circuit means including a second
“circuit, two of the control ?eld windings of the
electrical bridge circuit‘connecting said ?rst reg
ulating generator across the output terminals of
of the electrical bridge circuit, a ?rst regulating
‘generator, an armature current excited voltage
the ?rst electrical bridge circuit, a pair of arma
sustaining ?eld winding and a plurality of control
ture current excited ‘?eld windings for the ?rst
?eld windings for the ?rst regulating generator,
regulating generator, said armature current ex_
two of the control ?eld‘windings being differen
cited ?eld windings forming opposite legs of the "
tially connected, circuit means connecting one of 20 second electrical bridge circuit, a second reg
ulating generator having ?eld poles and mag
said differentially connected windings to be ener
gized in accordance with the voltage drop across
netic shunts for the ?eld poles of smaller ?ux
the motor armature, circuit means connecting
capacity than the ?eld poles, control windings
the other of the differentially connected windings
on the ?eld poles, said second regulating gen
to be energized in accordance with the electrical 25 erator being connected across the output ter
current traversing the series armature "circuit of
minals, of the second electrical bridge circuit,
the main generator and motor, a second regulat
and means for energizing the control windings
‘ing generator, an armature current excited
of the second regulating generator in dependence
voltage sustaining ?eld Winding and a control
of an electrical quantity of the motor.
?eld winding for the second regulating genera 30
10. In a variable voltage drive, the combina
tor, ?eld poles for the windings of the second
tion of, a motor, ‘an armature Winding and a
regulating generator, magnetic shunts of lesser
?eld winding for the motor, a main generator,
cross-sectional dimension than the ?eld poles,
an armature winding and a pair of control ?eld
fshunting the ?eld poles; circuit means connecting
windings for the main generator, circuit means
the control ?eld Winding of the second regulat 35 connecting the armatures of the main generator
ing generator to be energized in accordance with
and motor in series circuit relationship, a ?rst
the electrical current traversing the series arma
electrical bridge circuit, said pair of control ?eld
ture circuit of the main generator and motor,
windings for the main generator being connected
circuit means electrically connecting the ?rst
in opposite legs of the electrical bridge circuit,
regulating generator to energize a third control 40 a ?rst regulating generator, a pair of armature
?eld winding of the main generator, circuit means
‘current excited voltage sustaining ?eld windings
connecting the second regulating generator across
and a plurality of control ?eld windings for the
the output terminals of the electrical bridge cir
?rst regulating generator, a second electrical
cuit, means for supplying electrical energy to a
bridge circuit, said pair of armature current ex
third control ?eld winding of the ?rst regulating 45 cited ?eld Windings forming opposite legs of said
‘generator, to the electrical bridge circuit and to
second electrical bridge circuit, said ?rst regulat
the motor ?eld winding; and means for selectively
ing generator being connected in series with the
connecting the third ?eld winding of the ?rst
second electrical bridge circuit across the output
regulating generator and the electrical bridge cir
terminals of said ?rst electrical bridge circuit, a
main generator being connected in opposite legs
cuits to said means for supplying electrical energy. 50 second regulating generator, an armature cur
8. In a variable voltage drive, the combination
rent excited voltage sustaining ?eld winding and
of, a motor, a main generator for energizing the
a control ?eld Winding for the second regulat
motor, a pair of control ?eld windings for the
ing generator, said second regulating generator
main generator, a first electrical bridge circuit,
being connected with the armature current ex
said, pair of control ?eld windings for the reg 55 cited ?eld winding thereof across the output
ulating generator-being connected in opposite legs
terminals of the second electrical bridge circuit,
of the electrical bridge circuit, a ?rst regulating
means for exciting two of the control ?eld wind
generator, said ?rst regulating generator being
controlled in accordance with electrical quan
titles of said motor, circuit means including a
second. electrical bridge circuit connecting said
?rst regulating generator across the output ter
minals of the ?rst electrical bridge circuit, a
pair of armature current excited ?eld windings
for the ?rst regulating generator, said armature
current excited ?eld windings forming opposite
legs of the second electrical bridge circuit, a
second regulating generator connected across the
output terminals of the second electrical bridge
ings of the ?rst regulating generator in depend
ence of certain of the electrical quantities of said
motor, means for exciting the control ?eld wind
ing of the second regulating generator in ac
cordance with an electrical quantity of the motor,
and means for supplying direct current of con
stant value to a third control ?eld winding of
65 the plurality of control ?eld windings for the ?rst
regulating generator, to the ?rst electrical bridge
circuit and to the motor ?eldwinding,
GEORGE E. KING.
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