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Nov. 19, 1946.
2,411,377
A. W. KIMBALL
CONTROL SYSTEM
Filed June 14, 1944
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BY
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ATTORNEY
Patented Nov. 19, 1946
2,411,377
UNITED STATES PATENT OFFICE
2,411,377
CONTROL SYSTEM
Albert W. Kimball, Forest Hills, Pa., assignor to
Westinghouse Electric Corporation, East Pitts
burgh, Pa., a corporation of Pennsylvania
Application June 14, 1944, Serial No. 540,175
7 Claims.
(C1. 172-239)
2
My invention relates to control systems of the
voltage and the saturation dependent voltage
generated by the regulating generator.
variable voltage type and particularly to systems
containing an auxiliary regulating generator for
These and other objects and features, as well
as a speciñc example of a control system embody
limiting the load current of a motor to be con
trolled, systems and generators of this kind being
disclosed in the copending applications by J. G.
Ivy, Serial No. 496,596, filed July 29, 1943, and
Serial No. 532,975, filed April 27, 1944, both as
signed to the assignee of the present application.
An object of my invention is to provide a con
trol system of the type just referred to that pro
duces not only a load limiting regulating effect,
but is also distinguished by increased accuracy
and speed as regards its response of the motor
to changes in control adjustment while being sub
stantially free of hunting even at a high rate of
change of the control adjustments.
Another object of my invention, with reference
to hoists, particularly mine hoists, is to provide
a hoist control system in which the torque of
the hoist motor and hence the stress on the ropes
and other mechanical hoisting equipment are
automatically limited due to control characteris
tics inherent in the electrical control system and
in which the hoisting speed is a function of the
selected controller position regardless of the
amount of load, thus reducing the degree of at
tention and skill for operating the hoist.
In order to achieve these objects and in accord
ance with my invention, I provide the motor
generator combination of a variable voltage drive
with two auxiliary generators for controlling the
ñeld excitation of the main generator. One of
these auxiliary generators, hereinafter called the
“control generator,” has a self-excited field wind
ing rated for just sustaining the armature voltage
and further field means whose voltage is ad
justed under control by the operator. (When
referring in this specification to “self-excited”
windings, I use this term for designating a i'leld
winding which, in contrast to a “separately ex
cited” Winding, derives its excitation from the
energy generated in the armature of the same
machine.) The other auxiliary generator, here
inafter called the “regulating generator,” has
saturation characteristic so that it generates an
armature voltage substantially only when its ñeld
excitation exceeds a given finite magnitude. The
regulating generator has ñeld means excited in
dependence upon the load current of the motor
to be controlled. The armatures of both auxiliary
generators are connected to a ñeld winding of the
above-mentioned main generator so that its ex
CH
ing them, will be apparent from the following de
scription of the mine hoist control system shown
diagrammatically in Fig. 1 of the drawing, and
elucidated by the explanatory diagram of Figs. 2,
3 and 4, and the detail showing in Fig. 5 of the
pole structure of an appertaining regulating gen
erator.
Referring to the hoist control system shown in
Fig. 1, the hoisting equipment proper is schemati
cally indicated at | and includes a hoisting drum
._ whose shaft 2 is mechanically connected to the
armature I0 of a driving motor HM. The motor
has a separately excited winding || and a com
pensating series field winding l2. The ñeld wind
ing || is energized from a current source of sub
stantially constant voltage, and to this end is con
nected through an adjusting rheostat RI to an
exciter EX with an armature 50, two ñeld wind
ings 5| and 52, and a field rheostat R1. The ad
justment of rheostats RI and Rl need not be
, changed during the operation of the system.
The armature |0 of the hoist motor HM is
connected, in load circuit Al, with the armature
20 of a main generator MG which forms the cur
rent source of circuit AI. The main generator
“I MG has a main ñeld winding 2| connected in a
control circuit A2 which includes in series two
voltage sources represented by the armatures 30
and 40 of a control generator CG and a regulat
ing generator RG, respectively. A resistor R2 is
OD Si series-arranged in circuit A2. Numeral 22 de
notes a compensating or interpole winding of the
main generator MG.
The control generator CG has four ñeld wind
ings 3|, 32, 34, and 35 which cooperate in con
trolling the voltage impressed on the main gen
erator ñeld winding 2|. The resultant energiza
tion of winding 2| determines the voltage and
current supplied by the main generator arma
ture 2U through circuit A| to the hoist motor HM,
cri thereby controlling the torque and speed of the
hoisting equipment driven by the motor HM.
The current in circuit A2 is principally deter
mined by the excitation of ñeld winding 3|, here
inafter called the “pattern ñeld winding” of the
50 control generator CG. Field Winding 32 is self
energized and serves to amplify the control effect.
While the connection of winding 32 in circuit A2
is shown as a series arrangement, a shunt wind
citation depends on both the operator-adjusted 55 ing may be used instead. Considering the eX
citation of pattern ñeld winding 3| as a stand
2,411,377
ard and assuming that main generator MG sup
trol generator CG and is connected in series with
plies energy to the hoist motor rather than func
tioning in a regenerative sense, both windings
voltage adjusted at the controller CO.
this winding so as to be energized by the pattern
hereinafter called the “voltage winding,” is en
ergized in dependence upon the voltage in load
circuit AI, and to this end connected by leads 23
and 2d across the armature 2@ of the main gen
erator MG. Field winding 35 of control genera
tor CG serves to compensate for the IR drop in
the main circuit Al and is connected across
winding 22 through leads 23 and> 26 and in series
with a Calibrating resistor R3. A resistor in cil'
cuit Al may be used in place of coil 22, if desired,
to obtain excitation for windings 35 and 45,
Field
winding fifi of regulating generator RG is simi
32 and 35 act cumulatively while winding 3i acts
diiierentially with respect to the pattern field
winding 3|.
Field winding Sil of control generator CG,
lar in function to the voltage winding 34 of con
trol generator CG and is connected in series
therewith across armature 2li of main generator
MG, a Calibrating resistor R4 being inserted in
series with winding £54. Field winding d5, here
io inafter called the “regulating winding,” is excit
ed in accordance with the current in the feed cir
cuit Ai and to this end connected, through a cal
ibrating rheostat R5 and leads 23 and 25, across
the interpole or compensating winding 22 of gen
erator MG in parallel to the IR-drop compen
sating ñeld winding S5 of generator CG. When
in operation», both windings 35 and d5 are trav
ersed by a current whose magnitude varies in
accordance with the Voltage drop across the iield
'I‘he pattern ñeld winding 3|, serving to deter
winding 22 or other Voltage measuring resistor
mine the basic speed of the hoist motor as to
in circuit Ai fromwhom the windings 35 and 45
direction and magnitude, is energized from a cur
derive their energization.
rent source of constant voltage under control by
In order to achieve the control functions in
operator-actuated regulating and reversing
accordance with the above stated objects oi my
means. More in detail, pattern winding. 3l is
connectedV to mainsv X and Y of the exciter EX, 25 invention, a particular design of the two auxili
ary generators CG and RG and their appertain
a reversing switch RS being interposed in order
ing field exciting means is necessary, as will be
toselect the polarity of the pattern voltage im
set forth presently.
pressedV on iieldwinding 3l. The connectionin
The control generator CG is a small electric
cludes. a control device CO. which has a resistor
RS. connected between main Y and. reversing 30 generator, similar in design to conventional ex
citers. Like exciters, it possesses the ability to
switch RS.
accurately amplify small amounts of energy sup
The reversing switch RS, as illustrated, has
plied to its iieids into larger output amounts for
two movable contacts tiûand i6), each cooperat
the control of large electrical machines. How
ing with .two stationary contacts ti, 62 and il,
ever, the control generator possesses this ability
12, respectively. In one position of switch RS,
to a much higher degree and thus represents a
Contact 6G is in engagement with contact 6l, and
sensitive amplifier, capable of working on very
contact l@ with contact ll, in order to energize
small inputs to its fields to produce a very large
the hoist motor HM for operation~ in the hoist
output in the armature circuit. This sensitivity
ing direction. In its other position, the revers
ing switch RS connects movable contacts 6B, and 40 and amplification is due to the’ action of the self
energized ñeld winding 32 which feeds a small
1li with stationary contacts 62 and 1.2, respective
portion of the control generator output power
ly, for controlling the hoist motor to operate in
back into the control generator as excitation t0
the lowering direction, The control device CO is
produce still more output. IThe self-excited iield
preferably designed like acustomary master con
is just sufiicient to sustain the generated Voltage
troller, while the reversingA switch RSi and its con
tacts are preferably vformed by electromagnetic
but, by itself, is incapable of building up the out
contactors whichv are controlled in accordance
put. of the machine. Hence, the action of gener
erator CG is always under the control of one or
more of the separately excited iield windings 3l,
with the selected. hoisting or lowering position
of the master4 controller. Since the particular de
sign of the operator-actuated control elements,
here represented by CO and RS, isV not essential,
- 33, 34', and 35. Stating this another way, the re
sistance of the external control circuit A2 is ad
justed relative to the self-excited iield excita
for the invention proper and, as such, need not
involve novelty over the well'known andv custom,
tion so that the machine CG operates on its air
ary masterV controllers, the simplified illustration
gap line.
Y
With this adjustment of the self-energizedfield,
in Fig. 1 has beenchosen for the sake of. con
The armature 26 of the main generator lVIG
the ampere turns from the other field exciting
means (windings 3l, 33, 35,35) can be balanced
, and the armature 3Q of the control generator CG
are mounted on a common shaft 3 which, when
to the null point. This nullr condition exists when
venience and- clarity.
'
_
a field excitation which measures the motor speed
is balanced by the rleld- excitation of the pat
tern field winding caused by the standard or pat
tern voltage as adjusted by the operator by se
lecting the position of the master controller.
rI‘he motor speed corresponds to the` fundamen
in operation, is driven by a constant speed mo
tor Mi. Satisfactory operation can also be ob
tained if armature 3d is driven at constant speed
while armature 2D is actuated by a separate drive
whose speed does not vary excessively.
Armature ¿ââä of regulating generator RG is G) tal equation:V
mounted on a common shaft Ewith armature 59
Speed=constant >< (armature voltage-armature
of exciter EX. Shaft 5 is connected to a constant
IR drop)
speed motor M2. It will be understood, however,
x
that the illustrated arrangement can be modified
by using a single constant speed motor for the
operation of both shafts 3 and 5, or by connect
ing the two shafts 3 and '5 with each other so as
As stated previously, the Voltage responsive iield
winding se of generator CG measures the arma
turevoltage of hoist motor HM, and the IR-drop
field winding 35 measure the interpole IR drop
which is proportional to the armature IR drop
to obtain a single motor generator unit.
The regulating generator RG has three iield
ofthe motor I0. ' The relative polarities of. the
windings fil, dll, and 45. Field winding fil corre
sponds to the pattern iield winding 3l of the con 75 two windings 35 and 35 are such that their am
5
2,411,377
pere turns are subtractive and thus satisfy the
above equation. The resultant speed measuring
ampere turns of windings 35 and 34, as a whole,
are balanced against those of the pattern field
winding 3l .
6
after the shunt has been saturated, is similar to
that of a conventional machine.
Due to the fact that ampere turns from the
regulating ñeld winding 45 are used for saturat
ing the magnetic shunt, the output voltage of gen
When the motor is running at the speed called
for by any selected setting of the master con
troller, the speed measuring ampere turns cancel
ampere turns of the pattern ñeld. The entire
erator RG is controlled in response to the ar
when the load current of the motor HM tends to
exceed a given safe limit, the armature di) of gen
erator RG generates a bucking voltage which re
duces the resultant field excitation of main field
speed, and the voltage of the main generator
MG also approaches maximum, the corrective
effect required by the RG armature 4t to limit
the current in winding 2i oi‘ generator MG will
mature current (and hence torque) of the hoist
motor HM. As a result, the above-mentioned
bucking voltage of armature 4i) is not effective
excitation on the control generator comes now 10 before the magnetic shunt on the regulating gen
from the self-energized ñeld, and there is no tend
erator RG is saturated, and this saturation effect
ency to change the generator excitation. Should
occurs only when the load current of the hoist
the motor speed vary from the proper value, the
motor has exceeded a given safe limit value.
balance between the pattern and speed measuring
The control fields of the regulating generator
excitations is disturbed. The resulting excess
do not saturate the shunt when performing their
ampere turns then act to correct the error in mo
normal function since they are balanced against
tor speed. In this manner, the control genera
each other so that their net ampere turns are
tor CG provides a sensitive and accurate speed
normally zero. In other words, the small tran
regulation.
sient departures from zero, necessary to obtain
The regulating generator RG is so designed 20 the desired regulating function of iield windings
that the component voltage imposed on circuit
»I and $4, is insufficient to cause appreciable sat
A2 remains substantially zero under normal op
uration in the shunt, although these windings are
erating and load conditions of the system, so that
effective to produce the regulating anti-hunting
usually the entire neld excitation of the main
action mentioned presently.
generator MG is produced by the control gen~ 25
When during a control operation initiated by
erator in the above-described manner. However,
the operator, the hoist motor approaches full
winding 2l suiìiciently to prevent a further load
increase in the motor circuit Al. To accomplish
this limiting eiïect, the regulating generator RG
has a special characteristic, similar to that shown
in Fig. 2. This characteristic (curve V) differs
from that of conventional machines by having an
be less because the resultant speed-measuring
ñeld of the control generator Will then cancel a
greater portion of pattern field ampere turns
(winding 3l) which are tending to cause exces`
sive load voltage and current. The voltage field
(winding 44) on the regulating generator will
also cancel pattern ñeld ampere turns (winding
extended low voltage or zero voltage interval be
tween points E and F which are both displaced
fil), and this occurs in the same proportion as
from the zero point O by ñxed amounts oi eX~
in the control generator so that the corrective
citation. Line R represents the resistance line 40 eñect of the component voltage generated by the
of the generator.
armature 48 is reduced in the right amount to
A characteristic of this type can be obtained
maintain the same motor armature current in
by providing the ñeld poles of the generator with
circuit Al. It is this simultaneous occurrence,
a saturable magnetic shunt as exemplified by
and
its corrective eifect, of the regulating action
Fig. 4.
of the speed-dependent and operator-adjusted
In Fig. 5, numerals 5, to, and Sil denote the
shaft, armature, and stator frame, respectively,
voltages that decreases the tendency of hunting
and thus increases the accuracy, reliability, and
of the regulating generator RG. The pole struc
permissible speed of control. It is essential in
ture comprises a base portion 8l in good magthis connection that the component voltage of
netic contact with the stator frame and a pole 50 the regulating generator dil is directly introduced
shoe portion S2 adjacent to the armature. rI’he
into the ñeld circuit of the main generator MG
main pole portion E3 is shunted by a eaturable
so that the inherent time delays of the current
flux path 35 and contains an air gap or a mag
regulating means are reduced to a minimum.
netically reluctant shim iid, for instance of brass.
In order to further elucidate the above-de
The windings 4i, 44 and 135 of the generator are
scribed operation of the system, reference is had
arranged on the main pole portion 83. The air
to the schematic diagram of Fig. 3.
gap or shim at the top of the main pole portion
In this diagram the values along the ordinate
carries the entire pole flux and hence does not
represent the output voltage of the control gen
iniiuence the division of flux. It primarily de
erator CG, while the values along the abscissa
termines the spacing F-E of the zero voltage
represent the resultant ampere turns of the field
interval as well as the sha-pe of the characteristic
winding means of this same generator necessary
beyond points F and E according to the diagram
for obtaining the correlated output voltage. The
of Fig. 2. Because of this gap or shim, substann
straight line denoted by RL indicates the resist
tially all flux íiows through the shunt since the
ance line of the circuit A2 while the saturation
reluctance of this path is low, and almost none
curve
SC indicates the relation of ampere turns
of it is forced across the air gap into the arma
to generated volts under operating conditions
ture to generate voltage, as long as the resultant
where the output voltage of the regulating gen
field excitation is insuiiicient to saturate the
erator
RG is zero. Curve DC in Fig. 3 represents
shunt. The shunt 85 is so proportioned that it
the displaced characteristic which occurs when
saturates at an excitation corresponding to points 70 the
regulating generator RG generates output
F and E of Fig. 2 and then becomes unable to
voltage
due to the occurrence of an overload in
carry more flux. Consequently, upon saturation
the load circuit of the hoisting motor, as ex
of the shunt 85, an increasing field excitation
plained in the foregoing. This displacement re
forces liux across the air gap into the armature
so that now a voltage is generated. The action, 75 duces the field excitation of the main generator
ñeld winding 2l in accordance with the voltage
value denoted by RV in Fig. 3. The resulting
action is a corresponding reduction in the ar
mature voltage of the main generator MG, and
this action continues until the current in the?
voltage coil 3Q on the control generator CG has
caused a difference between the pattern and
other control fields equal to the ampere turns
indicated by DV in Fig. 3. From then on, the
control generator CG continues operating inl ac
cordance with the displaced saturation curve DC.
for controlling. said component voltages respec
tively, operator-controlled circuit means for pro
viding an> adjustable pattern voltage and circuit
means for providing a control voltage variable
in accordance with the voltage of said circuit,
said diiierent circuit means being connected with
said' control means of said control voltage sourcev
for varying said appertaining component voltage
in accordance with the differential value of said
pattern and control voltages, and means for caus
ing said regulating voltage source to vary the
The shape and slope of the current limiting
rate of change of its appertaining voltage com
portion of the voltage-ampere turns character
ponent when the current in said output circuit
istic of the control generator can be modified
passes through a given ñnite value, whereby saidby varying the combination of fields on the regu
lating generator RG. For instance, with the 15 current is substantially limited to a given maxi
mum value.
ñeld windings arranged as shown in Fig. 1, the
3. A motor control system comprising a vari
characteristic is of the type represented by curve
able speed direct current motor, a main voltage
CIr in Fig. 4. By providing a current responsive
supply means having a load circuit connected to
coil 44 on the regulatinggenerator RG but omit
ting the current coil Sli on the control generator 20 said motor for energizing the latter and main
control means for varying the voltage of said
CG, the characteristic can be changed to the type
circuit, a controlling voltage source and a reg
represented by curve C2 in Fig. 4.
ulating voltage source both connected to said
If desired, the regulating eiîect of the gen
main control means for controlling it in accord
erator RG can be amplified by providing it with
a self-excited shunt field winding. It is further 25 ance with a. resultant eiiect oi the component
voltages of said latter two sources, each of said
possible to omit a control generator of the type
latter two sources having means for controlling
represented by generator CG in Fig. 1 and to
said component voltages respectively, operator
arrange the appertaining control windings di
controlled circuit means for providing an adjust
rectly on the main generator, although it will be
able pattern voltage and circuit means for pro
understood that such a system is not as suitable
viding va, control voltage variable substantially in
for high power outputs as the one according to
accordance with the speed of said motor, both
the aboveV describedv embodiment of Fig. 1.
said circuit means being connected with said
These and other modifications and alterations
will be obvious to those skilled in the art and are
intended to be within the scope of the essential
features of my invention as set forth in the claims
control means of said control voltage source for
varying said appertaining component voltage in
accordance with the differential value of said
pattern and control voltages, and means for caus
ing said regulating voltage source to vary the
I claim as my invention:
rate of change of its appertaining voltage corn
1'. A variable voltage control system compris
ponent when the load current of said. motor eX
ing a main generator having an output circuit 40 ceeds a given maximum value.
and a main iield winding for controlling the
4. A variable voltage control system compris
voltage oi said circuit, a control generator and
ing a main generator having an output circuit
a regulating generator connected with said main
and a main field winding for controlling the
appended thereto.
iield winding for exciting it in accordance with
a resultant voltage depending upon the corn
ponent voltages generated by said latter two gen
erators respectively, each of said latter gener
ators having field means for controlling said
respective component voltages, operator-con
' trolled circuit means for providing an adjustable
pattern voltage and circuit means for providing
a control voltage variable in accordance with
the voltage of said circuit, said different circuit
means being connected with said field means of
said control generator for exciting said control
generator in accordance with the differential
value of said pattern and control voltages, said
regulating generator having a saturation char
voltage of said circuit, a control generator and
a regulating generator connected with said main
field winding for exciting it in accordance with
a resultant voltage depending. upon the com
ponent voltages generated by said latter twov gen
' erators respectively, each of said latter gener
ators having ñeld means for'controlling said re
spective
component
voltages,
operator-con
trolled circuit means for providing an adjustable
pattern voltage and circuit means for providing
a control voltage variable in accordance with
the voltage of said circuit, said different circuit
means being connected with said field means of
said control generator and regulatingv generator
acteristic so as to vary the rate of change of said
for exciting both in accordance with the difier
iinite value, and means for exciting said ñeld
means of said regulating generator in dependence
upon the load. current in saidl circuit, whereby
saidl load current is substantially limited to a 65
characteristic so as to vary the rate of change
appertaining component voltage when the excita 60 ential value of said pattern and control volta-ges,
said regulating generator having a saturationV
tion oi its íield means passes through a given
of said appertaining component when the current
in said output circuit passes through a given
finite value, whereby said current is substantially
limited to a given maximum value.
5. A motor control system comprising a vari
able speed direct current motor, a main generator
having an armature circuit connected with said
circuit and a main control means ior varying
the voltage oi said circuit, a controlling voltage 70 motor for energizing the latter and a main field
winding for contro-lling the Voltage of said cir
sourcerand a regulating voltage source both con
cuit, a control generator and a regulating gener
nected to said main control means for control
ator connected with said main ñeld winding forv
ling it in accordance with a resultant effect of
exciting it in accordance with a resultant voltage
the component voltages of said latter two'sources,
each of saidV latter two sources having means 75 depending upon the component voltages gener
safe maximum value.
2. A variable voltage control system compris
ing a main voltage generator having an output
2,411,377
ated by said latter two generators respectively,
each of said latter generators having field means
for controlling said respective component volt
ages, operator-controlled circuit means for pro
viding an adjustable pattern voltage and circuit
means for providing a control voltage variable in
accordance with the voltage of said circuit, said
different circuit means being connected with said
field means of said control generator and regulat
ing generator for exciting both in accordance with
the differential value of said pattern and control
voltages, said regulating generator having a sat
uration characteristic so as to vary the rate of
change of said appertaining component voltage
when the excitation of its ñeld means passes
through a given finite value, and means for ex
citing said ñeld means of said regulating gener
ator in dependence upon the load current in said
10
value of said pattern and control voltages, said
regulating generator having saturation charac
teristic so that its component voltage is normally
substantially zero, and means for exciting said
field means of said regulating generator so as to
cause said appertaining component voltage to as
sume an effective value when the load current in
said circuit exceeds a given limit magnitude.
7. A motor control system comprising a vari
able speed direct current motor, a main gener
ator having an armature circuit connected with
said motor for energizing the latter and a main
ñeld winding for controlling the voltage of said
circuit, a control generator and a regulating gen
erator having respective armatures series-con
nected with said main field winding in opposition
to each other for exciting said main iield winding
in accordance with the resultant differential of
circuit, whereby said load current is substantially
the component voltages generated by said latter
limited to a safe maximum value.
20 two generators respectively, each of said latter
6. A variable voltage control system compris
generators having ñeld means for controlling said
ing a main generator having an output circuit and
respective component voltages, operator-con
a main ñeld winding for controlling the voltage of
trolled circuit means for providing an adjustable
said circuit, a control generator and a regulating
pattern voltage and circuit means for providing
generator connected with said main field winding
. a control voltage variable in accordance with the
in opposition to each other for exciting it in ac
voltage of said circuit, said different circuit means
cordance with the resultant differential of the
being connected with said ñeld means or” said con
component voltages generated by said latter two
trol generator and regulating generator for excit
generators respectively, each of said latter gen
ing both in accordance with the differential value
erators having field means for controlling said
respective component voltages, operator-con 30 of said pattern and control voltages, said regu
lating generator having saturation character
trolled circuit means for providing an adjustable
istic so that its component voltage is normally
pattern voltage and circuit«means for providing
substantially zero, and means for exciting said
a control Voltage variable in accordance with the
Voltage of said circuit, said different circuit means 35 iield means of said regulating generator so as to
cause said appertaining component voltage to
being connected with said ñeld means of said
assume an effective value when the load current
control generator and regulating generator for
in said circuit exceeds a given limit magnitude.
exciting both in accordance with the differential
ALBERT W. KIMBALL.
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