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Патент USA US2404641

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July 23, 1946-
_ H. H. LEIYGH ETAL
2,404,541
CONTROL SYSTEM
Filed Feb. 1, 1944
2 Sheets-Sheet 1
lnvew?mmsr
Henry H. Leigh.
Gurdon Ewva?tam
-
Their 'Attcvnqey.
July 23, 1946.
H. H. LEIGH ETAL
CONTROL SYSTEM
Filed Feb. 1, 1944
27a
27a _
_
254047641
7
2 Sheets-Sheet 2
Figlb.
‘
Inventors:
Henry H. Leigh,
_ Gordqn\ 6&4,“
E.Wa?,er~,
by
“"7
Them Attorney.
Patented July 23,1946
2,404,641
UNITED STATES PATENT OFFICE
2,404,641
CONTROL SYSTEM
Henry H. Leigh and Gordon E. Walter, Scotia,
N. Y., assignors to General Electric Company,
a corporation of New York
Application February 1, 1944, Serial No. 520,616
14 Claims.
(Cl. 172-"—-239)
1
This invention relates to control systems, more
particularly to systems for controlling the start
ing operations of electric motors, and it has for
an object the provision of a simple, reliable, and
improved control system of this character.
More speci?cally, the invention relates to motor
2
switching mechanism is reclosed for the reverse
direction of rotation. The preconditioning means
itself may require a longer time to function than
is required by the reversing switching means to
reverse the motor connections. Accordingly, a
suitable time delay device is provided for pre
control systems in which direct current is sup
venting the reversing switching means from com
plied to a motor through electric valve apparatus
pleting the reversed connections until the precon
and in which provision is made for reversing the
ditioning means has had time to become effective.
direction of rotation of the motor, and a further 10
Additional electric valve apparatus is provided
object of the invention is the provision of means
for supplying direct current to excite the motor
for effecting the reversal of the motor in a mini
?eld. The control of this additional valve ap
mum of time without damage to the motor.
paratus is arranged to excite the ?eld strongly
A more speci?c object of the invention is the
when the directional contactors are open before
provision of means for effecting successful opera
starting from rest. Means are provided for pre
tion of the electric valve apparatus as an inverter
venting the strengthening of the motor field dur
during the reversal period, thereby to eliminate
ing the interval in which the reversing contactors
undesirable operating characteristics such as cur
are open during a reversal operation, thereby to
rent surges, sparking at the brushes, and violent
limit the armature voltage and to promote a suc
changes in shaft torque.
cessful inverter operation. Also, means are pro
A still more speci?c object of the invention is
the provision of means for effecting successful
inverter operation of the electric valves during
vided for delaying the strengthening of the ?eld
of the motor during the inversion period follow
ing the reversal of the connections of the motor
the stopping operation of the motor.
armature to the supply valve means until the
speed or the motor has been- reduced to a prede
In carrying the invention into eifect in one -
form thereof, suitable electric valve apparatus
is provided for supplying direct current to the
armature of the motor, together with means re
sponsive to the armature current for controlling
the valve apparatus to limit the current to a
safe value. Since this current limiting means
cannot become e?ective until current is actually
flowing, there is a period following the reconnec
tion of the motor to the supply valve apparatus
during a reversal operation in which the current I‘
limiting means is ineifective to limit the current.
Accordingly, means are provided for precondi
tioning the control of the electric valve apparatus
to limit to a predetermined value the current
which can be conducted by the electric valve ap- -
paratus at the beginning of the inversion period
before the current limiting means becomes fully
e?ective. One form of these means comprises
a control valve connected to control the supply
electric valve apparatus, a source of standard ~'
voltage, reversing switching means for connect
ing the armature to the supply valve apparatus,
and contacts on the reversing switching means
for connecting the grid of the control valve in
such a manner as to compare the output voltage '
of the supply valve apparatus to the standard
voltage source when the motor is disconnected
from the supply valve apparatus, thereby to con
dition the supply valve apparatus to conduct only
a predetermined amount of current when. the
termined low value.
For a better and more complete understanding
of the invention, reference should now be had to
the following speci?cation and to the accompany
ing drawings of which Figs. 1A and 1B are a
simple, diagrammatical illustration of an embodi
ment of the invention.
Referring now to the drawings, an electric mo
tor [3 having an armature Illa and a shunt
?eld winding lllb is supplied from a source of
alternating voltage H through a supply trans
former l2 and suitable electric valve apparatus
comprising electric valves I 3, I4, I?) and Hi. The
starting, stopping, and reversing of the motor it!
are under the control of a suitable controlling
accessory such as a push-button station I‘! and a
pair of speed controlling potentiometers l8 and
19. If desired, these speed controlling potentiom
eters may be mounted on the push-button station
control panel.
The secondary winding of the supply trans
former I2 is provided with a midtap 12a and
this midtap is connected to the bus 20 which be
comes the negative side of a D.—C. system, i. e.,
the negative armature terminal, the negative ?eld
terminal, and the negative control terminal. As
suming that the motor in is designed for operation
on 230 volts, the full secondary voltage of the
transformer will be' approximately 620 volts. Two
5'71/2-volt taps I21) and I20 either side of center
2,404,641
3
The purpose of the time delay relay 25 is to al
low time for the initial heating of the cathodes
of the electric valves before power is applied to
the anode-cathode circuit. Since normally open
contacts 25a of the time delay relay 25 are in
cluded in the energizing circuit of the ?eld loss
protective relay 26, which has normally open con
tacts 26b in the energizing circuit of the direc
provide a l15-volt center-tapped source of control
power for ?laments, transformers, phase shift
bridges, and relay excitation.
,
The current supplied to the ?eld winding it?)
from the source I I is controlled by electric valves
is and M. As shown, the anodes i311 and Ma of
electric valves 13 and Ill are connected by means
of conductors 2! and 22 to opposite terminals of
tional contactors 3i! and 31, the latter cannot be
the secondary winding of transformer E2. The
?lamentary cathodes i322 and Mb are heated by 10 closed to complete the power circuit of the elec
tric valves until a predetermined interval of time
means of current supplied to the cathodes through
after the connection of the supply transformer l2
a ?lament transformer 23, of which the primary
Winding (not shown) is connected to the 1l5-volt
taps i2?) and I20 of the supply transformer, and
the secondary winding 23a is connected to the ?l
amentary cathodes I31) and Mb. The secondary
to the source of alternating voltage I l.
The purpose of the ?eld loss protective relay
25 is to delay the application of voltage to the
armature of the motor until a safe ?eld excita
tion has been established and to interrupt the
winding 23a is midtapped and the midtap is con
nected to the conductor 24 which thus becomes
armature circuit in case of a ?eld failure.
Although the thyratron valves i3, M, £5, and
the positive terminal of the ?eld supply. Thus,
the ?eld circuit may be traced from the positive 20 it may be controlled by any suitable method, it
is preferred to use the method of phase shift con
conductor 24 through the normally open contacts
trol of the grid voltage. For the carrying out of
25a of a time delay relay 25, the operating wind
this method of control, a pair of phase shifting
ing 26a of a ?eld loss protective relay 26, through
networks, one for the armature thyratrons and
?eld winding i?b to the negative conductorzt.
a
The supply of current from the source H to
the armature 56a of the motor is controlled by
means of the electric valves l 5 and it. As shown,
the valves l5 and it, like the electric valves I3
and M, are connected for biphase recti?cation,
i. e., their anodes 15a and Eta are connected
through primary windings 21a and 2% of a spe
cial current transformer 2? to the opposite ter
minals of the secondary winding of- the supply
transformer 52. The cathodes 15b and E61) of
valves l5 and it are provided with suitable heat
ing units which are connected to the secondary
Winding 23b of the ?lament transformer 23. The
cathodes i521 and 157) are connected to the ter
minal 28 which thus becomes the positive side of
the supply for the armature. Thus the armature
circuit is readily traced from the positive terminal
28 through conductor 29, series ?eld winding lilo,
one or the other of the directional contactors 3d,
3 l, a heating element 32a of an overload protec
tive relay 32, through the armature lea, commu
tating ?eld winding ltd to the negative supply
bus 26.
Although the electric valves H3, E4, E5, and It
may be of any suitable type, they are preferably
grid-controlled, mercury vapor thyratron tubes.
25 one for the ?eld thyratrons, is provided.
The
phase shifting network for the armature thyra
trons comprises a resistor 33 and the alternating
current winding 34a of a saturable core type re
actor 34, and the network for the ?eld thyratrons
30 comprises a resistor 35 and the alternating-cur
rent winding 36a of a saturable core type reactor
e5. Both these networks are connected in par
allel across the low voltage terminals I21), I20 of
..
the supply transformer. The primary winding
35 31a of a grid transformer 37 is connected between
the midtap {2a and the junction point 33a of the
resistor 33 and reactor winding 34a. This grid
transformer has two secondary windings 31b and
310.
The secondary winding 81b is connected be
40 tween the cathode and control grid of armature
thyratron i5, and similarly the secondary wind
ing 310 is connected between the cathode and
control grid of the armature thyratron [6. A cor
responding grid transfo-rmer 33 is provided for
the ?eld thyratrons i3 and I4. It has a primary
winding 38a connected between the midtap [2a
and the junction point 350: of the resistor 35 and
reactance Winding 35a, and a pair of secondary
windings 38b and 380 which are connected be
tween the cathode and grid of the thyratrons l3
and M, respectively. The phase shift of the grid
The cathodes MD and E61) of the valves l5 and
voltages is produced by varying the reactance of
it which control the supply of current to the
the saturable core reactors, which is accomplished
armature are indirectly heated, and these valves
by varying the D.-C. saturation of these reactors.
are provided with shield grids 5c and {60 as
The control is such that when the saturable
well as with control grids E511 and ltd, respec 55
reactors are saturated, the voltages of the grid
tively. The valves l3 and it which control the
transformers are advanced to the in phase posi—
supp-1y of current to the ?eld windings have di
tion with respect to the anode transformer volt
rectly heated ?lamentary cathodes and have only
age, and when the reactors are unsaturated, the
single grids 33c and Me which are control grids.
In thyratron valves, the function of the control 60 voltages of the grid transformers tend to be out
of phase and lagging. Intermediate values of
grid is only to initiate the ?ow of current between
saturation produce intermediate phase relation
the anode and cathode during each positive half~
ships. Thus, when the saturable reactors 34 and
cycle of anode voltage. Once current has started
36 are fully saturated, the thyratrons l3, l4, I5,
to flow in the anode-cathode circuit, the grid ex
and iii are fully conducting, and conversely,
ercises no further control until the flow of cur 65
when the reactors are unsaturated, the thyra
rent through the valve has been interrupted by
some means external to the valve itself.
Once
trons are nonconducting. For intermediate values
of saturation, the thyratrons have corresponding
the current has ceased to flow, the'potential of
intermediate values of conductivity.
the grid will again determine the point in the
The push-button station I? is provided with a
positive half-cycle of anode voltage at which the 70
plurality
of push-button type switches 39, MI, and
valve will again become conducting. Thus, by
ill for controlling the starting, stopping, and di
varying the ?ring point, the average Value of cur
rection of rotation of the motor ii). The push
rent ?owing in the anode-cathode circuit can be
button switch 39 controls the starting of the
controlled. These valves are therefore grid-con
75 motor in the forward direction; the push-button
trolled arc recti?ers.
'
2,404,641
6
switch 49 controls the starting of the motor in
of valve as is connected to a voltage divider com—
the reverse direction; and the push-button
prising resistors 5m, Elb, and Bio. The electric
switch 4| controls the stopping of the motor.
valve 50 is connected between the slider [8a of
To the low voltage taps I21) and 120 of the
the speed controlling potentiometer l8 and the
supply transformer is connected the primary 5 junction point of the resistors 51a and SH). When
winding 42a of a control voltage supply trans
the voltage of the grid 500 is made less negative
former ‘42. The opposite terminals of the sec
with respect to its cathode, the current trans
ondary winding 4% of this transformer are con
mitted by the valve 5?) is correspondingly in
nected to the anodes 43a and 53b of a small
creased, and since this current flows through the
double diode recti?er valve 43 which furnishes a
resistor sea, the voltage drop across resistor 51a
separate source of low voltage D.-C. from which
is correspondingly increased and consequently,
the control electric valves are energized. . The
the voltage of the grid 490 is correspondingly de
saturating windings 34b and 36b of the saturable
creased so that the current transmitted by valve
reactors 34 and 35 obtain their energization from
119 is decreased and the armature voltage and
this source of direct voltage. This direct volt 15 speed are correspondingly decreased. Thus, in
age is ?ltered by means of a smoothing reactor
creasing the conductivity of electric valve 56 has
44 and a capacitor 45. The voltage across the
the effect of decreasing the voltage supplied to the
capacitor 45 is impressed On a circuit comprising
armature and conversely, decreasing the current
a resistance 46 in series with two glow tubes 47
conducted by electric valve at has the eifect of
and 48. These glow tubes 41 and 48 are gaseous 20 increasing the voltage supplied to the armature.
discharge devices which operate in that region
Since the lower terminal of resistor 53c and
of their characteristic in which the voltage drop
one electrode of glow tube ‘13 are connected to~
across the discharge supporting electrodes is sub
gether at point lite, and since the upper terminal
stantially constant over a wide range of current.
of resistor tie is connected to the grid 490, the
The voltage across the points 46a and 43a is ?xed 25 valve t9 compares the voltage drop across the
at a value which is determined by the type of
resistor tile with the voltage drop across the
glow tube used, and within the operating limits
tube 43.
of this equipment, this voltage is independent of
If the armature voltage or a portion of the
variations‘ in the A.-C. supply voltage. Any
armature voltage is impressed on the grid 500,
di?erence in voltage between the voltage drop 30 an increase in armature voltage will increase the
across the capacitor 45 and the constant voltage
conductivity of valve 50, thereby decreasing the
across the glow tubes 4'! and 43 is absorbed by the
conductivity of valve 49 and decreasing the volt
resistor 46.
age supplied by the thyratrons I 5 and 18, thereby
The voltage drop across the glow tube 41 is
to correct for the increase in armature voltage.
used to stabilize the voltage of the amplifier 35 If the armature voltage decreases, the reverse
valves which are connected between the points
action takes place and the decrease in armature
45a and 41a. The voltage drop across the glow
voltage is corrected. The position of the slider
tube 48 is the voltage standard with which signal
{3a on the armature speed control potentiometer
voltages are compared for controlling purposes.
determines the percentage of the total voltage
For the purpose of varying the direct current 40 drop across the valve 48 which is to be derived
which flows in the saturating winding 34b, a
and used as a preset indication of speed. The
suitable amplifying electric valve (is is provided.
voltage that is so derived and used as a reference
This valve is provided with an anode 49a, a
voltage is the voltage between the slider i805 and
cathode 49b, and a control grid 450. The D.—C.
the negative bus 2t. Since the cathode of the
winding 34b and the valve 49 are connected in 45 valve 50 is connected to the slider, then the posi
series across the glow tube ‘4'51 The control of
tion of the slider will determine the voltage of
the current through the D.-C. winding of the
the cathode relative to the negative bus 20. A
armature saturable reactor 34 is accomplished by
signal voltage is derived from the armature volt
proper choice of the grid-to-cathode voltage of
age by means of a voltage divider which com
the valve 49. As the voltage of the grid 490 is 50 prises resistor 52a, potentiometer 52b, resistor
made less negative with respect to the voltage
52c, and that portion of the potentiometer 53
of the cathode 49b, the current transmitted by
between the slider 53a and the negative bus 20.
the valve increases, thereby increasing the sa"
The signal voltage used is the voltage from the
uration of the armature saturable reactor 34,
slider 52d to the negative bus 20, and this signal
which, as stated in the foregoing, results in in 55 voltage is impressed on the grid 560 of valve 52!.
creasing the voltage applied to the armature of
Thus the grid-to-cathode voltage of the valve 58
the motor l6. Conversely, as the voltage of the
is the difference between the signal voltage and
grid 490 is made more negative with respect to
the voltage from the slider I 3a to the negative
the voltage of cathode 49?), the current trans
bus 20. The tendency of the circuit is to main
mitted by the valve decreases and this decreases
tain the signal voltage approximately equal to
the voltage supplied to the armature of the motor.
the reference voltage, 1. e., the voltage from the
An additional amplifying electric valve 5-13, which
slider 18a to the negative bus 20. Hence, the
is provided with an anode
a cathode 55b, and
armature voltage and the speed of the motor will
a control grid 530, is provided for the purpose of
be approximately proportional to the reference
varying the voltage on the grid 490 so that the 65 voltage tapped off by the slider 18a of the speed
speed of the motor IE} is maintained constant at
control potentiometer.
a preset value which is correlated with the posi
The voltage selected by the position of the
tion of the slider [8a on the speed controlling
slider [8a is a portion of the constant voltage
potentiometer 58, In other words, the electric
across the glow tube 48 and is therefore substan
valve 58 serves as a connecting and amplifying 70 tially constant. As the slider [8a is moved from
link between the armature speed controlling
position 0 to position 5, the preselected speed
potentiometer l3 and the electric valve 49 which
levels are progressively increased. When the
controls the saturation of the armature saturable
slider is at position 5, the maximum voltage can
reactor 36, and hence, controls the armature,
[be impressed on the armature of the motor.
voltage and speed of they motor £0. The grid 490 75
For the purpose of varying the saturating cur
2,404,641
7
rent of the ?eld saturable reactor 35, a pair of
electric valves 54 and 55 corresponding, respec
tively, in function to the valves 49 and 55 of the
armature control, is provided. The electric valve
54 has an anode 54a, a cathode 54b, and a, con
trol grid 55c; and similarly, the valve 55 has an
anode 55a, a cathode 55b, and a grid 55c. In the
8
in such a manner as to limit the armature cure
rent to the desired value. These means are il
lustrated as comprising the anode current trans
former 21, the control ampli?er valves 51 and 58
Cl and the double diode rectifying electric valve 59.
As shown, the two primary windings 21a and 21b
of the anode current transformer are connected
in series with the anode circuits of each of the
control of the ?eld current, the voltage across
armature thyratron valves, and this transformer
the shunt ?eld winding lllb is utilized as an in
dication of ?eld current. The connections and 10 is polarized in such a manner that when one of
the armature thyratrons conducts, the flux in
operation of the valves 55 and 55 are similar to
the
core is in one direction and when the other
the connections and operation of the valves 49
thyratron conducts, the flux is reversed. As a re
and 55 of the armature control. The electric
sult, an A.-C. voltage is induced across the sec
valves 54 and 55 operate to compare the voltage
across the ?eld winding lob, or a selectable por 15 ondary winding 21c and the magnitude of this
induced voltage is determined for a given Value
tion thereof, with a reference voltage Which‘ is de
rived from the voltage of the glow tube 48 by
means of the slider position on the ?eld control
potentiometer is which is connected in series
with a rheostat 55 across the glow tube 48. The
difference between the signal voltage derived
from the ?eld winding and the reference voltage
derived from the glow tube 58 is impressed on
the grid cathode circuit of the valve 55in such a
1
of primary current by the resistance load con
nected to the secondary and by the turn ratio be
tween primary and secondary windings. This
alternating voltage is recti?ed by the electric
valve 59 and appears as a direct voltage across
a voltage divider comprising potentiometer re
sistor 60, ?xed resistor 65a, and potentiometer
resistor 53.
The electric valves 51 and 58 are provided with
anodes‘
57a and 58a, cathodes 51b and 58b, and
creases, the conductivity of the valve 55 increases,
grids 51c and 580, respectively. The anode 51a
thereby decreasing the conductivity of the valve
is connected to the junction point between the
54 and the saturation of the ?eld saturable re
sections 5m and 5lb of the voltage divider to
actor 35, thereby to decrease the voltage supplied
to the ?eld winding. Conversely, a decrease in 30' which the grid of valve 59 is connected, and the
cathode 51b of valve 57 is connected to the point
the voltage across the ?eld winding has the effect
dla to which the cathode ildb of valve 59 is con
of decreasing the conductivity of the valve 55,
nected. The anode 53a is connected to the con~
thereby increasing the conductivity of the valve
ductor GI and the cathode 58b is'conn'ected to the
54 and increasing the ?eld voltage.
manner that if the voltage across the ?eld in
The armature speed control potentiometer l8 “
and the ?eld weakening control potentiometer
i9 are preferably combined on a common shaft
with the resistance portions l8 and l9 arranged
circumferentially and with the sliders so oriented
that with the speed control knob in the zero posi
tion, which may be assumed to be the full coun~
terclockwise position, the sliders Ilia and 59a will
also be in the zero position. Thus, when the
speed control knob is turned in a clockwise direc~
tion fro-m the zero position, the slider Eda of the
armature voltage potentiometer taps oil an in
creasing portion of the reference voltage of valve
45, but the slider Illa of the ?eld weakening
potentiometer slides along the contact strip I91)
and therefore taps off the full voltage of the tube
58 which corresponds to a condition of full ?eld
excitation. However, when the control knob
passes position 5, the slider of the armature speed
control potentiometer slides on the contact strip
:
58b so that it taps oif the full voltage of the tube
48 corresponding to full armature excitation, but
the slider l9a of the ?eld weakening potentiom
eter begins to tap oil decreasing portions of the
voltage across the tube 48 so that the ?eld is
progressively weakened as the movement of the 60.
control knob in a clockwise direction continues.
In the extreme clockwise position, which. is posi~
tion 9 on the dial, the armature thyratrons l5
and it are supplying rated voltage to the arma
ture, and the ?eld thyratrons l3 and M are sup
plying the minimum voltage to the ?eld winding
151).
Therefore, the motor rotates at maximum
speed.
For the purpose of limiting the armature cur
rent to a maximum permissible value, means are
provided for comparing a signal voltage derived
from the anode current of the armature thyra
trons with a reference voltage and utilizing the
difference of these signal and reference voltages
to control both the armature and ?eld thyratrons
grid 540 of the ?eld control valve 54 which, as
shown, is connected to the junction point be
tween the resistance sections 52b and 620 of a
voltage divider comprising the resistance sec
tions 62a, 62b and 520 connected across the D.-C.
control system buses 5i and 28. The potential
at the junction of resistance sections 62b and 520
when valve 55 is regulating the ?eld voltage, is
such that the potential of the cathode 58b is
slightly more negative than the potential of
cathode 511).
When small amounts of current flow in the
armature circuit, the voltage developed across the
secondary of the current transformer 21c and the
voltage recti?ed by the valve 59 will be so small
that the portion which is utilized as a signal
voltage, 1. e., the voltage between the slider 60b
and the negative bus 20 is substantially less than
the voltage across the valve 43, and consequent
ly, the grids of the valves 51 and 58 which are
connected to slider 65b are very much negative
With respect to their cathodes which are con
nected to the conductor 41a and to the junction
point between the resistance sections 6% and
620, respectively. An increase of armature cur
rent causes the voltage across the secondary of
the current transformer 27 to increase, and the
voltage recti?ed by the valve 59 increases cor
respondingly so that the voltage between the
slider 55b and the negative bus 20 ultimately
reaches a value approximately equal to the volt
age across the valve 48, and the negative grid
voltages of valves 5'! and 53 are reduced to the
value at which these valves begin to conduct cur
rent.
When valve 51 conducts current, it has the
same e?ect as if Valve 55 were conducting cur
rent, which is to decrease the current conducted
by valve 49 and thereby decrease the voltage sup
plied to the armature.
The operation of valve 58 is slightly different
2,404,641
10
This preconditioning circuit connects the grid 510
in that its cathode is connected to the grid cir
of control valve 51 to the junction point 61a of
cuit of the valve 54 instead of to the cathode of
resistors 61 and 6B which constitute a voltage di
valve 41, and its anode is connected to the posi
vider connected between the positive side of the
tive bus 61. When the grid of valve 58 is made
standard voltage, bus BI, and the positive side of
su?iciently less negative to cause current to ?ow
the output voltage of the armature thyratrons I 5
in the anode circuit, the e?ect of current flow
and I5. Included in this circuit are the normally
through valve 58 is to make more positive the po
closed interlock contacts 55a and Bla of reversing
tential of the junction point of the resistors
contactors 30 and 3!, respectively, This precon
52b and 520 to which the grid 540 of valve 54
is connected. This has the effect of increasing 10 ditioning circuit is effective, therefore, only when
both reversing contactors are dropped out as dur
the conductivity of valve 54 with the result that
ing a reversal operation, or when the motor is at
the ?eld of the motor [0 is strengthened, if it
rest or is being dynamically braked to rest.
has been in a ?eld weakened condition. Since
The point 571a on the voltage divider is selected
the cathode 58b is more negative than the oath
so
that at the instant of reconnection of the
ode 5'lb of valve 51 for low values of armature 15
armature to the thyratrons I5 and I6 during a
current, the valve 54 will be controlled slightly
reversal operation, the phase of the grid voltage
ahead of the valve 49 as the armature current
of the thyratrons is retarded to a point such that
increases, with the result that the ?eld will be
the armature current will not exceed a predeter
strengthened before the armature voltage is de
approximately full load
creased. To provide for a range of adjustment, 20 mined safe value, such
current.
The
time
required
for the precondition
the resistor 59 is made in the form of a poten
ing circuit to effect the retardation usually ex
tiometer.
ceeds the time required for the reversing con
When a motor is operated at rated armature
tactors to reverse the armature connections to
Voltage and at maximum rated ?eld current and
is carrying rated full load, it is said to be operat 25 the thyratrons. For the purpose of preventing
the reversing contactors 38 and 3| from com~
ing at base speed. If the motor I0 is being oper
pleting the reversing of the armature connections
ated in the ?eld weakened range, e. g, three times
to the thyratrons before the preconditioning
base speed, and if then the speed controlling
operation is suf?ciently complete, a suitable time
potentiometers I8 and [9 are suddenly changed
delay device such as the relay ‘i0 is provided.
to a position of lower speed, c. g., one-half base
This relay has normally open contacts 10a in
speed, the control would function to decrease the
cluded in circuit with the operating coils 30c
voltage supplied by the armature thyratrons l5
and 3lc of the reversing contactors 35 and 3!,
and I6 and to increase the voltage supplied to the
respectively, and the operating coil ‘Nb of the re
?eld winding by the ?eld thyratrons i3 and 14, as
lay ‘h'! is included in series with normally closed
a result of the action of the electric valves 49 and
contacts 301) and 3!!) of the reversing contactors
50, and 54 and 55. With the motor running at
30 and 3!, respectively. As a result of this inter
three times base speed and full ?eld applied as
connection, neither of the reversing contactors
quickly as the time constant of the magnetic cir
3i) and 3| can be reclosecl during the time fol
cuit will permit, the tendency is for the armature
countervoltage to increase to a value which is 40 lowing its dropout required for relay ‘H! to pick up.
Another conditioning circuit is completed by an
approximately three times full terminal voltage,
electric valve ll of which the anode ‘Ha is con
i. e., 750 volts in the case of a 250-volt motor. To
nected to the conductor 41a and thus to the oath
prevent such an undesirable increase in the ar
ode 57b of valve 51, and the cathode 'Hb is con
mature voltage, an additional electric valve 54 is
provided. This valve is provided with an anode 45 nected to the grid 510 of valve 51. The function
of valve ‘H is to prevent the grid 510 from becom
54a, a cathode 54b, and a grid 640. The anode
ing excessively negative at light motor loads and
54a of this valve is connected to the junction
delaying the response of the current limit
point of the resistors 52a and 62b of the voltage
control
to sudden increases in the armature cur_
divider to which the grid 540 of Valve 54 is con
nected, and the cathode 64b of valve 64 is con 50 rent.
In order to facilitate motor reversal at ?eld
nected to the conductor 47a, The grid 640 of
weakened speeds, means are provided to main
valve 84 is connected to the junction point 55a of
tain the previous strength of the ?eld during the
two resistors 55 and 55 which, together with the
interval in which both reversing contactors are
potentiometer 53, constitute a voltage divider
connected across the armature of the motor H). 55 open during the reversal period and to provide
full ?eld strength for starting the motor from
As thus connected, this valve 64 measures a ?xed
rest. To this end, an additional control relay 1?.
portion of the armature voltage, i. e., a portion
is provided. This relay has a normally closed
between the junction point 55a and the negative
contact 12a included in circuits between the
bus 25, and when this portion exceeds the voltage
drop across the reference voltage valve 48, the 60 cathode 55b of ?eld control valve 55 and con
ductor 41a, and a normally open contact 12?) be
valve 54 becomes conducting, thereby to increase
tween cathode 55b and slider l9a of the ?eld con
the voltage drop across the resistor 52a and de
trol potentiometer IS. The relay 12 is also pro
crease the potential of the grid 540 of valve 54, to
vided with normally open contacts 120 which,
prevent the saturation of the saturable reactor
36 which controls the ?eld thyratrons l3 and M. 65 when the relay is picked up, complete a sealing-in
circuit.
The action of valve 64 upon valve 54 is very simi
If the strength of the motor ?eld is increased
lar to the action of valve 55 except that the valve
too rapidly following the reconnection of the
54 receives its voltage signal from the armature
armature to the supply thyratrons [5, IS in a
circuit, whereas the valve 55 receives its voltage
reversal from a ?eld-weakened speed, success
signal from the ?eld circuit.
70 ful inverter operation may be defeated. To pre
In order to promote a rapid and smooth transi
' tion from recti?er operation to inverter opera
tion of armature thyratrons I5 and I5 during the
reversal period. a preconditioning circuit is pro
vent this too rapid strengthening of the motor
?eld by the action of valve 58, which operates on
valve 54 at high armature currents, a reverse
This reverse
vided for controlling the armature thyratrons. 75 “snubbing” circuit is provided.
2,404,641
11
12
“snubbing” circuit comprises an electric valve
713 having its anode ‘53a connected to the grid
54a of the valve 54 and having its cathode 13b
connected to the junction point Ma of two resis
tors ‘M and ‘I5 which, together with resistor 69,
8 l, the low voltage control transformer 42 is ener
gized and the full wave recti?er valve 43 sup
plies a recti?ed voltage to the buses GI and 20
which voltage is maintained constant by the
standard voltage regulator valves 4'! and 48.
Since the directional contactors 3i} anad 3! are
open, the operating coil 10b of control relay
constitute a voltage divider connected across
the standard voltage valve 48. The junction
point 75a of the resistors 15 and 69 is connected
to the common point ‘I6 of'the two reversing con
tactors by means of a conductor ‘H’.
The com
‘it! is connected across the standard voltage con~
ductors 6! and 20 through the normally closed
10 contacts 39?) and 3l-b of the directional contac
tors. Responsively to energization, relay 10 picks
mon point 16 of the two reversing contactors is
up and closes its normally open contacts 10a
connected to the positive side 28 of the armature
and 700. At this point in the operation, the
supply. The grid 130 of valve 13 is connected to
the negative bus 24] and consequently, except
grid 510 of the current limit control valve 51 is
connected through conductor 82 and the normal
when the armature is rotating in a direction op
posite to that which corresponds to whichever
1y closed contacts 30a and am of the reversing
contactors to the point'iila on the voltage di
of the two directional contactors is closed, the
grid 130 is so negative with respect to its cathode
viders El, 68 such that the current conducted by
the valve 57 produces an IR drop across the re
that valve 13 is non-conducting and has no e?ect
on valve 54 which directly controls the ?eld sat 20 sistor section cm which lowers the voltage on
' the grid 490 of valve 29 to a value which regu
urable reactor 36.
lates the voltage output of the armature thyra
During the interval in which both directional
contactors are dropped out during a reversal
trons I5 and I6 to a low value, c. g. 50 volts, such
that when a directional contactor is subsequent
from a given speed in one direction to the same
ly closed, the current supplied to the armature
given speed in the reverse direction, the ?eld
Illa of the motor‘ is limited to approximately
strength remains constant at the value set on
full load value.
the ?eld potentiometer I9. However, when re
versing from a high speed in one direction to a
Also at this point in the operation, the cathode
relatively lower speed in the opposite direction,
55b of control valve 55 is connected through the
the slider l9a of the ?eld potentiometer I9 is 30 normally closed contacts ‘5211 of relay ‘I2 and con
moved to a lower speed position in which cur
ductor 83 to the conductor Ma of the standard
rent conducted by valve 55 is decreased. This
voltage source, with the result that the cathode
55b is so positive with respect to its grid that the
tends to increase the current conducted by valve
valve-55 is nearly nonconducting. As pointed
54 thereby to strengthen the motor ?eld to such
an extent that upon completing the reversal of
out in the foregoing, this causes the valve 54 to
be nearly fully conducting, thereby to saturate
the armature connections, the voltage generated
by the motor is so high as to interfere with suc
the ?eld reactor 36 and advance the phase of
the grid voltage of the ?eld thyratrons ! 3 and
cessful inverter operation. To overcome this
tendency of the control to strengthen the ?elds
M so that these thyratrons supply full rated cur
during the operation of the directional contactors 40 rent to the shunt field winding Iiib, thereby to
for a reversal from a higher to a lower speed,
provide maximum starting torque. Since the
?eld current flows through the operating coil 26a
an additional electric valve ‘I8 is provided for
supplying a voltage to control valve 64 in such
of the ?eld protective relay 2%, this relay picks
a, manner as to prevent valve 54 from respond
up and closes its normally open contacts 26b. In
ing to the potentiometer IE! to strengthen the
closing, contacts 26b complete a circuit for the
motor ?eld. Valve ‘I8 is illustrated as a double
operating coil Eliia of a relay 85 which is con
diode valve having anodes 18a and 1% connected
trolled by the stop push button switch M to
to opposite terminals of the dynamic braking
effect the stopping operation of the motor. This
relay is known as the stop relay. The energizing
resistor ‘I9 which, when the directional contac
tors 30 and 3| are dropped out, is connected 50 circuit is traced from the low voltage tap I20
across the armature terminals by the normally
through conductor 8%, operating coil of stop
closed contacts 30d and Bid of the directional
relay, normally closed contacts 12d of relay ‘I2,
contactors. The cathode 180 of valve 18-is con
normally closed contacts of stop push button 4|,
nected by means of a conductor 80 to the point
contacts 260 of ?eld protective relay 26 to the
65a of the voltage divider to which the grid 640
low voltage tap I217‘. Responsive to energization,
of the valve 64 is connected.
the stop relay 85 picks up and closes its normally
With the foregoing understanding of the ele
open contacts 852) and opens its normally closed
ments and their organization, the operation of
contacts 8510, 85d and 856. Contacts 85?) in
the system itself will readily be understood from
closing complete a holding circuit in parallel with
the following detailed description.
contacts 72d of relay "i2.
To place the system in condition for opera
Assuming that it is desired to operate the
tion, the switch 8| is closed to connect the pri
motor at a speed above base speed within the
mary winding of the supply transformer I2 to
?eld weakened range, the knob of the speed
the supply source II. As a result, the operat
controlling potentiometer is moved until the
ing coil of the time delay relay 25 is energized
sliders 18a and I911 are in positions between 5
and after an interval of time which is deter
and 9 which correspond to the desired operating
mined by. the setting of its time delay device, and
speed. This has no immediate e?ect upon the
which is su?icient to provide for initial heating
thyratron valves I3, 54, I5, and I5, since at this
of the cathodes of the electric valves, the time
point in the operation, these valves are under
delay relay 25 closes its normally open con-l
the control of the preconditioning circuit.
tacts 25a to complete the ?eld circuit from the
To start the motor in the forward direction,
cathodes of the ?eld thyratrons I3 and I4 through
the forward push-button switch 39 is depressed
the operating coil 26a of the ?eld loss protective
to bridge its normally open contacts 39a, thereby
relay 26 and the ?eld winding I?b to the nega
to complete an energizing circuit for the oper
tive bus 20. As a result of the closing of switch
ating coil of the forward contactor 30. This cir
13
cult is traced from the low voltage tap
the supply transformer, through contacts
relay 10, contacts 39a of the forward
button switch, normally closed contacts
reverse push-button switch, normally
2,404,641
lZb of
10a of
push
of the
closed
14
to supply a current to the armature which is
many times full load value. However, the cur~
rent limiting control acting through valves 51 and
58 decreases the output of the armature thyra—
trons to the value determined by the setting of
the slider of the current limiting potentiometer
60. If, as assumed, the ?eld control has been set
for a speed in the ?eld weakened range, then the
contacts 86a of a reverse control relay, normally
closed interlock contacts of reverse contactor 3|,
operating coil of forward contactor 39 to the low
voltage tap l 20. In response to energization, the
current limit control acting through valve 53
forward contactor 3i! closes its main contacts 30f 10 will tend to maintain full ?eld until the armature
and 30g and its interlock contacts 30h and 301'
current tends to fall below the present limiting
and opens its interlock contacts 30a, 30b, 30c,
value. Thus, during acceleration to a present
30d and 397'. rl‘he main contacts 30f and 30g in
speed within the ?eld weakened range, the arma
closing complete the armature circuit from the
ture voltage is first allowed to build up at a rate
positive terminal 28 of the thyratrons through
determined by the load on the motor and by the
conductor 29, series ?eld winding lDc, contacts
value of the armature current which has been
30g, heating element 32a of the overload relay,
set upon the current limiting potentiometer 61!
armature [0a, and contacts 35)‘ to the negative
until full armature voltage is reached. At this
bus 20. At the instant of the closing of forward
point, there is a tendency for the armature cur
directional contactor 33, the armature thyra
rent to decrease. However, this tendency will
trons l5 and I5 are phased to supply approxi
make the grid voltage of the valve 58 more nega
mately full load current to the armature, owing
tive, thereby decreasing the conductivity of the
to the connection of the grid 510 of control valve
valve and making the voltage of the grid of valve
51 to point 61a of the voltage divider 61, 68 be
54 more negative, with the result that the ?eld
tween bus 6! of the standard voltage source and
thyratrons l3 and I 4 will supply less current to
the positive side 11 of the armature thyratrons l5
the ?eld. This results in maintaining the arma
and 16,. However, the simultaneous opening of
ture current substantially constant until the pre
interlock contacts 32a interrupts this precondi~
set ?eld weakened speed is reached, at which
tioning circuit so that for the remainder of the
point the armature current will drop to that value
accelerating period, the current supplied by
which is necessary to drive the load. Since the
thyratrons I5 andv Hi to the armature is con
system operates to maintain the maximum per
trolled by the setting of the slider 60b of the
missible value of armature current during the
current limit potentiometer to which the grid
acceleration, the load is accelerated to the pre
5110 is connected. Interlock contacts 3th in
selected speed in the minimum possible time con
closing complete an energizing circuit for the 35 sistent with the armature current limit at which
operating coil of control relay 12. This circuit
the control is set to operate.
is traced from low voltage tap [20 through con
At a predetermined low armature voltage, the
ductor 84 and the operating coil of relay ‘[2,
control valve 81 which is connected across the
contacts 30h of the forward contactor, contacts
armature in series with the operating coil 88a
39a of the forward push button, contacts 10a of 40 of relay 88 becomes conducting. Responsively
control relay iii, and thence to the low voltage
to energization, relay 88 picks up and closes its
tap l2b. In response to energization, relay ‘[2
contacts 88b in parallel with the normally closed
picks up and closes its contacts 12c to complete
contacts 86b and 89b of the reverse and forward
a holding circuit for the operating coil 300 of
control relays 86 and 89, respectively. Once
the forward contactor and a sealing-in circuit 45 picked up, relay 88 remains picked up until the
for its own operating coil in parallel with the
positive component of armature voltage is sub
contacts 39a of the forward push-button switch
sequently reduced approximately to zero. Nega~
which now may be released. Relay 12 in picking
tive components of armature voltage introduced
up opens its normally closed contacts 12a to in
by reversals will not cause the relay to drop out
terrupt the ?eld preconditioning circuit and
since they are blocked by the rectifying action
closes its contacts 12b to connect the cathode 55b
of valve 81.
of ?eld control valve 55 to the slider |9a of the
If it is desired to operate the motor in the re
preset ?eld potentiometer 29, to provide for
verse direction at the same speed, it is only neces
weakening the ?eld to the value preset on the
sary to depress the reverse push button 49 to open
potentiometer 19 as the armature current de 55 the normally closed contacts Md and close the
creases near the end of the acceleration. Fol
normally open contacts 4231). Contacts 49a in
lowing the interruption of the armature precon
opening interrupt the energizing circuit for the
ditioning circuit by the opening of interlock con
operating coil 3G0 of the forward contactor which,
tacts 36a, the armature current builds up at a
responsively to deenergization, drops out to the
rate partially determined by the inductance of
open position in which it is illustrated. Contacts
the D.—C. winding of the armature saturable re
30]‘ and 39g in opening disconnect the armature
actor 34. Contacts 3% in opening interrupt the
from the thyratrons l5 and i5, and contact 3001
energizing circuit for the operating coil 10b of
in closing completes the connection of the dy
control relay ‘H! which, in response to deenergiza
namic braking resistor 79 across the armature
tion, drops out and opens its normally open
terminals, thereby to produce a dynamic braking
contacts 19c.
torque which is effective in decelerating the
As a result of the completion of the armature
motor. Contacts 353a in closing again complete
circuit, the motor begins to accelerate to a speed
the preconditioning circuit between the grid 510
determined by the setting of the speed control
of the armature control valve 57 and the point
potentiometer. During acceleration, before the
61a on the voltage divider between the standard
armature oountervoltage has built up to a value
voltage bus 6! and the positive side of the out
corresponding to the preset speed which it is de—
put voltage of the supply valve apparatus, line ‘H.
sired to maintain, the phase of the grid voltage
Whenever the preconditioning circuit is made ef
of the armature thyratrons tends to be fully ad
fective by the reversing contactors being deener
vanced and hence, the armature thyratrons tend
gized, valve 51 operates in conjunction with Valve
2,404,641
15
49 to control the output voltage of thyratrons I5
and 16 in much the same manner that valve 59
operates when the thyratrons l5 and it are con»
16
dynamic braking circuit, and main contacts 3h‘
and My in closing connect the armature Illa to
the thyratrons :5 and is for the reverse direction
of rotation, and since the armature is still rotat
nected to the armature of the motor. An increase
ing in the forward direction, inverter operation
in the output voltage of thyratron-s i5 and is C1 ensues. The opening of interlock contacts 312)
makes the voltage of junction ?lo of resistors 6'1
interrupts the energizing circuit for the operating
and 68 less negative with respect to the cathode
coil of control relay ‘it which responsively to de
51b of valve 51 which increases the conductivity
energization, drops out and opens its contacts ‘Ilia
of valve 57, thereby decreasing the conductivity of
and 7&0. Simultaneously, interlock contacts 31a
10
valve 49 and the saturation of the saturable re
in openingr interrupt the preconditioning circuit
actor which decreases the output voltage. Con
between the grid 570 of control valve 51 and the
versely, a decrease in the output voltage of thyra
point Kilo on the voltage divider across the stand
trons l5 and i6 makes the voltage of junction
ard voltage source. The control of the armature
point 61a more negative With respect to the cath
thyratrons I5 and it during the inverter opera
15
ode Slb of valve 5?. This decreases the conduc
tion is now under the control of the current limit
tivity of valve 51 thereby increasing the conduc
potentiometer 60 to the slider Ellb of which the
tivity of valve 49 and the saturation of the
grid Bic of the current limit control valve 5'! is
saturable reactor with the result that the output
connected. Thus, the armature current during
' voltage of the thyratron-s is correspondingly in
inverter operation is limited to the value which
creased. Since during the preconditioning period
is preset upon the current limit potentiometer 60.
the only load on thyratrons l5 and i6 is a re
The closing of main contacts Sig of the re
sistance load consisting of resistor 62-) and the
verse contactor 3i connects the lower armature
various resistance voltage dividers, controlling the
terminal through conductor "H to the cathode
output voltage at a constant low value means
13b of the valve '13 in the reverse snubbing cir
holding the phase angle of the thyratron grid 25 cuit. Since the armature Illa is still rotating in
voltage at a de?nite retarded angle, which may
the forward direction, the polarity of the coun
be predetermined by proper selection of the cir
tervoltage is unchanged and the lower armature
cuit components. Thus, the phase of the grid
terminal is therefore negative, and this negative
voltage of the armature thyratron-s i5 and i6 is
voltage is applied to point 15a between which
regulated to a point that will permit armature 30 and line did is connected a voltage divider con
current in the order of full load current to ?ow
sisting of resistors ‘M and 15. The values of re
at the ?rst instant after the reverse contactor 3!
sistors ‘M and ‘it’: are so chosen that the poten
131855 up to initiate inverter action. Since the
tial of the cathode 13b of valve '13, which is con
sealing-in circuit of the control relay ‘i2 is inde
nected to their junction point ‘Ma, reaches the
35
pendent of the contacts of the reversing con
potential of the negative conductor 2i] at the same
tactors, relay ‘i2 remains picked up during this
time that the lower terminal of the armature at
reversing period and consequently the cathode
tains its maximum permissible negative value
55b of ?eld control valve
remains connected
with respect to the negative bus 26. The applica
to the slider i900 of the ?eld control potentiom~
tion of negative voltage to the cathode 13b ren
eter, and thus there is no tendency for the control 40 ders the valve 113 conducting and the resultant
to strengthen the ?eld prior to the reclosing of
voltage drop across the resistor Si, lowers the
the reversing contactor-s. Thus, the countervolt~
voltage of the grid 540 of valve 51!, thereby de
age of the armature and the conductivity of the
creasing its conductivity and weakening the ?eld
armature thyratrons i5 and iii are both regu
of the motor. As a result, the armature counter
lated to values which will be favorable to success
voltage is kept below the safe limit for inverter
i'ul inverter operation when the reverse contactor
operation and at the same time the ?eld strength
Si is closed.
is maintained as high as possible, consistent with
The closing of contacts Sill) completes an en~
successful inverter operation, to obtain strong re
ergizing circuit for the operating coil ill!) of con
versal torque. Thus, the tendency of the field
trol relay ‘ill which, responsively to energization,
current limit control valve 58 to strengthen the
picks up after a short time delay and closes its
?eld as the armature current approaches the
contacts We to complete an energizing circuit for
preset current limit is counteracted by the re
the operating coil 3 lc of the reverse contactor ii i.
verse snubbing circuit valve ‘I3 during inverter
This circuit is traced from the conductor 35,
operation.
through coil 35c, normally closed contacts tile
As a result of the inverter operation, a strong
of the forward contactor, normally closed con
regenerative braking torque is set up, and the
tacts 89a of forward control relay 89, normally
speed of the armature is rapidly decelerated to
closed contacts 3% of the forward push button,
rest. As the armature approaches zero speed, the
contacts diib of the reverse push button, and
countervoltage decreases and consequently, the
thence by the circuit previously traced to low 60 voltage of the cathode 73?) again becomes posi
voltage tap l2c of the supply transformer. The
tive and renders the valve 13 nonconducting so
relay ll! has sufficient time delay in its operation
that during the ensuing acceleration in the re
to delay the closing of the reverse contactor 3i
verse direction, the field control valve 54 is con—
until the retardation of the phase of the grid
trolled
by the field potentiometer I9 and the
voltage of armature thyratrons l5 and it is sub—
current limit potentiometer (ill acting through the
stantially completed.
control valve 58.
Responsively to energization, reverse contactor
A reversal of the operation of the motor from
‘Jl picks up and opens itsvnormally closed inter
a
high ?eld weakened speed to a lower speed is
lock contacts Slot, 3H), std, 3H6 and 3M‘, and
closes its main contacts 3i)‘ and Big and its in 70 accomplished by depressing the reverse push but
ton M3 and rotating the knob of the preset speed
terlock contacts 3th and 3h; Contacts 3th. in
control potentiometers l8 and 19 to a position
closing complete a holding circuit for the op
corresponding to the desired speed for the reverse
erating coil Bic independent of the contacts of
.direction of rotation. In other words, the slider
the reverse push button which may now be re
lea of the ?eld potentiometer i9 is moved into
leased. Contacts 3ld in. opening interrupt the
17
2,404,641
engagement with the contact strip I92), with the
result that the voltage of the cathode 55b of the
valve 55 becomes so positive with respect to the
grid voltage that the valve 55 becomes noncon
ducting and the valve 54 tends to become fully
conducting. If the valve 54 were permitted to
become fully conducting, the ?eld saturable re
actor 35 would be fully saturated and the ?eld
thyratrons l 3 and I4 would supply maximum cur
rent to the shunt ?eld winding IIib. In the pe~ 10
riod following the closing of the reverse con
tactor 3I, this strengthening of the motor ?eld
is prevented by the action of the valve ‘I3 in the
18
ward contactor and coil of reverse contactor to
low voltage tap I20. In response to energization,
reverse contactor picks up and closes its main
contacts 3!)‘ and Mg to connect the armature to
the thyratrons I5 and I6 for the reverse opera
tion. However, at this point the armature is still
rotating in the forward direction and consequent
ly, inverter action ensues, as explained in the
foregoing in connection with the reversal opera
tion. The inverter operation produces a strong
braking torque which rapidly decelerates the mo
tor.
The reverse contactor in picking up ener
gizes control relay at. The circuit is traced from
reverse snubbing circuit as described in the fore
low voltage tap 120 through coil 90a, contacts
going. However, in the interval in which both 15 ‘IE0 of relay 75, contacts 3Ii of reverse contactor,
forward and reverse contactors 3B and SI are
normally closed contacts 850 of stop relay to the
dropped out preceding the closing of the reverse
low voltage tap I217. Responsively to energiza
contactor, the valve 13 is not connected to the
tion, relay 9t picks up and closes its contacts 901)
armature I Get and is therefore inactive. However,
to complete a sealing-in circuit in parallel with
the strengthening of the ?eld during this period 20 contacts ‘Hi0 and 3| 2', and also closes its contacts
in which both forward and reverse contactors are
580 and opens its normally closed contacts 90d.
dropped out is prevented by action of the valve
In the closed position of the reverse contactor,
‘I8, the anodes of which are connected through
contacts 3129 are open and deenergize relay 10
normally closed contacts 30d and 3Id, respec
which drops out responsively to deenergization.
tively, to opposite terminals of the armature dur
Contacts 99d in opening disconnect the cathode
ing the period when both reversing contactors are
50b of the armature control valve 59 from the
slider I8a of the preset speed potentiometer I8,
open. During this period, the valve 78 supplies
a voltage to the junction point 65a of the resistors
and contacts 900 in closing connect ‘the cathode
50b to the negative bus 20. This is equivalent
65 and 66 to which the grid 640 of Valve 54 is con
nected. As a result, the valve 64 is rendered 30 to setting the slider l8a at the zero speed position,
conducting, thereby producing a voltage drop
and if the grid voltage, which is a measure of the
armature voltage, remained unchanged at this
point the valve 50 would become fully conducting
with the result that the armature thyratrons I5
potentiometer I9 to strengthen the ?eld during 35 and It would be rendered nonconducting before
this period.
the motor had been braked to rest. However,
when the reverse contactor 3| closed, the grid
As the forward speed of the motor approaches
across the resistor 62a which lowers the voltage
of the grid 540 of the ?eld control valve 54 su?i
ciently to counteract the tendency of the preset
zero, the inverter action ceases and the motor is
accelerated in the reverse direction in a manner
similar to the forward acceleration described in
the foregoing.
500 of valve 50, which was previously connected
to the positive terminal of the armature, is now
connected to the negative terminal and the con
duction of valve 50 is maintained at a low value
with the result that the grid voltages of thyra
trons I5 and I6 are controlled to maintain the
Assuming the motor is operating in the for
ward direction, and that it is desired to stop the
inverter operation, thereby to continue the rapid
motor: The stop push-button switch M is de
pressed to open its normally closed contacts there 45 deceleration of the motor. As the deceleration
continues, the negative grid voltage of valve 50
by to deenergize the stop relay 85. Responsively
is correspondingly decreased so that at zero speed
to deenergization, the stop relay drops out and
the thyratrons I5 and I5 are phased off and
opens its normally open contacts 85b and closes
cease conducting.
its normally closed contacts 85c, 85d, and 85e.
As soon as the thyratrons I 5 and I6 are phased
Since relay ‘I2 is picked up and will remain picked 50
off, the valve 87 ceases to conduct, thereby deen
up until the motor comes to rest, the stop relay
ergizing relay 88. Responsively to deenergization,
cannot be picked up again until the motor comes
relay 38 drops out and deenergizes relay ‘I2 which
to rest. Contacts 85d in closing complete an en
thereupon drops out and opens its contacts 12b
ergizing circuit for the operating coil of the re
verse relay 86 which extends from low voltage tap 55 and ‘I20 and closes its contacts 12a and 12d. Con
tacts ‘I20 in opening deenergize the reverse con
I20 through coil of reverse relay 85, normally
tactor 3| and the reverse relay 86. Responsively
closed contacts 890 of forward relay 89, normally
to deenergization, the reverse contactor drops out
closed contacts 3Iy‘ of reverse contactor 3I, con
to disconnect the armature from the thyratrons
tacts 85d of stop relay, contacts 120 of relay ‘I2,
I5, I 6. Contacts 1201 in closing complete the ener
contacts 8% of relay 88 to low voltage tap I2b.
gizing circuit for the stop relay 85, which picks
Responsively to energization, reverse relay 85
up to close its contacts 85b and to open its con
picks up and opens its normally closed contacts
tacts 85c, 85d, and 85e. Contacts 85b in closing
86a, 86b, and 860 and closes its normally open
complete a sealing-in circuit, and contacts 850
contacts 85d and 86e. Contacts 86min opening
in opening deenergize the relay 9B which drops
deenergize the forward contactor which there
upon drops out and disconnects the armature 1 out to open contacts 90b and 950 and to close
contacts 95d, thereby leaving the control in a
from the thyratrons I5, I 6. As a result, the relay
reset condition.
‘I0 is again energized over the circuit previously
Although in accordance with the provisions of
traced and picked up after a small delay to close
* its contacts 10a and lilo. This completes an ener TI) the patent statutes this invention is described
as embodied in concrete form and the principle
gizing circuit for the reverse contactor which is
thereof has been explained, together with the
traced from low Voltage tap I21) through contacts
best mode in which it is now contemplated apply
70a and 86e, normally closed contacts of forward
ing that principle, it will be understood that al
push button, normally closed contacts 85a of for
terations
and modi?cations will readily suggest
ward relay, normally closed contacts 30c of for 75
themselves to persons skilled in the art Without
2,404,641
l9
departing from the true spirit of this invention
or from the scope of the annexed claims.
What we claim as new and desire to secure by
Letters Patent of the United States is:
1. Control apparatus for an electric motor com
prising in combination, means for controlling the
supply of direct current to an electric motor com
prising electric valve apparatus provided with a
20
to said motor to control the direction of rotation,
and means responsive to said switching means
when said switching means is open for directly
connecting the grid of said auxiliary valve to the
output circuit of said electric valve means to re
tard said ?ring point to limit the current sup
plied to said motor before said current limiting
means becomes fully eiiective, and relay means
operatively associated with said reversing switch
control grid, a standard voltage source, means for
ing means for preventing the reversal operation
10
presetting an operating speed for said motor com
of said reversing switching means for the period
prising means for deriving a predetermined ref
of time required for said retarding means to be
erence voltage from said source, means for pro
come effective.
ducing a signal voltage proportional to the speed
4. A control system for an electric motor com
of said motor, and means responsive to the dif
rerence of said derived voltage and signal voltage 15 prising in combination, ?rst electric valve means
for controlling the supply of direct current to
for varying the conductivity of said valve means
the armature of said motor, additional electric
in accordance with said difference, means for pm
valve means provided with a control grid for con
iting the current supplied to said motor to a
trolling
the supply of direct current to the ?eld
predetermined value comprising a control cir
of said motor, forward and reverse contro1 de
cuit carrying current proportional to the current
vices and reversing switching means contro1led~
supplied to said motor and a control electric valve
thereby in the output circuit of said ?rst valve
connected to control the grid circuit of said valve
means
for controlling the direction of rotation
means and having a grid connected to said con
of said motor, a stop control device for control
trol circuit, reversing switching means in the out
ling the opening and closing of said switching
put circuit of said valve means, and means re 25
means, means responsive to the opening opera
sponsive to said switching means when said
tion of said switching means for controlling said
switching means is open for directly connecting
additional valve means to strengthen the ?eld
the grid of said control valve to the output circuit
of said motor, and means for preventing the
of said valve apparatus to adjust the conductivity
strengthening of said ?eld when said switching
of said valve means for inverter operation in re 30
means is open during a reversal of said motor by
sponse to operation of said switching means to
said reversing switching means.
effect reversal of said motor.
5. A control system for an electric motor com
2. Control apparatus for an electric motor com
prising in combination, a ?rst electric valve means
prising in combination, electric valve means for
for controlling the supply of direct current to
controlling the supply or" direct current to an
the
armature of the motor, additional electric
electric motor, means for limiting the current
valve apparatus provided with a control grid for
supplied to said motor to a predetermined value
controlling the supply of direct current to the
comprising a control circuit carrying current pro
?eld of said motor, forward and reverse control
portional to the armature current of said motor,
devices and directional contactors in the output
a control electric valve for controlling said electric
circuit of said ?rst electric valve means controlled
valve means and having a control grid connect
by said control devices for controlling the po
ed to said control circuit, a standard voltage
larity of the voltage supplied to said armature to
source, switching means in the output circuit of
control the direction of rotation, a stop control
said valve means, means responsive to said switch~
ing means when said switching means is open for 45 device for controlling said contactors to inter
rupt the output circuit of said ?rst electric valve
directly connecting the grid of said control valve
means, an electromagnetic switching device re
to the output circuit of said valve means to ad
sponsive to the closing operation of either of said
just the conductivity of said valve to a predeter
contactors and having a sealing in circuit inde
mined value, and an auxiliary electric valve hav
ing an anode connected to the cathode of said 50 pendent of said contactors for controlling said
additional valve means to maintain the ?eld of
control valve and a cathode connected to the
said motor at its existing strength when said re
grid of said control valve to render said auxiliary
versing contactors are open during a reversal op
valve conducting and thereby limit the negative
eration, and means responsive to stopping of said
voltage applied to the grid of said control valve
motor following an operation of said stop con
55
at low armature current of said motor.
trol device for interrupting said sealing in cir
3. A control system for an electric motor com
cuit to cause said electromagnetic switching de
prising in combination, electric valve means pro
vice to control said additional valve means to
vided with a control grid for controlling the
strengthen the ?eld of said motor.
supply or direct current to an electric motor, a
6. A control system for an electric motor com
standard voltage source, means for presetting an 60
prising in combination, ?rst electric valve means
operating speed for said motor comprising means
for supplying direct current to the armature of
for deriving a predetermined reference voltage
the motor, additional electric valve means for
from said source, means for producing a signal
supplying direct current to the ?eld of said motor,
voltage proportional to the speed of said motor,
reversing switching means for connecting the
and means responsive to the difference of said 65
armature of said motor to said ?rst valve means
derived voltage and signal voltage for varying the
for rotation in either direction, and means re
?ring point of said valve means in accordance
sponsive to the armature voltage of said motor
with said di?erence, means for limiting the cur
following a reversal of the connections of said
rent supplied to said motor to a predetermined
armature to said ?rst valve means for controlling
value comprising an auxiliary electric valve hav
said additional valve means to vary the excitation
ing a grid connected to be responsive to the cur
of said motor to limit the armature voltage of
rent supplied to said motor and having its out—
said motor to a predetermined value.
put circuit connected to control the ?ring point
'7. A control system for an electric motor com
of said valve means, reversing switching means
for selecting the polarity of the voltage supplied 75 prising in combination, ?rst electric valve means
2,404,641
21
22
for supplying direct current to the armature of
the motor, additional electric valve means for
supplying direct current to the ?eld of said motor,
prising in combination, electric valve apparatus
means for controlling said additional valve means
said motor, additional electric valve apparatus
comprising a control valve provided with a con
trol grid and means for supplying a variable
for supplying direct current to the ?eld of said
motor, a speed control device for controlling said
10. A control system for an electric motor com
for supplying direct current to the armature of
control voltage to said grid, reversing switching
additional valve means to vary the excitation of
means for connecting said armature to said valve
said motor ?eld, reversing switching mechanism
for connecting said armature to said ?rst electric
means for rotation in either direction, and means
for limiting the armature voltage of said motor 10 valve means for rotation‘ in either direction, and
to a predetermined value following operation of
means responsive to the armature voltage of said
motor during the period in which the armature is
said switching means to reverse the connection of
said armature to said ?rst valve means compris
disconnected from said ?rst valve means during
a reversing operation for controlling said second
ing a second control valve having an anode,
cathode, and control grid and connections from 15 Valve means to prevent strengthening the ?eld
of said motor by said speed control device in a
the cathode and grid of said second control valve
reversal of said motor from a high speed to a
to said armature and connections from the anode
relatively lower speed.
cathode circuit of said second valve to the grid
11. A control system for an electric motor com
of said ?rst valve to control said ?rst valve to
limit the excitation of said motor ?eld.
20 prising in combination, electric valve apparatus
8. A control system for an electric motor com
for supplying direct current to the armature of
prising in combination, ?rst electric valve means
said motor, additional electric valve apparatus
for supplying direct current to the armature of
for supplying direct current to the ?eld of said
the motor, additional electric valve means for
motor, a dynamic braking resistor, forward and
supplying direct current to the ?eld of said motor, 25 reverse directional contactors for connecting said
means for controlling said additional valve means
armature to said first electric valve means for
rotation in either direction and provided with
normally closed contacts for connecting said
comprising a control valve provided with a con
trol grid and means for supplying a variable con
trol voltage to said grid, reversing switching
means for connecting said armature to said ?rst
valve means for rotation in either direction, and
means for limiting the armature voltage of said
motor to a predetermined value following oper
ation of said switching means to reverse the
connection of said armature to said ?rst valve
means comprising a second control valve having
an anode, cathode, and control grid and con
nections from the cathode of said second control
valve to'the positive terminal of said armature
and from the grid of said control valve to the 40
dynamic braking resistor across said armature
when said armature is disconnected from said
?rst valve means, a speed control device for con
trolling said additional valve means to vary the
excitation of said motor ?eld, and means for
preventing strengthening the ?eld of said motor
when said armature is disconnected from said
?rst valve means during a reversal of said motor
from a high speed to a relatively lower speed com
prising a full wave recti?er valve having a pair
of anodes connected to points on said braking
resistor of opposite polarity and having its cath
negative terminal of said armature during normal
running operation of said motor thereby to main
ode connected to an intermediate point on said
until the reversal of said armature voltage is
control device, means responsive to operation of
75 said stop control device for controlling said re
resistor, a voltage drop device connected in the
tain said second control valve inactive, said re
output circuit of said full wave recti?er, and
versing switching means serving to reverse said
means responsive to the voltage across said volt
grid and cathode connections upon reversal of 45 age drop device for controlling said second valve
means.
the connections from said armature to said ?rst
valve means thereby to render said second con
12. Control apparatus for an electric motor
trol valve conducting While the voltage of said
comprising electric valve apparatus for supplying
armature is reversing and nonconducting when
a recti?ed voltage to the armature of the motor,
the reversal of said armature voltage is com 50 reversing switchingmeans for connecting said
pleted, and a connection from the anode of said
armature to said valve apparatus for rotation in
second control valve to the grid of said ?rst con
either direction, a stop control device, means re
sponsive to operation of said stop control device
trol valve to control said ?rst control valve to
for controlling said reversing switching means to
limit the excitation of said motor during said
reversal operation.
55 reverse the connections of said armature to said
9. A control system for an electric motor com
electric valve apparatus to provide for inverter
operation of said valve apparatus to brake said
prising in combination, ?rst electric valve means
for supplying direct current to the armature of
motor to rest, and means responsive to a prede
termined low speed of said motor to disconnect
said motor, additional electric valve means for
supplying direct current to the ?eld of said 60 said motor from said valve apparatus.
motor, means responsive to armature current for
13. Control apparatus for an electric motor
controlling said additional electric valve means
comprising electric valve apparatus for supplying
to strengthen the ?eld of said motor to limit
a recti?ed voltage to the armature of the motor,
reversing switching means for connecting the
the armature current to a predetermined value,
reversing switching means for connecting said 65 armature of the motor to said electric valve ap
armature to said ?rst valve means for rotation in
paratus for rotation in either direction, means
for producing an adjustable reference voltage,
either direction, and means responsive to the
armature voltage of said motor following a re
means for producing a signal voltage having a
predetermined relationship to the speed of said
versal of the connections of said armature for
counteracting the action of ?eld strengthening 70 motor, means responsive to the difference of said
voltages for controlling said electric valve appa
means thereby to control said additional valve
means to vary the excitation of said ?eld to limit
ratus to effect operation of said motor at a speed
the armature voltage to a predetermined value
corresponding to said reference voltage, a stop
completed.
2,404,641"
23
versing switching means to reverse the connec
tions of said armature to said valve apparatus,
means responsive to operation of said switching
24
speed corresponding to said reference voltage,
a stopping control device, means responsive to
operation of said stopping control device for con
means to adjust said reference voltage for zero
speed of said motor, and means responsive to a
predetermined low speed of said motor for con
trolling said reversing switching mechanism to
trolling said reversing switching means to dis
connect said armature from said valve apparatus.
14. Control apparatus for an electric motor
comprising electric valve apparatus for supply 10
switching device responsive to the reversal oper
ation of said reversing switching means for ad
reverse the connections of said armature to said
electric valve apparatus, an electromagnetic
justing said reference voltage for zero speed, an
electric valve connected to be responsive to the
countervoltage of said motor and an electromag
ing a recti?ed voltage to the armature of said mo
netic switching device controlled thereby for con~
tor, reversing switching means for connecting said
trolling said reversing switching means to dis
armature to said valve apparatus for rotation in
connect .said armature from said electric valve
either direction, a source of adjustable reference
voltage, means for deriving a voltage from the 15 apparatus at a predetermined low speed of said
countervoltage of said motor, means responsive
motor.
HENRY H. LEIGH.
to the difference of said reference voltage and
GORDON E’. WALTER.
said derived voltage for controlling said valve
apparatus to effect operation of said motor at a
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