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Патент USA US2406255

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Aug; 20, 1946. I ,_
P. w. ROBINS-0N
2,406,255
INDUCTION MOTOR CONTROL SYSTEM
Filed March 24, 1945
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Inventor‘:
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Percy W. Robinson,
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Aug. 20, 1946.
2,406,255
P‘. W. ROBINSON
INDUCTION MOTOR CONTROL SYSTEM
Filed March 24; 1945
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PercyWRobinsén,
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by
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2,496,255
Patented Aug. 20, 1946
UNITED STATES PATENT OFFICE
2,406,255
INDUCTION MOTOR CONTROL SYSTEM
TPercy W. Robinson, Scotia, N. Y., assignor to Gen
eral Electric Company, a corporation of New
York
Application March 24, 1945, Serial No. 584,559
5 Claims.
((31. 172-274)
2
1
My invention relates to a system and appa
ratus for controlling the speed of induction mo
tors above and below synchronism such that the
power factor will be high, the operation stable,
and the regulating apparatus will be relatively
simple in construction and operation, with low
maintenance and long life. My invention may
be considered as an improvement over the in
duction motor control scheme of United States
mutator brushes of regulating machine 4. The
exciting winding H] of machine 4 is supplied at
slip frequency jointly by the ohmic drop exciter
and a second induction regulator ll energized
through a transformer [2 from the secondary
voltage and frequency of main motor 2. The
ohmic drop exciter supplies the excitation of
?eld winding l0 necessary for power factor cor
rection and resistance drop in the excitation cir
patent to Hull No. 1,306,594, June 10, 1919, in 10 cuits, and the desired variation in this part of
the excitation for different speeds of the in
that in general it replaces one of the commutator
duction motor is taken care of by the induction
machines and the adjustable reversing rheostats
regulator 6. The speed control excitation volt
of Figs. 8 and 9 of the Hull patent with induc
age is supplied to winding 10 from the trans
tion regulators, thereby simplifying the control,
reducing the maintenance cost of the control ap 15 former l2 and the induction regulator H. The
induction regulators 6 and l I are of a type which
paratus, and greatly reducing resistance losses
vary the voltage with a substantially ?xed phase
therein.
angle between input and output and may be of
The features of my invention which are be
the type described in British Patent No. 287,684
lieved to be novel and patentable will be pointed
out in the claims appended hereto. For a better 20 of 1928. The excitation requirements of the in
duction regulators 6 and H are so related that
understanding of my invention, reference is made
they may be adjusted by a common reversible
in the following description to the accompany
pilot motor represented at [3 having a control
ing drawings in which Fig. 1 represents a pre
and reversing switch Ill. The transformer I2 is
ferred embodiment of my invention in which no
operating 25 desirable to segregate the induction motor sec
ondary from the circuit of ?eld Ii! at and near
synchronous speed, when the ohmic drop exciter
?cations that may be incorporated into the sys
voltage is small.
tem of Fig. 1 to reduce the size of the main in
In the arrangement of Fig. 1 if the induction
duction regulator employed. Fig. 3 shows by
regulator H has zero transformer ratio at syn
means of curves the percentage voltage adjust
reversing
switches
are
needed
in
through synchronous speed. Fig. 2 shows modi
ment of certain parts of the regulating appa
ratus at various speeds where the main induction
regulator voltage reverses at synchronous speed
and no ?eld reversing switch is used. Fig. 5
shows percentage excitation voltage speed curves
characteristic of the apparatus as modi?ed, as
represented in Fig. 2; and Fig. 4 shows corre
sponding percentage excitation voltage speed
curves such as would be obtained with the trans
former arrangement of Fig. 1 but using a re
versing switch as in Fig. 2.
Referring now to Fig. 1, l represents a source
chronous speed of the induction motor, it may
be used in place of a reversing switch for re
versing the ?eld winding Hi when going from
below to above synchronism and vice versa.
In the curve of Fig. 3 the abscissas represent
per cent of maximum speed regulation above and
below synchronism, while the ordinates repree
sent per cent of induction regulator transformer
ratio and per cent of motor secondary volts at
maximum speed regulation above and below syn~
chronism. The secondary voltage of motor 2
varies linearly with speed as represented by the
straight line V9. If the ohmic drop excitation
of polyphase power supply for the stator pri
voltage be neglected, the voltage which it is de
mary winding of main induction motor 2, a
smaller motor 3 for driving a compensated com 45 sired to apply to the exciting winding !0 for
various speeds, and hence, for various slip fre
mutator type speed regulating machine 4 with
quencies varies with the square of the slip fre~
interpoles and for an ohmic drop exciter 5, the
quency above and below synchronism, and hence,
supply to the latter being through an induction
can be represented by the parabolic curves V10,
regulator represented at 6 and a transformer l,
Fig. 3. This curve also represents the output
if needed. The ohmic drop exciter 5 is driven
voltage required of regulator I I.
with the main induction motor and converts line
If the insulating transformer I 2 has a l-to-l
frequency to the slip frequency of the main in
ratio, the straight line V9 also represents the per
duction motor. The rotor secondary winding of
cent of maximum voltage ratio of the induction
the induction motor is connected through slip
rings 8 and connections 9 to the polyphase com 55 regulator II. For example, at 5!! per cent of
2,406,255
3
maximum speed above or below synchronism, the
induction motor secondary voltage applied to reg
4
regulator ll; and curve R11 represents the per
cent of maximum voltage ratio for which the in
ulator ll (point a on curve V9) is 50 per cent of
duction regulator H is set. With this arrange
the induction motor secondary voltage at full
ment the regulator II has a maximum voltage
speed regulation (point I) on curve V9). The out Cl output of 21 per cent compared with a maxi
put-to-input voltage ratio of regulator II is 50
mum of 50 per cent for the arrangement repre
per cent of maximum ratio so that the output
voltage of H is 50% of 50%=‘)5% of the induc
tion motor secondary at 100 per cent speed reg
ulation or at point e on curve V10.
sented by the curves of Fig. 5. It is noted from
Fig. it that the transformation ratio of the reg
ulator Ii becomes zero and reverses at about 83
rl‘his volt
10 per cent of maximum speed regulation at which
age
of machine
matches 4the
at induced
50 per ?eld
cent voltage
of maximum
as the sec
point the induced ?eld voltage of machine 4
matches the secondary voltage of the induction
motor.
The transformation ratio of the transformer
cent of maximum. The induced ?eld voltage of 15 which supplies the induction regulator Il may
machine 6 is proportional to the product of flux
be altered to meet different requirements, and
and frequency which for this case is 25 per cent
in Fig. 2, I have shown the ?xed ratio trans
of maximum. At synchronous speed the sec“
former #201. as having two secondary windings l5
ondary frequency of motor 2 is zero; hence, trans
it}, the former supplying the regulator II
former it: has no e?ect which, at synchronous
and the latter in series with the secondary of
speed, has the desirable eifect of isolating the
the regulator output. Such an arrangement is
secondary of machine 2 from ?eld Winding it.
useful to replace worn-out contact-making reg
The voltage ratios of regulators ii and i l are also
ulating equipment such as is described in the
mum
ondary voltage,
and the
V9,secondary
is 50 per frequency
cent of the
is 50 per
Zero unless power factor correction of motor 2
previously mentioned Hull patent, while utiliz
is required. In the latter case regulator 5 may 25 ing an existing commutator machine at 4 with
have unequal effective stator and rotor turns in
out change in its ?eld winding H]. I will as
order to deliver quadrature voltage at its mid“
position through ohmic drop exciter 5. This
excitation is in the nature of direct current, and
sume that the stepdown transformation ratio of
the transformer !2a is 2 to 1 between its primary
and secondary windings. Then the voltage rela
current of a similar nature ?ows in the secondary 30 tions at various speeds could be as represented
of the main induction machine. Hence, the mo
in the curves of Fig. 5, where the voltage sup
tor 2 may be operated through synchronism or
plied for ohmic drop is neglected. Curve V9
held at synchronous speed with stability.
represents per cent of maximum induction motor
While passing through synchronisrn, the trans
secondary voltage plotted against per cent of
former ratio of regulators i5 and H pass through 35 maximum speed regulation one way from syn
zero and reverse. This reversal accomplishes the
chronism. Curve V10 represents the. percentage
same result as has heretofore been accomplished
induced volts at different speeds in ?eld [0.
by reversing the ?eld winding ill by a switching
Curve V15 represents the percentage voltage con
arrangement such as is shown in Fig. 2, and as
tributed by winding it‘ of transformer [2a at dif
a result, with the arrangement thus far de
ferent speeds. Curve V11 represents the per
scribed for Fig. 1 the reversing switch is not re
centage voltage output of regulator H and curve
quired for passing through sy‘nchronism, and
It the percentage regulator ratio, which is 100 per
hence, the motor may be operated through. syn~
cent at the synchronous and maximum speed
chronism
smooth, steady, and uninterrupted
manner while carrying load.
This arrangement
requires a relatively larger capacity regulator at
regulating points. Here the transformer voltage
“ curve V15 added to the regulator voltage V11
equals the induced ?eld voltage V10 of machine 4.
i 5 than do other arrangements to be described.
The curves may be further explained by consid
Consider. now, the arrangement of Fig. l as
ering the condition at, say, 25 per cent maximum
provided. with reversing contactors for the wind
speed regulation. Here the induction motor sec
lil of machine A such as is represented in Fig. 50 ondary voltage is 25 per cent of the value for
at II, i5, i9 and 2G in order that the motor 2
maximum regulation and this voltage is applied
may be operated through synchronism without
to the primary of the Z-to-l stepdown trans
reversing the transformation ratio of the reg
former 5204. This gives 121/2 per cent of the maxi
ulator ii at synchronous speed. In one case the
mum voltage V9 applied to the primary of regu
contacts at El and i8 are closed while those at
lator ii. As the regulator ratio R for this speed
i9 and 2%) are open, and for reversing, the con~
is that for 50 per cent ratio in the reverse sense,
tacts at 5'! and iii are opened and those at [9
its output voltage V10 in the reversed direction is
and 251 closed. Using such reversing contactors,
50% of 121/2%=61A1% of maximum secondary
it would be good economy to wind the ?eld wind
voltage V9. The winding it of transformer [2a
ing it of machine fl with a number of turns such 60 adds a voltage which is 1/2 of 25% of V9
that the induced shunt ?eld voltage is equa1 to
max.=—_l21[2%. Hence, the voltage applied to ?eld
the secondary voltage of the induction motor 2
winding ill by the transformer lid and regulator
at about 83 per cent of maximum speed regula
l l is the algebraic sum of
tion above or below synchronism. The relation
of induction motor secondary voltage to the volt 65 V11 and V15=~61/i%+121/2%:6%% of V9 max.
in the field circuit would be as shown by
which matches the induced ?eld voltage V10 at
the curves of Fig. 4i. In Fig. 4 the ohmic drop
this 25 per cent of maximum speed regulation
voltage is disregarded for the sake of simplicity,
point because at 25 per cent of maximum speed
and the curves for operation only one way from
regulation both the ?ux and frequency (propor
synchronous speed are represented. Curve V9
tional to induction motor slip) of machine 4 are
represents the secondary voltage of the induction
25 per cent of maximum, and the induced voltage
motor; curve V10 the voltage required to balance
is proportional to their product, or, 25% of
the induced voltage in the ?eld it of the ma
25% :6.25%. These same relations hold through~
chine ll. Curve V 11 is the voltage required to be
out the speed regulating range as shown in Fig. 5.
impressed upon the ?eld I3 from the induction 75
In all cases the speed is controlled by joint and
2,406,255
5
6
simultaneous control of the two induction regu
lators ii
ii. The ratio adjusting mechanism
for the two regulators is so connected together
as regards regulator positions as to obtain the
relationship desired in any particular case.
mation ratio adjustment at the synchronous
What I claim as new and desire to secure by
Letters Patent of the United States is:
l. A speed control system for induction motors
comprising in combination with a source of sup
mechanism for reversing the direction of the ex
citation of said regulating machine when operat
ing through synchronism is rendered unneces
speed of said induction motor and reverses the
direction of its transformation ratio when the
apparatus is adjusted to operate the motor
through synchronous speed whereby switching
sary.
ll, A speed control system for induction motors
ply, a wound secondary induction motor supplied 10
comprising in combination with a source of sup
therefrom, a commutator regulating machine
ply, a wound secondary induction motor having
concatenated with the secondary winding of the
its primary supplied from said source, a com
induction motor, said commutator machine hav
mutator regulating machine concatenated with
ing an exciting ?eld winding, a, transformer and
an induction regulator connected in series rela 15 the secondary winding of said. motor, an. exciting
winding for said regulating machine, a trans
tion between the secondary of said induction ma
former and an induction voltage regulator conchine and said ?eld winding for supplying speed
nected in series relation between the secondary
control excitation, an induction regulator and an
of the induction motor and exciting winding for
ohmic drop exciter connected in series relation
supplying speed control excitation, other means
between said source of supply and said ?eld wind
for supplying ohmic drop excitation to said exing for supplying ohmic drop excitation, said in
citing winding, said induction voltage regulator
duction regulators being of a type which vary
being of a type which changes its voltage trans~
their voltage transformation ratio at a substan~
formation ratio at a substantially ?xed phase
tially ?xed phase angle, and means for simulta
angle, means for simultaneously adjusting the
neously adjusting the ratio of said induction regu
transformation ratio of said induction regulator
lators for controlling the speed of said induction
and the value of the ohmic drop excitation for
motor.
regulating the speed of said induction motor from
2. A speed control system for induction motors
above to below synchronism or vice versa, said
comprising in combination with a source of sup
ply, a wound secondary induction motor supplied 30 regulating machine being designed to have an
induced ?eld voltage equal to the secondary volt
therefrom, a commutator regulating machine
age of the induction motor at approximately 83
concatenated with the secondary winding of the
per cent of maximum speed regulation of the
induction motor, said commutator machine hav
induction motor above and below synchronism,
ing an exciting ?eld winding, an induction regula
tor connected in series relation between the sec 42 the adjustment of the transformation ratio of
ondary of said induction motor and exciting
the induction regulator being arranged such
that at such approximate 83 per cent speed regu~
winding for supplying speed control excitation,
lating points the transformation ratio of the in‘
an induction regulator and ohmic drop exciter
connected in series relation between said source
duction regulator is zero and, reverses when go
of supply and exciting winding for supplying
ing from above to below such speed points and
has a maximum voltage transformation ratio at
on nic drop excitation, said induction regulators
the synchronous speed of the induction motor.
being of a type which vary their voltage trans
formation ratio at substantially a ?xed phase
5. A speed control system for induction motors
comprising a wound secondary induction motor,
angle, means for varying the transformation ratio
of said induction regulators for varying the speed
a source of supply therefor, a commutator regu
of said induction motor through synchronism,
lating machine concatenated with the secondary
and means for isolating the secondary winding
of said motor, an exciting winding for said regu—
of the induction motor from the exciting wind
lating machine, a transformer and an induction
ing of said commutator machine and ohmic drop
voltage regulator connected in series relation be
exciter at the synchronous speed of the induction
tween the secondary of said induction machine
and said exciting winding for supplying speed
motor.
3. A speed control system for induction motors
control excitation, said transformer having a
comprising in combination with a source of sup
stepdown ratio with a secondary winding sup
ply, a wound secondary induction motor having
plying the induction regulator and a secondary
its primary supplied from said source, a com
winding connected in series with the output of
mutator regulating machine concatenated with
said induction regulator, a second induction volt
the wound secondary winding of said induction
motor, a transformer and an induction voltage
regulator connected in series relation between the
secondary of said induction motor and exciting
?eld winding for supplying speed control excita
tion to said regulating machine, other means for
supplying ohmic drop excitation to the regulating
machine, said induction regulator being of a type
which varies its voltage transformation ratio at
a substantially ?xed phase angle, and means for
varying the transformation ratio of said induc
tion regulator to vary the speed of said motor,
said induction regulator having a zero transfor
age regulator and an ohmic drop exciter con
nected in series relation between said source of
supply and exciting winding for supplying ohmic
drop excitation for said control system, said reg
ulators being of a type having a substantially
?xed phase angle of transformation, means for
adjusting both induction voltage regulators si
multaneously to control the speed of said induc»
tion motor, and means for reversing the direction
of exciting current through said exciting winding
when operating through synchronous speed.
PERCY W. ROBINSON.
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