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Патент USA US2408227

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Sept. 24, 1946. ’
M, A_ PRINGLE
'
2,408,226
‘CONTROL SCHEME
Filed June 3, 1944
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Mark A. Prmy/e.
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BY
_
ATTORNEY
'
’ Sept- 24, 1946-
M. A. PRINGLE
' 2,408,226
CONTROL SCHEIIE
Filed-June 3, 1944'
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Mani“ A Pfakqc?e. '
Patented Sept. 24, 1946
2,408,226
UNITED STATES PATENT OFFICE
2,408,226
CONTROL SCHEME
Mark A. Pringle, Pittsbur gh, Pa., assignor to West
inghouse Electric Cor poration', East Pittsburgh,
Pa., a corporation of Pennsylvania
'
Application June 3, 1944', Serial No. 538,683
7 Claims.
1
(Cl. 172-289)
2
This invention relates broadly to a system of
tection of the synchronous motor in event of
control for a motor and more particularly to a
pulling out of step or synchronism.
system of control for a synchronous motor.
A speci?c object of the invention is to selec
In general, synchronous motors are started as
tively effect deenergization of the synchronous
induction motors by energizing the primary or
motor control system, or resynchronizing of the
armature windings with alternating current and
motor in event of pull-out.
once the motor speed has reached a value but a
Yet another object of the invention is to pro
few per cent less than synchronous speed, the
vide
in a synchronous motor control system,va
direct current or ?eld windings are energized and
the motor is synchronized to rotate at some speed l0 timing cycle independently controlled of the syn
chronous motor, and during which normal start
proportional to the frequency of the alternating
ing of the motor must be effected.
line currents.
More speci?cally, it is an object of this inven
Systems which provide automatic starting for
tion to provide a system of the character re
synchronous motors according to the above~de
ferred to, in which energization of the ?eld wind
scribed pattern, are quite often provided with a 15
ings is controlled in response to selected electri~
control or ?eld application device which is re
cal characteristics of the motor, and including a
sponsive to slip frequency and functions when
timing cycle established independently of the
the slip frequency has reached some predeter
synchronous motor and which functions in con
mined low value, usually 5% or less, to connect '
junction with the energizing control for the ?eld
the ?eld winding or windings to the source of 20 windings to prevent energization of the field wind
direct current to synchronize the machine. If
ings when the rate of change of the selected elec
trical characteristics is below a predetermined
such control device functions improperly, partic
ularly with motors excited from a source not re- ,
value.
lated to the motor, the ?eld windings may be en- '
‘
Other objects and advantages will be apparent
ergized at the beginning of the starting cycle and 25 from
a study of the following speci?cation when
an attempt thus made by the control system to
considered
in conjunction with the accompany—
synchronize the motor at substantially 100% '
ing drawings in which,
slip. Such a condition may not only seriously
_ Figure 1 is a schematic diagram of a syn
damage the synchronous machine, but also such
equipment which it may be driving. It is evident 30 chronous motor control system embodying the
principles of this invention.
that adequate ‘protection against premature ?eld
application is desirable.
'
’
Fig, 2 is a graphic representation of the oper
'
In addition, protection should be provided
against prolonged operation of the motor as an
induction motor under excess load, during start
ing and thereafter, in the event of ?eld failure at
the end of the starting cycle, loss of ?eld during
normal synchronous motor operation or pulling
out of step. Otherwise damage to the electrical
ating characteristics of the ?eld application de
vice illustrated in, Fig. l and, '
'
v
v
Fig. 3 is a schematic diagram of a synchronous
motor control system which is a modi?cation of
the control system of Fig. 1.
In a broad sense, the invention hereinafter dis
closed resides in the use of a timing device and
its auxiliary equipment operated independently
elements of the machine may result.
40 of the motor and its ?eld application control, and
A principal object of this invention is to pro
which functions in conjunction with the ?eld
vide in a system of control for a synchronous
application control for controlling the energiza
motor, protection against premature energization ,_
tion of the motor ?eld windings and for provid
of the ?eld winding.
ing protection against premature ?eld applica
Another object of this invention is to prevent 45 tion loss of ?eld, pull-out, etc.
_
prolonged operation of the synchronous machine
Referring
now
to
Fig.
1,
the
control
system for
as an excessively loaded induction motor during
the synchronous motor M comprises, generally, a
starting and thereafter.
main switch,‘such as C, for connecting the pri
Another object of this invention is to provide
mary or armature windings A of the synchronous
in a system of the character described, protection 50
motor to the sourceof alternating current indi
against ?eld failure or loss of ?eld, either at the
cated generally by the line conductors Ll , L2 and
end of the starting cycle or during normal syn
L3, and for establishing energizing circuits for
chronous motor operation.
Still another object of this invention is to pro
vide in a system of the character mentioned, pro
the elementsof the control system; a ?eld appli
cation device 56, which responds to armature cur
55 rent variations with slip-frequency of the ma~
2,408,226
3
4
chine, and a timing device 48, which embodies,
generally, a timing mechanism including the
motor 133M the electromagnetic relay 48C‘ and a
plurality of auxiliary control elements such as
the relays 48X and ABY.
Before proceeding with a description of the
control system in general, an understanding of
the operation of the control devices 56 and 48
should be had in order that the invention may be
more readily appreciated.
The ?eld application device 56 comprises a ?eld
application relay 56X having the armature oper~
ated contact members 56XI, a motor EtM, which
drives a plurality of contact disks EEMI, ESM‘Z,
nous motor M is accelerated as an induction
.
motor, the armature currents are gradually be
coming smaller and the slip-frequency lower in
alternations per second. When the speed of the
motor is approximately 95 to 98 per cent of the
synchronous speed, the relay magnetic pull falls
is provided with a single coil which is energized
to such a value that the magnetic forces hold
ing the armature in its operated position are
overcome by the increasing tension of the spring
2. As a result, the armature again drops out
and closes its contact members 56Xl. In this
last operated position, the armature contacts
56Xl complete a circuit across the conductors
X’ and Y’ including the contacts 5€XL the con
tacts 58172, the contact disc 56M4 and the coil
of the relay 43! for energizing the relay M which
in turn through its contacts IZIB and MC ener
through the medium of a bridge-type recti?er
gizes the ?eld windings of the synchronous mo
56M4, EGME and 56Mt in addition to a cam 4
and a relay EGY. The ?eld application relay 56X
tor. This causes the machine to be synchro
[0, from the current transformer T, which trans
former is energized according to the variations 20 nized, at which time the magnetic pull of the ?eld
application relay 56X, due to the drop in arma
of the currents in the conductor L2, connected
ture currents when the motor is synchronized,
with the synchronous motor M through the con
becomes a very low value. The motor 56M con
tact members C2 or the main switch C. The
tinues in its operation until it again reaches the
pivoted armature of relay 56X is provided with
a spring 2 which biases the armature away from 25 position indicated in Fig. 1, at which time the
energizing circuits for this motor are discon
the core to its switch closing position. The ten
nested.
sion of spring 2 is varied by means of a cam 4
The initial cycle of operation of the ?eld ap
which is driven ‘by the motor 56M. The combined
plication device 56 is controlled entirely by the
operations of the relay 56X and the motor EitM
produce operating characteristics, such as indi- 30 synchronous motor armature currents, hence this
period is termed the current limit acceleration
cated in Fig. 2.
period, and is indicated in the graph of Fig. 2 by
As will be seen from this ?gure as well as from
the portion CLA. The timing cycle begins imme
the position of the cam 4 in Fig. 1, the tension of
diately at the end of the period of current limit
the spring 2 at the beginning of the operating
cycle of the ?eld application device 56 is at its 35 acceleration and is controlled, in part, by the
maximum value.
This condition exists at the
beginning of the starting cycle for the syn
diminishing armature currents, as well as the
rapidity with which the relay spring tension is
increased. This period is known as the timing
chronous motor M. When the armature windings
interval and is designated TI in Fig. 2. This
of the synchronous motor are ?rst connected to
the conductors LI, L2 and L3, the current flowing 40 interval ends at approximately 95 to 98 per cent
of synchronous speed, as indicated by the dotted
through these conductors is of some relatively
line at the end of this interval. The dotted
high value. Accordingly, the coil of the relay
line FS represents full speed of the motor. Thus
55X has a high value current flowing there
it will be seen that by providing a period of cur
through. ‘This ?eld application relay is so de
signed that the average magnetic pull, as indi 45 rent limit acceleration, in which the motor is
brought up to about 90 per cent of synchronous
cated in Fig. 2 for the starting currents encoun
speed, and thereafter providing a timing inter
tered, is of some value higher than the initial
val, the motor may be accelerated to within but
spring tension. Accordingly, the relay armature
a few per cent of synchronous speed, at which
is moved to its switch. open position. As the
motor increases in speed, the current flowing 50 point it may be synchronized with a minimum
of electrical disturbance.
through the armature windings thereof, and,
The timing device 48 functions independently
hence, the current flowing in the conductor L2
of any of the characteristics of the synchronous
decreases. The average magnetic pull of the
motor M. Its sequentially operated contact mem
relay 56X correspondingly decreases until at some
point, which is determined entirely by the start 55 bers 48S and 48L of which 48S is the ?rst oper
ated contact, and 48L is the last operated con
ing characteristics of the motor, the relay mag
tact, are operated by the cams 6 and fl which
netic pull is no longer su?icient to hold the arma
are, in turn, driven by the motor 48M through a
ture against the bias of the spring 2. As a re
gear train I I, which includes a disk-type positive
sult, the armature drops out. Immediately upon
dropping out of the armature, the contact mem 60 clutch l2. This clutch is controlled by the arma
ture member of the electromagnet 48C, which
bers 56X! are closed and a circuit established
armature member also operates the moving ele
in part through these contact members to ener
ments of the contact members 48S and 48L, re
gize the motor 55M. The motor operates the cam
spectively, to their disengaged and engaged posi
4 in such a direction as to immediately reduce
the tensile loading of spring 2 to a very low 65 tions. The moving armature is hinged to a por
tion of the magnetic framework, not shown, and
value. Since, as shown in Fig. 2, the relay average
held away from its magnet core by a spring [4
magnetic pull is of some value higher than the
which is positioned below the point of hinging.
spring tension for this new setting, the armature
An arm, such as I6, is hinged substantially sen
of the relay 56X is immediately again attracted
to its switch open position. The motor 56M, 70 trally of the armature and is provided with a
bifurcated extremity lGa which operates the mov
however, continues in its operation and oper
ing elementof the clutch to engage the confront
ates the cam 4 in such a direction as to grad
ing faces when the armature member is moved
ually increase the tension of the spring 2, and
to its attracted position. Two contact ?ngers
hence, the switch closing bias applied to the
armature increases.
Meanwhile, the synchro— 75 l8 and 2!! are pivoted at the lower end of the
5
2,408,226
6
armature and each is free to move independently
Assuming a condition of normal operation, the
function of the system is as follows:
of the armature against the spiral springs 22.
The moving contact elements of the contact mem
bers 48S and 48L are fastened at the extremi
ties of the contact ?ngers l8 and 20. The sta
tionary contact elements are conveniently se
cured to the base of the relay. Coil springs,
such as 24, bias the contact ?ngers l8 and 20 in
a direction opposite to the bias provided by the
Closure of the switch S with the drum con
troller DC set in its off position completes a cir
cuit from the conductor X through the contact
segment DC2 of the drum controller, the back
contact members C5 of the main switch C, the
coil of the relay 52Y to conductor Y. This relay
immediately picks up, closing its contact mem
spiral springs 22. The mechanical forces applied 10 bers 52Yl and 52Y2. The contact members
by the spiral and the coil springs to the respec
52Yl complete a holding circuit for the coil 52Y
tive contact ?ngers are so arranged that when
the armature moves to the left, the force exerted
by the spiral springs on the contact ?ngers is
sufficient to bias the movable contact elements
against the bias of the coil springs 24 to their
resetting position. When the armature is moved
to the right, the spiral springs are unwound and
thus their force diminished. The bias of the
springs 24 on the contact ?ngers at this time pre
dominates; thus, when the latch elements 26 and
28' are actuated by theirv respective cams G and
8,. the movable contacts are operated by the coil
across the conductors X and Y, while the contact
members 52Y2 partially establish an energizing
circuit for the coil of the relay 52X. Operation
of the drum controller DC to its closed position
completes
springs 24. Suitable linkage 30 is provided be
tween the latch elements 26 and 28 that the cam -
6 may operate only the latch element 25. How
ever, the cam 8 upon operating the latch element
partially
established
circuit
the same time, the contact members C4, C6, C1
28, actuates the pivoted link 30 which, in turn,
and C8 are closed and the contact members C5
opened. Closure of the contact members C4
actuates the latch 26 to effect disengagement of
the contactv members 488.
From the foregoing it will be seen that the mo
tion of the armature of the electromagnet 480
causes the clutch disks to engage. but will not
close or open the contacts 48S and 48L, as the
case may be, until the trip mechanism latches 26 '
and 28 are released. When these latches are re
leased, and if the armature is still closed, the
this
through the contact segment DC3 of the drum
controller and the contact segment of the disk
contact 56M2. The relay 52X is thus energized
and closes its contact members 52X! which con
nect the operating coil of the main switch C
across the conductors X and Y. The main switch
C immediately'picks' up, closing its main line con
tacts C !, C2 and C3, thereby energizing the arma
ture winding A of the synchronous motor and
starting this motor as an induction motor. At
establishes, ‘in part, a tripping circuit for the coil
of the tripping solenoid 52T which latches the
main switch C in its closed position. This cir
cuit may be completed to e?ect tripping of the
contactor by operation of the drum controller DC
to its trip position, thus ‘completing the tripping
circuit through the contact segment DCI. ' Clo
sure of the [contact members C6 and CT of the
main switch C energizes the conductors X’ and
' Y’, which supply the control system. Energiza
springs 24, which, under this condition, provide lo tion of the conductors X’ and Y’ causes the relay
the predominating force to open the contacts
48X to pick up and close its contact members
483 and close the contacts 49L. When the elec
48Xl and 48X2. The energizing circuit for this
tromagnet 48C and the motor 48M are deener
operation may be traced through the contact
gized, the cams are returned to their initial posi
members 48Y2 of the relay 48Y, the coil of the
tion by means of a spring 32 which acts upon the
relay 48X, back contact members 48B of the re
shaft carrying the cams. At the same time, the
lay 40, the contact members 488, and thence to
armature moves to the left closing the contact
the conductor X’. Closure of the contact mem
members 48S and opening the contact members
bers 48Xl establishes a partial tripping circuit
48L. The latch members 26 and 28 are then
for the coil of the-tripping solenoid 52T, to pro
biased to latching positions. The settings of the ' vide
protection against premature ?eld applica
cams 6 and 8 can be varied to obtain the desired
tion. This circuit is completed upon premature
sequential operation of the contacts 488 and 48L.
energization of the ?eld winding by the contact
The relay 48X is operated immediately upon
members 49A of the relay 40, which is energized
energizing of the conductors X’ and Y’ of the
by the currents supplied to the ?eld winding F.
control system. The conductors X’ and Y’ are '
When
the. motor armature is connected to the
energized by the auxiliary contacts C6 and C7
conductors Ll, L2 and L3 as previously explained,
of the main switch. This relay functions in con
the coil of the .?eldrapplication relay 56X is ex
nection with the relay 4!] and the contact mem
cited with a fairly high current. As a result, the
ber 48S to provide premature ?eld application
armature is moved to its switch open position
contact arms l8 .and 20 are moved to the right
as viewed in Fig. 1 by the action of the coil
protection. The relay 48Y, which is energized GU and the contact members 55X! are open. This
upon closure of the contact members 48L, func
opens the starting circuit for the motor 56M,
tions in conjunction ‘with the relay 5€3Y which
which may be traced from the conductor Y’, the
forms a part of the ?eld application device 55,
motor 56M, contact disk 56M5, which in the posi
and which is controlled thereby. to provide pro
tion shown is conducting, contact members 56Y3
tection against prolonged operation of the motor
of the relay 55Y, contact members 56X! to the
as an excessively loaded induction motor.
conductor X’. Also at the time the main switch
The relay 4| is controlled as to the time of its
C closes, the electromagnet 48C is energized
energization by the ?eld application device 56
through a circuit which may be traced from the
at the contacts 56X! thereof in the circuit previ
conductor X’, the coil of electromagnet 43C, con—
ously traced for the coil of relay 4|. In'its en
tact members HF‘, the resistor R2 to the con
ergized position, its contact members MA are
ductor Y’. The motor MM is also energized,
open to open the ?eld discharge circuits and its
since it is connected in parallel with the coil of
contact members MB and “C are closed to con
nect the ?eld winding F to the source of direct
current which energizes this ?eld winding.
the electromagnet 48C. The electromagnet 48C
now closes, closing its seal-in contacts 4881 and
75 establishing a holding circuit for both its coil
2,408,226
7
and the motor 48M, which circuit is independent
of the contact members MF. Operation of the
8
across the conductors X’ and Y’ through .a cir
cuit including the link LS3 of the link switch LS
and its contact members 4ID. Closure of the
armature of the electromagnet 48C engages the
contact members ME completes the holding .cir
disk clutch l2, thus causing the cams 6 and 8
to be rotated. As the projection of the cam 6 Cl cuit for the relay 56Y, which includes the contact
engages the tripping latch 26, the contact mem
members SBXI, 5BY2, and the contact members
ME as previously explained. Opening of the con
bers 488 are opened. This opens the previously
tact members MF has no effect upon the ener
traced tripping circuit for the coil of the tripping
gizing circuits for the electromagnet 48C and the
solenoid 52T. The relay @835, however, remains
energized, since it is yet energized in a circuit 10 motor 48M, since the seal-in contacts 43SI by
pass the contacts 4 lF.
from the conductor X’, the contact members
As the projection of cam 8 engages the latch
56Yl , the link LSl of the link switch LS, the coil
member 28, the contact ?nger 2B is released and.
of the relay 48X, contact members 48Y2 to the
biased under the action of the spring 24 to en
conductor Y’.
gage the stationary contact of the contact mem
As the speed of the synchronous motor M_ in~
bers 48L. This completes an energizing circuit
creases, the magnetic pull of the relay 55X de
for the coil of the relay llllY across the conductors
creases suiiiciently that the armature is spring
X’ and Y’. The relay 48Y now picks up, closing
biased to its switch closing position. This closes
the contact members 56X! and completes the
its contact members 4BYI, 48Y3 and 48Y4. Since
energizing circuit for the motor 55M across the s the operating conditions are assumed normal, clo
sure of contact members 48Yl has no immediate
conductors X’ and Y’ through the medium of
effect upon the system. Closure of the contact
the contact disk 55M5 and the contact members
members 48Y4 shunts the coil of the electromag
55Y3. The motor immediately begins to rotate
in the direction indicated by the arrow adjacent
net 480 and the motor 48M from the circuit, thus
the cam 4. Thus the spring tension is reduced to 25 deenergizing both of these elements. Closure of
the contact members 48Y3 establishes a holding
some low value and, as shown in Fig. 2, the arma»
circuit for the relay 48Y, which may be traced
ture of the relay 56X is attracted to its switch
open position, thus again opening the contact
from the conductor X’, the link LS2 of the link
members 56Xl.
switch LS, the contact members 48Y3 and the coil
of the relay 48Y to the conductor Y’. This seals~
Opening of the contact members BBXI, opens
this relay in its energized position until the con
the starting circuit previously traced for the mo
ductors X’ and Y’ are deenergized through open
tor 55M. Another circuit for continuing the op
eration of the motor throughout the timing cycle
ing of the main switch C or opening of the link
is completed through the contact disc SEMI. At
LS2.
Deenergization of the coil of the electromagnet
the same time the coil of the relay 56Y is connect- :
ed across the conductors X’ and Y’ through the
43C and the motor 48M allows the armature of
the electromagnet 48C to move to the left, there
medium of the contact disks 56Ml and 58M6, the
by resetting the contacts 48S and 48L. At the
contact disc 56MB being a substantial duplicate
same time, the clutch I2 is disengaged and the
of the contact disc EBMI. This relay is thus en—
ergized and picked up, opening its contact mem 40 cams 6 and 8 are rotated to their inactive posi
bers 56Yl and causing the relay 48X to drop out
tions. Closure of the contact element 48S now
has no effect upon the tripping circuit for the
and also opening its contact members 56Y3 in the
starting circuit for the motor 56M and closing its
coil 52T, since the contacts 48Xl are open and the
relay 48X may not be energized until the contact
contact members 56Y2, which establishes a par
members 48Y2 are again closed.
tial holding circuit for the coil of the relay 56Y,
The protection afforded by the cooperating
which holding circuit also includes the contact
action of the various elements of the control sys
members ME of the relay 4| and the contact
tem may best be understood by assuming Vari
members 56X~|, and also partially establishes an
energizing circuit for the relay 4| in conjunction
ous operating conditions of the system.
with the contact disc 56M4, which is completed It
Premature ?eld application
when the contact members 56X] are later closed.
Premature
application of the ?eld winding F
The energizing circuit for the relay 4| may be
may most likely result from failure of the arma
traced from the conductor X’, the contact mem
ture of the ?eld application relay 56X to move
bers 56X! now open, the now closed contact
to its actuated position when the synchronous
members 56Y2, the now conducting contact disk
motor armature winding is connected to the line
5BM4 to the coil of relay M and thence to the con
by the main switch C. Under such a condition,
ductor Y’.
the motor 56M is immediately operated, the relay
As the motor armature currents decrease and
the magnetic pull of the ?eld application relay
56Y is energized through the contact disks 56Ml
56X decreases, the relay spring tension is grad co and 56MB to close its contact members 56Y2 and
the contact disk 56M4 completes the energizing
ually increased until, at 95 to 98 per cent of syn—
chronous speed, the curve of the average mag
circuit for the relay 4|, Thus the ?eld is ener
gized substantially at the beginning of the start
netic pull of field application relay 56X inter
ing cycle of the system. It will be remembered,
sects the curve of the spring tension, as shown in
Fig. 2, at which point the armature of the relay “ however, that the relay Mix is energized imme
56X drops out and closes its contact members
diately upon operation of the main switch C, thus
56XI, This immediately energizes the relay 4!
the contact members 48X! of this relay are closed
when the relay 40 is energized by premature ap
through the contact members 56Y2 and the con
tact disk 56M4. The relay 1-H picks up, opening
plication of the ?eld. The coil of the tripping
the ?eld discharge circuit at the contact mem~ ' solenoid 521‘ is energized by a circuit which may
bers MA and connecting the ?eld winding F at
be traced from the conductor X’, to the contact
contacts MB and MC to a suitable source of di
members 488, the contact members 40A of the
rect current, generally indicated by plus and
relay 40, the contact members 48X! and the coil
minus.
of the tripping solenoid 52T to the conductor Y.
The relay 4| establishes its holding circuit
The tripping solenoid armature thus moves to
2,408,226
~
~
l0
9'
the left and releases the main switch C to per
mit' its movement to its inoperative position,
relay 56X, due to a high average magnetic pull
throughout this timing cycle since the rate of
therebydeenergizing the system.
change of the motor armature currents is low,
has not been permitted to drop out, the timing
Field failure at end of starting cycle
5 cycle of the motor 56M can not begin; hence,
the ?eld Winding F of the synchronous motor
may not be energized to synchronize the machine.
For ?eld failure due to source voltage failure
at the end of the starting cycle, in which case the
timing device 48 is reset, the tripping solenoid is
The motor thus continues to operate as an in
energized by a circuit which may be traced from
duction motor. Since the contact disks 56MI and
56M5 remain in their initial insulated position,
the conductor X’, the contact members 488, the
now closed contact members 40B, since the relay
40 is deenergized due to failure of source voltage,
the relay ESY is not energized and the contact members EBYi thereof are closed. When the con
the link LS! of the link switch, the contact mem
bers 48Y| of the relay 48Y, which it will be re
membered is sealed in as long as the conductors
X’ and Y’ are energized, the coil of the tripping
solenoid 52T to the conductor Y. Hence, upon
failure of source voltage, the main switch C is
tact members 48L are closed, the relay 48Y im
mediately picks up, closing its contact members
éiSYl. This completes a tripping circuit for the
coil of the solenoid-tripping device ‘BET/which
may be traced from the conductor X’, the con
tact members 56Yl, the contact members 48YI,
tripped and the system deenergized.
the coil of the tripping solenoid 52T to the con
For ?eld failure at the end of the starting cycle 20 ductor Y. The system is thus immediately deen
due to failure of the relay 4| to operate upon
ergized.
establishing its energizing circuits, the coil of the
The foregoing description of the function of
tripping solenoid 52T is energized in the circuit
the system to protect the synchronous motor un
traced in connection with ?eld failure due to fail
der adverse operating conditions has provided
ure of source voltage.
The contact members of .
tripping-out of the main switch 0 and de-ener
gizing of the control system for all the adverse
operating conditions noted. If it is desired, for
example, in the event of pull-out to attempt re
synchronizing of the machine, the link switch LS
may be operated to its right-hand position.’ In
the relay 4! play no part in this energizing cir
cuit.
Loss of ?eld during normal operation as syn
chronous motor
The conditions existing when the synchronous
motor loses its ?eld during periods of its normal
operation as a synchronous motor when the link
switch LS is connected for tripping on pullout
only are similar to those existing as a result of
?eld failure at the end of the starting cycle. The
tripping circuit for the coil of the tripping sole
noid 521‘ is, in this instance, the same as that
described for ?eld failure at the end of the start
ing cycle.
Pull-out
If for any reason, with the link switch LS
connected for tripping on pull out, the synchro
nous motor pulls out of step or synchronism due
to increasing mechanical loading or moderate
weakening of the excitation of ?eld winding F,
the armature winding reaction produces current
surges in the conductors Ll , L2 and L3. Thus in
this right-hand position, the link LS3 is the only
conducting link of the switch.
Premature ?eld application
With the switch LS in its resynchronizing po
sition, premature ?eld application effects trip
ping of the main switchC to deenergize the sys
tem through the medium of contact members
4BXI, 40A and 48S vas in this same case with the
40
switch LS in its left-hand position. Tripping is
desired under premature ?eld application condi
tions primarily because it is an indication that
the ?eld application relay 56X has not functioned
properly, and in all probability, would again not
. function on a resynchronizing cycle.
Since the
damages which may result both to the synchro
nous machine and its connected equipment, are
serious, and prolonged external system disturb
ance which would result therefrom, is undesir
a manner similar to starting of the machine, the
average magnetic pull of the ?eld application re 50 able, immediate deenergizing of the system should
logically be had that a check of the system ele
lay 55X rises to some high value as shown at the
ments causing the faulty operation can be made.
right in Fig, 2 at the point designated PO and
the relay armature immediately is actuated to its
Field failure at end of starting cycle
switch open position. This opens the holding cir
Field
failure at the end of the starting cycle,
cuit at 56Xl for the coil of the relay 56Y, causing 55
resulting from failure of source voltage will pro
this relay to drop out and close its contact mem
vide operation of the motor as an induction motor
bers -56Yl. When the link switch is connected
only if the motor is lightly loaded, Under these
for trip out on pull out, this connects the coil
52T across an energizing circuit which may be
traced from the conductor X’, the contact mem
bers 5EYI, the closed contact members 48YI, the
conditions no serious effects may result. How
60 ever, if the load is heavy, the armature currents
will again rise, the relay 56X will pick up and a
resynchronizing cycle will be attempted. Trip
coil of the tripping solenoid 52T to the conductor
Y. The main switch C is thus tripped and the
ping-out of the main switch C is not effected even
system deenergized.
though, under these conditions, the relay 48Y
Prolonged operation as induction motor
During starting of the synchronous motor as an
65 is energized and its= contacts 48Yl are closed
because the contact members 4|E are closed, and.
the holding circuit through these ‘contact mem
bers for the relay 56Y completed. Since the func
excessively loaded induction motor, the ?eld appli
cation relay 56X is energized and the armature
tion of the system has been normal, the contact
thereof actuated to its switch open position. At 70 members 56XI are closed to maintain together
the same time, the timing device 48 is proceeding
with the contact members 56Y2 and ME, the
with its timing cycle independently of the char
holding circuit for the relay 56Y. Immediately
acteristics of the synchronous motor'to open its
upon occurrence of heavy armature currents due
contact members 48s and eventually close its
to anincrease in the mechanical load on the
contact members 48L. As the armature of the 75 motor, the relay 56X picks up and immediately
2,408,226
1l
12
a resynchronizing cycle for the synchronous
motor begins.
Should the relay 4i fail to operate at the end
of the starting cycle to apply direct current ex
citation to the ?eld winding F, the contact mem
as an induction motor for a prolonged period of
time, is the same with the link switch LS set in
the resynchronizing position as with the switch
tion. The motor then operates as an induction
motor until such time that the armature cur
rents may rise su?iciently to increase the cur
of direct current, such a source of direct current
may, for example, be that which is used to ener~
rent in the coil of the ?eld application relay ‘56X
by an ‘amount such that a resynchronizing cycle
may be initiated. If under resynchronizing con
this coil in the core is insuflicient to actuate the
armature member.
The coil £53K is connected across an inductance
element or reactor which is connected in series
with the ?eld discharge resistor in the ?eld dis
set in its tripping position. The ?eld applica
tion relay 56X picks up and remains up through
bers ME’ remain open, and thus when the con
out the timing cycle of the device 48 due to the
tact disks 56M! and 56MB open or‘ become non
slow change of the synchronous motor armature
conducting during the normal operating cycle of
currents, at which time the relay 48Y is ener
the motor 58M, the energizing circuit for the
gized and its contact members 48Yl, in conjunc
relay 56‘! is opened. Since the contact members
tion with the closed contact members 5BYI, es
ME are open, the holding circuit for this relay
tablish the energizing circuit for the tripping
is also open, hence when the contact disks 55M!
solenoid 52T.
and 56MB reach their insulating position, the
The embodiment of the invention illustrated in
relay ESY drops out. Immediately upon dropping
Fig. 3 is in many respects similar to that illus
of the relay 56Y, the starting circuit for the mo
trated in Fig. 1. The most important difference
tor 56M is completed. The cam 4 then operates
resides in the ?eld application device I56. This
to relieve the spring tension of the ?eld appli
device differs speci?cally from the ?eld applica
cation relay EBX, and the relay armature is at
tion device 5% illustrated in Fig. 1, in that a tim
tracted to. its switch open position to start a re
ing cycle is not provided after the relay I56 has
synchronizing cycle.
performed its operation. The timing device 48 is
in this application essentially identical with that
Loss of ?eld during normal operation as
of Fig. 1. In this system parts, corresponding to
synchronous motor
those of Fig. 1, have been given like reference
With the link switch LS connected for re
numerals.
synchronizing, loss of ?eld during normal opera 25
The ?eld application relay l56 is essentially a
tion of the motor, resulting from a failure of the
polarized relay and comprises a U-shaped core
source voltage, with the relay 4! remaining up
member about the opposite core extremities of
and its contact members 41E remaining closed,
which are wound the coils IEEX and I56Y. The
the relay l'atY will lbe held in its energized posi
coil ESBY is connected directly to a suitable source
ditions, the synchronous motor armature cur‘
rent remains high throughout the timing cycle
period established by the device 48, the relay IHTS!
upon closure of the contact members 48L is en
ergized, and in conjunction with the relay 56Y
establishes a tripping circuit for the main
switch 0.
Pull out
With the link switch LS in the resynchronizing
position, the holding circuit previously estab
lished for the relay llBY through the link LS2 no
longer exists. This relay is now entirely depend
ent for completion of its energizing circuit upon
the contact members 48L, thus when the timing
cycle of the device 48 is completed and the con- '
tact members 48L open, the relay NY is deener
gized and the contact members 48Y| are opened.
Thus upon pull-out of the synchronous motor
and operation of the relay 56X, a tripping circuit
for the main switch C when the contact mem 55
bers EBY! close, is not established. When the
contact members 56X! open, the holding circuit
for the relay 4| now established, in part, through
gize the ?eld winding F. The flux produced by
charge circuit. The impedance of this inductance
element varies with the frequency of the currents
induced in the ?eld winding circuit when the dis
charge circuit is closed. The frequency of these
induced currents is the slip-frequency of the ma
chine and decreases as the speed of the motor
approaches synchronous speed. Thus the alter
nating current, which ?ows in the winding ISEX,
is of high intensity and high frequency when the
motor armature winding is connected to its alter
nating current supply, and decreases in both in
tensity and frequency as the motor approaches
synchronous speed. The relay is so designed that
a time interval of certain duration, during which
the ?ux is of a value below a certain predeter
mined holding value, must exist before the relay
armature will drop out. The magnetic flux pro
duced in the relay core by the direct current
winding I'5GY and the alternating current coil
IESX are in opposition during alternate half cycles
of the alternating current cycles. When the fre
quency is high, the time interval during which
these contacts is interrupted at this point and
these
fluxes are in opposition is very small, hence
(50
the relay 4| drops out, thereby deenergizing the
the relay armature does not drop out. However,
?eld winding F. With interruption of the ?eld
as the alternating current frequency decreases,
winding current, the relay 40 drops out and closes
and at the same time the intensity of the alter
its contact members MB. This immediately en
nating current decreases, a point is eventually
ergizes the relay 48X through the contact mem
reached where the ?ux remaining to hold the re
bers 48S, the contact members 4013, the coil of
lay armature up is insufficient for a given interval
the relay 48X and the contact members 48Y2.
of time; As a result, the relay armature drops
The contact members 48X| are thus closed and
out.
a portion of the premature ?eld protection circuit
The operation of the‘ system is as follows:
established. From this ‘point on the resynchro
Pressing the start ‘button connects the coil of
nizing cycle proceeds in the same manner as for 70
the
main switch C directly across its direct our
starting the system.
‘
retn source of supply. The main switch immedi
Prolonged operation as induction motor
ately picks up and is latched in by the tripping
solenoid 52T. The main line contacts Cl, C2 and
The function of the system, should the motor
C3 are closed and the armature winding A of the
be heavily loaded in starting and thus operate
13'
2,408,226
motor is energized, starting the motor as an in
duction motor. Immediately the ?eld application
relay I56 picks up and opens its contact mem
bers I56A. As the motor accelerates and syn~
chronous speed is approached, this relay drops its 5
14
application device I56, a resynchronizing cycle is
begun.
"
Loss of field during normal synchronous motor
operation
armature to close the contacts I56A and thereby
In the event of loss of ?eld due to source volt
energize the relay 4! to energize the ?eld winding
age failure, the relay 4!] drops out and closes its
F at the contacts 41B and MC. During this in
contact members 403. This completes the trip
terval, however, the timing device 43 has been
ping circuit for the tripping solenoid through the
energized through the medium of the contacts 10 contact members C6, 4|D, 40X2, 483, the coil of
Cl and 48X3. The electromagnet 480 thus closes
tripping solenoid 52T and the contact members
its contact members 4881 and energizes the motor
C4 to the negative terminal. The contact mem
48M and, at the same time, engages the confront
bers 48X2 are closed under this condition, since
ing faces of the disk clutch 12. After a short
the contact members 4lD, which complete the
interval of time, the contact members
are 15 holding circuit for the relay 48X through the con
opened and at a later time, the contacts 5581;
tact members C6, are closed.
,
close. When the contact members 48L close, the
Should the relay 4| for any reason drop out
relay 48X is energized through a circuit which
and thus cause a loss of ?eld, the relay 48X im
includes the contact members C6, the contact
mediately drops out closing its contact members
members 48L and the coil of the relay li?X. This 20 40X3. The device 48 immediately starts another
relay immediately picks up and opens its contact
timing cycle. Should the motor pull far enough
members 40X3, thereby denergizing the coil of the
out of step, the slip-frequency currents become
electromagnet 48C and the motor 48M. The de
su?icient to operate the device I56 and a resyn
vice 48 now resets.
In this embodiment of the invention, protec 25
tion against the various faulty operating condi
tions noted in connection with Fig. 1 is provided.
chronizing cycle is immediately begun.
Pull out
In the event the motor should pull out of step
due to increasing mechanical load or weakening
Premature ?eld application
of the ?eld, the ?eld application relay I56 im
In the event that the ?eld application relay £55 30 mediately picks up and deenergizes the relay 4|.
fails to operate at the beginning of the starting
Since the ?eld circuit is now open, the relay 48,
cycle for the motor, the relay 4| is picked up and
drops out at the same time the relay 40X drops
causes the ?eld winding F to be energized. This
out, since its holding contacts MD are open.
immediately picks up the relay 48 and closes its
With the closing of the contact members 48X3,
contact members 48A. This establishes a circuit 35 the timing device 48 is again energized and a re
synchronizing cycle is begun.
for energizing the coil of the tripping solenoid
52T which may be traced from the positive termi
Prolonged operation as induction motor
nal through the contact members C6, the contact
members MD, the contact members 4E3Xi, the
Should the motor be started with too heavy a
contact members 483, the contact members 45A, 40 mechanical load, the ?eld application relay I56
holds its armature in the operated position
the coil of the tripping solenoid 52T and the con
throughout the timing cycle provided by the tim
tact members C4 to the negative terminal. The
ing device 48. At the close of this timing cycle,
mainswitch 0 thus moves to its inoperative posi
the contact members 48L close. This completes
tion and disconnects the motor from the line.
47) a circuit for the tripping solenoid from the posi
Field failure at encl'of starting cycle.
tive terminal through the contact members C6,
the contact members 48L, the contact members
In the event of failure of the source voltage for
483, the coil of the tripping solenoid 52T, and
the ?eld winding F, operation of the relay 4| will
the contact members C4 to the negative terminal.
not apply the energizing current to the ?eld wind
At the same time, closure of the contact members
ing. As a result, the relay 4?! remains deenergized
48L energizes the relay 48X opening its contact
and its contacts 48B remain closed. Under these
members
40X3 and allowing the timing device to
conditions, the tripping solenoid is energized
reset.
through a circuit beginning with a positive ter
From the foregoing it will be seen that the pro
minal through the contact members C6, the con
vision
of a timing cycle, by means of a device
tact members MD, the contact members MXZ oi
such as 48, during which timing cycle synchro
the relay 48X, now energized as a result of the
nizing operations of the motor must be completed,
closing of contact members 48L during the nor
provides
a control of the operating conditions of
mal timing cycle, the contact members 48B, the
the motor during its starting cycle, which pro
coil of the tripping solenoid 52T, and the contact
tects the motor against damage resulting from
members C4 to the negative terminal.
faulty operation.
Should the relay 4| fail to operate even though
The foregoing disclosure and the showings
its energizing circuit is completed, a trip circuit
made in the drawings are merely illustrative of
for the coil MT is not established because the con
the principles of this invention and are not to be
tact members MD of the relay 4| are open. The
considered in a limiting sense. The only limi
relay 48X picks up, allowing the timing device 48
tations are to be determined from the scope of
to reset, but since MD is open, drops out when
the appended claims.
the contact members 48L open causing the device
I claim as my invention:
48 to begin another timing cycle. This cyclic
1. A control system for a synchronous motor
operation of the device 48 continues and the motor
having
conventional windings including arma
continues to operate as an induction motor as
ture windings and ?eld windings comprising, in
long as the motor is very nearly at synchronous
combination, electrical means operative to ener
speed. When the speed drops sufficiently, due to
gize said armature windings, control means re
loading ofthe machine to produce suficiently
sponsive to selected electrical characteristics of
high slip-frequency currents to operate the ?eld 75 said
motor for energizing said ?eld windings, tim.
2,408,226
15
16
ing means having sequentially operated control
elements, means responsive to energization of said
?eld windings and operative in conjunction with
of direct current, control means responsive to
selected electrical characteristics of said motor
for effecting operation of said ?eld switch, a
timing device having normally closed contact
the ?rst operated of said control elements for
rendering said electrical means inoperative only
during the time limits determined by the ?rst
operated control element, means responsive to
the second operated of said control elements, and
members, a ?rst relay having contact members
which are closed upon energization of‘ said ?rst
relay, said ?rst relay being energized upon en
ergization of said system, a second relay ener
gized upon operation of said ?eld switch and
means forming a part of said control means and
operative in conjunction with said means respon
sive to the second operated control element when
the rate of change of said selected electrical
characteristics of said motor is below a predeter
mined value, for also rendering said electrical
means inoperative.
2. A control system for a synchronous motor
having conventional windings including armature
windings and ?eld windings comprising, in com
bination, electrical means operative to energize
said armature windings, control means respon
sive to selected electrical characteristics of the
synchronous motor for energizing said ?eld wind
having contact members which are closed upon
energization of said second relay, an energiz
ing circuit for said electromagnetic tripping de
vice including, the contact members of said ?rst
relay, the contact members of said second relay
and the normally closed contact members of said
timing device; the closed contact members of
said timing device being opened after‘ a prede
termined limit of time and being effective to
electrically open said energizing circuit for the
on electromagnetic tripping device.
6. In a system of control for a motor, the
combination of , a synchronous motor having con~
ings, timing means, and means responsive to en
ventional windings including armature windings
ergization of said ?eld windings and operative in
and ?eld windings, a source of alternating cur
conjunction with said. timing means within limits
of time established by said timing means, for ren
dering said electrical means inoperative.
3.. A system of control for a motor compris
ing, in combination, a synchronous motor hav
rent, a contactor for connecting and discon
necting said armature windings with said source
of alternating current, an electrical tripping de
vice for said contactor, a source of direct cur
ing conventional windings including armature ,
windings and ?eld windings, electrical means for
energizing the armature windings, control means
responsive to selected electrical characteristics
of the motor for energizing the ?eld windings,
timing means, means responsive to operations of
1‘
said timing means, and means forming a part of
said control means and operable in conjunction
with said means responsive to operations of said
timing means when the rate of change of said
selected electrical characteristics is below a pre
40
determined value, for rendering said electrical
means inoperative.
4. In a system of control for a motor, the com
bination of, a synchronous motor having‘ conven
tional windings including armature windings
and ?eld windings, a source of alternating cur
rent, a contactor for connecting and disconnect
ing said armature windings with said source: of
alternating current, an electrical tripping de
vice for saicL contactor, a source of direct cur 50
rent, a ?eld switch for connecting and discon
necting said source of direct current with said
?eld windings, control means responsive to se
lected electrical characteristics of‘ said motor
for e?ecting operation of said ?eld switch, a tim 55
ing device having normally open contact mem
bers, a, relay having contact members which are
closed upon operation thereof, said relay‘ being
rent, a ?eld switch for connecting and discon
necting said ?eld windings with said source of
direct current for synchronizing said motor‘, con
trol means responsive to selected electrical char—
acteristics of said motor for effecting operation
of said ?eld switch, a timing device having a
pair or sequentially operated contact members,
the ?rst operated of said sequentially operated
contact members being a normally closed con
tact and the second operated of the sequentially
operated contact members being a normally open
contact, a ?rst relay having contact members
which are closed upon energization of said ?rst
relay, said ?rst relay being energized upon en’
ergization of said system, a second relay ener
gized upon operation of said ?eld switch and
having contact members which are closed upon
energization of said second relay, a third relay
operated upon closure of said second operated of
the sequentially operated contacts, said third re
lay having contact members which are closed
upon operation of the third relay, parallel ener
gizing circuits for said electrical tripping means,
one of said circuits including the contact mem
bers of the ?rst relay, the contact members of
the second relay and the ?rst operated of the
sequentially operated contact members, and an
other of said circuits including said control
means and the contact members of said third
relay, and switching means operable in one po
sition to effect tripping of said contactor through
said parallel circuits, and in another position
operable to effect another synchronizing cycle
of said motor through said control means.
energized upon closure of said contact. mem
bers of said timing device, means forming a part 60
of said control means and controlled thereby, and
an energizing circuit for said electrical tripping
device including the contact members of said
7. In a system of control for a motor, the com
bination of, a synchronous motor having con
relay and said means forming a part of said con
trol means.
5. In a system of control for a motor, the
combination of, a synchronous motor having con
65
ventional windings including armature windings,
and ?eld windings, a source of alternating cur
rent, a contactor for connecting, and disconnect
ventional windings including armature windings
ing said armature windings with said source of
and ?eld windings, a source of alternating cur
alternating current, a source of direct current,
rent, a contactor for connecting and discon 70 a ?eld switch for connecting and disconnecting
necting said armature windings with said source
said ?eld windings with said source of direct cur
rent, control means responsive to selected elec
of alternating current, an electromagnetic trip
trical characteristics of said motor for effecting
ping device for said contactor, a source of direct
operation of said ?eld switch to synchronize said
current, a ?eld switch for connecting and dis
connecting the ?eld windings with said source 75 motor, a timing device, an electrical device for
17
2,408,226
effecting operation of said contactor to its dis
connected position, a first normally incomplete
electrical circuit for energizing said electrical
18
normally incomplete electrical circuit for ener
gizing said electrical means, means operable
after a predetermined limit of time greater than
that of said ?rst-mentioned limit of time for
gization of said ?eld windings by said ?eld switch, 5 completing said second electrical circuit and
for completing said electrical circuit and thereby
means for rendering said second electrical cir
energizing said electrical means, means operable
cuit inoperative.
after a predetermined limit of time for rendering
MARK A. PRINGLE.
said ?rst electrical circuit inoperative, a second
means, means operable upon premature ener
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