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Патент USA US2411710

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Nov. 26, 1946.
s. B. CRARY
2,411,710
REGULATOR SYSTEM
Filed Oct. 12, 1943
SOURFCE
SEPART
ETATXlOC/V
TSIYNE0RCOM
Inventor“ :
Selden ?crary,
by
‘
His Attorney.
Patented Nov. 26, .1946
2,411,710 ’
UNITED STATES PATENT OFFlCE
REGULATOR SYSTEM
Selden B. Crary,‘Schenectady, N. ‘Y., assignor
to General Electric Company, a corporation 0!
New York
1
Application October 12, 1943,'Serinl No. 505,955
8 Claims. (01. zoo-1)
This invention relates to regulator systems and
more particularly to improvements in automatic
voltage regulator systems for synchronous dy
2
.
everthe lowering action of the voltage regula
namo-electric machines, particularly synchro
tor‘is limited. In this manner the reduction in
kilowatt-loading permits a further reduction in
excitation so that normal voltage is maintained
nous generators.
at the sacri?ce of load.
In Patent 2,259,091, granted October 14, 1941,
on a joint application of Louis W. Thompson and
I
' An object of the invention is to provide a new
and improved regulator system.
myself and assigned to the present assignee, an
improved voltage regulator system having what
Anothei~ object of the invention is to provide
'an" improved automatic> regulator system for
may be called an automatic lower limit is de 10 synchronous dynamo-electric machines with an
scribed. By “lower limit” it is meant that the
upper limit to its operation.
regulator is provided with automatic means for
' A'i'urther object of the invention is to provide
preventing the excitation of the synchronous
'an‘improved'automatic voltage regulator system
machine from being lowered far enoughby the for synchronous generators which has both an
regulator to cause instability of the regulated 15 upper limit and a lower limit.
synchronous machine. This lower limit of ex
‘A‘ still further object oi the invention is to pro
citation is dependent upon the load on the ma
vide an improved automatic voltage regulator
chine, it being lower at light loads thanat heavy
system for a synchronous generator which is pro
loads.
Such a 'lower limit is particularly im- ' _ vided with a modi?ed lower limit control for au~
portant in the case of a synchronous machine 20 tomatically reducing the kilowatt loading of the
having a relatively low short circuit ratio. By
regulated machine.
“short circuit ratio” is meant the ratio of the
The invention will be better understood from
field current at rated voltage no load to the ?eld
‘the following description taken in connection
current at rated current during short circuit.
with the accompanying drawing and its scope will
High short circuit ratio machines are inherently 26 be pointed out in the appended claims.
relatively stable but they are large and expensive
' The single ?gure of the accompanying drawing
to manufacture, whereas low short circuit ratio
illustrates diagrammatically an embodiment of
machines. are smaller and less expensive but
have less inherent stability margin.
the invention.
7
As the present invention may readily be com
Another way of decreasing the size and cost 30 bined with the system of my above referred to
of a synchronous machine is to design it for
joint patent with Louis W. Thompson, I will ?rst
higher rated power factor operation as this gives
brie?y describe that system.
better utilization of the material in that the ma- .
Referring now to the drawing, there is shown
chine is not intended to carry much idleor ywatt- '
therein by way of example a three-phase syn
less current. However, when this is done there is 35 chronous generator I which supplies power to an
increased danger of overheating the machine as
interconnected system over a circuit 2. The
a result of its carrying too high a ?eld current,
generator is vdriven by a suitable prime mover 3
or armature current, or both, in proportion to
such, for example, as a steam turbine which is
the actual kilowatt load it is carrying.
provided with a throttle 4 whose position is con
In accordance with the present invention there 40 trolled by any suitable means such as a conven
is provided an improved automatic voltage regu
tional centrifugal speed governor Ii. The gen
lator system for synchronous machines which is
orator has a direct current ?eld winding 8 which
provided with an automatic upper limit of exci~
is energized by a separately excited direct cur
tation whereby the heating of the machine is
rent exciter 1. The voltage of the generator is
limited to a safe value. This upper limit may 45 controlled ‘by varying its excitation and this in
conveniently be combined with the regulator.
turn is accomplished by varying the excitation of
system of the above referred to patent so as to ‘ the exciter. To do this an automatic voltage
provide an automatic voltage regulator system
regulator 8 is provided. This regulator may be
having both upper and lower limits.
of any suitable type and may for example be a
In some cases the kilowatt loading of a syn 50 rheostatic regulator of the type shown in Thomp
chronous machine is not as important as the
‘son Patents 1,848,852 or 1,894,837, both of which
system voltage, and in accordance with another
are assigned to the assignee of the present ap
feature of the present invention there is pro
plication. The illustrated regulator is similar to
vided an arrangement for automatically reduc
that shown in the first-mentioned patent and it
ing the kilowatt loading of the machine when 55 includes a reversible motor-operated rheostat 8.
2,411,710
s. k
, ,
‘
3
The degree of excitation of the generator and
the amount of load carried thereby are com—
pared by means of a special switching arrange
ment Ill comprising a ?rst movable member II
which is operated by the rheostat and a second
movable member 12 which is operated by the
throttle.
The voltage regulator comprises a main volt
4
tactors to the — side of the supply source. The
high speed raise contactor is a normally open
contactor which is connected to short circuit the
motor-operated rheostat when it is closed. The
high speed lower contactor 21 is normally closed
and in this condition is connected to short cir
cuit a resistor 28 connected in series with the
motor-operated rheostat in the excitation circuit
of the exciter ‘I.
age resp'onsivedevice of any suitable form such
In order to limit the lowering action of‘ the
as a torque motor 13 connectedito'respond to the 10
regulator the low speed lowering circuit con
voltage of the generator I or circuit 2. As shown
trolled by the contact I5 is completed through
for the sake of- simplicity, the torque motor ter
a pair of contacts 29 and 30 carried respectively
minals are connected directly across‘ the circuit,
by the rotatable members H and i2 and the high
although it will be understood that in practice
speed lowering circuit controlled by the contact
potential transformers are usually interposed be
i9 is completed through a pair of contacts 3i and
tween the circuit, which is of relatively high volt
32
carried by the rotatable members H and I2
age, and the torque motor which has a relatively
- respectively.‘ In order to raise the excitation
low voltage rating. The torque motor is pro
to a safe value for maintaining synchronism as
vided with a shaft l4 and'the torque imparted ~
by the load on the generator, an
to this shalt by the motor is counterbalanced 20 determined
auxiliary branch circuit is provided for energiz
by a spring I5 so that'only when the voltage is
ing the low speed raise circuit which is normally
normal will a balance exist and the shaft be
controlled by the contact ll. This branch circuit
- in its normal position. Fixed to the shaft I4 is
extends from the positive side of the control
.-.a contact-carrying assembly consisting oi‘ four
source through a normally open'pair of contacts
insulated yieldably-mounted contacts l8, l1, l8
33 and it carried respectively by the rotatable
and i9. Contacts [8 and," are on opposite sides - members
H and i2 and through a conductor 33
of’ av rotating star wheel contact 20 and contacts
to the conductor 22.
i8 and I9 are on opposite sides of a rotating disk ‘
It is usually not convenient to mount the mo
contact 2l._ Contacts ziland'il are mounted on ~' tor-operated
rheostat close to the throttle for
the same shaft and are rotated by any suitable 30
the prime mover and therefore in order to sim~=
‘means such as a small electric clock type self
plify the mechanical driving connections for the
, starting synchronous motor (not shown). The
switching
means Ill, the latter is mounted closely
contacts are so arranged that when the voltage
adjacent to either the throttle or the rheostat
ris atitspredetermined normal value no contacts
and is shown by way of example as mounted
-. aremade between themv and they'are in the ‘posi
next
to the rheostat so that its rotatable mem
tions illustrated in the’ drawing. 1!, however, the
her i I may be driven by the motor-operated rheo
~voltagefallsrthe torque motor shaft N rotates
stat. As shown, they are interconnected by a
' .in.
counterg-clockwise vdirection, as viewed in 1
speed reducing gear box ii’. The rotatable
-the drawing, causing contact ll to engage con
member [2 which will then usually be fairly far
- tact 211 if the fallin voltage is smaliand in addi-v 40
away from the throttle is driven from the throt
_ tion. causing contact l8 to engage contact 2| if
tle by any suitable remote positioning means
the fall in voltage is relatively large. Similarly,
One such means is shown in the drawing and
~i1the¢voltage rises above normal, the shaft I4
consists of a Selsyn transmitter 36 and a ,Selsyn
-.»is turned in a clockwise direction, ?rst causing
receiver 3L These two devices are similar in
~ ‘only; contact [6 to engage contact 2G if the voltage
construction, being provided with single-phase
rise is small and then causing contact I9 to en
rotors energized by any suitable source of alter
gage contact it it the voltage rise is large. Com
nating current and which are mechanically con
1 tact I6 which makes engagement on small in
nected to the throttle l and the rotatable mem»
creases in voltage is known as the slow lower
;,c_ontact_and contact is which makes engagement
, on large increases in voltage is known as the
- ‘quick. lower. contact. ‘Similarly, contacts I‘! and
G8 are known as the slow ‘raise and quick raise
; contacts, respectively._
The reason contacts l8 1
vand l9 can engage contact 2| after contacts l6
and ilengage contact 20 is because of yieldable
- "spring mountings for contacts 16 and H. 'These
. permit further rotation of the shaft l4 and hence .
further inward movement of the contacts I! and
!9 after the contacts is and it, as the case may
be, engage the contact 29. The common contacts
Y28 and ‘ii are connected to one side of a suitable
. source of control current indicated by the +
symbol. The slow raise and lower contacts are
connected by means of conductors .22 and 23
. . to-the raise‘ and lower terminals of the driving
~ motor for the motor-operated rheostat 9, the
1 a, common terminal of this motor being connected
to the opposite side of the supply source as indi
cated by the. — symbol. The high speed con
tacts- i8 and is are ; connected respectively by»
means of conductors 2E and 25 to highspeed raise
60 her I? respectively.‘ Their stators aresimilar to
the stators of three-phase induction motors and
they are interconnected by a three-phase circuit '
88; With this system the rotors oi the devices
38 and 31 induce unbalanced voltages in the
55 stator circuit only when the rotors are out of
correspondence and these unbalanced voltages
cause currents to ?ow, thereby producing motor
torques in the devices. As the rotorposition of
the device 33 is determined by the position of the
throttle, the rotor oirthe receiver 31 will auto»
matically follow any changes in the position of
the transmitter so that the two rotors always
occupy corresponding positions with respect to
their stators.v Thus, the system is the electrical
65 equivalent of a mechanical drive between the
throttle and the rotatableqmember i2.
-
It may sometimes happen that as a result of the
' action of the lower limit means for the regulator
the voltage of the generator will continue to in
crease to seriously high values and, in fact, it may
be less important to leave the loader: the genera
ator undisturbed than it is to limit the voltage.
Therefore, in order to prevent the voltage from
{and 1 lower contactors 26 and 2'5. The circuits ’
rising too high under these conditions I provide
- . through thesegcontactorsrare completed by valso
. econnecting the operating windings 0f the CO?! 75 an additional rotary contact member as on the
“11,710
5
rent in ileld winding I and regulator head",
shaft l l which is provided with an insulating sec
tion 40 and which cooperates with a brush 4!
operated by the frame 12. The members Ii and
39 may be similar except that they are angularly
displaced approximately 180 degrees on the shaft
being responsive to the armature current of ma
chine l. Thus, regulator head "is providedtwith
a direct current torque motor ll connected‘in':
series with the ?eld winding i, the torque of
ii so that whenever the brush 32 is making con
tact with the contact member 3i the brush 4|
is on the insulating segment 40 and whenever
vided
maximum
this motor
withsafe
being
raisevalue
balanced
and oflower
?eld
bycontacts
current.
a. spring551.
52 and‘
at "a
the brush 32 is on the insulating part of the mem- '
cooperating: respectively with. a
center"
ber 3| the brush 4i makes contact with the con 10 star wheel contact. 55. which isrcocmected‘ to‘ tho‘
positiveside of the control source;
tact disk 39. Thus, current can ?ow from the
brush 4i to a collecting brush 42 which continu~
head
The‘iarmature
is provided
current
with 81responsive’
‘hm-Phil: Wm‘
ously engages the disk 3! whenever the excitation
motor I! which is energized. in accordancewith
lowering action of the voltage regulator is limited
armature current oi'the machine. i. by; means of
and the insulation 40 prevents the flow of cur
suitably connected current transiormersll‘. The
rent from the brush 4i to the disk 39 at all times
torque of motor “is balanced‘byaspring “at
when the lower limit means does not prevent the
regulator from lowering the excitation.
the rated maximum’ safe armature-currentvalue:
of the machine | and the torque motor“v layer»
The brush 4| is connected to the high speed
lowering contact IQ of the regulator by means 0! 20 ranged to operate raise and lowerco'ntacts-i?‘ and
‘l which cooperate with separate. rotating-star
the conductor 25 so that the collecting brush 42
contact wheels whichv are insulated from each;
is connected to the positive side of the source of
other. The one which cooperates with the lower
control current only when the voltage of the
contact BI is connected to the positive sideoi. the
generator is substantially above the normal value
held by the regulator, which will ordinarily be
the rated value of the machine I, and only when
the voltage lowering action of the regulator is
limited by the throttle position responsive means
which positions the brush 4i in accordance with
the kilowatt load on the machine I.
Energization of collecting brush 42 is arranged
to cause a reduction in the load on the generator
source of control current. as shown.
The-contacts oi the two regulator heads 49 and;
50 crew interconnected that when either of. the
lowering contacts engage their respective star.
wheel contacts the?eld current‘ot the generator
30 i is reduced. This may conveniently-be accom-I
plished by means of amotor-operated rheostat 4i '
having three resistor plates connected respec
tively in the phases. of the voltage regulator
torque motor 13. The two lowering contacts“
I‘. This is accomplished by connecting it by
means of a conductor 43 to the lowering circuit
for a reversible synchronizing motor 44 which 35 and 40 are connected respectively to the lowering
part 01' the split ?eld winding: for the motor
, controls the tension of a loading spring 4! for the
which operates the. rheostat 4| andthe raising
governor 4. . The synchronizing motor 44 is shown
. part of the split field. is connected to the positive
as a conventional split ?eld type motor whose
side of the source of. control current-throughthe
direction of operation is normally controlled by_
. raise and lower push button switches. By means 40 two sets of raise contacts or the regulator heads
of these switches the motor may be made to in
40 and." inseries;
crease or decrease the tension of the spring 4‘
The operation or thesystem is as follows:
thereby to raise and lower respectively the speed
Assume that prime mover 3- is being supplied
setting oi’ the governor 5 and hence to raise and
lower respectively the loading of the generator I.
In order to prevent overshooting oi this control
with steam and is drivingv the generator lat.
rated speed and that the generator i is supplying
power to the system over circuit 2 atrated volt
age. Under these circumstances the parts will
be in the positions shownin the drawing. 1! now
the voltage should fall for any reason the slow
raise circuit will be closed through the contacts
l1 and 2.0 it the tall in voltage‘ is slight, and in
means a so-called notching arrangement is pro~
vided in the form of a rotating cam or star whe‘el
contact 46 which intermittently makes and breaks
the circuit through the conductor 43 so that
whenever themotor 44 is operated automatically
it will operate intermittently instead of continu
ously. The contact wheel 46 is shown as being
driven by a motor 41.
addition the quick raise circuit will be closed
through the contacts II and. II it the tall in volt
age is substantial.‘ Closure of the slowraise cir
cuit will cause the motor-operated rheostat I
‘
In order to notify the station operator that load
to operate in a direction to cut out resistance in
the exciter ?eld circuit and closure 0! the high
speed raise circuit will cause the high speed con~~
is being taken oil the machine I an alarm relay
48 may be connected in' the conductor 43 so that
whenever current ?ows therethrough it will
close its contacts to operate any suitable alarm
or signal device.
tactor ,2! to short circuit the motor-operated
(ll) rheostat thereby producing a large decrease in
In order to prevent the voltage regulator from
exciter ?eld resistance and causing a rapid in
crease in excitation. The raising direction or
operation of the motor~operated rheostat is such
overheating the generator i in case the voltage
of its circuit falls too low it is provided with an
automatically operating upper limit. This may
as to rotate the rotatable member ii in a clock
wise direction, as shown in the drawing. when
the voltage returns to normal the raise circuits
are broken and the excitation raising operation
ceases. If new the voltage becomes higher than
normal the slow lowering circuit is closed it the
rise in voltage is small and in addition the quick
lowering circuit is closed it the voltage increase
is large. Closure of the slow lowering circuit
through the contacts i6 and 20 reverses the oper
ation of the motor-operated rheostat causing it
75 to insert more of its resistance in the excite: ?eld
be directly responsive to machine temperature or r -
to temperature rise but I prefer to use current
response because overcurrent is the primary cause
of overheating and as the machine will have rated
overcurrent or maximum current values it is more
convenient to provide means which will be actu
ated when these current values are exceeded.
As shown, the upper current limit means com
prises a pair of regulator heads 49 and'iil general
ly similar to the automatic voltage regulator head
4. regulator head 49 being responsive to the our
2,411,710
energize the motor-operated rheostat 6| in such
a manner that it reduces the resistance in the
main control circuit of the voltage regulator.
This in effect makes the voltage regulator think
that the voltage is higher than it actually is so
that it closes its lowering contacts and reduces
the ?eld current and this action will continue
highspeed'lowering contactor 27! to openthereby
‘ '
I
8
to the positive side of the control circuit so as to
circult and causing'it to rotate the member I I .
in a ‘counterclockwise direction, asviewed in the
drawing; Closure‘ of the'high speed lowering cir
cuit. through, the contacts i9 and 2| causes the
the resistor 28 in the ?eld circuit and
' cing the excitation.
, “observed that as the lowering opera
until both the armature current and the ?eld cur
rent are reduced to safe values. However, the
motor of the rheostat 6! will not reverse so as to
tion'of'thé 'niotoFoperated rheostat continues the.
29 and 3| approach, an angular position
he)?‘ disengage their cooperating con
raise the setting of the regulator until both the
armature and ?eld currents of the main machine
52“ so‘ that when a predetermined
ationis reached the lowering circuits
ke'n?by the separation of ‘the contacts
insulating pieces set in the contacts
are below their maximum safe values.
>
It will, of course, be obvious to those skilled in
the art that a motor-operated rheostat is not
essential in that the raise and lower coils of the
At' the same time that this happens
the
task” will have been rotated to a posi
I tionjin 'hich it is permitted toengage its coop
split ?eld for the motor of thelrheostat 6! could
be relay coils for controlling the short circuiting
ntact 14‘ thus completing 'a branch cir
io' energizing the motor-operated rheostat, 20 of a resistor in a circuit of the torque motor l3,
ln.t erraisi'ng‘direction. Actually, it is preferable
the resistor normally being un-short circuited
to:'pr‘ovi_de_._a ‘slight interval between the opening
of ‘the lowering circuit controlling contacts. 20
andthe closing of the raise circuit controlling
contacts so to prevent a pumping action of the 25
system.
"
'
‘
'-
»
v
' The ‘value of excitation below, which'the lower
ing circuits are‘rendered inoperative and the low
speed raise circuit is rendered operative is deter
mined by the‘ angular position of the rotatable
member I2. This is determined by the throttle
positionwhich'in its turn controls the load car
ried byjthe generator. I The drive for the‘member
i2 is‘ such‘that when the throttle is moved in an
7 opening" direction; so as to increase the load the
rotatable member I2; is turned in aclo'ckwise di
rection; as'viewed in'the drawing, withthe result
that‘the‘predetermined minimum value of excita
tionbelowjwhich the'lowering contacts, are inca
pacitated and the low speed raising circuit is ren
dered operative’ is increased. Similar-ma clos
whenever the ?eld and armature currents get too
high. However, the gradual control which is pro
duced by the motor-operated rheostat is prefer
able.
'
The value of the resistance of the rheostat 6i is
relatively small so that when it is all short cir
cuited the resulting reduction in terminal voltage
is also relatively small so-that the accompanying
reduction in armature current and ?eld current
cannot be made to fall to such values as to
jeopardize stability. In general, the value of this
resistance is so limited as not to allow under
exeited leading power factor operation of the gen
erator l. Also the speed of its motor is made very
slow so as not to reduce appreciably the voltage
regulator setting during transient faults or mo
‘ mentary disturbances.
While there has been shown and described a‘
4.0 particular embodiment of this invention, it will
be obvious to those skilled in the art that various
changes and modi?cations can be made therein
wise rotation of the member l2, thus decreasing
without departing from the invention and, there—
the, permissible minimum value of excitation.
fore, it is aimed in the appended claims to cover
,When the voltage gets high enough to close the 45 all such changes and modi?cations as fall within
high speed lowering contact IQ of the voltage reg
the true spirit and scope of the invention.
ing motion of the throttle causes a counterclock
ulator and the load, on the generator is too high
toallo'w further reduction in excitation, the cir
'
What I claim as new and desire to securebii
Letters Patent oi the United States is:
'cuit'will be completed through the brush iii and ,
1. In a synchronousuto-synchronous electric
50
the rotating contact 39 to the lowering ?eld wind
mg ‘of the synchronizing motor 44, so as to reduce
the'sp'eed setting of the governor and thus per~=
init a closingmotion of the throttle 4 which will
“cause the frame it to move in the closing direc
tion untileventually the lower limit will be raised
su?lciently to permit a decrease in the excitation
and consequently a decrease in voltage. .
-' Thefield'and armature currents will normally
be below their maximum safe values so that the
raise contacts til and-59 of the ?eld and armature
current responsive units lid and 59 will normally
be closedand consequently the rheostat at will
power system, a synchronous dynamoelectrlc ma
chine, an automatic voltage regulator responsive
to the voltage of said machine for controlling the
?eld current of said machine in a manner to
maintain the machine voltage at a predetermined
value, and means responsive to an abnormal oper
ating condition of said machine which is asso
ciated with dangerous overheating o1~ said ma
chine and cooperating with said voltage regulator
for lowering the voltage- setting of said regulator
below said predetermined value. '
,
stalled’condltion or else it may be provided with
2. In a synchronous-to-synchronous electric
power system having a synchronous dynamoelec
trio machine, an automatic voltage. regulator re
sponsive to the voltage of said machine for con‘
trolling the field current of said machine in a
manner to maintain the machine voltage at a
conventional limit switches _for deenergizing it
when it reaches its limits of operation. With alt
machine ?eld current and to machine armature
normally be turned'to its all-in position so that
all of its resistance will be inserted in the circuit
of the torque motor 53.’ The motor 6i may either
be designed to'be energized continuously in a
predetermined value, and means responsive to.
current and enacting with said voltage regulator
for lowering the voltage setting of said regulator
- i3 the regulator will tend to hold normal or rated
below said: predetermined voltage value whenever
voltage of the generator I. It now either the field
either of. said currents exceeds a predetermined
current'orthe armature current of the machine
maximum safe value, said means being operated
mi exceeds its maximum safe value the lower con
‘ tact at or the lower contact as will be connected 75 to restore the voltage setting of said regulator to
of this resistance in the circuit of the torque motor
9
2,411,710
10
its normal value when both said currents are less
than their respective maximum safe values.
3. In a synchronous-to-synchronous electric
stability values independently of the action of
said regulator, and means responsive to a prede
power system, a synchronous dynamoelectric ma- ,
chine, an automatic voltage regulator responsive
to the voltage of said machine for controlling the
excitation of said machine in a manner to main
tain the machine voltage substantially at a pre
determined value, means for preventing said reg
termined over-voltage condition of said generator
for actuating said speed setting adjusting means
so as to reduce the kilowatt loading of said gen
erator.
_ 7. In a synchronous-to-synchronous electric
power system, a synchronous generator, at prime
mover for said generator, a speed governor for
ulator from lowering the excitation of said ma ll
said prime mover, means for adjusting the speed
chine below predetermined minimum safe stable
setting of said governor for varying the kilowatt
values which vary in accordance with the kilo
loading of said generator, an automatic voltage
watt loading of said machine, and means respon
regulator for said generator for controlling the
sive to a predetermined overvoltage condition of
current of said generator so as to maintain
said machine for lowering the kilowatt loading lb ?eld
a predetermined normal generator voltage, said
of said machine.
generator having predetermined maximum safe
4. In a synchronous-to-synchronous electric
values of field current and armature current,
power system, a synchronous dynamoelectric ma
means‘for incapacitating the ?eld current low
chine, an automatic voltage regulator responsive
ering action of said regulator when the field cur
to the voltage of said machine for controlling the
rent is below predetermined maximum safe sta
excitation of said machine in a manner to main
bility values which are proportional to the kilo
tain the machine voltage substantially at a pre
watt load on said generator, means responsive to
determined value, means for preventing said reg
a predetermined overvoltage condition of said
ulator from lowering the excitation of said ma
generator for actuating said speed setting adjust
chine below predetermined minimum safe stable
ing means so as to reduce the kilowatt loading
values which vary in accordance with the kilo
of said generator, and means responsive to both
watt loading of said machine, means for raising
of said currents for lowering the voltage setting of
the excitation of said machine to said minimum
said regulator whenever either of'said currents
values independently of said regulator, and means
exceed their respective predetermined maximum
responsive to a predetermined overvoltage condi
safe values and for restoring the voltage setting
tion of asid machine for lowering the kilowatt
of said regulator to its normal value whenever
loading of said machine.
both of said currents are below their respective
5. In a synchronous-to-synchronous electric
predetermined maximum safe‘ values.
power system, a synchronous generator, a prime
8. In a synchronous~to-synchronous electric
mover for said generator, 9. speed governor for
power system, a synchronous generator having a
said prime mover, means for adjusting the speed 35 short circuit ratio of less than unity, a prime
setting of said governor for varying the kilowatt
mover for said generator, a speed governor for
loading of said generator, an automatic voltage
said prime mover, means for adjusting the speed
regulator for said generator for controlling the
setting of said governor for varying the kilowatt
?eld current of said generator so as to maintain
ie-ading of said generator, an automatic voltage
a predetermined normal generator voltage, means
regulator for said generator for controlling the
for incapacitating the ?eld current lowering ac
?eld current of said generator so as to maintain
tion of said regulator when the ?eld current is
a predetermined normal generator voltage, said
below predetermined maximum safe stability val
generator having predetermined maximum sate
ues which are proportional to the kilowatt load
on said generator, and means responsive to a pre
- values of ?eld current and armature current,
erator for actuating said speed setting adjusting »
means so as to reduce the kilowatt loading of
means for incapacitating the ?eld current lower
ing action of said regulator when the ?eld cur~
rent is below predetermined maximum safe sta
bility values which are proportional to the kilo
watt load on said generator‘, means for raising
the ?eld current to said predetermined minimum
a short circuit ratio of ‘less than unity, a prime
mover for said generator, a speed governor for
of said regulator, means responsive to a prede
determined overvoltage condition of said gen
said generator.
6. In a synchronous-to-synchronous electric
power system, a synchronous generator having
safe stability values independently of the action
termined overvoltage condition of said generator
said prime mover, means for adjusting the speed _ for actuating said speed setting adjusting means
setting of said governor for varying the kilo
so as to reduce the kilowatt loading of said gen
watt loading of said generator, an automatic volt
erator, and means responsive to both of said cur
age regulator for said generator for controlling
rents for lowering the voltage setting of said reg
the field currentv of said generator so as to main
ulator whenever either of said currents exceeds
tain a predetermined normal generator voltage,
their respective predetermined maximum safe
means for incapacitating the ?eld current low 00 values and for restoring the voltage setting of said
ering action of said regulator when the ?eld cur
regulator to its normal value whenever both of
rent is below predetermined maximum safe stabil
said currents are below their respective prede
ity values which are proportional to the kilowatt
termined maximum safe values.
load on said generator, means for raising the
65
?eld current to said predetermined minimum safe
SELDE'N B. CRARY.
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