Synchronous generator

This invention relates to a synchronous generator comprising a stator having output winding means connected to a load or loads and main voltage building up means including capacitor means and capacitor exciting winding means, said capacitor means being connected across said capacitor exciting winding means, said output winding means and said capacitor exciting winding means being provided on a common core; and a rotor having field winding means across which a rectifier means is connected; wherein said synchronous generator further comprises auxiliary voltage building up means provided in said stator, said auxiliary voltage building up means causing the output winding means to provide said stator with armature reaction when initial large current has flowed through said auxiliary voltage building up means from said output winding means to thereby build up output voltage across said output winding means with the start of said generator. The auxiliary voltage building up means may be provided either in a circuit including the output winding means or in a circuit including an auxiliary winding wound on a core for the output winding means.

BACKGROUND OF THE INVENTION 
One example of a field rotating type synchronous generator has been 
disclosed in Japanese Patent Application Publication No. 2367/1958. This 
generator comprises a stator having an output winding connected to a load 
and main voltage building up means including a capacitor exciting winding 
and a capacitor connected across the ends of the capacitor exciting 
winding, and a rotor having a field winding across which a rectifier is 
connected. In such a generator, residual magnetism in a rotor core causes 
a voltage to be induced across the capacitor exciting winding, and 
accordingly, a current of advanced phase flows through the capacitor 
exciting winding. Increased magnetic action by the advanced phase current 
causes an occurrence of self-excitation while armature reaction of the 
capacitor exciting winding causes an electromotive force of reverse phase 
to be produced in the field winding. The electromotive force causes a 
field current to flow through the rectifier from the field winding. Thus, 
the field core is more excited to build up an output voltage across the 
output winding and the capacitor exciting winding. The load current 
through the load and the exciting current through the capacitor exciting 
winding increase the field electromotive force of reverse phase through 
their composite armature reaction, which causes the field current through 
the field winding to be enhanced. Therefore, in addition to the advantage 
of its brushless type generator, this generator has the advantages that 
decreasing a voltage drop of the output winding by the load can be 
restrained and that variation in the voltage can be also restrained. 
However, it is impossible that the prior art generator assures the rapid 
build-up of the voltage, because the reverse phase electromotive force is 
induced in the field winding only by the armature reaction through the 
current in the capacitor exciting winding. In order to assure the rapid 
build-up of the voltage across the output winding, there should be used 
core material having less loss of the magnetomotive force, which causes 
the generator to be expensive. Also, in order to increase the voltage 
induced across the capacitor exciting winding by residual magnetism in the 
core, there should be increased the number of turns of the capacitor 
exciting winding and the value of the capacitor, which causes the 
generator to be large-scaled. 
SUMMARY OF THE INVENTION 
Accordingly, it is a principal object of the invention to provide a 
synchronous generator adapted to rapidly build up an output voltage across 
an output winding without using expensive core material and without 
increasing the number of turns of the capacitor exciting winding and the 
value of the capacitor. 
In accordance with the invention, there is provided a synchronous generator 
comprising a stator having output winding means connected to a load or 
loads and main voltage building up means including capacitor means and 
capacitor exciting winding means, said capacitor means being connected 
across said capacitor exciting winding means, said output winding means 
and said capacitor exciting winding means being provided on a common core; 
and a rotor having field winding means across which a rectifier means is 
connected; wherein said synchronous generator further comprises auxiliary 
voltage building up means provided in said stator, said auxiliary voltage 
building up means causing the output winding means to provide said stator 
with armature reaction when initial large current has flowed through said 
auxiliary voltage building up means from said output winding means to 
thereby build up output voltage across said output winding means with the 
start of said generator.

DETAILED DESCRIPTION OF THE EMBODIMENTS 
Referring now to FIG. 1, there is shown a single phase synchronous 
generator 1 comprising a stator 2 having an output winding 3 provided 
therein and a rotor 4 having a field winding 5 wound on a rotor core 6. A 
half-wave rectifier 7 is connected across the ends of the field winding 5. 
A load 8 is connected through a switch 9 to the output winding 3. 
Main voltage building up means 10 is provided in the stator 2, which 
comprises a capacitor exciting winding 11 and a capacitor 12 connected 
across the ends of the capacitor exciting winding 11. The output winding 3 
and the capacitor exciting winding 11 are wound on a common core not 
shown, so that the voltages across the output winding 3 and the capacitor 
exciting winding 11 may preferably have a phase difference of 90.degree.. 
The synchronous generator 1 of the invention also comprises auxiliary 
voltage building up means 13 provided in the stator. The auxiliary voltage 
building up means 13 comprises means to flow an initial large current 
through the auxiliary voltage building up means 13 until a predetermined 
degree of output voltage is fully built up across the output winding on 
initiation of the generator 1. 
In FIG. 1, the auxiliary voltage building up means 13 may comprise a 
thermally of sensitive resistor 14A of a positive temperature coefficient 
connected across the output winding 3 in a manner parallel to the load 8. 
Such thermally sensitive resistor may be commercially available as 
posister (trademark). 
In operation, since the thermally sensitive resistor 14A is of 
substantially lower resistance before starting of the synchronous 
generator 1, the output winding 3 is in the condition of being 
substantially shorted by the thermally sensitive resistor 14A. As the 
generator 1 is started, residual magnetism in the rotor core 6 causes a 
voltage to be induced across the capacitor exciting winding 11. The 
voltage across the capacitor exciting winding 11 permits an advanced 
current I.sub.12 to flow through the capacitor 12. At the same time, since 
a voltage is induced across the output winding 3, a current I.sub.14 which 
approximates a short circuit current flows through the thermally sensitive 
resistor 14A. Thus, the composite armature reaction by the current 
I.sub.12 through the capacitor 12 and the current I.sub.14 through the 
thermally sensitive resistor 14A permits a voltage to be induced across 
the field winding 5. It should be noted that the composite armature 
reaction is much larger than that only by the capacitor exciting winding 
11. As a result, the voltage across the output winding 3 is more rapidly 
built up. It should be also noted that the build-up of the output voltage 
across the output winding 3 never largely depends on materials of the 
core, which enables inexpensive core material to be used. It will be 
understood that such rapid build-up of the output voltage across the 
output winding 3 never requires so many turns of the capacitor exciting 
winding and so large capacitance of the electric capacitor 12. 
As the output voltage is built up, the resistance of the thermally 
sensitive resistor 14A rapidly increases, which causes the current in the 
thermally sensitive resistor 14A to decrease. Therefore, the thermally 
sensitive resistor 14A never become a load to the output winding after the 
build-up of the output voltage. Thus, an electric power can be effectively 
supplied to the predetermined load 8. 
In the embodiment of FIG. 2, the auxiliary voltage building up means 13 may 
comprise a series connection 14B of an electric resistor 15 having a 
substantially small resistance and a normally closed relay contact 16 
which is opened after a normal operation of the synchronous generator 1 is 
started. A relay coil 17 may be connected across the output winding 3 
through an electric resistor 18 and through its normally closed relay 
contact 16B. A normally open or self-holding relay contact 16C is 
connected at its one end through a resistor 19 to the point of junction 
between the resistor 18 and the normally closed relay contact 16B and at 
its other end to one end of the output winding 3. The normally closed 
relay contact 16A is opened by excitation of the relay coil 17. It should 
be noted that the relay coil 17 is excited by the output voltage fully 
built up across the output winding 3. It should be also noted that the 
resistors 18 and 19 are of substantially higher resistance. 
In the embodiment of FIG. 2, when a voltage is induced by residual 
magnetism in the rotor 4, a current which approximates a short circuit 
current is caused to flow through the normally closed relay contact 16A 
and the resistor 15. At that time, the relay coil 17 is never excited 
because there is no enough voltage across the relay coil 17 to excite it. 
As the output voltage is built up across the output winding 3, the voltage 
across the resistor 15 becomes higher, and as a result, the voltage enough 
to excite the relay coil 17 is applied thereto. As the relay coil 17 is 
excited, the normally open relay contact 16C is closed while the normally 
closed relay contacts 16A and 16B are opened. Thus, the resistor 15 is 
displaced out of the output winding 3, which causes the current 
approximating the short circuit current to be cut. Since the relay coil 17 
remains to be connected through the resistors 18 and 19 to the output 
winding 3, it is self-held unless the output voltage of the generator 1 is 
decreased. It will be understood that the resistors 18 and 19 have less 
effect on the load 8. It will be noted that the resistor 15 may be 
replaced by either of reversely parallel connected diodes, varister and 
the likes. It will be also understood that if the internal impedance of 
the relay coil 17 is fully higher, the resistors 18 and 19 may be omitted. 
FIG. 3 shows another embodiment of the auxiliary voltage building up means 
which may comprise a full wave rectifier 20 connected to the output 
winding 3 and a semiconductor switching device such as a transistor 21 
connected to the output of the full wave rectifier 20. A voltage divider 
22 of resistors 23 and 24 may be connected to the output of the full wave 
rectifier 20. A series connection of an electric resistor 25 and another 
transistor 26 may be also connected to the output of the full wave 
rectifier 20. The dividing point of the voltage divider 22 or the point of 
junction between the resistors 23 and 24 may be connected through a 
reversely disposed Zener diode 27 to the base of the transistor 26. The 
point of junction between the resistor 25 and the transistor 26 is 
connected to the base of the main transistor 21. 
In the embodiment of FIG. 3, when the induced voltage of the output winding 
3 is less than a predetermined value, the output or divided voltage of the 
voltage divider 22 never reaches the Zener voltage of the Zener diode 27, 
no base current flows through the transistor 26 with the result that it is 
not turned on. Then, a base current flows through the resistor 25 to the 
base of the transistor 21, and as a result, it is turned on. Thus, on 
starting the synchronous generator 1, a current which approximates a short 
circuit current is caused to flow through the output winding 3. As the 
output voltage is built up to the predetermined value, the Zener diode 27 
is broken down so as to be turned on, which causes the transistor 27 to be 
turned on. Thus, the base current no longer flows through the base of the 
main transistor 21, with the result that it is turned off so as to have no 
effect on the load 8. It will be noted that the transistor 26, the Zener 
diode 27 and the resistors 23, 24, 25 and 26 constitute a control circuit 
to turn on or off the main transistor. It will be also noted that the 
transistor 21 may be replaced by other semiconductor switching devices 
such as thyristor, gate-turn off thyristor, triac and the likes. 
FIG. 4 shows another embodiment of the synchronous generator 1 in which the 
auxiliary voltage building up means may comprise an auxiliary winding 3A 
wound on the stator common core. The auxiliary voltage building up means 
may be connected across the auxiliary winding 3A. In FIG. 4, the voltage 
building up means 13 is shown to comprise a thermally sensitive resistor 
14A of positive temperature coefficient. It will be understood that the 
operation of the embodiment of FIG. 4 is substantially identical to that 
of FIG. 1. After the build-up of the output voltage to the predetermined 
value, the high resistance of the thermally sensitive resistor 14A 
restrains a current from flowing therethrough. Thus, the auxiliary winding 
3A has no effect on the main output winding 3. 
FIG. 5 shows a capacitor exciting type three phase synchronous generator 1A 
constructed in accordance with the invention. Numerals 3u, 3v and 3w 
designate output windings of u, v and w phases, respectively, and numerals 
13u, 13v and 13w designate auxiliary voltage building up means provided to 
be connected to the output windings 3u, 3v and 3w, respectively. Main 
voltage building up means 10 may comprise a capacitor exciting winding 11 
wound on a core (not shown) common to that of one of the three output 
windings 3u, 3v and 3w. The capacitor exciting winding 11 and the 
corresponding output winding having the common core may be preferably 
disposed so that the voltages across them have a phase difference of 
90.degree.. The auxiliary voltage building up means 13u, 13v and 13w may 
comprise a thermally sensitive resistor 14A of positive temperature 
coefficient, although they may comprise either of those shown in FIGS. 2 
to 4. It will be understood that the operation of the embodiment of FIG. 5 
is substantially identical to that of FIG. 2. 
The synchronous generator 1 of FIG. 6 is substantially similar to that of 
FIG. 1, except that the positive thermally sensitive resistor 14A is 
connected between one end and a tap t of the output winding 3. It will be 
understood that in this embodiment, on initiation of the generator 1, the 
current which approximates the short circuit current flows through a 
portion 3a of the output winding and the thermally sensitive resistor 14A. 
In general, it takes a substantial time for the thermally sensitive 
resistor 14A having a positive temperature coefficient to be heated by 
itself. Therefore, in case that such thermally sensitive resistor 14A is 
connected across the whole output winding, as shown in FIG. 1, the latter 
is shorted by the thermally sensitive resistor for a substantial long 
time, during which the generator 1 has a substantial large load of the 
thermally sensitive resistor 14A. As a result, if the generator 1 is 
driven by an engine, for example, such a large load is applied to the 
engine on initiation of the generator, which causes the engine to stop. It 
should be noted that since, in this embodiment, the thermally sensitive 
resistor 14A is connected across only the portion 3a of the output winding 
3, a large current is restrained from flowing through the thermally 
sensitive resistor 14A on initiation of the generator 1, which causes the 
load to be smaller against the generator 1. 
It will be noted that the thermally sensitive resistor 14A may be connected 
between two taps t.sub.1 and t.sub.2 of the output winding 3 as shown in 
FIG. 7, so that another portion 3b of the output winding 3 is connected to 
the thermally sensitive resistor 14A. It will be also noted that the three 
thermally sensitive resistors 14Au, 14Av and 14Aw may be connected to the 
portions of the three output windings 3u, 3v and 3w of the three phase 
synchronous generator 1A, respectively, as shown in FIG. 8. In this case, 
a capacitor exciting winding (not shown) of main voltage building up means 
may be wound on a core common to that of one of the three output windings 
3u, 3v and 3w, in a manner identical to that of the embodiment of FIG. 5. 
The synchronous generator 1 of FIG. 9 is also substantially similar to that 
of FIG. 1, except that a switch 29 such as a push button switch may be 
connected between one end of the output winding 3 and the thermally 
sensitive resistor 14A. The switch 29 is closed after the revolution 
(r.p.m.) of the generator 1 reaches a predetermined value. This switch 29 
may remain closed during operation of the generator 1. This is because the 
thermally sensitive resistor 14A has a rapidly increased resistance by its 
self-heating on build-up of the output voltage. It should be noted that 
since the switch 29 is closed only after the revolution of the generator 1 
reaches a predetermined value, a power source such as an engine never has 
a large load applied thereto on initiation of the generator, and as a 
result, the engine is prevented from stopping before the revolution of the 
generator 1 reaches it. Even though the generator 1 is started while the 
switch 9 for the load 8 remains closed, the high output voltage is never 
built up across the output winding 3 unless the switch 29 is closed. 
Therefore, in case the load is an electric motor, it can be prevented from 
its danger. The switch 29 may be preferably a self-return type push button 
switch. 
In the embodiment of FIG. 9, the capacitance of the capacitor 12 and the 
number of turns of the capacitor exciting winding 11 may be so set that 
the output voltage is never built up only by the advanced current I.sub.12 
through the capacitor 12. In this design, only on closing of the switch 
29, the output voltage can be built up, and therefore, the switch 9 for 
the load 8 may be omitted. In this case, the switch 29 may be preferably 
also a self-return type push button switch. 
FIG. 10 shows a modification of the embodiment of FIG. 9, in which a series 
connection of the thermally sensitive resistor 14A and the switch 29 may 
be connected at one end to the one end of the output winding 3 and at 
other end to a tap t of the output winding 3 so that the series connection 
is connected across a portion 3c of the output winding 3. In this 
modification, the current approximating the short circuit current through 
the thermally sensitive resistor 14A on initiation of the generator 1 can 
be limited. Thus, a large load can be prevented from being applied to the 
generator. 
It will be noted that the three series connections of the thermally 
sensitive resistors 14Au, 14Av and 14Aw and the switches 29u, 29v and 29w 
may be connected across the three output windings 3u, 3v and 3w, 
respectively, as shown in FIG. 11. In this case, a capacitor exciting 
winding (not shown) of main voltage building up means may be wound on a 
core common to that of one of the three output windings 3u, 3v and 3w, in 
a manner identical to that of the embodiment of FIG. 5. 
Although some embodiments of the invention have been described and 
illustrated with reference to the accompanying drawings, it will be 
understood by those skilled in the art that they are by way of example, 
and that various changes and modifications may be made without departing 
from the spirit and the scope of the invention, which is intended to be 
defined only to the appended claims.