JPH05219767A - Power transmission system for engine - Google Patents

Abstract

PURPOSE:To make it possible to minimize fuel consumption of an engine, to enable the use of a cyclo converter having small capacity or an inverter, to make it possible to reduce the capacity of an AC generator and to offer a power transmission system of the engine capable of operating over most operation speed range with sine-wave voltage and current. CONSTITUTION:A series circuit of a breaker 4, a converter 5 or an inverter 6 and a breaker 7 is connected in parallel with a breaker 3 connecting an AC generator 2 connected to an engine 1 with an AC motor 8 driven by output thereof, and when the speed is lower than a specific value, power of the AC generator 2 is supplied to the AC motor 8 through the converter 5 and the inverter 6, while when the speed exceeds the specific value, the AC generator 2 is directly connected to the AC motor 8 electrically to execute speed control operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power transmission system for a prime mover, and more particularly to a power transmission system for a prime mover such as an electric propulsion system of a ship or an electric power system of a railroad vehicle powered by an internal combustion engine, that is, a diesel car. The present invention relates to a means for transmitting power of a prime mover in a system including a motor and an electric motor for the purpose of variable speed / reversible operation.

[0002]

2. Description of the Related Art A conventional propulsion device for an electric propulsion system of a ship is
For example, it is classified in Table 1 of "Journal of the Japanese Society of Ship Engineers" Vol. 19, No. 2, page 23. In these systems, the prime mover rotates at a constant speed except for one example, and there is no idea that the converter or the inverter bears a small output partial load.

"NAVAL ENGINEERS JO
Page 235 of “URNAL April / 82” describes an example in which the voltage and frequency of the generator are fixed at 6300 V and 60 Hz, and the motor and the generator are electrically directly connected at the maximum output.
It is shown on page 35. In this conventional example, until the maximum output is reached, three generators of 24 MW and 3600 rpm are fully operated, and the frequency converter controls the voltage, current, and frequency of the electric motor so that the frequency near the synchronous speed of the electric motor is 60 Hz. When this happens, directly connect the motor and generator directly. Therefore, each frequency converter has 34500 Hp
Since it has almost the same capacity as all the outputs, it is not possible to employ a small capacity converter or inverter. Further, the prime mover is basically operated at a constant speed.

Further, the above-mentioned "Journal of the Japan Society for Marine Vessels", No. 29
The conventional example of FIG. 6 on the page shows that the propeller drive electric motor is of a tandem type, but the electric motor is only a DC motor, frequency control is not performed, and a constant voltage constant frequency power supply is used.

On the other hand, in Japanese Patent Laid-Open No. 54-140123, there are a plurality of generators driven by a prime mover, one of them is operated at a constant speed rotation, and the remaining generators are operated at a low speed. It shows an example. The output of the generator that is operated at the rated speed is started by a motor that is started by a cycloconverter or an inverter, and the speed is controlled. When the synchronous speed of the electric motor and the synchronous speed of the low speed generator match,
The power source of the electric motor is switched to the power source of the generator during low speed operation, and thereafter, the speed of the electric motor is controlled by changing the rotation speed of the prime mover. However, no consideration is given to the inefficiency of the remaining generators at low speed operation.

[0006]

In the conventional power transmission system for a prime mover described above, even if the output of the prime mover changes, the prime mover rotates at a constant speed and the fuel consumption rate cannot be minimized. Therefore, there is a problem that even in a ship that does not normally run at maximum speed, the number of days that can be sailed is determined based on the fuel consumption during high-speed operation.

Along with that, a cycloconverter and an inverter, which have a large capacity and are expensive, have been adopted, and it has been difficult to reduce the cost.

Further, when a cycloconverter or an inverter is connected to an AC generator, ripple current flows in the AC generator, and it is necessary to take measures against temperature rise.

Furthermore, since the full load of the alternator is supplied to the electric motor through the cycloconverter and the inverter, the power factor of the generator is poor in most of the operating speed range, and the kVA capacity of the generator must be increased. Inevitably, it was a large and heavy system.

Since a motor and a generator interpose a cycloconverter and an inverter, most of the operating speed range cannot be operated with a sinusoidal voltage and current. Therefore, electromagnetic noise is generated in the electric motor and the generator, a reverse phase component is generated, and the internal loss is large.

The object of the present invention is to minimize the fuel consumption rate of a prime mover, to use a cycloconverter or an inverter having a small capacity, to reduce the capacity of an alternator, and to operate a sine wave in most operating speed range. It is to provide a power transmission system of a prime mover that can be operated with the voltage and current of.

[0012]

In order to achieve the above-mentioned object, the present invention provides a generator connected to a variable speed prime mover, an electric motor driven by the electric power, and a means for controlling the output or the rotational speed of the electric motor. In a power transmission system for a prime mover including, a series circuit of a second circuit breaker and a converter or an inverter is provided in parallel with a first circuit breaker that connects an AC generator and an AC motor, and the output or rotation speed of the motor is Below a predetermined value, the electric power of the AC generator is supplied to the AC electric motor through the series circuit, and when the output or rotation speed of the electric motor exceeds a predetermined value, the series circuit is disconnected, and the AC generator and the AC electric motor are connected. A power transmission system for a prime mover in which the first circuit breaker is electrically connected directly is proposed.

The series circuit may be a series circuit of the second circuit breaker, the converter and the inverter, or a series circuit of the second circuit breaker and the cycloconverter.

In any case, the winding of the electric motor may be divided into a winding supplied with power via the first circuit breaker and a winding supplied with power via the series circuit. Good.

The electric motor may be a combination of a main electric motor supplied with electric power via the first circuit breaker and a low output AC electric motor supplied with electric power via a series circuit. In that case, the generator may be a combination of a generator that supplies electric power to the main motor and a generator that supplies electric power to the low output AC electric motor. Furthermore, the prime mover
There may be two types of prime movers that drive the two types of generators, respectively.

To achieve the above object, the present invention also relates to a prime mover including a generator coupled to a variable speed prime mover, an electric motor driven by the electric power thereof, and a means for controlling the output or the rotational speed of the electric motor. In the power transmission system,
A series circuit including a second circuit breaker and a converter is provided in parallel with the first circuit breaker connecting the AC generator and the AC motor, and the low output DC motor driven by the DC output of the converter is coupled to the AC motor. When the output or rotation speed of the electric motor is equal to or lower than a predetermined value, power of the AC generator is supplied to the low output DC electric motor through the series circuit, and when the output or rotation speed of the electric motor exceeds the predetermined value. The present invention proposes a power transmission system for a prime mover in which the series circuit is disconnected and an AC generator and an AC motor are electrically directly connected by a first circuit breaker.

When the electric motor is composed of the main electric motor and the low-output electric motor, both can be operated in parallel.

[0018]

In the present invention, since the rotational speed of the prime mover is changed according to the output of the prime mover, it is possible to select an operating point that minimizes the fuel consumption rate. When the prime mover is a gas turbine, the gas generator of the gas turbine is used at low speed and
Since the absorption power of the compressor of the gas generator that is proportional to the power can be reduced, the effect of fuel saving is particularly remarkable. As a result, ships that do not normally run at maximum speed can extend the number of days that they can sail with the same amount of fuel as before.

Further, the capacities of expensive cycloconverters and inverters can be reduced, and a significant cost reduction can be achieved.

Furthermore, when a cycloconverter or an inverter is connected to an AC generator, ripple current flows through the AC generator, and it is necessary to take measures against temperature rise. In the present invention, however, the cycloconverter or inverter is used as a small load. Therefore, it can be said that there is almost no effect.

In most of the operating speed range, the synchronous motor or the induction motor directly serves as the load of the generator without passing through the cycloconverter or the inverter, so that the power factor of the generator is kept good and the The kVA capacity can be reduced and the size / weight can be reduced.

Motors and generators can be operated with sinusoidal voltage and current in most operating speed ranges without passing through a cycloconverter or an inverter. Therefore, it is possible to reduce the electromagnetic noise, the reverse phase component, and the internal loss of the motor and the generator.

[0023]

1 is a diagram showing a power transmission system configuration of an embodiment of a power transmission system for a prime mover according to the present invention. For the prime mover 1 such as a gas turbine or a diesel engine,
The alternator 2 is connected. The output of the AC generator 2 is supplied to the AC electric motor 8 via the circuit breaker 3 to rotate the screw, that is, the propeller 9. A series circuit of a circuit breaker 4, a converter 5 and / or an inverter 6 and a circuit breaker 7 is connected in parallel with the circuit breaker 3 on the output side of the AC generator.

FIG. 2 is a diagram showing the relationship between the required motor power and ship speed, and the relationship between the speed of the screw 9 and ship speed. Required power is screw 9
Is proportional to the cube of the number of revolutions of. That is, the required power is small when the ship speed is low, but increases dramatically as the ship speed increases.

FIG. 3 is a diagram showing an example of the relationship between the ship speed, the output of the gas turbine 1 used as a prime mover for a ship, and the shaft input of the screw 9. The rotational speed of the output shaft of the gas turbine 1 can be practically used within a speed range of up to 100% with a lower limit of 25 to 30% of the rating. When the lower limit rotation speed of the gas turbine 1 is NG ₁ and the maximum rotation speed is NGmax, the ratio becomes 4 to 3 times. In addition,
In the free turbine, the rotation speed of the output shaft can be used from 0 to 100%, but practically, the variable range is from about 1/3 of the rated speed to the rated speed.

If the rotation speed of the screw 9 is proportional to the speed when the speed is V ₂ at the maximum output P ₂ of the gas turbine 1, and when V ₁ = 1/3 V ₂ , NP ₁ = 1/3
NPmax. Therefore, the required power P _{1 at} this point is
It becomes (1/3) ³ of the value of P ₂ .

Therefore, in the basic embodiment of FIG.
When the speed is V ₁ or less, the electric power of the AC generator 2 is supplied to the AC motor 8 via the converter 5 and / or the inverter 6.
When the speed exceeds V ₁ , the AC generator 2 and the AC motor 8 are electrically directly connected to each other to execute the speed control operation.

In the present embodiment, since the rotational speed of the prime mover 1 is changed according to the output of the prime mover 1, it is possible to select an operating point that minimizes the fuel consumption rate. When the prime mover 1 is a gas turbine, the gas generator 2 of the gas turbine is used at low speed rotation, and the absorption power of the compressor of the gas generator 2 proportional to the cube of the number of revolutions can be reduced. The effect is remarkable. As a result, ships that do not normally run at maximum speed can extend the number of days that they can sail with the same amount of fuel as before.

Further, the capacities of the expensive cycloconverter 5 and the inverter 6 can be reduced, and a significant cost reduction can be achieved.

Further, when the cycloconverter 5 or the inverter 6 is connected to the AC generator 2, a ripple current flows into the AC generator 2 and it is necessary to take measures against temperature rise. However, the cycloconverter 5 or the inverter is used as a load at low output. Since 6 is used together, there is almost no effect.

In most of the operating speed range, the electric motor 8
However, the load of the generator 2 is directly applied without passing through the cycloconverter 5 or the inverter 6, so that the power factor of the generator 2 can be kept good, the kVA capacity of the generator 2 can be reduced, and the size / weight can be reduced.

The electric motor 8 and the generator 2 can be operated by a sinusoidal voltage and current in most operating speed ranges without passing through the cycloconverter 5 and the inverter 6. Therefore, it is possible to reduce the electromagnetic noise, the negative phase component, and the internal loss of the electric motor 8 and the generator 2.

FIG. 4 is a diagram showing a system configuration of a more specific embodiment of a power transmission system for a prime mover according to the present invention using an inverter. The gas turbine 1 is an AC generator 2
The governor provided in the gas turbine 1 controls the rotation speed of the gas turbine 1 while maintaining the minimum rotation speed of the gas turbine 1. The AC generator 2 generates AC power having a frequency corresponding to its rotation speed by the power of the gas turbine 1, and the AVR controls the voltage of the AC power. The circuit breaker 3 directly connects the AC generator and the electric motor so that the electric motor has a rotational speed synchronized with the electric generator. A series circuit of the circuit breaker 4, the converter 5, the inverter 6, and the circuit breaker 7 controls the electric motor 8 in the low speed range, reverse rotation control, and regenerative control, and returns when the circuit breaker 3 is closed or from the high speed range to the low speed range. In the case of opening, the control for phase synchronization of the AC generator 2 is executed.

Maximum number of revolutions of gas turbine NGmax = 360
When the rpm is 0 rpm, the lower limit rotation speed is NG ₁ = 1200 rpm, and the AC generator is a two-pole (2P) machine, the output frequency of the AC generator can be variable-speed operated between 60 Hz and 20 Hz. In this method, the fuel injection amount of the gas turbine is changed, the turbine inlet temperature is changed, and the output and the rotational speed are adjusted by the governor of the gas turbine.

When changing the speed of a ship from zero to V ₁ ,
While the circuit breaker 3 is opened, the circuit breakers 4 and 7 are closed, the voltage of the AC generator 2 is kept constant, the converter 5 and the inverter 6 are operated, and the frequency and voltage (current) of the inverter 6 are adjusted to control the electric motor 8 Control the torque and speed of. When the generated frequency of the electric motor 2 becomes 20 Hz, which is equivalent to 1200 rpm of the gas turbine 1, the inverter 6 is operated so as to synchronize the phase of the output frequency with the phase of the AC generator 2, and then the circuit breaker 7 is opened to open the circuit breaker. Turn on 3. The rotation speed of the electric motor 8 at this time is about 66 rpm. The output of the electric motor 8 at this time is approximately 25000 ps × (1 /
3) ³ = 926 ps. Therefore, the inverter 6
Even if the efficiency is taken into consideration, a small capacity of about 900 KVA is sufficient.

After electrically connecting the AC generator 2 and the electric motor 8 directly to each other, the rotation speed of the gas turbine 1 is changed and the AC generator 2 is changed.
Is changed and / or the excitation of the AC generator 2 is changed to change the voltage, and the voltage is controlled between the speeds V ₁ and V ₂ by the voltage and the frequency that match the characteristics of the electric motor 8. A synchronous motor or an induction motor is used as the electric motor 8 depending on the purpose.

FIG. 5 is a diagram showing the sharing of the control area of the electric motor with the ship speed and the screw input horsepower in the embodiment of FIG. 4 as parameters. In the inverter operating region, the AC generator 2 does not necessarily need to control the constant frequency (constant rotation) or the constant voltage, but the combination of the converter 5 and the inverter 6 requires the voltage, frequency, phase, The rotation direction etc. can be adjusted.

When the prime mover 1 such as the gas turbine is operated at a variable speed as described above, the fuel consumption in the low speed range can be significantly reduced.

FIG. 6 is a diagram showing a system configuration of an embodiment of a power transmission system for a prime mover according to the present invention using a cycloconverter. Even when using a cycloconverter,
The operation is the same as that of the embodiment of FIG. 4 except that the converter is different.

FIG. 7 is a diagram showing a system configuration of an embodiment of a power transmission system for a prime mover according to the present invention using a two-winding motor 8A. Basically the same as the embodiment of FIG. 4, but
Practically, in order to insulate the output circuit of the inverter 6 and the output circuit of the generator 2 so that the respective output voltages can be arbitrarily selected, the inverter winding and the AC generator winding are attached to the motor 8A. And are separately wound in the same stator. Therefore, it is also possible to close the circuit breaker 3 while the inverter 6 is operating, supply the electric power of the voltage different from that on the side of the inverter 6 from the AC generator 2 to the electric motor 8A, and perform the parallel operation. As a result, the electric motor 8 at the time of switching the driving power source
The shock of A can be reduced. On the contrary, the transition from the high speed range to the low speed range can be easily performed only by opening the circuit breaker 3.

FIG. 8 is a diagram showing the sharing of the control area of the electric motor with the ship speed and the electric motor output in the embodiment of FIG. 7 as parameters. It should be noted that 2 independent from the electric motor 8A of FIG.
Even if a method of adding a transformer between the electric motor 8 and the inverter 6 is adopted instead of the method of providing the winding, almost the same effect can be obtained. In this case, the characteristics of FIG. 8 and the characteristics of FIG. 5 can be realized. Further, in the system configuration of FIG. 7, the converter 5 may be a cycloconverter instead of the inverter 6.

FIG. 9 is a diagram showing a system configuration of an embodiment of a power transmission system for a prime mover according to the present invention, which also uses an electric motor 10A having a small independent winding as an AC electric motor for low output. The AC generator 2 is provided with a winding for an inverter circuit and a winding for directly driving the electric motor to form an AC generator with an inverter winding 2A, and the voltage applied to the inverter 6 is a voltage commensurate with the capacity. This is advantageous in reducing the cost of the converter 5 and the inverter 6. Further, when the large-capacity AC motor 8 is used with an extremely small output, the power factor and efficiency deteriorate, so the small-sized AC motor 10A for low output is used.
Is driven by the output of the inverter 6 to drive the screw 9. In the present embodiment, it is not necessary to synchronize the phases of the AC voltage when switching the power source of the electric motor 8, and the control can be simplified. The characteristics are basically the same as in FIG.

FIG. 10 is a diagram showing a system configuration of an embodiment of a power transmission system of a prime mover according to the present invention in which a DC motor 10B drives a low speed or low output region. The electric motor 10 that covers the low speed region of the ship is a DC electric motor 10B. In this way, the control circuit becomes extremely simple, the output of the generator 2 is rectified by the converter 5 using a thyristor, and this is used as a variable DC power source to control the DC motor 10B. The small DC motor 10B is
It is easy to manufacture, and complicated equipment such as the inverter 6 is not required, which is a great price advantage.

FIG. 11 is a diagram showing a system configuration of an embodiment of a power transmission system of a prime mover according to the present invention including two independent generators in the embodiment of FIG. Generator 2
B can be two independent AC generators, and the voltage can be controlled respectively. The electric motor is also provided with a large-capacity alternating-current motor 8 and a small-sized low-output alternating-current motor 10 as in the embodiment of FIG. The feature of this embodiment is that the voltage control function is omitted in principle in the converter 5 and the inverter 6. That is, in these circuits, the operation in which the harmonic component is minimized is executed, and only the frequency control is performed. The output voltage of the inverter is assigned to the voltage control circuit AVR1 of the AC generator. With this method, the electromagnetic noise of the device can be further reduced and the inductive obstacle can be prevented.

FIG. 12 is a diagram showing a system configuration of an embodiment of a power transmission system for a prime mover according to the present invention, which includes a booster. FIG. 13 is a diagram showing the sharing of the control region of the electric motor with the ship speed and the screw input horsepower in the embodiment of FIG. 12 as parameters. In the present embodiment, the cruise prime mover 11 is added, and the maximum output thereof is set to the output P ₁ or more that can be taken out at least at the stable minimum rotation speed of the main prime mover 1. The method of controlling the inverter 5 and the circuit breakers 3, 4, 7 is the same as that of the embodiment shown in FIG. 9 or 11. Speed V ₁ to V ₂
During the period, as shown in FIG. 13, the two prime movers 1 and 11 are operated,
The maximum output may be increased, or the cruise prime mover 11 may be stopped and the main prime mover 1 alone may be operated.

The feature of this embodiment is that it is different from the other embodiments.
Less frequent fuel consumption is required for ships that often travel at low speeds. This is because, in order to obtain the same output, it is more efficient to use the small prime mover 11 than to use the large prime mover 1 with a small output. Also, the prime mover 1,1
1 and AC generators 2 and 2C each have two, so even if either of the prime movers 1 or 11 fails during operation, the circuit breaker 1
The AC generators 2 and 2C can be switched and used by 3 and 14.

[0047]

According to the power transmission system for a prime mover of the present invention, the following effects can be obtained. (1) Fuel consumption can be reduced by 20 to 30% compared to a system in which a prime mover is rotated at a constant speed and high speed. (2) Compared with a system that controls the entire speed range, the capacity of the inverter or cycloconverter is about 1/20 to 1/30. (3) In the high output speed range, the output of the AC generator is directly supplied to the electric motor. Therefore, compared to a system in which a large amount of electric power is controlled by an inverter or a cycloconverter, the harmonic current flowing through the generator and the harmonic current component flowing through the electric motor become almost zero in the large power region. Therefore, it is possible to minimize the occurrence of electromagnetic noise and the occurrence of inductive damage. (4) In the high power region, various converters are not connected to the current control between the alternator and the electric motor, so the power factor of the load seen from the alternator improves and the capacity of the alternator (KV
A) can be reduced to about 2/3.

[Brief description of drawings]

FIG. 1 is a diagram showing a power transmission system configuration of an embodiment of a power transmission system for a prime mover according to the present invention.

FIG. 2 is a diagram showing a relationship between a required electric motor power and a ship speed, and a relationship between a screw and a screw rotation speed with respect to the ship speed.

FIG. 3 is a diagram showing an example of a relationship between a ship speed, an output of a gas turbine used as a prime mover for a ship, and an input of a screw shaft.

FIG. 4 is a diagram showing a system configuration of an embodiment of a power transmission system for a prime mover according to the present invention using an inverter.

FIG. 5 is a diagram showing sharing of a control region of the electric motor with the boat speed and the screw input horsepower in the embodiment of FIG. 4 as parameters.

FIG. 6 is a diagram showing a system configuration of an embodiment of a power transmission system for a prime mover according to the present invention using a cycloconverter.

FIG. 7 is a diagram showing a system configuration of an embodiment of a power transmission system for a prime mover according to the present invention using a two-winding motor.

FIG. 8 is a diagram showing sharing of a control region of the electric motor with the ship speed and the electric motor output in the embodiment of FIG. 7 as parameters.

FIG. 9 is a diagram showing a system configuration of an embodiment of a power transmission system for a prime mover according to the present invention, which also uses an electric motor having a small independent winding.

FIG. 10 is a diagram showing a system configuration of an embodiment of a power transmission system for a prime mover according to the present invention in which a low speed range is driven by a DC motor.

11 is a diagram showing a system configuration of an embodiment of a power transmission system of a prime mover according to the present invention, which includes two independent generators in the embodiment of FIG. 9. FIG.

FIG. 12 is a diagram showing a system configuration of an embodiment of a power transmission system for a prime mover according to the present invention including a booster.

FIG. 13 is a diagram showing sharing of a control region of the electric motor with the boat speed and the screw input horsepower in the embodiment of FIG. 12 as parameters.

[Explanation of symbols]

 1 prime mover 2 generator 2A AC generator with winding for inverter 2B 2 independent AC generators 3 breaker 4 breaker 5 converter 6 inverter 7 breaker 8 electric motor 8A 2 winding electric motor 9 screw (propeller) 10A low AC motor for output 10B DC motor for low output 11 Motor 12 AC generator 13 Circuit breaker 14 Circuit breaker

Claims (9)

[Claims] 1. A power transmission system for a prime mover, comprising: a generator coupled to a variable speed prime mover; an electric motor driven by the electric power; and means for controlling an output or a rotation speed of the electric motor, wherein the alternating current generator A series circuit of a second circuit breaker and a converter or an inverter is provided in parallel with the first circuit breaker connecting the AC electric motor, and when the output or the rotation speed of the electric motor is a predetermined value or less, through the series circuit, The power of the AC generator is supplied to the AC motor, and when the output or the rotation speed of the motor exceeds the predetermined value, the series circuit is disconnected, and the AC generator and the AC motor are separated by a first circuit breaker. A power transmission system for a prime mover, which is directly connected electrically. 2. A power transmission system for a prime mover, comprising: a generator coupled to a variable speed prime mover; an electric motor driven by the electric power; and means for controlling an output or a rotation speed of the electric motor, wherein the alternating current generator A series circuit of a second circuit breaker, a converter, and an inverter is provided in parallel with the first circuit breaker that connects the AC electric motor, and when the output or the rotation speed of the electric motor is equal to or less than a predetermined value, the series circuit is used. The power of the AC generator is supplied to the AC motor, and when the output or the rotation speed of the motor exceeds the predetermined value, the series circuit is disconnected, and the AC generator and the AC motor are separated by a first circuit breaker. A power transmission system for a prime mover, which is directly connected electrically. 3. A power transmission system for a prime mover, comprising: a generator coupled to a variable speed prime mover; an electric motor driven by the electric power; and means for controlling an output or a rotation speed of the electric motor, wherein the AC generator A series circuit of a second circuit breaker and a cycloconverter is provided in parallel with a first circuit breaker that connects the AC electric motor, and when the output or the rotation speed of the electric motor is a predetermined value or less, the series circuit is used. The power of the AC generator is supplied to the AC motor, and when the output or the rotation speed of the motor exceeds the predetermined value, the series circuit is disconnected, and the AC generator and the AC motor are electrically connected by the first breaker. A power transmission system for a prime mover, which is directly connected. 4. The power transmission system for a prime mover according to any one of claims 1 to 3, wherein the winding of the electric motor is a winding to which electric power is supplied via the first circuit breaker, A power transmission system for a prime mover, comprising a winding to which electric power is supplied via a series circuit. 5. The power transmission system for a prime mover according to claim 1, wherein the electric motor includes a main electric motor supplied with power via the first circuit breaker and the series circuit. A power transmission system for a prime mover, which comprises an AC electric motor for low output, which is supplied with electric power through the motor. 6. The power transmission system for a prime mover according to claim 5, wherein the generator includes a generator that supplies power to the main motor and a generator that supplies power to the low-power AC motor. A power transmission system for a prime mover. 7. The power transmission system for a prime mover according to claim 6, wherein the prime mover includes two types of prime movers respectively driving the two types of generators. 8. A power transmission system for a prime mover, comprising: a generator coupled to a variable speed prime mover; an electric motor driven by the electric power; and means for controlling an output or a rotational speed of the electric motor, wherein the AC generator A series circuit of a second circuit breaker and a converter is provided in parallel with the first circuit breaker connecting the AC motor, and a low output DC motor driven by the DC output of the converter is coupled to the AC motor. Provided, when the output or the rotation speed of the electric motor is equal to or lower than a predetermined value, the electric power of the AC generator is supplied to the low output DC electric motor through the series circuit, and the output or the rotation speed of the electric motor is the predetermined value. When it exceeds, the series circuit is disconnected, and the AC generator and the AC motor are electrically connected directly by the first breaker, the power transmission system of the prime mover. 9. The method of operating a power transmission system for a prime mover according to claim 5, wherein the main motor and the low-output electric motor are operated in parallel. How to operate the transmission system.