Single-shaft combined cycle plant, testing method for single-shaft combined cycle plant, and control device for single-shaft combined cycle plant

This single-shaft combined cycle plant comprises: a power generator; a gas turbine; a steam turbine that is driven by using waste heat from the gas turbine, and is connected to the power generator by a clutch when the rotational speed syncs with the rotational speed of the gas turbine; a steam turbine over-rotation prevention device; a gas turbine over-rotation prevention device; and a control device. The control device sets the power generator to an unloaded state and, whilst maintaining the rotational speed Ng of the gas turbine so as to be higher than the rotational speed Ns of the steam turbine and lower than the maximum rotational speed Nglim of the gas turbine, increases the rotational speed Ns of the steam turbine to the maximum rotational speed Nslim of the steam turbine (time t2-t4) and tests whether or not the steam turbine over-rotation prevention device operates normally.

TECHNICAL FIELD

The present invention relates to a single-shaft combined cycle plant, a testing method for a single-shaft combined cycle plant, and a control device for a single-shaft combined cycle plant.

BACKGROUND ART

In the related art, a technique for a single-shaft combined cycle plant is known. For example, PTL 1 discloses a method for testing whether or not an over-rotation prevention device of a single-shaft combined cycle plant is in a normal operation. In the single-shaft combined cycle plant, an output shaft of a steam turbine is connected to a generator, and an output shaft of a gas turbine is connected to the generator via a coupler (clutch). Then, in a state where the gas turbine and the steam turbine are operated at a test rotation speed which is equal to a normal operation rotation speed, a load connected to the generator is disconnected, and each rotation speed of the gas turbine and the steam turbine is increased, thereby testing whether or not each over-rotation prevention device of the steam turbine and the gas turbine is operated.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

Incidentally, in a single-shaft combined cycle plant, an output shaft of a gas turbine may be connected to a generator, and an output shaft of a steam turbine may be connected to the generator via a Synchro Self Shifting (SSS) clutch. The SSS clutch is a clutch that engages with shafts to be connected when rotation speeds of the shafts are synchronized with each other. In the single-shaft combined cycle plant configured in this way, when over-rotation prevention is tested for the steam turbine, if the SSS clutch engages with the shafts at high speed rotation, there is a possibility that the SSS clutch may be damaged.

The present invention is made in view of the above-described circumstances, and an object thereof is to test the over-rotation prevention of the steam turbine in a single-shaft combined cycle plant, without engagement with the shaft of the steam turbine and the shaft of the gas turbine to the generator by the clutch when the rotation speeds of the both shafts are synchronized with each other.

Solution to Problem

According to the present invention, in order to solve the above-described problem and to achieve the object, there is provided a single-shaft combined cycle plant including a generator, a gas turbine connected to the generator, a steam turbine driven by using waste heat of the gas turbine, and connected to the generator by a clutch when a rotation speed of the steam turbine is synchronized with a rotation speed of the gas turbine, a steam turbine over-rotation prevention device that stops an operation of the steam turbine, when the rotation speed of the steam turbine reaches a predetermined steam turbine upper limit rotation speed, a gas turbine over-rotation prevention device that stops an operation of the gas turbine, when the rotation speed of the gas turbine reaches a predetermined gas turbine upper limit rotation speed, and a control device that brings the generator into an unloaded state, that increases the rotation speed of the steam turbine until the rotation speed of the steam turbine reaches the steam turbine upper limit rotation speed while maintaining the rotation speed of the gas turbine to be lower than the gas turbine upper limit rotation speed, in a state where connection between the generator and the steam turbine by the clutch is released by setting the rotation speed of the gas turbine to be higher than the rotation speed of the steam turbine, and that tests whether or not the steam turbine over-rotation prevention device is in a normal operation.

According to this configuration, the rotation speed of the gas turbine is maintained to be lower than the gas turbine upper limit rotation speed. In this manner, the gas turbine over-rotation prevention device is not operated. Therefore, it is possible to prevent a possibility that the rotation speed of the gas turbine may be lower than the rotation speed of the steam turbine. As a result, the rotation speed of the gas turbine can be constantly maintained to be higher than the rotation speed of the steam turbine. Without engagement with the clutch, the rotation speed of the steam turbine can be increased until the rotation speed of the steam turbine reaches the steam turbine upper limit rotation speed. Therefore, in the single-shaft combined cycle plant, over-rotation prevention can be tested for the steam turbine, without engagement with the clutch that connects the steam turbine to the generator and the gas turbine.

In addition, when the rotation speed of the steam turbine reaches the steam turbine upper limit rotation speed, before the rotation speed of the gas turbine reaches the gas turbine upper limit rotation speed, it is preferable that the control device decreases the rotation speed of the gas turbine to a predetermined rotation speed which is higher than the rotation speed of the steam turbine.

According to this configuration, after the steam turbine over-rotation prevention device is operated, the gas turbine over-rotation prevention device cannot be operated. As a result, it is possible to prevent engagement with the clutch, when the rotation speed of the gas turbine is abruptly decreased and becomes lower than the rotation speed of the steam turbine due to the operation of the gas turbine over-rotation prevention device.

In addition, the gas turbine over-rotation prevention device may be an electronically controlled device controlled by the control device. When the rotation speed of the steam turbine reaches the steam turbine upper limit rotation speed, it is preferable that the control device causes the gas turbine over-rotation prevention device to stop the operation of the gas turbine.

According to this configuration, a normal operation of the steam turbine over-rotation prevention device can be tested. Consecutively, a normal operation of the gas turbine over-rotation prevention device can be tested.

In addition, the control device may start driving the steam turbine while operating the gas turbine at a rated rotation speed, and when the rotation speed of the steam turbine is equal to or higher than a predetermined rotation speed which is lower than the steam turbine upper limit rotation speed, it is preferable that the control device increases the rotation speed of the gas turbine at an increase rate which is the same as that of the rotation speed of the steam turbine.

According to this configuration, the gas turbine is operated at the rated rotation speed. In this manner, it is possible to use highest temperature waste heat when the gas turbine is in an unloaded state. Therefore, steam that satisfies a ventilation condition of the steam turbine can be quickly generated to start driving the steam turbine, and the rotation speed of the steam turbine can be quickly increased. In addition, when the rotation speed of the steam turbine is equal to or higher than a predetermined rotation speed, the rotation speed of the gas turbine is increased at the increase rate which is the same as that of the rotation speed of the steam turbine. In this manner, the rotation speed of the gas turbine is maintained to be higher than the rotation speed of the steam turbine. Accordingly, it is possible to prevent the gas turbine over-rotation prevention device from being operated.

In addition, the steam turbine over-rotation prevention device may be an electronically controlled device controlled by the control device. When the rotation speed of the steam turbine reaches the steam turbine upper limit rotation speed, it is preferable that the control device causes the steam turbine over-rotation prevention device to stop the operation of the steam turbine.

According to this configuration, it is possible to test whether or not the electronically controlled steam turbine over-rotation prevention device is in a normal operation.

According to the present invention, in order to solve the above-described problem and to achieve the object, there is provided a testing method for a single-shaft combined cycle plant including a generator, a gas turbine connected to the generator, a steam turbine driven by using waste heat of the gas turbine, and connected to the generator by a clutch when a rotation speed of the steam turbine is synchronized with a rotation speed of the gas turbine, a steam turbine over-rotation prevention device that stops an operation of the steam turbine, when the rotation speed of the steam turbine reaches a predetermined steam turbine upper limit rotation speed, and a gas turbine over-rotation prevention device that stops an operation of the gas turbine, when the rotation speed of the gas turbine reaches a predetermined gas turbine upper limit rotation speed. The testing method includes bringing the generator into an unloaded state, increasing the rotation speed of the steam turbine until the rotation speed of the steam turbine reaches the steam turbine upper limit rotation speed while maintaining the rotation speed of the gas turbine to be lower than the gas turbine upper limit rotation speed, in a state where connection between the generator and the steam turbine by the clutch is released by setting the rotation speed of the gas turbine to be higher than the rotation speed of the steam turbine, and testing whether or not the steam turbine over-rotation prevention device is in a normal operation.

According to this configuration, the rotation speed of the gas turbine is maintained to be lower than the gas turbine upper limit rotation speed. In this manner, the gas turbine over-rotation prevention device is not operated. Therefore, it is possible to prevent a possibility that the rotation speed of the gas turbine may be lower than the rotation speed of the steam turbine. As a result, the rotation speed of the gas turbine can be constantly maintained to be higher than the rotation speed of the steam turbine. Without engagement with the clutch, the rotation speed of the steam turbine can be increased until the rotation speed of the steam turbine reaches the steam turbine upper limit rotation speed. Therefore, in the single-shaft combined cycle plant, over-rotation prevention can be tested for the steam turbine, without engagement with the clutch that connects the steam turbine to the generator and the gas turbine.

In addition, when the rotation speed of the steam turbine reaches the steam turbine upper limit rotation speed, before the rotation speed of the gas turbine reaches the gas turbine upper limit rotation speed, it is preferable that the rotation speed of the gas turbine is decreased to a predetermined rotation speed which is higher than the rotation speed of the steam turbine.

According to this configuration, after the steam turbine over-rotation prevention device is operated, the gas turbine over-rotation protection device cannot be operated. As a result, it is possible to prevent engagement with the clutch, when the rotation speed of the gas turbine is abruptly decreased and becomes lower than the rotation speed of the steam turbine due to the operation of the gas turbine over-rotation prevention device.

In addition, the gas turbine over-rotation prevention device may be an electronically controlled device. When the rotation speed of the steam turbine reaches the steam turbine upper limit rotation speed, it is preferable that the gas turbine over-rotation prevention device is caused to stop the operation of the gas turbine.

According to this configuration, a normal operation of the steam turbine over-rotation prevention device can be tested. Consecutively, a normal operation of the gas turbine over-rotation prevention device can be tested.

In addition, the steam turbine may start to be driven while the gas turbine is operated at a rated rotation speed, and when the rotation speed of the steam turbine is equal to or higher than a predetermined rotation speed which is lower than the steam turbine upper limit rotation speed, it is preferable that the rotation speed of the gas turbine is increased at an increase rate which is the same as that of the rotation speed of the steam turbine.

According to this configuration, the gas turbine is operated at the rated rotation speed. In this manner, it is possible to use highest temperature waste heat when the gas turbine is in an unloaded state. Therefore, steam that satisfies a ventilation condition of the steam turbine can be quickly generated to start driving the steam turbine, and the rotation speed of the steam turbine can be quickly increased. In addition, when the rotation speed of the steam turbine is equal to or higher than a predetermined rotation speed, the rotation speed of the gas turbine is increased at the increase rate which is the same as that of the rotation speed of the steam turbine. In this manner, the rotation speed of the gas turbine is maintained to be higher than the rotation speed of the steam turbine. Accordingly, it is possible to prevent the gas turbine over-rotation prevention device from being operated.

In addition, the steam turbine over-rotation prevention device may be an electronically controlled device. When the rotation speed of the steam turbine reaches the steam turbine upper limit rotation speed, it is preferable that the steam turbine over-rotation prevention device is caused to stop the operation of the steam turbine.

According to this configuration, it is possible to test whether or not the electronically controlled steam turbine over-rotation prevention device is in a normal operation.

According to the present invention, in order to solve the above-described problem and to achieve the object, there is provided a control device for a single-shaft combined cycle plant including a generator, a gas turbine connected to the generator, and a steam turbine driven by using waste heat of the gas turbine, and connected to the generator by a clutch when a rotation speed of the steam turbine is synchronized with a rotation speed of the gas turbine. The control device includes a steam turbine over-rotation prevention device that stops an operation of the steam turbine, when the rotation speed of the steam turbine reaches a predetermined steam turbine upper limit rotation speed, and a gas turbine over-rotation prevention device that stops an operation of the gas turbine, when the rotation speed of the gas turbine reaches a predetermined gas turbine upper limit rotation speed. The control device brings the generator into an unloaded state, increases the rotation speed of the steam turbine until the rotation speed of the steam turbine reaches the steam turbine upper limit rotation speed while maintaining the rotation speed of the gas turbine to be lower than the gas turbine upper limit rotation speed, in a state where connection between the generator and the steam turbine by the clutch is released by setting the rotation speed of the gas turbine to be higher than the rotation speed of the steam turbine, and tests whether or not the steam turbine over-rotation prevention device is in a normal operation.

According to this configuration, the rotation speed of the gas turbine is maintained to be lower than the gas turbine upper limit rotation speed. In this manner, the gas turbine over-rotation prevention device is not operated. Therefore, it is possible to prevent a possibility that the rotation speed of the gas turbine may be lower than the rotation speed of the steam turbine. As a result, the rotation speed of the gas turbine can be constantly maintained to be higher than the rotation speed of the steam turbine. Without engagement with the clutch, the rotation speed of the steam turbine can be increased until the rotation speed of the steam turbine reaches the steam turbine upper limit rotation speed. Therefore, in the single-shaft combined cycle plant, over-rotation prevention can be tested for the steam turbine, without engagement with the clutch that connects the steam turbine to the generator and the gas turbine.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of a single-shaft combined cycle plant, a testing method for a single-shaft combined cycle plant, and a control device for a single-shaft combined cycle plant according to the present invention will be described in detail with reference to the drawings. The present invention is not limited by the embodiment.

FIG.1is a configuration diagram illustrating an outline of the single-shaft combined cycle plant according to the embodiment. As illustrated, a single-shaft combined cycle plant100includes a load10, a generator11, a gas turbine12, a steam turbine13, a clutch14, a control device15, a steam turbine over-rotation prevention device (hereinafter, referred to as an “ST over-rotation prevention device”)16, and a gas turbine over-rotation prevention device (hereinafter, referred to as a “GT over-rotation prevention device”)17. The control device15, the ST over-rotation prevention device16, and the GT over-rotation prevention device17may configure a device for performing a test operation of the single-shaft combined cycle plant including the generator11, the gas turbine12, the steam turbine13, and the clutch14.

The load10is connected to the generator11so that the load10can be electrically disconnected from the generator11. The generator11is connected via a single shaft to an output shaft12aof the gas turbine12and an output shaft13aof the steam turbine13. The generator11is driven by the gas turbine12and the steam turbine13to generate electric power, and supplies the electric power to the load10.

The gas turbine12includes a compressor121, a combustor122, and a turbine123. The gas turbine12mixes air compressed by the compressor121with a fuel supplied via a fuel supply valve124, causes the combustor122to combust the mixed air and fuel, and drives the turbine123by using generated combustion gas, thereby rotating to output shaft12a. Each component of the gas turbine12including the fuel supply valve124is controlled by the control device15.

The steam turbine13is driven by superheated steam supplied from a boiler device (not illustrated) that uses waste heat supplied from the gas turbine12to generate superheated steam. In this manner, the output shaft13ais rotated. A supply amount of the superheated steam supplied to the steam turbine13is adjusted by a steam supply valve131. Each component of the steam turbine13including the steam supply valve131is controlled by the control device15.

The clutch14is disposed between the output shaft13aof the steam turbine13and the generator11. The clutch14engages with the output shaft13aof the steam turbine13and the output shaft12aof the gas turbine12, when a rotation speed Ns of the output shaft13aof the steam turbine13and a rotation speed Ng of the output shaft12aof the gas turbine12are synchronized with each other. The clutch14is a so-called SSS clutch. The clutch14connects the output shaft13aand the generator11to each other, when the rotation speed Ns is equal to or higher than the rotation speed Ng, and disconnects the output shaft13aand the generator11from each other, when the rotation speed Ns is lower than the rotation speed Ng. Due to structural variations in manufacturing the clutch14, rotation speeds “to be synchronized with each other” include an error. Therefore, in the clutch14, for example, when the rotation speed Ns is equal to or higher than 2,995 rpm and the rotation speed Ng is 3,000 rpm. Accordingly, the output shaft13aand the generator11can be synchronized with and connected to each other. In addition, for example, when the rotation speed Ns is 3,004 rpm and the rotation speed Ng is 3,000 rpm, the output shaft13aand the generator11are not connected to each other. For example, when the rotation speed Ns is equal to or higher than 3,005 rpm, the output shaft13aand the generator11can be synchronized with and connected to each other.

The control device15controls each component included in the single-shaft combined cycle plant100. The control device15controls each component of the gas turbine12including the fuel supply valve124, and controls an operation of the gas turbine12. The control device15controls each component of the steam turbine13including the steam supply valve131, and controls an operation of the steam turbine13. In addition, the control device15controls the load10and the generator11to be switched between electrical connection and disconnection. In addition, the control device15controls an operation of a boiler (not illustrated) that uses the waste heat of the gas turbine12to generate superheated steam, and various devices and valves for supplying the generated superheated steam to the steam turbine13. In addition, the control device15performs test operation control for testing whether or not the ST over-rotation prevention device16and the GT over-rotation prevention device17are in normal operations. Details of the test operation control will be described later.

According to the present embodiment, the ST over-rotation prevention device16is an electronically controlled device, and is partially included in the control device15. As illustrated inFIG.1, the ST over-rotation prevention device16includes a rotation speed detection sensor161and a controller162. The rotation speed detection sensor161is a sensor that detects the rotation speed Ns. The rotation speed detection sensors161are connected one by one to the controller162. A plurality of the rotation speed detection sensors161may be disposed for one controller162.

According to the present embodiment, two controllers162are disposed in the control device15. Each of the controllers162is connected to one of the rotation speed detection sensors161. Each of the controllers162acquires the rotation speed Ns from the connected rotation speed detection sensor161, and performs over-rotation prevention control, based on the acquired rotation speed Ns. More specifically, each of the controllers162shuts off main valves of the steam turbine13, when the rotation speed Ns is equal to or higher than a predetermined steam turbine upper limit rotation speed (hereinafter, referred to as an “ST upper limit rotation speed”) Nslim. In this manner, each of the controllers162stops the operation of the steam turbine13. In addition to the steam supply valve131, the main valves of the steam turbine13indicate various valves needed to stop the operation of the steam turbine13in the single-shaft combined cycle plant100.

As described above, two controllers162are disposed therein. Here, the two controllers162are distinguished from each other, and will be referred to as a “first controller162a” and a “second controller162b”. The second controller162bis set so that the ST upper limit rotation speed Nslim is higher than that of the first controller162a. The second controller162bis disposed as a backup function when there is a problem in the over-rotation prevention control performed by the first controller162a.

According to the present embodiment, the GT over-rotation prevention device17is an electronically controlled device, and is partially included in the control device15. As illustrated inFIG.1, the GT over-rotation prevention device17includes a rotation speed detection sensor171and a controller172. The rotation speed detection sensor171is a sensor that detects the rotation speed Ng. The rotation speed detection sensors171are connected one by one to the controller172. A plurality of the rotation speed detection sensors171may be disposed for one controller172.

According to the present embodiment, two controllers172are disposed in the control device15. Each of the controllers172is connected to one of the rotation speed detection sensors171. Each of the controllers172acquires the rotation speed Ng from the connected rotation speed detection sensor171, and performs over-rotation prevention control, based on the acquired rotation speed Ng. More specifically, each of the controllers172shuts off main valves of the gas turbine12, when the rotation speed Ng is equal to or higher than a predetermined gas turbine upper limit rotation speed (hereinafter, referred to as a “GT upper limit rotation speed”) Nglim. In this manner, each of the controllers172stops the operation of the gas turbine12. In addition to the fuel supply valve124, the main valves of the gas turbine12indicate various valves needed to stop the operation of the gas turbine12in the single-shaft combined cycle plant100.

As described above, two controllers172are disposed therein. Here, the two controllers172are distinguished from each other, and will be referred to as a “first controller172a” and a “second controller172b”. The second controller172bis set so that the GT upper limit rotation speed Nglim is higher than that of the first controller172a. The second controller172bis disposed as a backup function when there is a problem in the over-rotation prevention control performed by the first controller172a.

Next, a testing method for the single-shaft combined cycle plant according to the embodiment will be described. As described above, as the testing method for the single-shaft combined cycle plant according to the embodiment, the control device15performs the test operation control for testing whether or not the ST over-rotation prevention device16is in a normal operation.FIG.2is a view for describing a temporal change in each rotation speed of the gas turbine and the steam turbine while the test operation control is performed. InFIG.2, a solid line indicates the rotation speed Ng, and a broken line indicates the rotation speed Ns.

As illustrated inFIG.2, the control device15first starts the operation of the gas turbine12. At this time, the control device15electrically disconnects the load10and the generator11from each other to bring the generator11in an unloaded state. The control device15brings the generator11in the unloaded state, and increases the rotation speed Ng of the gas turbine12until the rotation speed Ng of the gas turbine12reaches a rated rotation speed Ng1(time t1inFIG.2). Thereafter, the control device15maintains a state where the gas turbine12is operated at the rated rotation speed Ng1. In addition, the control device15uses the waste heat of the gas turbine12to generate the superheated steam by using a boiler (not illustrated).

When the superheated steam is sufficiently generated to drive the steam turbine13by using the boiler (not illustrated), the control device15starts the operation of the steam turbine13(time t2inFIG.2). The control device15increases the rotation speed Ns of the steam turbine13until the rotation speed Ns of the steam turbine13reaches the predetermined rotation speed Ns1. The predetermined rotation speed Ns1is set as a value which is lower than the ST upper limit rotation speed Nslim. The predetermined rotation speed Ns1is set as a value which is lower than the rated rotation speed Ng1of the gas turbine12by approximately 40 rpm, for example.

When the rotation speed Ns of the steam turbine13reaches the predetermined rotation speed Ns1(time t3inFIG.2), the control device15increases the rotation speed Ng of the gas turbine12at an increase rate which is the same as that of the rotation speed Ns of the steam turbine13. In this manner, while the same difference is maintained between the rotation speed Ng and the rotation speed Ns, the rotation speed Ns of the steam turbine13increases up to the ST upper limit rotation speed Nslim in the first controller162a(time t4inFIG.2). As a result, when the over-rotation prevention control is normally performed by the first controller162a, an operation stopping process of the steam turbine13is performed, and the rotation speed Ns of the steam turbine13decreases as illustrated inFIG.2. As illustrated inFIG.2, when the rotation speed Ng and the rotation speed Ns are increased at the same increase rate, if a difference between the rotation speed Ns and the ST upper limit rotation speed Nslim is equal to or smaller than a predetermined value, the control device15decreases the increase rate of the rotation speed Ng and the rotation speed Ns. In this manner, it is possible to prevent the rotation speed Ns from being abruptly changed since the over-rotation prevention control is performed, and it is possible to correctly determine the rotation speed Ns controlled by the over-rotation prevention control. In addition, when the rotation speed Ns is not close to the ST upper limit rotation speed Nslim, the rotation speed Ng and the rotation speed Ns can be increased at an early stage.

In addition, when the rotation speed Ns of the steam turbine13reaches the ST upper limit rotation speed Nslim (time t4inFIG.2), before the rotation speed Ng of the gas turbine12reaches the GT upper limit rotation speed Nglim, the control device15decreases the rotation speed Ng of the gas turbine12to a predetermined rotation speed (time t5inFIG.2). According to the present embodiment, the predetermined rotation speed is the rated rotation speed Ng1. The predetermined rotation speed may be a rotation speed other than the rated rotation speed Ng1. In addition, the control device15decreases the rotation speed Ng of the gas turbine12to the rated rotation speed Ng1at a rate where the rotation speed Ng of the gas turbine12is not lower than the rotation speed Ns of the steam turbine13. As a result, the GT over-rotation prevention device17is not operated. Accordingly, the GT over-rotation prevention device17does not operate, and the clutch does not engage with the shaft of the steam turbine13and the shaft of the gas turbine12since the rotation speed Ng of the gas turbine12does not decrease.

The test operation control is performed. Therefore, it is possible to test whether or not the over-rotation prevention control is normally performed by the first controller162a. According to the present embodiment, when it is confirmed that the rotation speed Ns of the steam turbine13is sufficiently decreased, the test operation control is completed. In addition, after the test operation control is completed, a user may select the followings. The operation of the single-shaft combined cycle plant100may be shifted to a normal operation, the operation of the single-shaft combined cycle plant100may be stopped, or a single operation test may be performed on the GT over-rotation prevention device17.

As described above, in the single-shaft combined cycle plant100and the testing method for the single-shaft combined cycle plant100according to the embodiment, the rotation speed Ng of the gas turbine12is maintained to be lower than the GT upper limit rotation speed Nglim. In this manner, the GT over-rotation prevention device17is not operated. Therefore, it is possible to prevent a possibility that the rotation speed Ng of the gas turbine12may be lower than the rotation speed Ns of the steam turbine13. As a result, the rotation speed of the gas turbine12can be constantly maintained to be higher than the rotation speed of the steam turbine13. Without engagement with the clutch14, the rotation speed of the steam turbine13can be increased until the rotation speed of the steam turbine13reaches the ST upper limit rotation speed Nslim. Therefore, in the single-shaft combined cycle plant100, the over-rotation prevention can be tested for the steam turbine13, without engagement with the clutch14that connects the steam turbine13to the generator11and the gas turbine12.

In addition, when the rotation speed Ns of the steam turbine13reaches the ST upper limit rotation speed Nslim, before the rotation speed Ng of the gas turbine12reaches the GT upper limit rotation speed Nglim, the control device15decreases the rotation speed Ng of the gas turbine12to a predetermined rotation speed (rated rotation speed Ng1) which is higher than the rotation speed Ns of the steam turbine13.

According to this configuration, after the ST over-rotation prevention device16is operated (after time t4inFIG.2), the GT over-rotation prevention device17cannot be operated. As a result, it is possible to prevent engagement with the clutch14, when the rotation speed Ng of the gas turbine12is abruptly decreased and becomes lower than the rotation speed Ns of the steam turbine13due to the operation of the GT over-rotation prevention device17.

In addition, when the control device15starts driving the steam turbine13while operating the gas turbine12at the rated rotation speed Ng1, and the rotation speed Ns of the steam turbine13is equal to or higher than the predetermined rotation speed Ns1which is lower than the ST upper limit rotation speed Nslim, the control device15increases the rotation speed Ng of the gas turbine12at an increase rate which is the same as that of the rotation speed Ns of the steam turbine13.

According to this configuration, the gas turbine12is operated at the rated rotation speed Ng1. In this manner, it is possible to use highest temperature waste heat when the gas turbine12is in an unloaded state. Therefore, steam that satisfies a ventilation condition of the steam turbine13can be quickly generated to start driving the steam turbine13, and the rotation speed Ns of the steam turbine13can be quickly increased. In addition, when the rotation speed Ns of the steam turbine13is equal to or higher than the predetermined rotation speed Ns1, the rotation speed Ng of the gas turbine12is increased at the increase rate which is the same as that of the rotation speed Ns of the steam turbine13. In this manner, the rotation speed Ng of the gas turbine12is maintained to be higher than the rotation speed Ns of the steam turbine13. Accordingly, it is possible to prevent the gas turbine over-rotation prevention device from being operated.

In addition, the ST over-rotation prevention device16is an electronically controlled device controlled by the control device15. When the rotation speed Ns of the steam turbine13reaches the ST upper limit rotation speed Nslim, the control device15causes the ST over-rotation prevention device16to stop the operation of the steam turbine13.

According to this configuration, it is possible to test whether or not the electronically controlled ST over-rotation prevention device16is in a normal operation.

According to the present embodiment, the ST over-rotation prevention device16and the GT over-rotation prevention device17are electronically controlled devices controlled by the control device15. However, the ST over-rotation prevention device16may be a mechanical device that automatically closes the main valves of the steam turbine13, when the rotation speed Ns reaches the ST upper limit rotation speed Nslim. In addition, the GT over-rotation prevention device17may be a mechanical device that automatically closes the main valves of the gas turbine12, when the rotation speed Ng reaches the GT upper limit rotation speed Nglim.

In addition, according to the present embodiment, a normal operation of the ST over-rotation prevention device16is tested by the first controller162a. However, a normal operation of the ST over-rotation prevention device16may be tested by the second controller162b. That is, without causing the first controller162ato perform the over-rotation prevention control, at time t4inFIG.2, the rotation speed Ns of the steam turbine13may be increased until the rotation speed Ns of the steam turbine13reaches the ST upper limit rotation speed Nslim in the second controller162b.

FIG.3is a view for describing a temporal change in each rotation speed of the gas turbine and the steam turbine while test operation control is performed according to a modification example of the embodiment. InFIG.3, control contents of the steam turbine13and the ST over-rotation prevention device16and control contents of the gas turbine12up to time t4are the same as those illustrated inFIG.2. Accordingly, description thereof will be omitted.

As the test operation control according to the modification example, when the rotation speed Ns of the steam turbine13reaches the ST upper limit rotation speed Nslim (time t4inFIG.3), the control device15operates the GT over-rotation prevention device17, and stops the operation of the gas turbine12. In this manner, as illustrated inFIG.3, the rotation speed Ng of the gas turbine12decreases similarly to the rotation speed Ns of the steam turbine13. According to this configuration, a normal operation of the ST over-rotation prevention device16can be tested. Consecutively, a normal operation of the GT over-rotation prevention device17can be tested. In this case, at least the GT over-rotation prevention device17needs to be an electronically controlled device controlled by the control device15.

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