Abstract:
The invention relates to a method for braking a rotor of a turbine engine, comprising a turning gear, with a drive supplied from an energy source, having an input shaft to which the rotor may be coupled, whereby, during a cooling phase for the turbine, the rotor may be driven by the drive using the coupled input shaft. According to the invention, a method for braking a rotor of a turbine engine can be achieved, in which the rotation of a rotor, caused by the airflow through the turbine, is slowed until the rotor stops, whereby after the end of the cooling phase, the drive drives the rotor in the reverse sense by means of the input shaft in order to brake the same.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2004/007945, filed Jul. 16, 2004 and claims the benefit thereof. The International Application claims the benefits of European Patent application No. 0301837.8 EP filed Aug. 13, 2003, all of the applications are incorporated by reference herein in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a method for braking a rotor of a turbine engine according to the claims and to a turning gear for driving a rotor of a turbine engine according to the claims. 
     BACKGROUND OF THE INVENTION 
     DE 524 329 discloses a device for the slow rotation of a steam turbine shaft. The exciting machine of the current generator coupled to the steam turbine shaft is operated as a motor in operational intermissions, in order to drive the turbine shaft. Since operating the generator as a motor requires higher rotational speeds than is necessary for rotary operation in the operational intermissions, a speed reduction gear is inserted between the rotor shaft and the drive shaft of the exciting machine. 
     It is known, furthermore, that, in a rundown program after the shutdown of a gas turbine, the rotor mounted in an oil bearing is rotated at a lower rotational speed in rotary operation, as it is known, by means of a turning gear. The components, heated and expanded through the operation of the turbine, are thus cooled, during this cooling phase, from the operating temperature of the gas turbine to the ambient temperature. The compressor sucks in ambient air and pumps this into the annular flow path for the combustion chamber and turbine, so that the components are cooled and heat is extracted from the gas turbine. 
     The oil bearing is in this case fed not only from a lubricating oil supply, but additionally from a boosting oil supply which serves for boosting the rotor hydrostatically during rotary operation. 
     After the turning gear has been switched off, an air draft through the compressor, the combustion chamber and the turbine may occur, which is designated as natural draft and depends on the weather situation. This air draft may become so large that, during the rundown program, the rotor of the gas turbine continues to remain in rotational movement, despite the turning gear being switched off. 
     The disadvantage of this is that the control of the gas turbine carrying out the rundown program does not then automatically switch off the oil supply of the oil bearing on account of the continual rotational movement of the rotor. The automated switch off of the oil supply of the oil bearing would take place only when the sensor arrangement monitoring the rotational speed detects the standstill of the rotor. This results in fault warnings from the controls which then require manual action. To brake the rotor, it is then necessary to switch off the oil supply manually, the rotor then rotating, unlubricated in the oil bearing, until it comes to a standstill. This may lead to wear and defects on the rotor and oil bearing. 
     SUMMARY OF THE INVENTION 
     The object of the invention is, therefore, to specify a cost-effective method for braking a rotor of a turbine engine, by means of which the rotational movement of the rotor caused by the air draft is slowed until the rotor stops. Furthermore, the object of the invention is to specify a gear corresponding to this. 
     The object relating to the method is achieved by means of the features of claim  1  and the object directed at the gear is achieved by means of the features of claim  6 . Advantageous embodiments are specified in the subclaims. 
     The solution proceeds in this case from the consideration that, after the conclusion of the cooling phase, to brake the rotor, the latter drives the drive in reverse operation by means of the coupled drive shaft. The turning gear, already conceived and designed for the rotary operation of the rotor, is thus operated cost-effectively in reverse operation. Existing turbines which already have a turning gear can be converted cost-effectively by means of minor additions or modifications. 
     During the rundown program, the control automatically carries out braking operation after rotary operation and then, after the standstill of the rotor is detected, can switch off the oil supply to the oil bearing. Manual action on the rundown program can thus be prevented. 
     In a first advantageous embodiment, after the conclusion of the cooling phase, the drive is separated from the energy source and is connected to a load element. The separation of the energy source terminates the drive of the rotor and therefore the rotary operation of the turbine. By the load element being connected to the drive, the reverse operation of the drive can be carried out. The air draft prevailing in the turbine maintains the rotational movement of the rotor. The latter transfers the rotational movement to the drive via the drive shaft. The rotational energy is converted by the drive and is then dissipated by means of a load element. The load moment for the rotor rises, with the result that the rotational movement of the rotor slows, until the latter comes to a standstill. 
     Advantageously, the drive is designed as a hydraulic motor which in reverse operation works as a hydraulic pump. 
     Expediently, the drive is designed as an electric motor which in reverse operation works as an electrical generator. 
     When the rotor is mounted by means of an oil bearing, the energy supply to the oil bearing can be switched off after the standstill of the rotor. 
     When the drive is designed as a hydraulic motor which in reverse operation works as a hydraulic pump and a throttle or a valve is provided as a load element, the liquid medium conveyed by the hydraulic motor in reverse operation can flow through a throttle or a valve. Thus, in the circuit for the medium, a load element is provided, at which the flow energy of the conveyed medium is dissipated. The hydraulic motor is in this case driven by the air draft which flows through the flow path of the turbine and which at the same time sets the rotor in rotational movement. In this case, in an advantageous development, the throttle or the valve are designed to be regulatable, so that the required load moment can be set at any time in order to brake the rotor. 
     In an advantageous embodiment, the load element is designed as an electrical consumer and the drive as an electric motor. The rotational energy of the rotor is converted into an electrical current by means of the electric motor, which in this case, in reverse operation, works as an electrical generator, and is transferred to the consumer. The load of the consumer is in this case dimensioned such that a deceleration in the rotation of the rotor commences until the latter has come to a standstill. It is advantageous, in this case, that the load element is regulatable. 
     In an advantageous development, the turbine engine is designed as a gas turbine. 
     According to an advantageous proposal, the turbine engine is designed as a compressor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained with reference to drawings in which: 
         FIG. 1  shows a longitudinal part section through a gas turbine, 
         FIG. 2  shows a diagrammatic illustration of a turbine engine with a turning gear. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a gas turbine  1  in a longitudinal part section. It has, inside, a rotor  3  which is rotary-mounted about an axis of rotation  2  and which is also designated as a turbine rotor or rotor shaft. An intake casing  4 , a compressor  5 , a toroidal annular combustion chamber  6  having a plurality of coaxially arranged burners  7 , a turbine  8  and the exhaust gas casing  9  succeed one another along the rotor  3 . 
     In the compressor  5 , an annular compressor duct  10  is provided, which narrows in cross section in the direction of the annular combustion chamber  6 . At the outlet, on the combustion chamber side, on the compressor  5 , a diffuser  11  is arranged, which is flow-connected to the annular combustion chamber  6 . The annular combustion chamber  6  forms a combustion space  12  for a mixture consisting of a fuel and of compressed air. A hot-gas duct  13  is flow-connected to the combustion space  12 , the hot-gas duct  13  being followed by the exhaust gas casing  9 . 
     Blade rings are in each case arranged alternately in the compressor duct  10  and in the hot-gas duct  13 . A guide blade ring  15  formed from guide blades  14  is followed in each case by a moving blade ring  17  formed from moving blades  16 . The fixed guide blades  14  are in this case connected to the stator  18 , whereas the moving blades  16  are fastened to the rotor  3  by means of a turbine disk  19 . 
     The rotor  3  is rotary-mounted by means of an oil bearing  21 . The oil bearing  21  is in this case fed not only from a lubricating oil supply, but additionally from a boosting oil supply which serves for boosting the rotor  3  hydrostatically during rotary operation. 
     When the gas turbine  1  is in operation, air is sucked in through the intake casing  4  by the compressor  5  and is compressed in the compressor duct  10 . The air provided at that end of the compressor  5  which is on the burner side is led through the diffuser  11  to the burner  7  and is mixed there with a fuel. The mixture is then burnt in the combustion space  10  so as to form a working fluid  20 . The working fluid  20  flows from there into the hot-gas duct  13 . The working fluid  20  expands at the guide blades  16  arranged in the turbine  8  and at the moving blades  18  so as to transmit pulses, so that the rotor  3  is driven and, together with the latter, a working machine (not illustrated) coupled to it. 
       FIG. 2  shows a hydraulic circuit diagram  35  of a turning gear  22 . An outlet P of the hydraulic assembly  23  is connected to the inlet of a pressure reduction valve  24 . The outlet of the pressure reduction valve  24  is flow-connected to the inlet of a flow regulation valve  25 , the outlet of which is connected to the inlet of a hydraulic motor  26 . The outlet of the hydraulic motor  26  is connected to the inlet of a pressure limitation valve  27 . The outlet of the pressure limitation valve  27  is flow-connected to the inlet T of the hydraulic assembly  23 . A drive shaft  28  of the hydraulic motor  26  is connected via a gear  29  to a rotor  30  of a turbine engine  31 . 
     The pressure reduction valve  24  and the pressure limitation valve  27  are actuated in each case electromagnetically. 
     The turbine engine  31  may in this case be designed as a compressor or else as a gas turbine  1 . 
     The hydraulic assembly  23  has a regulatable hydraulic pump  32  which is driven by a motor  33 . The inlet of the hydraulic pump  32  is in this case flow-connected to a hydraulic accumulator  34 . The outlet of the hydraulic pump  32  is designed as the outlet of the hydraulic assembly  23 . 
     The hydraulic circuit  35  is designed for three operating states: rotary operation, freewheel operation and braking operation. 
     When the turbine engine  31  is in operation, the drive shaft  28  of the hydraulic motor  26  is not coupled to the rotor  30  of the turbine engine  31 . Only when the turbine engine  31  is shut down is the drive shaft  28  coupled to the rotor  30 . 
     In a rundown program, the control of the turbine engine  31  starts rotary operation in order to cool the latter. For this purpose, the hydraulic motor  26  works as a drive motor which, by means of its drive shaft  28 , drives the rotor  30  of the turbine engine  31  via a gear  29  at a low rotor rotational speed of n=100 min −1 . For this purpose, the hydraulic motor  26  is fed from the hydraulic assembly  23 , the pressure reduction valve  24  allowing a pressure of approximately 150 bar in the hydraulic medium. For volume setting, the flow regulation valve  25  limits the throughflow of the hydraulic medium to a volume of max. 70 l/min. The pressure limitation valve  27  is in this case not actuated, so that there is no pressure drop there. In rotary operation, as a result of the rotation of the rotor  30 , air is pumped through the compressor duct  10 , the annular combustion chamber  6  and the hot-gas duct  13  by the moving blades  16 , so that the turbine engine  31  transfers the stored heat to the air more quickly. After the lowering of the temperature of the gas turbine  1  to below a predetermined limit value, rotary operation is set. 
     During subsequent freewheel operation, the drive shaft  28  remains connected to the rotor  30  via the gear  29 . The pressure reduction valve lowers the pressure of the hydraulic medium to 10 bar. The hydraulic motor  26  thus continues to be supplied with a sufficient quantity of hydraulic media, without an effective drive torque in this case being generated on the drive shaft  28 . The hydraulic motor  26  is thus decoupled from the hydraulic assembly  23  as energy source. The pressure limitation valve  27  remains set at 0 bar, so that there is no pressure loss in the hydraulic medium. The rotor rotational speed decreases on account of losses due to friction. 
     When, because of an air stream, designated as natural draft, which flows through the compressor duct  10 , the combustion space  12  and the hot-gas duct  13 , the rotor shaft is maintained at a rotational speed or the rotor rotational speed is prevented from falling below a predetermined limit rotational speed of n=10 min −1 , the control of the turbine engine automatically switches from freewheel operation to braking operation. 
     In braking operation, the drive shaft  28  of the hydraulic motor  26  is coupled to the rotor  30  of the turbine engine  31 . The pressure reduction valve  24  reduces the pressure in the hydraulic medium to 10 bar. The pressure limitation valve  27  is then activated in such a way that a pressure building up continuously is established there in the hydraulic medium. The pressure limitation valve  27  thus serves, in braking operation, as a load element for the hydraulic motor  26  operated in reverse operation. The hydraulic motor  26  is then driven by the rotation of the rotor  30 , so that the latter works as a pump. The hydraulic motor  26  consequently conveys the hydraulic medium further on to the pressure limitation valve  24  where a build-up of pressure in the hydraulic medium takes place. A load for the rotating rotor  30  is thereby generated and brakes and slows the rotation. Owing to the closing of the pressure limitation valve  27 , the desired braking torque is generated in order to bring the rotor  30  to a standstill. 
     After the limit rotational speed is undershot, the control of the turbine engine  31  automatically switches off the supply of the oil bearing  21  of the rotor  3  in order to conclude the rundown program. By the oil supply being prevented, friction is generated in the oil bearing  21  and brakes the rotor  30  to a standstill. This likewise prevents the rotor  30  of the turbine engine  31  from being set in rotational movement from standstill due to the natural draft. 
     After the oil bearing  21  has been switched off, the pressure limitation valve  24  can likewise be opened again, in order to relieve the hydraulic motor  26  and lower the pressure in the hydraulic medium. 
     Despite the internal leakage of the hydraulic motors  26 , the stopping of the rotor  30  is possible. 
     To stop the rotors  3 ,  30  rapidly, freewheel operation may also be skipped, so that rotary operation is followed directly by braking operation. 
     Where a stationary gas turbine is concerned, the working machine may also be used as a brake, a load element being connected instead of a payload. Thus, for example, the generator could be short-circuited as a working machine, the internal resistance of the generator then serving as a load element.