Abstract:
A method may involve monitoring a first set of electrical properties associated with an electrical grid configured to couple to a generator and determining whether a transient event is present on the electrical grid based on the first set of electrical properties. The method may also involve determining a mechanical power present on a shaft of the generator based on a second set of electrical properties associated with the generator, the electrical grid, or both when the transient event is present and sending the mechanical power to a controller associated with a turbine configured to couple to the generator, wherein the controller is configured to adjust one or more operations of the turbine based on the mechanical power.

Description:
BACKGROUND 
       [0001]    The subject matter disclosed herein relates to control of a power generation system following a transient grid event. More specifically, the present disclosure relates to adjusting an operation of a gas turbine following the detection of a transient event on an electrical grid connected to the turbine. 
         [0002]    A power generation system includes a prime mover that generates electrical power from other primary energy sources. An exemplary prime mover, a gas turbine, is a rotary mechanical device with a gas turbine shaft that drives an electrical generator to supply electrical power to a transmission grid. The transmission grid, in turn, supplies electricity to various power consumers. To ensure that the power generation system operates effectively, the turbine shaft speed and resulting grid frequency should be synchronized with each other within operational ranges. As such, when grid frequency changes abruptly due to a transient event, improved systems and methods for adjusting the turbine shaft speed in view of the transient even are desired. 
       BRIEF DESCRIPTION 
       [0003]    Certain embodiments commensurate in scope with the originally claimed embodiments are summarized below. These embodiments are not intended to limit the scope of the claimed embodiments, but rather these embodiments are intended only to provide a brief summary of possible forms of the embodiments described herein. Indeed, the embodiments described within the claims may encompass a variety of forms that may be similar to or different from the embodiments set forth below. 
         [0004]    In one embodiment, a system may include a turbine having a first controller configured to control one or more operations of the turbine. The system may also include a generator that may couple to the turbine, such that the generator may provide power to an electrical grid. The system may also include an exciter that may provide a direct current (DC) voltage and a DC current to a rotor of the generator. The exciter may also include a second controller that may monitor a first set of electrical properties associated with the electrical grid, determine whether a transient event is present on the electrical grid based on the first set of electrical properties, determine a mechanical power present on a shaft of the generator based on a second set of electrical properties associated with the generator, the electrical grid, or both when the transient event is present, and send the mechanical power to the first controller. 
         [0005]    In another embodiment, a method may involve monitoring a first set of electrical properties associated with an electrical grid configured to couple to a generator and determining whether a transient event is present on the electrical grid based on the first set of electrical properties. The method may also involve determining a mechanical power present on a shaft of the generator based on a second set of electrical properties associated with the generator, the electrical grid, or both when the transient event is present and sending the mechanical power to a controller associated with a turbine configured to couple to the generator, wherein the controller is configured to adjust one or more operations of the turbine based on the mechanical power. 
         [0006]    In yet another embodiment, a non-transitory computer readable medium may include computer-executable instructions that may cause a processor to monitor a first set of electrical properties associated with an electrical grid configured to couple to a generator, determine whether a transient event is present on the electrical grid based on the first set of electrical properties, determine a mechanical power present on a shaft of the generator based on a second set of electrical properties associated with the generator, the electrical grid, or both when the transient event is present, and send the mechanical power to a controller associated with a turbine configured to couple to the generator, wherein the controller is configured to adjust one or more operations of the turbine based on the mechanical power. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    These and other features, aspects, and advantages of the present embodiments described herein will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0008]      FIG. 1  illustrates a block diagram of a turbine-generator system, in accordance with an embodiment; 
           [0009]      FIG. 2  illustrates a flow chart of a method for sending a calculated mechanical power of a shaft during a transient event to a turbine, in accordance with an embodiment; 
           [0010]      FIG. 3  illustrates a process flow for calculating a mechanical power of a shaft during a transient event, in accordance with an embodiment; and 
           [0011]      FIG. 4  illustrates a flow chart of a method for adjusting operations of a turbine during a transient event, in accordance with an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
         [0013]    When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. One or more specific embodiments of the present embodiments described herein will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
         [0014]    A power generation system may include a turbine and a generator. The turbine may have a prime mover (e.g., turbine shaft) that may provide mechanical energy to the generator, which may then output a voltage or electric potential to a grid. The turbine may include a turbine controller that may adjust a speed at which the turbine shaft may rotate. In one embodiment, the turbine controller may receive an indication that a transient event has occurred on the grid. The transient event may cause the frequency of the voltage output by the generator to deviate from its rated frequency. As such, when a transient event occurs, the generator may adjust its power output to synchronize with the frequency of the grid. However, when the turbine controller attempts to react to the same transient event, the turbine controller may not be able to adjust the speed of the turbine shaft within the same amount of time that the generator synchronizes its output with the grid. This mismatch of the speed of the turbine shaft and the frequency output of the generator may potentially affect the dynamic behavior of the turbine itself 
         [0015]    That is, as the frequency decreases, the speed at which the turbine shaft rotates also decreases. For example, when a frequency drop in the grid occurs, a drop in speed in which the turbine shaft rotates also decreases because the speed is directly proportional with the grid frequency. In this case, the fuel intake of the turbine would increase based on sensing the drop in speed, which increases active power output to compensate for the drop in frequency. This increase of fuel intake may or may not match the required change in electrical power over some period of time. As a result, the speed in which the turbine shaft rotates may decrease and eventually result in a trip. Consequently, the turbine controller may shut off of fuel to the turbine (e.g., flame out). 
         [0016]    To provide enough time for prime mover to react, an exciter controller that controls the operation of the generator may detect or recognize the transient grid event at the initial stages of grid transient to its occurrence. Upon detecting the transient event, the exciter controller may send commands to the turbine controller to adjust the operation of the prime mover and compensate for the change in frequency of the generator. That is, the exciter controller may monitor electrical parameters, such as the power output and electrical frequency, of the generator and detect a transient event based on the electrical parameters. While a gas turbine is specifically discussed for explanatory purposes, the embodiments described herein apply to any prime mover and are not limited based on the exemplary system. Additional details regarding adjusting a load set point for a generator are provided below with reference to  FIGS. 1-3 . 
         [0017]    By way of introduction,  FIG. 1  illustrates a block diagram of a turbine-generator system  10 . As shown in  FIG. 1 , the turbine-generator system  10  may include a turbine  12 , a generator  14 , a switch  16 , a switch  18 , a starter component  20 , an exciter component  22 , and an electrical grid  24 . The turbine  12  may include any one or more turbines and may be configured as a simple cycle or a combined cycle. By way of example, the turbine  12  may include a gas turbine, a wind turbine, a steam turbine, a water turbine, or any combination thereof. In the turbine-generator system  10 , the mechanical work output by the turbine  12  may rotate a shaft of the generator  14 . In general, the generator  14  may then convert the rotation of the shaft into electrical energy that may be output to the electrical grid  24 . 
         [0018]    The starter component  20  may be a variable frequency drive, a load commutated inverter (LCI), or a similar type of electrical device that may output an alternating current (AC) voltage that may be provided to a stator of the generator  14 . In one embodiment, the starter component  20  may receive an AC voltage from an AC voltage source  32  and may convert the AC voltage into the controlled AC voltage, which may be provided to the stator of the generator via the switch  18 . 
         [0019]    The exciter component  22  may include an electrical circuit that provides direct current (DC) current and a DC voltage to field windings of a rotor of the generator  14 , thereby inducing a magnetic field within the generator  14 . The magnetic field may then cause the rotor to spin inside the generator and rotate the shaft of the generator  14 . In addition to creating the magnetic field within the generator  14 , the exciter component  22  may be used to control the frequency, amplitude, and phase properties of the voltage output by the generator  14 . As such, the exciter component  22  may be used to synchronize the voltage output by the generator  14  with the voltage of the electrical grid  24  after the generator&#39;s shaft rotates at its rated speed. 
         [0020]    The turbine  12 , the starter component  20 , and the exciter component  22  may include a turbine controller  26 , a starter controller  28 , and an exciter controller  30 , which may be used to control the turbine  12 , the starter component  20 , and the exciter component  22 , respectively. The turbine controller  26 , the starter controller  28 , and the exciter controller  30  may each include a communication component, a processor, a memory, a storage, input/output (I/O) ports, and the like. The communication component may be a wireless or wired communication component that may facilitate communication between each component in the turbine-generator system  10 , various sensors disposed about the turbine-generator system  10 , and the like. The processor may be any type of computer processor or microprocessor capable of executing computer-executable code. The memory and the storage may be any suitable articles of manufacture that can serve as media to store processor-executable code, data, or the like. These articles of manufacture may represent non-transitory computer-readable media (i.e., any suitable form of memory or storage) that may store the processor-executable code used by the processor to, among other things, perform operations that may be used to control the turbine  12 , the starter component  20 , and the exciter component  22 . The non-transitory computer-readable media merely indicates that the media is tangible and not a signal. The turbine controller  26 , the starter controller  28 , and the exciter controller  30  may communicate with each other via a communication network  34 . The communication network  34  may include an Ethernet-based network, such as the Unit Data Highway (UDH) provided by General Electric. 
         [0021]    Generally, the turbine  12  may rotate a shaft in the generator  14 , such that the generator  14  outputs a voltage. The voltage output of the generator  14  may then be synchronized with the voltage of the electrical grid  24  and provided to the electrical grid  24  via the switch  16 . In certain embodiments, the exciter controller  30  may monitor electrical properties of the grid  24 . As such, the exciter controller  30  may monitor the grid  24  for transient events such as a rise or fall in grid frequency, a rise or fall in active power or reactive power of the generator  14 , and the like. The transient event may include changes to electrical properties such as voltage, current, power, power factor, and the like. 
         [0022]    Prior to the occurrence of a transient event and during a transient event, the exciter controller  30  may continuously determine an amount of mechanical power that is present on a shaft of the generator  14 . That is, the exciter controller  30  may determine the amount of mechanical power present on the shaft of the generator  14  based on electrical data such as a terminal voltage output by the generator  14 , a line current output by the generator  14 , a power factor of the generator  14 , a frequency/slip value, a shaft inertia value, and the like. During the transient event, the exciter controller  30  may determine the mechanical power present on the shaft of the generator  14  and send the determined mechanical power to the turbine controller  26  via the communication network  34  or the like. 
         [0023]    Upon receiving the mechanical power from the exciter controller  34 , the turbine controller  26  may adjust the operations of the turbine  12  to provide stability between the electrical properties of the grid  24  in view of the transient event and the rotation of the turbine shaft. As such, when the transient event occurs on the grid  24 , the turbine controller  26  may adjust the rotation of the turbine shaft or compensate for the discrepancy between the rotation of the turbine shaft and the electrical properties of the grid  24  more quickly as compared to simply reacting to the transient event without the determined mechanical power. 
         [0024]    Adjusting the rotation of the turbine shaft or, more generally, adjusting the operation of the turbine  12  may include modulating an air and fuel ratio used by the turbine  12  to rotate the turbine shaft, operating the turbine  12  in different Dry Low NOx (DLN) modes, adjusting fuel splints in various nozzles that are used for combustion in the turbine  12 , and the like. Generally, by receiving the mechanical power on the shaft of the generator  14  during the transient event, the turbine controller  26  may continue the operation of the turbine  12  without causing instability in the combustion system of the turbine  12  or inducing compressor operation issues due to the transient event. That is, the turbine  12  may continue operating during the transient event such that operations of the turbine-generator system  10  may continue. 
         [0025]    With the foregoing in mind,  FIG. 2  illustrates a flow chart of a method  50  for sending a calculated mechanical power of a shaft during a transient event to a turbine in accordance with an embodiment. Although the method  50  is described below as being performed by the exciter controller  30 , it should be noted that the method  50  may be performed by any suitable processor. Moreover, although the following description of the method  50  is described in a particular order, it should be noted that the method  50  may be performed in any suitable order. 
         [0026]    Referring now to  FIG. 2 , at block  52 , the exciter controller  30  may monitor certain electrical properties associated with the grid  24 , the generator  14 , or both. The electrical properties may include a rise or fall in grid frequency, a rise or fall in active power or reactive power of the generator  14 , voltage output by the generator  14  or the grid  24 , current output by the generator  14  or the grid  24 , power output by the generator  14  or the grid  24 , power factor of the generator  14  or the grid  24 , and the like. These electrical properties may be monitored using sensors such as voltage sensors, current sensors, and the like. Additionally, the exciter controller  30  may simulate the electrical properties based on data received from the sensors. 
         [0027]    At block  54 , the exciter controller  30  may determine whether a transient event is detected on the output of the generator  14  or the grid  24  based on the monitored electrical properties. In one embodiment, the exciter controller  30  may detect the presence of a transient event according to the procedure described in U.S. patent application Ser. No. 14/315,727. Alternatively, the exciter controller  30  may monitor the electrical properties and determine that a transient event is present when the electrical properties change more than some threshold within a certain period of time. 
         [0028]    If the exciter controller  30  does not detect a transient event, the exciter controller  30  may return to block  52  and continue to monitor the electrical properties of the generator  14  and the grid  24 . If, however, the exciter controller  30  detects the transient event, the exciter controller  30  may proceed to block  56 . 
         [0029]    At block  56 , the exciter controller  30  may calculate the mechanical power on the shaft of the generator  14  during the transient event. In one embodiment, the exciter controller  30  may determine the mechanical power on the shaft of the generator  14  during the transient event according to the process flow diagram of  FIG. 3 . Generally, the process flow diagram of  FIG. 3  may determine the mechanical power (Pm) present on the shaft of the generator  14  based on certain properties such as accelerating power (Pacc) of the rotor in the turbine  12 , power output by the generator  14  (Pe), inertia (H) on the shaft, and the like. The accelerating power (Pacc) is determined according to Equation ( 1 ) provided below. The power output by the generator  14  (Pe) may be measured by excitation system via a sensor, potential transformer feedback, current transformer feedback, and the like. The inertia (H) may be determined using certain tests and physical properties of the shaft. 
         [0030]    As shown in the process flow diagram of  FIG. 3 , the derivative of the accelerating power (Pacc) may be multiplied by two times the inertia (H). The accelerating power (Pacc) may be characterized according to Equation 1 below. 
         [0000]    
       
         
           
             
               
                 
                   Pacc 
                   = 
                   
                     
                       ∫ 
                       
                         
                           Pacc 
                           H 
                         
                          
                         dt 
                       
                     
                     = 
                     
                       ∫ 
                       
                         
                           
                             Pm 
                             - 
                             Pe 
                           
                           H 
                         
                          
                         dt 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0031]    As such, with the process flow diagram of  FIG. 3  in mind, the mechanical power on the shaft of the generator  14  may be determined according to Equations (2) and (3) below. 
         [0000]    
       
         
           
             
               
                 
                   Pm 
                   = 
                   
                     
                       
                         d 
                         dt 
                       
                        
                       Pacc 
                       × 
                       2 
                        
                       
                           
                       
                        
                       H 
                     
                     + 
                     Pe 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   Pm 
                   = 
                   
                     
                       
                         
                           d 
                           dt 
                         
                          
                         
                           [ 
                           
                             ∫ 
                             
                               
                                 
                                   Pm 
                                   - 
                                   Pe 
                                 
                                 H 
                               
                                
                               dt 
                             
                           
                           ] 
                         
                       
                       × 
                       2 
                        
                       
                           
                       
                        
                       H 
                     
                     + 
                     Pe 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0032]    Referring back to  FIG. 3 , after calculating the mechanical power on the shaft during the transient event as described above, the exciter controller  30  may proceed to block  58 . At block  58 , the exciter controller  30  may send the calculated mechanical power to the turbine controller  26  via the communication network  34 . Upon receiving the calculated mechanical power, the turbine controller  26  may update a model based control program that is being executed to control the operations of the turbine  12  using the calculated mechanical power. 
         [0033]    With the foregoing in mind,  FIG. 4  illustrates a method  70  for adjusting the operations of the turbine  12  based on a calculated mechanical power. Generally, the method  70  is described as being performed by the turbine controller  26 , but it should be noted that any suitable processor capable of controlling operations of the turbine  12  may perform the method  70 . 
         [0034]    Referring to  FIG. 4 , at block  70 , the turbine controller  26  may determine whether a calculated mechanical power of the shaft in the generator  14  was received from the exciter controller  30 . If the turbine controller  26  has not received the calculated mechanical power, the turbine controller  26  may return to block  72  and continue to monitor whether it receives the calculated mechanical power. 
         [0035]    If the turbine controller  26  receives the calculated mechanical power, the turbine controller  26  may proceed to block  74  and adjust the operations of the turbine  14  based on the calculated mechanical power. That is, the turbine controller  26  may use the calculated mechanical power to determine an air and fuel ratio used by the turbine  12  to rotate the turbine shaft to provide the calculated mechanical power on the shaft, a Dry Low NOx (DLN) mode to use to provide the calculated mechanical power on the shaft, a combination of fuel splints in various nozzles to for combustion in the turbine  12  to provide the calculated mechanical power on the shaft, and the like. It should be noted that Dry Low NO x  (DLN) combustion systems may utilize fuel delivery systems that typically include multi-nozzle, premixed combustors. DLN combustor designs utilize lean premixed combustion to achieve low NO x  emissions without using diluents such as water or steam. Lean premixed combustion involves premixing the fuel and air upstream of the combustor flame zone and operation near the lean flammability limit of the fuel to keep peak flame temperatures and NO x  production low. 
         [0036]    Technical effects of the embodiments in the present disclosure include improving stability and effectiveness of the turbine-generator system  10  in light of transient events. That is, the operations of the turbine-generator system  10  may continue to be functional by performing the method described herein after the occurrence of a transient event. As a result, the turbine-generator system  10  may operate continuously and prevent the loss of power from the turbine-generator  10 . 
         [0037]    This written description uses examples to disclose embodiments described herein, including the best mode, and also to enable any person skilled in the art to practice the embodiments described herein, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the embodiments described herein is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.