Abstract:
According to one aspect of the invention, a system for controlling a temperature of a generator is provided, wherein the system includes a fluid supply in fluid communication with the generator and a heat exchange apparatus in fluid communication with the fluid supply, the generator and a cooling fluid source. The system also includes a first sensor configured to determine a first temperature of a fluid flowing from the heat exchange apparatus to the generator, a second sensor configured to determine a second temperature of the fluid flowing from the generator to the fluid supply and a controller configured to determine an operating limit temperature for the fluid based on the determined first and second temperatures.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to power generators and, more particularly, to a system for cooling a power generator. 
         [0002]    During the process of producing electricity, power generators create heat to be dissipated away from the generator to enable safe operation. Some generators use fluid cooling to dissipate this heat. In many generators, the fluid is a water or water solution. In the cooling systems the fluid is circulated through conduits proximate stator armature bars, wherein the fluid cools the stator to enable safe operation of the generator. 
         [0003]    In some fluid cooled generators, a temperature of the bulk cooling fluid leaving the generator is monitored to ensure that the generator is operating safely. A fixed threshold operating temperature is compared to the detected temperature to determine if the generator is safely operating or should be shut down (or “tripped”). The bulk coolant temperature is an average of the temperatures of the coolant through many parallel cooling paths, and may not directly measure the hottest temperature. In situations where the temperature of the cooling fluid entering the generator may vary significantly, related to the ambient temperature and environment, the generator may be shut down even though the stator is operating safely. For example, in situations where the ambient temperature is elevated and the coolant entering the generator is likewise elevated, the generator fluid outlet temperature may be elevated, yet the stator remains operational and effectively cooled, as the hottest coolant in the winding is below an acceptable level. Such situations can cause the generator to be tripped unnecessarily when safely operating, thereby causing costly power plant outages. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one aspect of the invention, a system for controlling a temperature of a generator is provided, wherein the system includes a fluid supply in fluid communication with the generator and a heat exchange apparatus in fluid communication with the fluid supply, the generator and a cooling fluid source. The system also includes a first sensor configured to determine a first temperature of a fluid flowing from the heat exchange apparatus to the generator, a second sensor configured to determine a second temperature of the fluid flowing from the generator to the fluid supply and a controller configured to determine an operating limit temperature for the fluid based on the determined first and second temperatures. 
         [0005]    According to another aspect of the invention, a method for controlling a temperature of a generator is provided, wherein the method includes directing a fluid from a heat exchange apparatus to the generator, directing the fluid from the generator to a fluid supply and determining a first temperature of the fluid flowing from the heat exchange apparatus to the generator. The method further includes determining a second temperature of the fluid flowing from the generator to the fluid supply and determining an operating limit temperature for the fluid based on the determined first and second temperatures. 
         [0006]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0007]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  is a schematic diagram of an exemplary cooling system to be used in a power generation plant; and 
           [0009]      FIG. 2  is an exemplary logic diagram of steps performed by the cooling system. 
       
    
    
       [0010]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0011]      FIG. 1  is a schematic diagram of an exemplary cooling system  100  to be used in a power generation plant. The cooling system  100  is configured to cool a generator  102  which is coupled to a power generation system  104 . The coupling may be a shaft or gear system configured to transmit mechanical energy from the power generation system  104  to the generator  102 . The power generation system  104  includes any system suitable for generating large amounts of power, including, but not limited to, a combined cycle turbine system, a gas turbine system or a steam turbine system. The cooling system  100  includes a tank  106 , a pumping device  108 , a pumping device  110 , a heat exchanger  112 , a heat exchanger  114  and a heat exchanger fluid source  116 . The cooling system  100  further includes a filter  118 , a controller  120 , a sensor module  122 , a sensor module  124  and a flow control device  126 . 
         [0012]    As depicted, a cooling fluid is directed via conduits between selected components of the cooling system  100  while the controller  120  transmits and receives signals, such as electrical signals, to and from other system components. The cooling fluid is directed along one or more conduits or other suitable fluid communication channels proximate a stator of the generator  102 . Current flow through windings in the stator generate heat that is transferred to conduits configured to absorb the heat. Accordingly, exemplary conduits are proximate to and/or in contact with the stator to enable thermal communication of the heat to the cooling fluid flowing through the conduits. The cooling fluid may be any suitable fluid with the desired properties for a cooling application. Examples of cooling fluid include water, a water-based solution and an antifreeze solution. 
         [0013]    Still referring to  FIG. 1 , after absorbing heat from the stator of the generator  102 , the cooling fluid is directed to the tank  106 , where the cooling fluid is treated to enable improved cooling of the cooling fluid by the heat exchangers  112  and  114 . As shown, the sensor module  124  is configured to measure one or more parameters of the cooling fluid flowing from the generator  102 . The sensor module  124  includes suitable sensors and hardware for performing the exemplary measurements. The measured parameters may include temperature, conductivity and pressure. In other embodiments, various parameters may also be measured, such as pH, dissolved H z , dissolved O 2 , and others. Accordingly, the exemplary sensor module  124  includes a temperature sensor, a pressure sensor and a conductivity sensor. The exemplary sensor module  122  also includes similar sensors and hardware configured to measure parameters of the cooling fluid before it flows into the generator  102 . Specifically, the sensor module  122  includes sensors configured to measure temperature, conductivity and pressure of the cooling fluid prior to flowing into the generator  102 . Accordingly, the controller  120  includes suitable hardware and software to process the measured parameters from the sensor modules  122  and  124 . 
         [0014]    Further, in an embodiment, the controller  120  uses the measured temperatures from the sensor modules  122  and  124  to determine the highest temperature of the cooling fluid in the stator cooling conduits and to further determine the operating limit temperature for the cooling fluid as it leaves the generator  102 . The operating limit temperature is determined using suitable software, algorithms and equations as described in further detail below. The operating limit temperature is the upper limit of a range of acceptable temperatures for safe operation of the generator  102 . In one embodiment, the operating limit temperature is determined in real time, wherein the sensor modules  122  and  124  measure the cooling fluid temperatures continuously to determine the operating limit temperature real time. The real time measurements and calculations may occur at any suitable interval, such as ranging from about 0.2 to about 50 Hertz (Hz). In one example, the measurements and calculations by the controller  120  and sensor modules  122  and  124  occur at about 20 to about 30 Hz. Further, in another example, the measurements and calculations occur instantaneously and in real time at about 25 Hz. As used herein the term controller refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. Further, as used herein the term real time refers to a process, step, method, apparatus or device that may be configured to perform at least one function or task at a selected interval. 
         [0015]    With continued reference to  FIG. 1 , after directing the cooling fluid to the tank  106 , the cooling system  100  directs the cooling fluid to the heat exchangers  112  and  114  via pumping devices  108  and  110 . The heat exchangers  112  and  114  may operate in parallel or may be used in alternating fashion, depending on cooling system needs and configuration. Further, in some embodiments, a single heat exchanger  112 ,  114  may be used to remove heat from the cooling fluid. The heat exchangers  112  and  114  are any suitable type of heat exchanger, such as plate and frame or shell and tube heat exchangers, wherein the heat exchanger fluid source  116  is configured to provide heat exchanger fluid to receive heat from the cooling fluid in the heat exchangers  112  and  114 . As depicted, control of a flow position of the flow control device  126  is controlled by the controller  120 , wherein the controller  120  can restrict flow of the heat exchanger fluid to the heat exchangers based on selected inputs, such as measured parameters (e.g., temperatures) from the sensor modules  122  and  124 . In some embodiments, the cooling system may not include the flow control device  126 . After cooling of the cooling fluid by one or both heat exchangers  112  and  114 , the cooling fluid is directed to the filter  118 , wherein contaminants are removed from the cooling fluid. The cooling fluid is then directed through the sensor module  122 , wherein parameters of the cooling fluid are measured and determined, as described above. The generator  102  then receives the cooling fluid, where conduits proximate the stator enable heat to transfer from the stator windings to the cooling fluid. As described below, the cooling system  100  is configured to determine the operating limit temperature in real time. The real time determination of the operating limit temperature allows an increased operating temperature for the cooling system  100  when the temperature increase across the generator  102  is below the determined operating limit temperature. Accordingly, the exemplary arrangement provides an increased range of operating environments and conditions for the generator  102 , thereby allowing safe power generation across a broad range of climates. 
         [0016]      FIG. 2  is an exemplary logic diagram  200  (or “flow chart”) of steps performed by the cooling system  100 . In one embodiment, the steps of the logic diagram  200  are performed by the controller  120 . A set of inputs  202  are received by a first block  204 , wherein the inputs  202  are inputs to an equation used to determine an operating limit temperature (T limit ). The inputs  202  include a sensed cooling fluid inlet temperature (T in ), a boiling point temperature (T boil ) and a constant (K bulk ) based on stator winding properties. In the embodiment shown in  FIG. 1 , the cooling fluid inlet temperature (T in ) is measured by the sensor module  122 . The boiling point temperature (T boil ) is a constant or static value for each system determined based on elevation, environment, cooling fluid properties and other relevant factors. An exemplary boiling point temperature (T boil ) for water at sea level is 100 degrees Celsius. The block  204  uses Celsius values for boiling point temperature (T boil ) and fluid inlet temperature (T in ). The constant K bulk  represents the relationship between the coolant temperature rise at the hottest location of the parallel paths in the coolant circuit in ratio to the coolant temperature rise observed between the inlet and outlet to the generator. The constant is a function of the physical arrangement of the cooling circuit within the generator. In an embodiment, the block  204  is used to determine the operating limit temperature based on two constant or static inputs, T boil  and K bulk , for a particular cooling system  100  application. As described above, the cooling fluid inlet temperature (T in ) is measured at a selected interval, wherein the continuous and repeated measurements enable a determination of the operating limit temperature (T limit ) in real time. 
         [0017]    As shown in block  206 , the operating limit temperature (T limit ) is compared to a determined cooling fluid outlet temperature (T out ), wherein the determinations and comparisons are in real time. In the embodiment shown in  FIG. 1 , the cooling fluid outlet temperature (T out ) is measured by the sensor module  124 . The comparison in the block  206  determines if the cooling fluid outlet temperature (T out ) is greater than or equal to the operating limit temperature (T limit ). If the comparison result is no, then block  208  directs the logic diagram to receive the inputs  202 , thereby providing an updated determination of the operating limit temperature (T limit ) based on a new measurement of inlet temperature (T in ). If the comparison result is yes, block  210  indicates that the power generation system  104  is tripped, wherein the generator  102  is shut down, taken off line and/or allowed to coast down to prevent damage. Block  212  also includes a comparison of the cooling fluid outlet temperature (T out ) to the operating limit temperature (T limit ). The block  212  may be described as an alarm comparison step, wherein step determines if the cooling fluid outlet temperature (T out ) is greater than or equal to the operating limit temperature (T limit ) minus a margin which may be 5 degrees (Celsius). If the comparison result is no, then block  214  directs the logic diagram to receive the inputs  202 , thereby providing an updated determination of the operating limit temperature (T limit ) based on a new measurement of inlet temperature (T in ). If the comparison result is yes, block  216  causes an alarm for the cooling system  100 , wherein an alarm, such as an audible and/or visual alarm, notifies an operator that the generator  102  is approaching the operating limit temperature (T limit ). As discussed above, the continuous or real time determination of inlet temperature (T in ), operating limit temperature (T limit ) and outlet temperature (T out ) enables generator  102  operation over a range of temperatures. In an embodiment, the real time determination of the operating limit temperature (T limit ) is based on an allowable level of temperature increase of the cooling fluid flowing across the stator, which then compared to the outlet temperature (T out ) in real time, thereby providing acceptable generator  102  operating temperatures for high, low and variable temperature climates. 
         [0018]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.