Abstract:
A thermocouple and a method for making the thermocouple. The thermocouple includes a thermocouple element shaft and at least one sleeve coupled to the thermocouple element shaft in at least one location of the thermocouple element shaft that is expected to experience wear.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Field of the Invention 
         [0002]    This invention relates generally to a thermocouple and, more particularly, to a disc cavity thermocouple for a gas turbine engine that includes one or more outer sleeves along a thermocouple element shaft, where the one or more outer sleeves are wider than the thermocouple element shaft and are located at expected wear locations of the thermocouple. 
         [0003]    Discussion of the Related Art 
         [0004]    The world&#39;s energy needs continue to rise which provides a demand for reliable, affordable, efficient and environmentally-compatible power generation. A gas turbine engine is one known machine that provides efficient power, and often has application for an electric generator in a power plant, or engines in an aircraft or a ship. A typical gas turbine engine includes a compressor section, a combustion section and a turbine section. The compressor section provides a compressed air flow to the combustion section where the air is mixed with a fuel, such as natural gas, and ignited to create a hot working gas. The working gas expands through the turbine section and is directed across rows of blades therein by associated vanes. As the working gas passes through the turbine section, it causes the blades to rotate, which in turn causes a shaft to rotate, thereby providing mechanical work. 
         [0005]    The temperature of the working gas is tightly controlled so that it does not exceed some predetermined temperature for a particular turbine engine design because too high of a temperature can damage various parts and components in the turbine section of the engine. However, it is desirable to allow the temperature of the working gas to be as high as possible because the higher the temperature of the working gas, the faster the flow of the gas, which results in a more efficient operation of the engine. 
         [0006]    In certain gas turbine engine designs, a portion of the compressed air flow is also used to provide cooling for certain components in the turbine section, typically the vanes, blades and ring segments. The more cooling and/or the more efficient cooling that can be provided to these components allows the components to be maintained at a lower temperature, and thus the higher the temperature of the working gas can be. For example, by reducing the temperature of the compressed gas, less compressed gas is required to maintain the part at the desired temperature, resulting in a higher working gas temperature and a greater power and efficiency from the engine. Further, by using less cooling air at one location in the turbine section, more cooling air can be used at another location in the turbine section. In one known turbine engine design, 80% of the compressed air flow is mixed with the fuel to provide the working gas and 20% of the compressed air flow is used to cool the turbine section parts. If less of that cooling air is used at one particular location as a result of the cooling air being lower in temperature, then more cooling air can be used at other areas in the turbine section for increased cooling. 
         [0007]    Two disc cavity thermocouples are commonly provided in rows  2 ,  3  and  4  of the blades in a gas turbine engine, and are used to measure temperature and control cooling for the row that the thermocouples are in. The thermocouple is installed by feeding the thermocouple down guide tubes approximately 5-6 feet in a manner known to those skilled in the art. When one thermocouple in a row fails, the turbine engine can still run using the other thermocouple that is in the same row. If both thermocouples in a particular row fail, the turbine engine loses the capability to control cooling for that row and also loses visibility to the disc cavity temperatures, thereby putting the rotor at risk for damage and/or failure. 
       SUMMARY OF THE INVENTION 
       [0008]    This disclosure describes a thermocouple for a gas turbine engine and a method for making the thermocouple. Thermocouple includes a thermocouple element shaft and at least one sleeve coupled to the thermocouple element shaft in at least one location of the thermocouple element shaft that is expected to experience wear. 
         [0009]    Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a cut-away, isometric view of a gas turbine engine; 
           [0011]      FIG. 2  is a cut-away, side view of a thermocouple inserted in a gas turbine engine using guide tubes; 
           [0012]      FIG. 3  is an illustration of an embodiment of a thermocouple according to the invention; and 
           [0013]      FIG. 4  is an illustration of another embodiment of the thermocouple according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0014]    The following discussion of the embodiments of the invention directed to a thermocouple is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. For example, the thermocouple configurations described herein are described as being used in connection with a gas turbine engine, however, the thermocouple configurations may be used in any instance where a preload on a thermocouple is required. 
         [0015]    Reference throughout the specification using phrases such as “various embodiments,” “some embodiments,” “one embodiment,” “some example embodiments,” “one example embodiment,” “an embodiment” or similar language means that a particular feature, structure or characteristic described in connection with any embodiment is included in at least one embodiment, meaning that the phrases set forth above, or similar language, as used throughout the specification, are not necessarily referring to the same embodiment. Particular features, structures or characteristics described in the specification may be combined in any suitable manner in one or more embodiments, thus, any failure to specifically describe a combination or sub-combination of particular features should not be understood as an indication that combinations or sub-combinations of features is/are not possible. 
         [0016]      FIG. 1  is a cut-away, isometric view of a gas turbine engine  10  including a compressor section  12 , a combustion section  14  and a turbine section  16  all enclosed within an outer housing  30 , where operation of the engine  10  causes a central shaft or rotor  18  to rotate, thus creating mechanical work. The engine  10  is illustrated and described by way of a non-limiting example to give context to the invention discussed below. Those skilled in the art will appreciate that other gas turbine engine designs will also benefit from the invention. Rotation of the rotor  18  draws air into the compressor section  12  where it is directed by vanes  22  and compressed by rotating blades  20  to be delivered to the combustion section  14  where the compressed air is mixed with a fuel, such as natural gas, and where the fuel/air mixture is ignited to create a hot working gas. More specifically, the combustion section  14  includes a number of circumferentially disposed combustors  26  each receiving the fuel that is injected into the combustor  26  by an injector (not shown) and mixed with the compressed air to be ignited by an igniter  24  to create the working gas, which is directed by a transition  28  into the turbine section  16 . The working gas is directed by circumferentially disposed stationary vanes (not shown) in the turbine section  16  to flow across circumferentially disposed rotatable turbine blades  34 , which causes the turbine blades  34  to rotate, thus rotating the rotor  18 . Once the working gas passes through the turbine section  16  it is output from the engine  10  as an exhaust gas through an output nozzle or exhaust gas diffuser  36 . 
         [0017]    Each group of the circumferentially disposed stationary vanes defines a row of the vanes and each group of the circumferentially disposed blades  34  defines a row  38  of the blades  34 . In this non-limiting embodiment, the turbine section  16  includes four rows  38  of the rotating blades  34  and four rows of the stationary vanes in an alternating sequence. In other gas turbine engine designs, the turbine section  16  may include more or less rows of the turbine blades  34 . It is noted that the most forward row of the turbine blades  34 , referred to as the row  1  blades, and the vanes, referred to as the row  1  vanes, receive the highest temperature of the working gas, where the temperature of the working gas decreases as it flows through the turbine section  16 . 
         [0018]      FIG. 2  is a is a cut-away, side view of a section  40  of a gas turbine engine, such as, for example, the gas turbine engine  10 , that includes a thermocouple  42  inserted into the turbine section  16  of the engine  10  using guide tubes in a manner that is known to those skilled in the art. The configuration of the thermocouple  42  in the gas turbine engine  10  described herein is known as a disc cavity thermocouple. Typically, there are two thermocouples  42  in each of row  2 , row  3  and row  4  of the turbine blades  34 . The thermocouple  42  includes a flexible thermocouple element shaft  44  having a thermocouple sensor  48  at a tip of the shaft  44 , where the sensor  48  is positioned to monitor the temperature of the working gas flowing in the turbine section  16  of the engine  10 . An electrical connector  46  is provided at an end of the shaft  42  opposite to the sensor  44  to provide an electrical connection to the sensor  48  through the shaft  44 . 
         [0019]    The thermocouple element shaft  44  passes through a first guide tube  50  that extends from a blade ring entry region through a blade ring region  60  of, for example, the row  38  of the blades  34 . The thermocouple shaft element  44  also passes through a second guide tube  52  that extends through a blade ring to vane region  62 , a third guide tube  54  that extends through a vane region into to interstage seal housing region  64 , and a fourth guide tube  56  that extends through the interstage seal housing region  64  and into a seal segment  58  where temperature readings of the cooling air are measured by the thermocouple  42 . The guide tubes  50 ,  52 ,  54  and  56  may or may not overlap one another, as is known to those skilled in the art. The number of guide tubes shown in  FIG. 2  is merely exemplary, as the number and location of the guide tubes may vary for a variety of reasons, such as the design of the engine  10 . 
         [0020]    It is known that the thermocouple  42  has a tendency to fail, as set forth above. The cause of thermocouple failure was originally thought to be misalignment between one or more of the guide tubes  50 ,  52 ,  54  and  56  and the thermocouple element shaft  44 , causing the thermocouple element shaft  44  that is within the guide tubes  50 ,  52 ,  54  and  56  to ride on one side of the guide tubes  50 ,  52 ,  54  and  56 , thereby causing the thermocouple element shaft  44  to wear. In an attempt to eliminate this misalignment potential, blade ring assembly processes were improved and hardware was changed to improve the alignment. However, these efforts failed to improve the situation, and failure of the thermocouple  42  continued to occur. 
         [0021]    The cause of failure of the thermocouple  42  has been determined to be the amount of preload applied to the thermocouple  42 . Too much preload causes a buckling effect that forces the thermocouple element shaft  44  to one side or the other, causing the thermocouple element shaft  44  to wear and eventually fail. However, a preload is required to keep the thermocouple  42  seated throughout thermal cycles of the gas turbine engine  10 . If not enough preload is applied to the thermocouple  42 , the thermocouple  42  becomes “unseated”, causing the temperature measurement to be inaccurate. Since preloading the thermocouple  42  is required, additional features must be added to the thermocouple  42  to protect the thermocouple element shaft  44  from premature wear. 
         [0022]      FIG. 3  is an illustration of a thermocouple  70  according to an embodiment of the invention that can replace the thermocouple  42 . Because most of the wear and failures of the thermocouple  42  occurs on portions of the thermocouple element shaft  44  that are not protected by the guide tubes  50 ,  52 ,  54  and  56 , i.e., occur on portions of the thermocouple element shaft  44  that are between a guide tube and next guide tube, the thermocouple  70  includes a thermocouple element shaft  88  having sleeves  76  and  80  that are located on regions of the thermocouple element shaft  88  that are not protected by guide tubes. The sleeves  76  and  80  may be located along the thermocouple element shaft  88  in any suitable region, as damage may occur in various places due to preload, i.e., damage may occur in areas that are protected by guide tubes. The thermocouple element shaft  88  includes element sections  74 ,  78 ,  82  and  86  that are regions of the continuous thermocouple element shaft  88  and that are smaller in diameter than the sleeves  76  and  80 . The sleeves  76  and  80  are a sheathing that is made of any material that is suitable for the high temperature environment of the turbine engine  10 , such as, by way of example, stainless steel. The sleeves  76  and  80  may be affixed over the thermocouple element shaft  88  to create the element sections  64 ,  68 ,  72  and  76  in any suitable manner, such as, by way of example, crimping or welding. An outer sheathing  72  extends from a terminal block to a location where the thermocouple  70  must make a turn or bend, as is known to those skilled in the art. 
         [0023]    The size of the sleeves  76  and  80  and the size of the element sections  74 ,  78 ,  82  and  86  that are part of the continuous thermocouple shaft  88  are determined by the inner diameter and radius of the guide tubes  50 ,  52 ,  54  and  56  that the thermocouple element shaft  88  must pass through while being installed and seated within during the life of the thermocouple  70 . In an exemplary embodiment, the element sections  74 ,  78 ,  82  and  86  may be approximately 0.125 inches in diameter, and the sleeves  76  and  80  may be approximately 0.25 inches in diameter. However, any suitable diameter may be used for the element sections  74 ,  78 ,  82  and  86  and the sleeves  76  and  80 . Furthermore, the position and the number of the sleeves  76  and  80  may be determined by the geometry of the guide tubes  50 ,  52 ,  54  and  56  and the gas turbine engine  10  being used, as well as by the most likely wear points. 
         [0024]    In this embodiment, the sleeve  80  is approximately four inches from an end of the element section  86 , and the sleeve  80  is between the element sections  82  and  86 . A spherical fitting  84  is affixed to the thermocouple element shaft  88  between the element sections  82  and  86  to act as a mechanical stop for a thermocouple tip in a manner known to those skilled in the art. The sleeve  80  is approximately two inches long. The sleeve  76  is between the element sections  74  and  78 . Both the element section  78  and the sleeve  76  are approximately two inches long as shown in the exemplary embodiment of  FIG. 3 . The thermocouple  70  may be made of any suitable material such as, by way of example, Inconel or stainless steel. The preload applied to the thermocouple  70  is approximately 0.2 inches, however, the preload applied to the thermocouple  70  may vary. 
         [0025]      FIG. 4  is an illustration of a thermocouple  90  according to another exemplary embodiment of the invention and can be used to replace the thermocouple  42 . The thermocouple  90  includes a thermocouple element shaft  112 , sleeves  96 ,  98 ,  102  and  104 , and element sections  94 ,  100 ,  106  and  108 . As shown in this embodiment, the sleeve  96  is between the sleeve  98  and the element section  94 . The sleeve  98  is between the sleeve  96  and the element section  100 . The sleeve  102  is between the sleeve  104  and the element section  100 , and the sleeve  104  is between the sleeve  102  and the element section  106 . Placing the sleeves  96  and  98  adjacent to each other and the sleeves  102  and  104  adjacent to each other provides the advantage of protecting the thermocouple  90  in locations where the thermocouple  90  has to bend and is likely to experience wear without compromising the ability of the thermocouple to bend. The sleeves  96 ,  98 ,  102  and  104  may be any suitable length, such as one or two inches. Similarly, the element sections  94 ,  100 ,  106  and  108  may be any suitable length. A spherical fitting  110  is affixed to the thermocouple element shaft  112  between the element sections  106  and  108  to act as a mechanical stop for a thermocouple tip in a manner known to those skilled in the art. An outer sheathing  92  extends from a terminal block to a location where the thermocouple  90  must make a turn or bend, as is known to those skilled in the art. 
         [0026]    The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the scope of the invention as defined in the following claims.