Patent Publication Number: US-2012025526-A1

Title: System and method for monitoring wind turbine gearbox health and performance

Description:
BACKGROUND OF THE INVENTION 
     Wind power is one of the fastest growing energy sources around the world. The long-term economic competitiveness of wind power as compared to other energy production technologies is closely related to the reliability and maintenance costs associated with the wind turbine. The wind turbine gearbox is generally the most expensive component to purchase, maintain, and repair. 
     The conventional vibration monitoring system is based on features uniquely associated with the gearbox bearing design, the gearbox gear design, and the gearbox shaft rotational speeds. For example, a speed of a main rotor is amplified to orders of magnitude by a multi-stage gearbox. Thus, the gear and bearing vibration signatures are high magnitude orders of the main shaft rotational frequency. Moreover, in operation, the main shaft speed is not precisely controlled. Therefore, the rotational speed of the main shaft varies based on the wind conditions and the generator loading. A small variation in the main shaft speed may cause significant variations in the bearing and gear vibration feature frequencies, especially those associated with the high-speed shaft. As a result, the conventional vibration monitoring system may be less effective in providing reliable information under all operating conditions. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A system and method are provided to monitor the health and performance of a wind turbine gearbox. A plurality of sensors coupled to the wind turbine gearbox provide input to a controller. The controller generates output information that includes performance and health information of the wind turbine gearbox based on the input received from each of the sensors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial view of an exemplary configuration of a wind turbine in accordance with various embodiments. 
         FIG. 2  is a cut-away perspective view of the nacelle of the exemplary wind turbine configuration shown in  FIG. 1 . 
         FIG. 3  is a simplified schematic illustration of an exemplary system that may be utilized with the wind turbine shown in  FIGS. 1 and 2  in accordance with various embodiments. 
         FIG. 4  is a graphical illustration of exemplary information that may be generated using the system shown in  FIG. 3  in accordance with various embodiments. 
         FIG. 5  is a graphical illustration of exemplary information that may be generated using the system shown in  FIG. 3  in accordance with various embodiments. 
         FIG. 6  is a graphical illustration of exemplary information that may be generated using the system shown in  FIG. 3  in accordance with various embodiments. 
         FIG. 7  is a graphical illustration of exemplary information that may be generated using the system shown in  FIG. 3  in accordance with various embodiments. 
         FIG. 8  is a graphical illustration of exemplary information that may be generated using the system shown in  FIG. 3  in accordance with various embodiments. 
         FIG. 9  is a graphical illustration of exemplary information that may be generated using the system shown in  FIG. 3  in accordance with various embodiments. 
         FIG. 10  is a graphical illustration of exemplary information that may be generated using the system shown in  FIG. 3  in accordance with various embodiments. 
         FIG. 11  is a graphical illustration of exemplary information that may be generated using the system shown in  FIG. 3  in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the invention will be better understood when read in conjunction with the appended drawings. To the extent that the figures illustrate diagrams of the functional blocks of various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry. Thus, for example, one or more of the functional blocks (e.g., processors, controllers or memories) may be implemented in a single piece of hardware (e.g., a general purpose signal processor or random access memory, hard disk, or the like) or multiple pieces of hardware. Similarly, the programs may be stand alone programs, may be incorporated as subroutines in an operating system, may be functions in an installed software package, and the like. It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings. 
     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. 
     Various embodiments described herein provide a health and performance monitoring system and method that may be utilized to monitor the health and performance of a wind turbine gearbox. By practicing at least one embodiment, the health and performance monitoring system and method enable personnel to monitor the health of the wind turbine gearbox. Specifically the health and performance monitoring system acquires health information that enables an operator to identify potential or current damage of a variety of components installed in the wind turbine gearbox. Embodiments of the system and method also enable an operator to identify the extent of the damage and to modify the operation of the wind turbine gearbox to extend the operational life of the wind turbine gearbox until repairs may be accomplished. Additionally, embodiments of the system and method enable the operator to ascertain the progression of damage to a component within the wind turbine gearbox and modify the operation of the wind turbine gearbox to based on the extent of the damage. 
     Embodiments of the health and performance monitoring system and method also acquire performance information from the wind turbine gearbox. The performance information may be transmitted to, and utilized by, remote personnel to monitor the current operational performance of the wind turbine gearbox. The performance information acquired from the gearbox may be compared to design performance information to enable designers to evaluate the operational performance of the wind turbine. Based on the evaluation, the designers may install upgrades to the wind turbine gearbox to improve or optimize the performance of the wind turbine gearbox. Embodiments of the health and monitoring system and method may also be configured to automatically adjust the operation of the wind turbine based on the health and performance information. For example, in some embodiments, the health and performance monitoring system may automatically stop or shut-down the operation of the wind turbine when the health or performance information indicates that a component within the gearbox is damaged or may have potential damage. 
       FIG. 1  is a pictorial view of an exemplary configuration of a wind turbine  10  in accordance with various embodiments. The wind turbine  10  includes a nacelle  12  housing a generator. The nacelle  12  is mounted atop a tower  14 , only a portion of which is shown in  FIG. 1 . The height of the tower  14  is selected based upon various factors and conditions to optimize the operational performance of the wind turbine  10 . The wind turbine  10  also includes a rotor  16  that includes a plurality of rotor blades  18  that are attached to a rotating hub  20 . Although the wind turbine  10  illustrated in  FIG. 1  is shown as including three rotor blades  18 , it should be realized that the wind turbine  10  may include more than three rotor blades  18  and there are no specific limits on the number of rotor blades  18  that may be installed on the wind turbine  10 . 
       FIG. 2  is a cut-away perspective view of the nacelle  12  shown in  FIG. 1 . In the exemplary embodiment, the nacelle  12  includes a controller  30  that is configured to perform health and performance monitoring of a gearbox  32  installed in the nacelle  12 . In some embodiments, the controller  30  may also be configured to perform overall system monitoring and control, including pitch and speed regulation, high-speed shaft and yaw brake application, yaw and pump motor application and fault monitoring. 
     For example, the controller may provide control signals to a variable blade pitch drive unit  40  to control the pitch of the rotor blades  18  (shown in  FIG. 1 ) that drive the rotating hub  20  as a result of wind. In some embodiments, the pitch of the rotor blades  18  are individually controlled using the blade pitch drive unit  40 . The drive train of the wind turbine  10  includes a main rotor shaft  42 , also referred to as a “low speed shaft”. The main rotor shaft  42  is connected to the rotating hub  20  and the gearbox  32  to drive a high speed shaft enclosed within the gearbox  32 . The configuration of the gearbox  32  is discussed in more detail below. The gearbox  32 , in some embodiments, is secured to a stationary frame  44  utilizing a pair of torque arms  46  and  48 . In operation, the rotation of the rotating hub  20  causes a torque to occur on the main rotor shaft  42  causing the main rotor shaft  42  to rotate. Torque is a pseudo-vector corresponding to the tendency of a force to rotate an object about some axis, e.g. to rotate the main rotor shaft  42  around a central rotational axis. The pair of torque arms  46  and  48  facilitate connecting the center of the rotational axis of the main rotor shaft  42  to a point where the force is applied, in this example, to the stationary frame  44 . Accordingly, rotor torque is transmitted via the main rotor shaft  42  to the gearbox  32 . The torque is then transmitted from the gearbox  32  to a generator  50 , via a coupling  52 . The generator  50  may be of any suitable type, for example, a wound rotor induction generator. 
     A yaw drive  54  and a yaw deck  56  provide a yaw orientation system for the wind turbine  10 . In some embodiments, the yaw orientation system is electrically operated and controlled by the controller utilizing information received from various sensors installed on the wind turbine  10 . The wind turbine  10  may also include a wind vane  58  as a back-up or a redundant system for providing information for the yaw orientation system. 
       FIG. 3  is a simplified schematic illustration of an exemplary system  90  that may be utilized to perform wind turbine gearbox health condition monitoring and performance assessment of an exemplary wind turbine gearbox, such as gearbox  32  shown in  FIG. 2 . In the exemplary embodiment, a cross-sectional view of the gearbox  32  is shown in  FIG. 3 . In the exemplary embodiment, the system  90  is coupled to the exemplary wind turbine gearbox  32 . As discussed above, the gearbox  32  is preferably coupled between the rotor  16  and the generator  50 . During operation, wind causes the rotor  16  to rotate. The rotational force of the rotor  16  is transmitted, via the gearbox  32 , to the generator  50 , which includes a generator rotor (not shown). The generator rotor typically operates at a rotational speed that is greater than a rotational speed of the rotor  16 . Thus, during normal operation, the gearbox  32  is configured to increase the speed of rotation produced by the rotor  16  to the more desirable speed for driving the rotor of the generator  50 . 
     In the exemplary embodiment, the gearbox  32  includes a gearbox housing  100 , which includes an input end cover  102 , a planet gear cover  104 , and a final stage cover  106 . The gearbox housing  100  is supported on the nacelle  12  by a pair of support pins  108 . The input end cover  102  of the gearbox housing  100  extends around and supports a planet carrier  110 , for rotation of the planet carrier  110  relative to the housing  100  about a central axis  112  of the planet carrier  110 . An input hub  120  on a first end of the planet carrier  110  is coupled to the main rotor shaft  42 , in a suitable manner, not shown, for rotation with the rotor  16 . The input hub  120  receives rotational force from the rotor  16  and rotates the planet carrier  110  relative to the gearbox housing  100  in response to that rotational force. The second end of the planet carrier  110 , as illustrated, is substantially open, with a detachably mounted end plate  122  attached to the second end of the planet carrier  110 . This removable carrier end plate  122  acts as a planet bearing support, as explained below. 
     The planet carrier  110  supports a plurality of planet pinions  124  therein for orbital movement about the central axis  112 . In the illustrated embodiment, three planet pinions  124  are provided, spaced apart equally about the central axis  112 . Bearings support the planet pinions  124  for rotation relative to the planet carrier  110 . Specifically, a first planet bearing  130 , mounted at the first end of the planet carrier  110 , engages and supports a first end of each planet pinion  124 , supporting that end of the planet pinion  124  directly from the planet carrier  110 . A second planet hearing  132 , which is mounted on a planet carrier end plate  134  engages and supports a second end of each planet pinion  124 , thereby supporting the second end of the planet pinion  124  indirectly from the planet carrier  110 . Each one of the planet pinions  124  has a plurality of external gear teeth  136  which, in the illustrated embodiment, are spur gear teeth. 
     The gearbox  32  also includes a ring gear  140 . The ring gear  140  is substantially fixed relative to the interior of the gearbox housing  100 . That is, the ring gear  140  has external splines that mate with splines on the interior of the housing  100 , preventing the ring gear  140  from rotating relative to the housing  100 . The ring gear  140  basically floats relative to the housing  100 , in that the ring gear  140  can move radially a slight amount, within the clearance between the external splines on the ring gear  140  and the internal splines on the housing  100 . The planet pinions  124  are substantially smaller in diameter than the ring gear  140 . 
     The ring gear  140  has an array of internal spur or helical gear teeth  142 . The internal gear teeth  142  on the ring gear  140  are in meshing engagement with the external gear teeth  136  on the planet pinions  124 . As a result, orbital movement of the planet pinions  124  about the central axis  112 , in response to rotation of the input hub  120  and the planet carrier  110  about the central axis  112 , causes the planet pinions  124  to rotate about their own axes relative to the planet carrier  110 . The rotational force transmitted from the rotor  16  to the input hub  120  is thus transmitted entirely to the planet pinions  124  to drive the planet pinions  124  to rotate about their own axes. 
     The gearbox  32  also includes a plurality of planet gears  150 . The number of planet gears  150  is equal to the number of planet pinions  124 . In the illustrated embodiment, therefore, three planet gears  150  are provided. Each of the planet gears  150  is fixed to one of the planet pinions  124  for rotation with its associated planet pinion  124 . Thus, in this exemplary embodiment, the gearbox  32  is a “compound” planetary gearbox. When the input hub  120  and the planet carrier  110  rotate, therefore, the rotational force of the input hub  120  is entirely transmitted through the planet pinions  124  to the planet gears  150  to drive the planet gears to rotate about the planet pinion axes. 
     The planet gears  150  are substantially larger in diameter than the planet pinions  124 . Each one of the planet gears  150  has a plurality of external gear teeth  152  which, in the illustrated embodiment, are spur gear teeth. The gearbox  32  also includes a single sun gear  160  mounted within the planet carrier  110 , surrounded by the planet pinions  124 . The sun gear  160  is radially supported by contact with the surrounding planet gears  150 , for rotation of the sun gear  160  relative to the gear box housing  100  about the central axis  112 . The sun gear  160  has a hollow bore along its axis, and along the axis of its shaft extension. A hollow tube  162 , fixed to the final stage cover  106  on the gearbox housing  100 , passes through the bore of the sun gear  160  and its shaft extension, substantially along the axis  112 , to conduct control wiring (not shown) through the gear box  32  to the rotor  16 . The sun gear  160  rotates relative to, but does not contact, the hollow tube  162 . The sun gear  160  is substantially smaller in diameter than the planet gears  150 . 
     The sun gear  160  has a plurality of external spur or helical gear teeth  164  that are in meshing engagement with the external gear teeth  152  on the planet gears  150 . As a result, rotation of the planet gears  150  about their axes, in response to rotation of the input hub  120  and the planet pinions  124 , causes the sun gear  160  to rotate about the central axis  112 . The rotational force of the input hub  120  and the planet carrier  110  is thus entirely transmitted through the planet gears  150  to the sun gear  160 , driving the sun gear  160  for rotation about the central axis  112 . 
     The gearbox  32  also includes a final stage  170 , including a final stage end plate  172 , the final stage cover  106 , an output pinion  174 , and an optional final stage gear  176 . The output pinion  174  may also be referred to herein as the high-speed shaft  174 . The final stage gear  176  is rotated with the sun gear  160 , about the central axis  112 , by a splined connection  178  at the end of the shaft extension of the sun gear  160 . The splined end of the shaft extension of the sun gear  160  floats within the clearance in this splined connection to the final stage gear  176 . Rotation of the high-speed shaft  174  drives the generator  50  thereby producing electrical energy. The final stage  170  is optional, and many gearboxes use the sun gear  160  as an input to the generator  50 . 
     Input torque from the rotor  16  and the input hub  120  is split among the three planet pinions  124  and thus among the three planet gears  150 , for transmission to the sun gear  160 . This configuration spreads the high torque provided by the rotating input hub  120  among the planets. However, the sun gear  160  is the one point in the gear train in which all the torque is concentrated. 
     As shown in  FIG. 3 , the system  90  also includes various sensing devices that are coupled to the gearbox  32 . The sensing devices are configured to collect various information that is related to the health and performance of the gearbox  32 . The information collected from the sensors enables personnel to monitor both the health and performance of the gearbox  32  and implement corrective repairs or upgrades based on the information. 
     The sensing devices may include for example, a first tachometer  200  that is installed proximate to the main rotor shaft  42 . In operation, the first tachometer  200  is configured to generate a signal that represents the rotational speed of the rotor shaft  42 . The system  90  may include a second tachometer  202  that is installed proximate to the high-speed shaft  174 . In operation, the second tachometer  202  is configured to generate a signal that represents the rotational speed of the high-speed shaft  174  and also the rotational speed of the generator  50 . 
     The system  90  may further include at least one strain gauge that is coupled to the gearbox  32 . In the exemplary embodiment, referring again to  FIG. 3 , the system  90  includes a plurality of strain gauges such as a first strain gauge  210  and a second strain gauge  212  that are each mounted proximate to the torque arm  46 . The system  90  may also include a third strain gauge  214  and a fourth strain gauge  216  that are each mounted proximate to the torque arm  48 . The strain gauges  210 ,  212 ,  214  and  216  provide strain information that represents the torque occurring at each respective torque arm  46  and  48 . The torque information may be utilized by an operator or designer to monitor the performance of the wind turbine and/or to initiate design improvements to the wind turbine  10  based on the torque information. For example, the torque information may be compared to predetermined or design torque information to determine whether the actual torque seen at the torque arms  46  and  48  are within operational guidelines. If the torque is not within operational guidelines, a designer may utilize the torque information and information from other sensors described herein to modify the design of the wind turbine  10  or the gearbox  32 . 
     The system  90  may further include at least one strain gauge that is configured to provide strain information on at least one component installed within the gearbox  32 . For example, the system  90  may include a strain gauge  218  and a strain gauge  220  that are each coupled to the ring gear  140 . It should be realized that the locations of the strain gauges  218  and  220  are only exemplary, and that other strain gauges may be installed on other gears within the gearbox  32 . 
     The system  90  may further include at least one proximity probe that is configured to provide motion information that represents the motion of various components within the gearbox  32 . For example, the system  90  may include a proximity probe  230 , a proximity probe  232 , and a proximity probe  234  that are each located proximate to the torque arm  46 . Moreover, the system  90  may include a proximity probe  236 , a proximity probe  238 , and a proximity probe  240  that are each located proximate to the torque arm  48 . In operation, the proximity probes  230 ,  232 , and  234  measure the motion of the torque arm  46  in an X-direction, a Y-direction, and a Z-direction. Additionally, the proximity probes  236 ,  238 , and  240  measure the motion of the torque arm  48  in an X-direction, a Y-direction, and a Z-direction. The combination of the proximity probes  230 ,  232 ,  234 ,  236 ,  238 , and  240  provides motion information that enables an operator or designer to determine the quantity of motion seen at the torque arms  46  and  48 , and thus the amount of motion of the gearbox  32 . The motion information may be compared to predetermined or design motion information to determine whether the actual motion seen at the torque arms  46  and  48  are within operational guidelines. If the motion is not within operational guidelines, a designer may utilize the motion information and information from other sensors described herein to modify the design of the wind turbine  10  or the gearbox  32 . 
     The system  90  may further include at least one accelerometer that is configured to provide information that represents the acceleration of various components in the gearbox  32 . The accelerometers may also provide information that indicates vibration, inclination, dynamic distance, or the speed of the various components within the gearbox. For example, the system  90  may include an accelerometer  250  that is mounted proximate to a main shaft bearing  252 . In operation, the accelerometer  250  may measure the speed or the vibrational characteristics of the main shaft bearing  252 . The system  90  may also include an accelerometer  254  that is mounted proximate to the ring gear  140 . The accelerometer  254  is configured to monitor the meshing between the ring gear  140  and the sun gear  160 . The system  90  may further include an accelerometer  256  that is mounted proximate to the a high-speed shaft  174 , and an accelerometer  258  that is mounted proximate to the final stage gear  176 . 
     The information from the accelerometers  250 ,  254 ,  256  and  258  may be utilized to evaluate the operational performance of the gearbox  32  and the vibrational characteristics of the various meshing components and various bearings within the gearbox  32 . The combination of the accelerometers  250 ,  252 ,  254  and  256  provides vibration information that enables an operator or designer to monitor health of the gearbox  32  by monitoring the quantity of vibration seen at the various locations within the gearbox  32 . The vibration information also enables a designer to initiate design improvements to the wind turbine  10  based on the vibration information. Additionally, the vibration information may utilized to determine the performance of the gearbox  32  by comparing the vibration information to predetermined or design vibration information to determine whether the actual vibration is within operational guidelines. If the vibration is not within operational guidelines, a designer may utilize the vibration information and information from other sensors described herein to modify the design of the wind turbine  10  or the gearbox  32 . 
     The system  90  may further include at least one temperature sensor. In the exemplary embodiment, the system  90  includes a temperature sensor  260  that is mounted proximate to the bearing  130  and a temperature sensor  262  that is mounted proximate to the bearing  132 . It should be realized that although the exemplary embodiment illustrates temperature sensors  260  and  262 , the system  90  may include other temperature sensors (not shown) that may be coupled proximate to other bearings within the gearbox  32 . In the exemplary embodiment, the temperature sensors  260  and  262  provide information that represents the temperature of the various bearings associated with each respective temperature sensor. The system  90  may further include a temperature sensor  264  that monitors the internal temperature of the gearbox  32 . 
     The information from the temperature sensors  260 ,  262 , and  264  provides temperature information that enables an operator or designer to determine the temperature of each respective bearing within the gearbox  32 , and to enable an operator to monitor the performance of the wind turbine and/or to also enable a designer to initiate design improvements to the wind turbine  10  based on the temperature information. Specifically, the temperature information may utilized to determine the performance of the gearbox  32  by comparing the temperature information to predetermined or design temperature information to determine whether the actual temperatures are within operational guidelines. If a temperature is not within operational guidelines, a designer may utilize the temperature information and information from other sensors described herein to modify the design of the wind turbine  10  or the gearbox  32 . 
     The system  90  may also include a plurality of oil particle counters  270  and  272 . The oil particle counters  270  and  272  are configured to identify various contaminants, such as for example, liquid contaminants or metallic particles that may be contaminating the lubricating oil supplying the gearbox  32  or oil within a respective bearing. It should be realized that although the exemplary embodiment illustrates two oil particle counters  270  and  272 , the system  90  may include additional oil particle counters (not shown) that may be coupled proximate to other bearings. In operation, the information from the oil particle counters  270  and  272  may be integrated to cover all gearbox monitoring conditions. 
     The information from the oil particle counter  270  provides information that enables an operator or designer to identify potential bearing wear and the extent of the bearing wear, e.g. by identifying metallic particles within the oil, for at least some of the bearings installed in the gearbox  32 . The oil particle counter  270  enables an operator to monitor the performance of the wind turbine and/or also enable a designer to initiate design improvements to the wind turbine  10  based on the coil particle content. Additionally, the oil particle counter information may utilized to determine the health of the gearbox  32  by comparing the oil particle counter information to predetermined or design oil particle counter information to determine whether the actual oil particle counter information is within operational guidelines. If information received from an oil particle counter is not within operational guidelines, a designer may utilize the oil particle counter information and information from other sensors described herein to modify the design of the wind turbine  10  or the gearbox  32 . 
     In the exemplary embodiment, the outputs from the various sensors described herein are coupled to the controller  30 . The controller  30  forms a portion of the exemplary wind turbine gearbox health condition monitoring and performance assessment system  90 . The controller  30  includes a computer  300 . As used herein, the term “computer” may include any processor or processor-based system including systems using controllers, reduced instruction set circuits (RISC), application specific integrated circuits (ASICs), logic circuits, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term “computer”. During operation, the computer  300  carries out various functions in accordance with routines stored in an associated memory circuitry  302 . The associated memory circuitry  302  may also store configuration parameters, imaging protocols, operational logs, raw and/or processed operational information received from the sensors, and so forth. 
     The controller  30  may further include interface circuitry  304 , also referred to herein as a front end, that is configured to received the inputs from the various sensors described herein. The interface circuitry  304  may include an analog-to-digital converter (not shown) that converts the analog signals received from the sensors to digital signals that may be utilized by the computer  300 . The interface circuitry  304  may also include signal conditioning capabilities for operating the various sensors. 
     The controller  30  may be coupled to a range of external devices via a communications interface. Such devices may include, for example, an operator workstation  306  for interacting with the controller  30 . The operator workstation  306  may be embodied as a personal computer (PC) that is positioned near the controller  30  and hard-wired to the controller  30  via a communication link  308 . The workstation  306  may also be embodied as a portable computer such as a laptop computer or a hand-held computer that transmits information to the system controller  30 . In one embodiment, the communication link  308  may be hardwired between the controller  30  and the workstation  306 . Optionally, the communication link  308  may be a wireless communication link that enables information to be transmitted to or from the controller  30  to the workstation  306  wirelessly. In the exemplary embodiment, the workstation  306  is configured to receive information from the controller  30  in real-time operation to enable a remote operator to monitor the performance of the gearbox  32 . 
     The workstation  306  may include a central processing unit (CPU) or computer  310 . In operation, the computer  310  executes a set of instructions that are stored in one or more tangible and non-transitory storage elements or memories, in order to process input data received from the controller  30 . The storage elements may also store data or other information as desired or needed. The storage elements may be in the form of an information source or a physical memory element within the computer  310 . The set of instructions may include various commands that instruct the computer  310  to perform various gearbox monitoring functions. The controller  30  and/or the computer  310  may be programmed to identify performance deficiencies within the gearbox  32 . For example, the computer  310  may be programmed to received the various sensor inputs generated by the sensors described above. The computer  310  may be further programmed to compare the sensors inputs to various design parameters stored n the computer  310 . Based on the comparison, the computer  310  may generate an output that represents a significant variation between the actual operational characteristics of the gearbox  32  and the expected or operational characteristics as determined based on the design information. Based on the information output from the various sensors, in some embodiments, the controller  30  or the computer  310  may automatically stop the operation of the wind turbine  10  when the health or performance information indicates that a component within the gearbox  32  is damaged or may have potential damage. 
     For example,  FIG. 4  is a graphical illustration of exemplary information acquired using the second tachometer  202  that is installed proximate to the high-speed shaft  174  where the X-axis represents time and the Y-axis represents the voltage output from the second tachometer  202 . In operation, the tachometer  202  generates a signal  400  that represents the rotational speed of the high speed shaft  174 . As shown in  FIG. 4 , each time a target (not shown), installed on the high speed shaft  174 , passes the tachometer  202 , a pulse  402  is generated. In the exemplary embodiment, the graph illustrates a plurality of pulses  402  and the time between each pulse indicating one whole rotation of the high speed shaft  174 . In the exemplary embodiment, the raw data received from the tachometer  202  is utilized by the controller  30  to generate the high-speed shaft rotational speed information shown in  FIG. 5 . The shaft speed information is further utilized in sensor signal processing to improve damage feature extraction by eliminating the variable shaft speed effects. It should be realized that although only a single tachometer graph is illustrated, the controller  30  may generate a graph for some or all of the tachometers described above. 
       FIG. 5  is a graphical illustration of the raw data shown in  FIG. 4  that has been converted to a shaft speed graph  450  using the controller  30 . As discussed above,  FIG. 4  represents the raw tachometer data received from the tachometer  202  mounted to the high speed shaft  174 . Whereas,  FIG. 5  represents actual rotational speed of the shaft  174  over time. In the exemplary embodiment, the raw signal  400  shown in  FIG. 4  is converted to the shaft speed graph  450  shown in  FIG. 5  using the controller  30 . Specifically,  FIG. 5  represents the high-speed shaft rotational speed during a speed up process after being digitized by the controller  30 . As shown in  FIG. 5 , as the speed of the wind turbine  10  increases, the rotational speed of the high-speed shaft  174  increases from approximately 9.96 Hz to approximately 13.24 Hz in 8 seconds. Though the high-speed shaft  174  speed change is relatively small, because the gearmeshing frequency and bearing frequencies are multiples (not necessarily an integer order) of the high-speed shaft  174  speed, the variations at the gearmeshing frequency and bearing frequencies is amplified. Specifically, as shown in  FIG. 5 , the rotational speed of the high-speed shaft  174  varies based on the wind speed and other factors. In the exemplary embodiment, the graph shown in  FIG. 5  is generated by the controller  30  and used by the signal processor to get accurate health condition features in processing the sensor data obtained by the front-end 
       FIG. 6  is a graphical illustration of an exemplary signal  500  generated using information received from the accelerometer  256  that is mounted proximate to the a high-speed gear set  114  where the X-axis represents frequency and the Y-axis represents the voltage output from the accelerometer  256 . 
     More specifically, during operation, as the teeth (not shown) in the gears of the high-speed gear set  114  mesh, at least some vibration occurs. This vibration is observed by the accelerometer  256  and transmitted to the controller  30  for processing. In one exemplary embodiment, the controller  30  applies a Fast-Fourier Transform (FFT) to the raw data received from the accelerometer  256  to generate the line  500  shown in  FIG. 6 . As shown in  FIG. 6 , a plurality of High Speed Gear-Meshing (HSSGM) locations are represented. For example, HSSGM  502  represents the fundamental gearmeshing frequency extracted from the signal acquired from the accelerometer  256 . Whereas, HSSGM  504  and HSSGM  506  are high order harmonics of the fundamental HSSGM  502 . Due to the speed variations, the FFT based analysis method may not adequately enable an operator to identify this gearmeshing frequency and amplitude, which contains gear tooth health conditions. This deficiency is further amplified in higher frequencies. For example, it is difficult to distinguish the second harmonic of the HSSGM  504  and the third harmonics of the HSSGM  506 . 
     As shown in  FIG. 6 , the signal HSS represents the averaged speed of the high-speed shaft  174 . During operation, the signal  500  indicates that the high-speed shaft frequency is approximately 10.5 Hz under the frequency resolution of 0.5 Hz. 
       FIG. 7  is a graphical illustration of advanced signal processing results  550  generated using the same information received from the accelerometer  256  as is used to generate the line  500  shown in  FIG. 6 . As shown in  FIG. 7 , the X-axis represents order domain of the signal  500  shown in  FIG. 6  and the Y-axis represents the acceleration (in g) output from the accelerometer  256 . More specifically, the signals that are blurred humps in the frequency domain shown in  FIG. 6 , appear as distinguished peaks  552 - 560  in the order domain shown in  FIG. 7 . In the exemplary embodiment, point  552  represents the rotational speed of the high speed shaft  174 . Moreover, point  554  corresponds to the gearmeshing order, while points  558 ,  560 , etc., represent higher orders of the gearmeshing order  554 . In this example, the high-speed gear pinion  174  has twenty teeth, thus the high speed gearmeshing order  554  is 20, which means 20 times meshing happened in one revolution of the high speed shaft. In the exemplary embodiment, the controller  30  applies the speed variation information generated in  450  to the raw data received from the accelerometer  256  to generate the line  550  shown in  FIG. 7 . Using the exemplary filter, the sidebands around each point  554 ,  556 ,  558 ,  560 , etc. are also easily distinguished enabling an operator or design engineer to identify the sidebands around each peak, which contain the gear teeth health information. This information may then be utilized by the operator to monitor the health condition of the gearbox  32 . As shown in  FIG. 7 , the variation due to the shaft speed change has been eliminated. Because the order analysis shown in  FIG. 7  is based on the high-speed shaft  174 , the order of the high-speed shaft  174  is exactly at 1 and the high-speed gearmeshing fundamental order is at 20 in this exemplary configuration. Furthermore, the higher orders of the high-speed gearmeshing frequencies are also clearly identifiable. 
       FIG. 8  is a graphical illustration of exemplary information received from the first strain gauge  210  that is mounted proximate to the torque arm  46  where the X-axis represents time and the Y-axis represents the strain during normal operation. As shown in  FIG. 8 , the line  600  represents the raw data acquired from the strain gauge  210  and the line  602  represents the filtered data. A wavelet transform based filter technique is used to effectively filter out the very low frequency component in the sensor signal. 
       FIG. 9  is a graphical illustration of exemplary information shown in  FIG. 8  after processing the strain information using a FFT. In the exemplary embodiment, the controller  30  applies the FFT to the filtered data  602  shown in  FIG. 8  to produce the line  604  shown in  FIG. 9 . As shown in  FIG. 9 , the strain data is utilized to determine the strain at this location due to the planetary gear  120  rotating through the ring gear  140 . The strain gauge response shown in  FIG. 9  can be used to determine the stress when the planetary gear meshes with the ring gear. Moreover, the determined stress may be compared to a predetermined stress to determine whether the gearbox  32  is operating within design parameters. It should be realized that similar information may be acquired for other gears within the gearbox  32  using the other strain gauges described above. 
       FIG. 10  is a graphical illustration of exemplary information received from the first strain gauge  210  that is mounted proximate to the torque arm  46  where the X-axis represents time and the Y-axis represents the strain during normal operation. As shown in  FIG. 10 , the line  610  represents the raw data acquired from the strain gauge  210  under a first loading condition. Line  612  represents the raw data acquired from the strain gauge  210  under a second loading condition. Line  614  represents the raw data acquired from the strain gauge  210  under a third loading condition. 
       FIG. 11  is a graphical illustration of exemplary information received from the second strain gauge  212  that is mounted proximate to the torque arm  46 . The line  620  represents the raw data acquired from the strain gauge  212  under a first loading condition. Line  622  represents the raw data acquired from the strain gauge  212  under a second loading condition. Line  624  represents the raw data acquired from the strain gauge  212  under a third loading condition. 
     A technical effect of the various embodiments is to provide a system that is configured to monitor both the performance of a wind turbine gearbox and also to determine the health of the wind turbine gearbox. The system includes various sensors that are coupled to the gearbox. The outputs from the various sensors are input to a controller. Information obtained from various sensors installed in the gearbox may be transmitted to the controller via a wired or wireless connection. Digitized sensor signals are then processed by the controller to extract bearing component health conditions and to assess gearbox performance. The information may also be transmitted to gearbox customers and engineers through a wired or wireless communication devices. Additionally, operators and designers may request actions needed through the communication device and the controller. 
     In operation, the controller is configured to utilize the sensor information to output information that enables an operator to monitor the performance of the wind turbine. Additionally, the controller is configured to output information that enables a designer to monitor the design of the wind turbine. Specifically, the operator may compare the sensor outputs to a predetermined set of outputs to determine whether the gearbox is operating within operational guidelines. Optionally, the controller may be programmed to compare the sensor outputs to the predetermined set of outputs and then generate an audio or visual indication when a sensor output exceeds a predetermined threshold or is not operating within operational guidelines. Additionally, the designer may use the same or different outputs to determine whether the gearbox is operating within design limitations. The designer may also utilize the sensor outputs to modify the wind turbine gearbox to improve the overall efficiency of the wind turbine. In various embodiments, the system is also configured to estimate various parameters that are not directly obtained from a respective sensor. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. For example, the ordering of steps recited in a method need not be performed in a particular order unless explicitly stated or implicitly required (e.g., one step requires the results or a product of a previous step to be available). While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing and understanding the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. 
     This written description uses examples to disclose various embodiments of the invention, including the best mode, and also to enable any person skilled in the art to practice the various embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention 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 languages of the claims.