Abstract:
A monitoring system for monitoring, in real time, a gap between a rotating portion and a stationary portion of a machine. The monitoring system includes an imaging device for forming a reference image of the gap and one or more next images of the gap, the imaging device including a portion disposed within the machine and a portion external to the machine. The system also includes an image processor coupled to the imaging device configured to monitor whether the gap is increasing or decreasing by comparing the reference image to the one or more next images.

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to monitoring and, in particular, to monitoring the distances or axial gaps between rotating and stationary parts in a turbine. Turbines are used for electrical power generation or to drive compressors and other rotary equipment. Turbines are expensive and need to be available and reliable for continuous operation. Such turbines typically include a rotor that rotates within an outer casing. The rotor includes buckets having a base and a blade. Nozzles in the casing are interspersed between the blades and provide direction to the heated vapor (steam or gas) to the blades. The vapor causes the blades to turn and, consequently, causes the rotor to turn. 
     Some turbines include one or more bucket stages. The bucket stages are positioned and retained axially by snap-ring type lockwires. These lockwires are typically held in the proper radial position by dowel pins staked in the turbine wheel dovetail hooks. Improper staking of a dowel pin or snapping of the lock wire can cause damage to the turbine and, consequently, a forced outage. For example, a bucket or a portion of the bucket could start moving because it is no longer constrained axially resulting in damage to downstream parts. 
     The most reliable bucket inspection methods utilize a borescope that enters the turbine through the casing. Such an inspection, however, requires taking the turbine out of service. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a monitoring system for monitoring, in real time, a gap between a rotating portion and a stationary portion of a machine is disclosed. The monitoring system of this aspect includes an imaging device for forming a reference image of the gap and one or more next images of the gap, the imaging device including a portion disposed within the machine and a portion external to the machine. The system of this aspect also includes an image processor coupled to the imaging device configured to monitor whether the gap is increasing or decreasing by comparing the reference image to the one or more next images. 
     According to another aspect of the invention, a method of monitoring a gap between a rotating portion and a stationary portion of a machine is disclosed. The method of this aspect includes receiving at an image processor an image of the gap while the machine is operating; comparing the image to a reference image; and generating an alarm in the event the image is different than the reference image. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a block diagram of a monitoring system according to one embodiment; 
         FIG. 2  is a block diagram of a monitoring system according to one embodiment in an example operating environment; 
         FIG. 3  is a difference view of the example operating environment of  FIG. 2 ; 
         FIG. 4  is a flow chart showing a method according to one embodiment. 
     
    
    
     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 
       FIG. 1  shows an example of a monitoring system  100  according to one embodiment. The monitoring system  100  is utilized to monitor turbine buckets for axial movement in one embodiment. 
     The monitoring system  100  of this embodiment includes an imaging device  102 . The imaging device  102  includes an imaging recording device  104  and an image transmission medium  106 . As illustrated in  FIG. 1 , the imaging recording device  104  is a camera but is not so limited. The image transmission medium  106  is an endoscope or other suitable fiber imaging system in one embodiment. The image transmission medium  106  conveys an image to the camera  104  from a location inaccessible by the camera  104 . For example, the image transmission medium  106  conveys an image from inside an operating turbine to the camera  104 . The imaging device  102  optionally includes an illumination system  108 . The illumination system  108  provides illumination to an end of the image transmission medium  106  to illuminate an area of interest. In one embodiment, the illumination system  108  includes one or more fiber optic cables for transmitting light to the area of interest. 
     In one embodiment, the camera  104  has an integration time of 1 microsecond or less. Such an integration time allows for the monitoring system to be utilized in environments, such as a turbine, where elements are moving at very high speeds. For instance, a turbine may rotate at a speed of 3000-3600 rpm. 
     The monitoring system  100  also includes an image processor  110 . The image processor  110  is a computing device in one embodiment. The image processor  110  receives images from the camera  104 . In one embodiment, the image processor  110  compares current images to a reference image to determine if conditions in an area of interest have changed. The image processor  110  may employ various image processing and comparison techniques. For example, the image processor  110  may utilize pixel comparison techniques or pattern recognition using neural networks to compare the current images to the reference image. 
     As discussed above, it may be beneficial to monitor the condition of buckets or other elements of a turbine while the turbine is operational. Accordingly, in one embodiment, the monitoring system  100  is utilized in a turbine while it is operating. In such an embodiment, the image transmission medium  106  and the illumination system  108  are displaced within a turbine and the transmission medium  106  conveys images from inside the turbine to the camera  104  while the turbine is running. In such an embodiment, the image transmission medium  106  and the illumination system  108  may be suitably shielded from heat. 
       FIG. 2  illustrates an operating environment  200  for the monitoring system  100  shown in  FIG. 1 . The operating environment  200  is generally shown as a portion of turbine. The turbine includes an outer casing  201 . The outer casing  201  typically includes borescope access holes provided therein. Such borescope access holes are utilized to inspect the turbine when it is off-line. According to one embodiment, portions of the monitoring system  100  are displaced within the outer casing  201  through one of these borescope access holes. 
     The monitoring system  100  of this embodiment includes the imaging device  102 , the camera  104 , the transmission medium  106 , the illumination system  108  and the image processor  110  as described in  FIG. 1 . In one embodiment the transmission medium  106  and at least a portion of the illumination system  108  are coupled to the imaging device  102 . 
     In the illustrated embodiment, portions of the transmission medium  106  and the illumination system  108  are disposed within the outer casing  201 . In one embodiment, a protective cover  202  protects the portions of the transmission medium  106  and the illumination system  108  disposed within the outer casing  201 . The protective cover  202  is clear and formed of material capable of withstanding the heat within a turbine in one embodiment. A bracket  204  or other retaining means holds the protective cover  202  and, thus, the portions of the transmission medium  106  and the illumination system  108  disposed within the outer casing  201 , in a fixed relationship relative to the outer casing  201 . As the outer casing  201  does not typically move, the fixed relationship between the protective cover  202  and the outer casing  201  ensures that the field of view of the transmission medium  106  (and thus, of camera  104 ) is held constant or nearly constant. 
     In the illustrative embodiment, the field of view is located between a blade  206  and a nozzle  208  of a turbine. In particular, the field of view is directed to an empty area  207  between the blade  206  and the nozzle  208 . In one embodiment, the blade  206  is a first stage blade and the nozzle  208  is a second stage nozzle. Of course, the blades  206  and nozzle  208  could be located in any stage of a turbine. 
     In operation, the camera  104  is utilized to monitor a field of view in the empty area  207 . The empty area  207  may also be referred to as an axial gap. The illumination system  108  provides illumination to the empty area  207  and the transmission medium  106  carries an image back to the camera  104 . In one embodiment, the transmission medium  106  is mounted by bracket  204  perpendicular to an axis of rotation of a turbine to capture an image of an axial gap between the blade  206  and nozzle  208  as input. 
     In one embodiment, the empty area  207  is located in a high temperature location. As such, the camera  104  is located outside of the transmission medium  106  transmits images from the high temperature location to the camera  104  which is located in a cooler location outside the casing  201 . 
     In operation, an image of the empty area  207  (e.g., an axial gap between the blade  206  and the nozzle  208 ) is taken and forms a reference image. Of course, image-processing techniques may be applied to the image. For example, known image processing techniques for removing the background information or noise and to prepare the image for further processing could be used. In addition, the image may need to be enhanced by increasing sharpness, removing blurs, etc. 
     In one embodiment, a second image is formed at a later time. The second image is compared to the reference image. Image comparison techniques including, but not limited to, pixel comparison techniques, pattern recognition using neural networks or image comparison by metric embeddings may be utilized to compare the images and note any changes between the two. 
       FIG. 3  shows a particular implementation of the monitoring system  100  of the present invention. In this illustration, the protective cover  202  that encases portions of the transmission medium  106  and illumination system  108  is disposed through a borescope access hole  302  in an outer casing  201  of a turbine. The outer casing  201  is coupled to a nozzle  208 . The nozzle  208  includes a lower portion  306  that is a diaphragm in one embodiment. The lower portion  306  surrounds a rotor shaft  308 . The rotor shaft  308  is coupled to one or more bucket bases  304 . The bucket bases  304  each support a blade  206 . The bucket base  304  (bucket) is separated from the lower portion  306  by an axial gap  305 . 
     The rotor shaft  308  rotates at a high rate of speed. In some cases, it may rotate at a speed of about 3000-3600 rpm. Accordingly, the camera  104  ( FIG. 1 ) has a frame rate with an integration time of 1 micro second or less in one embodiment. This allows for images to be taken as each bucket  304  rotates past the axial gap  305 . 
       FIG. 4  is a block diagram of a method according to one embodiment. At a block  402  a reference image is formed of an internal portion of a machine. The machine is a turbine in one embodiment. While the portion of the machine is an axial gap between turbine stages in one embodiment, the portion is not so limited and can include any internal portion of the machine. The reference image is formed by an imaging system that is implemented, in one embodiment, as the imaging system described above. Of course, other imaging systems may be utilized. 
     At a block  404  a next image is formed from the same location in the machine. In one embodiment, an image is taken each time a bucket passes a specific location within the machine. Of course, the next image can be formed at any time as long as it is after the reference image is formed. 
     At a block  406  the next image is compared to the reference image. Image comparison techniques including, but not limited to, pixel comparison techniques, pattern recognition using neural networks or image comparison by metric embeddings may be utilized to compare the images and note any changes between the two images. 
     At a block  408  it is determined if there are any differences between the reference image and the next image. In one embodiment, the difference may be in the size of an axial gap between two portions of a turbine. If there is no difference, processing returns to block  404 . If there is a difference, processing may pass directly to block  410  where an alarm is created. In one embodiment, however, the method also includes optional blocks  412  and  414 . Block  412  is entered in the event that there is a difference between the next image and the reference image and a counter is incremented. At optional block  414  it is determined if the counter has exceeded a threshold. If so, the alarm is created at block  410 . Otherwise, processing returns to block  404 . In short, optional blocks  412  and  414  provide for an extended sample of images having differences from the reference image to reduce possible single image aberrations leading to false alarms. It shall be understood that a new reference image may be formed at any time. As such, in some cases, after either block  408  or  414 , processing may return to block  402  rather than block  404  as illustrated in  FIG. 4 . 
     It shall be understood that while the terms “first,” “second” and the like have been used to distinctly identify certain herein, in the appended claims, the ordering and naming of certain devices may vary depending on the context. 
     In support of the teachings herein, various analysis components may be used, including digital and/or an analog system. The system may have components such as a processor, storage media, memory, input, output, communications link (wired, wireless, pulsed mud, optical or other), user interfaces, software programs, signal processors (digital or analog) and other such components (such as resistors, capacitors, inductors and others) to provide for operation and analyses of the apparatus and methods disclosed herein in any of several manners well-appreciated in the art. It is considered that these teachings may be, but need not be, implemented in conjunction with a set of computer executable instructions stored on a computer readable medium, including memory (ROMs, RAMs), optical (CD-ROMs), or magnetic (disks, hard drives), solid-state drive (SSD), or any other type that when executed causes a computer to implement methods of the present invention. These instructions may provide for equipment operation, control, data collection and analysis and other functions deemed relevant by a system designer, owner, user or other such personnel, in addition to the functions described in this disclosure. Accordingly, an embodiment if the present invention may include a monitoring system implemented in a computing device that determines if an axial gap in a turbine is varying in size based on comparisons to a reference image. 
     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.