Abstract:
A system for evaluating bearing metal temperature (BMT) to diagnose rotor misalignment and/or bearing wipe in an electrical machine. A first system is provided that includes: an input system for obtaining bearing metal temperature (BMT) readings from a first BMT sensor located proximate the turbine and a second BMT sensor located proximate the generator, and for obtaining operational data including lube oil inlet temperature, speed and power; a filter system for filtering bad input data; and a misalignment analysis system that issues a misalignment warning in response to one of the BMT sensor reporting an increasing temperature and the other BMT sensor reporting a decreasing temperature.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to diagnosing bearing thermal anomalies in an electrical machine such as a generator, and more particularly to evaluating bearing metal temperatures (BMT) to diagnose bearing misalignment and bearing wipe issues. 
         [0002]    Alignment changes in a generator rotor, which is a major cause of rotor vibration, leads to imbalance in the vertical loading on the bearing of the turbine and generator. This often results in babbit failure which in turn leads to bearing failure. Another cause of bearing failure is “bearing wipe,” which occurs due to a lack of sufficient oil cooling or oil flow. In many cases, the ultimate result of bearing failure is a forced outage of the generator, which is costly in terms of time and money. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    Described herein are techniques for evaluating trends in bearing metal temperature (BMT) to provide early detection of bearing failure. 
         [0004]    In one aspect of the invention, a system for identifying misalignments in a shaft of an electrical machine having a turbine and a generator is provided, comprising: an input system for obtaining bearing metal temperature (BMT) readings from a first BMT sensor located proximate the turbine and a second BMT sensor located proximate the generator, and for obtaining operational data including lube oil inlet temperature, speed and power; and a misalignment analysis system that issues a misalignment warning in response to one of the BMT sensors reporting an increasing temperature and the other BMT sensor reporting a decreasing temperature. 
         [0005]    In another aspect of the present invention, a system for identifying bearing wipe in a bearing that supports a shaft of an electrical machine having a turbine and a generator is provided, comprising: an input system for obtaining bearing metal temperature (BMT) readings from each of a plurality of BMT sensors located proximate the generator and turbine, and for obtaining operational data including lube oil inlet temperature, speed and power; and a steady state bearing wipe analysis system that issues a bearing wipe warning in response to one of the BMT sensors reporting an increasing temperature. 
         [0006]    In a further aspect of the present invention, a system for identifying bearing wipe in a bearing that supports a shaft of an electrical machine having a turbine and a generator is provided, comprising: an input system for obtaining bearing metal temperature (BMT) readings from each of a plurality of BMT sensors located proximate the generator and turbine, and for obtaining operational data including lube oil inlet temperature, speed and power; and a transient state bearing wipe analysis system that issues a bearing wipe warning in response to a detected spike from one of the BMT sensors during a startup or coast down of the electrical machine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a simple schematic of a generator unit in accordance with an embodiment of the invention; 
           [0008]      FIG. 2  is a schematic diagram of a computer system having a BMT analysis system according to one embodiment of the invention; 
           [0009]      FIG. 3  shows a graph for detecting rotor misalignment according to an embodiment of the present invention; 
           [0010]      FIG. 4  shows a graph for detecting bearing wipe according to an embodiment of the present invention; and 
           [0011]      FIG. 5  shows a graph for detecting bearing wipe according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Various embodiments of the present invention are directed to evaluating trends in bearing metal temperature (BMT) in rotor bearings of an electrical machine to detect anomalies associated with rotor misalignment and bearing wipe issues. Technical effects of the various embodiments of the present invention include the ability to identify such issues at an early stage using BMT data, thus providing the capability of taking corrective action at a very early stage. 
         [0013]      FIG. 1  depicts a simplified generator unit  11  that includes a generator  10  and a turbine  12  operationally coupled with a shaft  14 . A set of rotor bearings  16 ,  18 ,  20 ,  22  support the shaft  14  while allowing it to rotate. Each rotor bearing  16 ,  18 ,  20 ,  22  includes one or more bearing temperature sensors that collect temperature data from the bearing metal. In this example, bearing  16  includes a pair of turbine collector end sensors  24   a  and  24   b , bearing  18  includes a pair of turbine coupling end sensors  26   a  and  26   b , bearing  20  includes a pair of generator coupling end sensors  28   a  and  28   b , and bearing  22  includes a pair of generator collector end sensors  30   a  and  30   b.    
         [0014]      FIG. 2  depicts computer system  40  having a BMT analysis system  48  for analyzing BMT data  62  collected from the rotor bearing sensors to determine if a misalignment or bearing wipe issue exists. If an issue exists, one or more alarms  60  may be outputted. In addition to inputting BMT data  62 , operational data  64  including lube oil inlet temperature, speed, and power data is also collected, e.g., from associated sensors. 
         [0015]    In general, BMT analysis system  48  includes: a data input system  50  for reading in and managing BMT data  62  and operational data  64 ; a filter system  52  for identifying and discarding bad or out of range input data  62 ,  64 ; a misalignment analysis system  54  that evaluates BMT data  62  for trends indicative of a misalignment; a steady state bearing wipe analysis system  56  that evaluates BMT data  62  during steady state operations for trends indicative of bearing wipe; and a transient bearing wipe analysis system  58  that evaluates BMT data  62  during startup/shutdown operations for trends indicative of bearing wipe. Note that BMT analysis system  48  may include any one or more of the misalignment analysis system  54 , steady state bearing wipe analysis system  56 , and transient bearing wipe analysis system  58 . 
         [0016]    Filter system  52  may for example filter out noise, evaluate data quality, and identify bad sensors. It may also discard data that is out of range for a particular test. For instance, steady state bearing wipe analysis system  56  may only evaluate BMT data  62  when the rotor is rotating at a predefined operating speed range and power output range. 
         [0017]    Misalignment analysis system  54  essentially detects vertical alignment changes. Whenever there is any vertical alignment change in the rotor of a generator or turbine, there is unequal loading on the bearing of the turbine and the generator at the coupling end. This leads to an increasing BMT in the generator bearing and a decreasing BMT in turbine bearing or vice versa. Over time, one of the bearings shows an increasing temperature trend and one of the bearings shows a decreasing temperature trend. This simultaneous increasing and decreasing trend of the bearing BMT is a clear indication of any misalignment in the rotor. 
         [0018]    Since the cooling media for the bearing oil is exposed to ambient conditions, the ambient temperature can also have an effect on the BMT. Hence, to minimize the effect of ambient temperature, the monitoring parameter for the detection of misalignment may be implemented by a BMT rise calculation system  55  as the difference between BMT and the lube oil inlet temperature, referred to herein as BMT rise. 
         [0019]    The baseline value for the turbine bearing BMT and generator bearing BMT is calculated over time by baseline calculation system  57 , e.g., during a first week of collecting BMT data  62 . The increase and/or decrease of BMT rise from the baseline can be monitored and evaluated to determine if there is an indication of any misalignment issues. When the BMT from a generator coupling end sensor  28   a ,  28   b  ( FIG. 1 ) increases and the BMT from a turbine coupling end sensor  26   a ,  26   b  ( FIG. 1 ) decreases (or vice versa) relative to their respective baselines, an alarm  60  for bearing misalignment may be issued. 
         [0020]      FIG. 3  depicts an illustrative example in which a generator BMT baseline  70  and turbine BMT baseline  72  are established and shown as dotted lines. The generator BMT rise  74  and turbine BMT rise  76  are monitored over time. As can be seen, the generator BMT rise  74  is increasing and the turbine BMT rise  76  is decreasing relative to their respective baselines. At some predefined set of threshold values (e.g., product of BMT rise_ 1  and BMT rise_ 2  decrease&gt;−Y degrees F.; the BMT rise_ 1 &gt;P and BMT rise_ 2 &gt;−Q, etc.), an alarm condition can be issued indicating a misalignment. In one illustrative embodiment, misalignment analysis system  54  will issue an alarm if a BMT increase and decrease are detected and the product of the increase and decrease is greater than a threshold. 
         [0021]    As noted with regard to  FIG. 2 , steady state bearing wipe analysis system  56  that evaluates BMT data  62  during steady state operations for trends indicative of a bearing wipe. The lack of sufficient flow or cooling of lube oil is one cause that can lead to bearing wipe and can increase the BMT significantly. This increasing trend of BMT in a particular bearing is captured for the detection of bearing wipe under steady state operation of the unit. Here also the monitoring parameter is the rise from a baseline and whenever the rise is above a predefined threshold, an alarm for bearing wipe can be issued. As such, steady state bearing wipe analysis system  56  likewise includes a BMT rise calculation system  55  and a baseline calculation system  57 . In one illustrative embodiment, a bearing wipe problem may be identified at any of the eight sensors shown in  FIG. 1 . 
         [0022]      FIG. 4  depicts an illustrative example in which a baseline  80  is established and is shown as a dotted line. BMT rise  82  from one or more sensors is tracked. When the BMT rise  82  from the baseline value exceeds a threshold, bearing wipe is indicated and an alarm can be issued. 
         [0023]    Transient state bearing wipe analysis system  58  ( FIG. 2 ) evaluates BMT data  62  during transient operations for trends indicative of a bearing wipe issue. When a journal becomes scored, the oil film pressure profile across the length of the bearing is chopped into segments. The consequence of this is that the journal rides closer to the babbitt surface. This is not necessarily a problem at rated speed; however, below rated speed, during coastdown or startup, the oil film thickness is reduced in proportion to the speed. As the film thickness decreases a transition from hydrodynamic to boundary layer lubrication occurs. During this transition the oil film becomes thinner and, when already reduced by the scored journal, the film may not provide sufficient support. The result is oil film breakthrough, metal-to-metal contact, and wiping of the bearing. 
         [0024]      FIG. 5  depicts an illustrative example of a graph in which BMT is tracked during coastdown. As can be seen, in the case of a scored journal  90 , there is a peak or spike that occurs shortly after the turbine is tripped. Conversely, in the case of a normal journal  92 , no spiking occurs. Any technique may be utilized to identify a spike in the BMT data. 
         [0025]    In various embodiments of the present invention, aspects of the systems and methods described herein can be implemented in the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements. In one embodiment, the processing functions may be implemented in software, which includes but is not limited to firmware, resident software, microcode, etc. 
         [0026]    Furthermore, the processing functions can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system (e.g., processing units). For the purposes of this description, a computer-usable or computer readable medium can be any computer readable storage medium that can contain or store the program for use by or in connection with the computer, instruction execution system, apparatus. Additional embodiments may be embodied on a computer readable transmission medium (or a propagation medium) that can communicate, propagate or transport the program for use by or in connection with the computer, instruction execution system, apparatus, or device. 
         [0027]    The computer readable medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device). Examples of a computer-readable medium include a semiconductor or solid state memory, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Current examples of optical disks include a compact disk-read only memory (CD-ROM), a compact disk-read/write (CD-R/W) and a digital video disc (DVD). 
         [0028]      FIG. 2  depicts an illustrative computer system  40  having a processor  42 , I/O  44  and memory  46  coupled together with a bus  17 . Computer system  40  ( FIG. 1 ) can comprise one or more general purpose computing articles of manufacture (e.g., computing devices) capable of executing program code installed thereon. As used herein, it is understood that “program code” means any collection of instructions, in any language, code or notation, that cause a computing device having an information processing capability to perform a particular function either directly or after any combination of the following: (a) conversion to another language, code or notation; (b) reproduction in a different material form; and/or (c) decompression. To this extent, BMT analysis system  48  can be embodied as any combination of system software and/or application software. In any event, the technical effect of computer system  40  is to detect anomalies associated with rotor misalignment and bearing wipe issues. 
         [0029]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0030]    While the disclosure has been particularly shown and described in conjunction with a preferred embodiment thereof, it will be appreciated that variations and modifications will occur to those skilled in the art. Therefore, it is to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.