Abstract:
A non-intrusive method of monitoring the integrity of a rotating member comprising mounting at least one sensor in a stationary frame of reference in a casing over the rotating member, measuring the pressure field of the rotating member, comparing the measured pressure field with a corresponding reference pressure field, identifying variations in the measured pressure field, the variations indicative of a fault in the rotating member, and generating an output indicative of an identified fault.

Description:
FIELD OF THE INVENTION 
     This invention relates to non-intrusive techniques for monitoring the integrity of rotating mechanical components. More particularly, the present invention relates to a method and apparatus for monitoring the mechanical integrity of rotating components of a machine by monitoring the pressure fields generated by the rotating components. 
     BACKGROUND OF THE INVENTION 
     The recent deregulation in the power-generation industry has resulted in the formation of a spot market in electricity, wherein, during periods of heavy demand, the price offered for this commodity may be temporarily elevated by an order of magnitude over common levels. Recently, this approach has allowed the owners of several new power generation plants to literally pay for those assets in a short period of time. Consequently, the spot market, and end users desire to service the power generation market placed an added emphasis on the availability and reliability of the equipment to ensure that it is operational and available to meet the periods of peak demand. This scenario is true and equally applicable to other industries. 
     During operation of power generation equipment, several factors may likely lead to faults, thus causing machinery breakdown. Damage to compressor blades because of resonant (high-cycle fatigue) blade failures, foreign object damage (FOD), blade tip/casing rubs, and the like lead to compressor inefficiency and forced outages. 
     Land-based gas turbines used for power generation a compressor must be allowed to operate at a higher pressure ratio in order to achieve a higher machine efficiency. A compressor stall, as identified above with respect to aircraft turbines, may also occur in land-based gas turbines. Similar to the problems faced during the operation of aircraft gas turbines, if a compressor stall remains undetected and permitted to continue, the combustor temperatures and vibratory stresses induced in the compressor may become sufficiently high to cause damage to the turbine. 
     Thus, there is a need for a method and apparatus to non-invasively monitor the integrity of machinery components to determine the cause of performance degradation without disassembling the entire machinery. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a method and apparatus for non-invasively monitoring the integrity of an axial flow compressor by measuring the pressure fields generated by rotating compressor blades. A plurality of sensors are disposed about the compressor casing for measuring the pressure fields generated by each of the rotating blades of a blade row, the measured pressure field indicative of the integrity of the blade. 
     In one embodiment, the measured pressure signature from a single sensor is compared with respective baseline reference pressure signature to identify deviations from the reference values. Deviations in the measured contours are identified to determine faults in rotating components of the compressor. The present invention adds granularity to the concept of non-invasive monitoring by ascertaining the root cause of changes in performance without disassembly of operating machinery. 
     In another embodiment, the obtained pressure signature from a blade passage is compared to an average signature of the entirety of blade passages from a given blade row at a given point of time. Any variations in the comparison are identified to indicate a fault in a rotating blade. 
     In yet another embodiment, the present invention may be used to detect the mechanical spallation of thermal barrier coatings (TBC&#39;s) integrity of the rotating blades of a rotor in a gas turbine. 
     In a further embodiment, the present invention may be used to monitor periodic aerodynamic phenomena, such as for example, the occurrence of rotating stall on start-up of axial compressors. 
     In one aspect, the present invention provides a non-intrusive method of monitoring the integrity of a rotating member, comprising mounting at least one sensor in a stationary frame of reference in a casing over the rotating member; measuring a pressure field generated by the rotating member; comparing the measured pressure field with a reference value; identifying variations in the comparison step, the variations indicative of a fault in the rotating member; and generating an output indicative of an identified fault. The method further includes performing phase averaging of measured pressure fields to remove interference signal content, storing in real-time the measured pressure field data in a memory system; and freezing the memory system to protect the integrity of the stored data in the event of a failure. 
     In another aspect, in a compressor having a plurality of rotating blades, a method of monitoring the integrity of the rotating blades comprising disposing at least one sensor about the rotating blades to measure a pressure field of a rotating blade; comparing the measured pressure field with corresponding reference value to identify variations in the measured pressure field; and generating an output indicative of variations in the measured pressure field. 
     In yet another aspect, the present invention provides a non-intrusive method of monitoring the integrity of a rotating member of a gas turbine of the type having a compressor with a plurality of rotating members, a generator, and a turbine, according to various embodiments of the invention. 
     In a further aspect, an apparatus for monitoring the integrity of rotating components of a gas turbine, comprising at least one sensor operatively coupled to the compressor to measure the pressure fields of rotating components; a processor system operatively coupled to the at least one sensor for performing phase averaging of the measured pressure fields; and a comparator operatively coupled to the processor system for comparing the measured pressure field data with a reference value. The apparatus further comprises a user interface coupled to the comparator for identifying a faulty rotating component in the event of a deviation in the measured pressure field of the rotating component from the reference value. The sensor is preferably a dynamic pressure sensor or a hot wire anemometer. 
     In another apsect, a non-intrusive apparatus for monitoring the integrity of a rotating member, comprising: means for measuring the pressure fields of the rotating member; means for comparing the measured pressure fields with a reference value to identify a fault in the rotating member; and means for generating an output indicative of the identified fault. The apparatus further comprises means for performing phase averaging of measured fields to remove random signal content. 
     In yet another aspect, a non-intrusive apparatus for monitoring the mechanical integrity of a rotating member of a compressor, comprising at least one sensor operatively coupled to the compressor for measuring compressor parameters; a comparator operatively coupled to the at least one sensor for comparing the measured compressor parameters to corresponding reference values to identify a faulty rotating member; and a user interface coupled to a processor system for displaying an identified fault. 
     In a further aspect, a non-intrusive method of monitoring the integrity of a rotating member among a plurality of rotating members, comprising mounting at least one sensor in a stationary frame of reference in a casing over the rotating members; measuring the pressure fields of each of the rotating members of a blade row; performing an average of the measured pressure field; comparing the measured pressure field of a rotating member with the average pressure field; identifying a faulty rotating member in the event of a mismatch in the comparison step; and generating an output indicative of an identified fault. 
     The benefits of the present invention will become apparent to those skilled in the art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a high level block diagram of the present invention; 
     FIG. 2 shows pressure data acquisition system of the present invention; 
     FIG. 3 illustrates an exemplary contour plot for absolute wall static pressure in three blade-to-blade passages of a given blade row in accordance witht the present invention; 
     FIG. 4 illustrates a graph showing some of the data collected and synthesized to form a signature as shown in FIG. 3; 
     FIG. 5 illustrates a method of collecting pressure data by the data acquisition sub-system of the present invention; 
     FIG. 6 illustrates a method of averaging collected pressure data as shown in FIG. 4; 
     FIG. 7 illustrates a waveform resulting from phase averaging the waveform shown in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, there is shown a high level block diagram as indicated at  30  of the present apparatus for non-intrusively monitoring the integrity of rotating blades  42  (FIG.  2 ). Apparatus  30  includes data acquisition system  40  for collecting pressure data produced by rotating blades  42 . The data acquisition system  40  preferably includes sensors  41  (FIG. 2) for collecting compressor parameters. For convenience, the present invention will be described with respect to a single compressor of a gas turbine and data acquisition with respect to one row of blades is discussed. The pressure data collected by system  40  is averaged by system  50  to remove random variations in data due to interference. The averaged data from waveform averaging system  50  is received by waveform analysis system  60  wherein the averaged data is compared with reference data to locate a faulty rotating blade. The waveform analysis system  60  may be, for example, a comparator or the like. The processor system  50  may be, for example, a computer or a microprocessor system. Any deviations in the measured data are identified as being indicative of a fault in a rotating blade  42  (FIG.  2 ). A user is informed about a faulty blade via a user interface  70  such as, for example, a display device or the like. 
     FIG. 2 shows a data acquisition system of the present invention as illustrated in FIG. 1 wherein a few exemplary blades  42  are shown. It will be understood that several such blades are present in a blade row. Likewise, several such blade rows may exist in a single stage of a compressor. Pressure field data generated by rotating blades  42  and collected by sensors  41  is received in a signal conditioner of control computer  43 . Signals received by computer  43  are amplified and forwarded to an A/D converter  44  for converting analog signals to digital signals. Sensor  41  is preferably a pressure sensor, and several such sensors may be disposed in a continuous array in casing  47  of the compressor. The control computer  43  also controls such factors as gain, amplification, offset, and supply voltage to sensors  41 , appropriate selection of such factors being necessary for proper collection of pressure data. Wavetek™ generator  46  receives a signal from a gas turbine engine (not shown) and filters the received signal to produce a clean filtered signal prior to passing the filtered signal to A/D converter  44 . Once a single revolution of an blade is marked, a triggering event is received in the A/D converter  44  for initiating pressure data acquisition by sensors  41 . 
     Still referring to FIG. 2, pressure data collected by sensors  41  is processed in a waveform averaging system  50  by segmenting the data into several parcels (such as, for example, 128) corresponding to the time required for one complete revolution, and averaging those parcels, thus producing a contour. Alternatively, the data parcels may be processed, via a Fast Fourier Transform (FFT), prior to averaging by converting instantaneous low time-domain signals to instantaneous frequency-domain signals. The frequency-domain signals are then averaged to remove undesirable interferences. The A/D converter  44  may be operated by controller  45 . 
     FIG. 3 shows an exemplary contour plot for absolute wall static pressure for a healthy compressor produced by each of the rotating blades  42  of compressor  48  (FIG.  2 ). For the sake of brevity, only four blades  42  are shown. It will be understood that more than four blades may be present in a blade row. Sensors  41  are identified on the Y-axis and non-dimensional time is charted on the X-axis. In the exemplary embodiment, FIG. 3 depicts pressure contour plots of different blades within a single blade row wherein each rotating blade  42  is interrogated to monitor the differences in pressure contours indicative of the integrity of the blades  42 . The sensors  41  are preferably arranged axially across the blade passage. In the exemplary arrangement shown in FIG. 3, ten sensors are used. However, the number of sensor should not be construed to be limiting of the present invention. Pressure signatures are obtained by sensors  41  as the blade  42  passes beneath the sensors  41 . Each sensor  41  collects data over a particular circumferential “slice” of the blade passage. For example, the sensor over the leading edge slice is exposed to the leading edge of all of the blades in the blade row. 
     FIG. 4 shows some of the data that is collected and synthesized to form a signature as shown in FIG.  3 . FIG. 4 depicts the passing of a number of individual blades beneath a plurality of sensors deployed across the blade-to-blade plane. 
     FIGS. 5 and 6 illustrate the collection and averaging of the pressure data collected by sensors  41  (FIG.  2 ). FIG. 7 shows a waveform with a fault identified in one of the rotating blades  42 . Pressure contour data measured by sensors  41  is processed in waveform analysis system  60  where the measured pressure contours are compared with reference contours to identify a faulty blade. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it will be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.