|Title of Invention||
AN ON-LINE VIBRATION MONITORING APPARATUS FOR FAULT DIAGNOSIS OF A HIGH SPEED BOILER FEED PUMP.
|Abstract||The invention relates to an on-line continuous vibration monitoring apparatus for fault diagnosis of a high speed multistage, centrifugal boiler feed pump (BFP) in a power plant comprising triaxial mounts (2,4) for velocity probes (1,3) secured to each bearing housing at the drive end bearing (21) and the non-drive end bearing (41) of the BFP; the output signals generated at said velocity probes being routed to a display machine (6) for showing vibration severity by spectrum analysis and trending of spectrum analysis and trending of spectrum components relevant to BFPs, followed by condition assessment bar chart display.|
|Full Text||The present invention relates to a vibration monitoring apparatus for high speed Boiler Feed Pumps (BFP). More specifically the invention relates to an on line continuous vibration monitoring for fault diagnosis of a high speed multistage centrifugal BFPs in thermal power plants.
Normally condition monitoring of high speed multistage centrifugal Boiler Feed Pumps (BFP) is carried out manually based on vibration level measurements with portable instruments at periodic intervals in thermal power plants.
Continuous monitoring of overall vibration levels of bearing is being done in either vertical only or vertical and horizontal directions. In the event of the overall vibration levels reaching alarm levels, detailed vibration analysis of bearing is carried out at the location of the pump using a vibration analysing instrument by the Maintenance / Instrumentation staff in thermal power plants.
A need was felt for an on-line condition assessment of boiler feed pumps through vibration analysis. Such a full-fledged on-line system implemented on a PC can be directly used by maintancenance personnel in utilities for condition assessment, predictive maintenance scheduling for reliable operation through effective diagnosis. The system can guide the engineers regarding severity assessment based on International Standards, vibration levels in different modes of seventy measurement, spectral component trending, relative mechanical /hydraulic excetion content, etc. for Diagnosis and correction measures to be taken.
The BFP operating in thermal plants constitute one of the most critical equipment, the reliable operation of which has a direct influence on the power output of the utility. It is therefore essential to implement condition based predictive maintenance, which is the most reliable and cost effective technique for monitoring and diagnosing machinery faults well before irreversible deterioration, damage and unforseen catastrophic failures. In view of the above the present work consists of development of an on-line vibration monitoring, analysis, trending and condition assessment system for arriving at an effective predicitive maintenance program for BFPs.
The main objective of the present invention is primarily to develop an on-line vibration monitoring system that will continuously acquire vibration data from the bearings of the BFP and show the machine mimic display with the vibration severity at the various locations. Another objective of the invention is to provide spectrum analysis trending of spectral components relevant to BFPs and condition assessment on a continuous on-line basis.
The vibration response of a boiler pump feed is one of the major attributes for assessing its operating health. Any deviation in the assembly protocols, operating parameters, mechanical integrity will finally reflect in the vibration behaviour of the machine. The vibration phenomenon encountered in pumps is basically attributed to mechanical and hydraulic excitations. The principal sources of mechanical perturbation forces are unbalance of the rotor, misalignment, looseness, piping pulls etc., while the hydraulic perturbation forces are caused due to improper interaction in the passage of impeller/diffuser vanes in the water path.
The best measurement mode to define the vibration severity is found to be velocity mode (mm/sec RMS) on bearing and displacement mode (micrometer peak to peak i.e ( um p-p) on shafts (relative to the casing). Severity assessment is based on the standards evolved with large data base generated over a period of time. The measurement frequency range has been fixed based on the fundamental hydraulic vane passing frequency and the harmonics for a given set of impeller/diffuser vanes combination. Discrete frequencies related to mechanical and hydraulic excitation forces have been identified for trending and diagnosis purposes.
The present work has been carried out for feed pumps having 7/13 vanes in the impeller/diffuser respectively. The only factor that varies by changing this combination is the fundamental 'hydraulic vane passing frequency.
The severity criteria for BFP vibrations has been established using the large data base generated during the present work and during the failure investigations till date, in line with International Standards. The data base was generated by carrying out systematic vibration measurments on BFPs during the course of this work and also through failure investigations at various power stations.
The standards have been established in both for relative
shaft vibrations as well as for bearing vibrations in
displacement mode ( um p-p) and Velocity mode (mm/sec (peak/RMS)
The motor vibration severity standard has been given in velocity mode both in peak and RMS. These severity criteria were formulated taking into view the International Vibration Standards like VDI12059, IS4729, NEMA and MGI2051.
The transducers for vibration monitoring which are velocity output sensors are selected and first tested in the laboratory using a shaker system with sinusoidal excitation. The transducers gave satisfactory results with respect to a standard B&K accelerometer. Subsequently the transducers were tested on one of the BFPs at a thermal power plant using a triaxial mount. This evaluation is necessary to establish the performance of the transducers in the frequency range applicable to BFPs in comparison with a standard B&K accelerometer. For this purpose detailed vibration analysis of the pump is carried out with
the above transducers in the frequency range of 0-2000Hz at
180Kg/cm2 and 380 T/hr of the pump which corresponds to about
200 - 210MW of the TG set. The spectral analysis of the selected transducer outputs in overall and other excitation frequency amplitudes, compares well with that of a standard FFT Analyzer of Onosokki make. A comparative data set is presented in Table 1 and Figure 6.
Comparative data sets for Four transducers(B&K4384 and IMI Velocity Sensors)
(All levels in mm/sec peak)
TABLE 1. COMPARATIVE VIBRATION LEVELS OBTAINED USING THE ICP VELOCITY TRANSDUCERS AND STANDARD B&K ACCELEROMETER
The transducer system is compact when mounted on the bearing housing giving the triaxial vibrations simultaneously from the same location ideally suited to BFP.
The low frequency circuit noise is found to be negligible in spite of built in integration as compared to an aceelerometer.
The transducer gives satisfactory performance both in low and high frequency ranges within the temperature range prevalent on BFP bearing housings.
Thus the present invention relates to an on-line continuous vibration
monitoring apparatus for fault diagnosis of a high speed, multistage centrifugal boiler feed pump (BFP); in a power plant comprising triaxial mounts for velocity probes secured to each bearing housing at the drive end and non-drive end of the BFP; the output signals generated at said velocity probes being routed to a display machine for showing vibration severity by spectrum analysis and trending of spectral components relevant to BFPs, followed by condition assessment bar chart display.
Brief description of the accompanying drawings:
Fig.l. illustrates the location of BFP in thermal power plant overview.
Fig.2. Shows the process flow diagram of BFP.
Fig,3 is the general arrangement of a BFP machine train,
Fig.4. shows the cross sectional arrangement of BFP.
Fig. 5. illustrates in schematic form the on-line condition assessment system of present invention.
Fig. 6. shows comparative bar chart of ICP velocity transducers and standard accelerometer.
Fig. 7. shows comparative bar chart of vibration levels obtained using ONOSOKKI FFT analyzer with the present invention.
Vibration monitoring for the on-line condition assessment system for BFPs in thermal power plant is shown schematically in Fig. 5. The system comprises triaxially mounted velocity probes 1 at the drive end bearing 2 of the BFP and a second triaxially mounted velocity probes 3 at the non-drive end bearing 4. The triaxially mounted velocity probes 1, 3 provide vibration in horizontal, vertical and axial directions.
The velocity probes 1, 3 can be transducers and three such transducer can be fitted to each triaxial mount 2, 4 and each triaxial mount in turn is secured to a bearing housing of the BFP by means of bolts.
The transducer selected is a velocity output sensor such that the built in integration allows direct readings of velocity in mm/sec, its rugged sensing element coupled with protected electronics make this sensor ideal for both permanent and portable measurements. It has a linear output from 0-2.5 KHz frequency range and works in a temperature environment in direct contact with the bearing housings upto 120 C. A triaxial mounting arrangement is made to facilitate mounting of 3 transducers in single location to get horizontal, vertical and axial direction vibrations. The sensitivity of the transducer is 4 mV/mm/sec and the power supply/amplifier has *1/*10/*100 gain options.
The output signals from the triaxially mounted probes 1 , 3 are fed to a display machine 6 via a signal conditioner 5 for display of machine mimic showing vibration severity at various transducer locations as per International standards with appropriate colour coding. Other features are, spectrum analysis, trending of spectral components relevant to BFPs, indicate the relative mechancial/hydraulic status, conversion of the data to displacement units and total archiving of the data for about one year. Thus a system is provided that will continuously assess the mechanical condition of BFP based on vibration to enable the maintenance personnel to take corrective action at the appropriate time and avoid unscheduled forced outages.
The display machine 6 is a pentium desktop computer (233MHz) with 2.1GB HDD and 16MB RAM was procured with windows 95 operating system.
The basic requirement of multi channel data acquisition is achieved through a 8/16 channel 16-bit data acquisition card with an Analog to Digital Converter (ADC) of 100 KHz sampling rate. The input range of ADC is +lOV. the ADC is a high resolution/high performance multi function Analog-Digital and timing I/O board for PC AT and compatible computers. The signals are sent through a BNC interface adaptor for better signal routing and signal conditioning to facilitate low pass filtering and better signal grounding for undesirable noise elimination.
The condition monitoring software, is developed using a graphical programming system for data acquisition, analysis and presentation. This is an innovative programming methodology in which graphically assembled software modules are used.
Driver software for data acquisition, processing and presentation is developed in a graphical programming environment. Following is the sequence of software operation:
1. Addressing of data acquisition card by a pre-configured
2. Selection of channel starting with channel 0.
3. Data acquisition in the selected channel at a sample rate
of 8000 samples/sec and number of samples being 8192 (Power
of 2 for efficient FFT Analysis requirement)
4. Conversion from voltage to velocity units at 40mv/mm/sec
sensitivity, with linear range of amplitude settings.
5. Banning Window selection for better frequency/amplitude
6. Fundamental running speed input data of BFP.
7. Conversion from time domain to spectral domain and display
in separate panels.
Picking up of running speed (IX) and other harmonic (1.2X, 2X, 3X, 7X and 14X) amplitudes within a 20% bandwidth at the center frequency
9. Conversion of above harmonics to displacement amplitudes
with appropriate integration constants
10. Evaluation of overall level in velocity and displacement
modes with lower cut off at 25 Hz.
11 . Repetition of steps from 3 till the selected averages are complete
12. Averaging of all the overall levels and running speed
harmonics selected as per 8 and 9
13. Update the trend chart of the respective channel with
overall levels and harmonic components
14. Putting the overall levels at respective measurement
location ramps containing the severity color coding settings
on the machine mimic diagram.
15. Repetition of steps from 2. till all the six channels are
16. Evaluation of various harmonic amplitudes and display of
relative mechanical/hydraulic condition in the bar chart.
17. Repetition of steps from 1.
18. For noise analysis, the spectrum obtained as above
is converted to one-third octave band by evaluating the
spectral contents in each spectral band and converting
the same into standard dB level
The following are the salient features of the software.
developed for vibration monitoring/analysis and
1. Display of Time wave form and frequency spectrum (0-2 KHz range).
2. Display of the overall vibration levels with severity colour
coding in velocity mode in mm/sec (rms).
3. Display of significant excitation frequencies and their
levels in mm/sec (rms) attributable to various discrepancies
which can be used for condition assessment.
4. Display of the corresponding displacement levels in microns
(p-p) of the above excitation frequencies and also the
overall vibration displacement level.
5. Trending of the overall and the significant excitation
6. Display of 1/3 octave noise spectrum.
7. Display of relative mechanical/hydraulic assessment bar
After the testing of the transducers, software development for spectral analysis, trending and condition assessment, the complete monitoring system is installed for a BFP Unit in a Thermal Power Plant. When the pump is operating under full load conditions, the vibration signals from the tri-directional transducers are analyzed usiny the system continuously and trended for performance comparison with respect to standard spectrum analyser. The number of time records for averaging is chosen to match with the number of averages in a standard spectrum analyzer for processing and display. A comparative statement of the overall and other excitation frequency amplitudes are presented in Table 2 and Figure 7. While analyzing the vibration signals through the system and the FFT Analyzer, the signals are also recorded simultaneously on a four-channel instrumentation tape recorder as a backup, to enable the system testing in the laboratory with modified features of the software and for demonstration purposes.
Table 2 Comparative Spectral Data (multiple samples) Obtained using
Onosokkl Analyzer and the Present System (VSSBFP) for BFP-3B
1 . Observation of the system for a few months indicated good matching of the results in both frequency components and overall level in both velocity in mm/sec (rms) and in displacement mode in microns (peak to peak) with a standard FFT analyser.
2. The system facilitated the continuous trending of the
significant excitation frequencies that reflect the status
of mechanical/hydraulic condition of the pump. Figures
10 and 11 are typical output displays for BFP-4C and
3. Noise analysis and trend in one-third Octave format is
also achieved which compared well with conventional noise
1. An on-line continuous vibration monitoring apparatus for fault
diagnosis of a high speed multistage, centrifugal boiler feed pump
(BFP) in a power plant comprising triaxial mounts (2,4) for velocity
probes (1,3) secured to each bearing housing at the drive end bearing
(21) and the non-drive end bearing (41) of the BFP;
the output signals generated at said velocity probes being routed to a display machine (6) for showing vibration severity by spectrum analysis and trending of spectrum analysis and trending of spectrum components relevant to BFPs, followed by condition assessment bar chart display.
2. The apparatus as claimed in claims 1, wherein said velocity probes
(1,3) are arranged in the triaxial mounts so as to get vibration in the
horizontal, vertical and axial directions simultaneously from the same
3. The apparatus as claimed in claims 1 and 2, wherein said velocity
probes (1,3) are transducers.
4. The apparatus as claimed in the preceding claims, wherein the said
transducers are velocity output sensors allowing direct readings of
velocity in mm /sec.
5. The apparatus as claimed in the preceding claims wherein the display
machine 6 is apentium desktop computer.
6. The apparatus as claimed in preceding claims wherein said output
signals are routed to the display machine via a signal conditioner (5).
7. The apparatus as claimed in claim 6, wherein said signal conditioner
is a BNC interface adaptor to facilitate low pass filtering and signal
grounding for undesirable noise elimination.
8. The apparatus as claimed such as substantially herein described and
illustrated in the accompanying drawings.
|Indian Patent Application Number||945/DEL/1999|
|PG Journal Number||11/2008|
|Date of Filing||05-Jul-1999|
|Name of Patentee||BHARAT HEAVY ELECTRICALS LTD.,|
|Applicant Address||BHEL HOUSE SIRI FORT, NEW DELHI-110 049, INDIA.|
|PCT International Classification Number||G01D 21/14|
|PCT International Application Number||N/A|
|PCT International Filing date|