Vibrational Diagnostics Automatic System (VIDAS)

   

The specialists of the St.-Petersburg Central Boiler & Turbine Institute (CKTI) have worked out measuring & analyzing set "VIDAS" to be used on power generating equipment, performing following functions:

• Measurements of vibration (level, spectra, frequencies, phases etc.) of bearing supports (absolute) and that of shafts journals (relative) of steam turbine.
• Emission of alarm signals for warning of turbine operators or tripping the turbine, depending on the vibration level.
• Displaying and memorizing the parameters of vibration.
• Automatic analysis of the turbine vabrational behavior performing the diagnostics of eventual misfunctions in real time regime.

 Structure of the VIDAS hardware.

1. Analog part
• sensors of bearing supports absolute vibration
• proximity gauges for measurement of shafts relative vibration
• reference signal pick-up (key-phaser)
• alarm signals generating device (cassette type)
• commutation boxes, cables
• data acquisition devises (filters, amplifiers, integrators, analog-digital converters)
2. Digital part
• data processing device: industrial processor for standard 19"(performing low level program),Intel 486, 66MHZ
• Personal computer (performing upper level programs),connected with data processing device by Ethernet. Configuration: Processor Pentium II 400 MHZ,RAM 64 MB, Hard drive 4 GB
• Monitor 15", Floppy drive 3,5"

 Description of the VIDAS software

The VIDAS software may be installed (both low and / or upper level) separately from VIDAS hardware on any vibration measuring equipment.

1.Software for data processing (low level program)

The purpose of this program is to prepare the data for execution of upper level programs.
The functions fulfilled by low level program are as follows:

1. Polling and acquisition of all analog signals coming through analog-to digital converters. These signals may come from vibration gauges and from other instruments measuring technological parameters of the power unit.
2. Calculation of root mean square of absolute vibration velocity
3. Peak-to-peak values of absolute (bearings) and relative (shafts) vibration displacements
4. Statical displacements of shaft journals in bearing bores
5. Harmonic components of both bearings and shafts vibration of ?,1/2,1,2 ………16 of the speed of rotation (FFT)
6. Phase angles for all harmonic components
Time lag between two measurements is up to 3 seconds.

2.Upper level software

This set of software products contains monitoring, archiving and diagnostics programs and may be installed on any vibration measuring system provided the above mentioned data preparation procedure is fulfilled.

2.1. Monitoring

The purpose of monitoring program is to prepare and to display the parameters of vibration state of the turbine which are necessary to estimate the mechanical reliability of turbine operation. The displaying is organized in a user friendly way in forms of bar-diagrams, tables, graphs, orbits, mnemonic schemes and drawings according to the user's selection from the proposed menu. Following parameters are displayed:
   - Speed of rotation
   - R.M.S. for bearing absolute velocities in three directions
   - Peak to peak absolute and relative vibration displacement for bearings and shafts
   - Bearings and shafts vibration spectra
   - Time functions of vibrations
   - Orbits of bearings and shafts dynamical displacements
   - Shaft journals static displacements in bearings bores
This list of the parameters may be enlarged according to the user's requirements.

2.2. Archiving

According to this program all above mentioned parameters are memorized in the form displayed by the monitoring program. All the user has to do is to enter with the key board the date and the time of a moment to be investigated. The user interface here is the same as in monitoring program. The data massive is compressed by special routine which allows to memorize data for a period of several years.

2.3.Diagnostics

   The automatic diagnostics is performed according to the algorithm worked out by the CKTI specialists on the basis of their investigations on shaft-line models, theoretical calculations, researches carried out at site on operating turbines, adjustment works ("trouble shooting") and investigations of turbine accidents.
   The program allows to carry out diagnostics in two equally possible ways:
   1. Using only vibration signals
   2. Using both vibration signals and parameters characterizing operational regimes of the turbine (load, temperatures, pressures, etc )
The latter is more expensive but more trustworthy.
The diagnostics process starts when at least one of the diagnostical parameter exceeds preset limits.
   At first the special subprogram prepares the data base containing the so-called diagnostical parameters: vibration levels changing, ratios between bearings and shafts vibrations ,trends, functions, spectra, orbits, etc ). Then on the basis of collected parameters the cause of vibration change is detected by calculations according to VIDAS algorithm. If this cause is due to a certain misfunction or a defect of operating equipment this defect is displayed on the PS monitor with indication of its development (propagation) degree and location.
The whole described above procedure 4 - 6 seconds.
The examples of defects which may be detected by VIDAS:
   - Rotors unbalance
   - Radial misalignment of the rotors connections
   - Angular misalignment of the rotors connections
   - Abrupt unbalancing
   - Radial rubs of rotors against stator parts
   - Axial rubs of rotors against stator parts
   - Rubs in oil seals of the bearings
   - Propagation of a crack in the rotor
   - Oil whip (low frequency unstable vibration)
   - Steam whirl (loss of stability due to aerodynamic forces)
   - White metal (babbit) destruction of the bearings
   - Misalignment of the bearing supports
   - Rupture of the coupling bolts
   - Rotor flexure
   - Possibility of separation of the last stage rotating blade N …..
   - Short circuit in generator rotor windings
   - Asymmetry of generator rotor cooling channels
This list of diagnosed defects can be widened for a concrete type of power equipment.
The diagnostics program is open and may be easily adopted to a certain type of a turbine.
All diagnostical parameters can be displayed thus giving to the user the possibility to understand the reason of the diagnosis.

 References

   The VIDAS diagnostics program is being successfully used for the last eight years on several turbines at different power stations:
   LMZ turbine K-1200-240 at Kostroma PS
   LMZ turbine K-300-240 at KostromaPS
   LMZ turbine K-1000 60/3000 at South Ukrainian Nuclear PS
   Urals Turbine & Motors Plant (UTMZ) turbines T-250-240 and T-100 in Mosenergo Power system
   LMZ turbine K-200-130 at Cherpovets PS
   LMZ turbine T-180-130 at Gomel PS (Belarussia)
   Kharkov Plant turbine K-500-130/3000 at Smolensk Nuclear PS is in the process of installation