FIELD OF THE INVENTION
The present invention relates to a system for monitoring stator end winding vibration in generators particularly adapted at thermal power plants. More particularly the invention relates to an Online PC based digital stator end-winding vibration monitoring system for generators
BACKGROUND OF THE INVENTION
Block diagram in figure 2 of Annexure-1 depicts Winding Vibration Monitoring System of prior art using extensive hardware circuit for signal processing and also computer and software for frequency analysis and data storage and trend monitoring/plotting.
The prior art, multi-channel winding vibration monitoring systems generally use
hardware based signal processing. This involves sensing of vibration signals by
vibration transducers which are for each channel conditioned, amplified in
amplifiers, filtered and active amplifiers for noise elimination, a
multi stage integrating amplifiers, a plurality of attenuators, tuned for capturing vibration of frequencies; displays; signal level settings; comparators for alarm signal outputs; amplifiers/attenuators for recording signal output; dedicated front panel controls; and a plurality of calibration presets/control knobs/switches. Such processed and conditioned signal for each channel is then fed into the PC-based data acquisition system where it is converted into digital form and stored for trend monitoring or future data/post processing using the PC and the application software. Further, for resolution of the vibration signal into different frequency components for frequency analysis of signal, a separate processing (FFT) card and associated circuits are used. The whole arrangement is shown in block

diagram in figure-2. The following blocks indicated in figure-2, are implemented using hardware circuit on the PCBs (printed circuit boards) in prior art systems. All independent hardware for each channel. For example for a 12 channel system, there are 12 x number of PCBs required for implementation of following circuits :-
Input Filter Hardware circuit (1)
Vib. Mode Selector/Integrator (A,V,D) (2)
Filter Ckt. - 50 Hz-100 Hz-Σ (3)
Amplitude Detector & Selector for pk-pk/pk/rms Hardware circuit (4)
Display Gain Amplifier Hardware circuit (5)
Display Hardware circuit (6)
Amplifier circuit (7)
Alarm/warning level Setting/Alarm/warning Signal Detectn & Gen. (8)
Circuit for Alarm/warning Status Display for all channels (9)
Circuit for LED indication of Alarm/warning status, Relay Drivers &
Relays (10)
Circuit for Signal conditioning for Analog Sig. Output (11)
Circuit for Analog output- mV/4-20mA (12)
Sampling and Analog to Digital convertor card Hardware circuit (13)
DSP Card for frequency Analysis (14)
Signal Pocessing Software (15)
Data Storage and Display (16).
I. In the prior art as depicted in block diagram in figure 2 of Annexure-1, basic system of 12-channel winding vibration measurement system consists of 12 Nos. of vibration sensors (22) which converts vibration signal in acceleration mode into charge signal as pC/m/sec2 and 12 Nos of conditioning Amplifiers

(18) which convert the charge signal into voltage signal and gives output in the form of mV/m/sec2.
II. Signal Processing Hardware circuit for each channel (Blue dotted line block).
In the prior art system all independent hardware for each channel i.e. for 12 channel system there are 12 x number of hardwired circuits required for onward signal processing & functional implementation. Blue dotted line block consisting of following circuits represents one such channel,
Input Filter Hardware circuit (1) : This electronic circuit filter removes
unwanted noise signal.
Vib. Mode Selector/Integrator (A,V,D) (2): Vibration signal (being
simple harmonic motion) that can be measured in either Acceleration,
Velocity or Displacement mode. Signal sensed by vibration sensor is
proportional to acceleration. This signal is straight away processed by
selecting (A) Acceleration mode and suitably scaling the same by
amplifiers/attenuators.
Signal proportional to velocity i.e., mV/mm/sec is obtained by selecting
Velocity Mode (using Switches on the equipment) and passing signal
through electronic integrating circuit and suitably scaling the same by
amplifiers/attenuators.
Similarly Signal proportional to Displacement i.e. Microns or Micrometer (meter x 10-6) is obtained by selecting (D) Displacement Mode (using Switches on the equipment) and passing signal through one more electronic integrating circuit (thus double integrating

acceleration i.e. signal proportional to acceleration) and suitably scaling the same by amplifiers/attenuators.
Filter Ckt - 50 Hz-100 HZ- Σ (3) : The vibration signal so far has been in composite mode which consists of number of frequency components that were generated by the vibrating object and sensed by vibration sensor. In case of object under consideration i.e. winding of generator, vibration magnitude of unfiltered component, 50 Hz component and 100 Hz component are of interest and measured and displayed. So here vibration magnitude of unfiltered component is straight away processed by selecting 'Σ' mode and suitably scaling the same by amplifiers/attenuators. Vibration magnitude of 50 Hz and 100 Hz component is processed by selecting '50 Hz' mode and '100 Hz' mode and using electronic tuned circuit filters of 50 Hz and 100 Hz reply. Amplitude Detector & Selector for pk-pk/pk/rms (4) : Amplitude of vibration signal can be measured in pk-pk (peak to peak) or pk (peak) or rms mode. By switch selecting either of the modes, signal is passed through relevant amplitude detector circuit to detect the vibration in required mode.
Display Gain Amplifier Hardware circuit (5) & Display Hardware (6): The above mentioned processed signal is scaled to required magnitude for displays in digital displays (LED display). Amplifier circuit (7) and Alarm/warning level Setting/Alarm/warning Signal Detectn & Gen.
(8) : Here vibration signal of selected mode (A,V,D), frequency and amplitude is suitably scaled in amplifier circuit, compared with preset reference signals for generation of alarm and warning signals. For this

purpose there is also provision of circuit for setting reference signals for alarm and warning.
Circuit for Alarm/warning Status Display Screen (9) and Circuit for LED indication of Alarm/warning status, Relay Drivers & Relays (10): Alarm and warning signals generated above drive the Alarm/warning status LED indicators on t he Alarm/warning Status Display screen. Circuit for signal conditioning for Analog Sig. Output (11) and Ciruit for Analog output - mV/4-20mA (12) : Here vibration signal of selected mode (A,V,D), frequency and amplitude is suitably scaled in amplifier circuit and converted into analog voltage (mV) or current (4-20mA).
Problem with all the above arrangement is all the blocks have to be implemented in circuit hardware which is prone to hardware problems, measurement inaccuracies due to various uncontrollable factors like drift in component characteristics, environmental conditions, wear and tear of moving parts like due to frequent switching operations etc. Makes the equipment bulky and expandability of equipment to higher number of channel in the same equipment configuration extremely difficult. Moreover such systems becomes quite expensive to manufacture.
In the proposed system all these functions are achieved in software eliminating all these problems.
III. Data storage, data display on Monitor screen and Frequency Analysis; A: Data storage, data display on Monitor screen:

A/D Converter (17) : Here in computer analog d.c. signal proportional vibration measured and received for each channel from amplifier bloack 7' is sampled at convenient rate (rate determined only by display updation rate) and converted into digital form for each channel independently. Here sampling rate does not have any implication for further data processing.
Data Storage in DAS PC (18), Processed Data handfling s/w (19): Here digitized data for all the channels is processed and stored in suitable format, and displayed in Tabular format or graphical format simultaneously all channels or display monitor.
Blocks '17' to '21', which incorporates computer and software, have t o be added not for signal processing (which is achieved by circuit hardware as described above) but only for converting data into digital form and then for data storage and display in requisite formats which cannot be done by the above mentioned cicuits.
B: Frequency Analysis:
A/D Converter (13), DSP Card for frequency Analysis (14), Signal Processing S/W (15) and Data Storage and Display (16): Here, in a separate DSP processor board and software installed in it and specifically integrated with main software in computer, analog ac signals for all 12 channels - suitably conditioned for this processor -are inputted parallel. All these analog ac signals are then sampled at predetermined sampling rate and converted into digital form. This sampled digital data is subjected to digital signal processing in this DSP processor board involving substantial electronic circuit which is again hardware circuit. This signal processing converts vibration signal in

time mode into frequency mode and displays on the monitor screen in the form of frequency spectrum for further study and analysis and investigation purpose. Further having data already available in digital form same is converted into requisite format and stored in the files on mass storage devices.
Blocks '13' to '16', which use computer and software, have to be added just for converting data into digital form and then for signal processing for frequency analysis and subsequently for data storage and display in requisite formats which cannot be done by the above mentioned circuits.
The main drawbacks/disadvantages of the prior art systems are:
1. extensive use of electronics hard ware circuits for processing of conditioned vibration signal (output from input conditioning amplifiers).
2. use of independent channels for signal processing increasing electronics hardware.
3. lack operational reliability due to having a large nu7mber of electronics components, circuits and inter connections,
4. higher cost.
5. need separate DAS computer and software.

6. need to maintain a large volume of spares at PCB card level.
7. difficulty in maintenance for end users, since these systems comprises a large no. of modules, PCBs and interconnections using complex hardware circuit.
8. distributed layout of these systems for example conditioning amplifiers are disposed at turbine floor well away from the monitoring and signal processing system in the control room which interalia requires more hardware, cabling and space, and make system operation difficult.
9. needs frequent calibration because of use of large no. components whose characteristics drift with the passage of time.
10.calibration and adjustments is exhaustive and time consuming in such systems.
11. highly prone to electromagnetic and tribo-electric noise signals.
12. lesser overall accuracy in measurement.
13. upgradation of system features at later date is difficult and costlier.

OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to a propose an On-line
Continuous Stator End-Winding Vibration Monitoring System for generators in
power plants, which eliminates the disadvantages of the prior art.
Another object of the invention is to an object of the present invention to a propose an On-line Continuous Stator End-Winding Vibration Monitoring System for generators in power plants, which eliminates the plurality ofl.circuit hardware by implementing the hardware in data acquisition computer having a digital signal processing software.
A still another object of the present invention is to an object of the present
invention to a propose an On-line Continuous Stator End-Winding Vibration
Monitoring System for generators in power plants, which can be implemented in
a general purpose computer with common configuration haveing ISA/PCI interface
slots and interrupt driven DMA memory access.
A further object of the present invention is to an object of the present invention to a propose an On-line Continuous Stator End-Winding Vibration Monitoring System for generators in power plants, which is compact, cost-effective, and provides accurate measurement data.
SUMMARY OF THE INVENTION
The End Winding Vibration Monitoring System according to the present invention uses high speed signal sampling and digital signal processing techniques, thereby minimizing using of hardware circuits. Most of signal processing-is-achieved. using

DAS and software for continuous online data display, frequency analysis and data storage and trend monitoring/plotting using on board software and hardware in the PC which is a general purpose computer having ISA/PCI interface slots and interrupt driven DMA memory access.
In this system the electrical signals of vibrations sensed by piezo-electric transducers are conditioned in the input signal conditioning amplifier and then fed to the computer for digital signal processing through DAS interface circuit. This DAS interface circuit translates conditioned analog signals into digital ones by high speed sequential sampling at definite sampling speed, for all 12 channels in the form useable for direct digital signal processing in digital signal processing software. The digitally processed signal using specially developed software FFT processes (Fast Fourier Transform - technique of digital signal processing for frequency analysis) end winding vibration signals for all twelve channels to get required frequency components and digital processes signals (to get amplification, filtering and double integration) to obtain the final vibration signal magnitudes in different modes like displacement, velocity or acceleration and in pk-pk or pk or rms and in specific formats like tabulation and graphical plot of a trend over a period of time providing all the relevant information. Display of trend of processed vibration data in a specific format in trend plot is shown in figure-4 of Annexdurfe-1. The DAS sys tern carries out tasks of signal data storage and retrieval, post processing and trend plotting in the same signal processing hardware and software that is available on board in desk top PC with normal configuration eliminating need of additional PC hardware and software as also signal interfacing requirement.
The system in its DAS and interface circuit also provides features of alarm/warning signal processing for alarm/warning level setting, detection and

providing channel wise alarm/warning signal status display on computer screen, in the form of LED displays on relay d river cards and TIL digital driver signal output for direct driving of relays using on board software and hardware in the PC which is normal desk top PC with common configuration having ISA/PCI interface slots and interrupt driven DMA memory access.
This PC based_systemi and its software in_conjunction with minimum interface circuit provides standard analog signal outputs, for 12 channels, to be connected to central digital data acquisition/processing system and it does not require any additional hardware for converting indicated/measured data into suitable standard analog output signal.
The system is useful in advance detecting of faults for example, loosening of winding, weakening of insulation because of abrasion leading to increased R F/partial discharges, loosening of wedges in HV electrical machines. Thus, t he system is useful for monitoring integrity including condition of the stator winding overhang structure during its operation.
This inventive system consists of at least one piezo-electric accelerometer, low-noise signal cables, a multi-channel signal, conditioner, a multiplexed data acquisition interface, DAS cards, a general purpose, computer, Digital Signal Processing Soft ware, structure, an Operating System Software. Measuring points/locations of pick-up installation and routing of cable are selected so as to allow an accurate e and vibration measurement in both directions viz. radial and axial and at both ends namely, the turbine end and exciter end.

According to the invention system, the electrical signals of vibrations are sensed by piezo-electric transducers, and conditioned in the input signal conditioning amplifier and then fed to the computer for digital signal processing through DAS interface circuit. This DAS interface circuit translates conditioned analog signals into digital ones by high speed sequential sampling at definit e sampling speed, for all 12 channels in the form useable for direct digital signal processing in digital signal processing software.
The basic digital signal processing of vibration signal samples of each channel is achieved as described below.
These vibration signal sample sequence x(n) is periodic with period N so t hat x(n) =x(n+kN) for any integer value k. Here n is number of samples, N is sampling period.
This is represented in terms of a Fourier series by a sum of sine and cosine sequences i.e. equivalent complex exponential sequences with frequencies thast are integral multiples of t he fundament al frequency 2-rr/N associatged with t he periodic vibration signal sequence. In contrast to the Fourier series for continuous periodic functions, there are only N distinct complex exponentials having a period that is an integer submultiple of the fundamental period N.
If the Fourier series representation of periodic sequence x(n) of periodic signal with frequency 2n/N is represented as


Then, the coefficients of X(k) in eq. (1) are obtained by the relation

In these discrete Fourier transform pair Eq.(2) gives frequency analysis transform. This gives frequency components X(k) in the range of frequency (2n/N)nk defined by N distinct frequencies.
Computation of this Fourier transform directly gives different frequency components in vibration signal i.e. filtering of signal is achieved using numerical method without having to resort to electronic filtering hardware/circuit. This basic computation of discrete Fourier transform from sampled vibration time signal is obtained by the digital signal processing software residing in data acquisition computer along with other processing softwar e.
As the vibration signal of all the channels are sampled sequentially, so does t he discrete Fourier transform computation and hence frequency analysis of vibration of all channels is obtained sequentially.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non-limiting exemplary embodiment of the invention represented in the accompanying drawings.
Figure 1A Block diagram of Digital vibration monitoring system.

Figure IB Schematic lay-out of accelerometers and signal flow diagram according to prior art.
Figure 2 on-line continuous startor end winding vibration monitoring system of prior art.
Figure 3 on linc continuous stator end Winding vibration monitoring system according to the present invention.
Figure 4 Shows a graphical trend of winding vibration over a period of 256 minutes corresponding t o 100 HZ according to t he invention.
Figure 5 Pictorial view of the assembled system of the invention at a stand-alone location.
DETAILED DESCRIPTION OF THE INVENTION
As shown in figure IB, PI to P12 constitute twelve numbers of accumulators (pick-ups) installed in the stator winding overhang of generator. The Pick-ups PI to P6 are installed at the turbine end of the generator on bar nos. 21, 1 and 41 (corresponding to slot numbers in the stator core) such that the pick-up PI senses vibration in radial direction at bar no. 21, and the pick-up (P2) senses vibration in tangential direction at bar no.21.
The pick ups P7 to P12 are installed at the turbine end of the generator on bar nos.22, 2 and 42 (corresponding to slot numbers in the stator core) such that the pick-up P7 senses vibration in radial direction at bar no.22 and the pick up (P12) senses vibration in tangential direction at bar no.22.
The cables PI to P12 from all the pick-ups from the turbine end and the exciter end are routed inside the generator and taken out from two airtight flanges and

through field cabling to charge the multi channel signal conditioners to the DAS cards inside the PC installed at the control room.
In the system inventive and as shown in Figure 1A & IB basically the vibrations are sensed by highly sensitive piezo-electric transducers (pick-up) which convert the mechanical vibration into electrical signal. The electrical signal is conditioned in the signal conditioner and then fed to the general purpose computer for digital signal processing through the DAS interface computer . This DAS interface translates conditioned analog signals into digital signals for computer processing. The digitally processed signal using the software structure displays the final vibration signal magnitudes in different formats for example, tabulation or graphical plot of a trend over a period of time.
By digital processing of the vibration signals from the extremely noisy & complex mixture of vibration frequency, the vibration signals of 100 Hz frequency are detected, stored & displayed for magnitude & trend monitoring of the vibration signal and assess the electrical & mechanical condition of the winding. With simultaneous data acquisition/measurement at different measuring points it is possible to locate possible source of faults.
As shown in figure 4, a trend of winding vibration at level 100HZ frequency over a period of 256 minutes is exhibited. The second line in the plot (just above the graph) displays maximum value (Ymax) of the vibration during the period.
All the above i.e. data acquisition, digital signal processing, display storage, analog output and alarms signal processing are achieved using on board software and hardware in the PC which constitutes the general purpose desk top PC with common configuration having ISA/PCI interface slots having interrupt

driven DMA memory access. The invention eliminates using extensive separate hardware like FFT processing card, and additional PCB boards for signal conditioning, as used in prior art.
As shown in figure 3, the vibrations signals are sensed by a plurality of piezo¬electric transducers (22) and conditioned in an input signal conditioning amplifier,(18) and fed t o a platform (23) i.e. DAS (A/D Interface, D/A Interface, DSP based Application Software for digital signal processing through DAS interface computer). This DAS interface translates conditioned analog signals into digital ones for computer processing through algorithm explained in annexure-II.
In the block (1) of DAS (Block-Multiplexing Input Sig. Sampling A/D Interface ckt (12-ch), a high speed sequential sampling at predetermined rate of analog signal of each channel corresponding to Nyquist criteria of sampling speed, is achieved. This is carried out simultaneously for 12 channels in the form useable for direct digital signal processing.
In the blocks (19) & (20) (Blocks-DSP for frequency Analysis and Signal processing Software), the Input Signal which was Sampled, Multiplexed (12-ch), and converted into digital form in block (1), is now subjected to Digital Signal Processing for frequency analysis of vibration signal to obtain required frequency components. This signal processing converts vibration signal in time mode into frequency mode and displays on the monitor screen in the form of frequency spectrum. Further, the digital data is converted into requisite format and stored in the files on mass storage devices as indicated in block (21). This eliminates the need of substantial number of hardware necessary in prior art, for filtering

the signal, minimizes noise in the signal including signal processing cross which interalia improve reliability of measurement.
In the blocks (2), (3) (4),(5),(6),(7),(8), (Blocks-Vib. Mode Selector/Integrator (A,V,D), the earlier processed signal is further processed to convert the incoming vibration signal proportional to acceleration into displacement by double integration. This also eliminates extensive circuit for each channel for filtering, integrating and signal amplification/scaling as is done in case of other systems. This also minimises noise signal and signal processing errors due to overloading and thus improving reliability of the measurement.
(13) & (14) (Blocks Output Signal conditioning, D/A converters, Interface csircuit). For Analog Signal Output and Analog output-mV,-4-20 mA), the PC based system processes the signals to provide standard analog signal outputs (voltage or current) proportional to displacement magnitude of vibration signal of 100 Hz component to be connected to central digital data acquisition/processing system and it does not require any additional hardware for converting indicated/ measured data into suitable standard analog output signal.
(9), (10) (Block-DSP for frequency Analysis and Signal processing Software). Accordingly, storage and retrieval of processe3d signal dat a, post processing, and trend plotting in a single processing hardware, eliminates the need for additional PC hardware, FFT processing hardware cards and software including signal interfacing means.
(11) &. (12) (Block for Tabular display of data CH1-CH12 and Block for Graphical Trend display & Plotting). A display of trend of the processed vibration data in a

specific format can be exhibited as shown in the trend plot (figure 4) and for accessing the details of the data.
(15),(16) & (17) Feature has been provided for alarm/warning signal processing for alarm/warning level setting, detection and providing chasnnel wise alarm/warning signal status display on the computer screen, in the form of LED displays on relay driver cards and TTL digital driver sign al output for direct driving of relays (Block for alarm/warning level setting/alarm/warning signal detection & generation and Block for alarm/warning status display on screen for 12 channels and Block for LED indication of alarm/warning status, Relay drivers & Relays).
Integration of the system (consisting of input signal cables, conditioning amplifiers, dignal processing and display system, relay circuits, analog output circuits, plotter, power supply) as such in a single locastion stand alone system makes it easy to handle. (Pictorial view in the form of figure 5).
A total of 12 channel is provided for vibration monitoring at various location spreaded over t he entire end winding region at both the turbine and exciter end of the generator which is expandable to further 16 or 32 channels.
PERFORMANCE TESTING AND FIELD TRIAL OF THE SYSTEM
The performance of the complete End Winding Vibration Monitoring System developed as stated herein as such was thoroughly checked in laboratory by simulating the vibrations using electromagnetic exciter and measuring the same and comparing the results with standard equipments. The complete system was further trial tested on generators at test bed during works testing of

generators as well as on generator of captive power house and also field trial testing carried out at site in one of the Thermal Power Stations. After carrying out extensive field trials of the system it has been established that results obtained using this state of art system are comparable to the results obtained by prior art system.

-21-We Claim:
1. An end winding vibration monitoring system to detect possible source of fault in the stator windings of generators of thermal power plant, the system comprising a plurality of piezo-electric type accelerometers disposed along the turbine end and exciter end to sense mechanical vibration of the generator;
- a low noise signal transmitting cable (2);
- a charge signal conditioning amplifier (3);
- a data acquisition multiplexer/DAS cards (4);
- a computer apparatus with in-built data signal processing
software, along with a display unit (5) ; and
- an analog to digital converter (17), wherein one half of the
accelerometers installed at the turbine end of the overhung
portion of the stator winding, and the other half installed at
the turbine end of the generator, the accelerometer is
enabled to measure real-time vibration data axially and
radially at both exciter and turbine end.

ABSTRACT

TITLE: AN END WINDING VIBRATION MONITORING SYSTEM TO DETECT POSSIBLE SOURCE OF FAULT IN THE STATOR WINDINGS OF GENERATORS OF THERMAL POWER PLANT
The invention relates to an end winding vibration monitoring system to detect possible source of fault in the stator windings of generators of thermal power plant, the system comprising a plurality of piezo-electric type accelerometers disposed along the turbine end and exciter end to sense mechanical vibration of the generator; a low noise signal transmitting cable (2); a charge signal conditioning amplifier (3); a data acquisition multiplexer/DAS cards (4); a computer apparatus with in-built data signal processing software, along with a display unit (5) ; and an analog to digital converter (17), wherein one half of the accelerometers installed at the turbine end of the overhung portion of the stator winding, and the other half installed at the turbine end of the generator, the accelerometer is enabled to measure real-time vibration data axially and radially at both exciter and turbine end.
{Fig. 3}