|Title of Invention||
"AN INTEGRATED ON LINA MONITORING PRIS DEVICE WITH AN INDUCTION MOTOR FOR FAULT DETECTION OF THE SAID MOTOR."
|Abstract||The invention relates to an integrated on line monitoring IRIS device with an inductor motor for fault detection of the said induction motor characterized by an IRIS unit, Field Interactive unit (2) and a power supply unit, the IRIS units (8) acquires signals from the sensors for the parameters voltage, current, vibration, temperature and speed of the said motor, the said device being linked to a host PC (9), precise computations of true RMS of the said acquired signals being carried by the interaction between the said device and the PC and detecting fault for the critical values for the said parameters of the induction motor.|
|Full Text||The invention relates to an apparatus for Induction motor monitoring and fault detection and accurate assessoment of the condition of such motors. The apparatus uses state of the art digital signal processing (DSP) electronics.
Induction motors are widely used in industries, particularly in power plants for critical auxiliaries like boiler feed pump, ID fan, FO fan and PA fan. Sudden failure of a motor in such critical areas will result in loss of valuable power generation.
The present mointoring system of such induction motors comprises besides a number of protection devices, different meters which continously display voltages, currents, temperatures and overall vibration levels.
There are disadvantages associated with a present system of monitoring and fault detection of Induction motors.
One of the main disadvantages with the existing monitoring system is that it will not provide the full information needed to asses the condition of the motor. For example, one of the motors might have had a motor bar failure. A simple measurement of current magnitude will not give any indication of the fault.
Another disadvantages with the existing monitoring system is that in case of mechanical faults which may not cause appreciable increase in the overall vibration level and remains undetected.
Yet another disadvantage with the existing monitoring system is that in case where overall vibration level is high, it Mill not be able to assign a specific cause and maintenance personel will have to resort to the costly option of opening the motor to detect the cause of the abnormal vibration.
Thus the object of the present invention is to provide an apparatus for close mointoring and accurate assessment of the conditions of induction motors. In the case of parameters like temperatures and vibrations, trends over a period provides a good insight into the probable behaviour of the machine.
Another object of the present invention is to provide an apparatus (IRIS) which provides on line measurement of parameters, on—line spectrum computation and analysis, and the capacity of data storage for trending and further analysis.
Another object of the present invention is to provide an apparatus which combines the monitoring of both electrical and mechanical parameters instead of using separate devices as at present. An indepth analysis of both parameters is essential to determine the condition of the motor.
Yet another object of the present invention which provides computer based computation of spectrum and its analysis from parameter monitoring values.
According to the present invention there is provided. An apparatus (IRIS) for induction motor monitoring and fault detection comprising a TRT linked to a host PC , the said TRT8 is linked to field terminal blocks and the field terminal blocks is linked to potential transformer PT, current transformer Vibration VIB, RTD's and tacho generator, Tach for receiving signals from the motor.
The nature of the invention, its objective and further advantages residing in the same Mill be apparent from the following description made with reference to non—limiting exemplary embodiments of the invention represented in the accompanying drawings.
Figure 1 System architecture of IRIS
Figure 2 Single IRIS system configuration
Figure 3 Flow chart of IRIS
Figure 4 Multiple IRIS configuration
Figure 5 Hardware configuration of IRIS (2 sheets)
Figure 6 Overall Digital signal processing flow chart
Figure 7 Overall 8O86 or process software flowchart
Figure 8 current spectrum of healthy and broken motors.
Figure 9 Flow chart for detection of motor bar failure.
In accordance of the prevent invention, comprehensive monitoring systems monitors both electrical and mechanical input* for accurate assessment of the health of the motors.
The IRIS system has been designed and developed for induction motors using state—of—the—art digital signal processing (DSP) electronics, It is a comprehensive monitoring system taking both electrical and mechanical inputs. It continuously monitors voltages, currents, temperatures, speed and vibration signals. It performs on-line spectrum computation of current and vibration signals. Spectral analysis is used for detecting critical faults like rotor bar failure and faults based on vibration harmonic components. The system has a graphic LCD display for display of waveforms and spectra of different signals. It has a host PC link for data archiving, trending and further analysis.
The IRIS system was designed keeping these prerequisites in view. The IRIS system collects electrical and mechanical data of the motor — voltages, currents, temperatures, speed, and vibration levels. IRIS is based on the latest digital signal processing hardware which equips the system with the ability to perform on-line spectrum computation. IRIS has a graphics display for time and frequency domain waveforms. There is a resident expert rule module for interpretation of vibration harmonic data. The user is presented with conclusive fault
detection so that he can take corrective action. IRIS is also provided with a keyboard by using which the user can navigate through the different screens displaying parameter data. The keyboard is also used for parameter limit setting. IRIS has a host computer link. The host computer will be located in the control room while the IRIS unit will be located near the motor. Archiving, trending the further data analysis can be done on the host computer. In applications where a number of motors have to be monitored, a multiple IRIS scheme can be configured with each motor having its own IRIS unit and all the IRIS units connected through a serial link to the host computer.
IRIS is an instrument (apparatus) developed for the close health monitoring and fault detection of induction motors (I). The basic inputs for this instrument are current and voltages from all three phases, six channels of winding temperatures, motor speed and four channels of vibration signals. Current signals are sensed using a current Transformer (CT's) (4) of suitable ratio depending on the motor rating. Input line voltages are sensed through potential transformers (PT's) (3). Winding temperatures are acquired using thermocouples of RTD's (6) mounted embedded in the motor windings. Speed signal is derived from the tacho-generator (7) coupled to the motor shaft or an Optical speed
encoder. The vibration sensors are mounted to the motor's mechancial assembly. These vibration sensors (5) are mounted on either side of the motor shaft i.e. DE and NDE.
IRIS acquires all the above signals at pre-set sample intervals and stores them in its internal memory after conversion to engineering units. After the acquisition, the Fast Fourier Transform
The complete electrical and mechanical parameters of the Induction Motor are made available in a single IRIS to perform a comprehensive and co-ordinated monitoring and fault detection. In the IRIS using the graphic display on the front panel the above data is displayed to the operator on request both in numeric as well as graphic modes.
With the above measured and derived parameters IRIS detects various electrical and mechanical faults in the induction motor using the limit checking criteria. In addition, it also
detects certain defects using the set of boolean equations which are coded in the IRIS application firmware. All the set points, limiting values and motor configuration parameters are field programmable using the front panel keyboard.
IRIS has a host computer (9) interface to transfer the data to the external computer (PC) for extensive/detailed analysis. In PC by performing long term statistical data analysis, the historical data for critical motors can be generated. Also relationships between and among paramters can be studied. A single PC can be connected to a multiple IRIS units monitoring a number of induction motors in a network. By this a chain of motors can be monitored from a centralized remote location.
IRIS is designed around sophisticated microprocessor and digital signal processing electronics enabling it to perform multi-variable analysis leading to a comprehensive monitoring and protection system for electric machines. IRIS accepts currents and voltages as electrical inputs and vibration, temperature and rpm as mechanical inputs. It also accepts motor start signal as a digital input to monitor the number of starts of the motor. IRIS
can be configured to any rating of motor by suitably changing the configuration parameter*. IRIS functions can be broadly classified into three categories i
a. b. c.
Host computer link for data analysis
Acquisition and Monitoring IRIS monitors the following parameters and gives the continuous display of them both graphically and numerically.
Numerical Numerical Numerical Numerical Numerical Numerical Numerical
Graphics & numerical
Graphics & numerical
Graphics & numerical
Graphics & numerical
Center frequency peak& magnitude
Center frequency peak& magnitude Steady state Steady state Steady state Steady state Steady state Steady state Tacho-generator Computed XI component of vibration Computed X2 component of vibration Computed X3 component of vibration Computed X4 component of vibration
20. Active power
21. Reactive power
22. Apparent power
23. Power factor
Numerical Numerical Numerical Numerical
Computed from voltage & current Computed from voltage & current Computed from voltage & current Computed from voltage & current
24. No. of starts Numerical Computed from ON/OFF
switch of motor as digital i/p
25. Line frequency Numerical Computed from voltage
waveform Fault detection
IRIS detects various types of faults in a motor by comparing set points with measured quantities. The system being highly programmable in nature, the user can set the limits for various faults. The faults detected by IRIS can be divided into two groups :
a. Electrical faults
b. Mechanical faults
Depending on the severity of the fault, IRIS either issues an alarm or a trip command (relay output) apart from a visual display of fault message.
IRIS detects the following electrical faults on an electrical machine :
IRIS detects overvoltage whenever the voltage in any phase increases more than the overvoltage limit which is 10% above the normal voltage. Similarly the system detects undervoltage whenever the voltage in any phase drops below the undervoltage set point which is 10% below the normal voltage.
IRIS detects the overcurrent or overload fault whenever the current drawn by the motor in any phase exceeds 1.1 times that of the normal current at a speed less than the normal rated speed.
c. Voltage unbalance/Current asymmetry
IRIS detects voltage unbalance whenever the difference between the currents in two phases is more than 20% of normal current and the line voltage of any one phase is 15% less than the normal voltage.
d. Blocked rotor
Whenever the motor draws current which is more than 4 times of the normal current in al phases at normal voltage IRIS detects it as blocked rotor condition, Also during this condition the rate of change of speed of the motor is zero.
e. Reverse phase sequence
Whenever the motor supply terminal sequence is changed while connecting or reconnecting a motor, IRIS detects it as reverse phase sequence.
ingle phasing fault is detected when the load current in any one of the phases is zero and the load currents in the other two phases are more than 1.5 times the normal current.
g. Prolonged start
IRIS detects the prolonged start fault by comparing set normal starting time with the actual starting time. If the normal starting time is less than the actual measured starting time, the prolonged start message will be displayed by IRIS
h. Over temperature
IRIS displays over temperature fault whenever the actual temperature exceeds the over
temperature set point
i. Rotor bar failure
Rotor bar failure is a critical fault which cannot be detected by normal measurement of RMS values. It has been reported in the literature and in various research papers that rotor bar failure will cause predominant effect on the current spectrum . Ideally in a healthy electrical machine there exists only the fundamental harmonic and very low to zero strengths of other harmonics. But in case of a motor with rotor bar failure the spectrum will have sidebands on either side of the fundamental. In IRIS the rotor bar broken fault is detected by detecting the presence of sidebands in the current spectrum.
IRIS detects various types of mechanical critical mechanical faults by comparing the vibration levels with set points. Whenever the actual levels exceed the set levels, the fault is detected. Rule based logic for the detection of certain mechanical faults in an induction motor is built into the system. However the fault detection logic may require modifications depending on the mechanical details of the motor . These modifications can be made in IRIS by simple firmware changes.
Host Computer Link
IRIS has a host computer link to support extensive data analysis. IRIS periodically sends the data to host computer for update at a remote location. The host PC apart from performing normal display of all the parameters also performs other functions for long term performance analysis. On the host PC the trending of certain critical parameters like vibration levels can be shown and by observing the upward or downward trend of the particular parameter action can be taken by the operator. Also due to the large storage capacity, large amounts of data can be stored for archiving and analysis.
The IRIS system consists of the following units :
1 IRIS unit
2 Host PC
Each IRIS unit has been designed to cater to one motor. For a group of motors, multiple IRIS configuration can be used.
The IRIS unit acquires signals from the following field sensors :
Sensor Parameter No. of channels
1. Potential transformers Voltage 3
2. Current transformers Current 3
3. Vibration probes Vibration 4
4. RTDs Temperature 6
5. Tachogenerator Speed 1
6. Motor ON/OFF switch No. of starts 1
The signals from these sensors are terminated on terminal blocks. A cable connects the terminal blocks to the 48-pin Halting connector in the IRIS unit.
Multi-IRIS system organization
In such applications where there are many number of electrical machines working in one bay/shop floor, IRIS units can be connected in a network. This multiple IRIS network can have a single host computer link where in the data from any IRIS unit can be observed, in a multi-IRIS configuration host PC communicates to each IRIS unit with a motor tag and obtains the data of that particular motor. This provides the operator with the facility of accessing the data of any motor from a centralized location. The communication link between the host computer and the IRIS units is a serial communication link.
The hardware of IRIS system consists of the following sub-systems :
1. IRIS unit
2. Field Interface Unit
3. Power Supply Unit
The IRIS unit is housed in a 300 * 200 * 100 mm rectangular enclosure. It has a front panel consisting of a touch sensitive keyboard and a graphic LCD display. The touch sensitive keyboard enables the user to enter all the necessary set points and to monitor all
the relevant data. The IRIS field data is organized in certain groups which can be selected for display as per user requirement through the keyboard. The functions of each key will be displayed in the display itself to help the user navigate through the different screens. The graphical display unit is used to display numerical as well as graphical data as per keyboard selection. The display resolution is 240 * 64 pixels . The display size is 100 * 40 mm. This is the main sub-system of the IRIS system comprising of the CPU card and the Input & Output card. The CPU card is a 300 * 200 mm PCB having the Digital Signal Processing and 8086 microprocessor hardware.
The main functions of the IRIS unit are:
1. Data acquisition from the following sensors
a. 3 phase voltages from potential transforms
b. 3 phase currents from current transformers
c. 4 vibration channels
d. 6 RTD channels for temperatures
e. 1 tachogenerator speed signal
2.Computational function for the following parameters
a. RMS values of voltages and currents in all three phases
b. Grid frequency from the sampled data
c. Power factor and power parameters
d. Spectrums for current and vibration
e. Number of starts
3. Man-machine interface functions :
a. It accepts parameter set points from the keyboard
b. it will perform display functions on a graphic LCD display
4. Input and output field signals interface:
a. It accepts a digital input from the auxiliary contact START/STOP switch of
the motor for number of starts computation
b. It issues an output command to an external hooter in the event of any severe
fault in the motor
The CPU card of the IRIS unit works on two processors. It is built around Analog Devices ADSP 2101 DSP and the 8086 Intel CPU. These two processors together perform all the necessary functions of IRIS unit.
The I/O card of IRIS consists of circuitry needed for signal conditioning of field inputs in order to suit the CPU card for further processing. It has the following feature : 1.16 digital input channels with optical isolation
2. 8 digital output channels with optical isolation
3. 6 temperature channels
4. 8 vibration channels
Field Interface Unit:
The Field Interface Unit is a stand-alone hardware unit comprising of a PCB measuring 300 * 100 mm located external to the IRIS unit used for interfacing field signals to the IRIS unit. Its main function is to receive the field signals from the motor and sending them to the IRIS unit for further processing.
FIU has the following hardware components :
a. 6 channels of 4-20 ma transmitters which directly accept RTD inputs.
b. 4 nos. of relay outputs
c. Surge protection components for all the incoming signals from the field
d. Transfer lines for vibration signals
Power Supply Unit
Power supply unit is a DC power supply card which feeds power to the IRIS unit. The power supply unit accepts AC input 230 V +/- 10% and provides required regulated DC power supplies to the IRIS unit
IRIS software consists of two types :
a. Firmware in the IRIS unit
b. Software on the host PC if host PC is connected
Basically the IRIS unit firmware is for controlling the CPU card having Analog Devices ADSP 2101 and Intel 8086 processors. The IRIS host PC software will perform the communication function and displays whatever be the information received from the local IRIS unit.
The system firmware consists of ADSP 2101 (DSP) and Intel 8086 processor instructions.
The DSP firmware consists of the following:
1. Sampling of electrical signals
2. Sampling of vibration signals
3. RMS value calculation of voltages, currents, rpm, vibration signals
4. Calculation of frequency from sampled voltage waveform
5. Computation of FFT(Fast Fourier Transform) of current signals
6. Computation of FFT of vibration signals
The 8086 firmware consists of the following:
1. Conversion to engineering units voltages, currents, temperatures, speed, vibration
2. Limit checking and fault setting
3. Keyboard and display functions
The keyboard and display are organised around five function keys. Each of the function keys is for a different parameter group/function.
Key Associated parameter/function
Fl VOLT AGES,POWER QUANTITIES,
F5 SETTING OF PARAMETER SET POINTS
Under each function key, there are a number of screens. Going up and down the screens under a particular function key will be by using the ENTER/BACK keys.
Host PC Link:
For communication with the host PC a data table is prepared in the IRIS unit and flow chart. This table is split into two blocks. Each block of data is assigned a separate start of text (sot) code. A flag decides the data block to be transmitted. Depending on the flag status, the corresponding data block is transferred to the transmit buffer. The checksum for the buffer is computed. The block start of text is first transmitted. The data block is transmitted next followed by the check sum and the end of text character. In the host PC, a proprietary add-on card handles the communication. In case of a multi-IRIS system, a machine ID field is present in the data block to identify the machine for which data is being received. After receiving each data block into a temporary buffer in the PC, checksum is computed and matched with the checksum received. Data is transferred from temporary buffer to actual buffer only when checksums match.
Software on the host PC
On the host PC side, the software is in Turbo-C. A proprietary add-on communication
card acquires the data from individual IRIS units. The memory in this card is mapped onto
the PC memory. The C program accesses this memory block. The displays are menu
driven and open up with a default page which displays the following parameters - RMS
and peak values of voltages, currents, RPM, vibration strengths and peak frequencies and
temperatures. There are different pages for the following :
Faults : The current status of all faults is given in this page.
Trends : Trends for temperatures, currents and vibration signals are given in different
Power : The power quantities - KW,KVA,KVAR and power factor are displayed in a
The resources of the DSP section are as follows:
1. 16 bit fixed point DSP processor
2. 8k non volatile RAM
4. ADC with 8 channel multiplexer
5. ADC with external 8 channel multiplexer
The resources of the 8O86 section are as follows!
1. 8086 CPU
2. 8k static RAM
3. 8k non-volatile RAM
4. Port lines for keyboard i/f, digital i/ps, digital o/ps
5. Communication interface.
Having described the invention, what is claimed as new and desired to secure by letters Patent is i
1 An on-line condition monitoring and fault detection system
(IRIS) for induction motors using both electrical and mechanical
parameters in a single instrument.
2 The system is realised using multi-processor architecture
comprising of a digital signal processor (DSP) and a 16 bit 8O86
03 The on-line data transfer between the processors is through
multi-port memory with a built-in bus arbitration logic.
4 On-line signal FFT computation for spectral analysis using
16 bit DSP (ADSP 2101).
5 Precise computation of true RMS of sampled signals from
6 On-line graphical representation of waveforms and spectrum*
of different parameters on a stand—alone instrument -IRIS.
7 On-line detection of rotor bar failure using the continuous
current spectrum analysis
08 Rule based logic for the detection of mechanical faults in
an induction motor is built into the stand-alonge IRIS system
09 Field configurable for any rating of motor
10. In a group of motors, pertaining to a process, the inter dependence of one motor on another can be studied using individual IRIS units by connecting them in a network.
The invention described hereinabove is in relation to a non-limiting embodiment and as defined by the accompanying claims.
1. An apparatus (IRIS) for induction mtoro monitoring and
fault detection comprising a TRT8 (8) linked to a host PC the
said TRTS (8) is linked to field terminal blocks (2) and the
field terminal blocks is linked to potential transformer PT (3),
current transformer , vibration VIB O), RTD's (6) and tachno
generator, TACh (7), for receiving signals from the motor (1).
2. An apparatus (IRIS) for induction motor monitoring and
fault detection wherein the sensors provides following signals as
data acquisition, 3 phase voltages from Potential transformers PT
(3), 3 phase currents from current transformer, CT (4), 4
Vibration channels, VIb (5), 6 RTD (6) channels for temperatures,
1 tachogenerator, Tach (7) for speed signal.
3. An apparatus (IRIS) for industion motor monitoring and
fault detection as hereinabove described and illustrated.
|Indian Patent Application Number||452/DEL/1997|
|PG Journal Number||10/2008|
|Date of Filing||24-Feb-1997|
|Name of Patentee||BHARAT HEAVY ELECTRICALS LTD|
|Applicant Address||BHEL HOUSE SIRI FORT, NEW DELHI-1100049.|
|PCT International Classification Number||H02K 17/08|
|PCT International Application Number||N/A|
|PCT International Filing date|