DETECTION OF BROKEN BARS IN INDUCTION MOTOR USING VOLTAGE PATTERN ANALYSIS

[inayatu6]

DETECTION OF BROKEN BARS IN INDUCTION MOTOR USING VOLTAGE PATTERN ANALYSIS
SUBMITTED BY
VIBHA.IK
S7 E1
College Of Engineering, Trivandrum
2007-11 batch

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CONTENTS
INDUCTION MOTORS
FAULTS
DETECTION METHODS
PROPOSED DETECTION METHOD-VOLTAGE PATTERN ANALYSIS
EXPERIMENTAL SETUP
RESULTS
CONCLUSION
REFERENCE

INDUCTION MOTORS
FANS
CENTRIFUGAL PUMPS
MOST MACHINERY TOOLS
CRUSHERS
PUNCHING PRESS
TRACTION

WHY INDUCTION MOTORS?
SIMPLICITY
RUGGED CONSTRUCTION
RELATIVELY LOW MANUFACTURING COST
SPEED VARIATION
HIGH EFFICIENCY
HIGH POWER FACTOR

FAULTS
Bearing faults
Stator interturn short-circuits
BROKEN BARS
FAULTY ROTOR PERFORMANCE
Distortion in magnetic field distribution across rotor
Asymmetrical magnetic pattern across rotor
Deterioration of mechanical parameters

EXISTING DETECTION METHODS
MOTOR CURRENT SIGNATURE ANALYSIS
POWER SPECTRUM ANALYSIS

PROPOSED METHOD-VOLTAGE PATTERN ANALYSIS
Make use of easily accessible signals(line to line voltage) for monitoring
Extract information on voltage oscillations which serve as the basis for failure determination
No advanced mathematical algorithms and time demanding computations are needed
Simple method

BASIC IDEA
Maintaining speed constant irrespective of the rotor fault
Adjusting the supply voltage in order to balance the effect of distorted field distribution
For that adjust the duty cycle of inverter
DUTYCYCLE : ratio of on period to total period
Time record of generated voltage is obtained and further analyzed for the detection

SPEED ADJUSTING
Inverter fed drives
Vector field control is used(FOC-field oriented control,PTC-predictive torque control)
Then filter high frequency components. Rotor bars defect can be easily identified in low frequency.

BLOCK DIAGRAM OF PTC
Outputs a reference flux value according to the torque demand.
IFC generates appropriate voltage references that will drive the inverter.
BLOCK DIAGRAM OF FOC
FOC
FOC is more accurate than PTC
Produces smoother output voltage pattern of inverter
Widely used control approach
In this not only speed but also the flux is compared
EXPERIMENTAL SETUP
3kW IM
Rated Torque 20Nm
Speed 1500rpm
Squirrel cage rotor
44 rotor bars
7 broken bars
Constant load torque applied to shaft by means of ELECTROMAGNETIC BREAKS and measured using DYNAMOMETER
Contd ..
Control algorithms implemented using TI TMS320F28335 microcontroller.
Laboratory built inverter linked control stage to the IM.
Two line-to-line voltages measured with different probes at the inverter terminals.
Filtration of obtained signal using 3rd order low-pass filter with cut off frequency 36Hz.

EXPERIMENTAL SETUP

Average duty cycle at CONSTANT SPEED OF 1000rpm at various loads

Average duty cycle at CONSTANT LOAD of 15Nm at various speeds
AVERAGE DUTY CYCLE IN TERMS OF VARIANCE
Determines possible faulty conditions
Determines degree of error
CONCLUSION
The broken rotor bars manifest itself through the oscillation in average voltage vector magnitude impressed to the IM
When the magnitude of the oscillation(i.e. variance) exceeds a certain level , there will be a fault in the rotor of IM.
Detection relies on measuring phase voltages.
Easily implemented in inverter-fed drives.
Significant computational power not required.
Study the cases with even smaller number of bars

REFERENCE
[1] ] P.J. Tavner, "Review of condition monitoring of rotating electrical
machines," Electric Power Applications, IET, vol.2, no.4, pp.215-
247, July 2008.
[2] M.E.H. Benbouzid and G.B. Kliman, "What stator current processing based
technique to use for induction motor rotor faults diagnosis?,"
IEE Trans. Energy Conv., vol.18, no.2, pp. 238-244, June 2003.
[3] D. Pouliezos and G. S. Stavrakakis, Real Time Fault Monitoring of
Industrial Processes, Kluwer Academic Publishers, 1994.
[4]P. Vas, Parameter Estimation, Condition Monitoring, and Diagnosis
of Electrical Machines, Clarendon Press, Oxford, 1993.
[5] F. Filippetti, G. Franceschini, C. Tassoni, and P. Vas AI techniques
in induction machines diagnosis including the speed ripple effect,
IEE Trans. Ind. Applicat., vol.34, no.1, pp. 98-108, Jan./Feb. 1998.

THANK YOU
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