12-11-2012, 11:27 AM
HEALTH MONITORING, FAULT DIAGNOSIS AND FAILURE PROGNOSIS TECHNIQUES FOR BRUSHLESS PERMANENT MAGNET MACHINES
pHEALTH MONITORING.ppt (Size: 542.5 KB / Downloads: 41)
INTRODUCTION
Over the past decade, Permanent Magnet Synchronous Machines (PMSMs) and Brushless DC machines (BLDCs) have gained significant popularity in the industry, especially where high performance is required, owing to higher efficiency, high output power to volume ratio, high torque to current ratio, etc.
Some of the commonly occurring faults in PMSMs are eccentricity, bearing failure, demagnetization of permanent magnets, short circuit in the stator or armature winding, etc.
Health monitoring and fault diagnosis of the machine could help in scheduling preventive maintenance to length their lifespan and avoid catastrophic system failure.
ARMATURE FAULTS
Armature faults are usually caused by winding insulation
failure, which frequently happens in the regions where end
windings enter the slots. The reasons which cause insulation failure could be
Manufacturing defect
High operation temperature/Cooling system malfunction
Machine overloading
Transient high voltage
Vibration caused rubbing
PERMANENT MAGNETIC FAULTS
For permanent magnet machines, field fault typically refers
to a failure in the permanent magnets, where demagnetization
is the most common issue. The demagnetization could be
uniform over all poles or partial over certain region or poles.
Conditions that could cause permanent magnets in a PMSM
to demagnetize include
MECHANICAL FAULTS
Mechanical faults typically refer to bearing failure and eccentricity in most machines. Bearing is a mechanical component which consists of two rings and a set of balls rolling between them and it has been recorded as one of the
dominant causes for electric machine failure. It could be caused by
Metal fatigue
Unbalanced stress
Improper installation
Corrosion/Contamination
These problems could result in vibrations and noise during
machine operation, which are usually measured and
processed as diagnosis indicators .
FAULT SIGNATURE DETECTION TECHNIQUES
Stator current frequency analysis is the most frequently
used technique for machine fault diagnosis. It is usually
called Motor Current Signature Analysis (MCSA).
Fast Fourier transform (FFT) method is widely used for frequency
analysis.
Since only current measurement is required, this
method can be used for simultaneous multi-fault detection. In
addition, this technique is also non-invasive, and costeffective.
Since FFT doesn’t contain the information about time, for
non-stationary operated machine, short time Fourier
Transform (STFT) can be applied.