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Adjustable Speed Drives (ASD) are already widely employed in industrial and technological applications for their significant advantages of speed control and efficiency. However, over the last decade a growing number of premature failures has been experienced in motors fed, in particular, by pulse width modulation converters.
Indeed, overvoltages at motor terminals together with short rise time and high switching frequency, caused by the supply waveform, can lead to premature breakdown of insulations of electrical components, causing motors failures.
PD measurements can detect on-going degradation processes that could lead to the damage of the electrical apparatus insulation and, unavoidably, to sudden breakdowns.
PD measurement analysis and consequent diagnosis allow Condition Based Maintenance (CBM) program and best practices to be set up.Electrical asset state is usually assessed by submitting it to Time Based Maintenance (TBM) programs, carried out at fixed intervals. However, for the most critical equipments, a Condition Based Maintenance (CBM) program is much more advisable. Applying a CBM program means keeping the electrical state of the equipment under continuous control.By means of CBM potential sources of problems are detected at a very early stage, allowing relevant countermeasures to be taken before harmful and irreversible events happen, hence, failure rate can be kept at a constant level chosen by the asset manager. Unexpected breakdowns, causing long forced stops, can be avoided, thus limiting infrastructure maintenance costs due to loss of revenues and repair after failure.
PD measurements can be carried out both on-line, with the equipment under test supplied by the ASD converters, and off-line, with the electrical system supplied by an external voltage source.
However, off-line tests can be carried out only periodically, when the motor is under maintenance. Moreover, stress profiles in offline tests may be noticeably different from those experienced in service.
One of the critical issues for the measurement and diagnosis of induction motors may be represented by the repetitive impulsive waveforms generated by power electronic drives.
Techimp in the last years has addressed this issue and has developed an ultimate technology suitable for converter fed motors and, in general, Adjustable Speed Drive (ASD) applications.