Stator insulation problems associated with low voltage and medium voltage PWM drives
Bibliographic record
Abstract
About 15 years ago, the short risetime pulses caused by voltage source, pulse width modulated converters were first recognized as a cause of stator winding insulation failure in low voltage motors. The root cause was found to be the large number of PWM voltage pulses from the drive, which caused partial discharges between turns in the stator. These discharges eventually eroded the magnet wire insulation, resulting in failure. Since the first reports of failures, motor manufacturers have developed many ways to eliminate or slow down this process. Medium voltage motors rated up to 7200 V and driven by pulse width modulated, voltage-source converters are now being introduced. Although relatively rare to date, such systems are expected to play a larger role in cement plants in the future. Early experience with 4160 volt motors driven by such converters again shows that the voltage pulses from the drives may also adversely affect the stator insulation. However, it seems that different aging processes tend to occur in medium voltage stators compared to those in low voltage motors. In particular, the aging can be accelerated as a result of dielectric heating of the groundwall insulation caused by the high frequency components of the drive voltage. In addition, the voltage stress control coatings often used in medium voltage motors have much higher capacitive currents flowing in them when driven by converters - leading to more rapid thermal destruction of the coatings. The processes involve are described. The paper also reviews the development of new IEC standards that for the first time will define the stator insulation requirements in a converter duty motor
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".