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Development of methods allowing the test and the comparison of low-voltage motors insulation systems running under partial discharges (fed by inverter)

Abstract : Since the development of power electronic components, which allowed the manufacturing of reliable and efficient inverters, variable speed drives using inductive motors have become more and more popular. The PWM technique has proven to be a very effective method of rotational speed control. However, the fast changing voltage pulses, with very steep slopes (in the order of a few kV/µs), has brought new hazards for the electrical insulation system of such motors. Very high frequency harmonic components of PWM voltage will result in significant overvoltage due to an impedance mismatch between the cable and the motor. As an effect, the voltage seen by some parts of the insulation system may exceed the Partial Discharge Inception Voltage (PDIV) stating localized partial discharges activity. The insulation system in low-voltage machines (called type I) is based almost entirely on polymer materials, which are not able to support partial discharge activity throughout their lives. Due to the use of frequency inverters especially the primary insulation of the magnet wire is endangered in comparison with system-powered machines. As a result this is often the weakest link of the insulation system leading to a premature breakdown of the machine. The aim of this thesis is to investigate and analyze the aging process of the enameled wire exposed to different factors and to propose a method allowing to predict their lifespans in given conditions. This study introduces a prediction based on the Design of Experiments method and the statistical Weibull distribution. Thanks to the model obtained with short multi-stress (temperature, voltage, frequency) aging tests, it is possible to predict the results of significantly longer ones. Moreover, the adapted methodology is proposed that allows to predict the scatter of the long tests basing on the short-time results dispersion. The predictions are compared with the experimental data in order to prove the model accuracy.
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Submitted on : Wednesday, July 8, 2020 - 3:25:20 PM
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  • HAL Id : tel-02893797, version 1

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Mateusz Szczepanski. Development of methods allowing the test and the comparison of low-voltage motors insulation systems running under partial discharges (fed by inverter). Electric power. Université Paul Sabatier - Toulouse III, 2019. English. ⟨NNT : 2019TOU30073⟩. ⟨tel-02893797⟩

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