Research into rotating machine turn insulation life under repetitive impulse voltages from power converters

在工频正弦电压下，旋转机械线圈或棒绝缘的设计已经很好地理解，测试程序已经标准化，这已经很好地服务于行业。然而，今天，由电力电子控制的中压（13.8 kV）旋转机器在工业厂房和可再生能源发电中变得越来越普遍。可调速驱动器（ASD）的电力电子元件通过直接电压源的脉宽调制器（PWM）合成变频正弦波形。电力电子馈电时的过电压、电场分布和局部放电对旋转机械的绝缘提出了新的挑战。**** ASD技术需要新的测试程序，本研究的目的是提供由电力电子控制的旋转机器绝缘，与传统的工频供电机器具有相同的可靠性水平，而目前情况并非如此。从PD的实验室研究和现场监测来看，如果PD开始涉及大量能量，它们将增加，有时在增加和消除期间交替，直到它们导致绝缘失效或击穿。**** IEC 600341842标准认为老化因子是峰对峰电压，因此，老化应力是由外加电压产生的电场，与电压波形无关。这意味着PD（老化驱动器）不会从正弦波形转变为重复脉冲波形，因此只要电源电压的频率和峰对峰电压相同，任何电压波形的寿命时间都是相同的。最近研究旋转机器匝绝缘寿命特性的出版物表明，正弦和重复脉冲电压下的PD和寿命都有显著差异。事实上，PD的幅度、重复率和时间行为取决于电源波形的形状，更重要的是，取决于电压波形的上升时间。*与交流正弦电压相比，重复脉冲对加速老化的影响已被明确地挑选出来，并且根据脉冲的上升时间，PD过程中涉及的能量可能明显高于交流。这反映为更短的寿命时间，并且这种行为可以适当地建模。****本研究拟采用正弦波形和功率电子波形对匝绝缘试样进行加速寿命试验，同时监测老化直至击穿过程中的局部放电，以探索不同波形下匝绝缘试样的局部放电时间行为。通过研究正弦和脉冲波形下的失效时间行为，可以推断出适用于电力电子馈电绝缘老化的寿命模型类型。*********

The design of rotating machine coil or bar insulation under power frequency sinusoidal voltage is well understood and testing procedures have been standardized which have served the industry well. However, today, medium voltage (13.8 kV) rotating machines, controlled by power electronics, are becoming common place in industrial plants and in renewable generation. The power electronics of an adjustable speed drive (ASD) synthesizes a sinusoidal waveform of variable frequency by means of a pulse width modulator (PWM) from a direct voltage supply. The overvoltage, electric field distribution, and partial discharge (PD) experienced by the insulation when fed by power electronics presents new challenges in the insulation of rotating machines.**** The ASD technology requires new test procedures and the purpose of this study is to provide rotating machine insulation, controlled by power electronics, the same level of reliability as conventional, power frequency supplied machines, which, at the present time, is not the case. From both laboratory studies and field monitoring of PD, if PD is incepted involving significant energy, they will increase, sometimes alternating between increasing and extinction periods, until they cause insulation failure, or breakdown. **** The IEC 600341842 standard considers that the aging factor is the peak-to-peak voltage, and therefore, the aging stress is the electric field resulting from the applied voltage and independent of the voltage waveform. This implies that PD, which is the aging driver, would not change from sinusoidal to repetitive impulse waveforms and consequently the life time is the same for any voltage waveform provided that the frequency of the supply voltage and the peak-to-peak voltage are the same. Recent publications investigating the life characteristics of rotating machine turn insulation has shown that both PD and life time under sinusoidal and repetitive impulse voltages differ significantly. In fact, the PD magnitude, repetition rate, and also time behavior, depend on the shape of the supply waveform and more importantly, on the rise time of the voltage waveform.*The influence on accelerated aging from repetitive impulses, compared to AC sinusoidal voltage, has been clearly singled out and depending on the rise-time of the impulses, the energy involved in the PD process can be significantly higher than under AC. This reflects into shorter life times, and such behavior can be suitably modelled.**** This research proposes to investigate accelerated life tests on turn insulation specimens using sinusoidal and power electronic waveforms while monitoring PD during aging, up to breakdown, in order to explore the PD time behavior under different waveforms. By investigating the failure time behavior under sinusoidal and impulse waveforms, the type of life model that can be applied to power electronics fed insulation aging can be inferred.*********