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

对工频正弦电压下旋转机械线圈或线棒绝缘的设计有了较好的了解，并规范了试验程序，为行业提供了良好的服务。然而，今天，由电力电子控制的中压(13.8千伏)旋转机械正成为工业工厂和可再生能源发电的常见场所。变速驱动器(ASD)的功率电子设备通过脉冲宽度调制器(PWM)从直流电压源合成频率可变的正弦波形。当电力电子设备供电时，绝缘所经历的过电压、电场分布和局部放电(PD)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械绝缘，其可靠性水平与传统工频供电的电机相同，但目前情况并非如此。从局部放电的实验室研究和现场监测来看，如果局部放电开始涉及大量能量，则局部放电会增加，有时会在增长期和消光期之间交替，直到导致绝缘故障或击穿。*IEC 600341842标准认为老化因素是峰间电压，因此，老化应力是由施加电压产生的电场，与电压波形无关。这意味着，作为老化驱动器的PD不会从正弦脉冲波形改变为重复脉冲波形，因此，只要电源电压的频率和峰峰值电压相同，任何电压波形的寿命都是相同的。最近发表的研究旋转机械匝间绝缘寿命特性的文献表明，正弦脉冲电压和重复脉冲电压下的局部放电和寿命都有很大差异。事实上，局部放电幅度、重复率以及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指出，根据脉冲上升时间的不同，局部放电过程中涉及的能量可能显著高于交流电压。*本研究建议使用正弦和电力电子波形对匝间绝缘试件进行加速寿命试验，同时监测老化直至击穿的局部放电，以探索不同波形下的局部放电时间行为。通过研究正弦波形和脉冲波形下的失效时间行为，可以推断出可以应用于电力电子器件绝缘老化的寿命模型的类型。

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.*********