变频电压作用下高压电机云母绝缘的寿命评估

Life-Time Investigation of Mica-Based Insulation for High Voltage Machines Subjected to Converter-Like Voltages

变频高压电机在工业领域得到越来越广泛的应用，源于它可根据实际负荷需求控制电机的输出功率，由此可降低资产成本和能耗。在某些场合下，变频技术已由两级结构发展为多级结构，电压波形由矩形波变更为与脉冲波叠加的正弦波，其特征为离散的脉冲电压幅值、脉冲重复频率和脉冲上升时间。问题是与工频交流电压相比，这种变频电压如何影响电机绝缘的老化？本文将介绍产生与多级变频电压波形相似的电压发生装置。试验装置的灵活性在于可将交流电压和脉冲电压与叠加不同纹波因数的变频电压进行比较，进而研究纹波因数对云母绝缘寿命的影响。我们定义纹波因数（纹波因数ripple content）为脉冲电压幅值与总峰．峰值电压的比值。试验结果表明：在纹波因数占比至少达到43％的条件下，峰．峰值电压和基频（而不是脉冲重复频率）影响绝缘老化速率。

The industrial use of converter fed high-voltage machines is steadily growing. The driver behind the growth is the possibility to control the output power from the machine to be adjusted to the actual needed power of the load. This leads to a more cost- and energy efficient use of the assets. For some applications the development of the converter topology has gone from 2-level to multi-level, which has changed the voltage waveshape from a square-wave looking voltage to a sinusoidal looking voltage superimposed with a ripple of pulses, characterized by their discrete pulse voltage amplitudes, the pulse repetition frequency, and the pulse rise-time. The question is how this type of converter-like voltage will affect the aging of the machine insulation in comparison to power frequency ac voltage. This paper presents the test set-up for generating voltage wave-shapes similar to multi-level converter output voltages. The flexibility of the test set-up to combine ac and pulsed voltages into converterlike voltages with different ripple contents, has enabled a study of the influence of the ripple content on the lifetime of mica-based insulation. We define the ripple content as the ratio between the pulse voltage amplitude and the total peak-to-peak voltage. It is shown that the peak-to-peak voltage and the fundamental frequency, and not the pulse repetition frequency, influence the insulation aging rate up to a ripple content of at least 43 %.