【作者】 王鹏；

【导师】 吴广宁；

【作者基本信息】 西南交通大学 ， 电力系统及其自动化， 2013， 博士

【摘要】 由于在节能、调速等方面的显著优点,变频电机在各领域得到了广泛应用。变频器采用脉宽调制技术,输出具有高频、快速变化的方波脉冲电压,给电机绝缘带来了新的问题。一般认为,电机端部过电压引起的局部放电是变频电机绝缘失效的主要原因。对此,IEC制定相关标准,规定对低压散绕和高压成型电机,分别应测试其局部放电起始放电电压(PDIV)和耐电晕性能,以避免变频电机服役期间因局部放电导致电机绝缘早期失效。然而,标准执行中,以下问题亟待解决：①脉冲电压下的局部放电与逆变器产生的干扰在时域和频域发生重叠,局部放电信号提取较为困难,PDIV测试时信噪比常不能满足要求；②PDIV测试时必须考虑脉冲电压参数对局部放电统计特性的影响,而这种影响规律尚不明确；③电压参数对寿命测试结果的影响可能会造成的耐电晕性能测试结果的不准确。针对以上问题,本研究从以下方面展开工作：首先,研制能输出各种电压参数的脉冲电压发生装置并搭建重复脉冲电压下局部放电测试平台。结合使用IGBT开断和功率放大技术,产生了上升时间最短为50ns,电压频率、占空比和幅值在较宽范围内可调的重复方波脉冲电压。采用高频电流传感器(HFCT)和超高频方法,结合相应滤波和移频技术,设计了适用本研究的局部放电离线检测和在线监测系统。然后,利用该系统,在不同脉冲电压参数下,研究了聚酰亚胺单点接触试样局部放电统计特性,总结出脉冲电压参数对局部放电统计特性的影响规律并对相应机理进行了解释,从而为低压散绕电机PDIV测试中信噪比的提高和脉冲参数的选择提供了参考依据。最后,利用单点放电试样,在不同参数的重复方波脉冲电压下,进行了电老化实验研究。根据所得寿命及局部放电统计数据,对方波脉冲电压参数对寿命测试结果影响进行了统计分析及机理解释。研究结果发现：等待初始电子产生时快速变化的脉冲引起的激发电压升高改变了局部放电时频特性,局部放电幅值和电磁信号高频能量随着脉冲电压上升时间的减小而增大；由于局部放电的记忆效应,放电幅值和相位随着脉冲频率的增大而减小,脉冲电源占空比的变化会引起局部放电PRPD谱图的不对称分布；在具有相同峰峰值和频率的正弦和方波脉冲电压下,变频电机漆包绝缘寿命具有显著差异；由于脉冲频率对局部放电过程中表面电荷积累特性的影响,不同频率脉冲电压下局部放电统计特征会发生改变,造成绝缘试样寿命与脉冲电压频率具有非线性关系。研究结论可为变频电机局部放电检测标准的修订提供理论参考和实验依据,从而改进低压散绕电机和高压成型电机的绝缘测试技术和测试手段,最终提高变频电机绝缘系统的可靠性。更多还原

【Abstract】 Power electronic drives using asynchronous motors are extensively used in various fields because they offer a number of remarkable advantages such as improved controllability and energy efficiency. Using pulse width modulation technology, an inverter output voltage with high frequency and fast-changing features, which brings new problems to motor insulation systems. Partial discharge (PD), induced by the motor terminal overvoltage, is generally recognized as the main reason for the premature failure of insulation in inverter-fed motors. To reduce the effect of the aforementioned problem, the International Electrotechnical Commission (IEC) released related technical specifications (TS), which require PD inception voltage (PDIV) and corona resistance performance to be tested for low-voltage random-wound and high-voltage form-wound motors, respectively, to avoid premature insulation failure and thus, increase insulation reliability. However, when carrying out the TS, there are following problems should be solved.①The overlapping of disturbance and the PD pulses in the time and frequency domains makes PD signal extraction difficult and thus, low signal to noise ratio (SNR).②To choose suitable repetitive square wave voltage parameters when performing PDIV measurements, the effect of voltage parameters to PD features should be considered accordingly. However, this effect is unclear.③When performing life tests on stator or insulation samples under repetitive square wave voltage conditions in high-voltage motors, the influence of voltage parameters on test results could cause inaccurate test results.Therefore, to solve the aforementioned problems, this study focuses on the following aspects:First, by using an insulated-gate bipolar transistor (IGBT) and power amplifier technologies, an impulse generator, which can output repetitive square wave voltages at50ns (the shortest) rise time, and with adjustable frequency, duty cycle, and voltage magnitude, was designed. To suppress the disturbance appearing at the rise and fall flanks of the impulse voltage, both the high-frequency current transformer (HFCT) and ultra-high frequency (UHF) methods with suitable filtering and frequency shifting technologies were adopted. In this manner, the PD measurement system for off-line detection and online monitoring was designed. Second, resorting to the aforementioned experimental system, the statistical features of the PD were studied by focusing on the single PD specimen made from enameled wires insulated by polyimide. Based on the high number of data, the effects of repetitive square wave voltages on PD features were summarized. The mechanisms of these effects were also provided. Lastly, electrical aging was performed on a single PD specimen under repetitive square wave voltages with different parameters. Statistical analysis was performed based on life data, and explanations for the results were provided based on PD data obtained during electrical aging.Experimental results showed that the overvoltage caused by waiting for initial electrons could change the PD time and frequency domain characteristics. PD magnitude and high frequency electromagnetic energy increase as the increase of impulse voltage rise time. High-frequency square wave voltage can give rise to PD events with low magnitudes and phases. Changing the voltage duty cycle can cause the asymmetric shapes of phase resolved partial discharge (PRPD) maps. When stressed by sinusoidal and square wave voltages with the same peak-to-peak voltages and frequencies, the insulation life of enameled wires insulated by polyimide exhibited significant differences. Insulation lifetime does not decrease linearly with frequency because of the influence of square wave voltage frequency on surface charge accumulation.The conclusions of this study will provide theoretical and experimental references to revise the TS for PD measurement on inverter-fed motors. Consequently, insulation-testing technologies for low-voltage random-wound and high-voltage form-wound motors will also be improved; thus increasing their insulation reliability.更多还原