【作者】 周凯；

【导师】 吴广宁；

【作者基本信息】 西南交通大学 ， 电气系统控制与信息技术， 2009， 博士

【摘要】 随着电力电子技术的发展,变频调速交流传动系统在牵引机车中得到广泛应用。但采用该系统后,逆变器输出的PWM(脉冲宽度调制)高压方波脉冲的上升沿很陡、频率很高,导致在PWM脉冲电压下牵引电机绝缘过早失效。传统交流电机绝缘设计方法和理论已不完全适用于变频调速电机,因此对变频电机绝缘技术进行系统的研究迫在眉睫。已报道的研究成果大多以散绕组变频电机为研究对象,对成型绕组变频电机的研究很少。本论文在总结国内外变频电机绝缘技术研究成果的基础上,以影响变频牵引电机绝缘老化的两个主要因素:局部放电(PD)和空间电荷为具体的研究对象,详细地研究了变频牵引电机绝缘的局部放电和空间电荷的行为及机理,老化特征及表征参量等。通过这些研究,将极大地促进变频条件下绝缘老化和击穿理论的发展,使变频调速技术应用前景更加广泛。设计了一种新的脉冲电压下局部放电测量系统和统计分析软件。采用高频响应特性较好的NiZn铁芯材料,采用小波包算法来分解传感器输出信号,从而去除脉冲电压快速上升和下降过程所带来的干扰,提取出脉冲电压下的局部放电信号。根据工频电压下局部放电分析方法,通过时间开窗和统计,使用专用的脉冲电压下局部放电分析软件可得到脉冲电压下的各种放电谱图,以便更深入分析脉冲电压下的局部放电行为和机理。对脉冲电压下的空间电荷测量方法、影响因素进行了讨论,并研究了脉冲电压波形参数对空间电荷行为的影响。设计了基于电声脉冲法的空间电荷分布直接测量系统和热刺激电流测量系统。讨论了陷阱参数的计算方法,对比了高斯拟合和动力学方程拟合对活化能计算的影响。对不同脉冲频率老化对绝缘微观结构的影响进行了讨论,聚酰亚胺膜的寿命主要与高温峰的活化能和电荷量有关,低温峰的活化能和电荷量对试样的寿命影响不大,脉冲电压下,活化能可能随老化程度加剧而减小。根据空间电荷测量结果,分析了不同的脉冲频率、电压幅值、电压极性、脉冲电压上升时间和绝缘层数对空间电荷行为的影响。研究了不同参数的脉冲电压对纳米和非纳米聚酰亚胺膜、电机定子绕组的绞线对试样的局部放电行为的影响。分析了不同参数的脉冲电压对不同绝缘材料的局部放电起始放电电压(PDIV)、局部放电参量(平均放电量和放电次数)、相位分辨模式的影响,脉冲频率增加和电压上升时间的缩短都会导致反向电场作用增强,从而导致局部放电行为的差异。此外,通过扫描电镜(SEM)和局部放电分析结果,纳米膜具有三层结构,表层纳米颗粒导致其表面电导率大,能削弱局部放电作用,而且表面的纳米颗粒层具有良好的保护作用,导致放电对绝缘内部损伤较小。为探讨高压方波脉冲下绝缘的加速老化机理和老化特征,对电机定子绕组的绞线对试样进行了老化。比较分析了脉冲电压和工频电压下样本老化特征的不同,脉冲电压下老化后样本很容易出现“放电丛”现象,该现象主要是由于脉冲电压下较强的反向电场作用而导致。对匝间和对地绝缘样本在脉冲电压下老化后的矩特征参量进行了对比分析,其平均放电量的偏斜度和老化时间存有联系。更多还原

【Abstract】 With the development of high power semiconductor devices, frequency control drive systems are widely used in the field of locomotive traction. Pulse Width Modulated (PWM) technique which provides motor supply voltages is characterized by square waveforms, width modulated, with steep rise front slew rate up and high pulse repetition frequency. For this reason, electrical insulation of traction motor can be premature failures under such pulse waveforms. Because design and manufacture technology of AC motor is not completely suitable for traction motor supplied by such adjustable speed drives anymore, it is essential that comprehensive research for electrical insulation of electric motor supplied by PWM voltage. However, some past research achievements are generally based on lower power electric motor made by dispersed windings, and very little work has been carried out for high power electric motor made by module windings. The thesis is based on the latest research results at home and abroad, and partial discharge (PD) and space charge which are major factors leading to aging of insulations are used as main study objects. Activity and mechanism of PD and space charge of insulation system of traction motor supplied by adjustable speed drives is investigated .Furthermore, In order to investigate the influence of square wave pulse on aging and failuare of winding insulation, aging characteristics of winding insulation are also studied. These reasearch results will greatly promote advancement of theory of aging and breakdown under such pulse condition. As a result, frequency control technique can be widely used.A novel PD signal measurement system and statistic analysis software is presented under square wave pulse voltage. From comparison of response of sensors made by different ferrite core, the sensor made by NiZn ferrite core is more suitable for transferring PD signal at pulse voltage. Also, wavelet package is used to filter interferences generated by steep rising and trailing edge of square wave. According to PD statistical method under sinusoidal waveform, time window and PD statistics are performed. Depending on special statistic analysis software, phase resolved PD patter at square wave voltage is also defined to further investigation of PD activity and mechanism. Measurement method and influencing factors of space charge under pulse voltage is discussed, and effects of parameters of pulse waveform on activity of space charge are investigated. The device based on Pulse Electro-Acoustic method (PEA) is developed in order to directly measure distribution of the space charge, and thermally stimulated current (TSC) is also designed to measure energy level of space charge in polymer. Computing methods of trap parameters are compared through gauss fitting and kinetic model fitting. After different pulse frequency voltage aging of polyimide film, changes of microstructure of polyimide film is investigated. Moreover, lifetime of polyimide film is related to activation energy and charge quantity of high temperature peak in the TSC curve, whereas activation energy and charge quantity of lower temperature is nearly independent of lifetime. Under pulse voltage, it is possible to decrease of activation energy with aging. According to the measurement results of space charge, effects of different pulse frequency, voltage amplitude, polarity, rise time and insulation layers on activity of space charge are analyzed.Effects of different pulse waveform on PD activity of nano hybrid polyimide film, normal polyimide film and twisted pair specimens of winding are investigated under pulse voltage. Through measurement results of PD inception voltage (PDIV), PD parameters including mean discharge quantity and discharge number, phase resolved PD pattern of different materials specimens, increase of pulse frequency and decrease of rise time of pulse waveform both results in enhancement of inverse electric field when polarity of pulse waveform reverses. For this reason, different PD activity can be observed. Furthermore, through analysis of SEM (scanning electronic microscope) and PD parameters, three layers of nanophase hybrid polyimide film have been observed which lead to large surface conductivity and suppress PD activity. Due to protective effect of nanophase layers to PD damage, damage of PD hardly occurs in the interior of nanophase polyimide film.In order to investigate accelerated aging mechanism and characteristics of insulations under square wave pulses, aging experiments of twisted pair specimens of stator winding of traction electric motor are performed. Comparative tests are carried out under AC sinusoidal and square wave pulse conditions. Obvious clusters of discharge number occur with the increase of pulse voltage aging time, whereas no similar phenomenon can be observed after sinusoidal voltage aging. It indicates inverse electric field at pulse condition is more intensive than at AC sinusoidal condition. Furthermore, analysis of the moment parameters of PD statistics operatorsat different aging time is also performed in order to show relationship between PD statistics operators and aging time. The results show that there is a relation between skewness of mean discharge quantity and aging time.更多还原