Life Model for PWM Controlled Induction Motor Insulation using Design of Experiments Method

According to numerous industrial surveys, the failure rate of stator insulation is much higher for Pulse Width Modulated (PWM) controlled induction motors than for the motors with sinusoidal voltage supply. Voltage spikes, high slew rate of spikes, and repetition and harmonics of PWM voltages generate higher electrical and thermal stresses in motor insulation that result into premature failure. In this paper, the Design of Experiments (DoE) method has been proposed to estimate the life of PWM controlled induction motor insulation. The insulation stress under PWM voltages is quantified by three factors viz. spike magnitude, spike frequency and voltage harmonics factor. These stress factors are experimentally computed for PWM controlled induction motor at different switching frequencies. Keeping these stress factors as input, a fuzzy logic model for insulation life is subsequently developed. This model is fine tuned to match the results obtained through insulation aging test with PWM voltages. The fuzzy logic data is analyzed by statistical techniques such as, ANOVA and Standardized Pareto Chart. A full factorial Design of Experiments technique is then applied to the fuzzy logic results to get the first order model relating the insulation life of induction motor with the stress factors. This model can be directly used for insulation life estimation of PWM controlled induction motors.     

基于介质损耗分析研究变频电机绝缘老化特性

变频牵引调速电机匝间绝缘承受来自逆变器的连续高压脉冲方波的作用,其老化机理与工频正弦电压作用下具有很大差异。笔者通过采用两种电压源对模拟变频电机匝间绝缘和对地绝缘的绞线对试样进行老化试验,测量了tanδ随老化时间的变化趋势,分析了电压形式对匝间绝缘和对地绝缘介质损耗产生和发展的作用机理。试验结果表明:脉冲电压下,匝间绝缘内部有放电发生时,放电与空间电荷协同作用使绝缘缺陷迅速增多;无放电时空间电荷反复注入和抽出造成绝缘损伤。交流电压下绝缘介质发热主要由局部放电造成,而脉冲电压下主要是由空间电荷所导致。对地绝缘由于其绝缘结构,呈现槽放电现象,空间电荷的引入大大加速了绝缘的老化。     

高压方波脉冲下局部放电的相位分布特征

针对局部放电可导致变频电机绝缘过早损坏这一问题,笔者分别在方波脉冲下和工频下,对匝间绝缘电磁线进行了老化试验和局部放电测量,主要对脉冲电压下局部放电的相位分布特征进行分析,并与工频下进行了对比。结果表明:脉冲条件下,随老化时间的增长,放电相位呈展宽趋势且出现明显的离散特征;高相位放电的出现是部分缺陷迅速发展的标志,是绝缘失效的先兆。     

基于数字局部放电检测的大型电动机主绝缘老化特性的研究

大型电动机在长期的运行过程中,要遭受电,热,机械等多因子应力的联合作用,使主绝缘逐渐老化,为了研究主绝缘老化机理,评估其剩余寿命,需要对电动机定子线棒进行多因子应力综合老化试验,并寻找能反映主绝缘老化程度的特征参量;本文采用先进的数字局部放电检测技术对不同老化阶段的试样线棒进行了综合测试,分析了局部放电各参量与试样线棒老化程度的关系,给出了各种反映绝缘老化特性的指纹图形,测试结果表明,随着试样线棒的进一步老化,局部放电量,放电次数,放电能量呈增长趋势,最大放电脉冲相位产生偏移,其偏斜度由大变小,这为评定大型电动机主绝缘的剩余寿命提供了参考依据。     

用超宽频带局部放电检测技术评定电机线棒老化状态的实验研究

在大型电机运行过程中 ,由于电、热、机械和环境应力的联合作用 ,其绝缘性能会逐渐下降。在实验室中通过多因子加速老化实验模拟了电机线棒在实际运行中的老化。对不同老化程度的线棒 ,使用超宽频带局部放电检测技术测试了试样的局部放电 ,并分析了放电信号在时域和频域随老化时间的变化情况。实验结果表明 ,随着试样线棒绝缘的不断劣化 ,放电脉冲时域波形的高频振荡不断加剧 ,脉冲宽度不断减小 ;同时 ,频域中的高频分量越来越丰富 ,谱峰逐渐增多 ,并且在高频段出现特征峰分布     

高压脉冲方波下聚酰亚胺薄膜电老化寿命模型

逆变器输出的高压脉冲方波会导致变频调速牵引电机绝缘过早损坏,其老化机理与工频交流电压下不同.利用一种高压脉冲绝缘老化试验系统模拟变频器对变频调速牵引电机定子绕组绝缘的老化作用,以聚酰亚胺薄膜为试验对象,研究了脉冲方波幅值、频率对绝缘寿命的影响,提出了高压脉冲方波下绝缘材料的电老化寿命模型.     

An Advanced Stator Winding Insulation Quality Assessment Technique for Inverter-Fed Machines

The lifetime of the stator winding insulation is reduced when operated with pulsewidth-modulation inverters, since insulation degradation is accelerated due to increased thermal and electrical stresses on the motor. This paper focuses on a new approach for monitoring the condition of the stator insulation for failure-prone inverter-fed machines. The main concept of the proposed technique is to apply a dc and/or variable-frequency ac test voltage to the stator insulation using the inverter and to perform standard offline insulation tests whenever the motor is not operating. This allows the stator insulation to be tested more frequently as compared to offline tests performed once every three to six years during periodic maintenance. Two methods for testing the insulation with minimal modifications to the inverter circuit are proposed and verified experimentally. The results show that the proposed technique provides a simple low-cost solution for detecting stator insulation degradation at an early stage for reliable operation of inverter-fed machine systems, since the insulation condition can be monitored frequently. This does not only helps prevent forced outages and safety risks due to insulation breakdown but also helps perform maintenance in an efficient manner, since individual motor maintenance can be prioritized and scheduled based on its present condition.     

PWM脉冲电压下电磁线绝缘老化机理分析

随着电力电子技术的发展，脉宽调制(PWM)电源得到了广泛应用。由于该电源输出电压是一系列脉冲电压，有可能导致变频电机绝缘过早破坏。目前，有关高压连续脉冲电压下绝缘材料失效机理各方观点尚未达成一致；过去的研究大多停留在宏观水平，主要是定性的实验研究，缺少微观定量分析的支持。针对上述问题，本文对变频电机定子绝缘的电磁线进行了老化实验。在此基础上，通过热刺激电流和脉冲下局部放电参数的关系，揭示了老化时间和陷阱参数(如峰值位置、陷阱能级)的联系。同时测量了局部放电参数(如起始放电电压、最大放电量、放电相位分布)随老化时间的变化。上述工作的开展，为更深入的脉冲电压下绝缘老化机理研究打下了坚实的基础。     

Output filters for PWM drives with induction motors

When an induction motor is energized from a pulse width modulated (PWM) inverter, through long connecting cables, its insulation system can be severely stressed. The high dv/dt voltage pulses at the output of the inverter cause traveling waves in the connecting cable between the inverter and the motor. When the traveling wave reaches the motor, a large impedance mismatch is present which leads to a reflected voltage wave that, when added to the incoming incident wave, can reach two times the inverter output voltage. The resulting overvoltage at the motor terminals stresses the insulation system and can lead to reduced motor life. Various output filter arrangements can be used to condition the inverter output voltage before it is applied to the cable. The advantage of adding output filtering is that the dielectric stress on the motor insulation and the inverter cable charging current can both be reduced. The major disadvantages of adding filtering is that they represent extra cost, they require extra mounting space, and they introduce extra losses in the system. The most commonly used types of inverter output filters are: simple output line inductors; output limit filter; sine wave output filter; and motor termination filter. These filters are discussed     

Partial discharge inception and propagation characteristics of magnet wire for inverter-fed motor under surge voltage application

In inverter-fed motor coils, surge voltages with the rise time of several tens or hundreds of nano-second may cause partial discharge (PD) and degradation of electrical insulation performance of the inverter-fed motor coils. This paper discusses PD inception characteristics as well as PD propagation characteristics after PD inception for magnet wire of inverter-fed motor under surge voltage application. Experimental results firstly revealed that PD inception voltage (PDIV) decreased with the increase in the length of enamel-coated wire, which was evaluated in terms of the stressed wire contact length under surge voltage application, i.e. size effect. We proposed a regression line for the size effect on PDIV for the electrical insulation design of inverter-fed motor coils. Secondly, PD propagation characteristics were also investigated under the higher voltage application, and their mechanisms were discussed in terms of generation probability of initial electrons, space charge behavior in the wedge-shaped air gap, charging on the enamel surface and so on     

变频牵引电机定子绕组内部电压分布特性的研究

分析PWM逆变器驱动的变频牵引电机定子绕组内部电压分布特性,对研究定子绕组绝缘失效和进行绝缘结构设计有重要意义。文章依据变频牵引电机定子绕组结构形式,建立绕组的分布参数电路模型,采用有限差分方法求解得出绕组内部电压分布情况,然后用实际测试结果验证模型的有效性,基于该模型讨论脉冲上升沿时间和电缆对绕组内部电压分布特性的影响。研究结果表明:上升沿时间越短,绕组内部电压分布越不均匀,线圈和匝电压幅值越大,而电缆长度对绕组内部电压分布影响较小,但绕组内部电压幅值增加了约40%。     

变频牵引电机定子绕组绝缘老化特性研究

对比测量了不同运行年限的变频牵引电机的定子绕组绝缘诊断参数,包括绝缘电阻、介质损耗因数、局部放电起始电压(PDIV)、剩余击穿电压等特征参数,以及沿绕组不同部位的绝缘材料取样进行了热失重分析(TGA)来研究绝缘老化特征。介电性能测量结果表明,与新电机相比,运行后定子绕组的绝缘介电性能有不同程度的下降,出槽口附近绝缘的老化程度高于槽内。TGA分析结果表明,使用了长达10年的牵引电机定子绕组绝缘性能略有下降,且线圈下层边的绝缘老化比上层边明显。     

用于变频电机绝缘测试的PWM电压发生器

在变频电机绝缘测试中,重复脉冲方波电压不能完全模拟变频器输出的PWM电压反映变频电机绝缘失效机理,并且同一实验中使用不同电源影响实验数据的一致性。该文章设计了一台直接输出式PWM电压发生器,既可以输出模拟变频器实际的SPWM电压和SVPWM电压用于绝缘测试,又可以输出重复脉冲方波电压开展对比实验。首先,设计了基于FPGA的脉冲信号发生器,产生基波频率、开关频率可调的SPWM、SVPWM触发脉冲以及频率、占空比可调的重复方波脉冲;然后,设计了基于固态推挽开关的斩波器,在脉冲信号的触发下输出对应的双极性高压脉冲;最后,使用该脉冲电压发生器开展了SPWM电压下变频电机绝缘局部放电实验,验证了系统的可靠性和实用性。     

A Method of Sensing Line Voltages for Parameter Adaptation of Inverter-Fed Induction Motor Servo Drives

Most high-performance inverter-fed induction motor drive systems require signals corresponding to the input voltages of the motor for parameter adaptation. Low-performance systems require the signals for stabilization. The voltage signals are used in the controller circuit and therefore require isolation. Isolation of the voltage signals is not a cost-effective solution in low-power motor drive systems. The fact that the base drive signals to the transistor inverter are isolated makes them the ideal choice for the reconstruction of the motor line voltages. A method of sensing line voltages from the base drive signals of the transistor inverter circuit is described. A step-by-step derivation of the voltage sensing algorithm is given which leads to a simple realization. The synthesized voltages are used in parameter adaptation for inverter-fed induction motor drives. The sensing scheme has been implemented on a laboratory prototype, providing experimental results which are presented.     

基于连续高压脉冲方波的绝缘老化寿命模型

变频电机定子绝缘承受来自逆变器的连续高压脉冲方波,其老化机理与工频正弦电压作用下具有很大差异.本文设计了一种连续高压脉冲绝缘老化试验系统,以聚酰亚胺薄膜为试验对象,研究了脉冲幅值、频率以及温度对绝缘寿命的影响,提出了基于连续高压脉冲方波的绝缘老化寿命模型.     

变频电机绝缘材料失效主要因素与寿命评估方法

分析了引起变频电机绝缘材料过早失效的主要因素,介绍了变频电机绝缘材料寿命评估检测设备的主要参数,提出标准定义中脉冲上升时间存在的问题,给出了脉冲电压上升率指标,指出在用示波器测试上升时间时应注意的问题,最后介绍了变频电机绝缘材料的寿命评估方法.     

SVPWM电压下变频电机绝缘耐电晕寿命研究

实验研究了空间矢量脉宽调制(Space Vector Pulse Width Modulated,SVPWM)电压开关频率(6 kHz、12 kHz、18 kHz)和基波频率(10 Hz、50 Hz、100 Hz、150 Hz、200 Hz)对变频电机绝缘材料耐电晕寿命的影响,并与相同开关频率50 %占空比重复脉冲方波电压下的耐电晕寿命进行对比。实验表明：开关频率越低,耐电晕寿命越长,耐电晕寿命的时长和分散性在不同基波频率下的波动越大;开关频率越高,耐电晕寿命越短,耐电晕寿命的时长和分散性在不同基波频率下的波动越小。50 %占空比重复脉冲方波能够用于替代SVPWM波预测变频电机绝缘的耐电晕寿命,但在开关频率较低时不能准确反映其统计特性;开关频率越高,50 %占空比重复脉冲方波对SVPWM电压下变频电机绝缘耐电晕寿命时长和分散性的预测越准确。研究结果有望为变频电机绝缘性能实验评估提供理论和实验依据。     

Frequency domain modelling of random wound motor windings for insulation stress analysis

The use of conventional low voltage induction motors fed by pulse width modulated (PWM) inverters has begun to present important problems. These waveforms consist of steep-fronted pulses having very short rise times (about 100 ns in modern IGBT bridges) and high frequency repetition rates (up to 20 kHz) whose immediate consequences are additional electrical stresses in an induction motors insulation system. In this paper a frequency domain model for the analysis and characterization of the internal voltage distribution in random wound coils is presented. The model allows voltage prediction in time domain when an inverse fast Fourier transform (FFT) transformation is performed, and requires only a few frequency domain impedance measurements. This methodology will be useful for accurately predicting the voltage distribution in motor windings during the design stage, and reducing the risk of premature failure in motor insulation. Experimental and theoretical results are presented and compared and model effectiveness using different approximations is studied.     

高速机车牵引电机定子绕组匝间电压分布特性的仿真研究

基于JD116型变频牵引电机,建立定子槽模型,通过有限元分析定子槽的电磁场计算绕组分布参数值;利用MATLAB仿真软件建立变频调速牵引电机定子绕组高频等效电路模型,探讨了电机定子绕组匝间电压的分布特性.仿真结果表明,增大输入脉冲电压的上升沿时间、减小等效匝对地电容和绕组自感可以改善绕组匝间电压的分布.该结果为变频牵引电机绝缘材料的选取、绝缘结构的优化设计提供了理论依据.     

PWM逆变器驱动异步电动机采用长线电缆时电压反射现象的研究

PWM逆变器驱动的异步电动机,在逆变器和电动机之间采用长线电缆传输时,会产生电压反射现象,导致在电动机端产生过电压,高频阻尼振荡,使电动机绝缘老化,造成电动机在短期内绝缘击穿等事故,这是PWM逆变器驱动异步电动机采用长线电缆所产生的负面效 应,文中首先分析了长线电缆传输时由于长线电缆的分布参数所产生的电压反射现象及其所造成的过电压等负面效应,分析表明电动机端产生的过电压与逆变器输出PWM脉冲上升时间和电缆长度有关。PWM脉冲上升时间愈短,电缆愈长,反射现象愈明显。采用低成本无源滤波技术可消除这种负面效应,文中分析和设计了一种一阶RC电动机端滤波器,用于接在异步电动机的接线端上,实验结果表明该滤波器可有效地减少电动机端过电压等负荷效应,从而提高系统的可靠性。