国际电动机能效标准最新进展

简要介绍了目前各国电动机能效标准现状，以及国际电工技术委员会IEC／TC2正在制定的能效标准IEC60034-30的情况及对各级能效指标的考虑。对目前世界各国的能效水平，以及各级效率的各项指标做了详细对比。     

国际电动机能效标准最新进展

简要介绍了目前各国电动机能效标准现状,以及国际电工技术委员会IEC/TC2正在制定的能效标准IEC60034-30的情况及对各级能效指标的考虑。对目前世界各国的能效水平,以及各级效率的各项指标做了详细对比。     

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.     

低速磁浮列车直线牵引电机绝缘结构设计

根据直线异步牵引电机的设计技术规范,通过模拟线棒的绝缘试验论证,确定直线牵引电机的绝缘结构,并据此成功试制直线牵引电机。该电机目前已安装于3辆低速磁浮列车车辆上,进行整体车辆的试验调试,累计运行了36km。     

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。     

A novel output filter topology to reduce motor overvoltage

When an induction machine is supplied with a voltage-source pulsewidth-modulation (PWM) inverter, a ringing voltage overshoot appears at motor terminals due to steep PWM voltage pulse propagation along the motor cable. It has been reported that in particular situations, when very long motor cables are used and retrofit installations, the overvoltage could stress motors with poor insulation. This paper presents a novel inverter output filter topology consisting of an LC filter which has the star point of the common-mode capacitors clamped to the + and - dc-link rails by the means of two diodes. The proposed filter drastically reduces the voltage overshoot at the motor terminals, thus reducing motor insulation stress. This is a cheap alternative to more known industrial solutions.     

Xml语言在新一代电力自动化系统中的应用

当前使用的变电站自动化系统和能量管理系统(EMS)已经不能满足计算机、通信等技术的发展需求,因此IEC制定了针对变电站自动化的61850标准和针对EMS系统的61970标准来建立各异构系统的统一数据模型。Xml语言凭借其独特的优点在以上2种新的标准中得以广泛应用。本文对Xml语言做了简单介绍,并分别介绍了Xml在这2种标准中的应用,最后简单讨论了Xml在实现基于这2种新标准的异构系统中数据交换中的应用。     

光纤复合架空地线(OPGW)电力行业标准与其他标准的比较

光纤复合架空地线(0PGw)国际标准有IEC-60794-4-1和IEEE Std 1138；国内机械行业制定了JB／T8999-1999行业标准；国家标准的报批稿已经完成，正在上报等待批准；目前该产品的电力行业标准DL／T832-2003已由国家经济贸易委员会批准颁布，并于2003年6月1日正式实施。由于上述几个标准制定的时间和偏重的方向不同，因此各个标准在技术要求、检验规则和具体指标方面都有所不同。文中主要阐述了光纤复合架空地线电力行业标准的制定情况以及该标准与其他几个标准的主要不同点。     

高效高压中型异步电机绝缘结构设计分析

针对高压电机定子主绝缘减薄后电场的分布问题,本文以YKK400 -6(690 kW)中型高压异步电机为例,建立定子绕组静电场的计算模型.在边界条件不变的基础上,通过对场强最大值及电场集中系数分析计算,对定子绕组主绝缘进行减薄处理,并结合设计要求给出了主绝缘角部合理的圆角半径.在电场计算的基础上对主绝缘减薄前后的线圈进行介质损耗角正切与瞬时工频击穿电压试验.结果表明,新的绝缘结构满足要求.本文可为电机定子主绝缘的减薄及绝缘结构设计提供理论依据.同时也可达到提高电机效率的目的.     

Correction factors for positive dc voltages

Direct-current voltages are used mainly to test equipment utilized in HV dc transmission systems, as an alternative to ac for testing cables, capacitors, insulations in which internal discharges may lead to degradation of the insulation under ac testing conditions, in investigations in discharge physics and dielectric behavior. For atmospheric air the voltage measurements under any conditions are related to the standard conditions employed in the IEC-60 standard. It is demonstrated that the IEC correction procedure is not adequate for dc voltage measurements at high altitude; for example for rod-plane gaps there is a difference >10% between experimental data obtained at 2240 m above sea level and those corrected with the IEC-60 procedure. This is mostly a consequence of the fact that the physical model employed, which is based on the field of propagation of streamers, fails to account for the combined effect of humidity and altitude. It is surmised that the propagation field of the prebreakdown streamers varies linearly with the air-density. The experimental rod-plane results obtained by the authors are better modeled by an alternative semi-empirical model     

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     

Evaluation of Breakdown Characteristics of Oil-immersed Transformers under Non-standard Lightning Impulse Waveforms - Method for Converting Non-standard Lightning Impulse Waveforms into Standard Lightning Impulse Waveforms

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of oil-immersed transformers and thus reduce equipment cost while maintaining high insulation reliability, it is required to identify the insulation characteristics under non-standard lightning impulse waveforms that are associated with actual surge waveforms in the field and quantitatively compare them with the characteristics under the standard lightning impulse waveform. In the previous research, field overvoltages in the lightning surge time region were analyzed, and four typical non-standard lightning impulse waveforms were defined. These four waveforms were used to measure the breakdown voltages and the partial discharge inception voltages on three models of the winding insulation elements of oil-immersed transformers. The average breakdown voltages were evaluated in terms of the overvoltage duration. This paper describes a method for converting of non-standard lightning impulse waveforms into standard lightning impulse waveforms with equivalent stress for the insulation. The constructed algorithm was applied to four examples representing two types of non-standard lightning waveforms. Due to the conversion into standard lightning impulse waveforms, the crest values were reduced by 14% to 26%. This seems to be a potential for reduction of lightning impulse insulation specifications of oil-immersed transformers.     

Fuzzy Logic-based Electrothermal Life Model for Inverter-fed Induction Motor Insulation

Pulse width modulated adjustable speed drives used in industries lead to significant advantages in terms of performance, size, and efficiency. But, the output voltage and the current waveforms become non-sinusoidal leading to an increase in voltage and thermal stresses. This results into accelerated insulation aging and premature failure of the motors. With multiple stresses, the life models for insulating materials become complex and ambiguous. This article presents the fuzzy logic application to derive an electrothermal life model to investigate the synergic effects of voltage and thermal stresses on intrinsic aging of inverter-fed induction motor insulation. Three parameters, viz. voltage stress factor, waveform slope stress factor, and spike frequency factor, are proposed to describe the insulation stresses for pulse width modulated voltages. These parameters are computed from the experimental results at different switching frequencies and are used in fuzzy logic-based life estimation algorithms. The results of the fuzzy logic life model are verified by performing the accelerated aging test with the same pulse width modulated voltages on paper insulation. An electrothermal life model is derived from the fuzzy logic results, which can be directly used for the life estimation of any general purpose low-voltage inverter-fed induction motor insulation.     

Voltage endurance testing

The medium-voltage ASD stator insulation systems operate under greater stress than those using the sine-wave power. The repetitive short rise-time pulses generated by most ASDs cause an additional stress. The pulses are often increased by the effect of the cable between the ASD and motor. It is incumbent on the user and ASD manufacturer to account for the magnitude, rate of rise, and repetition rate of these pulses. The medium-voltage machines powered by ASDs operate with some level of PD. The machine manufacturer must ensure that the insulation system will provide adequate life in the PD environment. VE testing is a well-understood and accepted method to qualify insulation systems. It is a reliable means to compare new insulation systems with the documented existing ones. The TS describes several qualification procedures based on the knowledge of the converter waveform. These will assure that all parts of the machine insulation system will present acceptable test life.     

Effect of surge voltage risetime on the insulation of low-voltagemachines fed by PWM converters

This paper investigates the repetitive surge-voltage withstand of low-voltage mush-wound machines operated on adjustable-speed drives (ASDs) using insulated gate bipolar transistor (IGBT) semiconductor technology. Historical work on surge testing of motor insulation has focused on one or more of the following aspects: (1) large horsepower motors; (2) medium-voltage form-wound motors; (3) single-shot impulse-type transients; or (4) low-voltage machines with surge risetimes >200 ns. IGBT drives can have risetimes of 50-200 ns. Thus, a new study on electrical stress of insulation systems due to the nonlinear voltage distribution of mush-wound motors when subjected to repetitive steep dV/dt square-pulse waveforms (rather than impulse wave testing) is presented. Magnitude and risetime of the repetitive ASD surge-voltage transient induced on the machine terminals is reviewed first. Next, surge propagation into the winding was investigated to identify maximum voltage stress points on the conductor insulation. Potential failure mechanisms observed at these points are then discussed. The significance of decreasing surge risetime and increasing cable lengths on internal nonlinear voltage distribution is studied with experimental results from a 7.5-hp motor with a tapped stator winding     

Identification of Thermally Safe Load Cycles for An Induction Motor Position Servo

Advances in the available performance of induction motor-inverter systems permit these drive systems to meet progressively more demanding performance criteria. High-performance servos require the induction motor to produce high torque and power. The severely repetitive load cycles stress the motor's insulation with high operating temperatures. The traditional rating of the induction motor based on ac line operation is not useful under these circumstances. In spite of the complexity of the thermal problem, an approximate thermal calculation procedure will allow servo designers and users alike to predetermine thermally safe load cycles for induction motor servo drives. Study is directed to the formulation of a simplified thermal model of vector-controlled induction motor servos rated between 1 and 15 kW and to the subsequent use of this model to predict thermally safe load cycles. A set of normalized curves relating duty cycle and torque is presented for the available classes of motor insulation. Theoretical results are supported by experimental verification on an existing vector-controlled induction motor servo system.     

Analysis of steep-fronted voltage distribution and turn insulationfailure in inverter-fed form-wound AC motor

As a potential source of turn insulation failure, the steep-fronted voltage at the motor terminal generated by pulsewidth modulation drive switching or cable ringing is not uniformly distributed among the coils of the windings and among the turns of the coils. This paper presents a detailed electromagnetic analysis of the parameters of a transient model of coil and coil group which includes iron loss, skin, and proximity effects. The finite-difference method is applied to solve the model for the interturn and intercoil voltage distributions. The simulation is compared to a simplified lattice diagram analysis and to test results. A turn insulation surge-withstanding capability study is then presented with a flexible insulation test system that models the repetitive steep-fronted voltage stress and temperature stress     

A new approach to enhance power quality for medium voltage ACdrives

A new approach to medium-voltage variable-frequency static AC motor drives offers improvements in power quality. Harmonic current injection into the power lines is below the most severe requirements of IEEE Standard 519-1992. The power factor of this new type of drive exceeds 94% at full load and is above 90% at 10% load. Motor voltage and current waveforms are improved so that torque pulsations are reduced. Peak voltage stress on motor insulation does not exceed peak input line voltage, and no zero sequence voltage is imposed. Drive efficiency exceeds 96%. This paper describes the new approach and some of the results achieved     

基于TCP/IP的IEC60870-5-104远动规约在电力系统中的应用

根据国际电工委员会制定的IEC-60870-5-101和IEC-60870-5-104远动规约，我国已经制定了相应的配套标准DL/T634-1997和DL／T634．5104-2002。IEC-60870-5-101远动规约已经在我国电力系统中得到了较为广泛的应用，而IEC-60870-5-104作为采用标准传输协议子集的IEC-60870-5-101的网络访问，由于涉及到网络编程以及颁布时间较短，在电力系统中应用很少。作者详细介绍了IEC-60870-5-104的网络参考模型、帧格式结构和TCP连接建立过程，并根据工程实践，分析了IEC-60870-5-104的实现方法以及应注意的要点，最后提出了拓展IEC-60870-5-104使用范畴的一些设想。     

高压电机定子采用散绕组的绝缘结构分析

高压电机的定子通常采用成型绕组,同时需配套开口槽,导致电机成本增加、气隙磁场谐波含量增大、齿槽转矩增大等一系列问题。为了解决上述问题,可以采用散嵌圆铜线绕组。对于高压电机采用散绕组,绝缘问题是关注和研究的重点。以1台高压散绕组电机为例,利用有限元法分析了高压电机采用散绕组的绝缘结构可靠性,分别分析了匝间绝缘、主绝缘、层间绝缘和端部绝缘的绝缘情况以及主绝缘被冲片毛刺划伤情况下的电场强度分布,并根据分析结果针对电机槽内绝缘做出了优化,制造了1台样机并对样机进行了耐电压试验。验证了高压电机定子采用散绕组在一定程度上是可行的,为高压电机定子绝缘结构设计提供了参考。