变频电机轴电流的分析

从轴电流产生原理的角度出发,分析了变频电机轴电流产生机理及危害,并介绍了非常实用的轴电流检测分析方法,最后提出了通过抑制电源谐波、加装碳刷、实用尖峰电压吸收器(SVA)等措施来防止变频电机轴电流危害。     

变频电机轴电流产生因素分析及对策

分析了变频电机轴电流产生机理、流通路径及危害,阐述了轴电压测量方法和经验限值,并从变频电机本身运行机理和结构角度出发,介绍了防止变频电动机轴电流危害的措施。     

变频技术对交流电动机轴电流的影响与预防

阐述了变频电源中的高频谐波增大了大中型电机的轴电流,分析了高频轴电流的产生机理,提供了轴电流烧损轴承的判断方法.为减少轴电流的危害,提出了转轴绝缘、轴承绝缘和均衡接地电压等防止变频电动机轴电流危害的具体措施.     

变频技术对交流电动机轴电流的影响与预防

变频电源中的高频谐波增大了大中型电机的轴电流。分析了高频轴电流的产生机理,提供了轴电流烧损轴承的判断方法。为减少轴电流的危害,提出了转轴绝缘、轴承绝缘和均衡接地电压等防止变频电动机轴电流危害的具体措施。     

变频技术对交流电动机轴电流的影响与预防

变频电源中的高频谐波增大了大中型电机的轴电流。分析了高频轴电流的产生机理，提供了轴电流烧损轴承的判断方法。为减少轴电流的危害，提出了转轴绝缘、轴承绝缘和均衡接地电压等防止变频电动机轴电流危害的具体措施。     

变频电动机轴电流的产生及控制

简述了变频电动机轴电流的产生及其危害,介绍了几种消除变频电机轴电流的方式。     

PWM变频调速电机轴承电磁损伤的机理研究

介绍了电机轴承电磁损伤的几种形式，重点研究了脉宽调制(PWM)变频调速电机轴承电磁损伤的机理，给出了电机定子绕组中性点电压和轴电压的测量结果，建立了PWM变频调速系统的物理模型，并对轴电压和轴承电流进行了计算机仿真，仿真结果与测量结果相吻合。     

变频电机轴承电气损伤的原因及措施

变频电机在激励工作电压中会产生轴电压现象,常用方法是采用绝缘轴承处理。但如果此方法不能及时处理时,由轴电压引起的轴电流会危害电动机运行的稳定性。通过对变频电机电气性能的分析,提出全新的轴电流损伤的解决方案,通过建立放电旁路,安装导电环将轴承接地,以降低轴电压,避免发生轴承电气损伤的故障。     

汽轮发电机轴电压轴电流在线监测装置的研制

本文简要介绍汽轮収电机轴电压产生原因及危害、轴电压、轴电流测量的工作原理、功能、试验及应用等情冴。轮収电机轴电压轴电流在线监测装置能提供収电机轴电压和轴电流在线检测,及时収现过高的轴电压和轴电流,保证了収电机安全可靠运行。     

变频电机轴电流的防止

阐述采用逆变器供电的变频电机，因电源存在许多高压脉冲，高频谐波增多，以及电动机铁心磁路不平衡等，在电机绕组和转轴上产生感应电压。为减少轴电流的危害，除电机制造需满足磁路平衡外，提出加装电源滤波器，前后轴承都要绝缘处理等防止变频电动机轴电流危害的措施。     

发电机组轴电流的危害及轴电流保护

介绍轴电压、轴电流产生的原因及对机组带来的危害,提出防范办法.结合龙滩水电站轴电流保护的配置情况,阐述了其轴电流保护的设计及应用.     

水轮发电机轴绝缘监测方法及效果分析

当绝缘薄弱时,低值的轴电压也可能对发电机部件造成一定的危害。结合现场测量数据对轴电压的性质作了分析,列举出对发电机造成损坏的各种情形。在其检测手段上,分别对轴绝缘检测法和轴电流测量法的原理进行了分析,对三峡电站的应用效果作了评估,比较了两种方法的特点优劣,提出了应用注意事项和优化手段。     

Support Vector Machine for Classification of Voltage Disturbances

The support vector machine (SVM) is a powerful method for statistical classification of data used in a number of different applications. However, the usefulness of the method in a commercial available system is very much dependent on whether the SVM classifier can be pretrained from a factory since it is not realistic that the SVM classifier must be trained by the customers themselves before it can be used. This paper proposes a novel SVM classification system for voltage disturbances. The performance of the proposed SVM classifier is investigated when the voltage disturbance data used for training and testing originated from different sources. The data used in the experiments were obtained from both real disturbances recorded in two different power networks and from synthetic data. The experimental results shown high accuracy in classification with training data from one power network and unseen testing data from another. High accuracy was also achieved when the SVM classifier was trained on data from a real power network and test data originated from synthetic data. A lower accuracy resulted when the SVM classifier was trained on synthetic data and test data originated from the power network.     

贵州煤中氟赋存形态分析

采用高温水解-离子色谱法,对中国贵州11种煤中氟的含量进行测定,并研究了贵州煤中氟含量与挥发分、灰分、氯含量、三态硫含量以及碱金属的关系。结果表明,贵州煤中氟含量普遍较高,最低为166.99 mg/kg,最高为1 614.46 mg/kg,平均为715.20 mg/kg,高于全国的平均含量;贵州煤中氟含量与煤化程度无关,与灰分也无相关性;煤样中氟的含量与氯的含量无相关性,而与有机硫呈现明显正相关;随着煤中碱金属含量的增加,煤中氟含量呈上升趋势,煤中氟与碱金属(Na,K,Ca,Mg)总量存在正相关关系。贵州煤中氟主要以无机形式存在。     

Light emission in XLPE subjected to HV in high vacuum andpressurized gas

The spectral and spatial resolution of electroluminescence, the light emitted from polymeric insulation subjected to high electric field, is studied in a test cell pressurized to 215 kPa with ultra high purity nitrogen gas. The paper also describes light emission from crosslinked polyethylene (XLPE) subjected to HV in an ultra high vacuum test cell. It is shown that the characteristics of light emitted from XLPE in the evacuated test cell are quite different from the light emitted when the test cell is pressurized. The mechanisms responsible for light emission under high vacuum condition are described and it is suggested that care should be taken when interpreting the light detected from polymeric insulation subjected to high electric fields     

A calculation method for determining the concentration of potentially acid substances in feedwater of once-through boilers

The problem of chemically monitoring the products resulted from destruction of organic substances in the steam-water path of a supercritical-pressure power unit is considered. The level at which the concentrations of acetic and formic acids have to be measured is determined, and the results from measurements of electric conductivity and pH in feedwater and steam are given. A procedure that allows the conditional concentration of acetic acid in steam to be calculated from measured electric conductivity in feedwater and steam is presented.     

Electrostatic Charges on Clays

Cation charges present on the surfaces of clay minerals are expected to play a major role in industrial processes involving dry electrostatic separation of granular mixtures containing clay particles. A recent promising potential application has been the removal of clay from British Columbia pulverized coals prior to burning. The clay minerals kaolinite and montmorillonite form the main component of the ash in most Canadian coals: kaolinite is eastern coals and montmorillonite in western coals. The electric charges present on the surfaces of the clay mineral kaolinite have been analyzed from an application point of view, namely, for their ability to transfer onto and remain on other surfaces after contact and separation. Kaolinite samples homoionized with calcium and sodium were prepared from natural kaolin, and the charge transfer after contact and separation with coal was compared for various dry densities of the kaolinite. The results show the following. 1) The electric charge transfer from calcium kaolinite is substantially larger than that from both the sodium kaolinite and natural kaolinite. Charge transfer from untreated montmorillonite exceeds that from all kaolinite samples. 2) The charge transfer after 100 contacts is inversely proportional to the dry density of the clay on a semilog scale. The phenomenon is believed to be related to the changes which occur in the total contact area and in the electrical conductivity of the clay.     

Analysis of Induction Motors Fed from Constant Current Source Taking Core-Loss and Saturation into Consideration

In this paper, a mathematical model of induction motor fed from constant current source as influenced by core-loss and saturation is presented. In the model, the equivalent core-loss resistance is split for the first time among the stator and rotor circuits. The actual value of the magnetizing inductance in the motor model is considered to account for the magnetic-circuit saturation. The transient and steady-state characteristics of an induction motor supplied from a constant lein current are presented. For completeness, the characteristics are compared with those of the same motor when fed from constant voltage source. The effect of core loss on motor performance is significant when the motor is fed from constant current source. Moreover, the effect of magnetic-circuit saturation is to improve the performance when the motor is fed from constant current source. Comparison between experimental and calculated steady-state performances are also presented.     

发电机绝缘诊断专家系统的研究

通过对发电机绝缘老化机理以及当前绝缘诊断方法的分析 ,提出了分布式绝缘诊断专家系统的思想。该专家系统以局部放电在线监测为基础 ,融合温度和振动传感器的数据 ,采用从局部到整体、从分析到综合的分析思路。整个专家系统的诊断分为局部放电的纵向分析、综合分析、统计分析及离线试验数据分析 4层。用黑板型专家系统实现上述设计思想并给出了实现方案     

双馈风电机组超速脱网机理分析及实例

近年来,风电机组大面积脱网事故屡有发生,给所连接电网带来冲击.以往关于风电机组脱网的研究主要集中于风电机组受扰后的电磁暂态过程.事实上,当电网故障扰动导致双馈风电机组Crowbar保护动作后,也打破了风电机组的转矩平衡.如果风电机组在受扰后的机电暂态过程中不能建立新的转矩平衡,将会引起风电机组超速保护动作,致使机组脱网.分析了配有Crowbar保护的双馈风电机组受扰后的机电暂态过程,揭示了双馈风电机组受扰后超速脱网的机理,推导了超速脱网的条件.运用所提出的分析方法,分析了一个风电机组超速脱网的工程实例,结果表明所提出方法是有效的.