An acoustic diagnostic technique for use with electric machineinsulation [comment with reply]

The authors' original approach [see ibid.,vol. 1, no. 6, p. 1186-93, 1994] of employing ultrasonic nondestructive testing techniques to search for stator bar insulation defects is commented upon. The comments provided are very welcome since the authors feel this is an important new technique in the armory of diagnostic tools available for assessing the health of generator stator insulation     

对电流致热型设备红外诊断技术的探讨

红外检测项目是高压电气设备定期检测和巡检的内容。为此,对红外技术和电气设备红外检测的原理作了简介,对电流致热型电气设备缺陷红外诊断的方法作了重点论述,并指出对外部热故障和内部热故障的判断应注意的事项。广州增城供电分公司开展红外检测工作的检测实践证明,红外诊断技术对于及时发现电流致热型电气设备的外部缺陷和部分内部缺陷是非常有效的。     

An advanced technique for detecting inter-laminar stator core faults in large electric machines

An advanced technique for detecting incipient inter-laminar insulation failure in stator cores of large electric machines is proposed in this paper. The proposed scheme is an offline method based on low flux stator core excitation that employs a new probe. An iron-core probe is placed in the wedge depression area of the stator and scanned axially to detect the variation in the measured flux due to a fault. Two fault indicators that provide clear indication on fault severity and location are proposed in this paper. A 120-MW ac machine stator was tested under a number of intentionally inserted fault conditions using portable field equipment recently developed. The experimental results show that the fault existence, location, and severity can be determined reliably using the proposed scheme. It is also shown that the fault detection sensitivity and reliability, inspection speed, and user convenience are significantly enhanced.     

An electric traction drive for electric vehicles

Problems of expanding the range of speed regulation in electric transport vehicles by replacing gear-shift transmission with a two-channel electric drive comprising two electric motors, each coupled with its own reducing gear units possessing different gear ratios. The output shafts of these reducing gear units are coupled to one differential speed-reduction device. To solve this problem, a mathematical model of the electric-motor drive has been developed and the static characteristics of the individual motors and characteristics of the motors with their output shafts driving one differential speed-reduction device have been determined. Steady conditions of the operation of a two-channel electric drive are considered. To describe real changes in the speed variables, the electromechanical transducer is approximated in the mathematical model with nonperiodic first-order links. The functions of the controlling effects, which are formed on the basis of the criterion of fullest utilization of electric machines with respect to their electromagnetic torque in stable conditions and in transient processes, were determined. Recommendations are given on application of the proposed solution to traction mechanisms, which should meet increased requirements to acceleration of electric-motor vehicles.     

A hybrid modelling technique for underwater acoustic scattering

A numerical method using impulse analysis of a transmission-line matrix is used to model the scattering of underwater acoustic waves. The method is demonstrated by observation of plane and curved wavefronts travelling through the medium, and by plane wavefronts being scattered by a reflecting boundary.     

An efficient diagnostic technique for distribution systems based on under fault voltages and currents

Service continuity is one of the major aspects in the definition of the quality of the electrical energy, for this reason the research in the field of faults diagnostic for distribution systems is spreading ever more. Moreover the increasing interest around modern distribution systems automation for management purposes gives faults diagnostics more tools to detect outages precisely and in short times. In this paper, the applicability of an efficient fault location and characterization methodology within a centralized monitoring system is discussed. The methodology, appropriate for any kind of fault, is based on the use of the analytical model of the network lines and uses the fundamental components rms values taken from the transient measures of line currents and voltages at the MV/LV substations. The fault location and identification algorithm, proposed by the authors and suitably restated, has been implemented on a microprocessor-based device that can be installed at each MV/LV substation. The speed and precision of the algorithm have been tested against the errors deriving from the fundamental extraction within the prescribed fault clearing times and against the inherent precision of the electronic device used for computation. The tests have been carried out using Matlab Simulink for simulating the faulted system.     

建筑用尼龙护套电线

随着我国改革开放的不断深入,建筑业得到了迅猛发展.建筑物内部敷设的低压动力、照明电线电缆,用量极大.在一些发达工业国家,此类电缆已占电缆总销售额的40%以上.该类电缆品种繁多,因其使用场合不同,而各有其特殊的性能要求.     

主设备保护技术发展新动向

国内外大型发电机和高压变压器的主保护设计整定工作一般都不是基于科学的、充分的绕组内部故障分析计算,很多情况下设计工作变成设计人员的主观判断或经验应用,有些技术文件也显得陈旧过时.在发电机内部短路分析计算软件已经国家鉴定之后,完全有条件使发电机(变压器)主保护设计工作定量化、科学化.阻抗保护不能作为大型发变组的绕组近后备保护.我国特有的很少采用零序差动保护的情况应该改正.     

主设备保护技术发展新动向

国内外大型发电机和高压变压器的主保护设计整定工作一般都不是基于科学的、充分的绕组内部故障分析计算,很多情况下设计工作变成设计人员的主观判断或经验应用,有些技术文件也显得陈旧过时。在发电机内部短路分析计算软件已经国家鉴定之后,完全有条件使发电机(变压器)主保护设计工作定量化、科学化。阻抗保护不能作为大型发变组的绕组近后备保护。我国特有的很少采用零序差动保护的情况应该改正。     

声学技术在大电机槽楔松动检测中的应用

本文将声学技术应用于大电机定子槽楔松动的无损检测中,研制出一套数字化声学检测系统,对发电机定子槽楔的松紧状态进行现场实测。提出了槽楔松动的定量标准。研究了松动槽楔在电机定子中的分布。为客观、准确、定量地检测发电机定子槽楔的松紧状态创造了条件。     

混凝土断裂试验中的声发射特性研究

声发射技术作为一种现代无损检测技术,能简便快捷地判别混凝土在受力状态下内部缺陷的产生与发展,是混凝土材料断裂力学研究的重要分析手段和有效的评价途径。文章首先阐述了声发射技术在混凝土检测领域的国内外研究与应用现状,特别是在大坝混凝土领域的研究进展。课题组通过改进现有试验装置和更新改造测量设备,将声发射检测系统引入混凝土双K断裂参数试验中,新装置不仅能够精确控制试验中的加载速率,而且可以实时监测试件的起裂状态,能够准确判断试件的开裂和失稳破坏的时刻和特征。文章根据混凝土断裂临界状态的声发射识别特征,建立了混凝土断裂的声发射判据。试验结果表明,利用声发射特征参量可以准确判断试件的起裂时刻,与传统的应变法测量的起裂时刻吻合的较好,并且这种判据更加直观,便于现场操作,从而为声发射技术在混凝土断裂参数的测试中应用提供了理论与技术支撑。     

Detection of electric treeing of solid dielectrics with the method of acoustic emission

The paper presents results of research of electrical treeing of solid dielectrics with the method of acoustic emission (AE). The study was performed with an alternating voltage of 50 Hz in the range up to 21 kV (RMS) on methyl polymethacrylate or crosslinked polyethylene samples. They were of cuboidal shape of the dimensions 25 × 10 × 4 mm. One of the cuboid sample walls of the dimensions 25 × 4 mm was covered with a conducting paint. On the opposite wall, a surgical needle of T-25 type was screwed. The distance between the electrodes (the needle and the wall covered with a conducting paint) was in the range 0.5–2.0 mm. Registered signals were denoised with wavelet transformation method and then there were analyzed. The following parameters were analyzed: a sum and rate of acoustic emission counting, a sum and rate of acoustic emission events, RMS value of the electric signal leaving the converter. Spectrum and spectrogram were also analyzed. It was found that AE signals are generated during electrical treeing of solid dielectrics. Values of chosen parameters increased their values when the process begins. There are also some dominant frequencies ranges, different for different kinds of dielectrics, connected with the treeing.     

A simplified modelling technique for electric power system dynamical studies

The problem of large-scale system model simplification is considered. A linear transformation is introduced which provides block diagonalization of the original system state equations, permitting division into decoupled subsystems. General requirements concerning the retainment of the dominant modes of the original system by one subsystem are proposed. Application to a two-time-scale separation into slow and fast subsystems, suggested by power system analysis, is then presented. An iterative technique leading to block diagonalization without the need to compute all the eigenvectors is described. This technique is tested on an illustrative example. A comparison between the solutions obtained by a reduced-order system, the classical zeroth-order approximation and integration of the original system equations is given. State variable plots are inspected and commented upon.     

电网故障诊断系统的一种设计与实现

电网故障诊断是保证电力系统安全稳定运行的重要手段。针对我国目前电网自动化水平的具体情况 ,提出了基于开关跳闸信号、保护信息及故障录波信息的分层式故障诊断方法。用此种方法诊断 ,不仅可以诊断简单故障和复杂故障 ,而且还可以诊断故障类型、故障相别 ,并完成故障测距 ,为运行人员迅速切除故障提供了可靠的保证     

Artificial neural network based fault diagnostic system for electric power distribution feeders

This paper describes the development of a fast, efficient, artificial neural network (ANN) based fault diagnostic system (FDS) for distribution feeders. The principal functions of this diagnostic system are: (i) detection of fault occurrence, (ii) identification of faulted sections, and (iii) classification of faults into types, e.g. HIFs (high impedance faults) or LIFs (low impedance faults). This has been achieved through a cascaded, multilayer ANN structure using the back-propagation (BP) learning algorithm. This paper shows that the FDS accurately identifies HIFs, which are relatively difficult to identify with other methods. Test results are generated using the Manitoba Hydro 24 kV distribution feeder. These results amply demonstrate the capacibility of the FDS in terms of accuracy and speed with respect to detection, localization, and classification of distribution feeder faults.     

New International Electrotechnical Commission standards for regulating acoustic noise and vibration of electric machines

The results of a comparative analysis of the new International Electrotechnical Commission (IEC) standards for regulating the normative values of noise and vibration of electric machines and national standards valid in the territory of the Russian Federation are presented in this article. The most essential advantages and disadvantages of new IEC standards have been specified. Principal problems that domestic developers and electric machines manufacturers may experience due to the planned transition from local to new IEC standards have been considered.     

A 2-dimensional Kerr-effect technique for electric fielddistribution in liquid dielectrics

Based on the electro-optical Kerr effect, an attempt is made to develop a measurement technique for the two-dimensional distribution of the electrical field in dielectric liquids. For rapid, two-dimensional measurements, it is convenient to introduce a computer-controlled electronic camera for optical detection. However, because of the two-dimensional non-uniformity resulting from the system components, the measurement principle needs a two-dimensional analysis. To simplify the mathematical analysis, square pulsed modulations are employed. The influence of the system non-uniformity is eliminated by use of both optical and electrical modulations. To improve the system sensitivity, an optimum system setup is analyzed. To decrease the effect of the noise component resulting from the EHD (electrohydrodynamic) motion of the dielectric liquid, a diagnostic image lock-in technique is proposed. The validity of the two-dimensional measurement principle and the effectiveness of the diagnostic image lock-in processing are examined by the measurement of the electrical field distribution in a nitrobenzene specimen between two parallel plate electrodes     

A novel dehumidification technique using electric field

A completely new concept of dehumidification is presented. The polar nature of the electronic bond structure between oxygen and hydrogen atoms in a water molecule is utilized to attract them using an electric field. It is possible to single out and remove the water molecules from the air inside a room to make the room dehumidified. A theoretical formulation is developed and a simple experiment was performed to validate the theory. Unlike the conventional dehumidification process, this process does not involve any condensation of the moisture and hence requires a very small amount of power. The technique can also be very useful for air-conditioning as well     

电能质量与合理用电

根据谐波电流系列的产品标准及电能质量标准介绍了谐波产生的原因、定义与危害。结合实例,进行了电器产品用电符合性分析,并提出了电器产品设计和电能汲取的建议。     

An automated system for remote energy monitoring of mobile objects with electric drives

An approach to automation of remote energy monitoring of a mobile object with an electric drive is suggested. The approach is focused on solving the problem of generating statistics using analysis of energy consumption profiles. Structural solutions to arranging a system providing collection, transmission, and processing of measuring information from mobile object energy customers are considered. Based on the mixed implementation, a scheme of the measuring unit including a set of temperature, voltage, current, and speed sensors is developed. A data exchange scheme corresponding to the upper level of energy monitoring automation is developed. The control level in the scheme is established by JEVis local and global information systems with an open source. It is proposed to use a VIDA44M module remote telemetry and control line as a controller to collect data. The modules of the energy monitoring system can be supported by one server or distributed among several ones forming a cloud server. The data collection controllers communicate wirelessly with the server. The main calculation parameters of mobile object power supply, as well as the results of energy profile processing using hardware-in-the-loop simulations of the static and dynamic electric drive load, are considered. Based on the graphic profiles obtained by automated energy monitoring, one can assess the energy consumption of mobile objects, including public transport vehicles in a specific form, compare flow rates between similar objects, reveal faults or improper adjustment of the equipment, rank objects in power consumption, work out solutions to replace inefficient parts and mechanisms, predict power consumption, etc. As a result, power supply indices can be calculated and energy efficiency can be estimated; in addition, as energy audit of a transport company can be carried out and management decisions concerning energy efficiency can be suggested.