Dielectric spectroscopy in time and frequency domain for HV power equipment. I. Theoretical considerations

Most dangerous breakdowns are caused by the aging effects of HV insulation systems used within HV components, and there is still a lack of appropriate tools to diagnose such systems non-destructively and reliably in the field. This review introduces the theoretical background of dielectric spectroscopy in the time and frequency domains and provides an overview about the specific measuring methods based on this background. The specific methods treated are used for diagnosing electric insulation materials used in power engineering. It indicates that some of these methods may not be sufficient to gain full information about the actual conditions of a test object and that either measurements of polarization and depolarization currents (PDC in the time domain or measurements of C-tan/spl delta/ values (or complex permittivity) in the frequency domain (FDS) should be preferred to obtain a "dielectric response function" which offers much more information to judge the actual state of an insulation material or system.     

Field experiences with measurements of dielectric response in frequency domain for power transformer diagnostics

Some new methods, based on characterization of the dielectric response of transformer insulation in time and frequency domains, have been pointed out by CIGRE as suitable to assess moisture content in pressboard and paper. Measuring devices available today on the market are quite robust in field conditions; however there is a risk that undesired internal and external factors might influence the measurements. These influences can lead to mistaken interpretation of insulation wetness. Operators should therefore be aware of the risks appearing at different measuring conditions and of the precautions that can be taken to minimize their effects. This work presents a systematic investigation on the influence of some factors on the results of dielectric response measurements in field conditions. The errors that can be committed during the measurements if certain precautions are not taken, with different equipment connected in parallel, are evaluated. The influence of rain and electromagnetic disturbances are also analyzed proposing solutions to attenuate their effects. Finally, a discussion on the influence of temperature distribution follows. The work is concentrated on frequency response measurements, although some results from the use of polarization and depolarization current technique are also discussed.     

高压电力设备绝缘诊断的声学检测技术

对高电压设备绝缘缺陷的声学检测技术进行了分类,评述了国内外的声学敲击检测、声发射检测和超声检测等技术的原理、系统及优缺点,并探讨了绝缘状态声学诊断最有应用前景的检测技术。     

Investigation on the transformation of time domain spectroscopy data to frequency domain data for impregnated pressboard to reduce measurement time

The accuracy of different transformation methods for time domain dielectric response data to frequency domain and their limits are studied. First an approximated analytic function is considered, second an extended Debye model for the dielectric behavior of impregnated pressboard. The last method is a numerical integral form and Fast Fourier Transform. Hamon approximation relates time domain data at t to frequency domain data at f=0.1/t and gives the results by sole measurement of polarization current. Dielectric diagnosis of high voltage apparatus can be done by using Hamon approximation in minimum duration. All transformation methods show similar results and they are analyzed in order to demonstrate the limits of the methods.     

Magnetic resonance spectroscopy data analysis: time or frequency domain?

Comparisons of time and frequency domain methods are presented forin vitro ¹H andin vivo ³¹P magnetic resonance spectroscopy (MRS) data. Many distortions in the MR spectrum, introduced by applying the Fourier transform to a nonideal free-induction decay (FID), can be handled more elegantly in the time domain, where operations are carried out directly on the measured signal. It was found that if the measured signal is well conditioned—high signal-to-noise ratio (S/N), no truncation, no baseline problems—then both time and frequency domain methods give the same results within the error limits. However, distortions in the measured signal make analysis by time domain methods preferable over frequency domain methods. In all applications, the use of prior knowledge appeared to play an important role.     

Temperature dependent dielectric spectroscopy in frequency domain of high-voltage transformer oils compared to physicochemical results

The temperature dependent dielectric spectroscopy in frequency domain is compared to physicochemical and electrical tests that are periodically applied on highly insulating transformer oils. Complex permittivity and tan/spl delta/ data are obtained as a function of frequency and operation temperatures, to demonstrate the polarization phenomena and the induced loss intensification by the thermally stimulated currents. The acquired dielectric data of oil samples collected from 201 operating high voltage (HV) power transformers, were correlated to their corresponding physicochemical ones in order to demonstrate the future potential employment of the proposed measuring technique in the field of high voltage engineering, towards reliability monitoring of oil filled electrical equipment (OFEE).     

Influence of rise time on dielectric parameters extracted from time domain spectroscopy in the context of generator stator insulation

The low-frequency dielectric response of generator stator winding insulation materials was calculated from high voltage time domain spectroscopy measurements. These results were used to calculate the theoretical response after the application of a voltage function consisting of a ramped voltage followed by a constant level voltage. The rate of rise of the ramped portion of the voltage function was shown to influence the well known and much used polarization index (PI) and insulation resistance (IR) parameters.     

High voltage studies of dielectric materials for HTS power equipment

The discovery of high temperature superconductors (HTS) has triggered renewed interest in the study of dielectric materials at cryogenic temperatures. While considerable work was done in the 1970s and 1980s on dielectrics immersed in liquid helium for low temperature superconducting applications, there remains a need for dielectric research at liquid nitrogen temperature for HTS applications, requiring experimental data oriented toward practical situations. We report on AC breakdown (puncture and/or flashover), and impulse breakdown of solid materials in either vacuum or in liquid nitrogen. Solid materials which we examined, include fiberglass reinforced plastics, epoxies with and without filler, and polymeric tape. Combinations of some of these materials have also been studied at low temperatures. Additionally we have measured permittivity and dissipation factor for materials for which these parameters are not available at 77 K. Finally, we also discuss specific applications for HTS cables including breakdown and aging studies on model cables, with lapped tape electrical insulation, immersed in liquid nitrogen.     

Time domain dielectric spectroscopy study of biological systems

The main principles of time domain dielectric spectroscopy, its application to conductive systems and possible methods of electrode polarization corrections in time domain are introduced. A comprehensive theoretical and experimental study of static and dynamic dielectric properties of different biological systems including globular, and membrane proteins, hydrate water, human erythrocytes, and normal and malignant blood cells of different types is presented in the paper.     

鹤岗矿务局热电厂高压变频器改造实例

介绍鹤岗矿务局热电厂锅炉系统工况,对其中主要耗能设备,如送风机、引风机和锅炉给水泵等,提出节能降耗的措施。对现场设备进行变频调速改造后,厂用电率大幅度下降,取得很好的节能效果,改善了电机的运行工况。     

Applications of superconductivity to electric power equipment

A brief survey is presented of the potential applications of superconductive devices to electric power systems. Areas of principal interest include high-capacity transmission, energy storage, and power generation by rotating machinery, magneto-hydrodynamics and nuclear fusion. Some elements of superconductivity are discussed, including the properties of appropriate materials; these superconductive devices vis-à-vis the conventional counterparts in terms of reduction of power losses, decreased weight and size, and increased current capacity. An assessment is made of the time frame and the possibilities for introduction of superconductive devices into power systems.     

湖南电网2007年高压开关设备非计划停运分析

对湖南电网110～500 kV高压开关设备非计划停运情况进行了统计,分析了主要影响因素,提出了降低高压开关设备非计划停运率的措施.     

A mixed frequency and time domain approach for accurate evaluation of the dynamics of lemp-excited lossy multiconductor power lines

Contents  In this paper a mixed frequency and time domain approach is proposed for the analysis of the dynamics of multiconductor power lines excited by indirect lightning. First, the excited line is represented through an equivalent frequency-domain m-port, and the effects of the lightning excitation are taken into account via terminal equivalent lumped sources. In Frequency domain it is easy to include in the model the skin-effect in the wires and the finite conductivity of the ground. By means of a semi-analytical inversion procedure, the time-domain equivalent circuit is derived. This allows treating in a correct way the study of fast transient and non-linear loads such as surge arresters. Using the above procedure, simulations have been carried out in order to evaluate the shielding effect of the ground wires and to analyse the effects of surge arresters. The results agree with those obtained in literature by using different methods. Received: 13 November 2000     

容性设备介损在线测试的探讨

对容性设备在线测试中所涉及到的问题进行了探讨 ,从传感器的选择、电压信号的采样以及测试仪器信号获取等方面 ,对于容性设备的介质损耗值测试的准确性和有效性进行一定的分析 ,阐述了容性设备在线测试的可行性     

Computation of high-frequency and time characteristics of corona noise on HV power line

This work presents an algorithm for the computation of frequency and time characteristics of the corona noise in power-line carrier communications. In the frequency domain, the corona noise is represented with a power spectral density and with a Gaussian noise voltage with variable root mean square value in the time domain. Simulations results are compared with measurements on an actual 400-kV power line.     

基于时、频域自相似性的配电变压器环境噪声识别方法

配电变压器位于开放的嘈杂环境中,环境噪声对基于声音的设备运行状态在线监测具有突出影响.如何识别和剔除含噪声干扰的录音片段,是推进基于声音的配电变压器状态在线监测亟待解决的瓶颈问题.分析指出配电设备正常和异常的运行声音与各种环境噪声在时域和频域上的差异性特征,提出基于时、频域自相似性的配电设备录音数据中含环境噪声片段的识...     

基于dsPIC的工频通信系统装置研制

针对我国配电网工频通信信道特性,开发了一种基于数字信号控制器的工频通信系统装置,包括子站装置和用户终端.对工频通信系统构成,以及信号调制和信号解调原理进行了介绍.在此基础上,设计了适合我国配电网信道特性的工频通信系统装置.装置由主控单元、过零检测电路、信号调制/解调电路等部分组成,详细介绍了主控单元的选择和各功能电路的...     

定子主绝缘受潮频域介电参量提取及状态评估

针对吸收比等传统电气参数测试结果分散性大、易受外界干扰等问题,提出将频域介电谱技术引入发电机定子主绝缘受潮状态评估过程.对不同老化状态的定子主绝缘样品进行受潮试验,得到不同状态样品的吸收比和介质损耗频域谱.结合灰色关联法,深入分析测试结果,划分四种绝缘受潮状态和四个特征频段,通过特征频段的介损积分值构建标准状态向量组,...