Accelerated life tests on a new water tree retardant insulation forpower cables

This paper describes the results of an investigation in which 15 kV rated cables insulated with a new water tree retardant cross-linked polyethylene (TR XLPE) were subjected to accelerated aging tests under a controlled voltage stress and thermal load cycle conditions. Cables insulated with conventional XLPE and a commercially available TR XLPE were used as reference test populations to affirm the test methodology. Under the chosen conditions, cable life of the new TR XLPE as calculated using Weibull and log normal statistical distributions, was more than twice that for the reference TR XLPE. Extensive diagnostic measurements (water content, dissipation factor, water tree analysis) were performed on failed cable samples to bring out the differences between the three insulations. Electron micrographic investigations revealed the size and distribution of micro voids in the new TR XLPE to be smaller supporting its extended life under these tests. The experimental details of the accelerated life tests are also documented in a clear manner facilitating any archival of the data for future analysis and comparison     

Accelerated aging tests for polymer insulated cables under wetconditions

The effectiveness of various aging test procedures utilized in the past to evaluate aging in polymeric cables under wet conditions is examined. It is pointed out that the prime parameters affecting the aging rate and its mechanisms are those of electrical stress, frequency, water solution, temperature, mechanical strain, and testing time duration. Any valid fixed-time or time-to-breakdown test procedure that is based on the stress/frequency acceleration concept must, therefore, be carefully specified and defined in terms of these parameters     

A general review of polymeric insulation for use in HVDC cables

The authors present a review article of the properties of XLPE and an examination of the origins of space charge and how it is measured. The space charge in the insulation and the conduction current can affect the electric stress distribution in the insulation. The effect of morphology on the electrical properties of polyethylene is discussed in detail.     

Long term accelerated aging tests on distribution cables under wetconditions

Two accelerated aging test procedures are proposed for use on solid dielectric extruded distribution cables under wet conditions. One test method is a fixed time duration test in which the degree of cable specimen aging is assessed in terms of breakdown tests, while the other test method is a time to breakdown test in which the cable specimens are voltage stressed until failure ensues     

浅谈交联聚乙烯电力电缆的交接、预防性试验

该文阐述了交联聚乙烯 (XL PE)绝缘电力电缆的交接、预防性试验有关问题 ,提出 6～ 10 k V和 35 k V交联聚乙烯电力电缆不同的试验方法和内容     

电力电缆诊断检测技术综述

电力电缆是电能传输的重要载体之一,其运行可靠性直接影响电力系统的供电安全。电力电缆诊断检测技术既包含对已发生故障的诊断、定位,也涵盖对电力电缆运行状态的监测,及时发现电缆老化等缺陷或故障隐患,对提高电缆运行的可靠性具有重要意义。文章简介电力电缆老化等缺陷及发生故障的机理,梳理常见电力电缆诊断检测技术并比较它们的优劣,在此基础上结合智能电网发展趋势,探讨电力电缆诊断检测技术的发展趋势和面临的挑战。     

Life model based on space-charge quantities for HVDC polymeric cables subjected to voltage-polarity inversions

This paper illustrates a new model that enables the estimation of life of polymeric insulation subjected to DC stress, both in the presence and in the absence of voltage polarity inversions. The derivation of the model parameters is based on the results of space charge measurements and accelerated life tests realized at constant DC stress, which allows the characterization of the performance of insulating materials under DC electrical stress to be carried out in short times. The expected life of a cable in service can be evaluated by means of this model, provided that the rate of voltage inversions expected during its life is known or estimated. The model is applied here to results of tests carried out on polyethylene-based materials for cable insulation, and model parameters are calculated resorting to two different approaches. A satisfactory fitting of life test results is achieved, thus confirming the validity of the proposed model.     

Impedance of a double submarine cable circuit using different typesof cables within a single circuit

The interconnection between the Upper and Lower Peninsulas of Michigan has recently been upgraded from a single 138 kV circuit to a double 138 kV submarine power cable circuit. The original circuit consisted of four single-conductor cables, the fourth cable serving as a spare phase conductor. The second circuit was formed by adding two new single conductor cables and combining them with the spare cable from the original circuit. The use of two different types of cables in one circuit causes that circuit to be unbalanced. The series impedance and shunt admittance matrices of the circuits were studied to investigate the degree to which they were unbalanced, so that the impedance relays protecting the cable could be properly set. Measurements were made on the cables after they were installed and these were compared to calculations made with the ATP EMTP Cable Constants program     

Long-term forecasting: a critical review of direct-trend extrapolation methods

A treatment is given of probabilistic autonomous models, i.e. statistical models of direct-trend extrapolation for long-term electrical energy demand forecasting. A methodology of mathematical modelling for global forecasting based on regression analysis is presented. A critical survey of the most common regression models is given, as well as the original algorithms and results of the class of combined exponentially-polynomial regression models. Data of increasing electricity consumption for a number of Yugoslavia urban areas (populations from several thousand up to 1.5 million) are processed, in order to draw conclusions about the applicability of the regression models considered. The results of Yugoslav demand forecast up to the year 2000 are presented. Although the processed data are typical of the conditions in developing countries, satisfactory agreement has been observed with the behaviour of forecasting models applied to the data for West Germany, a typical developed country.     

Diagnosis of moisture in oil/paper distribution cables - Part I: Estimation of moisture content using frequency-domain spectroscopy

Dielectric spectroscopy (dielectric response measurements) has been applied for nondestructive estimation of humidity in oil-paper cable insulation. The experiments have been based upon two field-aged cables, 20 and 50 years old. Paper samples from these cables have been characterized and subjected to environments with different relative humidity. Dielectric loss and capacitance have been measured in a frequency range 1 MHz to 1 kHz and related to the moisture content determined by Karl Fisher titration. A method has been verified where the moisture content is correlated to the minimum value of loss tangent (tan/spl delta/). A number of field measurements have been performed where the method has been applied to estimate the moisture content in the distribution cables.     

Generalization of data on critical heat fluxes for flow swirled using a tape

The available data on critical heat fluxes for boiling of subcooled and saturated liquid in tubes with twisted tape inserts are considered. Experimental data obtained by different researchers are generalized, and an equation for calculating critical heat fluxes for both smooth tubes and tubes with flow swirling by means of a tape is proposed.     

Applications of cortical signals to neuroprosthetic control: a critical review.

Cortical signals might provide a potential means of interfacing with a neuroprosthesis. Guidelines regarding the necessary control features in terms of both performance characteristics and user requirements are presented, and their implications for the design of a first generation cortical control interface for a neuroprosthesis are discussed.     

A study on the ageing process for polyester resin using improved Weibull statistics

Surface tracking on organic solid insulators is one of the main reasons for failure in high voltage systems. Due to various factors, such as humidity, pollution, ice load, increase in local voltage, etc., it is hard to estime the lifetime of an insulator. For many years, Weibull statistics have been widely used and accepted as a successful mathematical method of predicting the remaining lifetime of an insulating material. The basic reliability function can perform well for predefined conditions. However, it might be insufficient in lifetime prediction in multi-variable conditions. In this research, a model based on improved Weibull statistics is proposed for estimating the breakdown time of polymeric insulation material. By using appropriate parameters, this improved model can estimate the remaining lifetime within a reasonable accuracy in varying external conditions such as voltages, contaminant flow rates and applied load. To determine the model parameters, several tests are performed according to the IEC 587 accelerated inclined plane tracking test method by investigating the breakdown times of polyesters under various external conditions generated artificially in the laboratory. The calculated results are found to be in good agreement with the experimental data.     

基于IEC 61850-9-2接口的保护动模试验

介绍了基于IEC61850-9-2接口的保护试验所作的探索,全面验证了保护接口的可用性和稳定性。试验结果证明,采用这一数字接口的保护的动作行为和传统保护一致。     

Evaluation of insulation performance of polymeric surface using a novel separation technique of leakage current

This paper describes a novel method to separate the leakage current, obtained in polymeric materials during a salt fog aging test, into three components of conductive current, corona discharge current and dry band arc discharge current. First, we investigated that the relationship between optical emissions due to discharges and a leakage current. Based on experimentally defined discharge types, the separation of the leakage current was carried out. Finally, the polymer surface was analyzed using an electron spectroscopy for chemical analysis (ESCA), and the change in the polymeric constituents was evaluated. The results showed that the cumulative charges due to the dry band arc discharge and the corona discharge to the total charge were about 20 and 10%, respectively. It was also found that a high temperature vulcanized (HTV) silicone rubber could retain its insulation performance better than a room temperature vulcanized (RTV).     

A critical review of the literature on the organization impact ofinformation technology

A critical review of the literature on the impact of information technology on organizations is presented. The impact is discussed at four different levels-individuals, groups, organizations, and societies. Issues discussed include ergonomics, stress, job satisfaction, attitudes, industrial relations, leadership, power, politics, decision-making, organization structures, and organizational changes affecting individuals, groups, and organizations. This review points to some directions along which more comprehensive surveys should be done in the future     

Realization of polymeric optical integrated devices utilizing organic light-emitting diodes and photodetectors fabricated on a polymeric waveguide

Direct fabrication of organic light-emitting diodes (OLEDs) and organic photodetectors (OPDs) on polymeric substrates, i.e., polymeric waveguide substrates to form flexile optical integrated devices is demonstrated. The OELD and OPD were fabricated by organic molecular beam deposition (OMBD) technique on a polymeric or a glass substrate, for comparison. The device fabricated on a polymeric substrate shows similar device characteristics to that on a glass substrate. Optical signals of faster than 100 MHz have been created by applying pulsed voltage directly to the OLED utilizing diamine derivative, or rubrene or porphine doped in 8-hydoxyquinolinum aluminum derivatives, as an emissive layer. Electrical signals are successively converted to optical signals for optical transmission of moving picture signals with OLED fabricated on a polymeric waveguide. OPDs utilizing phthalocyanines derivatives with superlattice structure provide increased pulse response with input optical signals, and the OPD with the cutoff frequency of more than 5 MHz has been realized.     

Insulation failure in telecommunication cables resulting from water condensation in aerial terminal closures and its prevention using a humidity-controlling polymer

Insulation failure in telecommunications cables after extended use in aerial terminal closures has been examined. Extensive cracking and sea salt deposition were observed on the polyethylene (PE) insulation of wires in a terminal closure recovered from the field after 27 years of service. The insulation failure mechanism appears to be the formation, by bulk water condensation with deposited sea salt dissolution on degraded PE insulation, of ionically conductive pathways among the PE insulation cracks. An experiment using wires with PE insulation that was deliberately cut to simulate cracking showed that controlling the humidity within the terminal closure is an efficient way to prevent insulation failure. A field experiment showed that placing a polymer that absorbs moisture when the humidity is high and releases it when the humidity is low in the closure effectively buffered changes in humidity, thus preventing water condensation. Another experiment using wires with deliberately cut insulation in a terminal closure with 100% RH and with the water-absorbent polymer placed inside showed that the resistance of the wires stayed at around 10⁸ Omega without fluctuation. Since the absorbent polymer continues to function for many years, this proposed prevention method is well suited for practical application