Analysis of the harmful effects to buried oil pipeline from power line short-circuit fault

Based on the transmission line theory of the buried metallic structures,the concerned harmful effects to the buried oil and natural gas pipelines caused by the power line short-circuit fault are further discussed.A closed-form expression of the induced voltage caused by the short-circuit fault of the ultra-high voltage power(UHVAC) transmission line is given.The transmission line model of the buried pipeline is set up and a set of formulas for calculating induced voltage on the pipeline and the parameters of the buried pipeline in actual environment condition are given.At last,the characteristic of the harmful effects on the buried pipeline from the power line short-circuit fault are discussed.     

应用FBG应变箍传感器的管道安全监测研究

为了对管道的腐蚀以及泄漏进行长期、实时监测, 研发了一种光纤Bragg光栅(FBG)应变箍传感器,利用研发的传感器测量管道的环向应变,通 过环向应变的测量实现管道腐蚀以及泄漏的监测。为了探讨本文方法的可行性,将研发的FB G应变传感器安装在PVC管道上,进行腐蚀与泄漏的模拟实验,实验结果表明,研发的FBG应 变箍传感器可以测量到管道壁厚变化以及泄漏产生的负压波信号。表明用研发的传感器进行 管道腐蚀以及泄漏的方法是可行的。     

Induction effects of 2-D structures on buried pipelines

The implementation of cathodic protection systems is very complicated since many factors can contribute for current flowing off the pipe. The design requires the characterization of the parameters impacting the corrosion process, such as soil resistivity, size of the pipe and quality of the coating. The authors study the effect of geomagnetic fields on the pipe-induced currents considering it as an additional cause of corrosion. A theoretical method previously implemented to model the currents induced on pipes embedded in homogeneous soils indicated a dependence between the intensity of the currents and the electrical resistivity of the soil, and predicted that a drainage of current through the pipe would occur at zones of shallow electrical discontinuities. They present another method for the calculation of the induced currents that allows the authors to consider also multilayered structures and lateral discontinuities in the Earth resistivity. Applying this method, they quantify the currents induced in pipelines embedded in different bidimensional structures in order to obtain an estimation of the effects produced by the presence of such kinds of terrains. They then applied this method to model measured data. Field work was performed along a 200 km-route of a pipeline system. In this zone, the pipe-to-soil potential was measured at different sites and a geophysical study was made to determine the discontinuities in soil resistivities. They obtained a correlation of the measured currents and soil resistivity consistent with the theoretical predictions     

Integration of high frequency current shunts in power electroniccircuits

The majority of power electronic converters employ some kind of current measurement. Current transformers and current sensors employing Hall elements are convenient to use since they are galvanically isolated, and have therefore very good noise characteristics. Shunts on the other hand are very cost effective since it only involves placing a low value resistance in the circuit and amplifying the voltage drop to an acceptable level. Novel geometries are suggested as extensions of shunt design concepts for integrating inexpensive current measurement shunts directly into loads and various other structures. Typical applications would be as high power dissipation loads with low inductance, for use at low voltages where it is necessary to measure current or as permanently installed current sensors     

Design and experimental study on FBG hoop-strain sensor in pipeline monitoring

Pipeline monitoring is an important task for the economic and safe operation of pipelines as well as for loss prevention and environmental protection. The circumferential strain is of significance in pipeline integrity monitoring. In this paper, an indirect pipeline corrosion monitoring method based on the circumferential strain measurement is firstly proposed, with main objectives at designing a circumferential strain measuring device. Combined with unique advantages of optical fiber sensing, an FBG hoop-strain sensor was designed and encapsulated. Its enhanced sensitivity mechanism in the circumferential strain measurement and manufacturing technique is detailed. The experimental study of the developed FBG hoop-strain sensor is conducted on a PVC model pipeline to investigate its characteristics, including reliability and some tentative dynamic tests. Results of model tests show that the FBG hoop-strain sensor demonstrates good performance in the circumferential strain measurement, and can be considered as a practical device for pipeline health monitoring.     

管道超声内检测发射电路设计

在深入分析超声检测发射电路的基础上,设计了基于RLC串联谐振的发射电路,电路以场效应管为开关元件,电感储能形成高频、高压脉冲,建立了发射电路理论模型,分析了电路参数对高压窄脉冲的影响,理论计算产生的宽频高压脉冲激励信号与实验测量结果一致。该电路不需要提供直流高电压,只需要5V单电源供电,就可稳定获得宽度小于1μs,幅度大于400V,且无余振的高压窄脉冲。电路具有结构简单、体积小、不需要直流高压、功耗低、易于集成等特点,满足管道超声内检测的要求。     

Autonomous system for oil pipelines inspection

Maintenance of oil pipelines is an issue of great concern for oil companies. Any possibility of leakage must be detected before the leakage occurs and a preventive action should be taken in order to avoid losses of oil and ecological disasters. One of the main causes of oil pipelines leakage is the corrosion of the bottom part of the pipeline due to accumulation of water and other corrosive substances.One of the methods used to check the conditions of the oil pipelines is the running of a data acquisition device through all the length of the pipeline (that can be km) to gather information about the corrosion and its position inside the pipeline. This device is commonly referred to as pig. The Brazilian oil company, PETROBRAS, wanting to have the technology of such device to detect corrosion in their oil pipelines proposed to the Department of Mechanical Engineering of the Escola Politécnica da Universidade de São Paulo a joint project to the development of a pig that could run uninterruptedly in long oil pipelines gathering corrosion data for the preventive maintenance of their oil pipelines. The result of the project was the development of an ultrasonic pig with 16 ultrasonic transducers with on-board energy system and acquisition and storage systems. Also, comprised in the presented solution was the development of a software to analyze the collected data and give the position of the corrosion spots along the pipeline. This paper presents in detail the implementation and design issues related to the development of the ultrasonic pig. Also, some experimental data will be shown as confirmation of the effectiveness of the developed system.     

The battery voltage distribution: a possible tool for surveying the state of health of stand‐alone PV systems

Degradation phenomena can remain unnoticed over long periods in stand‐alone PV systems, before eventually causing service interruption. Problems include battery capacity reduction because of ageing, PV array capacity reduction because of wiring corrosion or excessive dirtiness, and mis‐adjustment of controller set‐points. This underlines the practical interest of an easily applicable method of early detection, so that preventive measures can be taken in good time. This paper proposes the use of the battery voltage distribution, as a tool for surveying the state of health of stand‐alone PV systems. Expected distributions can be derived by judicious modelling; while observed distributions can easily be obtained from systematic voltage measurements which are already made in many PV systems worldwide. Comparison between expected and observed distributions allows relatively simple diagnosis rules to be derived. Copyright © 2005 John Wiley & Sons, Ltd.     

State estimation of output-decoupled complex systems withapplication to fluid pipeline

Most industrial processes are complex systems, characterized by nonlinearity, high order, and even implicit dynamics. The design of a Luenberger-type observer or an extended Kalman filter for state estimation of such systems presents, in general, considerable difficulties. The authors show that a state estimator can be designed and implemented very easily if the system is output-decoupled, as is often the case in process monitoring and control applications. Simulation study and experiments on an experimental water pipeline show that the proposed estimator works very well. Its estimation accuracy is nearly the same as that of an extended Kalman filter, while its computational expenditure is almost as small as the real-time system model     

Noise Determination in Differential Pair-Based Second Generation Current Conveyors

The aim of this paper is to give simple design guidelines for the noise evaluation in differential pair-based second generation current conveyors (CCIIs). Input noise voltage and current have been expressed in terms of some well known constants and MOS g _m values, so allowing a very fast estimation of the noise level. The presented theory has been verified, as an example, on two fabricated low voltage low power CCII topologies. Theoretical values, simulations and on chip measurements are also shown and their good agreement confirms the validity of the presented idea.     

A numerical model of avalanche breakdown in MOSFET's

An accurate numerical model of avalanche breakdown in MOSFET's is presented. Features of this model are a) use of an accurate electric-field distribution calculated by a two-dimensional numerical analysis, b) introduction of multiplication factors for a high-field path and the channel current path, and c) incorporation of the feedback effect of the excess substrate current induced by impact ionization into the two-dimensional calculation. This model is applied to normal breakdown observed in p-MOSFET's and to negative-resistance breakdown (snap-back or switchback breakdown) observed in short-channel n-MOSFET's. Excess substrate current generated from channel current by impact ionization causes a significant voltage drop across the substrate resistance in short-channel n-MOSFET's. This voltage forward-biases the source-substrate junction and increases channel current causing a positive feedback effect. This results in a decrease of the breakdown voltage and leads to negative-resistance characteristics. Current-voltage characteristics calculated by the present model agree very well with experimental results. Another model, highly simplified and convenient for device design, is also presented. It predicts some advantages of p-MOSFET's over n-MOSFET's from the standpoint of avalanche breakdown voltage, particularly in the submicrometer channel-length range.     

Lightning-induced voltages in a satellite launch-pad protection system

Modern satellite launch pads are provided with lightning protection systems to take care of direct lightning strike to the satellite launch vehicle during the launch preparation period. This paper presents the results of the study on induced voltage on the conductors interlinking the towers of such a protection system due to a nearby lightning strike. The variation in the induced voltages with lightning-strike distances as well as ground conductivities are studied and the results presented in the paper. It has been seen that the waveshape of the induced voltage depends on conductor height and striking distance, whereas the ground conductivity has negligible effect on the induced voltage.     

Effects of drivetrain hybridization on fuel economy and dynamic performance of parallel hybrid electric vehicles

Hybrid electric vehicles have proved to be the most practical solution in reaching very high fuel economy as well as very low emissions. However, there is no standard solution for the optimal size or ratio of the internal combustion engine and the electric system. The optimum choice includes complex tradeoffs between the heat engine and electric propulsion system on one hand and cost, fuel economy, and performance on the other. Each component, as well as the overall system, have to be optimized to give optimal performance and durability at a low price. In this paper, we look at the effects of hybridization on fuel economy and dynamic performances of vehicles. Different hybridization levels from mild to full hybrid electric traction systems are examined. We also present the optimum level of hybridization for typical passenger cars. This study shows that low hybridization levels provide an acceptable fuel economy benefit at a low price, while the optimal level of hybridization ranges between 0.3 and 0.5, depending on the total vehicle power.     

Thermal instability of low voltage power-MOSFETs

This paper analyzes an anomalous failure mechanism detected on last generation low voltage power metal oxide semiconductor (MOS) devices at low drain current. Such a behavior, apparently due to a kind of second breakdown phenomenon, has been scarcely considered in literature, as well as in manufacturer data sheets, although extensive experimental tests show that it is a common feature of modern low voltage metal oxide semiconductor held effect transistor (MOSFET) devices. The paper starts by analyzing some failures, systematically observed on low voltage power MOSFET devices, inside the theoretical forward biased safe operating area. Such failures are then related to an unexpected thermal instability of the considered devices. Experimental tests have shown that in the considered devices the temperature coefficient is positive for a very wide drain current range, also including the maximum value. Such a feature causes hot spot phenomena in the devices, as confirmed by microscope inspection of the failed devices. Finally, it is theoretically demonstrated that the thermal instability is a side effect of the progressive die size and process scaling down. As a result, latest power MOSFETs, albeit more efficient and compact, are less robust than older devices at low drain currents, thus requiring specific circuit design techniques     

高精度电流源电路的设计

提出了一种高精度的电流源电路,通过V/I变换,将由带隙基准电压电路产生的与温度和电源电压无关的带隙基准电压转换成与温度和电压无关的高精度基准电流,并通过高精度电流镜结构产生所需的镜像电流,有效地抑制了由于温度、电源电压、负载阻抗的变化及干扰对电流源的影响.用HSPICE对改进前后的电路进行对比测试,结果表明,改进后电流镜的镜像误差约减小90%,电流源的精度显著提高.     

A quick response peak detector for variable frequency three-phasesinusoidal signals

An instantaneous peak detector for three-phase variable frequency sinusoidal signals is proposed. The three-phase characteristic is fully used in the proposed detector to achieve instantaneous response and frequency independence characteristics. A very simple hardware implementation circuit is also presented for minimizing the number of analog computational components. Moreover, the proposed detector possesses excellent linearity and low sensitivity to small voltage unbalance and harmonic distortion. Because of its promising accuracy and transient response, it can be used in many systems such as the voltage regulator of an uninterruptible power supply (UPS), an automatic line voltage regulator, or electric generators, etc., to improve the system transient performance. Theoretical analysis, hardware implementation, and some experimental results are also detailed in this paper     

Techniques for fast simulation of models of highly dependablesystems

With the ever-increasing complexity and requirements of highly dependable systems, their evaluation during design and operation is becoming more crucial. Realistic models of such systems are often not amenable to analysis using conventional analytic or numerical methods. Therefore, analysts and designers turn to simulation to evaluate these models. However, accurate estimation of dependability measures of these models requires that the simulation frequently observes system failures, which are rare events in highly dependable systems. This renders ordinary Simulation impractical for evaluating such systems. To overcome this problem, simulation techniques based on importance sampling have been developed, and are very effective in certain settings. When importance sampling works well, simulation run lengths can be reduced by several orders of magnitude when estimating transient as well as steady-state dependability measures. This paper reviews some of the importance-sampling techniques that have been developed in recent years to estimate dependability measures efficiently in Markov and nonMarkov models of highly dependable systems     

A new concept for test equipment for testing large HV and UHV cables on-site

The number of projects involving long and extra long HV and UHV AC cables as well as HVDC cable connections can be observed to increase (Cao et al., 2008; Kabouris et al., 2006). At the same time, operating voltage levels are increasing, accentuating the need for more powerful on-site test systems needed to prove the integrity of the insulation before energization. Low cost and ease of operation are other important features of such systems. As a matter of fact, traditional methods and test systems for routine and on-site testing of these cables come to their limit – technically and economically – as the lengths and voltage levels increase (Marelli, 2008). The logistics for the arrangement of tests as well as the testing itself are challenging (Schr?der et al., 2006). Development of power electronics has now made it possible to realize high voltage DC interconnections that do not exhibit polarity reversal at reversal of power flow. As a result of this, extruded XLPE cables are now coming to the fore in high voltage DC application, although methods and test equipment for routine and on-site testing show some open issues so far. Space charges in the insulation, initiated by the test voltage during testing, are unacceptable, and this leads to the requirement that testing must be made at an alternating voltage, which can be very low frequency without creating space charge. Available test equipment for power frequency testing is not feasible for testing extruded DC cables, among other reasons, due to the lengths usually associated with DC cables. These open issues can be solved with a newly developed on-site test system that provides the reliability of established test methods and test equipment, but exhibiting lower weight, dimensions and power consumption compared to existing systems. At the same time, the on-site test system as well as the prearrangement of the tests and the testing itself are less cost intensive. Extra long cables (i.e. high capacitance) could be tested with the equipment, which by virtue of its smaller dimension is easier to handle and thus reducing the testing logistics dramatically. For example where one of the systems on the market would require two trailers of equipment for a test on a high voltage cable, only a single trailer would be needed with the new system, or a roll on/roll off test can be carried out without the use of any crane on-site. A reduction in weight by a factor of 3 is expected compared to today’s on-site test equipment, a gain which also is reflected in reduced volume.     

Low voltage stress induced leakage current and time to breakdown in ultra-thin (1.2–2.3 nm) oxides

Ultra-thin gate-oxide reliability is an essential factor in CMOS technologies. The low voltage gate current in ultra-thin oxide of metal–oxide–semiconductor devices is very sensitive to electrical stresses. It can be used as a reliability monitor when the oxide thickness becomes too small for traditional electrical measurements. In this paper, the low voltage stress induced leakage current (LVSILC) for various oxide thicknesses ranging from 1.2 to 2.3 nm is investigated during constant voltage stress (CVS). From the LVSILC measurements, we shown that time to breakdown can be deduced as a function of the stress voltage. We also study the effect of elevated stress temperature on the time to breakdown. We show that temperature dependence of the time to breakdown is non-Arrhenius and decreases in a drastic way with a slope of 0.036 decade/°C.     

Semantics in Image and Video Retrieval Systems

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