Protection of motors against high voltage switching surges

The authors review the results from an extensive Electric Power Research Institute (EPRI) project on turn insulation capability of motors and also review other publications in order to quantify the surge environment and the surge strength of typical utility motors. The results are compared with standards for the surge strength of motors. The application of vacuum switchgear are surge capacitors is critically examined. Guidelines for new and existing motor installations, a procedure for analyzing surge related failure, and some recommendations for motor manufacturers are provided     

Small induction motor noise calculation

There has been an increasing demand for a quiet induction motor. Electromagnetic noise is jarring to the ear. Most offensive electromagnetic noise is generated when the natural frequencies of the stator coincide with or are close to the frequencies of the magnetomotive forces. In this paper, electromagnetic noise is calculated by boundary element method (BEM) program using the electromagnetic forces of Maxwell stress. The natural frequency and behavior of the stator are calculated by mechanical finite element method (FEM), considering the contact between stator core and frame. Spring elements are introduced between the stator frame and the stacked core. Vibration is calculated by mechanical FEM. Calculated and experimental noise level were within 3 dB(A) at 1200 and 4080 Hz.     

牵引电动机轴承寿命计算方法研究

以ZQDR-410型牵引电动机为例,用4种方法计算了轴承的受力和轴承寿命。通过计算发现,用不同的计算方法计算出的轴承寿命相差很大。对造成差异的原因进行了分析,最后提出了一种作者认为比较合理的计算方法。     

Estimation of peak transient voltages at wind turbine generator terminals

This paper proposes equivalent circuits and a method for the estimation of the peak transient voltages at generator terminals in wind turbines equipped with back‐to‐back converters. Equivalent circuits as well as a way of phase‐to‐phase and phase‐to‐ground voltages estimation in back‐to‐back converter are presented. Proposed theoretical background is well confirmed by small‐scale measurements. It is shown and proven that phase‐to‐ground voltages represent a dominating threat for the wind turbine generators insulation. Copyright © 2014 John Wiley & Sons, Ltd.     

圆筒形多层砌体非稳态热计算

对圆筒形多层砌体非稳态传热用有限差分法进行了分析,提出圆筒形多层炉墙非稳态传热的界面层温度计算公式、外表面层温度计算公式以及炉墙温度场计算公式。计算结果表明,炉墙外表面温度计算值与实测值误差仅为4.06％。吻合较好,可满足工程要求。     

Practical ambiguities during calculation of energy ratios and their impacts on life cycle assessment calculations

The energy ratio metrics are increasingly important means of assessing the efficiency of energy production for emerging biofuels platforms, making comparisons among multiple alternatives, and formulating policies to foster commercialization of sustainable energy systems. However, these metrics are susceptible to inadvertent or meaningful mathematical manipulation, whereby the same dataset can be used to compute dramatically different values of energy return on investment (EROI). In this study, previously published life cycle assessment (LCA) data for algal biofuels, corn ethanol, and switchgrass ethanol are used to demonstrate how seven seemingly reasonable EROI formulations give rise to a wide range of output values. It is then demonstrated that production of bioelectricity, and to a lesser extent, other co-products, significantly increases EROI ambiguity. Overall, the EROI results are used to illustrate how EROI ambiguity makes it difficult to properly assess the energetic favorability of a particular energy system or to make accurate comparisons among multiple systems. It is then recommended that all future biofuels studies restrict themselves to usage of “EROI₁”, which documents all input and outputs as explicit terms, to mitigate EROI ambiguity and improve policy decision-making.     

Calculation of machine winding electrical parameters at highfrequencies for switching transient studies

This paper describes a multiconductor transmission line approach for calculating the machine winding electrical parameters for switching transient studies. The technique is based upon the solution of the one dimension diffusion equation in the slot of electrical machines. The coil electrical parameters are calculated considering both the magnetic flux in the iron and in the air. Several practical formulations for calculating the winding electrical parameter are proposed which take into account the machine winding design characteristics. The computer models are validated by a comparison of measured and calculated results in two high voltage induction motors     

三点击实法的程序计算方法

根据三点击实法的原理,用计算器编程计算压实度D和最优含水量与填土含水量的差值(w0p-wf),较传统作图法省时省事.该方法快捷、准确,是土石坝施工中控制粘性土压实质量的实用方法.     

电站锅炉效率在线计算方法

提出了一种电站锅炉效率的在线计算方法 ,它基于燃煤的低位发热量、燃煤的灰分、排烟温度、氧量、飞灰含碳量和参考温度计算锅炉的效率 ,适用于电站锅炉燃烧的监控和优化运行     

Investigation of the effect of repetitive voltage surges on epoxyinsulation

The aging of epoxy electrical insulation by unipolar, repetitive voltage surges has been investigated to determine whether such surges can precipitate premature failure of high-voltage motor windings and gas insulated switchgear spacers. A full factorial statistical test was devised and performed on 180 pure epoxy insulation specimens to examine the effect of voltage magnitude, polarity, and surge repetition rate on the life of unfilled epoxy specimens containing a needle-plane electrode geometry. All factors and interactions were determined to have a significant effect on the life, and life prediction equations were estimated. Increasing the voltage magnitude or repetition rate, decreased or increased the life, respectively. Aging was found to occur at as low a stress as 2 MV/cm. Gradual aging of the epoxy does occur under repetitive voltage surges. Based on a realistic number of surges with typical voltage amplitudes which can normally occur from vacuum switchgear during service, gradual deterioration of the epoxy turn insulation in motor stator windings is possible in some situations. Situations where surge aging may occur are identified     

A new approach to direct torque control of induction motor drivesfor constant inverter switching frequency and torque ripple reduction

In this paper, a new approach to the direct torque control (DTC) of induction motor drives is presented. In comparison with the conventional DTC methods, the inverter switching frequency is constant and is dramatically increased, requiring neither any increase of the sampling frequency, nor any high frequency dither signal. The well-developed space vector modulation technique is applied to inverter control in the proposed DTC-based induction motor drive system, thereby dramatically reducing the torque ripple and speed ripple. As compared to the existing DTC approach with constant inverter switching frequency, the presented new approach does not invoke any concept of deadbeat control, thereby dramatically reducing the computations. Experimental results are illustrated in this paper confirming that the proposed DTC method has the above-mentioned features even at the low speed range down to ±1 r/min     

汽轮机性能老化轨迹的现场实用确定方法

对现行的汽轮机性能老化轨迹确定方法进行了分析,推出了现场利用高压缸效率相对变化率来计算老化系数的公式,给出了老化折算系数、日常老化系数预测、最终老化系数确定的方法,举例对老化系数进行了预测、确定和分析。方法简单实用,且老化系数能贴近本机实际,可供研究机构和兄弟电厂借鉴。     

宁夏汉延渠斗口闸孔出流的水力计算

分析了宁夏汉延渠斗口闸孔出流存在的主要问题。通过试验提出了闸后暗涵自由出流、淹没出流以及有压管流流态的判别方法,提出了相应的水力计算公式,可供工程采用。     

Analytical technique of lighting surges induced on grounding meshof PWR nuclear power plant

It is noted that an analytical technique is needed to make a qualitative and predictive evaluation of transient voltages induced on local grounding meshes and instrumentation cables by a lightning strike on a lightning rod in a PWR (pressurized water reactor) power plant. An experiment with lightning surge impulses in a PWR power plant was set up to observe lightning-caused transient voltages. Experimental data are compared with EMTP (electromagnetic transient program) simulation results, and an improved simulation method is developed. The improved method provides a good estimation of induced voltages on grounding meshes and instrumentation cables. An accuracy factor of 3-5 was reached     

展望21世纪的内燃机车和内燃动车

展望了21世纪初叶世界铁路牵引动力总的发展趋势,特别是内燃机车和内燃动车的发展趋势及其在铁路牵引动力中的地位;概述了世界主要国家和厂家为21世纪准备的内燃机车和内燃动车;特别指出了21世纪中国内燃机车和内燃动车的革新和发展方向。     

Power generation potential of liquified natural gas regasification terminals

The share of liquified natural gas (LNG) in the international trade of natural gas (NG) is continually increasing. This presents increasing opportunities to build power plants to generate electricity at LNG regasification terminals rather than wasting the power generation potential of LNG at about −162°C by regasifying it by seawater, ambient air, or by burning NG. Typically, over 5% of the NG received at LNG plants is used to liquify the remaining incoming gaseous NG at environmental conditions. Theoretically, all the energy consumed at LNG liquefaction plants can be recovered at LNG regasification terminals. In this study, the theoretical and practical power generation potential of regasified LNG is investigated by performing energy and exergy analyses. It is shown that up to 0.191 kWh of electric power can be generated during the regasification of LNG per standard m³ of NG regasified. The potential economic gains associated with power generation at LNG regasification facilities are demonstrated by analyzing the 2018 LNG imports of Turkey as a case study and the world. It is shown that the 314 million tons of LNG imported globally in 2018 has the electric power generation potential of 88 billion kWh with a market value of over 10 billion USD. It also has the potential to offset 38 million tons of CO₂ emissions.     

Monte Carlo analysis of wind farm surge arresters risk of failure due to lightning surges

This paper presents a Monte Carlo procedure intended for the assessment of the metal-oxide (MO) surge arresters risk of failure in onshore wind farms. It focuses on the energy withstand (absorption) capability of the MO surge arresters in relation to lightning surges and in terms of their risk of failure assessment. Presented methodology accounts for the fact that the lightning itself is stochastic in nature and that the MO surge arrester energy capability is a statistical quantity. The well-known backsurge phenomenon is employed as a means for studying the MO surge arresters energy stresses due to lightning surge transients (in onshore wind farms), where the associated transient (i.e. high-frequency) models of particular wind farm components feature prominently. Necessary numerical simulations are carried-out with the well-known EMTP-ATP software package. This procedure could be seen as beneficial in selection of the optimal MO surge arrester energy withstand capability for wind farm projects situated in areas marked with high keraunic levels and/or having high soil resistivity.     

Different surface treatments on performance of super capacitor pole terminals

本工作介绍了超级电容极柱端子两种表面处理（喷铜磨削和镀银）方式下，组装成模组后内阻的差异，集成为储能电源装车使用后，内阻一致性变化差异，得出超级电容极柱端子两种不同表面处理对其使用性能的影响差异结果。最终结果表明，镀银超级电容比喷铜磨削超级电容的初始性能和使用性能都更优。