Design and Testing of Three Earthing Systems for Micro-Grid Protection during the Islanding Mode

This paper presents and tests three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types when the MG transferred to the islanding mode. The main contribution of this work is including the models of all micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included with the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the islanding mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current pro-tection relays. With using TN earthing system, touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited values during islanding mode. For the two others earthing systems (TT and IT), fault currents are small and nearly equal to the over load currents which make over current protection relay can not differentiate between fault currents and overload currents. All models of micro sources, earthing systems, inverters and control schemes are built using Matlab?/Simulink? environment.

Comparison the Performances of Three Earthing Systems for Micro-Grid Protection during the Grid Connected Mode

This paper presents, tests and compares three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types during the connected mode. The main contribution of this work is including the models of all the micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included in the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the connecting mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current protection relays. With using TN system, Touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited value if current limiter is included with the transformer of the main grid which connects MG. For the two others earthing systems (TT and IT), fault current is small and nearly equal to the over load current which make over current protection relay can not differentiate between fault current and overload current. All models of micro sources, earthing systems, inverters, main grid and control schemes are built using Matlab?/Simulink? environment.

Calculation of Earthing System at Bangladesh Storm Water Pumping Station

A Storm Water Pumping Station funded by the World Bank is under construction and commissioning,of which the earthing system design is a crucial part for the electrical design.Based on IEEE and BS standards,this article fully introduces the analysis methodology and calculation of the system within the framework of the World Bank supported project.A solution of this practical case satisfied with the requirements of international standards is shown in order to bring experience and convenience for engineers who are dedicated to projects abroad.

Effects of Grounding (Earthing) on Massage Therapists: An Exploratory Study

It is well known that massage therapists often develop a number of health problems relatively early on in their career. A preliminary study showed that grounding massage therapists during their work may alleviate some of the health problems they encounter. A doubled-blind randomized controlled trial was designed to examine the effects of working and sleeping grounded for 4 weeks on massage therapists’ blood viscosity, stress (through HRV), inflammation (IFN-γ, IL-6, TNF-α, and hsCRP) and oxidative stress (MPO and MDA) biomarkers. The results show stress reduction as measured by heart rate, respir-atory rate and hear rate variability (HRV) and a lowering effect on blood viscosity that lasted for at least one week after ungrounding, with systolic blood viscosity becoming significantly lower at the end of the study. Inflammation markers (IFN-γ, TNF-α, and hsCRP) increased rapidly, within one week, after ungrounding. The findings suggest that grounding is beneficial for massage therapists in multiple domains relevant to health and wellbeing.

Research on the Fault Location Principle for the Earthing Electrode Line of the UHVDC Transmission System

The UHVDC transmission line transports large-capacity power, and its safety operation has very important rule on the safe operation of grid. Currently, in the DC transmission system, the earthing electrode line has the functions of ground potential fixing and bipolar imbalance current circulation during the operation of bipolar balance. Therefore the monitoring to the earthing electrode line operation is very essential. This article firstly introduced the current situation of the research on the earthing electrode line fault location method, then built the relevant PSCAD/EMTDC model for simulation verification of the current using Time Domain Reflectometry for the UHVDC earthing electrode line, and at last analyzed the reasons for the formation of the blind monitoring zones.

EarthingMethod for Protection of a Railway Rail Weighbridge System against Lightning

The rail weighbridge system of a railway freight station is introduced firstly, and then the earthing method for protection of the rail weighbridge system against lightning based on YLG-60 equipotential bonding surge protection device is shown.

Effects of the extrusion parameters on microstructure,texture and room temperature mechanical properties of extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy

Microstructure,texture,and mechanical properties of the extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy were investigated at different extrusion temperatures(260 and 320℃),extrusion ratios(10:1,15:1,and 30:1),and extrusion speeds(3 and 6 mm/s).The experimental results exhibited that the grain sizes after extrusion were much finer than that of the homogenized alloy,and the second phase showed streamline distribution along the extrusion direction(ED).With extrusion temperature increased from 260 to 320℃,the microstructure,texture,and mechanical properties of alloys changed slightly.The dynamic recrystallization(DRX)degree and grain sizes enhanced as the extrusion ratio increased from 10:1 to 30:1,and the strength gradually decreased but elongation(EL)increased.With the extrusion speed increased from 3 to 6 mm/s,the grain sizes and DRX degree increased significantly,and the samples presented the typical<2111>-<1123>rare-earth(RE)textures.The alloy extruded at 260℃ with extrusion ratio of 10:1 and extrusion speed of 3 mm/s showed the tensile yield strength(TYS)of 213 MPa and EL of 30.6%.After quantitatively analyzing the contribution of strengthening mechanisms,it was found that the grain boundary strengthening and dislocation strengthening played major roles among strengthening contributions.These results provide some guidelines for enlarging the industrial application of extruded Mg-RE alloy.

A review on biomedical and dental applications of cerium oxide nanoparticles——Unearthing the potential of this rare earth metal

Nanotechnology deals with particles ranging from 1 to 100 nm in size called as nanoparticles.These nano particles exhibit unique properties which find an application in many industries and medical fields.A growing body of evidence points out the newer developing technologies adopted in the field of medicine in terms of target therapies,imaging systems,drug deliveries,etc.is through the incorporation of nanoparticles.Cerium oxide nanoparticles have gained attention in the last decade due to exceptional properties such as redox activity,biofilm inhibition,antibacterial activity,anti-inflammatory activity,etc.The method of synthesis of cerium oxide nanoparticles plays a pivotal role in its application.It exhibits redox properties and catalytic activity and thus has found its use in biomedical applications.Nanoparticles are incorporated into dental materials such as restorative cements/sealants,adhesives,and denture systems to improve their properties.Among the various metal oxide nanoparticles,ce rium oxide nanoparticles(CeO_(2)NPs)are known to exhibit lower toxicity to mammalian cells and possess unique antibacterial mechanism.In addition,they exhibit potent properties such as antitumor,antiinflammatory,antibacterial activities,and functions as an immunosensor.CeO_(2)NPs have excellent scavenging properties for reactive oxygen species,which is why they are being considered for therapeutic purposes.In this review,various methods of synthesis of CeO_(2)NPs are discussed.Several factors that determine the particle size and morphology of these materials are important for biomedical and dental applications.Emphasis is given to preparation methods and variables such as calcination temperature,which have a profound effect on particle size and morphology.This article also presents various applications of CeO_(2)NPs in the biomedical and dental fields.

京津风沙源区NPP时空变化及其对治理工程实施的响应

利用遥感大数据对生态治理工程区域的净初级生产力和固碳能力进行长期动态监测可以实现对治理工程的实施效果的评价,同时为区域“碳中和”目标的实现及可持续发展提供有力支撑。利用Google Earth Engine(GEE)云计算平台,基于改进的CASA模型对京津风沙源治理工程区域的NPP进行计算。运用Sen斜率分析和MK趋势分析方法对2001—2020年间的NPP进行时空变化分析,并分析NPP对京津风沙源治理工程实施的响应。结果表明:1)在京津风沙源工程治理期间,京津风沙源区NPP总体呈波动上升趋势,平均增速为2.21 gC m^(-2)a^(-1),其中极显著增加区域占38.03%,说明京津风沙源治理工程对我国“碳中和”任务起到了积极作用,增加了区域的固碳能力;2)空间尺度上,京津风沙源区NPP和固碳量空间异质性较大,空间分布上主要呈现东部高,西部低的特点,其中,暖温带落叶阔叶林区域最高,温带荒漠区域最低;3)治理工程的实施所带来的NPP增长的速度在不同的区域并不一致,2001—2020年的NPP增速京津冀地区(4.74 gC m^(-2)a^(-1))>山西地区(4.52 gC m^(-2)a^(-1))>陕西地区(3.53 gC m^(-2)a^(-1))>内蒙古地区(1.55 gC m^(-2)a^(-1));4)生态工程实施所带来的生态环境的改善总体呈现先慢后快的特点,绝大部分区域后十年间的变化速率都显著大于前十年,而在生态环境较为恶劣、荒漠区域广布的内蒙古地区,生态环境的改善则具有一定的滞后性,2001—2010年NPP增速仅为0.04 gC m^(-2)a^(-1),直到2011年,NPP才开始有较为明显的增长,2011—2020年NPP增速为1.67 gC m^(-2)a^(-1)。风沙源治理工程需要长期坚持,才能取得更明显的成效。

基于变化更新的中东欧国家森林覆盖制图

[目的]分析中东欧国家森林资源覆盖状况,了解中东欧各国林业的现实情形和独特优势,为中国与中东欧国家加强林业合作提供基础数据。[方法]基于Google Earth Engine(GEE)平台获取中东欧国家2020年生长季无云影像,利用随机森林算法对影像进行分类,应用连续变化检测和分类算法得到森林变化信息并更新初步分类结果,最终获得中东欧国家土地覆盖分类结果。利用欧盟统计局土地利用/覆盖区域框架调查(LUCAS)数据、目视解译数据以及联合国粮农组织统计数据(FAOSTAT)对本研究分类结果进行验证和评估,结合谷歌高分辨率影像对制图结果进行分析。[结果]本研究分类结果利用LUCAS数据和目视解译数据的森林类型用户精度分别为0.930和0.911,生产者精度分别为0.860和0.956,总体精度分别为0.810和0.881,整体上优于GlobeLand30 2020产品(森林类型用户精度分别为0.920和0.900,生产者精度分别为0.690和0.840,总体精度分别为0.700和0.832)。根据研究结果计算出中东欧国家总体森林覆盖率为39.6%,相比GlobeLand30 2020结果(34.4%),与FAOSTAT的森林覆盖率(40.0%)更接近。目视上看,本制图结果在细节刻画上比GlobeLand30 2020产品更丰富,更能准确反映森林分布特征。截至2020年,中东欧国家森林覆盖呈北部、东南地区和西南地区丰富密集,中部分布广泛且相对较少的特点,爱沙尼亚、拉脱维亚、斯洛文尼亚、黑山等国家森林分布茂密,波兰、匈牙利等国家森林分布较为稀少。[结论]针对中东欧国家森林覆盖应用需求,本研究提出基于产品变化更新的森林覆盖制图方法,生产了中东欧国家2020年森林覆盖产品。本研究方法可为大区域森林覆盖制图提供新的借鉴和参考,结果有助于宏观了解中东欧国家森林覆盖状况。

基于Sentinel-5P的长三角大气NO_(2)污染特征及影响因子分析

基于哨兵-5P(Sentinel-5 Precursor,Sentinel-5P)卫星反演的NO_(2)柱浓度数据,利用Google Earth Engine云平台,结合自然因子和人为社会因子数据,分析长三角地区大气NO_(2)柱浓度的污染特征及影响因素。结果显示:(1)Sentinel-5P卫星反演的NO_(2)柱浓度数据与地面观测站NO_(2)质量浓度具有较好的相关性(r≥0.59,p<0.01),可较为准确地反映长三角地区大气NO_(2)污染状况;(2)长三角的大气NO_(2)柱浓度呈现季节性的周期波动,呈“冬高夏低”变化趋势;(3)大气NO_(2)柱浓度具有显著的空间异质性,整体上东北高,西南低,呈现出一条六安至台州,即“西北—东南”方向的NO_(2)柱浓度分界线,以及一个以环太湖城市群为中心的西南向“U形口”;(4)植被指数、高程、全社会用电量、第二产业产值、第三产业产值是长三角大气NO_(2)柱浓度空间分布的重要影响因子,区域大气NO_(2)柱浓度受因子交互作用显著,高程及植被指数与其他因子的交互作用q均在0.6以上。

Electrical Installation Safety Assessment of Buildings in Kumasi, Ghana

This study aims to evaluate the safety status of electrical installations in residential and commercial buildings within the Suame ECG strategic business unit, Ghana, focusing on compliance with international and Ghanaian wiring standards. The research assesses key factors influencing safety, including the certification of electricians, the quality of cable brands used, proper cable sizing, adherence to wiring color codes, the awareness and use of Residual Current Circuit Breakers (RCCBs), and the protection of earth electrodes. A descriptive research design was utilized, involving extensive field surveys and electrical installation audits. Data were collected using standardized tools and analyzed with SPSS software to evaluate the professional competencies of artisans and their adherence to safety standards. The findings indicate significant safety risks, with 69.7% of electricians lacking proper certification, leading to the widespread use of non-approved cable brands, improper cable sizing, and deviations from wiring color codes. Additionally, deficiencies were found in the awareness and use of RCCBs and the protection of earth electrodes. The study concludes with recommendations to enhance electrical safety, including mandatory certification for electricians, public awareness campaigns, regular inspections, and ongoing training and development programs. These measures are crucial for improving the overall safety and quality of electrical installations in the Suame area, Ghana.

基于GEE的苹果园地遥感信息提取研究——以陕西省渭北旱塬区为例

准确掌握苹果园空间分布及动态变化对苹果产业发展及规划具有重要意义。以陕西主要种植区———渭北旱塬区14个县(区)为研究区,基于Google Earth Engine(GEE)云计算平台,以2020年Sentinel-2卫星影像的Level-2A级数据为数据源,结合实地采样获得的461个苹果园样本点,构建包含光谱特征、遥感植被指数、纹理特征和地形特征等共计21个特征作为分类特征集,利用随机森林分类方法对研究区苹果园地空间信息进行提取。结果表明,研究区苹果种植面积为23.03万hm^(2),连片种植的苹果园主要分布于延安市洛川县、渭南市白水县、咸阳市淳化县和咸阳市彬州市,种植面积分别为3.54、3.21、2.90万hm^(2)和2.51万hm^(2);包含光谱特征、遥感植被指数、纹理特征和地形特征的分类特征集在提取苹果园空间格局方面效果最优,苹果园地提取的总体精度和Kappa系数分别为94%和0.86,高于其他分类特征组合。研究成果可为未来陕西省苹果产业合理规划及果园精细化管理提供科学依据和数据支撑。

基于GEE的Landsat-8与Sentinel-2影像在棉花种植提取中差异性分析及提取方法对比研究

棉花作为南疆地区重要的经济作物之一,在经济工作中起着至关重要的作用。及时、准确地获取棉花种植面积,对农业政策和经济发展具有重要意义。为了实现这一目标,需要综合分析不同方法和遥感数据对最终棉花种植面积制图精度的影响。本研究以新疆阿克苏地区棉花种植区为例,借助Google Earth Engine云平台,采用随机森林法(RF)、支持向量机法(SVM)、最小距离分类法(MDC)等3种机器学习方法,利用2类中分辨率影像提取棉花种植信息,充分评估使用的档案数据和官方统计数字。结果表明,采用Sentinel-2方法和RF获得了最优棉花图,随机森林法分类器的总体精度、Kappa系数和用户精度分别高达97.4%、96.7%和91.1%,分别比Landsat-8图像和RF模型的结果高出7.3百分点、0.081、2.8百分点。与官方统计数据相比,采用RF、SVM、MDC对Sentinel-2和Landsat-8图像的棉花种植面积估算图的精度分别为98.4%、95.8%、79.6%和90.3%、83.7%、72.5%。很明显,Sentinel-2和RF模型的组合与官方数据的一致性最高。对比分析结果表明,Landsat-8和Sentinel-2数据可用于大范围复杂种植结构的棉花高精度测绘。本研究结果有望为棉花大面积鉴别提供一定的理论指导和实践指导。

基于GEOVIS Earth Studio的高中地理教学案例开发——以“河流地貌”为例

信息技术与教学的融合发展是教育改革发展的方向,地理信息技术在教育信息化2.0时代给地理教育提供了丰富的教学资源,可有效提高教学效果。本文通过挖掘GEOVIS Earth Studio平台在地理教学中的功能优势,构建其教学应用模式,以人教版必修《地理1》“河流地貌”为例阐明平台操作过程并进行案例教学设计,创新地理教学技术手段,促进中学地理教学的信息化进程。

中国西南山地城市生态环境质量长时序变化及其评价——以重庆市为例

为研究中国西南地区山地城市的生态环境质量,选择以重庆市为例,利用遥感技术和Google Earth Engine(GEE)平台,构建遥感生态指数(RSEI,remote sensing ecological index),评价重庆市2000年~2021年的生态环境质量及其长时序变化。为探讨山地城市生态环境质量的主要影响因素,选取海拔、坡度、气温和降水四个影响因子,得到RSEI的海拔依赖性与坡度依赖性以及RSEI与气候因子的响应关系。结果表明:①遥感生态指数RSEI总体呈上升趋势,生态质量为“优”的面积增加了130.27%,生态质量为“差”的面积减少了65.68%,生态环境有明显的改善;②从RSEI随海拔、坡度变化曲线可以看出,0 m~1800 m范围内RSEI缓慢增加,1800 m~2800 m范围内开始减小,RSEI随坡度增加而增长,坡度>40°之后RSEI趋于平稳;③从RSEI与气候因子的响应曲线可以看出,温度和RSEI呈负相关,温度越高,RSEI越低;随着降水的增加,RSEI指数逐渐上升。研究表明,使用GEE平台可以对多云雾、植被覆盖度高的西南山地城市的生态环境质量进行长时序的监测和评价。研究结果可为中国西南地区山地城市的生态环境保护提供精细化管理,从而根据区域特色进行环境治理,实现生态环境与经济的协调发展。

基于GEE的阿拉善左旗植被时空变化特征及驱动因子分析

利用MODIS归一化植被指数产品(MOD13A1)和ERA5气象数据,基于GEE云平台以内蒙古阿拉善左旗为研究对象,研究该地区2000-2020年生长季植被覆盖度的时空变化特征,并结合降水、气温和地形数据研究气象要素、人类活动和地形条件对植被覆盖变化的驱动性。结果表明:(1)阿拉善左旗的植被覆盖主要集中在西北部,20 a间生长季植被覆盖度整体呈下降趋势,但在2012-2016有明显上升趋势。(2)降水和气温对阿拉善左旗的植被覆盖影响不明显,但降水影响程度略高于气温,而人类活动则明显有助于阿拉善左旗植被的改善。(3)阿拉善左旗植被覆盖度在不同海拔高度上呈现明显差异,海拔越高植被覆盖度越大,有必要针对不同海拔高度制定相应的改善措施。

基于Google earth engine渭-库绿洲果园遥感提取

针对干旱区果园大面积遥感提取困难、识别精度低等问题,本研究基于GEE(Google earth engine)平台,综合应用Sentinel-1/Sentinel-2影像构建特征集。通过对比原始特征组合、Jeffries-Matusita(J-M)距离、属性重要度3种优化方式,结合随机森林(Random forest,RF)分类方法,对比得到最佳优化方式,探索果园最优分类特征集。结果表明:识别效果最好的方案为G17 JM,总体精度为91.25%,kappa系数为0.89,面积精度为82.55%。最优特征集为B8_asm、B8_ent、B8_idm、NDVI re3、B6、B7、a、e、b、EVI、B11、B8A、B8、VV。使用J-M距离进行特征集优化,有效降低数据量、提高计算效率,更有利于精确遥感识别果园种植面积。表明GEE快速、准确获取果园种植面积的可行性,为获取果园动态变化提供强有力的基础。

基于物候特征的时序SAR水稻指数构建及验证

准确获取水稻的种植分布情况对于农业生产管理具有重要意义。针对多云雨地区缺乏有效光学影像影响水稻识别的问题,该研究以多时相Sentinel-1 SAR影像为主要数据源,基于后向散射系数的时序变化提取多个特征构建遥感指数以实现水稻提取。首先采用SG(savitzky-golay)滤波算法对不同地物的后向散射系数时序曲线进行平滑处理;然后计算像元与水稻样本点在水稻生育期内时序曲线的动态时间规整距离、像元时序曲线最小值与水体的差异、像元时序曲线最大值与植被的差异这3个值以量化水稻生育期的不同特征,并将三者相乘作为归一化差异水稻遥感指数(normalized difference rice index, NDRI)进行阈值分类后得出水稻空间分布情况。为验证该模型的有效性,该研究选取云南省盈江县为研究区。结果表明:1)基于时序SAR特征能够实现对水稻实现准确提取,模型总体精度达到89.42%,Kappa系数为0.82;2)盈江县2023年水稻种植面积为199.83 km^(2),且大盈江沿岸种植面积占全县的90.76%,水稻种植存在明显的集聚性。该研究为多云雨地区的水稻空间分布的准确提取提供一种方法,并可为相关农业政策制定提供参考。

基于MODIS-EVI的四川省2000—2020年植被覆盖变化趋势的地形分布特征

通过Google Earth Engine获取MODIS-EVI数据,在ArcGIS中运用趋势分析和分布指数等方法定量分析四川省2000—2020年的植被覆盖度变化趋势的地形分布特征。结果表明:在植被覆盖变化中,增加类型的面积占46.35%,减少类型的面积占45.81%,不变类型的面积占7.84%;植被覆盖减少类型主要分布在高程小于500 m、3000—4500 m,坡度小于5°,平地、南坡、西南坡,平原、台地等区域,以灌丛和草地为主;植被覆盖增加类型主要分布在高程500—3000 m,坡度5—15°,东北坡、东坡、东南坡,丘陵、小起伏山地、中起伏山地等区域,以耕地和林地为主;植被覆盖不变类型主要分布在高程大于4500 m,坡度大于15°,北坡、西坡、西北坡,大起伏山地、极大起伏山地等区域,以建设用地和高山植被为主。研究结果从宏观上揭示了四川省近20年植被覆盖变化趋势的地形分布特征,可以为四川省在未来的生态植被恢复方案的制定提供一些参考。