含DG的配电网保护新方案

分布式电源(DG)接入配电网弥补了大电网的很多不足。然而大量的DG的接入改变了传统配电的拓扑结构,给传统的继电保护带来了巨大的压力。配电网中潮流和故障电流会随着DG的出力以及负荷的情况实时变化。使得继电保护出现拒动、误动及灵敏度降低等问题。本文提出了一种基于通信技术和自适应电流保护相结合的新方案,在一定程度上解决了DG接入配电网带来的问题。通过MATLAB验证,本方案具有较大的保护范围和灵敏度高等优点。     

采用保护测试仪的无源电流保护试验方法

无源电流保护整组试验目前普遍采用大电流发生器,通过在电流互感器一次侧增大电流方式来完成.在电流保护动作值较大时,大电流发生器输出电流幅度通常达不到要求,以致整组试验无法完成.提出将保护测试仪2个电流源设定到串联输出方式,使最大输出容量剧增,进而完成无源电流保护整组试验.     

保护接地与漏电总保护

保护接地与保护接零,都是传统的防触电手段。漏电保护开关出现后,随着其性能的不断提高,ＴＴ系统（保护接地系统）增加了安装漏电保护开关的要求,在农村低压电力技术规程中规定：“ＴＴ系统应装设漏电总保护和漏电末级保护”。但是随着《电力法》的颁布和实施及农村用电的发展,漏电总保护不完善之处逐渐暴露出来,必须引起高度重视。漏电总保护的漏电动作电流要躲过电网正常泄漏电流,因此它的灵敏度不高。如按农村低压电力技术规程规定,选用ＤＺ１５Ｌ－４０型漏电保护开关,其额定漏电动作电流７５ｍＡ,额定漏电不动作电流４０ｍＡ…     

断路器零序电流保护与剩余电流保护的区别

低压断路器具有的接地保护功能一般分为零序电流保护和剩余电流保护,在实际应用中两者之间的区别如下. 1 零序电流保护     

电流互感器的极性与电流保护

在电力系统中电流互感器的作用是把大电流变成小电流,将连接在继电器及仪表的二次回路与一次电流的高压系统隔离,并将一次电流减小到5安或1安两种标准的二次电流值.电流互感器的极性与电流保护密切相关,特别是在农电系统中,电流保护起主导作用,所以必须掌握好极性与保护的关系.下面介绍一下电流互感器极性和常用电流保护的关系,以及易出错的二次接线.     

对提高微机电流保护灵敏度的构想

微机保护应该发展为具有自动识别系统运行方式和故障状态的能力 ,并针对状态的改变 ,实时的调整保护的性能 ,使继电保护达到最佳效果。就小电流接地系统如何提高灵敏度和判别故障类型为例 ,加以说明。1　提高灵敏度在单电源小电流接地系统中 ,常规电流保护受系统运行方式和故障类型的影响 ,往往灵敏度不能满足要求 ,而在微机保护中 ,上述问题仍然存在 ,可以说不少微机保护的原理基本上和传统的保护一样 ,仅仅是传统保护的翻版 ,特别在电流保护上更为明显。归结起来 ,主要是电流保护的定值是固定不变的 ,不能适应不断变化的运行方式、不同故…     

剩余电流保护系统运行及管理讲座(二)农村低压电网剩余电流保护系统

1农村低压电网剩余电流保护装置 1.1剩余电流动作保护器 1.1.1 家用及类似用途剩余电流断路器 家用及类似用途剩余电流断路器可分为带过电流保护和不带过电流保护2种,适合于非专业人员使用.主要使用在商店、办公楼、饭店及城乡居民住宅等建筑物中,对低压线路和用电设备进行保护.     

变压器差动保护的不平衡电流应对措施

1 比率差动保护原理简述 变压器差动保护是变压器的主保护,所谓比率制动特性差动保护,简单说就是使差动电流定值随制动电流的增大而按某一比率提高,使制动电流在不平衡电流较大的外部故障时有制动作用,而在内部故障时制动作用最小.之所以采用比率制动,是为了防止保护区外故障引起不平衡的差动电流造成保护误动.由多微机实现的比率差动保护的动作特性如图1所示.     

母差保护向量集中测试方法

针对传统母差保护向量测试方法效率低、安全风险高的问题,提出一种母差保护向量集中测试方法。该方法采用试验仪器在一次侧加电流模拟负荷电流,以指定间隔为基准,检查其他间隔电流幅值和相位,从而判断二次回路接线是否正确。实际应用表明,该方法能够极大地提高工作效率,降低安全风险。     

过电流保护误动作分析

电力系统在运行时常常因为系统中的过电流保护发生误动作而造成事故,给经济带来巨大的损失。该文针对过电流保护误动作进行分析,且针对各种情况提出了应采取的措施,并提出了过电流保护改进的方向。     

Overland water and salt flows in a set of rice paddies

Cultivation of paddy rice in semiarid areas of the world faces problems related to water scarcity. This paper aims at characterizing water use in a set of paddies located in the central Ebro basin of Spain using experimentation and computer simulation. A commercial field with six interconnected paddies, with a total area of 5.31 ha, was instrumented to measure discharge and water quality at the inflow and at the runoff outlet. The soil was classified as a Typic Calcixerept, and was characterized by a mild salinity (2.5 dS m⁻¹) and an infiltration rate of 5.8 mm day⁻¹. The evolution of flow depth at all paddies was recorded. Data from the 2002 rice-growing season was elaborated using a mass balance approach to estimate the infiltration rate and the evolution of discharge between paddies. Seasonal crop evapotranspiration, estimated with the surface renewal method, was 731 mm (5.1 mm day⁻¹), very similar to that of other summer cereals grown in the area, like corn. The irrigation input was 1874 mm, deep percolation was 830 mm and surface runoff was 372 mm. Irrigation efficiency was estimated as 41%. The quality of surface runoff water was slightly degraded due to evapoconcentration and to the contact with the soil. During the period 2001–2003, the electrical conductivity of surface runoff water was 54% higher than that of irrigation water. However, the runoff water was suitable for irrigation. A mechanistic mass balance model of inter-paddy water flow permitted to conclude that improvements in irrigation efficiency cannot be easily obtained in the experimental conditions. Since deep percolation losses more than double surface runoff losses, a reduction in irrigation discharge would not have much room for efficiency improvement. Simulations also showed that rice irrigation performance was not negatively affected by the fluctuating inflow hydrograph. These hydrographs are typical of turnouts located at the tail end of tertiary irrigation ditches. In fact, these are the sites where rice has been historically cultivated in the study area, since local soils are often saline-sodic and can only grow paddy rice taking advantage of the low salinity of the irrigation water. The low infiltration rate characteristic of these saline-sodic soils (an experimental value of 3.2 mm day⁻¹ was obtained) combined with a reduced irrigation discharge resulted in a simulated irrigation efficiency of 60%. Paddy rice irrigation efficiency can attain reasonable values in the local saline-sodic soils, where the infiltration rate is clearly smaller than the average daily rice evapotranspiration.     

瓦房店市水果生产标准化发展研究

瓦房店市是我国重要的水果生产基地,在国内水果生产领域占有重要地位。随着水果市场化的不断深入,如何满足和适应国内外市场需求成为瓦房店市水果生产的关键问题。从瓦房店市水果生产实际出发,阐述了实施水果生产标准化的必要性,提出了发展水果生产标准化的具体措施。     

金谷子耐旱TG118引种试种及推广应用

对引进的谷子新品种金谷子耐旱TG118进行品种比较试验和多点试种。结果表明：该品种抗旱、耐瘠、适应性强,稳产、高产、抗病抗风抗倒伏强,品质优良,粮草兼用,种植简单,省工易管;一般产量在6000kg/hm2以上,比当地主栽品种增产20%以上。最高产量达9450kg/hm2,适于在辽西北地区推广应用。     

对《种子法》存在问题的探讨

《种子法》是我国种植业第一部法律。自实施以来,为依法加强种子管理提供了有力的法律支撑,促进我国种子产业发生翻天覆地的变化。但随着依法管理工作的深入和种子产业的快速发展,《种子法》及配套规章的一些问题逐步显现出来。对《种子法》及配套规章存在的问题进行深入分析,对需要进一步补充的章节以及需要调整的内容进行深入探讨,以求更加完善和明确。     

Review of the Egyptian experience in implementing land drainage projects

About 30 years have passed since the Government of Egypt embarked on implementing a series of large scale drainage projects. At present, about 3.8 million acres have been provided with drainage systems on the basis of systematic pre-drainage investigations and designs. The target is to provide drains in approximately 6.4 million acres in the Nile Valley and Delta.The implementation of the subsurface drainage system is carried out by the public sector and private contractors under direct supervision of governmental regional departments. The implementation process depends on many factors related to the drainage material, machinery, manpower, site requirements, farmers and organizations involved. Problems and constraints are sometimes challenging, however, the annual rate of implementation has gradually increased to 170,000 acre/year.This paper discusses the different aspects involved in the implementation process of drainage systems. The development in materials, machinery and construction technologies will be reviewed. Institutional and management factors are going to be also considered.     

和谐社会理论建设的几点哲学思考

在新世纪,面对机遇和挑战,党的十六大把“社会更加和谐”作为全面建设更高水平的小康社会的一个重要目标。中国人素有社会和谐的理想;西方人自古也向往社会和谐;借鉴东西方两种和谐社会思想的经验、教训,构建社会主义和谐社会理论。     

A European irrigation map for spatially distributed agricultural modelling

We present a pan-European irrigation map based on regional European statistics, a European land use map and a global irrigation map. The map provides spatial information on the distribution of irrigated areas per crop type which allows determining irrigated areas at the level of spatial modelling units. The map is a requirement for a European scale assessment of the impacts of irrigated agriculture on water resources based on spatially distributed modelling of crop growth and water balance. The irrigation map was compiled in a two step procedure. First, irrigated areas were distributed to potentially irrigated crops at a regional level (European statistical regions NUTS3), combining Farm Structure Survey (FSS) data on irrigated area, crop-specific irrigated area for crops whenever available, and total crop area. Second, crop-specific irrigated area was distributed within each statistical region based on the crop distribution given in our land use map. A global map of irrigated areas with a 5′ resolution was used to further constrain the distribution within each NUTS3 based on the density of irrigated areas. The constrained distribution of irrigated areas as taken from statistics to a high resolution dataset enables us to estimate irrigated areas for various spatial entities, including administrative, natural and artificial units, providing a reasonable input scenario for large-scale distributed modelling applications. The dataset bridges a gap between global datasets and detailed regional data on the distribution of irrigated areas and provides information for various assessments and modelling applications.     

粉质仪和拉伸仪在面粉生产中的应用

在介绍粉质仪和拉伸仪结构和原理的基础上,探讨了粉质曲线中吸水率、形成时间、稳定时间、弱化度和评价值等指标与面粉品质的关系,以及如何根据拉伸曲线中面团最大拉伸阻力、延伸度和拉伸曲线面积等指标来评价面团品质,并结合生产实际,概述了粉质仪和拉伸仪在面粉生产中的作用。     

农村信息化服务的现状及建设措施

分析当前我国农村信息化服务的现状,提出加强农村信息化服务的新举措。     

车辆ABS控制算法的研究及探讨

对现代汽车的ABS控制算法作了一些简单的介绍,同时指出了它们的一些缺陷,相应地提出了几种对ABS的其它控制方法并加以探讨,其中着重论述了ABS门限值控制算法中参考车速的确定方法和基于附着系数的控制算法。