110、220kV变压器中性点过电压计算分析及其保护方式

为了限制短路电流和满足继电保护整定的需要,在110、220 kV系统中,只有部分变压器中性点接地运行。本文详细论述了在各种故障情况下(单相接地故障,雷电进波,非全相运行)不接地变压器中性点过电压的产生机理,通过理论推导得到了计算变压器中性点过电压值的理论公式并计算了中性点过电压理论值,指出:当系统发生单相接地故障时,变压器中性点过电压即为故障点的零序电压;单相接地短路点离母线越近,变压器中性点过电压越大;当失地系统发生单相接地时,变压器中性点电压将上升到相电压。并在电磁暂态分析程序ATP中计算了一个110 kV系统中不接地变压器中性点在各种故障情况下的过电压值,仿真计算结果与前面理论论述计算完全符合,证明本文提出的变压器中性点过电压产生机理和过电压理论计算是完全正确的,并根据取得的中性点过电压值给出了110、220 kV变压器中性点的保护方式。通过理论分析和仿真验证,证明减小接地程度系数(增加系统接地点)和选择合适的中性点保护避雷器是降低变压器中性点过电压的有效措施。

Monitoring of Soil Loss from Erosion Using Geoinformatics and Geotechnical Engineering Methods

In this study, the position of all major rill and gully erosion sites were located using hand held GPS （Global Positioning System） receiver during reconnaissance surveys. Based on severity rating and geopolitical considerations, six of the erosion gully sites were selected for monitoring. Control points were established around each of the gully sites using three Leica 500 dual frequency GPS receivers by method of DGPS （differential GPS） surveys. Detailed topographical survey of the gully sites was carried out using total stations. With the aid of SPOT satellite imageries in combination with total station data and GIS （geographic information system） location maps, contoured maps along with DEM （digital elevation model） were generated using ARCGIS 9.2 software. The morphological parameters of the gullies including depth, width, length and area of the gullies were determined. Volumetric estimate of the amount of soil loss from gully erosion was also carried out. Soil samples were recovered from the gully sites to determine their erodibility and other parameters to be used for soil loss modeling. The result of the studies was used as an indicator for determining the gully initiation point. Slope-area relationship and threshold of gully initiation was established. The minimum volume of soil loss occurred in gully No. 2 （Queen Ede）. The minimum AS^2 value was 345 while the maximum was 3,267.

Partitioning of vertical water loss in reed swamp wetlands:Theory,research and application

This paper proposes an on-site monitoring system for evaporation （Ew） and evapotranspiration （ET） in wetlands called the Compensation Evapotranspiration Observation System. Considering the characteristics of wetlands environment and emergent plants, the vertical flux of water loss in wetlands can be separated using the system based on compensation principle. A comparison research on water loss through ET in reed （Phragmites australis） stands between Zhalong wetland and Baiyangdian wetland was carded out in 2004-2009. In Baiyangdian wetland, the ET rates from three reed stands with different leaf area indexes were measured. The results show that annual ET in Zhalong wetland was 739-886 mm during study period. Comparatively, annual ET of the three reed stands in Baiyangdian wetland was 970-1117 mm, 1261-1452 mm and 1759-2035 ram, respectively. The ET rates in Baiyangdian were stronger than in Zhalong because of the effects of geography and climate characteristics. Moreover, seasonal dynamic changes and influence factors of transpiration-acting factor from the two wetlands were also analyzed. It is indicated that the transpirafion-actng factor can be affected by geographic location, aboveground biomass, plant growth and climate conditions.

An Integrated Quantitative Method to Simultaneously Monitor Soil Erosion and Non-Point Source Pollution in an Intensive Agricultural Area

In China, some areas with intensive agricultural use are facing serious environmental problems caused by non-point source pollution(NPSP) as a consequence of soil erosion(SE). Until now, simultaneous monitoring of NPSP and SE is difficult due to the intertwined effects of crop type, topography and management in these areas. In this study, we developed a new integrated method to simultaneously monitor SE and NPSP in an intensive agricultural area(about 6 000 km2) of Nanjing in eastern China, based on meteorological data,a geographic information system database and soil and water samples, and identified the main factors contributing to NPSP and SE by calculating the NPSP and SE loads in different sub-areas. The levels of soil total nitrogen(TN), total phosphorus(TP), available nitrogen(AN) and available phosphorus(AP) could be used to assess and predict the extent of NPSP and SE status in the study area.The most SE and NPSP loads occurred between April to August. The most seriously affected area in terms of SE and NPSP was the Jiangning District, implying that the effective management of SE and NPSP in this area should be considered as a priority. The sub-regions with higher vegetation coverage contributed to less SE and NPSP, confirming the conclusions of previous studies, namely that vegetation is an effective factor controlling SE and NPSP. Our quantitative method has both high precision and reliability for the simultaneous monitoring of SE and NPSP occurring in intensive agricultural areas.

Capacity of soil loss control in the Loess Plateau based on soil erosion control degree

The capacity of soil and water conservation measures, defined as the maximum quantity of suitable soil and water conservation measures contained in a region, were determined for the Loess Plateau based on zones suitable for establishing terraced fields, forestland and grassland with the support of geographic information system(GIS) software. The minimum possible soil erosion modulus and actual soil erosion modulus in 2010 were calculated using the revised universal soil loss equation(RUSLE), and the ratio of the minimum possible soil erosion modulus under the capacity of soil and water conservation measures to the actual soil erosion modulus was defined as the soil erosion control degree. The control potential of soil erosion and water loss in the Loess Plateau was studied using this concept. Results showed that the actual soil erosion modulus was 3355 t·km^(–2)·a^(–1), the minimum possible soil erosion modulus was 1921 t·km^(–2)·a^(–1), and the soil erosion control degree was 0.57(medium level) in the Loess Plateau in 2010. In terms of zoning, the control degree was relatively high in the river valley-plain area, soil-rocky mountainous area, and windy-sandy area, but relatively low in the soil-rocky hilly-forested area, hilly-gully area and plateau-gully area. The rate of erosion areas with a soil erosion modulus of less than 1000 t·km^(–2)·a^(–1) increased from 50.48% to 57.71%, forest and grass coverage rose from 56.74% to 69.15%, rate of terraced fields increased from 4.36% to 19.03%, and per capita grain available rose from 418 kg·a^(–1) to 459 kg·a^(–1) under the capacity of soil and water conservation measures compared with actual conditions. These research results are of some guiding significance for soil and water loss control in the Loess Plateau.

Sediment Pollution Assessment of Abandoned Residential Developments Using Remote Sensing and GIS

The current economic crisis has left numerous residential developments in the southeastern United States in various stages of construction. Many of them are currently graded and essentially abandoned, creating a major source of sediment runoff to waterways. Residential development locations with significant bare soil areas were identified through classification of Landsat 5 TM satellite imagery and subsequently verified from high-resolution county aerial photographs. The revised universal soil loss equation (RUSLE) was used in a geographic information system (GIS) as a tool for prioritizing identified locations on the basis of potential soil loss assuming the worst case scenario of a completely unmaintained site. Initial GIS identification indicated 301 sites with a total bare soil area of 2 378 ha over three counties in Upstate South Carolina. A random sample of 153 sites was visited over 17 days and assessed using a mobile GIS, global positioning system (GPS), and digital camera for field validation. Results indicated that 78% (119) of the sites were classified correctly (residential construction sites in varying stages of completion); 88% of identified areas were less than 25% built compared to the previous year; 48% were categorized as moderate to severe problems. Abandoned and unfinished developments in Upstate South Carolina may represent a major source of sediment pollution to streams. Well-maintained erosion control devices may be useful in preventing offsite sedimentation.