Analysis of a Large Grounding System and Subsequent Field Test Validation Using the Fall of Potential Method

This paper examines various aspects of the design process and subsequent field test measurements of a large and complex substation grounding system. The study and measurements show that soil layering and lead interference can have a significant impact on the appropriate test location that yields the exact substation ground impedance. Applying a specific percentage rule such as the 61.8% rule for uniform soils to obtain the true ground impedance may lead to unacceptable errors for large grounding systems. This poses significant problems when attempting to validate a design based on raw test data that are interpreted using approximate methods to evaluate substation ground impedance, and determine ground potential rise (GPR), touch and step voltages. Advanced measurement methodologies and modern software packages were used to obtain and effectively analyze fall of potential test data, compute fault current distribution, and evaluate touch and step voltages for this large substation. Fault current distribution between the grounding system and other metallic paths were computed to determine the portion of fault current discharged in the grounding system. The performance of the grounding system, including its GPR and touch and step voltages, has been accurately computed and measured, taking into account the impedance of the steel material used of the ground conductors and circulating currents within the substation grounding system.

Proposal of Walking to Prevent a Fall of a Planetary Exploration Legged Rover Using Effect of Loose Soil Caused by a Propagation of Vibration

In this study,a walking method that prevents a fall of the planetary exploration-legged rover is proposed.In the proposed walking method,the leg is sunk by giving vibration to the ground.The posture of the rover is changed to prevent a fall of the rover by sinking the leg.First,the relationship between the kind of vibration and the subsidence of the leg is confirmed.In this experimental result,the leg is shown to be easy to sink to the ground by giving vibration.Moreover,the larger the vibratory force is,the easier the leg sinks to the ground.Finally,the legged testbed walks on the loose ground with a slope using the proposed walking method.In this experimental result,the testbed is difficult to fall down when it uses the proposed walking.Moreover,the angle of a slope that the testbed can walk becomes large by using the proposed walking.

复杂环境下跨路桥梁拆除爆破方案优化研究

福建省大井垄大桥因道路改造需爆破拆除,该桥梁为钢筋混凝结构,长187 m,宽24 m,中间有5排墩柱,共6跨,跨径30 m,周围环境复杂,桥梁底面距离桥下马路最高达到29 m,需严格控制爆破飞石、爆破振动、触地振动等危害。通过理论分析并运用ANSYS/LS-DYNA数值模拟软件对对称起爆、单向起爆和中间起爆三个预选方案进行模拟,通过对比爆堆范围和触地振动大小,发现中间起爆方式效果最好。通过对比不同排间延期时间的模拟结果,对原设计的短延期爆破方案进行优化,最终采用中间起爆长延期的爆破方案。同时采用预铺缓冲层、多层缠绕防护和砂土堤防护等措施来控制爆破危害。现场爆破结果表明:采用优化方案和振动控制措施后取得了良好的爆破效果,大桥实际爆堆形态与模拟结果大致吻合,各监测点的峰值振动速度与模拟结果较为接近,对周围重要设施的影响均符合要求。

大型构筑物拆除爆破振动与塌落触地振动分析

对某两连体石灰窑的拆除爆破振动进行了监测,采集了石灰窑爆破及塌落产生的振动数据。石灰窑拆除塌落触地振动的场地常数K为0.132,衰减指数α为1.489,得出石灰窑塌落触地振动经验公式。爆破振动最大振动速度为3.287cm/s,主频主要集中在6.104~28.076Hz;塌落触地振动最大振动速度为7.322cm/s,主频主要集中在2.441~6.714Hz。塌落触地振动速度比爆破振动速度大,主频更接近建筑物的固有频率,因此,在大型构筑物倒塌方向应采取缓冲措施。这些资料可为石灰窑、烟囱及楼房等大型建筑物的爆破拆除设计及对周围环境的影响评估提供参考。

埀直型孔轮式排种器适应高速精密播种的途径

通过对垂直型孔轮式排种器结构及技术参数的优化选择,找到了该排种器适应高速精密播种的途径。从而打破了此类排种器不能适应高速精密播种的局限,使之成功地适应了12km/h的大豆、玉米等中耕作物的高速精密播种。

某都市农庄办公楼控制爆破拆除

介绍了昆明市绿水青山都市农庄办公楼的控制爆破拆除,楼房总高21.00m,建筑面积为2772m2,大楼属框架-剪力墙结构,共5层,拆除高度较高、工程量大、结构坚固,针对楼房的建筑结构特点和周边环境要求,采用多切口的定向倒塌和分区块延期控制爆破技术对建筑楼房进行拆除。通过经验公式和工程实践,对实施拆除爆破时所引起的建筑楼房周围地面质点的振动速度和大楼塌落触地振动速度进行理论计算分析。分析结果表明其振动速度和塌落引起的地面振动速度均在安全值以内,确保了周围环境和建筑物的安全,验证了拆除控制爆破的有效性和安全性。

十八层危楼抢险爆破安全设计

分析、研究十八层危楼抢险爆破中爆破引起的振动，空气冲击波和爆破飞石可能危及的范围，据此采取控制措施。