空载变压器投运电压不平衡问题的探讨

空载投入变压器,从低压侧加压,高压侧相电压出现不平衡;而从高压侧加压,低压侧出现相电压不平衡,两种状态下线电压均平衡。此现象是什么原因造成,能否投入运行?是否影响发电机并列?就空载变压器投运电压不平衡问题进行探讨,得出在变压器各种试验满足规程要求的前提下,测得空载变压器线电压平衡,用户可以放心使用,对电气设备和发电机并列不会有什么影响。     

水体下综放开采可行性分析

余吾煤业现有630万吨煤炭资源处在绛河水体下,煤层厚度在4.0～6.2m之间,现导水裂隙带经验公式不能够满足其水体下安全开采,存在开采后突水隐患,为了确定开采后上覆岩层导水裂隙带极限高度是否波及地表,研究区在9个井下钻孔进行了井下仰孔双栓塞分段注水测试和仰孔直观法电视成像仪探测,对涌水量进行了监测、水质进行了对比研究,并通过模拟实验进一步研究不同采厚条件下发育高度.观测、监测及模拟结果表明:采动后导水裂隙带发育高度取决于采厚,为水体下采煤水的防治提供了可靠数据,三个工作面的试采成功,为水体下采煤提供了应用范例.     

常压微波等离子体微波功率对硫化氢分解效率的影响

为了除去石油加工过程中所产生的含有大量有毒气体硫化氢的尾气,采用常压微波等离子体法研究了在纯氩、纯二氧化碳及氩与二氧化碳混合气体三种载气条件下,微波功率对硫化氢分解效率的影响.含有硫化氢的源气在微波的作用下形成等离子体射流从而被分解成氢气和单质硫.结果表明:一定范围内(400～1 100W)增加微波功率有利于提高硫化氢的分解效率,当微波功率继续增加时,不同的载气(纯氩气、纯二氧化碳、氩气与二氧化碳混合气体)条件下,其分解效率变化趋势不同.在纯氩载气条件下,微波功率继续增加,硫化氢的分解效率会下降;在纯二氧化碳载气和氩气与二氧化碳混合载气条件下,硫化氢的分解效率随微波的继续增加而不变.相同微波功率条件下,载气为氩气和二氧化碳混合气体时,硫化氢分解效率最高,说明二氧化碳载气有利于促进硫化氢的分解.当气源为二氧化碳、氩气及硫化氢混合气体,且流量比为8∶1∶1,总流量为1 000mL/min,微波功率为1 300W时,硫化氢转化率最高达98.64%.从节能方面考虑,在实际应用中微波功率可设定为900W.     

中国体型模特玩偶娃娃衣袖原型研究

基于模特体型玩偶在市场上对青少年的影响,对市场上常见的模特体型的玩偶娃娃进行了相关尺寸的测量与统计,按照统计结果进行体型分类,在体型分类下制定了中国体型模特玩偶的原型设定数值并根据此数值利用立裁的方式进行反复修改设计出了中国体型模特玩偶的衣袖原型纸样．验证结果表明,在静态与基本动态状态下,其具有合理性及应用性．     

Buffeting numerical simulation coupled with aerodynamics and structure based on MDDES

Unsteady effect of seriously separated flow is the main factor of modern aircraft buffeting. So accurate simulation of this complex flow becomes the basis associated with the research of aircraft buffeting. This paper constructs an unsteady numerical simulation method for separation flow based on modified delayed detached eddy simulation (MDDES) method by considering both modern computer resources and the credibility of simulating separation flow. The proposed method is also verified through the simulation of the separated flow by a typical fighter at high angle of attack. And then a robust and efficient technology for deforming mesh is established using radial basis function (RBF) and infinite interpolation method. Moreover, the platform for numerical simulation of buffeting is set up in combination with the structural dynamics equations in the modal space, by which the research of vertical tail buffeting caused by edge vortex is carried out on a fighter at large angle of attack. Through spectrum analysis of time-domain response of pressure pulsation on the location of vortex rupture, the results show that the pulsation frequency of vortex structure with different scales covers the inherent modal frequency of vertical tail structure. Compared to the Reynolds-averaged Navier-Stokes equations, the MDDES method can distinguish the more detailed and higher frequency small-scale vortex structure. Unlike flutter, displacement acceleration response of each mode in buffeting is dominated by its own mode. There exists strong coupling between the first bending mode and first torsion mode, and it leads to acceleration and large inertia impact of structure, which is the main factor causing structural fatigue. In sum, the obtained results verify the validity of the numerical means and the corresponding methods in the paper.     

Study of partial discharge characteristics at repetitive square voltages based on UHF method

Due to overvoltage produced by inverter output,inverter-fed motor insulation systems often experience fast electrical aging process,especially when partial discharge(PD) is incepted.Before putting into use,the PD detection should be performed on inverter-fed motors at repetitive square voltages to avoid the PD caused insulation deterioration when the motors are collected to inverters having specific characteristics.However,unlike PD tests at AC/DC voltages proposed in IEC 60270,the PD detection at repetitive square voltages is much more complex because of serious interference generated by impulse generator.To solve the problem,ultra-high frequency(UHF) method seems recommendable for its preferable signal-to-noise ratio(SNR).The chief aim of this study is to investigate PD pulse and statistical characteristics of turn-to-turn insulation for inverter-fed traction motors.A square-shaped Archimedes antenna,specially designed for the PD detection at repetitive square voltages of fast rise times,was used to perform PD tests on turn-to-turn insulation models.Time and frequency analysis results indicate that energy component of generator disturbance and PD pulses are mainly distributed in the 0-0.5 GHz and 0.6-1.5 GHz range,respectively.Based on the results,suitable filter was designed for power disturbance suppression.Additionally,resorting to the sensor unit(i.e.antenna and filter) and the PD test system,the PD statistical features at square voltages of different frequencies were obtained.Experimental results show that higher frequency will give rise,statistically,to PD of lower magnitudes distributing at smaller phases.A reasonable interpretation of this phenomenon was presented.Lastly,according to the PD statistical features,some suggestions for the PD detection system design,generator parameter optimization and the PD pulse extracting were given.The results of this work would be beneficial to the increase of the sensitivity when performing the PD detection on insulation systems for inverter-fed motors at repetitive square voltages and thus,improving the reliability of inverter-fed motors.     

真空环境下的二元冰制备特性研究

采用理论分析与试验相结合的方法,对真空环境下的二元冰生成动态特性进行研究。分析了闪蒸室内压力、水套温度、供水温度、速率、不同水质等各因素对二元冰晶生成的影响。研究结果表明:闪蒸室压力、供水水温、水质以及水滴初始直径、速率都对二元冰真空制备具有较大的影响,其中,闪蒸室压力升高,水滴闪蒸、结冰速率明显下降;供水温度越低,水滴达到同一状态所需的时间越短;水滴初始粒径的增加,水滴闪蒸、结冰的进程明显变慢。闪蒸室温度对水滴的闪蒸、结晶影响不是很大。     

光纤传感技术在岩土工程安全 监测中的应用

详细介绍了光纤光栅传感技术及其特点、光纤BFG光栅传感器技术特性指标及选择,给出了光纤传感技术在国内岩土工程安全监测中成功应用的实例。研究结果为从事岩土工程安全监测设计、现场监测的人员提供参考和借鉴。     

乌江沙沱水电站水轮机选型分析

沙沱水电站水头运行范围50～74.9 m.电站受阻出力多为汛期季节性电能,在综合考虑减少受阻出力及水轮机稳定运行的情况下,对61、62.5、64、65.5、67m五个额定水头方案进行了比较分析,最终确定了经济、合理的水轮机参数.     

佳芦河流域“7·27”暴雨洪水浅析

以佳芦河流域2012年“7·27”暴雨洪水为例,采用场次暴雨洪水资料,分别统计流域面平均雨量、暴雨中心最大2h雨量、大于50 mm以上降雨笼罩面积、次洪洪量、次洪输沙量等指标,分析暴雨洪水输沙关系.结果表明:该次暴雨中心雨量和最大2h雨量最大,面雨量是该地区1971年以来的最大值;与历史洪水相比,相似的降雨量综合因子产生的次洪洪量和次洪沙量具有明显的减少趋势,下垫面削峰作用显著,水土保持成效明显.