光纤式温度监测技术及其应用

近年来,各种型号的户内开关柜在变电站得到了普遍使用.开关柜在长期运行的过程中,柜体中断路器的触头和母线排连接处等部位,因为老化等原因会引起接触不良,导致触头和母线排连接处等部位过热.如果热故障现象严重且得不到及时发现和处理,将可能导致接触不良部位烧毁,甚至引起火灾.……     

热能设备的热工测试《连载》

7.热电偶热接点的制作 按照热电偶产生电动势的原理,组成热接点的两根热电偶系只要紧紧绞合在一起也是可以的。但因热接点处于高温下,往往还会接触有腐蚀性的气氛,或会受到机械的应力冲击或温度的变化,绞合的热接点在使用时间长久后会造成接触不良而影响其性能,因此一般总要将接点焊接起来或焊在被测件金属上。通常采用的焊接方法有以下几种:     

导线接触不良问题的探讨

导线与导线、导线与电器、导线与配电装置等的接点随处可见,如果对这些接点处理不当或检修不及时,会带来很多的危害,甚至引起火灾.……     

微型发电机故障与排除

TS-3型同步农家微型发电机常见故障及排除方法主要有: 一、不发电或电压太低 1.故障原因: ①接线有错误。②无励磁。③接触不良:a.炭刷与滑环接触不良或电刷压力不够。b.接线松动或接触不良。c.电线接头虚假焊或断头。④转速太低。⑤整流桥损坏。⑥转子线圈短路或断路。⑦电压表失灵。     

光伏直流配电故障诊断及火灾风险评估技术

长期服役的光伏发电系统直流配电故障概率高、火灾风险及危害大,严重影响光伏电站的运行安全、发电与出力能力,并对电站运维提出故障与火灾精准检测的技术挑战。为此,从生产现场直流配电柜故障分析入手,揭示接触不良、绝缘劣化、故障电弧、电气火灾的演变机理;分析国内外故障电弧诊断与火灾检测技术的理论成果应对在运电站电弧火灾的有效性,提出故障电弧预诊断与火灾检测技术的应用解决方案。研究结果表明,提出的故障电弧诊断与火灾检测技术应用方案,弥补直流继电保护对串联电弧故障无法保护的不足,能够有效诊断故障电弧并检测烟雾和高温,避免火灾及其扩大事故的发生。     

用热电偶测温时,是否只要将热接点贴在或焊在被测件表面上就可得到正确的温度值?

答: 采用热电偶测温的特点是:只要热接点和冷接点的温度确定后,便能得到相应的电动势,而与热电偶中间点的温度无关。但当把热电偶热接点贴紧,甚至焊在被测表面上时,热接点的温度也不一定与被测点的温度完全一致。下面分别就不同情况分析造成这种误差的原因。 1.当测量具有保温层的金属壁面温度时(即要求沿被测表面垂直方向的热流尽可能小,例如通过测量管壁温度确定管内蒸汽温度等),     

使用电器取暖设备应注意防火

进入冬季,各家各户已开始使用电器取暖,如何安全正确使用电器取暖,应注意以下几点:使用电器取暖存在的火灾隐患1.取暖器质量不高或选用不当;2.电源线连接不牢或选用线径太小,容易造成接触电阻增大而发热起火;3.导线过热或绝缘损坏而造成短路;4.电热毯里面的电热元件接触不良打火;5.使用时间过长或用完后未及时切断电源而起火。使用电器取暖应采取的防火措施1.要选择合格的产品并掌握正确的使用方法;2.合理选择电源线径,导线连接要牢固;3.发现导线有过热或绝缘损坏,要及时更换;4.电热元件如有接触不良,应及时进行维修;5.使用的电源插头应保持…     

由电动自行车火灾频发引起的思考分析

阐述了因拼改装现象普遍、管理不到位、配套设施跟不上等原因,导致电动自行车火灾风险增大,火灾频发的情况.以电动自行车火灾风险危害性为切口,简述火灾多发的原因,并介绍了相应的消防管理措施和预防手段.     

热处理电炉用电动机的断相保护

一般的热处理电炉使用电动机是不少的,例如为了保证炉内温度均匀,就设有强制循环系统,循环系统靠电动机来带动的。实际使用过程中,电动机要经常烧坏的,电动机烧毁的原因很多,其中主要原因是电动机的单相运行,而造成电动机单相运行的原因不外乎如下: (1)电源保险烧断。 (2)电动机接线头松动或接触不良。 (3)电源馈线折断或接触不良。 (4)交流接触器某一相触点因烧损而接触不上或接触不良。 (5)某一相热继电器断开。 (6)电动机某一相绕组断线或接触不良。 电动机单相运行的故障在实际生产中是不     

东风4型机车柴油机曲轴碾瓦的原因和防止措施

列举了实际发生的柴油机碾瓦的故障现象,根据连杆弯曲、曲轴变形、瓦背与瓦孔接触不良,曲轴箱变形、清洁度不良等故障原因,提出了相应的预防措施.     

空心微珠疏油改性及其在抗烧蛋白泡沫中的应用(英文)

用含氟硅烷偶联剂对空心微珠进行了疏油改性处理,通过接触角变化评价其疏油改性效果.结果表明,疏油改性处理后,空心微珠与煤油的接触角可达118°.向蛋白泡沫灭火剂中添加疏油改性空心微珠之后,三相泡沫内部可形成稳定的骨架结构,有效屏蔽了热辐射向内层的传递,显著增强了泡沫在油面的稳定和抗烧性能,该方法有望用于油品火灾的扑救.     

基于振动信号的GIS隔离开关触头接触缺陷试验研究

为判断气体绝缘开关设备(GIS)开关触头是否出现接触不良的机械缺陷,利用一台110kV GIS为主体建立的试验平台,采集开关触头正常接触、触头中度接触不良、触头严重接触不良3种机械状态下的振动信号进行分析。结果表明,GIS振动信号频谱分布以100 Hz及其整数倍频分量为主,接触缺陷出现后,100、200Hz幅值变化明显;振动信号100Hz幅值与电流平方成正比关系,拟合方程斜率随缺陷程度的增大而增大,可通过斜率大小的改变判断触头接触情况。     

DF4B型机车的起动电路分析及改进建议

通过对DF4B型机车起动电路原理结构的分析 ,找到了机车主接触器主触头烧损的原因 ,指出该电路存在的缺陷 ,并提出改进建议。     

D1300电动风机电机轴承振动过大故障分析及处理

D1300电动风机电机轴承振动过大，频谱分析，轴承下垫块与轴承座接触不好，加装不锈钢皮，研磨、刮削，增加轴承紧力。     

Analysis of the Correlation between the Level of Contact Degradation and the Dynamic Resistance Curve in Circuit Breakers

The DRM （dynamic contact resistance measurement） in high voltage circuit breakers is a manner of evaluating the internal ageing condition of the chamber. DRM is similar to static contact resistance measurement testing, but instead of measuring a single value when the breaker contacts are closed （static value）, the ohmic resistance is measured at various contact positions, from the beginning of the contact opening until a complete separation of the contacts. The relationship between the contact resistances of the new circuit breaker and the ageing circuit breaker in operation provides subsidy for the evaluation of both the main and arcing contact conditions. This research aims to analyze the correlation between the various levels of degradation of the contacts and the configuration of the DRM curve. This work considers curve samples from new acceleration tests. breaker chamber contacts and different levels of degradation by     

Estimating the thermal contact conductance of metals by ultrasonic waves

Experiments and numerical simulations were performed to study heat transfer through a contact interface between two metallic solids in order to clarify the effects of roughness and waviness of the contact surface on the mean thermal contact conductance h_m. In the experiments, the characteristics of an ultrasonic transmission were also investigated so as to obtain a relation between h_m and the transmitted sound energy ratio, with and without attenuation, at the contact interface E_r. Ten pairs of brass specimens were tested in an atmospheric environment at room temperature. Each specimen was a cylindrical block 40 mm in diameter and 45 mm long. The contact surface was finished by polishing, grinding, milling, or turning. Mean nominal contact pressures p_m from 0.08 to 1.67 MPa were applied to the test columns. Our analysis takes account of the radial distribution of thermal contact conductance, using numerical solutions of the two-dimensional cylindrical heat conduction equation to simulate the heat transfer experiments. From the simulations, the effects of roughness and waviness on the temperature fields around the contact surfaces and on h_m were clarified. Finally, for flat rough surfaces, an empirical correlation expression between h_m and E_r is proposed. Using this expression, h_m can be predicted to within about ±50%. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(2): 130–141, 1998     

Prediction of thermal contact conductance based on the statistics of the roughness profile characteristics

The roughness profiles of some common machined surfaces were measured. Four different criteria for determining contact peaks are presented. The distributions of the roughness profile height and the contact peak height were calculated. Based on the statistics of roughness profile characteristics, the thermal contact conductances for surfaces with different roughnesses were predicted. The results showed that the contact peak’s criterion is crucial to the calculation of the distribution of the contact peak height. It has, however, limited influence on the prediction of thermal contact conductance. On the other hand, using several statistical roughness parameters or a single roughness profile is not adequate to describe the topography of the contact surface because of the contact surface’s anisotropy. The values of predicted thermal contact conductance for surfaces with different roughness profiles form a steady prediction strip.     

细水雾灭油池火过程中火焰强化现象的实验研究

细水雾灭火初期,在短时间内会观察到剧烈燃烧的火焰强化现象。设计了多组实验对比不同燃料在不同工况下的火焰强化现象,发现液滴通过撞击油盘燃料引起的液滴飞溅可以增大燃料与空气的接触面积,强化火焰燃烧。细水雾在燃料内发生扬沸也可能强化火焰,但增益效果不明显,同时燃料气化率对于火焰强化程度有很大关系。     

Modelling the PERC structure for industrial quality silicon

The passivated emitter and rear cell (PERC) structure has significant efficiency advantages over the conventional 100% metallised back contact structure for industrial quality multicrystalline silicon. For this material the PERC structure also has only a slightly lower efficiency potential than a more complex structure with rear local diffusions. The PERC structure has previously only been modelled for high efficiency applications. In this work, an optimisation of the PERC structure was performed over a range of wafer resistivities and material qualities. It was shown that the PERC structure has a broad optimum in back contact design, allowing flexibility in manufacturing. There was little difference between a stripe structure and a dot structure of the same contact fraction provided the back contact spacing was optimised in each case. It was shown that contact resistance was negligible in PERC cells compared to spreading resistance for optimised back contact spacings. It was also demonstrated that an analytical expression due to Cox and Strack provided a good approximation for spreading resistance in thick PERC cells, but underestimated the spreading resistance in thinner PERC cells.     

Stability of contact line accompanied by solidification

The cooling rate in actual roll casting systems is markedly decreased by contact resistance between the chilled roll and melt (or solidified shell). In this study, focusing on the dynamic behavior of a contact line, the mechanism generating the contact resistance is experimentally investigated using liquid paraffin as a melt and flat plates as chilled surfaces. The experimental results obtained show that the smoothness of the solidified shell is closely related to the stability of the contact line. The range of immersion velocities of the plate, and stable contact lines appear only at middle immersion velocities. The range of immersion velocity in which stable contact lines appear becomes narrower with increasing undercooling degree of the plate. The unstable contact line appearing at high immersion velocities results from the dynamic nonwetting condition at the contact line. The unstable contact line at low immersion velocities is closely related to the formation of a solidified shell in the vicinity of the contact line and to the interface temperature upon contact between the melt and the chilled surface. © 1998 Scripta Technica. Heat Trans Jpn Res, 26(6): 360–371, 1997