Loss and recovery of hydrophobicity, surface energies, diffusioncoefficients and activation energy of nylon

The loss of hydrophobicity of nylon 6/6 caused by immersion in saline water for up to 336 h at different conductivities (0.005 to 100 mS/cm) and different temperatures (0 to 98°C) and its subsequent recovery in air (during 4500 h) have been investigated. The hydrophobicity is determined by measuring the static contact angle &thetas; between the tangent to a droplet of distilled water and the horizontal surface. The changes in the surface roughness and in the weight of the specimens were determined and correlated with the changes in the contact angle. It has been found that &thetas; decreased with increasing conductivity and increasing temperature of the saline solution. After removal from the solution, the higher the conductivity and temperature, the longer it took for &thetas; to recover in air. &thetas; decreased from 70° to 54° after nylon was subjected for 521 h to a uniform field of 15 kV_dc/cm in air. The surface free energy of nylon was determined as a function of time of immersion, the conductivity and temperature of the solution and during the recovery in air. The surface energies calculated for the virgin specimen are in good agreement with the literature. The diffusion coefficient of water into nylon increased from 0.23×10^-12 m²/s at 23°C to 7.4×10^-12 m²/s at 75°C. The activation energy was determined to be 59.4±2.2 kJ/mol. For unaged nylon the surface energies were determined at 23°C to be γ_S=44.7 mJ/m², γ_SD=29.3 mJ/m², γ_SH=15.4 mJ/m², W_SL =97.7 mJ/m² and γ_SL=19.8 mJ/m²      

Electrical Breakdown Properties and Space Charge Formation in High Temperature Region in Ultraviolet Ray Irradiated PVC

Polyvinyl chloride (PVC) is the most popular insulating material for electric wiring instruments. However, an exothermic reaction above 150 °C may cause deterioration of the insulating properties of PVC. Therefore, it is important to clarify the heat degradation in PVC, not only to investigate the ignition of electrical wiring products but also to use electrical products safely. It is known that ultraviolet (UV) irradiation causes chemical deterioration of PVC and an increase in its conductivity. Generally, it has been thought that the electrical breakdown properties, electrical conduction, and insulating performance are affected by space charge accumulation in an insulating material. A high temperature pulsed electroacoustic (PEA) system usable up to 250 °C has been developed, and the PEA system can measure the space charge distribution and conduction current in the high temperature range simultaneously. In this investigation, the space charge distribution and conduction current were measured up to electrical breakdown in a non‐UV irradiated sample (normal PVC) and in 353 nm and 253 nm UV‐irradiated PVC samples in the range from room temperature to 200 °C in a DC electric field. In the short wavelength UV irradiated PVC sample (253 nm, 300 h), a deterioration of breakdown strength at 90 °C to 150 °C and negative packet‐like charges were observed at 60 °C and 100 °C, a positive charge accumulated in front of both the anode and cathode above 90 °C, and a higher electric field near the cathode side because the positive charge of the cathode side was greater.     

沿面型介质阻挡放电的电气特性

沿面型介质阻挡放电在气流控制等方面具有十分广阔的应用前景。本文对其放电机理进行了分析,指出放电过程中在介质板表面积聚的电荷处会形成一虚拟电极,与放电空间其他电荷共同作用,对放电过程产生影响。基于此,建立放电的等效模型,推导了放电功率的计算公式,并与Lis-sajous图形计算的放电功率比较,具有较好的吻合。讨论了外加电压、频率对放电特性的影响:外加频率相同时,随着外加电压的增加,每半周期内传输的放电电荷不断增大,且其变化趋势与功率增长趋势基本一致,呈非线性增加,同时放电面积增大,功率增加;外加电压一定时,放电功率与频率成正比。     

多针-平板介质阻挡放电提高玻璃表面憎水性的研究

用大气压空气中多针-平板电极结构的DBD对玻璃表面进行憎水性改性。通过测量水接触角、表面电阻和湿闪电压等研究了这两种形式DBD产生的等离子体处理前后玻璃的表面特性以及处理电压和处理时间对改性效果的影响。结果表明：在玻璃表面涂一层二甲基硅油并经等离子体处理后，能在玻璃表面生成一层长效、致密的憎水膜。随处理电压和处理时间的不同，改性效果不同，当处理电压10kV、处理时间8min时提高憎水性效果最明显。     

Electrical and thermal analysis of polymer insulator undercontaminated surface conditions

Electrical and thermal analysis of a 15 kV silicone rubber distribution insulator was made under contaminated surface conditions. The electric field on the insulator surface and in the surrounding area was determined by using the finite element method technique, while the temperature distribution along the insulator surface was calculated by solving the heat transfer differential equation numerically. A special mathematical treatment was used to reduce the heat transfer equation into a 1-dimensional problem. The effects of initial surface contamination upon the features of electric field was studied. The dependence of the change in insulator surface temperature as a result of leakage current flowing over the contaminated surface on the physical parameters involved in the heat conduction process was studied and is presented in detail     

聚氯乙烯绝缘电线表面为何有“电”

聚氯乙烯绝缘电线若其表面附着一些导电脏物和在潮湿环境下带电使用时 ,用验电笔接触其表面 ,发现电笔氖管发光闪烁 ,用户认为电线“漏电”,电线质量有问题 ,不能安全使用。该文介绍了针对这情况进行调查及试验 ,认为电线质量并无问题 ,而是由极微量的电容电流引起的 ,并不危及人身安全 ,用户可安心使用。     

Loss and recovery of hydrophobicity on RTV coating surfaces. Lossof hydrophobicity [comment and reply]

For original paper see ibid., vol. 1, no. 4, p. 601-4 (1994). Discusses the optimal contamination layer to be allowed on an RTV coated insulator. Is there at all such an optimal quantity? Does such an optimal contamination layer depend on the thickness of the RTV coating? The question of differences in silicone rubber properties to embed surface pollutants as well as to recover hydrophobicity has been analysed at length. Do the original authors have data which indicate the diffusion of the low molecular weight (LMW) fraction from thinner and thicker RTV coatings? A reply by the authors is appended     

Electrical Breakdown and Space Charge Formation at High‐Temperature Region in Long‐Time Heating Treatment PVC

Polyvinyl chloride (PVC) is widely used as an insulating material in various electrical products. It is reported that an exothermic reaction reaching temperatures above 150 °C can be caused by overload currents or inferior electrical wire connections before the ignition of electrical products. The exothermic phenomenon may cause deterioration of insulating properties in PVC due to its chemical decomposition. It is necessary to clarify the degradation of insulating properties in PVC under thermal stress exceeding 150 °C for the safe use of electric products. In this investigation the space charge distribution and conduction current in the heat‐treated PVC sheet were measured in the range from room temperature to 200 °C in the presence of a dc electric field, using a high‐temperature PEA system. Positive charge injection and increasing conduction currents were observed before breakdown above 100 °C in 100 °C 300‐h heat‐treated samples and in non–heat‐treated samples. The results indicate the thermal breakdown process from the analysis of conduction currents and electric fields. In samples exposed to higher temperatures (150 °C 100 h), the breakdown strength deteriorated strongly in the range from room temperature to 90 °C. Increases in conduction current were observed in the entire temperature range before breakdown of the 150 °C 100‐h heat‐treated PVC. This indicates that heat treatment above 150 °C degrades the breakdown properties in the range from room temperature to 90 °C due to thermal decomposition accompanied by dehydrochlorination in PVC. The electric field is intensified near the cathode due to positive charge accumulation, and the breakdown strength begins to deteriorate only above 90 °C. This shows that thermal stress exceeding 150 °C causes deterioration of insulating properties and that the breakdown process is affected by space charge formation in PVC.     

Electrical resistance of electroconductive plastic composite with carbon fiber filler

To obtain a new electroconductive composite, the vapor-grown carbon fiber (VGCF) has been applied to the thermoplastic resin composite as a conductive filler. The stability of electrical conductivity of the composite is investigated. The resistivity of VGCF composite is 1.7 × 10^?1 Ω·cm at room temperature which is one order smaller than that of commercial grade composites with carbon filler. The stability of electrical conductivity, under temperature change (?35 to +60°C) and for exposure tests (at room temperature and at 60°C), the VGCF composites have high degree of stability. The stability of electrical conductivity of the present composites are superior to those of conventional carbon fibers such as PAN-based, under tensile stresses and bending stresses. It is suggested that the fine conductive networks in the present composites give rise to these desirable performances.     

PVC、PS与浒苔共热解过程分析及动力学研究

为了更好地处置废塑料中主要典型组分聚氯乙烯（PVC）与聚苯乙烯（PS），将其与浒苔在氮气气氛中进行了共热解研究。结果表明:提高升温速率，可以使主要热解温度区间朝着高温区移动，热解速度变大；随着浒苔质量分数的增加，PVC与浒苔共热解主要热解温度区间朝着低温区移动，PS与浒苔共热解主要热解温度区间朝着高温区移动；PVC与浒苔共热解具有较好的协同作用，PVC质量分数为75%时，相对值可达34.5%；PS与浒苔共热解具有一定的抑制作用，PS质量分数为50%时，其协同作用相对值可达28%；动力学分析表明，一级动力学模型可以很好地描述二者的共热解过程，二者存在动力学补偿效应。     

Electrical, chemical and mechanical processes in water treeing

Water treeing is a complex phenomenon involving several processes with many synergistic effects. Although a huge number of papers on the subject have been published over the last 25 years, there is no comprehensive theory able to describe the often contradictory experimental results. However, there are some tendencies that are always observed, whatever the experimental conditions. A critical review of some electrical, chemical and mechanical processes is made. In fact, water treeing is likely to be due to a mixture of all these processes. When existing data is examined carefully, it appears that very few theories can explain the results. It is concluded that voltage and frequency are major aging factors, and the role of oxidation may be less important than sometime was suggested. The energy of ion reduction is pointed out as a factor that may possibly influence water tree initiation and growth. The solubility parameter of additives and solutions is another factor that deserves some attention. Finally, the polymer morphology appears to affect water treeing greatly through modifications of its mechanical properties. Before a detailed model could be proposed, several studies remain to be done and thorough investigations devoted to the initiation phase and to synergistic effects are required. The development of a reliable and significant accelerated aging test simulating field conditions is also suggested     

Electrical injury: mechanisms, manifestations, and therapy

Human contact with strong electrical power sources often results in complex injury patterns which have been difficult to explain and even more difficult for survivors to overcome. Fundamentally, there are two basic modes of tissue injury: direct effects of strong electric fields on proteins and cellular structures and indirect effects related to joule heating. Historically, tissue injury due to direct effects of electric forces have received no consideration with respect to understanding electrical injury. Recently, substantial progress has been made in understanding this aspect. The structural characteristics of nerve and skeletal muscle tissue renders them particularly vulnerable to injury by supraphysiological electric fields. How the injury manifests from the combination of thermal and electric effects depends on several variables including the tissue field strength, duration of exposure, frequency, and current path. This review describes the destructive changes to cellular structure resulting from exposure to commercial electrical power sources and the resulting manifestations at the organ system level. Finally, several important new therapeutic approaches to treat and possibly reverse the molecular alterations of electrical shock are discussed.     

Thermal step and TSDC measurement in PVC

The space charge behavior of some polyvinylchloride (PVC) samples with different molecular microstructures, obtained through chemical modification of PVC has been analyzed by means of the thermal step (TS) and the thermally stimulated discharge current (TSDC) techniques. The magnitude of the space charge distribution has been shown to be lower as the degree of chemical modification increases. Combining the TS and the TSDC methods allowed us to study minority carriers, which could not be observed by a single TS measurement     

Loss and recovery of hydrophobicity on RTV coating surfaces

Studies are reported on decay and recovery of hydrophobic properties on clean and contaminated surfaces of silicone rubber based RTV coating. Treatment that led to hydrophobicity losses were water immersion and water condensation with and without a presence of dc electric field. Contact angles (receding angles) and surface leakage currents were measured on the treated surfaces. A suppression of the leakage current was observed and its link to the diffusion of the low molecular weight fraction from the polymer bulk and dry band arcing is discussed. Attempts aiming to restore the lost hydrophobic properties are also described. As a means of recovery, resting at ambient atmosphere, under UV irradiation, and in vacuum at elevated temperature, was applied. The efficiencies were verified through measurements of receding angles, surface leakage currents, and thermally stimulated depolarization currents     

采用图像分析与神经网络识别绝缘子憎水性

为了快捷准确的识别复合绝缘子的憎水性等级,提出了基于图像分析与神经网络的绝缘子憎水性识别方法.试验获取各个憎水性等级的绝缘子图像,对图像进行直方图均衡增强、自适应中值滤波处理后,利用二维Otsu阈值法对图像进行分割;然后,提取4个与绝缘子憎水性相关的4个特征量,以这4个特征量作为输入向量,以相应的憎水性等级作为输出向量,通过训练得到优化的BP(back propagation)神经网络识别模型,并用于绝缘子憎水性等级的识别.试验结果表明该方法能够准确识别绝缘子的憎水性等级,总识别率超过了90％,准确度达到了实际应用的要求,为在线检测绝缘子憎水性奠定了基础.     

复合绝缘子表面憎水性和污秽对其湿闪电压的影响

提出一种染污复合绝缘子的湿闪络试验方法，给出不同憎水性和污秽条件下复合绝缘子的干、湿闪电压，并根据试验结果对其干、湿闪机理进行了分析。试验结果表明：复合绝缘子的湿闪电压随表面憎水性的减弱而降低，干闪电压与表面憎水性无关；表面存在污秽时，绝缘子的湿闪电压较清洁表面有明显下降；其表面憎水性的不同仍然影响着复合绝缘子的湿闪电压；在不同盐密条件下，涂污的复合绝缘子湿闪电压也随表面憎水性的减弱而降低；重污秽条件下其表面憎水性较差时的湿闪电压要比憎水性良好时下降11％。     

Efficient numerical modeling of random rough surface effects in interconnect resistance extraction

Owing to the decreasing skin depth in high‐speed analog and digital circuits, surface roughness is playing an increasingly important role in interconnect parasitic extraction. However, the random nature of surface roughness and the complicated electromagnetic behavior baffle satisfactory solutions to the extraction exercise. This paper utilizes a numerically formulated effective conductivity as an efficient measure of the rough surface effects in the resistance extraction to avoid the global discretization of interconnect surfaces. Two numerical methods based on different boundary element formulations are proposed to compute the mean effective conductivity for interconnects with random surface roughness. Numerical experiments compare these two methods in different rough surface patterns to evaluate their efficacy. Copyright © 2008 John Wiley & Sons, Ltd.     

Specification, Selection, and Maintenance of Foreign Electrical Equipment

General techniques of the three groups required to design, install, and maintain foreign electrical equipment are presented. The goals of the groups, design, construction, and maintenance engineering, for building and operating a plant are compared in reference to obtain the best equipment, installation methods, and minimum downtime problems necessary to produce a quality product at the lowest possible cost. The problems of foreign equipment are of the same type and magnitude as United States equipment. Proper planning by management with engineers and supplemented by an adequate spare parts supply necessary for proper maintenance will provide the necessary technical know-how.