Leakage currents precede short circuits in PVC‐insulated cable when exposed to external radiant heat

The mechanism of how and when an arcing short or a physical short occurs on a polyvinyl chloride (PVC)‐insulated cable when exposed to radiant heat flux has been found experimentally. How this mechanism acts on the size of the resulting arc beads is also considered. As a physical short usually changes into an arcing short in an instant, it is difficult to determine which type of short circuit occurs as the first phenomenon. To solve this difficulty, a short circuit current was limited to the order of an ampere, which is large enough to trigger an arcing short, and short circuit tests were conducted with a PVC‐insulated cable. Before an arcing short, a small amount of leakage current in the order of milliamperes was observed flowing through PVC insulation, which gradually increased and finally turned into an arc. On the other hand, no leakage current was observed before a physical short. These results indicate the following mechanism: When PVC insulation between conductors in a cable melts when a heat flux is applied, conductors often come close to and into contact with each other. In this case, the leakage current is unrecognizably small because the PVC insulation is not yet carbonized and still has a high resistivity. Meanwhile, when conductors do not come into contact with each other, PVC insulation is gradually carbonized and the leakage current increases until an arcing‐through‐char occurs. Copyright © 2016 John Wiley & Sons, Ltd.     

Mechanisms and modes for ignition of low‐voltage,PVC‐insulated electrotechnical products

PVC is the most common insulation material used for wiring in low‐voltage (LV) service. ‘Low‐voltage’, in the context of this paper, is taken to be 120–240 VAC. The electrotechnical products considered include insulated wires, cables and cords, and also appurtenant termination devices, e.g. male plugs or female taps. Well‐known factors leading to the ignition of PVC‐insulated wiring and related products include: (a) manufacturing defects; (b) grossly excessive current; (c) over‐insulation, sometimes augmented by overcurrent; (d) localized heating due to strand breakage; (e) localized heating due to mechanical strand severing by staples or nails; and (f) localized heating due to failed terminations. Other failure modes are known but have received only limited study. These include (i) excessive force and creep; (ii) chemical interaction effects; and (iii) breakdown under voltage surge conditions. Additional research is needed in these areas. The proximate cause of ignition involved with many of the above mechanisms is arc tracking (arcing across a carbonized path). In turn, it is shown that PVC is especially susceptible to becoming charred, it requiring only approximately 160°C for the material to become semiconducting during short‐term exposure (around 10 h), while longer‐term exposure (around 1 month) may cause failures at temperatures as low as 110°C. Some limited data exist which suggest that standard UL and IEC temperature classifications are unduly optimistic, as applied to PVC. Fire can originate if wiring or equipment cannot withstand a powerline surge. Mains‐connected electrical appliances need to be designed to resist 6000 V surge voltages, even though this is not mandated in most of the current UL and IEC standards. Data are presented showing that the IEC 60112 wet‐tracking test gives especially misleading results for PVC and should be improved or abrogated. Copyright © 2005 John Wiley & Sons, Ltd.     

Identifying causes for certain types of electrically initiated fires in residential circuits

While there are many circumstances that can lead to residential electrical fires, it is useful and practical to identify and document potential hazardous conditions and provide physical explanations of electrically initiated fires. Failure modes for a variety of parallel and series arc faults are described along with circuit breaker response, electrical data, photos, and video frames to explain the conditions that led to a hazardous condition. This work identifies some of the various conditions that can create overheated hazardous conditions and shows how wire insulation is commonly the first to ignite. Conditions explored include bundled extension cords under rugs, abused NM‐B at a load center entrance, broken wires and loose connections. Physical phenomena investigated include glowing connections, series and parallel arcing faults. Low and high current arc energies are discussed and compared to the combustible energy of volatile gases produced from wire insulation to illustrate the wide difference in the arc energy compared to chemical combustion energy from the decomposed PVC. Electrical wire insulation properties were also measured on various wire types to show the effects of thermal aging. Hardness of the wire insulation and cracking of the insulation was used as a measure of insulation lifetime at 140^°C. Copyright © 2010 John Wiley & Sons, Ltd.     

汽车用环保PVC电缆料的研制之一——PVC聚合度的选择

比较了S-1000型、S-1300型和P-2500型PVC树脂的物理性能、耐老化性、力学性能及其电缆料的性能,以及采用不同厂家的1000型PVC树脂生产的绝缘电线的外观质量。结果表明:①高聚合度PVC树脂在老化白度、耐热性、增塑剂吸收量、力学性能等方面都优于普通聚合度PVC树脂,且具有更好的耐老化性及更低的脆化温度;②从力学性能、绝缘性能方面考虑,高聚合度PVC树脂更适合生产电线电缆等软制品,但应注意其熔体流动性大幅下降。     

电线电缆阻燃化研究现状

分析了电线电缆火灾的成因和危害;简要介绍了低烟低卤阻燃聚氯乙烯电线电缆料的发展现状和方向;重点介绍了低烟无卤阻燃聚烯烃电线电缆料的阻燃机理和研究现状;提出了阻燃剂的无卤化、抑烟和低毒是当前和今后电线电缆阻燃研究领域的前沿课题,但在阻燃电缆的应用上还需进一步深入研究。     

Determination of PVC cable insulation degradation

Assessing the degradation of electrical cable insulation is an important feature in extending plant life. The older generating stations are extensively wired with PVC insulated cables, and procedures have been developed to assess degradation using micro specimens in a manner that does not destroy the function of the cable. Material degradation of accelerated aged specimens was systematically monitored by measuring melting or glass transition temperatures ( Tg ), gel content, infrared peroxide absorbance, relative hardness, and plasticizer loss. The shift in the Tg or the characteristic melting peak predicted the maximum exposure temperature of the PVC. The peroxide absorbance and gel content measurements were sensitive indicators of degradation. The relative hardness as measured by thermo-mechanical analyzer (TMA) penetration distance and plasticizer content decreased as the material aged. The results obtained on micro specimens were related to the ultimate elongation values, which have been the traditional measure of degradation.     

Study of the electrical properties of flame retardant poly(vinylchloride) using positron annihilation lifetime spectroscopy

Since the large fire at the Brown Ferry cable plant which occurred at noon on March 22, 1975 in Alabama, attention has been given to the use of flame retardant cable in buildings to meet fire safety requirements. Flame retardants are used in wire and cable applications to prevent the conversion of an electric spark into fire and subsequently to prevent the spread of fire throughout a structure along the wiring. There are many substances used as flame retardants in wires and cables. In Egypt, Multi‐Purpose Reactor insulation and jacket cables have been constructed from a flame retardant substance, poly(vinylchloride) (PVC). In the present work, elemental and X‐ray fluorescence analyses have been performed to determine the composition of PVC in the jacket cable samples. In addition, the conductivity (σ), permittivity (?′), and dielectric loss (?″) as well as positron annihilation lifetime (PAL) are measured in the temperature range 30 to 140 °C. It is found that the amount of chlorine in the flame‐retardant PVC (FRPVC) jacket cable is significantly higher (5%) than the conventional PVC jacket cable. Inverse relationships between σ and free volume size and fractions (V, f) through the temperature range are obtained. However, a distinct positive relationship between σ and I₂ above 100°C is found. The results of PAL and electrical measurements indicate that FRPVC has good electrical insulation properties below 100°C. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 638–644, 2005     

The effect of accelerated ageing of building wires

The fire performance of two electric cables (building wires) designed for indoor use has been tested, both as new products and after accelerated thermooxidative ageing. The cables were aged for a maximum time of 16.5 weeks at 80°C. The cables are commercially available, and were constructed using a PVC material in one case and a non‐halogenated polyolefin‐based material, called Casico, in the other. The effects of ageing on the fire performance of the cables, and the chemical changes that have caused the observed fire behaviour, have been investigated and are discussed. Special attention is paid to the behaviour of the plasticizers that are used in the PVC cable, and how the fire behaviour is affected by the loss of plasticizers from the cable and by the migration of plasticizers between the parts of the cable (insulation, bedding and sheathing). Copyright © 2007 John Wiley & Sons, Ltd.     

船用丁苯橡胶绝缘电力电缆剩余寿命评估

采用实验室加速热老化并结合Arrhenius热老化方程,对船用丁苯橡胶绝缘新电缆的使用寿命进行预测。然后将新电缆实验数据中的性能失效值作为使用中电缆实验性能失效评判标准值,对使用中的丁苯橡胶绝缘电力电缆的剩余寿命进行计算,通过计算两者之差得到使用中电缆的剩余寿命,计算结果基本和实际情况一致。证明了利用该方法对使用中的电缆的剩余寿命进行评估可靠实用,为使用中的电缆预防性更换提供理论和实践依据。     

Numerical simulations of a full‐scale cable tray fire using small‐scale test data

This paper presents a computational fluid dynamics (CFD)‐based modeling strategy for the prediction of cable tray fire development. The methodology is applied to a set of five horizontal trays (each 2.4‐m long and 0.45‐m wide) that are positioned with a 0.3‐m vertical spacing and set up against an insulated wall. Each tray contains 49 power PVC cables. Ignition is performed with an 80‐kW propane burner centrally positioned at 0.2 m below the lowest tray. A collection of four groups of cables per tray (made of one homogeneous material) is considered. These groups are separated by longitudinal slots of air to “mimic” their relatively “loose arrangement.” The thermal properties and surface ignition temperature are estimated from cone calorimetry (CC). When the ignition temperature is reached, the cables burn according to a prescribed heat release rate per unit area (HRRPUA) profile obtained from CC, as is or in a modified shape. A realistic flame pattern is predicted. Furthermore, using only data from CC, the peak HRR is underpredicted, and the time to reach the peak is overpredicted. The proposed “design” for the modified HRRPUA CC‐profile significantly improves the results.     

福建沿海某区域10kV架空绝缘导线失效分析

通过宏观拍照、傅立叶变换红外光谱(FTIR)、热重(TG)分析和扫描电子显微镜(SEM)等方法详细分析了福建省沿海某区域雷击烧蚀的部分失效样品,使用有限元分析方法分析了绝缘子负荷侧的受力情况。结果表明,失效样品主要表现出断链,氧化老化较少。炭黑量过多会使绝缘层过早失效。绝缘子负荷侧存在最大的应力和应力变形,使得设计上"先天不足"架空绝缘导线在电弧电流产生的堆积热量和应力作用下力学性能降低,产生大量裂纹。绝缘材料本身避免"绝缘薄弱处"是从根本上真正提高架空绝缘导线寿命的关键。     

Vertical flame spread on charring materials at different ambient temperatures

A new flame spread apparatus for the measurement of flame spread rates at different ambient temperatures is presented. A 2‐m long sample is pre‐heated with air to the desired temperature and ignited from its lower end with a small propane burner. The flame spread is traced with thermocouples in contact with the sample surface. The features and function of the new apparatus are described, as well as series of vertical flame spread experiments on cylindrical birch rods and electrical cables made of polyvinylchloride (PVC) and flame retardant non‐corrosive (FRNC) materials. Vertical flame spread rates 6–62 mm/s (temperature range 22–271 °C) were determined for birch samples, 3–24 mm/s (22–190 °C) for PVC cable samples, and 0–4 mm/s (22–293 °C) for FRNC cable samples. Small‐scale experiments with thermogravimetric analysis and cone calorimeter were performed to characterize the sample materials in terms of their thermal and fire behaviour. Copyright © 2012 John Wiley & Sons, Ltd.     

Processability,rheology, and thermal,mechanical, and morphological properties of postconsumer poly(vinyl chloride) bottles and cables

The processability, rheology, and thermal, mechanical, and morphological properties of three different commercial poly(vinyl chloride) (PVC) compounds blended with postconsumer PVC bottles and PVC cables were examined with respect to the recycled PVC content. The addition of PVC bottle recyclates [recycled bottles (RBs)] into virgin PVC bottle (VB) and virgin PVC pipe (VP) compounds caused a progressive reduction in the average torque. No thermal degradation or color change in the RB‐blended PVC compounds used was detected through carbonyl and polyene indices from IR analysis. The rheological properties for VP compounds were more sensitive to RB addition than those of VB compounds. The extrudate swell ratio did not change with the RB content. The decomposition temperature for the VB and VP compounds increased at 60–80% RB, whereas the glass‐transition temperature was unaffected by the RB loading. The 20 and 80 wt % RB loadings were recommended for the VB and VP compounds, respectively, for the optimum impact strength, the blends showing ductile fracture with a continuous phase. At the optimum impact and tensile properties, introducing RB recyclates into the VB compounds gave better results than the VP compounds. The hardness and density of the VB and VP compounds did not change with the RB content. The RB property change was comparatively faster than that of recycled PVC pipes. Adding the PVC cable recyclate [recycled cable (RC)] to virgin PVC cable (VC) had no obvious effect on the torque value of the RC/VC blends. The decomposition temperatures of the RC/VC blends stabilized at 20–60% RC and tended to decrease at 80% RC. The ultimate tensile stress was improved by the addition of the RC compounds, whereas the hardness and density of the VC compounds were unaffected by the RC content. It was concluded that the optimum concentrations of PVC recyclates to be added to virgin PVC compounds were different from one property to another and also depended on the type of virgin PVC grade used. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2738–2748, 2003     

电场对水树老化XLPE电缆修复效果的影响

为提高水树老化交联聚乙烯(XLPE)电缆注入式修复效果,研究了在施加不同电场时,水树老化XLPE电缆的注入式修复效果,以获得较好的修复方式。将水树老化后的电缆样本分别在不施加电压、施加直流正极性电压、直流负极性电压以及施加工频交流电压的情况下进行注入式绝缘修复。注入式修复期间,测量4组电缆样本的泄漏电流并对电缆样品切片后进行扫描电子显微镜观测。结果表明,注入式修复时施加电压明显提高了电缆的修复效果,而施加直流正极性电压时,修复液与水反应后的生成物颗粒团聚小,在水树区域分布均匀,注入修复液后4 h水树老化XLPE电缆的泄露电流下降至10μA,修复效果在4组样本中最优。     

以太西无烟煤为碳源制备单壁碳纳米管

以太西无烟煤为碳源,研究了用直流电弧放电法大批量制备单壁碳纳米管的工艺条件,考察了放电气氛及压力、催化剂种类及其用量和煤基炭棒的炭化终温对单壁碳纳米管产率的影响,采用发射光谱技术对电弧等离子体进行了实时监测,用透射电子显微镜、拉曼光谱技术、热重技术和物理吸附技术等对单壁碳纳米管产品进行了分析表征。研究表明,以稀土氧化物Y2O3和过渡金属Ni为催化剂、煤基炭棒为阳极,在0.05MPa氦气下电弧放电,可实现单壁碳纳米管的批量制备,单壁碳纳米管的产量随着煤基炭棒炭化终温的升高而增大。电弧放电得到的煤基单壁纳米碳管以管束形式存在;单壁碳纳米管粗产品中金属催化剂含量低于40%(质量);所得到的煤基单壁碳纳米管的直径在1.5～2.4nm之间,比表面积为199m2.g-1,孔容为0.388cm3.g-1,其中中孔占60%。光谱分析表明,电弧等离子体中存在大量的C和一定的CN活性物种。     

Experimental and numerical analysis of the influence of cable tray arrangements on the resulting mass loss rate and fire spreading

In the context of industrial buildings and power plants, electrical installations and cable trays represent a main fuel load and a potential initial fire source due to possible short circuits or comparable malfunction. Furthermore, a fire can spread from one tray to additional trays mounted above and/or horizontally on one tray. Because of the high significance of cable fires, several research projects have been carried out, investigating the fire behaviour of cables from small‐scale tests, eg, the cone calorimeter, up to large‐scale tests, analysing complete cable tray constructions. The goal of the work presented in this paper is the extension of the knowledge regarding the influence of geometrical parameters like the packing density and tray distance on the burning behaviour and fire spread of cable tray installations. The results are considered, together with test results from the literature, to quantify the main physical parameters describing the burning behaviour. In a next step, the general applicability of these parameters as input data for the parametrization of the source term of numerical simulations is shown. The test results show that the burning behaviour and the fire spreading highly depend on the cable arrangement of the cables on the cable tray, in combination with other boundary conditions. By applying the results as input for a fire simulation, the mass loss rate is considered appropriately.     

氙灯加速老化对聚酯纤维/PVC柔性复合材料力学性能影响的研究

聚酯纤维/PVC柔性复合材料由于多用于户外,易受阳光照射而老化,从而影响材料的力学性能。通过模拟大气环境较好的氙灯耐气候试验箱,考察了氙灯加速老化对聚酯纤维/PVC柔性复合材料顶破性能和撕裂性能的影响。采用CRT材料试验机,研究了聚酯纤维/PVC柔性复合材料的顶破性能和撕裂性能的变化,并比较了两种不同撕裂模式的破坏机理;采用FTIR研究了PVC涂层吸收峰和峰强的变化;采用SEM研究老化前后涂层表面的微观形貌。研究表明:氙灯人工气候老化下,聚酯纤维/PVC柔性复合材料的老化机理主要是羰基化合物和共轭双键的形成;柔性复合材料撕裂性能下降明显;不同撕裂模式对评价柔性复合材料差异较大。     

Development and characterization of reactively extruded PVC/polystyrene blends

PVC/PS blends are obtained through a reactive extrusion–polymerization method by the absorption of a solution of styrene monomer, initiator, and a crosslinking agent in commercial suspension‐type porous polyvinyl chloride (PVC) particles, forming a dry‐blend with a relatively high monomer content. These PVC/styrene dry‐blends are reactively polymerized in a twin‐screw extruder in the melt state. They do not contain monomer residues as detected by GC. The transparency, fracture surface morphology, thermal stability, rheology and static and dynamic mechanical properties of these blends are compared to physical PVC/PS blends at similar compositions. Owing to the high polymerization temperature (180°C), short PS chains are formed in the reactive extrusion process. These short chains are dispersed both as a separate phase of ～2 μm particles (recognized by SEM) and also as molecularly dispersed chains enhancing plasticization and compatibilization. The molecularly dispersed short PS chains tend to plasticize the PVC phase, reducing its melt viscosity and glass transition temperature. The content of the short PS chains forming the dispersed separate PS particles is too low for DMTA to detect a separate T_g. Thus, reactively extruded PVC/PS blends exhibit single T_g transitions at lower temperatures compared with the neat PVC. Migration of the PVC's low‐molecular‐weight additives (lubricants and thermal stabilizer) to the PS phase is observed in the physical PVC/PS blends, causing antiplasticization of the PS phase. This results in both reduction of the T_g and an increase in the thermal stability of the PS phase in the physical PVC/PS blends. Comparing TGA thermograms of reactively extruded and physical PVC/PS indicates that the PS formed in the extruder is different from the commercial PS. This can stem from various chemical reactions that can take place in the studied reactive polymerization process. Polym. Eng. Sci. 44:1473–1483, 2004. © 2004 Society of Plastics Engineers.     

A multi-phase AC arc discharge and its application in in-flight thermal treatment of raw glass powders

The in-flight melting technology with multi-phase alternating current (AC) arc was developed for the purpose of saving energy and shortening production cycle for glass industry. The 6-phase arc and 12-phase arc were used to investigate the in-flight melting behavior of soda-lime and alkali-free glass powders. Results showed that the vitrification degree of raw materials and the shrinkage of particle diameter increased with the increase of input power. The higher melting temperature and viscosity were responsible for the lower vitrification degree of alkali-free glass powders. Compared with 6-phase arc, 12-phase arc improved the vitrification degree of raw material for the longer residence time and higher plasma temperature under the same transformer current. The high vitrification degree achieved in short time indicated that the new in-flight melting technology with multi-phase ac arc would be a promising method for energy conservation in glass industry.     

Molecularly imprinted PVC beads for the recognition of proteins

Ultrathin films of molecularly imprinted polymer (MIP) were prepared by photoiniferter on PVC beads for the selective uptake of lysozyme, taken as a model protein. Acrylamide was selected as the functional monomer and N,N‐methylenebisacrylamide as the crosslinking agent. The copolymerization process was confined to the surface of the PVC beads grafted with diethyldithiocarbamate iniferter initiator in the presence of lysozyme. After extraction of lysozyme from the shell of the PVC‐MIP beads, the latter were then used as artificial receptors for the rebinding of lysozyme. The sequential steps of the modification of PVC beads were monitored by XPS, infrared and Raman spectroscopies. The imprinting step was found to be essential as the PVC‐MIP beads could recognize lysozyme but not the non‐imprinted beads (PVC‐NIP). The binding properties of PVC‐MIP beads were determined using UV spectroscopy from adsorption isotherms of lysozyme, cytochrome, and myoglobin. The imprinted beads were found to be highly selective toward lysozyme over the competitive proteins. This work shows the interest of photoiniferter as an efficient mean for the design of molecularly imprinted polymer beads for rapid, selective removal of proteins. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43694.