基于累积损伤曲线的电寿命模型步进应力试验方法及在XLPE电缆中的应用

交联聚乙烯（XLPE）的反幂函数电寿命模型（IPM）表征了XLPE电缆绝缘的长期耐压特性,包括电压耐受指数（VEC）在内的IPM模型参数是电缆绝缘设计和预鉴定试验电压选取的重要依据。步进应力试验具有耗时短、效率高的优点,适用于求取电缆样品的电寿命模型参数。然而,步进应力试验参数的选择尚无规程可参考,目前主要依靠经验和主观确定,严重影响了试验结果的有效性和可比性。将固体绝缘材料累积损伤“D-t曲线”作为判断绝缘失效机理的主要依据,分析不同试验参数下步进应力与恒定应力试验的等效性,提出适合工程应用的步进应力试验参数选取及现场试验方案。通过该方法设计绝缘厚度分别为2.8 mm和3.5 mm的2种模型电缆的步进应力试验,并获取2种模型电缆的IPM电寿命模型参数,验证该方法的可行性。     

基于累积损伤曲线的电寿命模型步进应力试验方法及在XLPE电缆中的应用

交联聚乙烯（XLPE）的反幂函数电寿命模型（IPM）表征了XLPE电缆绝缘的长期耐压特性,包括电压耐受指数（VEC）在内的IPM模型参数是电缆绝缘设计和预鉴定试验电压选取的重要依据。步进应力试验具有耗时短、效率高的优点,适用于求取电缆样品的电寿命模型参数。然而,步进应力试验参数的选择尚无规程可参考,目前主要依靠经验和主观确定,严重影响了试验结果的有效性和可比性。将固体绝缘材料累积损伤“D-t曲线”作为判断绝缘失效机理的主要依据,分析不同试验参数下步进应力与恒定应力试验的等效性,提出适合工程应用的步进应力试验参数选取及现场试验方案。通过该方法设计绝缘厚度分别为2.8 mm和3.5 mm的2种模型电缆的步进应力试验,并获取2种模型电缆的IPM电寿命模型参数,验证该方法的可行性。     

Estimation of thermal breakdown voltage of HVDC cables - A theoretical framework

The insulation in a DC cable is subjected to both thermal and electric stress at the same time. While the electric stress is generic to the cable, the temperature rise in the insulation is, by and large, due to the ohmic losses in the conductor. The consequence of this synergic effect is to reduce the maximum operating voltage and causes a premature failure of the cable. The authors examine this subject in some detail and propose a comprehensive theoretical formulation relating the maximum thermal voltage (MTV) to the physical and geometrical parameters of the insulation. The heat flow patterns and boundary conditions considered by the authors here and those found in earlier literature are provided. The MTV of a DC cable is shown to be a function of the load current apart from the resistance of the insulation. The results obtained using the expressions, developed by the authors, are compared with relevant results published in the literature and found to be in close conformity     

舟山多端柔性直流工程过电压与绝缘配合

舟山多端柔性直流工程过电压与绝缘配合研究为工程实施提供了基础技术支撑.为确定避雷器保护配置方案及设备绝缘水平,开展了成套设计研究,确定了工程的主回路参数及主接线.按照舟山多端柔性直流工程控制策略建立了电磁暂态仿真模型,模型中的换流器子模块电容、联结变压器、桥臂电抗器及直流电抗器电感值、接地方式的选择和电缆参数的选取均对过电压仿真结果有较大影响.在详细开展设备参数研究的基础上,为了选取并用于建模,开展了过电压研究,确定了主要设备的绝缘水平.对于本工程关键设备——直流电缆,提出采用30％的绝缘裕度以确保运行安全,并最终确定其绝缘水平为510 kV.研究结果已应用于舟山多端柔性直流工程,研究手段为其他同类工程提供了参考.     

Recommendations in HV DC testing of MV cable insulation

Research and field reported data supports the theory that high voltage DC testing can reduce the life of both unaged and aged medium-voltage cross-linked polyethylene (XLPE) cable insulation. This research led an industry movement to eliminate factory DC testing, and reduce the field level and frequency of DC testing. DC factory testing identifies an imperfection in the insulation wall as well as mechanical damage. The test sequence in the factory is to perform the AC voltage withstand and corona tests first, followed by the DC withstand test. The AC withstand and corona test levels today are very demanding and locate the same insulation imperfections. Therefore, it can be inferred that today's level of AC withstand and corona testing positively locates insulation imperfections and the following DC testing is redundant and not required. Statistical analysis of factory testing shows that DC testing after AC withstand and corona tests has no additional benefit. The changes and recommendations made by the Association of Edison Illuminating Companies to DC testing are outlined     

EPR直流馈电电缆裂损放电特性及其应用

根据乙丙橡胶直流馈电电缆敷设方式,开展了直流馈电电缆绝缘裂损放电试验,以及放电信号检测电缆绝缘裂损故障的可行性研究。试验研究结果表明由于运行电压低,绝缘良好的直流馈电电缆检测不到放电,当电缆绝缘层发生破损后,直埋电缆在一定的条件下发生漏电痕放电;桥架电缆绝缘破损较小时也会发生类似直埋电缆的漏电痕放电,绝缘破损较大时(电缆芯裸露)会对桥架发生拉弧放电。直埋电缆可行性模拟试验结果表明电缆放电现象与其绝缘裂损具有良好的对应关系,能够预警其绝缘裂损,但也与外界环境相关。土壤湿度小时容易发生放电,土壤湿度大时,不易发生放电,会产生较大的直流泄漏电流;综合监测直流泄漏电流和放电信号方能有效地实现直流馈电电缆绝缘裂损故障监测。     

The improved voltage life characteristics of EHV XLPE cables

Although many researchers have investigated voltage life characteristics of XLPE cables, the voltage life curve of XLPE insulation has not been made clear because of large deviations in the obtained data. Moreover, the voltage life curve of a XLPE cable, which is significantly affected by defect size and shape, cannot be applied to another cable having different defects. The authors obtained an intrinsic stress life curve of XLPE which included no defects. The intrinsic stress life curve demonstrates the existence of a threshold stress, which causes no degradation in the insulation. The application of the intrinsic stress life curve makes possible to estimate the voltage life curve of any cable with known defects. A method for calculating the defect size that would not initiate any degradation in XLPE insulation under a given electrical stress is proposed     

陷阱参数及其与交联聚乙烯电缆绝缘状态（英文）

Space charge issues have raised many attentions in recent years,especially in high voltage direct current(HVDC)application.Space charge accumulation in insulation system will give rise to acceleration of ageing and even cause premature failure of the material.However,from another angle,space charge might be also considered as a diagnostic tool of ageing for insulation materials.In this paper,a trapping-detrapping model has been developed to estimate trapping parameters of cross-linked polyethylene(XLPE)cable sections,which were taken from different HVAC operation conditions of 12 years and 8 years.The results reveal that,for both cable sections,samples from the inner location have the greatest trap density and the deepest trap depth.Additionally,breakdown strength tests and FTIR(Fourier-transform infrared)measurements on those samples have been carried out.From FTIR measurement results,the degree of oxidation among three layers could be found by the carbonyl index values.The oxidation degree of aged cable at the outer layer is higher than that at the other two layers probably because of the most sufficient contact with oxygen.Also,it has been noticed that the results from these measurements show some correlations with the estimated trapping parameters,especially for breakdown strength.     

Impulse breakdown superposed on ac voltage in XLPE cable insulation

This paper discusses tree inception and breakdown voltage characteristics of XLPE cable insulation subjected to impulse voltages superimposed on ac voltage. The tree initiation tests were performed on laboratory-molded specimens equipped with needle electrodes, whereas the breakdown tests were conducted on a full-sized cable. The impulse tree initiation stress was found to be dependent on the magnitude of the pre-applied ac stress and the relative polarities of the impulse and the ac peak at the instant of their superposition. Although the impulse polarity has an effect on the tree inception, the general behavior is that the tree inception stress always decreases with an increase of the pre-applied ac stress. This phenomenon is discussed in terms of the space charge effect and the influence of the impulse voltage application itself. The impulse strength of a full-sized cable insulation was found to be independent of the pre-applied ac stress as long as that stress did not exceed the operating stress of a 500 kV cable insulation. However, subjecting cable insulation to higher ac stresses before impulse application caused a reduction of its breakdown strength as compared with the insulation without ac prestressing     

Fuzzy Logic-based Electrothermal Life Model for Inverter-fed Induction Motor Insulation

Pulse width modulated adjustable speed drives used in industries lead to significant advantages in terms of performance, size, and efficiency. But, the output voltage and the current waveforms become non-sinusoidal leading to an increase in voltage and thermal stresses. This results into accelerated insulation aging and premature failure of the motors. With multiple stresses, the life models for insulating materials become complex and ambiguous. This article presents the fuzzy logic application to derive an electrothermal life model to investigate the synergic effects of voltage and thermal stresses on intrinsic aging of inverter-fed induction motor insulation. Three parameters, viz. voltage stress factor, waveform slope stress factor, and spike frequency factor, are proposed to describe the insulation stresses for pulse width modulated voltages. These parameters are computed from the experimental results at different switching frequencies and are used in fuzzy logic-based life estimation algorithms. The results of the fuzzy logic life model are verified by performing the accelerated aging test with the same pulse width modulated voltages on paper insulation. An electrothermal life model is derived from the fuzzy logic results, which can be directly used for the life estimation of any general purpose low-voltage inverter-fed induction motor insulation.     

直流电缆屏蔽料对XLPE绝缘空间电荷的影响

随着交联聚乙烯（XLPE）绝缘直流电缆电压等级的提高,对半导电屏蔽料的质量及可靠性的要求也越来越高。选用了2种国外高电压等级用直流半导电屏蔽料、一种国产较为优秀的半导电屏蔽料和国内XLPE直流电缆绝缘料作为试验材料,测试了3种屏蔽料的热、电性能,屏蔽与绝缘的复合性能,研究了3种屏蔽料对XLPE绝缘空间电荷的影响。通过对试验结果的综合分析,提出了炭黑填充量、炭黑粒径和基体树脂以及界面结合情况是影响半导电屏蔽料体积电阻率和空间电荷注入的关键因素。     

高压交联电缆现场交流耐压试验

分析了直流耐压试验对交联聚乙烯电缆存在的缺点和问题 ,通过比较 ,选择了变频谐振装置在山东电网开展高压交联电缆的现场交流耐压试验 ,并介绍了交流耐压实例     

Selectivity of damped AC (DAC) and VLF voltages in after-laying tests of extruded MV cable systems

The purpose of HV after-laying tests on cable systems on-site is to check the quality of installation. The test on extruded MV cable systems is usually a voltage test. However, in order to enhance the quality of after installation many researchers have proposed performance of diagnosis tests such as detection, location and identification of partial discharges (PD) and tan /spl delta/ measurements. Damped AC voltage (DAC) also called oscillating voltage waves (OVW) is used for PD measurement in after-laying tests of new cables and in diagnostic test of old cables. Continuous AC voltage of very low frequency (VLF) is used for withstand voltage tests as well as for diagnostic tests with PD and tan /spl delta/ measurements. Review on the DAC and VLF tests to detect defects during on-site after-laying tests of extruded MV cable systems is presented. Selectivity of DAC and VLF voltages in after-laying testing depends on different test parameters. PD process depends on type and frequency of the test voltage and hence, the breakdown voltage is different. The withstand voltage of XLPE cable insulation decreases linearly with increasing frequency in log scale. Experimental studies with artificial XLPE cable model indicate that detection of defects with DAC or VLF voltage can be done at a lower voltage than with DC. DAC voltage is sensitive in detecting defects that cause a breakdown due to void discharge, while VLF is sensitive in detecting defects that cause breakdown directly led by inception of electrical trees.     

Dielectric strength of transformer insulation at DC polarityreversal

Among special insulation tests for DC power converter transformers, polarity reversal tests can be substituted by applied AC voltage tests from a stress similarity in oil ducts. In order to investigate equivalent levels of other insulation tests to polarity reversal tests, the dielectric strength of a transformer at polarity reversals was examined by use of a model of typical oil/paper composite insulation. From the comparison of polarity reversal and other insulation tests, it was found that dielectric strength of transformer insulation at polarity reversals is phenomenally similar to that under switching impulse stresses. Equivalent AC test voltage to polarity reversal test was also estimated from the experimental results. The breakdown characteristics of polarity reversal tests showed that partial discharges at polarity reversals impose less harmful stress on insulation barriers than those at usual AC or impulse tests     

Development of extruded ethylene propylene rubber insulated superconducting cable

A superconducting power cable is one of the promising ways of underground transmission of huge electric power in the future. The authors have long proposed the idea of the extruded polymer insulation for superconducting cables. The prominent features of the design are to exploit the excellent electrical properties of polymer in the cryogenic temperatures and to separate the helium coolant from the electrical insulation. Although the extruded cross-linked polyethylene cable has proved ability at the liquid nitrogen temperature, the cable insulation cracked due to mechanical stress during cooling to the liquid helium temperature. To overcome this problem, ethylene propylene rubber (EPR) was selected as a new insulating material considering the good results of mechanical and electrical tests of EPR samples at cryogenic temperatures. An extruded EPR insulated superconducting cable 15 m in length was fabricated and a cooling test down to the liquid helium temperature and a voltage test at the liquid helium temperature were carried out with fair success. This is a breakthrough in terms of the electrical insulation design of cryogenic cables.     

Partial discharge study in transformer oil due to particle movement under DC voltage using the UHF technique

Converter transformers are one of the key components in high voltage DC power networks. The insulation of these transformers is stressed by both AC and DC voltages. Therefore, AC and DC voltage tests are routinely applied during factory tests to verify the performance of the insulation structure. Partial discharges in an insulation system are incipient discharges that can damage materials and may eventually lead to complete failure of the insulation system during operation. Recently it has been shown that monitoring such discharges formed under AC stress is feasible using Ultra High Frequency (UHF) measurement technique and that there is a reasonable correlation between the partial discharge magnitude and the amplitude of the UHF signal generated by partial discharges. However, the partial discharge activity under DC voltages is not fully understood. This paper describes a study using the UHF technique to improve our understanding of particle-induced partial discharge activity under DC voltages in mineral oil insulation. UHF signals generated due to conducting particle contamination in transformer oil under AC and DC voltages are compared and analyzed. A method for distinguishing particle discharges in regions of high or low electric field stress is proposed based on frequency-domain analysis of the measured UHF signal.     

电热联合老化对XLPE电缆绝缘特性的影响

为了探究达到设计寿命的高压交联电缆继续运行的可靠性,文中对一回实际运行32 a的110 kV高压交联聚乙烯(XLPE)电缆采用预鉴定试验方法,进行为期180 d的电热循环加速老化试验。通过综合分析比较试验过程中电缆绝缘内、中和外层的电场强度和温度场变化的差异,并将各绝缘层试验条件转化为导体芯表面得到相应的等效试验条件,发现电缆绝缘中层和外层的等效试验条件接近电缆的实际运行情况。通过相关理化实验分析比较试验前后电缆绝缘各层的微观和聚集态状况。结果发现:绝缘内层在严苛的试验条件下热氧化降解占主导;绝缘中层虽然发生一定的氧化降解,但晶体结构仍有所改善;绝缘外层的结晶形态在温度效应的热刺激下趋于完善。因此,可以评估该退役电缆的其余部分在实际运行条件下仍具有长期服役的潜能。     

Long-term electrical performance and life model fitting of XLPE andEPR insulated cables

The results of life tests performed on XLPE and EPR cable models are presented and discussed. The performance of the two insulating materials when subjected to electrical stress are compared on the basis of characteristic parameters derived by the best-fitting life models. It is found that while EPR is well described by linear models, XLPE data fit curvilinear life models, showing a tendency to electrical threshold. Hence the fundamental parameter for XLPE characterization is the threshold value, while the voltage endurance coefficient should be used to characterize EPR     

挤包绝缘高压直流电缆应用现状与研究展望

挤包绝缘高压直流电缆已成为远距离、大容量输电线路建设的主要装备之一,现阶段广泛应用的挤包绝缘直流电缆以交联聚乙烯(XLPE)绝缘为主.针对XLPE绝缘高压直流电缆研发和应用中的绝缘空间电荷特性、副产物脱气等主要问题进行全面综述,指出在工业化生产方式下,超纯净体系XLPE绝缘材料是目前用来缓解空间电荷问题和实现电缆批量化...     

10 kV电缆中间接头典型施工缺陷的电场及局放特性研究

电力电缆故障多发生于中间接头位置,而施工缺陷是引发中间接头故障最主要的原因。为评估电缆中间接头典型施工缺陷的危害性,文中建立电缆中间接头三维有限元模型,分析电缆中间接头存在硅脂涂抹不均匀、主绝缘划伤和接头受潮3种施工缺陷时的电场分布规律,探究不同缺陷位置与场强之间的关系,并搭建工频交流电压局放试验平台对试样进行局放试验。结果表明:硅脂涂抹不均匀时,空气间隙在应力锥周围造成的电场畸变程度最严重;远离应力锥时,场强逐渐减小。主绝缘划伤时,电场畸变最为严重,空气间隙在外半导切断处场强最大。接头受潮后,当水膜位于应力锥附近时,电场畸变程度最为剧烈。相同加压条件下,接头受潮、硅脂涂抹不均匀、主绝缘划伤3种缺陷造成局部放电的次数依次增加。