王飞鹏(1976-), 男, 博士, 研究员, 主要从事工程电介质、电功能聚合物及其应用研究, (E-mail)
变压器油的绝缘性能是影响电力设备安全运行的关键因素。采用氟化和直流电晕充电处理聚丙烯无纺布,并将其用于变压器油的净化,考察其过滤性能。结果表明:在氟化过程中,聚丙烯的部分C-H键被C-F键取代,同时聚丙烯纤维的平均直径减小,粗糙度增加,制备得到了超疏水滤膜。将氟化后的滤膜进行电晕充电并用于变压器油的净化发现,过滤后的油样相对于用原始滤膜过滤后的油样绝缘性能得到更多恢复,击穿电压升高,微水含量、相对介电常数和介质损耗因数降低。
The insulation property of transformer oil is a critical factor affecting the safe operation of power equipment. The nonwoven polypropylene (PP) electret films used for purification of transformer oil were treated by fluorination and DC corona charging, and the oil filtration properties were investigated. The results show that the C-H bonds in polypropylene can be replaced by C-F bonds during fluorination process and the mean diameter of fibers decreases while the roughness of the fibers increases, which represents the super-hydrophobicity. When the fluorinated PP films were corona charged and applied to transformer oil filtration, it was observed that the aged oil filtered by the modified films got a better recovery of insulation properties in comparison to that of oil filtered by original PP films. There was a great increase in the breakdown voltage. Furthermore, the content of moisture, the relative dielectric permittivity and loss factor decreased significantly.
电力变压器是电网系统中的核心枢纽设备,其绝缘运行状况的好坏和健康水平直接关系着电网的安全稳定运行[
滤芯是变压器油净化设备中的关键部件。近年来,通过熔喷技术制备的无纺布滤膜被广泛应用[
直接氟化是表面化学改性的一种方法[
为了得到一种高性能的净化变压器油的滤膜,本研究中首先通过氟化对无纺聚丙烯滤膜进行处理,探究不同氟化浓度对其化学成分、表面形貌和疏水性的影响规律。然后采用直流电晕充电的方法使聚丙烯驻极体滤膜带电,并测量其等温表面电位衰减特性。将氟化与电晕充电的滤膜用于老化变压器油的净化,通过测量油样的微水含量、工频击穿电压和频域介电响应(FDS)来研究其过滤性能。
试验中采用滤膜材料为浙江朝晖过滤技术股份有限公司生产的厚度约250 μm、克质量约30 g/m2的无纺聚丙烯滤膜。先将原始滤膜在60 ℃真空干燥箱中干燥8 h,随后将样品放入氟化反应釜中,控制反应气压为0.1 MPa,分别设置氟气浓度为6‰、1%和2%,在常温下反应30 min后取出样品。使用场发射扫描电子显微镜(SEM)观察氟化与未氟化样品表面形貌及纤维结构,并采用傅里叶红外光谱仪(FITR)对其表层化学组成进行分析,以此来表征PP纤维的氟化效果。用氟气浓度0、6‰、1%和2%处理的样品分别编号为F0、F6‰、F1%和F2%。
为了在纤维间建立电场,需要对PP滤膜进行极化处理,目前工业上大量使用的驻极体极化方法有热极化和电晕充电法[
直流电晕充电与等温表面电位衰减测量装置
Setup for DC corona charging and isothermal initial surface potential (ISPD) measurement
本研究中用于净化试验的变压器油在实验室加速老化得到,老化试验采用国产25#矿物油与0.13 mm厚的牛皮绝缘纸。试验步骤参照文献[
使用原PP试样、氟化试样(F1%)和氟化充电试样(命名为CF1%)分别过滤400 mL老化油样。为反映不同滤膜的过滤性能,采用卡尔费修水分仪,绝缘油介电强度测试仪和Concept80宽频介电和阻抗谱仪分别测量油样过滤前后的微水含量、工频击穿电压、相对介电常数和介质损耗因数。
氟化聚丙烯全反射红外光谱图
ATR-IR spectra of fluorinated PP samples
使用场发射扫描电子显微镜(SEM)测量得到试样的表面形貌如
氟化聚丙烯扫描电镜图
The SEM images of fluorinated PP samples
氟化聚丙烯纤维直径分析
Fiber diameters of fluorinated PP samples
聚合物表面能和粗糙度的变化会引起其亲疏水性改变。含氟材料是自然界表面能最低的材料之一[
氟化聚丙烯水滴接触角
Water contact angles of fluorinated PP samples
等温表面电位衰减(ISPD)特性是评估驻极体电荷稳定性的主要方法之一[
氟化聚丙烯初始表面电位
Initial surface potential of fluorinated samples
样品 | F0 | F6‰ | F1% | F2% |
初始电位/V | 1 005 | 1 375 | 1 355 | 1 395 |
氟化聚丙烯的归一化等温表面电位衰减曲线
Normalized isothermal surface potential decay curves of fluorinated PP samples
研究表明,驻极体的电荷稳定性与驻极体内陷阱深度和密度密切相关[
变压器油中水分含量是影响其绝缘性能的重要因素,较高的水分含量会直接导致变压器油击穿电压下降及介质损耗因数增大。为研究氟化滤膜的油水分离效果,采用卡尔费修水分测量仪对油中的水分进行测量,结果如
不同滤膜过滤前后油样中水分含量
The moisture contents of oil samples filtered by different PP samples
为进一步分析使用不同滤膜过滤老化矿物油前后油样的绝缘性能,使用IJJD-80绝缘油介电强度自动测试仪测试油样的工频击穿电压。试验中采用标准圆形平板电极,电极间距离为2.5 mm,测试前将油样搅拌90 s,静置180 s,每个样品测试9次击穿电压,最后取其平均值作为击穿电压。
不同滤膜过滤前后油样击穿电压
The breakdown voltage of oil samples filtered by different PP samples
变压器油中的水分和杂质含量是影响其击穿电压的关键因素,当变压器油中水分含量较低时,不会对击穿电压造成影响,而油中悬浮的水分含量升高时会迅速降低其击穿电压。氟化后滤膜对减少油中水分有一定的效果,在一定程度上提高了变压器油的击穿电压。同时,在变压器油老化过程中还会生成纤维、金属颗粒、碳颗粒和胶体粒子等杂质,这些杂质在电场作用下容易形成杂质小桥,导致击穿电压下降[
变压器油老化产生的杂质不仅会降低油的击穿电压,也会影响油的导电性和极化特性,改变其介电性能。近年来,以介电响应理论为基础的频域介电谱法成为一种新型的电气绝缘诊断技术,可以获得变压器油介电常数、介质损耗因数等极化参数与测量频率的关系[
不同滤膜过滤前后油样相对介电常数频域响应谱图
The relative permittivity of oil samples filtered by different PP samples
不同滤膜过滤前后油样介质损耗因数频域响应谱图
The loss factor of oil samples filtered by different PP samples
介质损耗因数的改变主要反映变压器油中的损耗,当频率较低时,变压器油中电导损耗与极化损耗同时存在,此时介质损耗因数较高,随着频率升高,极化损耗逐渐减小,介质损耗因数降低。油含杂质越多,其电导率和载流子含量越高,介质损耗因数越高,这一现象在低频部分更明显。
测试发现,通过原PP滤膜过滤后油样的
笔者采用氟化和直流电晕充电技术对聚丙烯驻极体滤膜进行处理,并研究其变压器油净化性能,得到如下的结论:
1) 氟化处理后聚丙烯驻极体滤膜中部分碳氢键被碳氟键取代,随着氟化浓度增加,聚丙烯纤维直径减小,粗糙度增加,孔隙率增大。同时由于引入了低表面能的氟元素,滤膜的疏水性显著提高。
2) 氟化作用可以改变聚丙烯滤膜内部陷阱分布,增加深浅陷阱能级和密度,从而改变膜的电荷稳定性。氟化浓度较低时形成的浅陷阱较多,电荷稳定性降低;氟化浓度大于1%时,能形成更多深陷阱,电荷稳定性增强。因此通过控制合适的氟化浓度可获得高电荷稳定性的聚丙烯驻极体滤膜,从而增加滤膜的使用寿命和过滤效率。
3) 氟化和电晕充电后的滤膜用于变压器油净化具有优异的过滤性能。氟化增加了滤膜的纤维粗糙度和疏水性,可滤除老化油中的更多杂质和水分;电晕充电在滤膜的纤维间形成电场,在静电力作用下吸附溶于油中的胶体粒子,从而显著提升了老化油的击穿电压,降低了相对介电常数和介质损耗因数。
蔡胜伟, 王飞鹏, 陈程, 等.植物绝缘油击穿放电故障特征气体分析[J].重庆大学学报, 2017, 40(12):52-58.
CAI Shengwei, WANG Feipeng, CHEN Cheng, et al. Fault characteristic gas analysis of breakdown discharge of vegetable insulating oil[J]. Journal of Chongqing University, 2017, 40(12):52-58. (in Chinese)
陈江波, 王飞鹏, 蔡胜伟, 等.变压器植物、矿物绝缘油的微生物降解机制及差异[J].重庆大学学报, 2018, 41(2):61-68.
CHEN Jiangbo, WANG Feipeng, CAI Shengwei, et al. Microbial degradation mechanisms and differences of plant and mineral insulating oil of transformers[J]. Journal of Chongqing University, 2018, 41(2):61-68. (in Chinese)
廖瑞金, 张福州, 袁媛, 等.含双氰胺的新型绝缘纸制备及其油纸绝缘体系热老化试验[J].重庆大学学报, 2013, 36(7):47-51.
LIAO Ruijin, ZHANG Fuzhou, YUAN Yuan, et al. Preparation of a dicyandiamide-contained novel insulation paper and an experiment on the thermal aging characteristics of relevant oil-paper insulations[J]. Journal of Chongqing University, 2013, 36(7):47-51. (in Chinese)
Chu K H, Park M, Kim H Y, et al. Preparation and characterization of polypropylene non-woven fabrics prepared by melt-blown spinning for filtration membranes[J]. Bulletin of the Korean Chemical Society, 2014, 35(6):1901-1903.
Das D, Waychal A. On the triboelectrically charged nonwoven electrets for air filtration[J]. Journal of Electrostatics, 2016, 83:73-77.
Thakur R, Das D, Das A. Study of charge decay in corona-charged fibrous electrets[J]. Fibers and Polymers, 2014, 15(7):1436-1443.
陈钢进, 肖慧明, 王耀翔.聚丙烯非织造布的驻极体电荷存储特性和稳定性[J].纺织学报, 2007, 28(9):125-128.
CHEN Gangjin, XIAO Huiming, WANG Yaoxiang. Charge characteristics and stability of non-woven polypropylene fabric electrets[J]. Journal of Textile Research, 2007, 28(9):125-128.(in Chinese)
王飞鹏, 张涛, 李剑, 等.表层氟化环氧树脂的直流闪络特性[J].高电压技术, 2018, 44(2):372-379.
WANG Feipeng, ZHANG Tao, LI Jian, et al. DC flashover characteristics of surface fluorinated epoxy[J]. High Voltage Engineering, 2018, 44(2):372-379. (in Chinese)
安振连, 赵敏, 汤敏敏, 等.氟气处理孔洞聚丙烯膜显著改善的电荷存储特性[J].物理学报, 2008, 57(9):5859-5862.
AN Zhenlian, ZHAO Min, TANG Minmin, et al. Significantly improved charge deposit properties of the cellular polypropylene film modified by gaseous fluorine[J]. Acta Physica Sinica, 2008, 57(9):5859-5862. (in Chinese)
Kilic A, Russell S, Shim E, et al. The charging and stability of electret filters[M]//Kilic A, et al. editors. Fibrous filter media. Elsevier, 2017: 95-121.
廖瑞金, 周旋, 杨丽君, 等.变压器油纸绝缘热老化过程的中红外光谱特性[J].重庆大学学报, 2011, 34(2):1-6.
LIAO Ruijin, ZHOU Xuan, YANG Lijun, et al. The mid-infrared spectra characteristic of the transformer oil-paper insulation in thermal ageing process[J]. Journal of Chongqing University, 2011, 34(2):1-6. (in Chinese)
Barbes L, Radulescu C, Stihi C. ATR-FTIR spectrometry characterisation of polymeric materials[J]. Romanian Reports in Physics, 2014, 66(3):765-777.
An Z L, Cang J, Chen X, et al. Impact of interface between polyethylene and surface fluorinated polyethylene on space charge accumulation in the layered structures[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2013, 20(1):339-336.
Song J L, Huang W B, Liu J Y, et al. Electrochemical machining of superhydrophobic surfaces on mold steel substrates[J]. Surface and Coatings Technology, 2018, 344:499-506.
Wang J W, Rychkov D, Gerhard R. Chemical modification with orthophosphoric acid enhances surface-charge stability on polypropylene electrets[J]. Applied Physics Letters, 2017, 110(19):192901.
Thyssen A, Almdal K, Thomsen E V. Electret stability related to the crystallinity in polypropylene[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2017, 24(5):3038-3046.
李金忠, 张乔根, 李原, 等.直流电压下油纸绝缘杂质小桥的形成过程[J].高电压技术, 2016, 42(12):3901-3908.
LI Jinzhong, ZHANG Qiaogen, LI Yuan, et al. Generation process of impurity bridges in oil-paper insulation under DC voltage[J]. High Voltage Engineering, 2016, 42(12):3901-3908. (in Chinese)
姚翠娥, 王荣武.驻极工艺对PP熔喷非织造过滤材料静电性能的影响[J].山东纺织科技, 2014, 55(1):1-4.
YAO Cuie, WANG Rongwu. Research on electrostatic properties of polypropylene meltblown filters[J]. Shandong Textile Science & Technology, 2014, 55(1):1-4. (in Chinese)
杨丽君, 齐超亮, 吕彦冬, 等.变压器油纸绝缘状态的频域介电谱特征参量及评估方法[J].电工技术学报, 2015, 30(1):212-219.
YANG Lijun, QI Chaoliang, LÜ Yandong, et al. Characteristic parameters and assessment methods of frequency-domain dielectric spectroscopy of oil-paper insulation for transformers[J]. Transactions of China Electrotechnical Society, 2015, 30(1):212-219. (in Chinese)
Zhou Y, Hao M, Chen G, et al. Study of the dielectric response in mineral oil using frequency-domain measurement[J]. Journal of Applied Physics, 2014, 115(12):124105.
Kohtoh M, Kaneko S, Okabe S, et al. Aging effect on electrical characteristics of insulating oil in field transformer[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2009, 16(6):1698-1706.