Surface Roughness and Hydrophobicity of Composite Insulators PDF - EEIC 2013

3rd International Conference on Electric and Electronics (EEIC 2013) Surface Roughness Effect on the Hydrophobicity Characteristic of Operating Composite Insulators Song Wang...

3rd International Conference on Electric and Electronics (EEIC 2013) Surface Roughness Effect on the Hydrophobicity Characteristic of Operating Composite Insulators Song Wang Tian Yuan State Grid Beijing Electric Power Company China Electric Power Research Institute Beijing, China Wuhan, China e-mail: [email protected] e-mail: [email protected] Jun Zhou, Qian-yu Wang College of Electrical Engineering Wuhan University Wuhan, China Abstract—Pretreatment needs to be done before measuring the Through the examination, hydrophobicity decreases after hydrophobicity of the composite insulators. However, the the pollution flashover accidents of operating composite necessity of such pretreatment is questionable for operating insulators. As a result, hydrophobicity should be composite insulators. Therefore, surface roughness of light measured according to DL/T 864-2004, in order to replace pollution level, heavily pollution level, chalking and the impact the insulators in time before hydrophobicity decreases to of surface roughness on hydrophobicity characteristic (HC) level HC6. On-site measurement is difficult due to the was investigated in this paper. The paper does the research on environmental limit, so the hydrophobicity experiment the result indicated the surface roughness is one of main factor should be temporarily performed in laboratory. The about the pretreatment effect on HC level and static contact hydrophobicity characteristics experiment is mainly divided angle. The pretreatment effect on HC level and static contact angle seemed to be very obvious and the percentage of static into three parts: classification, recovery and migration. contact angle changed up to 15.3%, as the surface roughness The silicon rubber jacket is covered with pollution and was varied. The Ra and RSM of different pollution level shed pulverized powder during the on-site operation, so percentage change up to 130% and 269%. While Ra and RSM of pretreatment need to be carried out to remove the pollution high surface roughness degree reach up to 3.242μm and 400μm, so as to measure the hydrophobicity of silicon rubber itself. the hydrophobicity on the composite insulators lost permanent. However, the measured results before and after the The surface roughness can lead the water drop to two kinds of pretreatment varied a lot. For measurement aims to grasp the states transitions and it can make sample static contact Angle hydrophobicity state of composite insulators timely, in-lab changed up to 31% within 10 minutes, which will also cause hydrophobicity experiment should be performed on the the different results of two measurement methods. Surface surface within the same practical operating state. In order to roughness of composite insulators was suggested as the added analyze the impact of different surface states of silicon parameter in hydrophobicity tests. rubber jacket on hydrophobicity, in this paper, surface roughness is chosen as a quantifiable parameter to denote the Keywords- hydrophobicity; operating composite insulators; characterization for different degree of pollution and surface roughness; static contact angle; HC levels test pulverized powder attached to the surface of silicon rubber jacket, as well as pretreatment effect. Introduction of surface I. INTRODUCTION roughness measurement can not only provide the basis for The excellent hydrophobicity of composite insulators hydrophobic classification method, but also remind testers makes the contamination resistance in high performance. measuring errors due to surface roughness changes which Compared to porcelain and glass insulators, the make static contact angle method and hydrophobic sizing hydrophobicity characteristic of composite insulators make method not equivalent. At present, domestic and overseas small water drops, instead of water film in humid researches on hydrophobic are mainly concentrated in environment, condensed on the surface, which will greatly classification, recovery and migration, while surface improve surface resistance of composite insulator beyond roughness of operating composite insulators received less doubt. As to wet flashover and pollution flashover of attention. transmission line, the critical voltage in industrial frequency This paper starts from experimental research about will increase while times will decrease significantly. Thus it whether the pretreatment of hydrophobic measurement is can be seen that this characteristic has an important value to influential to hydrophobic characteristic of composite ensure the long-term safety and reliability of transmission insulators, analyzes the relationship between hydrophobic lines. changes and various surface roughness caused by pretreatments, also studies the impact of several types of © 2013. The authors - Published by Atlantis Press 327 rubber jacket surface roughness under different pollution During the experiment, surface roughness of each rubber situations on hydrophobic characteristics. On this basis, jacket should be taken as the mean value of three times modification suggestions of hydrophobic measurement measurements, and the stylus force should be less than 0.5N. method referred to DL/T 864-2004 were put forward. The purpose is to make hydrophobic measurement and evaluation III. TESTING EQUIPMENT AND SAMPLES methods precisely evaluate the practical operation states of Under the requirements of the relevant standards , operating composite insulators. watering can is chosen in hydrophobic classification method (HC). Hydrophobic Angle measurement uses optical contact II. THE SURFACE ROUGHNESS MEASURING METHOD Angle measuring system of type CAM200. In addition, type Surface profile method was commended in this paper as A Shore durometer is selected, so as type TR-200 surface the surface roughness measuring method. Surface profile is roughness instrument shown in Fig. 3 and the sampling the intersection between plane and actual surface as shown in length is set as 0.8mm. fig.1. The measuring method is to detect the surface of composite insulators using a stylus in order to obtain the surface profile and calculating parameters. Figure 3. Surface Roughness Instrument In this paper, 15 operating composite insulators are Figure 1. Surface Profile chosen from 12 different voltage grade lines various from 100kV to 500kV in 12 different provinces, where operating Where surface profile parameters include amplitude, environment includes eight typical climate regions , and distance, hybrid, curve and related parameters. This paper five major domestic manufacturers are contained. Sampling focuses on the amplitude parameters and distance parameters. points of rubber jacket are all on the high voltage terminal. As the profile peak and profile valley of the composite insulator surfaces are randomly distributed, amplitude IV. TEST RESULTS AND ANALYSIS parameters can be denoted as Ra using the arithmetic mean between sampling lengths of profile peak and profile valley A. Hydrophobic Characteristic and Static Contact Angle showed below: Before and After the Pretreatment of Rubber Jacket 1 1 There are two different opinions in electric power l ∫0 Ra = Z ( x) dx , (1) industry about whether pretreatment should be required on where l denotes the sampling length, Z(x) denotes the the surface of rubber jacket during hydrophobic vertical coordinate. measurement: some people think that pretreatment is needed Meanwhile, distance parameters can be denoted as RSM to reduce the interference of pollution for hydrophobic using the mean value of profile element width within measurement; while others hold that in order to master the sampling length XS as shown in fig.2: hydrophobic characteristic of operating composite insulators, pretreatment is not required so as to keep the surface state of 1 m RSM = ∑ XS , m i =1 i (2) rubber jacket the same as practical operation. In this paper, half the surface of every rubber jacket gets where XSi denotes the width of ith unit, m denotes the pretreated while other half remains the same, and the results number of profile element width within sampling length. of hydrophobicity test are presented in tab.1. In this table, A1, Profile element is the combination of profile peak and profile A6, A9, A14, A15 are operating in the light pollution level valley. (equivalent salt deposit density is lower than 0.006 mg/cm2, non-soluble deposit density is lower than 0.2 mg/cm2); A2, A3, A4, A5, A8, A10, A11, A12 are operating in the heavy pollution level (ESDD is lower than 0.05 mg/cm2, NSDD is lower than 0.5 mg/cm2); A7, A13 are operating in chalking composite insulators (ESDD is lower than 0.02 mg/cm2, NSDD is lower than 1.0 mg/cm2). Figure 2. Profile Element Width XS 328  TABLE I. RESULTS OF HYDROPHOBICITY TEST a) Light Pollution Level Before the pretreatment, Ra was between 0.288μm to Hydrophobic 0.876μm, RSM was between 66.7μm to 193.5μm, the surface Static Contact Angle Classification Shore A profile is more uniform as shown in Fig.4. After the Pretreated No Pretreated No pretreatment, Ra is between 0.293μm to 0.893μm, RSM is A1 HC3 HC4 121.2 118.8 65 between 66.7μm to 193.5μm. A2 HC6 HC2 140.5 133.1 47 A3 HC1 HC2 126.6 125.2 58 A4 HC2 HC6 126.4 129.7 70 A5 HC2 HC1 121.6 134.3 67 A6 HC2 HC1~2 131.9 136.3 62 A7 HC5 HC2 110.6 119.8 53 A8 HC6 HC6 111.8 128.9 38 A9 HC2 HC2 119.9 128.8 62 A10 HC2 HC2 125.7 128.0 65 Figure 4. Surface Profile of Light Pollution Level A11 HC3 HC1 122.6 131.6 45 A12 HC2 HC1 131.9 115.4 48 b) Heavy Pollution Level A13 HC6 HC1 118.5 123.7 62 Before the pretreatment, Ra was between 0.458μm to A14 HC1 HC1 113.4 115.8 50 0.911μm, RSM was between 125.5μm to 304.2μm, the surface A15 HC1 HC1 114.6 113.9 52 profile is more uniform as shown in Fig.4. After the pretreatment, Ra is between 0.494μm to 0.985μm, RSM is From the above table it can be seen that: the hydrophobic between 135.4μm to 329.0μm. classification results with and without pretreatment are c) Chalking Surface opposite, and the static contact angles differ 15.3%, fully The roughness measurement of seriously pulverized illustrated the great impact of pretreatment on hydrophobic surface profile shows a deeper amplitude parameter (Ra is classification and static contact angle. Meanwhile, there between 1.284μm to 1.724μm), and a smaller distance exists a certain relationship between hardness and its change parameter(RSM is between 95.4μm to 114.7μm). After the tendency. As a result, we suggest that pretreatment is not pretreatment, Ra (1.656μm ~ 3.878μm) and RSM (281.0μm ~ required in hydrophobic measurement of composite 352.2μm) all have obvious increase. insulators. Otherwise, the results cannot match the practical Equation (3) is obtained though the data analysis of operation state. amplitude parameter variation Ra1 and Shore A: B. Roughness Comparison Before and After Pretreatment Ra1= 0.088ln(A)-0.1893 （3） of Rubber Jacket Ra1 denotes the amplitude parameter variation (Ra before pretreatment minus Ra after pretreatment). From equation (3) Results of roughness test before and after the we can found out that after the pretreatment, roughness Ra in pretreatment of rubber jacket using type TR-200 surface high hardness value decreased, while Ra in low hardness roughness instrument are listed below. value increased. No matter how hard the chalking surface gets, there will be obvious changes before and after the TABLE II. RESULTS OF SURFACE ROUGHNESS TEST pretreatment. Pretreatment Without Pretreatment C. Relationship between Surface Roughness and HC Ra RSM Ra RSM As we can see in Fig.5, there is an explicit relationship A1 0.764 119.2 0.893 146.8 between hydrophobic classification measurement result and A2 0.708 298.1 0.458 188.6 distance parameter RSM. A3 0.885 140.2 0.911 204.3 A5 0.876 329.0 0.743 304.2 A6 0.804 193.5 0.758 169.7 A7 1.656 281.0 1.284 114.7 A8 0.677 162.8 0.586 147.9 A9 0.856 135.4 0.826 125.5 A10 0.494 212.8 0.594 132.1 A11 0.985 174.5 0.877 159.8 A12 0.799 258.4 0.533 146.4 A13 3.878 352.2 1.724 95.40 A14 0.296 75.5 0.311 64.40 A15 0.288 66.7 0.293 58.80 Figure 5. Relationship between HC Level and RSM 329  However, relationship between HC level and amplitude D. Relationship between High Surface Roughness and parameter Ra is not clear and disperses widely, so the rule Hydrophobic Classification similar to Fig.5 cannot be display. After the comparison Sand paper was used on the sample surface to form a analysis of profile measured by surface roughness instrument, partial surface while Ra=3.242μm and RSM =400μm, as well we think there are two main reasons lead to this phenomenon. as a static contact angle descent 89.0°~93.5°. Even when put Firstly, when the amplitude parameter of chalking surface Ra it in the oven at temperature 30°C for 1 month, surface is higher, surface crack is filled with superfine silica powder hydrophobicity cannot restore, while other parts of the and dust. This will make RSM small enough to present sample can return to HC1~HC2, as shown in fig.7. homogeneous surface profile (shown in the left half of Fig.6 (a)), similar to light pollution surface (shown in Fig.4), which can prevent water drops from crossing the surface crack filled with superfine silica powder. As a result, the contact angle of ejecting water drops caused by HC level performed as Cassie model (principle is shown in Fig.6(c)) with a great hydrophobicity. Secondly, after the pretreatment (shown in Fig.6 (b)), powder filling the surface crack gets removed, amplitude parameter Ra remains high while distance parameter RSM increases significantly, which lead the ejecting water drops move into surface crack with a poor (a) Results of HC level hydrophobicity. (b) Scraped Surface Roughness Profile Figure 7. Hydrophobicity and Profile (Ra=3.242μm) When roughness reaches a certain value (Ra≥3.242μm, (a) Surface Roughness Profile of A13 (before pretreatment) RSM≥400μm), from the high roughness surface test, we can know that hydrophobicity of material itself cannot play a leading role. At this time, even though the silica hasn’t aging, there exists no hydrophobicity. E. Impact of Roughness on Hydrophobic Recovery characteristic With or without pretreatment, hydrophobic recovery characteristic of rubber jacket differs a lot. After the pretreatment, hydrophobicity of some rubber jackets may recovery in 48h, while those without pretreatment can’t. However, during the test, most static contact angles are (b) Surface Roughness Profile of A13 (after pretreatment) greater than 90°, result in inconsistency. The surface roughness measurement showed us that, after immersing in deionized water for 96h, there are different degrees of increase in Ra. Those in high values increase a lot while those in low ones are smaller. It should be pointed out that, RSM shows no obvious change. F. Impact of Roughness on Hydrophobic Migration characteristic Inert material diatomite used in hydrophobic migration is between 106μm~150μm in diameter, with which surface structure gets more complicated. Size, shape, adhesion and (c) Principle of Cassie Model coating way of diatomite particle directly affect Ra and RSM, Figure 6. Analysis of Chalking Surface which will further influence the measurement results. Most hydrophobicity of sample rubber jackets cannot migrate onto the surface (shown in Fig.8), while migration situation of new samples is better. 330  Here is the reason. While statics contact angle is in Cassie model, it isn’t affected by the amplitude parameter, statics contact angle change a little when roughness changes. On the high roughness surface, quantity and strength of ejecting water in HC level may change the Cassie model to Wenzel model, while statics contact angle remains in Cassie model. All these lead to the conflict. However, on smaller roughness surface, conflict will not be obvious. (a) HC Level Results c. Statics contact angle shows no classification function. Under existing standards, θav≥90°,θmin≥85°, just to meet the hydrophobicity (θ≥90° should be considered as the hydrophobic surface in chemical category). VI. CONCLUSION a. Impact of surface roughness on hydrophobic characteristic of operating composite insulators is obvious, (b) Migrated Statics Contact Angle among which HC level results and distance parameter RSM have obvious corresponding relation, while corresponding Figure 8. Comparison of Statics Contact Angle in Hydrophobicity Migration relation with Ra isn’t ideal due to surface powder filling. b. Roughness of rubber jacket varied before and after The above test results fully illustrate that surface pretreatment, and the trends are all related to hardness. roughness of composite insulators has a great influence on However, no matter how hard the chalking surface is, hydrophobic characteristic. obvious changes will take place both before and after the pretreatment. V. RELATIONSHIP BETWEEN SURFACE ROUGHNESS AND c. There are obvious changes in hydrophobicity and STATICS CONTACT ANGLE statics contact angle both before and after pretreatment of rubber jacket. As a result, pretreatment should not be put Statics contact angle method is one of the hydrophobicity forward before the hydrophobicity measurement of operating measurements. During the tests, surface roughness will cause composite insulators. Otherwise it will lead to the deviation the following problems: of measurement results. a. Surface roughness lead to obvious statics contact angle d. Measurement methods of statics contact angle and HC lag (shown in Fig.9 (a) and (b)), statics contact angle level is inequitable, which is common on high roughness changed from 126.0° in 10s to 87.0° in 10min. surface. In that case, HC level is suggested for its similarity Analysis showed that this is the process classical with operating conditions. Cassie model slowly transforming to Wenzel model (shown e. Surface roughness measurement is suggested in HC in Fig.9 (c) and (d)), phenomenon caused by various surface level to better correspond the HC hierarchical relationship roughness. and degree of aging on rubber jacket. REFERENCES Yang Yingjian, Wu Guangya, Zhang Qin, Zhang Rui, Yuan Tian, etc. The researches about age of the composite insulators and RTV. WuHan State grid electrical power research institute, 2012:15-16. GB/T3505 Geometrical Product Specifications (GPS)-Surface texture: Profile method – Terms, definitions and surface texture parameters， (a) statics contact angle (10s) (b) statics contact angle (10 min) Beijing: China Standard Press, 2000. DL/T864 Application guide of composite insulators for AC overhand lines with a nominal voltage over 1000 V, Beijing:China Electric Power Press, 2004. SUI Tao ， WANG Jiadao ， CHEN Darong. Energy analysis for transition from Cassie state to Wenzel state. Journal of Chemical Industry and Engineering (China), 2011, 62(5): 1352-1357 Guan Zhicheng, Liang xidong, Zhang RenYu, Chen Yuan. Hydrophobicity Life—span of Silicone Rubber Composite Insulator. (c) Cassie model (d) Wenzel model HIGH VOLTAGE ENGINEERING, 1998，24(1):6-8. Qu Ailan ， WEN Xiufang ， PI Pihui ， CHENG Jiang ， YANG Figure 9. Statics Contact Angle Lag Zhuoru. Study on Super hydrophobicity of Composite Silica Film Surface. Journal of Inorganic Materials, 2008,23(2), 377-378 b. Impact of roughness change on statics contact angle is Wang Xiao-dong , Peng Xiao-feng. Self-aggregation of vapor-liquid smaller than HC level. Especially on high roughness surface, phase transition [J]. Progress in Natural Science , 2003, 13 (6) :451- measurement results conflict. 456 331  Wang Xiaodong, Peng Xiaofeng, Lu Jian-feng, Wang Bu-xuan. DL/T810-2002 Technical specification for ±500 kV DC long rod Measuring Technique of Contact Angle and Contact Angle Hysteresis composite insulators[s]. Beijing, China: China Electric Power Press, on Rough Solid Surfaces: Measuring Technique of Contact Angle. 2002. Journal Of basic Science and Engineering, 2003,11(2), 174-181. WANG Jianguo, LIU Yang, FANG Chunhua, etc. Performance XU Tao, WU Guang-ya, ZHOU Wen-jun. Flashover Voltage influence of high temperature vulcanization silicone rubber by Characteristic of 1000kV AC Transmission Line Insulator Strings alternating current corona discharge[J]. Acta Polymerica Sinica, Under Polluted Conditions. High Voltage Engineering, 2007, 33(7):9- 2009(4): 33-337. 13. YANG Kai, ZHENG Nan, ZHANG Guanjun, et a1. Analysis of WU Wei-ning, WU Guang-ya，ZHANG Rui Causation analysis and surface trapping parameters of solid insulation dielectric[J]. High countermeasures of pollution flashover of transmission and Voltage Engineering, 2007, 33(9): 13-16. distribution equipment[J]. High Voltage Engineering, 2004, 30(7), 9- XU Zhiniu, Wang Guoli, ZHAO Lijuan, ZHAO Peng, WANG Gang, 11. Static contact angle algorithm of hydrophobicity detection[J]．High GB/T 19519. Composite insulators for a.c. overhead lines with a Voltage Engineering，2012，38(8): 1891-1900. nominal voltage greater than 1000V – Definitions, test methods and Jia Zhidong，Fang Su，Gao Haifeng，et a1．Development of RTV acceptance criteria, Beijing: China standard Press, 2004. silicone coatings in China: overview and bIh1iography[J]. IEEE TANG Liangrui，ZHAO Chunhui，QI Bing. Hydrophobic Detection Electrical Insulation Magazine, 2008, 24(2): 28-4I. Based on Ant Colony Algorithm. High Voltage Engineering, 2009, Kevin E， James X， Weijun Y， et a1.Degradation of a silicone 35(6): 1322-1326. based coating in a substation application[J]. IEEE Transactions on TU Youping, TONG Yuliang, WANG Qian etc. Influence of Power Delivery, 1999, 14(1): 188-193. Humidity on Ozone Aging Performance of HTV Silicon Rubber. High Voltage Engineering, 2011, 37(4), 844-846. LAN Lei, WANG hanliang, WEN xishan. Accelerated corona aging BIOGRAPHIES test analysis and lifetime prediction of HTV silicone rubber. High Voltage Engineering, 2012, 38(4), 782~789. YUAN Tian was born in 1980, male, Ph.D. candidate. His XU Zhiniu, LV Fangcheng, LI Man, LI Ming-he. Study of Silicone engineer research direction is insulator testing and anti- Rubber Hydrophobicity Representation Method Using Dynamic contamination of the lines. Contact Angle. High voltage Apparatus, 2010, 46(10): 8-9. ZHOU Jun was born in HuBei, China, on Nov 10, 1980. He GAo Haifeng,W ANG Yongfu, ZHU Keneng, et. Analysis on effect received the B.S. degree and Ph.D. degree of high-voltage of hydr0phobicity on anti-pollution flashover performance of line insulators[J]. High Voltage Engineering, 2011, 37(2): 284-289. and insulation technology from Wuhan University, Wuhan, LIANG Ying, LI Chengrong, DING Lijian, et a1. Effect of corona China. His major fields of interest are Power System discharge on the hydrophobicity recovery of HTV silicone rubber[J]. Operation and Control and LCC technology. High Voltage Engineering, 2008, 34(1): 30-40. 332