Performance Analysis of 33 kv Polymer and Porcelain Insulators under Various Pollution Conditions at Costal Regions

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1 Volume 114 No , 1-9 ISSN: (printed version); ISSN: (on-line version) url: ijpam.eu Performance Analysis of 33 kv Polymer and Porcelain Insulators under Various Pollution Conditions at Costal Regions N.Sumathi 1 R.Srinivasa Rao 2 V.S.N.K.Chaitanya 3 1 EEE Department, University College of Engineering (A), JNTU Kakinada, Andhra Pradesh, India. eeesuma@gmail.com 2 EEE Department, University College of Engineering (A), JNTU Kakinada, Andhra Pradesh, India. srinivas.jntueee@gmail.com 3 EEE Department, University College of Engineering (A), JNTU Kakinada, Andhra Pradesh, India. chaitu824@gmail.com Abstract Pollution on the surface of insulator reduces reliability and quality of power system. Due to the pollutions contaminations on the surface of insulator leakage current will increase and breakdown voltage will decrease. In this paper, it is proposed to study experimentally the effect of different types of artificial pollutions on 33 kv outdoor porcelain and polymeric insulators for their performance at Indian coastal regions. The types of pollutants used are sea-salt, cement and urea. The pollutions are made artificially and are sprayed on to the insulator according to IEC 657. After spraying, it was left for 24 hours completely to dry naturally. This process was repeated for seven days till a thick visible layer is formed on the surface of insulator. Electrical tests were performed to measure leakage current and breakdown voltage to predict the effect caused by pollution on the insulators. The experimental results proved that polymeric and porcelain insulators are greatly affected by salt and urea contamination compared to cement contamination. Due to water molecule reabsorbing property of urea maximum leakage currents are high in urea pollutions and salt pollution. It is also proved that compared to porcelain, polymer insulators has high breakdown strength. Key Words: Ceramic Insulator; ; dust; Leakage Current (); Polymer Insulator; sea salt; urea pollution 1 Introduction Electrical insulators are used to separate power lines from ground structures and to provide mechanical support to power lines. They are placed at different places like high altitude sites, substations, traction substations, near industrial fields and train roofs. Insulators placed in polluted areas get contaminated uniformly or non-uniformly with local dust, natural dust, bird feces etc. The dust particles on the surface of insulator along with pollutants mix up with moisture, fog, rain and dew and get contaminated. When the insulators are 1

2 energized even at rated voltage leakage current increases gradually degradation takes place on the surface of insulator and finally leads to flashover. Hence pollution accumulation on the surface of insulators reflects the characteristics of insulator [1-4]. In outdoor, pollution distribution on the insulators may be uniform or nonuniform because transmission and distribution lines run along and across the road, factories, sea shores, and fertilizers [5-8]. The main pollutants that affect the properties of insulator are sea-salt, cement and urea [9-1]. The effect of pollution on insulator surface depends on type of material used to make the insulator. Ever since porcelain insulators were used for insulation, transmission and distribution lines. But nowadays these are replaced by polymer silicone insulators especially for ultra high voltages because of their advantages like light weight, hydrophobicity, easy handling and non-breakable [11-12]. In ceramic insulators increase of pollution deposits gradually increases the leakage current and finally it may leads to flashover. While for composite insulators made of polymeric materials, leakage current depends on the surface resistance which depends on hydrophobicity. At polluted conditions these insulators make themselves hydrophobic by transfer of low molecular weight components and hence leakage current does not increase continuously. However in polymeric insulators temporary variations in leakage currents due to pollutions are similar to that for ceramic ones. Standard laboratory tests to evaluate the performance of insulators in outdoor contamination have been developed by IEEE and IEC 657 [13]. Specific pollution tests to evaluate the polymeric insulators performance is under considerations as per IEC [14]. In this paper, an artificial pollution experiments were carried on both 33kV polymer and porcelain insulators each type four specimens, to investigate the influence of pollution on the insulators. The tests were done for three types of pollutions cement, urea and salt. From experimental tests, breakdown voltage and maximum leakage current were recorded. A comparison was made between the porcelain and polymer insulators to predict which type of insulator is more affected by these pollutants. The effect of different contaminations on insulators is also analyzed. The research results are useful to design the insulators operated in severe pollution conditions and can be used as a guide for design of external insulation. 2 Experimental Evaluation 2.1 Geometrical configurations and conditiong of test specimens: The experimental investigations were carried out on 33kV polymer and porcelain insulator specimens for four numbers of each type. The polymeric insulator specimens are named as A, B, C and D whereas porcelain specimens as a, b, c and d. The geometrical configuration of the test specimens are tabulated in Table I. 2

3 Table.I Geometrical configurations S.No Particulars Polymer Porcelain 1 Length of the insulator (mm) Dry Arcing Distance (mm) Creepage Distance(mm) Specific Creepage Distance (mm/kv) Shed Diameter (mm) Number of Sheds Core diameter (mm) Shed Thickness(mm) Shed Spacing (mm) Fig 1. Test Specimens at Polluted Conditions All specimens are cleaned so that all traces of dirt and grease are removed from the surface of insulator. Then insulator is rinsed with de-mineralized (DM) water to clean and free from any grease, and it is dried naturally. Before every subsequent contamination the insulator was washed with DM water to remove all traces of pollution and then dried for 24 hours. Then the insulators were polluted by spraying the contamination on the surface of insulator by spraying method as per IEC 657. The contaminated solution was sprayed on the surface of insulator totally and specimen are left to dry naturally for 24 hours. This process was repeated for seven days till a uniform layer is formed on the surface. Similarly urea and cement contaminations were prepared and sprayed on test specimens as per the above procedure till a pollution layer is deposited. Figures 1a, 1b shows insulator during test under urea condition, 1c, 1d under cement pollution and 1e, 1f under salt pollution. 2.2 Test arrangement and test procedure: Insulator specimen are mounted in vertical position and energized as per the circuit diagram shown in Fig.2. One end of the test specimen is connected to high voltage terminal and the other end connected to ground with a ground clearance of 2 meters. From control panel, voltage is applied in steps and appropriate leakage current is recorded. Voltage is increased until breakdown takes place. 3

4 Fig 2. Experimental setup. 3 Test Results In order to predict the performance of insulators, leakage current and breakdown voltage are measured for all the specimens of polymer and porcelain. 3.1 Measurement of and : Leakage current () and Breakdown voltage () were measured for the following cases: 1. Four specimens of 33kV polymer insulators under dry, salt, cement and urea pollution. 2. Four specimens of 33kV porcelain insulators under dry, salt, cement and urea pollution Measurement of and for 33kV polymer insulators: All 33kV polymeric insulator specimens are conditioned and pollution is applied by spraying method for several days till a thick layer is observed. Then the samples are energized as per the above test procedure. The specimen during test with flashover was shown in Fig 3.Leakage current and breakdown voltage were recorded and tabulated in Table II. and are measured for all the polluted contaminated specimens. Fig.3 Specimen during testing Table II and of 33kV Polymer Insulators Condition A B C D Dry

5 With the help of these test results performance polymer insulator under pollutions were evaluated. Performance characteristics are shown in Fig.4. From Fig 4, for specimen A it is observed that among all pollutions leakage current values are high in salt and cement contamination compared to urea and in specimen B the values are almost same in all contaminations. In case of specimen C values under salt and urea are similar with a little difference but higher compared to cement. For specimen D, values are higher in salt pollution compared to urea and cement, and values of are same in urea and cement contaminations. Leakage current(µa ) Sample A Applied Voltage Lekage current(µa) Sample B Applied Voltage 6 5 Sample C Lekage current(µa) Applied Voltage Fig.4 Performance Characteristics of polymer Insulators This shows that the effect of salt contamination is more on polymer material compared to urea and cement. However the mixture of salt, urea and cement can cause a great increase of leakage current and finally degrades insulator surface and finally leads to breakdown. Because urea is highly soluble in water and it is having a property to reabsorb the water. Hence the presence of carbamide molecules on the surface of insulator when mixed with wet molecules increases leakage current thereby degrading the insulator surface. From Table II, by calculating average breakdown voltage of all specimens, it is observed that among all contaminations breakdown voltage is low in salt and cement compared to urea. This shows that salt and cement molecules degrades the insulator surface fast compared to urea however under urea pollution the leakage currents are higher. From the results of leakage current with respect to applied voltage it is also observed that for polymeric insulators the average leakage current of four specimens is more in urea contamination compared to salt and cement contaminations. In case of individual specimens maximum leakage current for all the specimens is varied in between 38.1 to 51 µa under salt condition. While under cement it is varied between 32 to 53.6 µa and for urea it is 42 to 5.5 µa. Hence it is conclude that the effect of silica SiO2, alumina, sodium chloride, iron and fly ash is more on polymer material which 5

6 affects the characteristics breakdown voltage and it also depends on ionic compounds Measurement of and for 33kV Porcelain insulators: All 33kV porcelain insulator specimens are conditioned and pollution is applied by spraying method for several days till a thick layer is observed. Then the samples are energized as per the above test procedure. Leakage current and breakdown voltage were recorded and tabulated in Table III. Table III and of 33kV Porcelain Insulators a b c d Condition Dry Leakage current(µa) Sample a Leakage current(µa) Sample b Applied Voltage Applied Voltage Leakage current(µa ) Sample c Leakage current(µa) Sampe d Applied Voltage Applied Voltage Fig.5 Performance Characteristics of porcelain Insulators and are measured for all the polluted contaminated specimens. With the help of these test results performance porcelain insulator under pollutions were evaluated. Performance characteristics are shown in Fig.5. From Table III for all the specimens a, b, c, d, it was observed that the average is low in cement and urea contaminations compared to salt. This shows that there is an effect of urea, cement and salt contaminations on the characteristics of porcelain insulators. Hence urea and cement together can cause a great damage to porcelain insulators. From these test results it is concluded that the effect of fertilizers and sea salt is more on porcelain insulators when insulators are located nearer to these pollution sources. Hence from the results, it concluded 6

7 that for porcelain insulators the leakage current is more in urea and salt contaminations compared to cement contamination because the breakdown takes place early in cement pollution compared to salt and urea. 3.2 Test Results comparison for polymer and porcelain insulators: By comparing the characteristics of both polymeric and porcelain insulators in all polluted conditions it observed that the effect of pollution on porcelain insulators is higher compare to polymer insulators. The influence of salt, cement and urea pollution is less in case of polymer compared to porcelain insulators. Based on the experimental data the breakdown voltage of polymer insulators in cement and urea contaminations it is 23% higher than that porcelain insulators, while for salt is 1%. Fig 6 shows the comparison of breakdown voltage at various conditions for both the porcelain and polymer insulators. Among all the pollutions in porcelain insulators the breakdown takes place early in cement contamination compared to salt and urea POLYMER PORCELIAN 12 1 PORCELIAN POLYMER FOV Leakage Current(µA) SALT CEMENT UREA SALT CEMENT UREA Fig.6 Comparision Fig.7 Comparision Fig 7 gives the comparison of leakage current for polymer and porcelain insulators at salt, cement and urea pollution conditions. Under urea contamination leakage current for porcelain insulator is 58% higher the polymer insulators and for salt condition it is 57%. While for cement contamination it is 1%. It is noticed that urea contamination will affect more on the performance of porcelain insulators. From results it is concluded that polymer insulators are able to withstand for higher voltages compared to porcelain in salt and urea contaminations. Further the effect of cement contamination on polymer and porcelain is less. Conclusion The main pollutants found on the surface of insulator under practical conditions are salts, cement and local dust. The characteristics of insulators are dependent on pollutants. In this paper a research has been conducted on polymer and porcelain specimens under different polluted conditions. Leakage current and breakdown voltage under polluted conditions are examined to predict the performance of insulator. Based on the data measured it can be concluded that polluted porcelain insulators have of 57%, 1% and 58% high leakage currents respectively for salt, cement and urea contaminations compared to polymer insulators and among salt, cement and urea pollutions flashover takes place early in cement pollution. The breakdown voltage is high in contaminated areas compared to non-polluted. 7

8 Acknowledgment We would like to gratitude University College of Engineering, JNTU Kakinada for their support in completion of this work. References [1]. H. Terrab, A. Bayadi, Experimental study using design of experiment of pollution layer effect on insulator performance taking into account the presence of dry bands, IEEE Transactions on Dielectric and electrical insulation, Vol. 21, pp , 214. [2]. M.El-A.Slama, A.Beroul and H.Hadi, Influence of the linear Non-uniformity of pollution layer on the insulator flashover under impulse voltage estimation of the effective pollution thickness, IEEE Transactions on Dielectric and electrical insulation, Vol. 18, pp , 211. [3]. R.Boudissa, S.Djafri, A.Haddad, R.Belaicha and R.Bearschi, Effect of insulator shape on surface discharges and flashover under polluted conditions, IEEE Transactions on Dielectric and electrical insulation, Vol. 12, pp , 25. [4]. P.Wilkins, Breakdown voltage of high-voltage insulators with uniform surfce-pollution films, IEE proceedings, Vol. 116, pp , [5]. Zhijin Zhang, Xiaohuan Liu, Xingliang jiang, Jianlin Hu and David Wenzhong Gao, Study on AC flashover performance for different types of porcelain and glass insulators with non-uniform pollution, IEEE Transactions on Power Delivery, Vol. 28, pp , 213. [6]. J.A.Eeir, Road salt on outdoor insulators, IEEE Electrical Insulation Conference, pp , 214. [7]. M.A.Douar, A.Mekhaldi and M.C.Bouzidi, Flashover process and frequency analysis of the leakage current on insulator model under non-uniform pollution conditions, IEEE Transactions on Dielectric and electrical insulation, Vol. 17, pp , 21. [8]. Xingliang Jiang, Shaohua Wang, Zhijin Zhang, Jianlin Hu and Qin Hu, Investigations of breakdown voltage and non-uniform pollution correction of short specimens of composite insulator intended for 8kV UHVDC, IEEE Transactions on Dielectric and electrical insulation, Vol. 18, pp. 71-8, 21. [9]. Kunikazu Izumi and Kenzo Kadotani, Applications of Polymeric Outdoor Insulation in Japan, IEEE Transactions on Dielectric and electrical insulation, Vol. 6, pp , Oct [1]. Reuben Hackam, Outdoor HV Composite Polymeric Insulators, IEEE Transactions on Dielectric and electrical insulation, Vol. 6, pp , [11]. J. F.Hall, History and Bibolography of Polymeric Insulators, IEEE Transactions on Power Delivery, Vol. 8, pp , [12]. T.Kikuhi, S.Nishimura, M.Nagao, KIzumi, Y.Kubota, and M.Sakata, Survey on the Use of Non-Ceramic Composite Insulators, IEEE Transactions on Dielectric and electrical insulation, Vol. 6, pp , [13]. IEC 657: Artificial pollution test on high voltage insulators to be used on AC systems,, [14]. IEC Standard 62217: Polymer insulators for indoor and outdoor use with a nominal voltage >1V-general definitions, test methods and acceptance criteria,

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