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EFFECT OF EXPOSURE CORONA DISCHARGE AGAINST NATURE OF CHANGE HYDROPHOBIC SURFACES SPECIMEN CERAMIC HIGH VOLTAGE INSULATOR Harry Prabowo1 and Tumiran2* Jurusan Teknik Elektro dan Teknologi Informasi, Universitas Gadjah Mada, Indonesia 2 Jurusan Teknik Elektro dan Teknologi Informasi, Universitas Gadjah Mada, Indonesia *Email:
[email protected],
[email protected] 1
Abstract: Criteria a good insulator that can be shown to function properly isolate and also the characteristics of high hydrophobic surface. Performance of an insulator is affected by the type of insulating material as well as environmental factors such as humidity, pollutants, and the phenomenon of corona discharge appears on the conductor. This study aims to determine the effects of corona discharge generated or generated by a needle-plane electrode of a hydrophobic insulator surface properties, which in this study using ceramic specimens. Tests carried out by the method of providing an alternating voltage 9 kV to 11 kV on the electrode needle-plane in order to produce a corona discharge in needle-plane electrodes. Between the needle electrode and surface of ceramic specimens were placed droplets of pure water and drops of water that has been littered with volcanic ash. The ceramic specimen surface has been coated by liquid nano silicon (“Nanokote”). The distance between the needle-plane electrodes on the surface of the ceramic specimen is set equal to 1 cm. Corona exposure of the specimen performed for 2 minutes. The results of these tests it was found that the contact angle of water drops 0 0 on a single ceramic specimen surface will become smaller from 87.64 to 20.26 after a given exposure corona exhibit hydrophobic properties changed to hydrophilic surfaces. According to the description, this paper examines the effects of corona discharge exposure of the hydrophobic properties of the surface of the insulator.
1 INTRODUCTION The application of a high voltage transmission line causing new problems. Some problems of high voltage application can be categorized into three areas of problems, the symptoms corona discharge, issue conductor insulation and isolation of equipment problems. [1]
The study emphasized on the test characteristics of hydrophobic materials are ceramic insulator corona exposure. Ceramic insulator materials have previously been given a layer of silicon nano ("Nanokote") Observations by the hydrophobic nature of the contact angle of water drops (droplets) on the surface of ceramic insulator specimen.
Corona occurs when there is emission in the vicinity of the electrodes resulting from the ionization of the gas in the system when the pressure isolation voltage. Have any impact on lower quality corona insulator and cause system failure. The phenomenon of corona discharge can also occur in the cavity of the insulator and conductor and insulator interface. [3]
2 THEORY 2.1 Corona discharge Corona is due to the ionization of the air, the air molecules lose electrons. Because electrons and ions will be separated, so that if there is an electric field in the vicinity, the free electrons will experience an accelerating force motion, so that there was a collision with another molecule. That places the ions and electrons new. This process will run continuously and the number of free electrons and ions are manyfold when the voltage gradient is quite large and the event is called the corona. [1]
The phenomenon of corona discharge is also a cause that affects all the problems associated with the insulator, since the insulator is an important component that determines the performance of the distribution of electrical energy. [4] Insulator with ceramic base material, glass, and porcelain tend to have a low hydrophobicity which has only a water contact angle of less than 300, this condition is in the category of hydrophilic, so that if operated in an environment that does not fit, poor electrical performance is not optimal to prevent formation of a layer of water on the surface of the insulator, so that the conductivity of the insulator surface is high so high leakage current. [5]
Corona discharge generally involves two asymmetric electrode. The electrode has a very curved surface (like the tip of a needle or small diameter wire) and the other electrode has a low
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curvature (like a plate or the ground). High curvature ensures a high potential gradient around the electrode, creating a plasma.. 2.2 Ceramic Insulator Ceramic insulators are made from a mixture of clay materials in a pure state has the chemical formula Al2O3 2SiO2 2H2O, called kaolin, silica minerals are quartz (SiO2) and feldspar [(K,Na) AlSi3O8], the outer shell coated with glass material that insulating materials are not porous. Glass coating on the surface of ceramic insulator becomes slick and shiny, so it does not absorb water.
Figure 1 : Ceramic surface contact angle According to the image can be classified into 3 major sections : 1. Materials that are wet (Hydrophilic) which has a contact angle with the surface of a liquid insulating material is less than 300 (θaverage< 300). 2. Materials that are almost wet (partially wetted) which has a contact angle with the surface of a liquid insulating material in the interval 300 to 890 (300 < θaverage < 890). 3. Material that is not wet (hydrophobicity) which has a contact angle of the liquid with the surface of the insulating material over 900 (θaverage > 900) [6]
Table 1 : Properties of ceramics Density Length expansion coefficient (α) Compressive strength Tensile strength Buckling strength
2.3-2.5 gram/cm3 3x10-4-4.5x10-6 /0C 4000-6000 kg/cm2 300-500 kg/cm2 with coatings 200-300 kg/cm2 without coatings 80-100 kg/cm
3 RESEARCH METHODOLOGY The research was conducted at the Laboratory of High Voltage Engineering in the Department of Electrical Engineering and Information Technology, Faculty of Engineering, Universitas Gadjah Mada.
Table 2 : Electrial properties of ceramics Breakdown voltage Resistivity Permittivity ( ) Tan δ
10-30 kV/mm 1011-1014 Ω cm 6-7 0,015-0,02
3.1 Testing equipment include : a) High voltage testers using high voltage test equipment UGM EL O41 - High Voltage Testing Device D – 205 – 52 ex – Japan. b) 50 µL micropipette. c) Measuring cup. d) Screen. e) Camera. f) Digital weight scales. g) Needle-plane electrode.
2.3 Hydrophobic and Hydrophilic Hydrophobic surface is easily wetted surfaces. Hydrophobic nature of the material is determined by the ratio of the cohesive forces of water with the force of adhesion between water and solids. Hydrophobic is the most useful properties of the insulator, because it can prevent the formation of water covering the surface between the tip insulator. A hydrophilic surface can be considered as if the contact angle is less than 900 ( < 900) or hydrophobic if the contact angle is more than 900 ( > 900). [2] Measurement of the contact angle on the ceramic surface by the equation: θaverage = 0.5 x [θ1+ θ2] θaverage, θ1 and θ2 are respectively the mean contact angle ceramic surface, contact angle left edge and right edge of the contact angle. While D is the diameter of the water drops.
Figure 2 : Needle-plane electrode
Hydrophobic properties of an insulating material can be determined by measuring the contact angle as shown in Figure 1.
3.2 Material in this research include: a) Ceramic (porcelain) b) Pure water (distilled water : H20)
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c) d) e) f)
Ceramic cleaning fluid Isopropyl alcohol Silicone nano ("Nanokote") Volcanic ash
(d) Figure 5 : The contact angle of pure water at several ceramic specimens (a) without coating nano silicon (b) once a nano silicon coating (c) 2 times the silicon nano coating (d) 3 times a coating of silicon nano.
3.3 The research phase Phase of the research: 1. Ceramic coating First ceramic material coated nano silicone fluid to fill the pores in the ceramic surface with nano-particles of silicone, so that the surface becomes hydrophobic ceramics that have high contact angles ≥ 900. 2. Testing the breakdown voltage variation range needle-plane electrode with ceramic materials. 3. Droplet surface preparation of ceramic materials. 4. Setting focus or camera distance with drops of water (droplet). 5. Testing the influence of the corona of the contact angle droplets (droplet). 6. Droplet contact angle measurement.
Contact angle measurement data plotted a graph to determine the effects of repetition coating the surface with silicon nano ceramic specimen to the increasing droplet contact angle.
Figure 6 : Graph the relationship between the contact angle with the number of coating. 4.2 Measurement of contact angle after a single drop of water exposed to the corona discharge a) Tests with drops of pure water Table 3 : The process of change in pure water droplet contact angles are given exposure to corona discharge. State Time (second) Contact Angle (θ) 0
87.040
15
850
30
83.390
4.1 Measurement of contact angles of water drops on the surface of the ceramic.
45
82.390
Here are some photos of contact angle measurement and droplet diameter after specimen surface ceramic coated silicon nano.
60 75
81.240 55.650
final
20.260
Figure 4 : Schematic of testing for the observation droplet exposed by the corona. 4 RESULTS AND DISCUSSSION
Measurement data obtained plotted a graph of the effect of duration of exposure corona operations against droplet contact angle. (a)
(b)
Figure 7 : Graph of the average contact angle for exposure during corona discharge.
(c)
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Figure 9 : Illustration of the measurement of the contact angle of droplet on the surface of the ceramic specimens.
b) Testing with drops of water containing pollutants
a) Tests with drops of pure water
Figure 8 : Graph of average droplet contact angles that contain pollutants during corona discharge exposed. Table 4 : The process of change in contact angle of droplets containing pollutants of volcanic ash are given exposure to corona discharge. State Time Contact (second) Angle (θ) 0
Figure 10 : Graph showing the relationship of exposure duration operations corona to the distance between the two droplets. State of two droplets
Time
0
86.95
0 second 0
6
75.015
12
57.630
22
60.490
32
59.950
42
67.870
52
61.260
62
67.840
72
68.480
82
63.480
92
64.480
102
59.70
112
58.250
122
57.050
final
65.910
4 second 8 second 12 second 24 second 48 second 72 second 96 second 120 second final Figure 11 : Two droplets of pure water are given exposure to the corona discharge b) Testing with water drops containing pollutants
4.3 Measurement of contact angle two drops of water (double droplet) adjacent
Table 5 : Two droplets containing pollutants are given exposure to the corona
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State of two droplets
Table 6 : Among drops of water (5 droplets) that were exposed corona discharge.
Time (second) 0
State of five droplets
Second
6 36 72 108 final
5 CONCLUSION According to data from the results of some testing that has been done, can be summed up as follows: 1. Contact angle of water droplets (droplet) to be increased for each additional layer of hydrophobic (silicone nano).
Figure 12 : Graph changes the distance between droplets containing pollutants are exposed by corona discharge
2. Hydrophobic nature of the surface of the ceramic specimen turned into hydrophilic. At the time of initial contact angle of 87.640 then the ceramic surface after corona were exposed for 2 minute to 20.260.
4.4 Measurement of contact angles of among water drops of the adjacent
3. Decrease in contact angle droplet containing pollutants that occur, not significant compared with the decrease in the contact angle of pure water droplet. 4. Testing 2 drops of water (double droplet) is approximated by a certain distance, the corona showed that exposure causes two drops of water could be getting closer or further away together or vice versa.
Figure 13 : Illustration of the measurement of the contact angle of droplet on the surface of the ceramic specimens.
6 ACKNOWLEDGMENTS Researchers are very grateful to the high voltage engineering laboratory technician, Mas Daryadi Mas Prasetyohadi and Rachmat Parlindungan Flores, in the Department of Electrical Engineering and Information Technology, Faculty of Engineering, Universitas Gadjah Mada, who has been instrumental in helping the passage of the research process. Figure 14 : Graph showing the relationship corona exposure duration operations against multiple droplet spacing.
7 REFERENCES [1] Arismunandar, Artono (2001).Teknik Tegangan Tinggi, Jakarta, PT Pradnya Paramita.
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[2] Prabowo, Harry, et al (2007). Hydrophobic Measurement of RTV Silane Epoxy Resin After Exposed In Tropical Climate. Proceedings ICEEI-International Conference on Electrical Engineering and Informatics, 17-19 Juni 2007, ITB-Institut Teknologi Bandung, Bandung, Indonesia. [3] Mayerhoff, Evan. (2007). Corona and its Effects, www.highvoltageconnection.com, accessed 25 Agustus 2012. [4] Prabowo, Harry, et al (2005). The Effects of Tropical Climate Aging on Dielectric Properties of Silane Epoxy Resins. Proceedings ISH 14International Symposium on High Voltage Engineering, 25-29 Agustus 2005, Tsinghua University, Beijing, China. [5] Prabowo Harry, et al (2005). SEM and FTIR Analysis of The Performance of RTV Silane Epoxy Resin After Obtaining Sea Pollution in Tropical, Proceedings ISH 14-International Symposium on High Voltage Engineering, 2529 Agustus 2005, Tsinghua University, Beijing, China. [6] Prabowo Harry, et al (2005). Methodology to Study The Electrical Performance of RTV Silane Epoxy Resin as The High Voltage Polimeric Materials Insulator in Tropical Climate, Proceedings ISH 14-International Symposium on High Voltage Engineering, 2529 Agustus 2005, Tsinghua University, Beijing, China. [7] Kasap, S.O. (2000). Principles of Electrical Materials and Devices, Engineering International Edition, McGraw Hill. [8] Zhu,Y., et al (2006). A Study on Hydrophobicity of Silicone Rubber Exposed to Corona Discharge. University of Miyazaki, Japan.
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EFFECT OF EXPOSURE CORONA DISCHARGE AGAINST NATURE OF CHANGE HYDROPHOBIC GLASS SURFACES SPECIMEN HIGH VOLTAGE INSULATOR Harry Prabowo1 and Tumiran2* Jurusan Teknik Elektro dan Teknologi Informasi, Universitas Gadjah Mada, Indonesia 2 Jurusan Teknik Elektro dan Teknologi Informasi, Universitas Gadjah Mada, Indonesia *Email:
[email protected],
[email protected] 1
Abstract: Insulation is an important part of the power system to maintain the continuity of the distribution of electric energy and protect electrical equipment from a variety of disorders. Insulators made of glass, an insulator that is widely used in Indonesia. Such materials have the disadvantage that when in a state of humid or rain will wet the surface, because these materials have a small water-repellent properties of the contact angle of water is less than 300, so it is classified to absorb water (hydrophilic). Wet surfaces can be used as a conductor of electrical current media which in turn causes the voltage flashover or breakdown. Moreover, if the insulator is placed in areas that a lot of pollutants. Pollutants that stick to the surface of the insulator along the water, and if it contains metal (conductor), will decrease the flashover voltage. In order to have the ability to hold the insulator surface flashover voltage, the insulator is made to have the properties of water-repellent (hydrophobic). The purpose of this study was to determine the effect of corona exposure arising from high voltage to the changing nature of the hydrophobic insulator surface, and also to determine the failure mechanism of the insulator due to the hydrophobic nature of the change. These tests use this type of glass insulators, using high voltage test equipment in the laboratory as a source of test voltage and corona generating devices, as well as insulating specimens using liquid coating product “Nanokote” for hydrophobic coating. Testing varied by adding volcanic ash as a pollutant. Step testing with water droplets and pollutants exposes the insulator below the corona. The results showed that when the water drops exposed corona, there will be a decrease in the contact angle of the surface of the insulator. It shows the changing nature of the original hydrophobic insulator surface changed to hydrophilic. Changes in the surface properties such as permanent hydrophobic coating has been damaged by exposure to the corona effect.
1
conductor, without making the current flows between conductors.
INTRODUCTION
Based on conductivity, solids are divided into three kinds, namely, conductors, insulators and semiconductors. The third difference is the substance of each wide band gap. The wider the band gap, the more difficult substances to electron flow. Electron flow in the conduction band. Conductor in its outer bands are the valence electrons are free, while semiconductors and insulators do not exist, therefore, the matter requires energy to move electrons in the tape to the outside. Energy to move the electron expressed in the band gap. Semiconductors need little energy to move the electrons, due to a short distance, contrary to an insulator. The more energy supplied to the material, then the material will be a conductor. [2]
Insulation for high voltage is usually made of a liquid or solid that has a penetrating resistance is much higher than the air or the atmosphere. [3] Good insulator must have a high waterrepellent properties (hydrophobic). When insulators are placed in areas that have a high level of pollution, such as industrial areas, chemical dust particles will stick to the surface of the insulator. The potential pollutant layer becomes conductive when mixed with water and atmospheric moisture conditions. Insulator surface conductivity increases with increasing pollutants attached, and led to a decline in the ability to isolate the insulator. 2. THEORY
Electrical insulator is a material that can not be missed or difficult to transfer electrical charge, as in the insulator material, valence electrons are tightly bound to the atoms. The materials used in electrical and electronic equipment as an insulator, or inhibiting the flow of electric current. Isolator also useful as a load-bearing or separator between
The contact angle is the angle formed between the surface of the insulating material with pure water droplet. Pure water or distilled water is dripped on the surface of the insulating material. The contact angle of water droplets explains the characteristics of an insulator, the absorbing
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a.
properties of water (hydrophilic) or the properties of water-repellent (hydrophobic). Determine the size of the contact angle of a material is hydrophobic or hydrophilic insulators. Hydrophobic properties that are important for an isolator. Hydrophobic insulator will be better able to withstand voltage and current while wet polluted conditions, compared hydrophilic insulator. [1]
b. c. d. e. f. g.
High Voltage Testing Device, Type D205 (52), Ogawa Seiki Co.., Ltd.. 5 KVA capacity. Input voltage 220 volts. Output voltage, for DC test 50 KV, AC test 70 KV, 200 KV impulse test. Frequency 50 Hz [4] Corona generator ord needle electrode plane High-resolution camera Temperature, air pressure and humidity meters Specimens of glass insulator Liquid silicon nano ("Nanokote") Pure water and pollutants (volcanic dust)
Figure 1. Measurement of contact angle on specimen surface.
……….(1) Figure 2. Schematic of testing for the observation droplet exposed by the corona.
θtotal is the mean between the contact angle on the left edge and the contact angle on the right edge of a pure water droplet.
Test steps are as follows:
This study uses a glass insulator material specimen. Glass material has several advantages: 1. Strong high dielectric, approximately 140 kV / cm. 2. Low expansion coefficient. 3. Easily designed (because of strong high dielectric). 4. Compressive strength greater than porcelain. 5. Material density is almost evenly (homogeneous).
1. Coating glass surfaces with nanoscale silicon liquid product of "Nanokote" to produce a hydrophobic glass surface. 2. Mixing pure water with volcanic ash pollutants. 3. Testing the breakdown voltage of the corona generator or needle plane. 4. Testing the influence of corona exposure to water droplet contact angle. 5. Testing the influence of corona exposure to water droplet contact angles were berpolutan. After a glass surface hydrophobic and breakdown voltage value of the test plants corona, calculated by corection factor in order to result the standard voltage value according the following equation:
weakness glass insulators are: 1. Easy water vapor condenses on the surface. Therefore, dust and dirt will easily accumulate on the surface, this event will facilitate the flow of leakage current as well as the occurrence of flashover voltage. 2. Glass materials have properties like fragile porcelain materials.
……….(2) The purpose of this study is to prove that when the surface of the glass insulators are given exposure to the corona, the duration will decrease the dielectric resistance represented by changes in the nature of the original hydrophobic insulator surface deformed to hydrophilic.
………(3) 4 RESULTS AND DISCUSSSION 4.1 Measurement contact angle of water droplet before exposed corona
3 RESEARCH METHODOLOGY The study was conducted at the Laboratory of High Voltage Engineering and Electrical Engineering Department of Information Technology, Faculty of Engineering, Universitas Gadjah Mada.
Table 1. Measurement of contact angle Coated amount
Testing equipment consists of:
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Contact angle (0)
0
10.5
1
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2
69
3
94
effect of duration of exposure corona operations against contact angle of pure water droplet.
A growing number of repetitions glass surface coating with nano-liquid silicon, then the larger the contact angle, the surface properties of glass to be more hydrophobic. 4.2 Concept of measurement of contact angle water droplet during exposed corona
Figure 4. Measurement of contact angle of single water droplet exposed corona. 4.3 Contact angle measurement of some water droplet exposed corona 4.3.1 Measurement of two pure water droplet Table 3. Measurement of two pure water droplet during exposed corona
Figure 3a. Illustration of water droplet start to exposed corona.
Time (second)
Figure 3b. Illustration final condition of water droplet exposed corona Table 2. Measurement of water droplet during exposed corona. Time (second)
State of droplet
Contact angle (0)
0
80
30
52.5
60
60
72
49
75
37.5
78
35
90
16
120
12
ϴ1
ϴ2
x
0
72.5
100
2.4
2
67
99
2.3
4
67
100
2.3
6
63.5
97
2.0
8
58
52
1.3
10
50.5
51.5
0.6
12 14 16 30
Contact angle data measured corona exposure results were plotted into a graph to determine the
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State process of two droplets
36.5 42.5 47.5 48
0 0 0 0
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60 90 120
46 45 43
(second)
0 0
droplet
angle (0)
20
61
40
60
60
58
80
52
100
44
120
36
130
33
0
The measured contact angle data is plotted into a graph to determine the effect of duration of exposure corona operation against two droplets of pure water.
Based on the measured contact angle data is plotted into a graph to determine the effect of duration of exposure corona operations against polluted water contact angle of droplets.
Figure 5. Deformation of contact angle of two pure water droplet exposed corona 4.3.2 Measurement of five pure water droplet Table 4. Measurement of five pure water droplet during exposed corona Time (second) 0
Figure 6. Measurement of contact angle of polluted water droplet exposed corona
State process of five droplets
4.5 Contact angle measurement of some polluted water droplet exposed corona
20 40 60
Table 6. Measurement of two polluted water droplet exposed corona Time State of two droplets ϴ1 ϴ2 x (second) 92 93 2.5 0
62 64 66 68 70 76 Air breakdown voltage occurs on the second needle electrode plane 78th. 4.4 Contact angle measurement of polluted water droplet exposed corona Tabel 5. Measurement of polluted water droplet exposed corona Time State of water Contact
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20
46
37
4.6
40
41
41
9.9
60
40
42
10.5
80
40
42
10.4
100
38
41
10.4
120
36
37
10.4
~
36
37
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larger breakdown voltage. Water droplet corona affected will be good conductor. 8. Glass insulator material specimens that have been exposed to the corona, the layer will be damaged. So that the glass surface hydrophobic properties remain intact, then resurfacing should be done with liquid silicon nano-products from the "Nanokote". 6 ACKNOWLEDGMENTS Researchers are very grateful to the high voltage engineering laboratory technician, Mas Daryadi Mas Prasetyohadi and Bayu Kurniawan, in the Department of Electrical Engineering and Information Technology, Faculty of Engineering, Universitas Gadjah Mada, who has been instrumental in helping the passage of the research process.c.
Figure 7. Deformation of contact angle of two polluted water droplet exposed corona
5 CONCLUSION 1. High voltage testing of corona generator or needle plane electrode is the greater distance between the electrode and insulator, the breakdown voltage will be increased. Voltage level increase based on the distance interval approached linearly state relations.
7 REFERENCES [1] Prabowo, Harry, et al (2007). Hydrophobic Measurement of RTV Silane Epoxy Resin After Exposed In Tropical Climate. Proceedings ICEEI-International Conference on Electrical Engineering and Informatics, 17-19 Juni 2007, ITB-Institut Teknologi Bandung, Bandung, Indonesia. [2] Halliday, Resnick, (2008). Chapter 41 Electrical Properties of Materials, 8th Edition, Wiley International Student Edition. [3] Kuffel, Zaengl, (2000). High Voltage Engineering: Fundamentals, 2nd Edition, Newnes. [4] Instruction Manual, 1979, High Voltage Testing Device-Type D205, Ogawa Seiki Co., Ltd., Tokyo.
2. Breakdown withstand voltage increase occurs around 6% in the glass specimen, after coated with liquid “Nanokote”, then will be reduced to the same as before the breakdown voltage coated. It was after some time tested for corona exposure. 3. Testing the exposed corona to pure water droplet, experienced a decrease in the hydrophobic nature of the glass specimen surface, as shown by the large downward from the contact angle of 800 to 100. 4. Testing a few drops of pure water is a decline exposed corona contact angle value. But the decline is not significant when compared with single water droplet test. Corona energy is used to reduce contact angle of water droplet, divided into each droplet. 5. Testing mixed drops of water and volcanic dust exposed corona, also experienced a decrease in the contact angle. Value is still much smaller decline than pure water. This is because many materials (silica) contained in volcani dust as pollutan. 6. Some water droplet exposed corona will experience a widening of the surface, can droplet distance closer or far towards widening hanging droplet, respectively. That is because the droplet experiencing polarization. 7. Testing five drops of water occurs when exposed corona breakdown voltage. When Rainy conditions (much water Droplets) likely to be the
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