FIGHTING POLLUTION IN THE CRETAN TRANSMISSION SYSTEM 25 Years experience

Transcription

1 FIGHTING POLLUTION IN THE CRETAN TRANSMISSION SYSTEM 25 Years experience J.Stefanakis PPC E. Thalassinakis PPC K. Siderakis University of Patras D. Agoris University of Patras E.Dialynas NTUA Abstract This paper presents the issue of the high voltage installations pollution as it relates to Crete and the efforts that have been made to deal with the problem in the last 25 years. More specifically it focuses at the following points: 1. Geographical and climatic features of the island as they relate to pollution. 2. Basic characteristics of the Cretan Power System. 3. The pollution problem under the specific local circumstances and a historical flashback to the last 25 years, showing the measures and techniques that have been taken and the corresponding results. 4. The research program that has begun in collaboration with Patras University. 5. Summary- Questionnaire 1. Geographical and climatic features of the island 1.1 Location of the island As it is apparent in the figure 1 Crete is situated in the Mediterranean basin the southernmost part of Europe, Figure 1. Location of the island

2 2 1.2 Crete morphology The shape and morphology of the island contribute to some specific features closely related with the pollution problem on the high as well on the medium voltage installations. The island (see figure 2) is 26 km long and 15-6 km wide. As a result, it has a Figure 2. Morphology of Crete relatively long coastline (146 km), mostly rocky. This fact, coupled with the strong winds, results in the dispersal of atomized seawater droplets and their deposition on the insulators. On the other hand, the interior of the island is quite mountainous with three main mountainous formations with more than 2 m altitude. 1.3 Micro Environments It s quite important to mention that the variety of morphological features (plenty of hills, valleys and gorges) creates various climatic microenvironments, which make parts of the Power System well protected and some others totally exposed to severe marine pollution (see figures 3 and 4). Figure 3. Samaria Gorge Figure 4. Hilly landscape It should be made clear that although salty seawater is not the only polluting agent, it is by far the most important. 1.4 Climate (west-east) Speaking of the climate we should point out the very a long dry period usually starting at he end of April and very often terminated at the end of October (see figure 5) April 21 Heraklion Crete

3 Although the total amount of rain fall on the island is significant, it is unevenly distributed during the year and throughout the island. At this point we have to point out that the west part of the island has the advantage of receiving almost double rainfalls in comparison to the east part. This is a very important characteristic, which, in combination with the stronger winds in the east, makes the pollution problem by far more severe at the east side October September Nov ember August December July January June February May March April Figure 5. Crete climate Precipitation The following diagram (figure 6) shows the average precipitation in Iraklion district from 94 to 98. The valley of the diagram shows clearly this dry period although the average makes it less evident Precipitation (mm) (94-98) Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. Nov. Dec. S1 Figure 6. Precipitation 1.6 Temperature In the next diagram (figure 7) the probability density of temperatures for three characteristic months (February, May and August) is depicted. Figure 7. Probability density of temperatures It comes out that the most probable temperature for February, (which is the coldest month of the year), is about 16 degrees Celsius, the corresponding temperature for August, which together with July, are the warmest months, is below 3 degrees Celsius. If one compares this diagram with the corresponding values from other parts of mainland Greece, one can prove the fact that Crete has indeed a milder climate as a result of the dominant influence of the surrounding sea April 21 Heraklion Crete

4 4 1.7 Relative Humidity Next diagram (figure 8) gives the probability density of relative humidity for two months (July and August). It can be seen that the most probable relative humidity, which for July is about 6%, and for August is about 67 %. The most interesting information on this diagram comes from the part of the surface under the curves situated to the right of the vertical line at about 75 % r.h. As it is known from the bibliography, the problem of pollution with its two contributors (contamination and humidity) becomes really severe only when the relative humidity exceeds a threshold of about 75 %. It is something that we ll have the chance to verify later from our own measurements. From this point of view we note that July is a month with a low probability pollution problem and, on the other hand, August is a crucial month because of the summer long accumulated contamination and the fact that humidity quite often exceeds the crucial threshold. 1.8 Wind Figure 8. Probability density of relative humidity Next diagram (figure 9) gives the mean (ten minutes averaging) wind speed for the year 2 of eastern Crete where the Wind potential is the highest and where the majority of Wind Farms (W/F) are located Jan. Feb. Mar. Apr. May Wind speed (m/sec) 'eastern Crete' June July Aug. Sep. Oct. year Nov. Figure 9. Mean wind speed Dec. S1 Figure 1. Tree bent to the wind Summer months (June, July and August) have the most winds and no precipitation at the same time. The following picture (figure 1) with the tree totally bent to the wind, in a place not far from Iraklion speaks for itself April 21 Heraklion Crete

5 11 ΥΣ Καστελ ίου 13 4 ΥΣ Αγ ιάς ΘΗΣ Χαν ίων ΥΣ Χαν ίων ΥΣ Γεωργιούπολης ΥΣ Ηράκλειο ΙΙ ΑΗΣ Λιν οπεραμάτων ΥΣ Ρεθύμνου ΥΣ 66 KV ΑΗΣ Λιν. ΥΣ 15 KV ΑΗΣ Λιν. ΥΣ Ηράκλειο Ι 12 ΥΣ Ηράκλειο ΙΙΙ ΥΣ Μοιρών 9 Α/Π IWEC O 7 ΥΣ Πραιτωρίων ΥΣ Γουβών ΥΣ Σταλίδας Μελλοντικές Εγ καταστάσεις ΥΣ Αγ. Νικολάου 3 5 ΥΣ Ιεράπετρας ΥΣ Σητείας A/Π Αχλάδια Α/Π Ανεμόεσσα Α/Π Κριά ΥΣ Μαρων ιάς Α/Π Ξηρολ ίμνη Α/Π Τοπλού 6 Α/Π Ρόκα 2 Α/Π Aeolos ΑΗ Σ Αθερινόλακου Contamination Issues on High Voltage Installations Wind Direction The wind chart (figure 11) shows clearly the dominant wind directions being north northwest. Figure 11. Wind chart The consistent north winds blowing during the summer period are a common feature of Aegean Islands and have a great influence on the mild climate of the them. 2. Basic characteristics of the Cretan Power System 2.1 Cretan Power System (CPS) The CPS (see figure 12) includes two Power plants one in Heraklion and the other in Hania with total capacity of 515 MW Figure 12. Cretan Power System Till June 21, the total installed W/F capacity is 67 MW, and an additional number of some new Wind Farms of total capacity 54 MW has been approved for installation and are expected to start producing at the end of the year 22. The Transmission System has two voltage levels. The main part of the System works at 15 kv but there is also a small old part working at 66kv, which is going soon to be April 21 Heraklion Crete

6 6 upgraded also to 15kv. There are 12 substations of 15 kv and 2 substations of 66 kv. The total length of Transmission Lines (T.L.) is about 532 km long. It is interesting to mention that Corsica, another Mediterranean island bigger than Crete with more energy consumption, has a 6kv Transmission System. The peak load of the island is always in the summer because of tourism and last year it came up to 418 MW (mean hourly peak). 2.2 System Characteristics As it is already apparent, the characteristics of the Cretan Power System are the following: -It s a small system -It is isolated from the mainland -It s located mainly near the coast and especially the north coast where the biggest cities and most of the hotels are located. This has to be considered in combination with the more frequent north winds so the marine pollution becomes really very severe. -The numerous W/F installed during the last few years, because of the corresponding national law and European funds, have as a result the operation of the System with high Wind Power Penetration (WWP), often approaching the levels of 3-4%, which is a world wide record. Next diagram (figure 13) speaks for itself. 25, 2, 15, 1, 5,, Penetration Total Load Wind :: 1:12: 2:24: 3:36: 4:48: 6:: 7:12: 8:24: ΦΟΡΤΙΑ ΣΥΝΟΛΟ Α/Π Συντ. Διεισδ. Figure 13. Wind Power Penetration The blue line gives the load, the green line is the wind production and the red one shows the resulting WWP, reaching, on this day, the significant level of 4%. -The characteristics mentioned above, describe a rather vulnerable and sensitive System. 3. The pollution problem under the specific local circumstances 3.1 Severe pollution problem April 21 Heraklion Crete

7 7 As it is already mentioned the long dry period, the variety of climatic microenvironments, the prevailing strong north winds, the fact that the System is isolated and fault sensitive and also located near the coast, contribute to a severe pollution problem, which needs special approach and study. 3.2 Impacts of Pollution Some of the impacts of the pollution that have been verified in our System are the flashovers (figure 14), the corrosion on the metal parts (figure 15) and the acoustic noise. Figure 14. Flashover on insulator Figure 15. Corrosion on the metal part 3.3 Transmission System s upgrade If one wants to follow up the pollution problem through the years, one is obliged to focus at the milestone years when the System was gradually built and upgraded. -The first 66kv T.L. from Heraklion to Chania was built at early 6s. It was a T.L. on wooden structures and from the beginning of its operation the pollution phenomenon made its appearance with the burning of the upper parts of the structures. To solve this problem copper wires were placed along the horizontal wooden crossbeams in order to make the potential equal. -Next milestone year was 1969 with the operation of a new line to Eastern Crete, an area where the pollution problem proved to be much more severe. Because of the severe pollution conditions there were times that the line couldn t be re-energized after being out due to a flash over. -The existing 15kv Transmission System came into operation gradually from 76 to 79 and this brought a new era in the pollution affairs. 3.4 Faults Figure 16 shows the total faults on the Transmission System during the last two decades from pollution and other causes % 19.6% Figure 16. Faults on the transmission System April 21 Heraklion Crete

8 8 The remarkable points here are first that pollution is indeed an important source for the System faults and second it is apparent that there has been some progress in the fight against pollution from one decade to the next. 3.5 Measures against pollution The measures that have been taken are distinguished into two categories, preventive and corrective. -Regarding (T.L.) the preventive measures consist of: the increase of the insulation level (between 3.2kv/cm and 3.9 kv/cm) the use of composite insulators -Regarding Substations: straight from the beginning the 15 kv Substations were designed with metal cladding at the medium voltage side there is one 66kv building enclosed substation. two new G.I.S. substations are also planned for installation. Corrective measures include dead washing, live washing with helicopter and the use of hydrophobic coatings. 3.6 Insulators A great variety of different insulator materials and profiles have been used and tested in the Cretan Transmission System. After the completion of the new double circuit line, most part of which is already constructed, the insulator map of the T.L s becomes: Composite 3% Porcelain fog type 19% Porcelain normal 21 % Glass fog 25% Glass normal 5% 3.7 How important is the profile? -Although 4 Kv don t exist on Crete a number of 4 kv insulators were used in a T.L., which was upgraded from 66kv to 15 kv. The performance of these insulators couldn t be worse. From 85 until the end of 94, 294 of these insulators out of 531 (percentage55%) were replaced because of deterioration after flashovers. In the same period and in the same line, for the type 15 kv insulator, only 23 pieces out of 3,2 were replaced (percentage.7 %). If we look carefully at the two different insulator type profiles (figure 18), we can notice that: For the 15Kv type the exposed outer surface is the 53% of the total surface On the other hand, for the 4Kv type the exposed outer surface is only the 36% of the total surface. This leads, in our opinion, to a better self cleaning of the first type, under our special meteorological conditions with the long dry period and the strong winds. Last but not least, the design of the insulator profile should take into consideration the specific conditions under which, the insulator is going to operate and perhaps it should be tested in the field before the general application April 21 Heraklion Crete

9 9 3.8 Washing The first maintenance work against pollution was dead washing with sponges and buckets, a primitive method for cleaning the insulators, which was implemented from 1978 until 81. On the diagram of the figure 18 we can see the corresponding faults on the System at that first period. During the following years 82,83,84 no 15 washing was done and the favorable meteorological conditions helped so that 8 TOTAL FAULTS the System didn t experience many 6 faults. This break was short lived and in the System experienced flashovers with the corresponding consequences. After that, it was well understood that the care for the pollution was of first priority for the stability and Figure 18. Faults due to pollution reliability of the System and a new method for dead washing with pressurized water (figure 19) was introduced both in the Substations and the T.L. as well. This method was initiated in 1985 and it has been in use since then, although it is combined with other methods as well. 1 Figure 19. Pressurized water washing - -In a similar way T.L. insulators are washed. Suitable vehicles with water tanks and high pressure pumps and water jets are used and the technician climbs up onto the tower to wash the insulators. It is worthwhile to mention that our personnel performs this kind of work also in the double Circuit Line, washing the one circuit dead, although the other is under voltage. -After 1995 P.P.C. has introduced the method of live washing with helicopter for the T.L (figure 2). Figure 2. Live washing with helicopter April 21 Heraklion Crete

10 1 This kind of washing is used both in the Cretan Power System as well as in some parts of the mainland Power System, which also suffers from some kind of pollution. Its main advantages are that it is a fast method and that you don t need to take the lines out of service. The disadvantages are, that under strong wind conditions, a situation not rare in Crete, the helicopter cannot fly and that for lines going parallel in a small distance from each other the access for the inner strings is not possible. In those cases we have to employ our old methods. 3.9 Coatings Another category of corrective measures is the use of coatings - the first coating that was used was silicon grease. It s a material that needs replacement every 6 months due to saturation and loss of its hydrophobic properties. This method was applied in sensitive elements such as Lightning arrestors, bushings, some circuit breakers etc. It is considered a time consuming and expensive method. - Next, we proceed to the application of the Room Temperature Vulcanized Materials (RTV s). They are materials with a much longer life and superior hydrophobic properties. - The implementation of this method started in 1998 and we have proceeded with rather fast steps because we believe in the efficacy of these materials. Since the first application we have never washed the corresponding installation and the results until now are very promising (no flashover occurred). Figure 21. Application of RTV s - The application of these materials (see figure 21) is performed by our own maintenance personnel. Up to now we have covered the two Substations of the Power Plant in Linoperamata, substations with severe pollution problems, and the Substations of Ierapetra and Sitia in eastern Crete while Soroni in Rhodos is covered by 5%. - A 15kv gate with about 4 insulators needs on average 7 kg of RTV and takes about 17 man-hours of expert labor April 21 Heraklion Crete

11 Total quantities of RTV s The bar diagram of figures 22 shows the total quantities of RTV s of two different manufacturers that we have used in the last three years, a total of more than 3Kg. (KG) 2 15 Material B Material A 268 total 334kg Figure 22. Quantities of RTV s used 3.11 Money savings In the photo of the figure 23 there is an aerial view of the Linoperamata Power Plant with two substations (one 15kv and another 66kv). They are exposed to marine as well as industrial contamination. Now the substations are totally covered with RTV s and the money already saved from the first year of application was significant. Figure 23. View of the Linoperamata It must be stressed that the great savings in this case come from the fact that because the washing is done during the high load season and because of the overall configuration of the System, we have to take out of service the cheap Base Units and put in operation the very expensive Gas turbines As can be seen from figure 24, for the twice a year wash policy, only the additional fuel cost is $ 24. On the other hand, with the RTV s policy, the materials cost was $ 139 and the application cost with our own personnel came up to $ 48. Savings of about $ 53 during the first year of the RTV s life. Linoperamat a Substation Washing twice/year RTV's material cost 52 million drx =$ 139 application cost 18 million drx =$ 48 additional fuel cost 9 million drx =$ 24 Total cost 7 million drx =$ 187 Savings 2 million drx = $ 53 Figure 24. Money savings April 21 Heraklion Crete

12 Actions and results In the combined Gant and bar diagram of fig. 25 the implemented pollution fighting methods and the corresponding faults because of pollution can be seen. It is apparent that the strategy and the variety of measures that have been implemented have borne some fruits. Figure 25. Action and results On the other hand, the exception of the year 92 when the System experienced a lot of faults (5), despite the equally intensive care and effort, shows the real dimensions of the pollution problem, a phenomenon depending on many parameters, that always keeps you on your toes. 4. Research program in collaboration with Patras University. 4.1 Efforts at two levels For this reason effort was given at two different levels - the first level refers to the new materials and technologies already discussed. - the second level with keeping in touch with the latest developments as they relate to the field. In line with this level, a research program has been signed between PPC and the High Voltage Laboratory of Patras University. The aim of this collaboration is the execution of special measurements in order to monitor the various parameters of the phenomenon and to keep in contact with the relevant progress made world-wide. 4.2 Research program The purpose of this program is first the better understanding of the pollution phenomenon in Crete and second the performance of new materials (composite insulators of different shapes, materials and manufactures, RTVs etc.) The means by which this will be achieved are: - measurements in the field (leakage current etc.) April 21 Heraklion Crete

13 13 - measurements of climatic parameters ( temperature, humidity etc.) - Lab measurements at the High Voltage Laboratory of Patras University. 4.3 Measurements Data for the meteorological parameters come either from the National Meteorological Service or by our own measurements. With an instrument that is already installed we are in the position to measure temperature, rainfall, humidity, winds, as well as ultra violent radiation. The purpose of these data is to draw the meteorological map of the Cretan System and find out the crucial times that we have to cope with the pollution problem. - The equivalent salt density deposition (ESDD) measurement helps us to take decisions about when and where to wash. - The leakage current measurement will give us valuable information about the behavior of various organic materials and their ageing under our field conditions. We need to know which coating and which composite insulator has better performance. 4.4 On Line leakage current and meteorological parameters monitoring System Figure 26 shows a view of the leakage current and meteorological parameter monitoring System, which is installed in the Heraklion II Substation. Figure 26. Leakage current and meteorological parameter monitoring System In the figure 27 leakage current sensor at the base of the insulator and wind sensor can also be seen. 4.5 Leakage current waveform Figure 27. Leakage current sensor at the base of the insulator and wind sensor In the next few diagrams some of our own measurements are presented. Figure 28 gives the leakage current waveform, in a half a second time window April 21 Heraklion Crete

14 Peak Waves for OLCA24 installed at SUBSTATION IRAKLION 2 (24/5/2 to 8/8/2) 12 1 Chan 2 current Chan 2 voltage Current (ma) Voltage (kv) ms -15ms -1ms -5ms ms 5ms 1ms Peakw ave occured at 11/6/2 11:35:18 πμ 15ms 2ms Figure 28. Leakage current waveform The red waveform is the leakage current and the blue one is the corresponding phase to ground voltage. It s interesting to notice that leakage current suddenly surges from zero to about 6 ma and disappears after some cycles in order to come later at random. This picture already gives the identity of the random character of this phenomenon. The small leakage current of 6mA corresponds to some pollution activity. As it is known from the bibliography there is not an accurate model determining the current threshold above which flashover occurs, but it is generally acceptable that it should stay below one Ampere, in order to be on the safe side. 4.6 Leakage current waveform A zooming into the characteristics of this current (see figure 29), shows that it is a resistive current, as it is in phase with the voltage, and that implies energy dissipation. It can also be seen that it is not a pure sine but it stays near zero before the voltage achieves a considerable value. Peak Waves for OLCA24 installed at SUBSTATION IRAKLION 2 (24/5/2 to 8/8/2) Chan 2 current Chan 2 voltage Current (ma) Voltage (kv) ms -9ms -8ms -7ms -6ms Peakw ave occured at 11/6/2 11:35:18 πμ -5ms -4ms Figure 29. Resistive current 4.7 Fast Fourier Transform Next picture (figure 3) gives the fast Fourier transform for the same current waveform. The 3 rd harmonic is the most important one and as it is known from the bibliography the considerable harmonics reach as far as the 6 th -7 th April 21 Heraklion Crete

15 15 Peak Waves for OLCA24 installed at SUBSTATION IRAKLION 2 (24/5/2 to 8/8/2) , Chan 2 current Chan 2 voltage FFT Current (ma ) Voltage (kv) ms -15ms -1ms -5ms ms 5ms 1ms Peakw ave occured at 11/6/2 11:35:18 πμ 15ms 2ms Figure 3. Fast Fourier Transform 4.8 Accumulated energy loss Figure 31 shows the accumulated energy loss on the surface of two insulators for a period of one month (June 2) due to the leakage current. Both lines correspond to porcelain post insulators but the red one with RTV coating. The dissipated energy for the bare one (left hand axis) was 18 KJ and for the RTV coating was only 3.5 kj (left hand axis). The comparison is overwhelming in favour of the RTV. OLCA24 installed at SUBSTATION IRAKLION 2 (24/5/2 to 26/6/2) 18, 17, 1 Accumulated Energy Loss 2 Accumulated Energy Loss 16, 3 15, Accumulated Energy Loss (kj), 14, 13, 12, 11, 1, 9, 8, 7, 6, 5, 4, 2 1 Accumulated Energy Loss (kj), 3, 2, 1, 12: πμ 28/5/2 12: πμ 12/6/2 12: πμ 27/6/2 4.9 Energy loss in Linoperamata Figure 31. Accumulated energy loss Assuming the same energy loss for every insulator in the Linoperamata substation, we can estimate with a simple calculation, that for the same month (last June) a total amount of 55 KWh of energy was saved after the coatings were applied. 4.1 Comparison of two coatings Figure 32 gives a first comparison between the two RTV s already used OLCA24 installed at SUBSTATION IRAKLION 2 (24/5/2 to 26/6/2) 1 Accumulated Energy Loss 7 Accumulated Energy Loss Accumulated Energy Loss (kj) Figure 32. Comparison between the two RTV s 12: πμ 3/5/2 12: πμ 6/6/2 12: πμ 13/6/2 12: πμ 2/6/2 12: πμ 27/6/ April 21 Heraklion Crete

16 16 The two materials appear to have the same efficacy although it s too early for us to have reliable results Accumulated charge Figure 33 gives the accumulated positive charge during the same month and the two lines give the charges for a bare and a covered with RTV insulator. Once again the comparison is 18 C to.11 C. Accumulated Pos/Neg Charge (C), OLCA24 installed at SUBSTATION IRAKLION 2 (24/5/2 to 26/6/2) : πμ 12: πμ 12: πμ 28/5/2 12/6/2 27/6/2 Accumulated Pos/Neg Charge (C), 1 Accumulated Pos/Neg Charge 2 Accumulated Pos/Neg Charge Figure 33. Accumulated positive charge 4.12 Positive/negative peak current Next diagram (figure 34) shows the positive and negative peak leakage currents for a period of about two weeks. We notice that there is no current during the whole period except for some hours in one day when pollution activity is recorded. Pos/Neg Peak Current (ma) OLCA24 installed at SUBSTATION IRAKLION 2 (23/6/2 to 9/7/2) 12: πμ 12: πμ 26/6/2 3/7/2 12: πμ 1/7/2 2 Pos/Neg Peak Current Figure 34. Positive and negative peak leakage 4.13 Positive/negative peak current vs. humidity If the relative humidity is included in the same diagram (see figure 35), one can notice that it is kept below the 75% during the whole period except for that crucial time when leakage current is recorded. This strengthens the already mentioned comment that in order to have considerable leakage current and pollution activity, relative humidity must exceed a specific threshold April 21 Heraklion Crete

17 17 Humidity (%), OLCA24 installed at SUBSTATION IRAKLION 2 (23/6/2 to 9/7/2) Pos/Neg Peak Current (ma), 2 Pos/Neg Peak Current Humidity (%) Figure 35. Relative humiditypositive and negative peak leakage : πμ 26/6/2 12: πμ 3/7/2 12: πμ 1/7/ Relative humidity threshold A zooming into that specific day (see figure 36), the picture regarding the humidity threshold becomes much clearer. Pos/Neg Peak Current (ma), Humidity (%), Windspeed (m/s), OLCA24 installed at SUBSTATION IRAKLION 2 (23/6/2 to 9/7/2) 12: πμ 6: πμ 12: μμ 6: μμ 1/7/2 1/7/2 1/7/2 1/7/2 12: πμ 2/7/2 2 Pos/Neg Peak Current Humidity (%) Windspeed (m/s) Figure 36. Relative humiditypositive and negative peak leakage 5. Epilogue As an epilogue the following questionnaire is proposed for answers: - Composite insulators or RTV s have better performance? - What is more dangerous, drizzle or fog conditions? - Is aging more due to the leakage current or to corona phenomenon? - What is the role of the corona in the final flashover? - Which type of pollution is more difficult to overcome by all hydrophobic materials? - How many years is it estimated that RTVs will last with no washing in our own conditions and what should be done after their degradation? - What type of insulator profile is the most suitable for subtropical conditions (fog type, aerodynamic etc.)? - What is the upper level for the leakage current so we can be on the safe side? - Is the heat capacity of the insulator material an important parameter, in the formation of the dew on its outer surface, which has to be considered in the insulator design? - Is the smoothest distribution of the field on the outer surface the most important factor in the design of the insulator, or are there other dynamic parameters that should be considered in the design? April 21 Heraklion Crete