Hava taşıtlarında kablolarda elektriksel ve ısıl zorlanmaların incelenmesi
Investigation of electrical and thermal stresses in aircraft cables
- Tez No: 664934
- Danışmanlar: PROF. DR. ÖZCAN KALENDERLİ
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2021
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Elektrik Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Elektrik Mühendisliği Bilim Dalı
- Sayfa Sayısı: 121
Özet
Havacılık sektöründe ihtiyaçlar ve görev gereksinimlerin zaman geçtikçe artması bu alanda yeniliklerin doğmasına neden olmuştur. İşletme maliyetlerini ve yakıt tüketimini azaltmak ve bu doğrultuda uçakların ağırlığını düşürmek amacı ile daha yüksek gerilimli uçak kavramı ortaya çıkmıştır. Artan gerilim seviyeleri ile birlikte kablolama sisteminde ağırlık ve hacimsel olarak azalma sağlanmaktadır. Buna karşılık artan gerilim seviyesi ile birlikte fazladan yalıtım çalışmalarına gereksinim duyulmaktadır. Bu çalışmada uçaklardaki kablolama sistemine yönelik fiziksel zorlanma olayları ele alınmıştır. Havacılıkta kullanılan kablolama sistemlerin elektriksel ve ısıl analizleri üzerine çalışılmıştır. Kablolarda elektrik alan incelemeleri için Comsol'da elektrostatik bir model oluşturulmuştur. Kablo demetlerinde oluşan elektrik alan hesaplamaları sonlu elemanlar yöntemi ile yapılmıştır. Yalıtkan malzemenin içindeki hava boşluğunun elektrik alan üzerine etkisi incelenmiştir. Ayrıca yalıtkandaki hava boşluğu için farklı şekiller incelenmiş olup farklı şekillerdeki hava boşluklarının kabloda oluşturduğu elektrik alan şiddetleri incelenmiştir. Kablo yalıtkanındaki boşluklarda elektrik alan şiddetinin yüksek olduğu gözlemlenmiş ve elektrik alan şiddetinin yüksek olduğu bölgelerde hava boşluğu olduğunda bu değerin daha da arttığı görülmüştür. Kabloların içerisinden akım geçtikçe kabloda bir ısınma meydana gelmektedir. Artan sıcaklık ile de kablonun akım taşıma kapasitesinde azalma meydana gelmektedir. Bu tezde kablodan geçen akımın sıcaklık ile ilişkisi incelenmiştir. Bu doğrultuda Comsol'da ısı aktarımı aracı kullanılarak model oluşturulmuştur. Ayrıca kablolar arasındaki uzaklığın akım taşıma kapasitesine etkisini gözlemlemek adına analizler yapılmıştır. Kablolar birbirlerine yaklaştıkça sıcaklığın arttığı ve kablonun akım taşıma kapasitesinin azaldığı görülmüştür. Kablolarda kısmi boşalma başlangıç gerilimleri yüksek olmasına rağmen havacılıkta irtifanın artması ile basıncın düşmesi ve kullanılan gerilim değerinin de artması sonucu kısmi boşalma başlangıç geriliminin düşmesine neden olmaktadır. Bu yüzden kablolarda oluşan üç elektriksel boşalma türü de matematiksel olarak hesaplanmış bu değerlerin en küçük olanı kısmi boşalma başlangıç gerilimi olarak seçilmiştir. Aynı zamanda bu gerilim değerine güvenli çalışma gerilimi olarak da ifade edilebilir. Farklı kablo boyutları ve aynı hava boşluğu mesafeleri için gerilim değerleri hesaplanmış ve güvenli çalışma gerilimleri bulunmuştur. Aynı zamanda kablo yalıtkanını da değiştirerek kablo yalıtkanının güvenli çalışma gerilimi üzerine etkisi incelenmiştir.
Özet (Çeviri)
The increasing needs and mission requirements in the aerospace industry have led to innovations in this field. The concept of higher voltage aircraft has emerged in order to reduce operational costs, fuel consumption and reduce the weight of aircraft accordingly. Weight and volume decreasing of wiring system are provided with increased voltage level. Whereas extra insulation work is required with increased voltage level. In this study, stress events related to the wiring system in aircraft are discussed. Electrical and thermal analysis of wiring systems that used in aerospace industry have been studied. In addition, safe operating voltages for different cable sizes and different insulation materials have calculated and the results have compared. Electrostatic model is created in Comsol in order to electrical field investigation of cables. Electrical field calculations in cables have been made with finite element method. The air gap in the insulation material on the effect of electric field has investigated. It has been observed that the electric field value is high in the air gaps in the cable insulation and this value increases even more when there is an air gap in the regions where the electric field value is high. The effect of different geometric shapes of air gap in the cable insulation on the stress has been examined. Besides the effect of air gaps that have different geometric shapes, the effects of the location of air gaps on the cable, the dimension of air gap and number of air gaps have been examined. Electrical fields for as the variety geometric shape of air gaps that are sphere, cube, cone and cylinder shape air gaps have calculated on the cable. When looking at the stress values of the electric field according to the analysis values, it was seen that the cube shape of the air gap in the cable has the highest value of the stress of the electric field. In order to examine the effect of the positions of the air gaps in the cable, electric field analyzes have made for a distance of 6.5 mm, 8.5 mm, 10.5 mm and 12.5 mm from the conductor of cable. According to the analysis results, the electric field stress in the air gap closest to the conductor has 50 kV/m, while the electric field strength in the air gap farthest from the conductor has calculated as 18 kV/m. In this case, it has been observed that the electric field stress value that occur the air gap in the insulation decreases as it goes away from the conductor. In order to observe the effect of the size of the air gaps in the cable, the analysis of the spherical air gaps that have different radius have been made. Electric fields have calculated for the sphere radius of 0.25 mm, 0.5 mm, 0.75 mm and 1 mm. It has been observed that as the radius of the air gaps increases, the electric field in the air gaps increases.The effect of the number of air gaps in the cable have been investigated. Therefore, four air gaps have placed randomly on the cable insulation and the results have been analyzed. Electric field analyzes have made on the cable for three, two and one number of air gaps. It has been observed that when the number of air gaps is higher, the electric field values that occur in the air gaps are large, and as the number of air gaps decreases, the electric field values that occur in the air gaps decrease. When the obtained results have evaluated, it was understood from the analysis results that the positions of air gaps in the insulation of cable should also be taken into consideration. Heat occurs in the cables as the current flows through the cables. The current carrying capacity of the cable decreases with the increasing temperature. In this thesis, the relationship between the current passing through the cable and the temperature has been investigated. For this reason, model was created using the heat transfer tool in Comsol. In addition, analyzes have been made to observe the effect of the distance between the cables on the current carrying capacity. It has been observed that as the cables get close to each other, the temperature increases and the current carrying capacity of the cable decreases. The cable selected for analysis can withstand up to 200°C. Cables have placed vertically, horizontally and triangular positions, and thermal analyzes have made for three cables that have distance between 75 mm, 30 mm and adjacent. The current values obtained when the cables reach the temperature they can withstand have been compared. It has been observed that the current carrying capacity of the cables decreases as the cables approach each other in both horizontal and vertical orientation. The lowest current carrying capacity is calculated in the cable placement in triangle layout. In addition, by changing the ambient temperature, the effect of different temperature values on the current carrying capacity of the cables was also examined. Current carrying capacity has been calculated for each identical cables at 20 ° C, 50 ° C and 70 ° C. According to the analysis results, it has been determined that the current carrying capacity value of the cables decreases as the ambient temperature increases, they had reverse ratio. Although the partial discharge inception voltages (PDIV) of in cables are high, as a result of decreasing pressure with increasing altitude and the increase the operating voltage level in aerospace causes a decrease the PDIV. Therefore, the electrical discharges in the cables have been mathematically calculated, and the smallest of these values has been chosen as the PDIV. The lowest PDIV could be used to determine a safe operating voltage (SOV) for a cable system. PDIVs have calculated for different cable sizes and same air gap distances and safe operating voltages have found. At the same time, by changing the type of cable insulation, the effect of cable insulation on safe operating voltage has been investigated. Calculations of partial discharge voltages in cables are made for different cable sizes. In addition, safe operating voltages have been calculated for different types of cable insulations are PTFE, XLPE and PVC. For this, safe working voltages between cables and between cable and grounded surface have been calculated. As a result of the analysis, it was observed that the lowest safe operating voltage occurred between the cable and ground surface. Safe operating voltage is lower in cables with large diameter values. Additionally, when the insulation types are evaluated, PVC insulated cables with the highest dielectric coefficient have lower safe operating voltages. For this reason, it would be more advantageous to use PTFE insulators with lower dielectric coefficient in cables. Consequently, while making cable design or cable selection in aircraft, attention should be paid to environmental conditions as well as the technical characteristics of the cable. While the ambient temperature of the cable affects the current value that the cable can carry, the settlement place of the cables gains also important. The effect of the voltage applied to the cables that causes the electric field stress on the discharge event on the cable that will occur in the cable has been examined within the scope of this study. The effects of the type and size of the cable insulation, the air gaps occur in the cable insulation on the electric field stress in the cable were examined. Cables to be designed considering these factors will be longevity and effective against all kinds of electrical and thermal stress that may occur in aircraft cables. In aircraft, cables are placed in the air environment via the support of structural parts. Although the cable selection is made by considering the current carrying capacity of the cable, as in the literature, there are differences in calculation criteria. SAE AS50881 standard is taken into consideration when choosing cables in aerospace industry.
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