Sonlu elemanlar metodu ile doğru akım motorunun magnetik alan incelemesi

thumbnail.default.placeholder
Tarih
1995
Yazarlar
Özoğlu, Yusuf
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Fen Bilimleri Enstitüsü
Institute of Science and Technology
Özet
Bu çalışmada, 30 kW, 440 V ve 1500 d/dak'hk bir doğru akım şönt motorunun nonlineer koşullar altındaki elektromagnetik alan dağılımı sayısal bir metodla incelenmiştir. ANSYS isimli sonlu elemanlar metodunu kullanan bir analiz programı bu sayısal çözüm için kullanılmıştır. Burada motorun magnetik alan davranışı incelenirken başlıca şu aşamalar gerçeldeştirilmiştir: 1. Bilgisayar destekli geometrisini oluşturmak. 2. Sonlu elemanlar modelini oluşturmak 3. Yük ve sınır koşullarım uygulamak. 4. Magnetik alan analizini yapmak. 5. Sonuçlan grafik olarak alıp değerlendirmek. Sonuçta motorun hava aralığı uyarma alan şekli, endüvi alan şekli ve yardımcı kutup alan şekli tespit edilmiştir. Bu inceleme öncelikle doğru alam motorunun uyarma alam ve endüvi alam için yapılmış olup toplam alan çıkartılarak endüvi reaksiyonu gösterilmiştir. Daha sonra yardımcı kutup alam bulunarak, bu alanın magnetik nötr bölgenin geometrik nötr bölge ile çakışmasını sağladığı ve endüvi reaksiyonunu ortadan kaldırdığı gösterilmiştir. Ayrıca doğru akım motorunun uyarma alanının endüvideki dağılımı incelenirken akı yığılmasının hangi bölgelerde arttığı ve bu yığılmanın geleneksel hesaplarda öngörülen sınırları aşıp aşmadığı araştırılmıştır. Ayrıca geleneksel hesapla bulunan diş dibi endüksiyonu ile ANSYŞ sonlu elemanlar analiz programı kullanılarak bulunan diş dibi endüksiyonu karşılaştırılmıştır. Sonlu elemanlar analizi ile tesbit edilen diş dibi endüksiyonu % 1-2'lik bir farkla geleneksel hesapla bulunan değere yaklaşık eşit çıkmıştır. Sonuçta bu metod ile yapılan alan dağılımı incelemelerinin geleneksel metodlarla yapılmış alan hesaplarım doğruladığı görülmüştür. Ayrıca hava arahğmdaki alan eğrileri örneğinde olduğu gibi geleneksel hesapla tesbit edilememiş ayrıntılarda görülebilmiştir. Sonuçlar bölümünde açıklanan nedenleri de gözöüne alırsak sonlu elemanlar metodu tasarımcılara elektrik makinalanmn tasannu ve üretiminde büyük avantajlar sağladığı anlaşılmıştır.
In this study, electromagnetic field of a DC shunt motor of 30 kW, 440 V, 1500 rpm, has been examined by numerical method [1]. A finite elements analysis program named ANSYS has been used for the numerical solution [2-5]. The following major steps have been achieved during examination of the magnetic field distribution of the motor : 1. Forming computer-aided geometry of the motor. 2. Forming model of finite elements. 3. Application of load and boundary conditions. 4. Analysis of magnetic field. 5. Obtaining the results in the form of graphics and evaluation thereof. A brief description of each of the above mentioned steps have been given thereunder: Geometry of the motor has been drawn in ANSYS program. As the motor has the property of symmetry, a model of finite elements for only 1/4 of the has been formed. Thus complexity in one hand and overloading of the computer memory in the other hand has been avoided. For finite elements model, nR relative permeability of various materials used in the motor or characteristic values there of as per B-H magnetization curves have been entered as data inputs [1]. The following material regions are present in the model: 1. Air (free space) 2. Conductors (motor windings) 3. Permeable regions (laminated steels) 4. Permeable regions (iron) Material properties have been given in Figure 1. Planel3 has been selected from the ANSYS elements library as the type of element to be used [4]. The said PLANE13 element has been linear property for four-node quadrilateral (triangular form also exists) used for two dimensional models. vui MOBX FOR MATERIAL 1 wool -«aa.toa -sM.lie -*«.Ma #3o.?le Us.itm «na.itt (a) (b) (c) (d) Figure 1. Material properties (a) for air (b) for windings (c) for laminated steels (d) for iron Y Axial n Q Surface number. Node system / @\ KEYOPT(4)=l ' X Radyal Figure 2. PLANED element properties IX Quadrilateral form has linear shape functions, i.e., can account for linear variation of the potential field. Property of Plane 13 have been given in Figure 2. Special care has been exerted to select the air-gap and the elements in the teeth in small in small dimensions. Thus, increase the number of nodes in the high precision regions. The method of finite elements divides the region into sub-regions called "elements" and estimates a vector potential approximation function for the end points of the elements, named as "nodes" and computes the vector potential values for each of these nodes. The next step is apply load and boundary conditions to the model of finite elements. Vector potential value, A for the boundary conditions has been given as zero at such conditions where the flux lines are in parallel to the boundary. The same value has been given unconditional in cases where the flux lines are in perpendicular to the boundary. The application of load has been made by entering the current densities in the motor windings by taking the current directions into account. In the fourth step, the model has been analyzed for the following three conditions: 1. Current exists in the motor excitation windings. 2. Current exists in the motor armature windings. 3. Current exists in the motor commutating windings. Excitation field curve for the air gap of the motor has been given in Figure 3. As can be seen, B magnetic flux density is maximum at the bottom of the pole, whereas it is zero at geometric neutral region. It has been determined that Bdmax, maximum magnetic flux density in the motor teeth under excitation conditions is 2.4150 [T] which is lower than the maximum permissible value of 2.5 [T]. On the other hand, the bottom of the teeth, Bd is 2.3 [T] is which is approximately equal to the value obtained through conventional methods. The armature field curve for the air-gap is given in Figure 4. The field value equals zero in the mids of the poles whereas it is maximum at the geometric neutral region. The axis of the armature field is fixed at 45° electrical degrees from the main field (excitation field) axis. The effect of armature field is seen to be that of creating flux sweeping across the pole faces; thus its path in the pole shoes crosses the path of main field flux. For this reason, this phenomena is called armature reaction. It evidently causes a decrease in the resultant air gap flux density under one half of the pole and an increase under the other. When current exists in both excitation and armature windings, is observed that these two fields overlap each other and consequently the field is not equal to zero at the geometric neutral region; instead, it slips by the angle of p\ The field curve of commutating pole the air gap when current exists in the commutating pole winding is given in Figure 5. As seen, Magnetic flux density, B takes the maximum value at the geometric neutral region in the reverse direction of the armature field, whereas it equals zero before reaching the poles. Thus, title effect of the armature field which is the cause of the armature reaction is estimated. The interpole field must be sufficient to neutralize the armature reaction in the interpolar region.
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1995
Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 1995
Anahtar kelimeler
Doğru akım motorları, Manyetik alanlar, Sonlu elemanlar yöntemi, Direct current motors, Magnetic fields, Finite element method
Alıntı