Sürekli mıknatıslar ve mıknatıslayıcılar
Başlık çevirisi mevcut değil.
- Tez No: 55488
- Danışmanlar: PROF.DR. İLHAMİ ÇETİN
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 64
Özet
ÖZET : Günümüzde, ekonomik dengelerin ve yaşam biçiminin gelişmesi, teknolojinin gelişmesine bağlıdır. Teknolojik gelişimi gerçekleştirebilmek için belirli konularda bilgi birikiminin oluşması gerekmektedir. Gelişen teknolojinin ürünü olarak ortaya çıkan ender toprak sürekli mıknatıs malzemeleri, sürekli mıknatıs teknolojisinin değişmesinde etkili olmuştur. Sürekli mıknatıs malzemeleri, bir kere mıknatıslandırıldıktan sonra mıknatıslığını sürdürebilen malzemelerdir. Sürekli mıknatısların ve onların üretiminde karşılaşılan bazı temel sorunların ülkemiz sanayisine tanıtılması bu tez çalışmasının temel amacıdır. Tezin birinci bölümünde amacın kapsamına yer verilmiştir, ikinci bölümde, sürekli mıknatıslar ve malzemeleri tarihsel süreç içerisinde irdelenerek günümüz sürekli mıknatıs malzemeleri tanıtılmıştır. Üçüncü bölümde sürekli mıknatısların magnetik özellikleri ile ilgili kavramlar açıklanmıştır. Dördüncü bölümde sürekli mıknatıslı sistemlerin analizi ve özellikle sürekli mıknatıslı motörlerde yaşanan sorunlar irdelenmiştir. Beşinci bölümde ise sürekli mıknatıs malzemelerinin mıknatıslandırılmasında kullanılan araçlar olan mıknatıslayıcıların analizi ve işletme biçimleri açıklanmıştır. Daha sonra ise mıknatıslayıcı güç elektroniğ devresindeki tristörlerin termik zorlanması ve verimi incelenmiştir. Altıncı ve son bölümde çalışmamız esnasında ortaya çıkmış olan önemli noktalar özetlenmiştir.
Özet (Çeviri)
SUMMARY Magnets including permanent magnets and electromagnets have an important contribution in the evolution of current technologies. Specially, electric motors have achieved the current technology's developed level with this contribution. The level achieved by the permanent magnet material has caused the superiority of the permanent magnet motors on the motors which are fed on other two sides. 1. Continuos direction change is easier in permanent magnet motors than in motors fed on other two sides. 2. Permanent magnet motors are lighter and smaller than other wound motors. 3. Permanent magnet motors are more elastic in shape and size than other motors. This property helps permanent magnets to be widely used in space and automotive sectors. 4. Specially low power permanent magnet motors are cheaper than wound motors. In parallel to the properties mentioned above, the permanent magnet motors are widely being used each day. Therefore, examination of the electromagnetic properties of permanent magnet systems and the current permanent magnet materials together with the equipment used to magnetize these materials are increasingly becoming important. The main purpose of this thesis is to present the permanent magnet systems to our country's industry and to make a contribution in the knowledge accumulation of these systems. In the first chapter, the content of the thesis in parallel to its purpose will be explained. In the second chapter, periodic development and the areas in which the permanent magnet materials are used will be explained. Currently used permanent magnet materials and their physical as well as chemical properties will be explained. Oldest known permanent magnets are the stones called lodestones which were found in Magnesia region in Thessalya. Many scientists have tried to explain the physical as well as the chemical properties of these magnet stones. William Gilbert required artificial magnets for the manufacture of compasses and dip circles which were used as navigation instruments. He recognised that iron made hard was the best material for artificial magnes. His dip circles used a magnet 1 0to 12 in long and he described a magnet as thick as a goose quill and about 8 in long. Gilbert described three methods by which permanent magnetism could be given to stell. 1. Touching with a lodestone, which was drawn from the middele of the needle to the end, or touching opposite ends with the different poles of the lodestone. 2. Forging a horizontal specimen or drawing a wire pointing north-south in earth's magnetic field. 3. Magnetizing by long exposure to the earth's magnetic field without the plastic deformation requred in above. Until 1930's, chrome steel and other hard steel magnets had been used as magnetic materials. The lowe energy densities of early manufactured permanent magnets did not permit the use of permanent magnets in any type of machine other than very low power control machines and signal transducer. In 1930, an Alnico permanent magnet material that consists of VI10% Al, 25% Ni and 65% Fe had been produced in Japan. The high flux densities and reasonable energy products of Alnico magnets permitted their use in power applications, and permanent magnet motors with ratings up to several horsepower were developed for commercial application. DC generators and alternators with ratings of many kilowatts were also developed for military and aerospace applications using Alnico magnets. However, the low coercive force of this class of PM limited its applications to relatively constant current applications where transient disturbances were not present. Widespread use of PMs in commercial and aerospace applications were made possible with the advent of ceramic or ferrite PMs in the 1950's. Although the flux densities available in this class of PM are much lower than those of the Alnico class, the high coercive force of ferrite PMs made possible the adaptation of PM machines to the conventional machine armature reaction and transient environment. A great many automotive motors were converted to ferrite PM excitation and, as a result, the PM dc motor is probably the most widely-used dc motors configuration today. The ferrite class of PMs generally offers a cost saving over all other types of PMs and is produced in extremely large quantities today for almost all types of PM applications. The next major evolution affecting PMs came with the advent of commercial rare-earth permanent magnets in the 1960's, and this evolution is ongoing today.The early rare-earth PMs offer the high flux density of the Alnico class and even high coercive force than the hard ferrite class, resulting in much higher energy densities than any previous class of permanent magnets except for various exotic and costly alloys such as platinum-cobalt. Samarium-cobalt, while having excellent technical characteristics, is relatively expensive and uses a large percentage of cobalt, which is a strategic material in several parts of the world today. A more recent development in rare earth PMs is the neodyumium-iron-bron (NdFeB) alloy which has PM characteristics comparable or superior to most of the samarium-cobalt alloys and has the potential for much lower cost. In the third chapter, magnetic properties of the permanent magnets will be mentioned and the main concepts concerning these properties will be explained. Under Curie temperature, the parallel momentum electrons of ferrimagnetic and ferromagnetic materials combine and form the small areas called magnetic fields, which have specific directions, each direction differing from the other. However, these magnetic fields can be directed in the same direction by exogenous magnetic field. After which, the material gains the property of permanent magnetism. One of the distinguished marks of a magnetic material is the nonlinear relationship between the flux density B and magnetic field intensity H. This relation is called Hysteresis loop. The coercive force, remnant and (BH)max energy are the other important characteristics of permanent magnet materials. Remnant is the amount of the field density left after the magnetic field is removed from a material that has reached up to saturation flux density. The coercitive field is a measure of the resistance shown to an exogenous field to remove the magnetism of a material. (BH)max. energy is a characteristic effective in determining the volume of the magnet used and determining the point to be used to achieve the highest possible efficiency. In order to gain permanent magnet property, a permanent magnet material should be faced with its magnetic field force at saturation Hs for certain period. The energy spent during this process is directly proportional with the square of magnetic field force at saturation, with the volume of permanent magnet and with the permeability of the space. In the fourth chapter, the problems arising in design of the permanent magnet systems and procedures for their solutions will be explained. For permanent magnet excitation, the object is to determine the size of the permanent magnet. The first step in this process is to choose a specific type of permanent magnet, since each type of magnet has unique characteristic that will vupartly determine the size of the magnet required. In practical design this choice will be based on cost factors, availability, available space in magnetic circuit, and the magnetic and electrical performance specifications of the circuit. Most permanent magnets are nonmachinable and usually must be used in circuit as obtained from the manufacturer. The dimension and volume of the magnet used in permanent magnet system is directly proportional with volume of air space of the system and is inversely proportional with the magnetic energy of the magnet. This means, the more the magnetic energy, the smaller the volume of the permanent magnet will be. On the other hand, by reducing the volume of the magnet, the leakage factor of the magnetic circuit can be reduced. In the fifth chapter magnetizer equipment used for magnetization of the non magnetized materials will be examined. A magnetizer consists of the magnetizer head or coils making up the magnetic field and of the power electronic circuit supplying the current passing through this coil. Magnetizer heads are produced with and without magnetic circuit with coils. Magnetic circuit's existence in magnets limits its magnetic field force at saturation. However, magnetic circuits may concentrate the magnetic field on the volume of magnet. This means, the energy needed for a magnetizer is decreased. Magnetizing the permanent magnet before or after application is an important problem. If there is a difference between the curves of the permanent magnets before and after application, then the magnet should be magnetized after application. Generally, there is not enough space in coils used for magnetizing the magnets after application. Therefore, impulse current with a high peak point is made flow from the magnetizer coil by holding the number of the winding low. Magnetizers are divided into two according to the circuit passing through the magnetizing coil as impulse current magnetizers and direct current magnetizers. Generally, volumes of the winding in the magnetizing coil of the dc current magnetizer is high and magnetizing current density is over 200A/rnm2. The current passing through the magnetizing coil of dc magnetizer is changing directly proportional with the voltage applied to the coil and inversely proportional with the coil resistance. In the impulse current magnetizer, the electrostatic energy accumulated in capacitor is discharged over the magnetizing coils. The capacitor with appropriated value is initially charged from network over a rectifier and after the energy in the capacitor reaches the needed level, it is discharged over the magnetizer coil by the power electronic circuit. After the appropriate thyristor in power electronic circuit is fired, working styles in different waves than the magnetizer coil dominate. 1. Short impulse magnetizing. 2. Long impulse magnetizing. 3. Demagnetization Having a high magnetizing current, short time and a nonlinear starting Hysteresis curve of magnetizing material, makes the determination of the magnetizer magnetic field difficult. When the material to be magnetized is rare-earth in impulse current magnetizer, it should be considered that the eddy current effects on the magnetization are because of the Short time magnetizing current and high conducting material. Therefore, in magnetic field analysis of the impulse current magnetizer will examine with the finite element field analysis. Accordingly, two ways have been formed for the examination of the impulse magnetizers. 1. Step by step solving the differential equation concurring the magnetic field with the aid of the differential equation formed over the electric circuit. 2. Solving the differential equation concurring the magnetic field and the equation formed over electric circuit at same time. VUlIn Magnetizers, it is benefited from the thyristors as power electronic switch element. However, magnetization's high current and its being a transient process requires the thyristors to be selected appropriately to this process. The inner resistance of power electronic element causes an energy loss as a heat. This loss is equal to the multiple of the difference of the voltage between the ends of the power electronic element and the current passing through it. This loss is increasing the junction temperature up to the permissible point and can destroy the element. Therefore, the junction temperature of the power electronic element is required to be determined specifically in the magnetizers which have high currents. In this type of process, the junction temperature of the thyristor is equal to the addition of starting junction temperature and the temperature increase of each level of power loss. The temperature increase of each level of power loss is equal to the multiple of transient thermal impedance and the increase of power loss. In the examination of the junction temperature of power electronic element, the transient thermal impedance concept used is obtained through lumped thermal model. In this model, a capacitor and a resistance which shows the temperature capacity and the resistance of the system respectively are used for modeling. If this model is analyzed through circuit analysis concept, the temperature of node of the thermal system is the addition of two functions, one starting to cool from T0 and the other starting to heat towards Tm. The ratio of the junction temperature obtained through the lumped and transient model to the loss of the thermal power of thyristors is called transient thermal impedance. Accordingly, transient thermal impedance is the addition of cooling thermal impedance is the addition of cooling thermal impedance and the heating thermal impedance. According to the definition of thyristor thermal impedance junction temperature is equal to sum of starting temperature of the element and the temperature increase obtained during the transition period. The power loss obtained during the transition period is equal to the multiplication of the difference of voltage between the ends of the thyristor and the current running through the element. Efficiency of thyristors may be defined similar to energy converting systems. Accordingly, efficiency of a thyristor is the ratio of the power transmitted to load to the power supplied from the network. Efficiency depends on the firing angle of the thyristor, inner resistance, load resistance and threshold voltage when the thyristor load is pure resistance. The thyristor firing angle should be zero in order to get the maximum possible efficiency from a thyristor. The transient junction temperature of thyristors is the addition of the junction temperature and the temperature reached during this process. By reducing the former temperature makes us able to increase the latter which also enables us to pass high currents through the element. Apparently, application of the above mentioned process into the magnetization of the magnetizers by using cooling devices to reduce the starting junction temperature will enable us to increase the current to be passed through the magnetizers required to magnetize them. Therefore, the thyristor elements, used in power electronic circuits of magnetizers for magnetizing the rare earth magnets, are cooled by forcely cooling system. These thyristors are covered by resin together with cooling surface. Additionally, PTC elements whose resistance's are varying with temperature are placed on cooling surface to enable the thyristor temperature to be sensed. The control system used in the applications of forcely cooling system should have the following functions: 1. It should control the temperature of the water in the cooling water container with a thermostat, and should prevent the thyristor from starting if the temperature is above the required level. 2. It should control whether the cooling water pumps are working or not and if not it should prevent the thyristors from starting. 3. It should control the temperature of each thyristor if the thyristors are working independently then it should stop the thyristor which reached the maximum temperature level. If the thyristors are working parallel then it should stop all parallel working thyristors. 4. It should control whether sufficient cooling water reaches the thyristors. ixA PLC program written in SIMENS SIMATIC S5 language according to the above principles is in Appendix 1. In the sixth and last chapter, the conclusions resulting from the thesis will briefly be explained.
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