Tesis doctoral de Joaquim Lloberas Valls
Electric machines with high temperature superconductors evolve continously. Nowadays exists some configurations of high temperature superconductor melt textured motors as flux trapped, reluctance or histeresis machines. depending on the electric machine and the refrigeration system (zfc, fc), these regims can be obtained using the capacity of hts to trap field, their diamagnetic or histeretic properties. configuration of axial flux and permanent magnet machines (afpmm) is more compact, having a higher power density than radial flux motors. The technology of permanent magnet rotors is more eficient due to the absence of copper losses and the reduction of ferromagnetic losses achieving its efficiency compared with radial permanent magnet motors. Afpmm have a large variety of applications. These are used in high power aplications as maritime transport generators and low power applications as robotics; its low inertia is due to the capacity of permanent magnet to obtain a high magnetic field density. The properties of htsc allow their aplication on this kind of machine. The high temperature melt textured superconductors can trap magnetic fields over 17 tesla at 29 k. Then, they are a good alternative for a motor that has to obtain a high magnetic density. it is designed and built a flux axial motor with ybco pellets. The principal aims are the study and analisis of caractheristics of torque front motor speed working on histeresis design. The behaviour of ybco samples on a flux trapped motor applying a process cooled by field (field cooled, fc) has been studied too. the study of the application of bulk materials on low power motors and low inertia motors is interesting due to the aractheristics of other superconductors as coats that have limitations on their curvature radius and consecuently can not apply on low dimension motors. A common fault of superconducting coats on nitrogen liquid (77k) are the air bubbles generation on their surface because it is a hot point on the coat and consecuently belongs a none superconductor state. to apply these materials on an electric motor and achieve an electromagnetic torque, the geometry of electric motor has to be adapted at the materials or, if not, these materials has to be mecanized. the decision is to apply these materials on electric machines with a planar gap. That is possible applying axial or lineal electric motors. Then, it is decided to apply an axial flux electrical motor. the axial geometry allows to hold textured samples using their principal direction of magnetization, c axis, anc covering the whole polar surface. the design and construction of flux axial motor consists on two conventional armatures from a permanent magnet axial flux motor. The armatures has 24 active slots and one passive slot to reduce reluctance cogging effects. The armatures are winding with a three phase winding forming eight poles. the design and construction of a rotor consists with a none conductor and none magnetic support holding eight samples of ybco on the boundary of rotor. histeresis motor results show the dependency of electromagnetic torque with the rotor frequency due to the remanent magnetization and the eddy currents of the ybco samples.With the configuration of axial flux motor with eight poles and the design of rotor with eight ybco samples simmetrically disposed is achieved a torque of 0.35 n·m applying a peak current per phase of 30 a at a frequency of 47.5 hz. premagnetizing samples of ybco with a field cooled process at a field of 0.5 t is obtained a field trapped of 0.2 t. applying a peak current per phase of 30 a. At a frequency of 6 hz,is obtained an electromagnetic torque of 1.5 n·m. In this experiment, just is magnetized the samples to achieve 0.5 t into the gap. A limitation on the magnetization using stator armatureis the ferromagnetic sheet that it is saturated at 1.5 t approx. Another limitation is the high density of current applied on the conductors. also it is analized the decreasement of the magnetization front the applied current. It is realized a test of 30 minuts aplying a pic of current of 30 a at a frequency of 6 hz and obtaining the same value of torque between is achieved a permanent regime and after 30 minuts. it is shown also, that the synchronous regime obtained for magnetization through a fc process has a variable slip. The possible reasons for this phenomena could be the asymmetries in the armature poles and the remanent magnetic profiles of the cilindric ybco samples. concluding, the motor with high temperature superconductors magnetized by a fc process works at a higher power density compared with the motor with high temperature superconductors working on histeresis regime due to its high magnetic field into the gap. This process could improve the efficiency and the torque density. after the study of the axial flux motor with cylindrical samples of ybco it is shown the high energy to inject to the armature windings to magnetize the samples in situ in a fc process. for this reason is designed and built a new motor working on a flux trapped regime achieved by a fc process and compared with the motor built before in the same conditions of temperature, inject current and frequency. that design consists on two conventional armatures with a disc rotor where it is hold eight rings of ybco with a ferromagnetic core. This configuration allows to achieve a magnetic remanence on the samples more cuadrangular and stabilize the synchronism between stator and rotor. it is achieved a field trapped on the rings of ybco from 0.15 t to 0.2 t. the regime obtained is totally sincron. It is achieved a constant torque of 0.25 n·m; the reduction of torque is refered to the lowest magnetization power of rings and the lower injected magnetic power.
Datos académicos de la tesis doctoral «Cap al motor superconductor. motors de flux axial de camp atrapat amb mostres de ybco«
- Título de la tesis: Cap al motor superconductor. motors de flux axial de camp atrapat amb mostres de ybco
- Autor: Joaquim Lloberas Valls
- Universidad: Politécnica de catalunya
- Fecha de lectura de la tesis: 24/03/2009
Dirección y tribunal
- Director de la tesis
- Ricardo Bosch Tous
- Tribunal
- Presidente del tribunal: Luis ignacio Eguiluz moran
- pilar Suárez marcelo (vocal)
- alfredo Alvarez garcia (vocal)
- Javier Poza lobo (vocal)