| HTS bulk can trap much magnetic flux for its strong pinning function and has higher flux jumping field than low temperature superconductor bulk, which is the basic factor for HTS bulk used as the permanent magnet. The bulk must be magnetized before used as a magnet. Pulse magnetization is simple and fast. The loss is small and the time of pulse can be changed according to electrical circuit. So the pulse magnetization is regarded as one of the most promising method in practical field.We simulated the single pulse magnetization process using flux flow-creep model and MAXWELL equations and carried experiment to test the validity of the theory. It seems that the simulation results are coincident with the experimental ones. We also can see that much heat generated during the pulse magnetization process and resulted in the temperature rise, which reduce the electrical current density of HTS bulk. The point, which has the highest temperature, is near the edge of the bulk.The effect of single pulse magnetization has close relation with amplitude of pulse field. If the pulse field is small, the remnant magnetic field of bulk cannot be saturated and a dip produced at the center of bulk. On the contrary, if the amplitude of pulse field is very high and exceeds a certain value, the remnant magnetic field of bulk decreases because of much heat and thermal stress produced by the temperature rise will make the bulk cracked. We can use the ferrite yoke technic and multi-pulse technic to improve the shape of magnetic field. In order to avoid the crack, the epoxy resin is impregnated into the bulk and the strength of bulk can be improved.Several HTS bulks are overlapped to meet the need in practice. Vertical overlapping can increase axial field, but horizontal laying has little influence on the axial field.We designed a synchronous electrical motor, whose rotor is composed of overlapped HTS bulks. The simulation results show that the motor can rotate stably as the synchronous speed.
|
PDF Full Text Request