Research On The Thermal Field And Active Water Cooling System Design Of An Air-core Compulsator

Compensated pulsed alternator is a new kind of pulsed power supply based on the principles of armature reaction compensation and magnetic flux compression. The compensator is considered as the prime candidate for power electric guns, because it performs in one unit the function of kinetic energy storage, electromechanical energy conversion, power conditioning and repeatability. In order to maximize energy stores and power densities, compulsators are designed as air-core prototype. However, one major challenge for air-core configuration is the management of the high winding temperature-rise during repetitive pulse firing, due to the poor thermal conductivity of composite materials. In this paper, based on an experimental machine, the thermal field and active water cooling system design of an air-core compulsator have been studied.In order to obtain an accurate discharge current, transient FEM electromagnetic analysis model has been built and testified by a no-load test. A typical railgun is assumed as the discharge load, and the ohmic losses of the coils and eddy current losses of the compensating aluminum shield have been calculated based on the analysis model, which provide a foundation for the thermal field calculation.In this paper, 3-D finite element thermal model has been built using an effective thermal conductivity of the air gap to analyze the thermal field of the compulsator, and find out the hottest spot. We also performed temperature-rise test to validate this model, and the calculated results agree well with the measured data. The test results also indicate that a forced cooling system is essential to be designed so as to reduce the temperature of the coils in effect.Based on this thermal analysis model, three typical operating conditions with different discharge cycles are analyzed in this paper, and the relationships between the hottest spot temperature and the discharge number are presented.Finally, for the purpose of stabilizing the hottest spot temperature of the coils at given level during repetitive pulse firing, active cooling system has been designed and simulated. Based on the computational fluid dynamics (CFD) method, the influence of the inlet velocity on cooling effect has been also studied in this paper.The entire research process and analysis methods mentioned in this study can be further used for thermal field analysis and coolant system design of different kinds of compulsators. It also provides the theoretical and experimental guides for the optimization and fabrication scheme of the engineering CPA in the future.