Study On The Cooling Technology Of Permanent Magnet Governor

Based on the characteristics of simple structure, high efficiency and energy saving, green environmental protection, effectively isolating vibration, the permanent magnet governor is widely used in adjust speed and transmission system of rotating machinery such as pump, centrifugal fan, etc. During the running process, the eddy current loss and slip power loss mostly dissipates in the form of heat, which causes the temperature of each component rising, and irreversible demagnetization happens to permanent magnet at high temperature, making adverse effects on its reliability and performance. Present study of permanent magnet governor are mostly focused on the characteristics of electromagnetic field, analysis of energy saving effect and so on, as for the study on the temperature distribution and cooling technology is rarely seen.The numerical simulation of the structure factors’ influence on the temperature field and flow field was carried out with the method of(computational fluid dynamic) CFD. Using the Design Modeler module of ANSYS Workbench to establish the permanent magnet governor model, and then simulation analyzed the flow field with the help of ANSYS Fluent software. For the original model the simulation results show that: within the original model exists a range of flow dead zones;because of the less viscous, only the air near the rotor wall rotates at high speed, and the air surrounded by the conductor rotor and the permanent magnet rotor can only rotates at low speed within this central region but cannot effectively flow out and participate in convective heat transfer; the flow of inlet and outlet is only 0.57kg/s; the mainly function is the thermal conductivity of air, and the highest temperature of permanent magnet reaches up to 120.2℃.In order to strengthen the heat transfer and improve the cooling effect of permanent magnet governor, add blades on both sides, which can not only drive more air to enhance the heat transfer also increase the heat transfer area reduce the thermal resistance to realize the purpose of cooling. In order to study the impact of the number and structure of blades for the flow field and temperature field, 13 models with different number of blades and 11 models with different angle of blades was built and numerical simulated by the method of computational fluid dynamics. From the result compared can be seen that: when adding 10 blades with the angle of 60°on both sides, the degree of turbulent was aggravated, and the flow of inlet and outlet was improved to 1.28kg/s, the temperature is reduced to 107.6℃C, 12.6 ℃ lower than the original model. But the high temperature air in the central area surrounded by two rotors still cannot convect with the external cold air. And some fluid retention dead zones exist. Then some holes are opened on both sides of conductor rotor and permanent magnet rotor to increase fluid convection between the central area and the outside environment, which provides a channel for air to flow in and out. The total volume of inlet and outlet is up to 2.37kg/s, and the highest temperature decreases down to 73.3℃,36.3℃lower than the previous structure. The cooling effect is remarkable.For the same purpose, add fins on the outer edge of the conductor rotor surface to increase the heat dissipation area of the fluid with the outside space and the driving force of the circumferential flow, improve the disturbance to the whole flow field, thus can increase the amount of the circulation air in the permanent magnet governor and heat convection. Build 6 models with different fin height, and then conducted the simulation analysis. The result shows that when the fin height is 20 mm, velocity of air in the outer hood is significantly improved, and turbulence degree increased, besides the flow dead zones decreased. Compared with the original model, the total volume of inlet and outlet is up to 2.307kg/s, but due to the air gap between two rotors is too small which leads to the high temperature in central region cannot flow out. The fins only improved the heat dissipation area of permanent magnet governor and improved the convection, and the highest temperature is 19.52℃ lower than the original model. Open holes through the outer circumferential surface of the two rotors so as to provide a channel that high temperature air can flow out. Simulation results show that: after the optimization of structure the fluid retention dead zone is down to very small, the total volume of inlet and outlet reach to 2.307kg/s, the high temperature air in the central region can flow out through the holes for convective heat transfer. The highest temperature of permanent magnet is reduced down to 72.62 ℃, that’s to say this structure has a good cooling effect.In order to determine the optimal cooling structure of permanent magnet governor so as to achieve the best cooling effect, make the side cooling structure and outer circular cooling structure together, the result shows that the total volume of inlet and outlet was increased up to 2.92kg/s by this cooling structure far more than the original 0.57kg/s, so to the single direction of cooling structure, and the highest temperature of permanent magnet is reduced down to 56.18℃ far less than the original model of 120.2 ℃.The numerical simulation of fluid flow field and temperature field was carried out to get the distribution of the temperature field and the highest temperature of permanent magnet. To facilitate through improving the cooling structure to strengthen the cooling effect so to reduce the highest temperature, which provide a theoretical basis for the development of high-power permanent magnet governor with the ventilation-cooling structure.