Guojun Yang

Thermal Analysis and Simulation of Auxiliary Bearings and Its Application in the High Temperature Reactor-10

The auxiliary bearing is applied to provide mechanical uphold for the rotational dropping rotor when contact event happens due to the active magnetic bearing (AMB) failure emergencies. During the rotor drop process, the auxiliary bearing will endure huge impact force and friction heat generation. The thermal behavior will affect the mechanical interaction and dynamic behavior of the auxiliary bearing and even induce rapid failure especially when excessive temperature growth occurs. The Institute of Nuclear and New Energy Technology (INET) of Tsinghua University in China has proposed the 10 MW high-temperature gas-cooled reactor (HTR-10). It is designed to guarantee the inherent safety and economic competitiveness. The dry-lubricated ceramic auxiliary bearing is utilized to protect the AMB and aims to ensure the safety of the AMB system in the HTR-10 in the case of the special operational requirements in the reactor. This paper simulates the process of the rotor drop on the auxiliary bearings in the AMB system of the helium blower of the HTR-10, including the analysis of thermal growth based on the Hertzian contact model and a one-dimensional (1D) thermal heat transfer network model. The study results demonstrate the validation of the bearing models and elucidate different responses between mechanical and ceramic auxiliary bearings during contact events. The research in this paper offers important theoretical bases for the auxiliary bearing design to guarantee the safety of the whole system.

Dynamic Analysis for the Rotor Drop Process and Its Application to a Vertically Levitated Rotor/Active Magnetic Bearing System

Active magnetic bearings (AMBs) have been utilized widely to support high-speed rotors. However, in the case of AMB failure, emergencies, or overload conditions, the auxiliary bearing is chosen as the backup protector to provide mechanical supports and displacement constraints for the rotor. With lack of support, the auxiliary bearing will catch the dropping rotor. Accordingly, high contact forces and corresponding thermal generation due to mechanical rub are applied on the dynamic contact area. Rapid deterioration may be brought about by excessive dynamic and thermal shocks. Therefore the auxiliary bearing must be sufficiently robust to guarantee the safety of the AMB system. Many approaches have been put forward in the literature to estimate the rotor dynamic motion, nonetheless most of them focus on the horizontal rotor drop and few consider the inclination around the horizontal plane for the vertical rotor. The main purpose of this paper is to predict the rotor dynamic behavior accurately for the vertical rotor drop case. A detailed model for the vertical rotor drop process with consideration of the rotating inclination around x- and y- axes is proposed in this paper. Additionally, rolling and sliding friction are distinguished in the simulation scenario. This model has been applied to estimate the rotor drop process in a helium circulator system equipped with AMBs for the 10 MW high-temperature gas-cooled reactor (HTR-10). The HTR-10 has been designed and researched by the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University. The auxiliary bearing is utilized to support the rotor in the helium circulator. The validity of this model is verified by the results obtained in this paper as well. This paper also provides suggestions for the further improvement of auxiliary bearing design and engineering application.

Thermal Growth Simulations of the Rotor and Auxiliary Bearing Contact Events

As an essential component in the system of the HTR-10 helium turbine generator electromagnetic bearings, auxiliary bearings provide mechanical backup protection in case of the events of magnetic bearing failure happen. When contact events happen, highly localized and transient temperatures will arise from frictional heating over the dynamically varying contact area in the very short term and dissipate through the bearing in the longer term. When excessive temperature level occurs, rapid failure may be anticipated, thus it will become a serious threat to the safety of the HTR. This paper presents a detailed analysis of thermal growths due to the mechanical rub for a rotor drop on auxiliary bearings. With the aim to numerically analyze the heat generation and temperature rise, a 1D thermal model of the ball bearing composed of heat transfer network and heat sources based on heat transfer equations is established. The Matlab codes are developed to complete the numerical analysis, and an infrared method is utilized to investigate the temperature rise at the rotor/inner race contact surface. By the comparison between simulation results and the experimental data, this paper illustrates the thermal growth during a rotor drop process, which is highly non-linear. The results reveal that the axial contact force is critical to the bearing heat generation, and the ceramic balls with superior thermal properties are recommended.Copyright

Influence of bias current of active magnetic bearing on robustness and dynamic performance of the system

The Bodes integral is applied to analysis the robustness of active magnetic levitation systems. Based on the linear model, it is found that the unstable pole of open-loop system is determined by the bias current, and larger bias current leads to unstable pole farther away from the imaginary axis. The bias current strongly influences the dynamic performance of the levitation system. Larger bias current is needed to achieve better dynamic performance, such as higher stiffness and larger load capacity, while unstable pole farther away from the imaginary axis implies larger Bodes integral and worse robustness. The tradeoff between robustness and dynamic performance of the system is studied. The minimum available bandwidth that is necessary to achieve certain peak value of sensitivity function magnitude is derived. Simulation study is carried out to demonstrate the analysis method and to validate the results.