Degradation Characteristics and Mechanism Analysis of Bimetal Sheet of Low Voltage DC Circuit Breaker
Xing Yunqi1,2, Wang Zihan1, Yang Guangzheng1, Wang Yan1, Zhao Chengchen3
1. State Key Laboratory of Reliability and Intelligence of Electrical Equipment Hebei University of Technology Tianjin 300130 China; 2. People Electric Appliance Group China Wenzhou 325600 China; 3. College of Engineering and Technology Tianjin Agricultural University Tianjin 300392 China
Abstract A low-voltage DC circuit breaker plays a role in power distribution, control, and protection in low-voltage DC systems. As the core component of overload protection of low-voltage DC circuit breakers, the reliability of thermal release directly affects the safe and stable operation of the DC system. However, during service, the thermal release is subjected to large temperature stress fluctuations, the degradation mechanism is not clear, and the reliability evaluation is difficult. Therefore, the simulation model of thermal release is established to determine the key parameters of thermal release performance degradation. The degradation mechanism of thermal release is revealed by the accelerated life test, and the degradation mechanism of the bimetal sheet is explained from the perspective of molecular dynamics. Firstly, a three-dimensional finite element model of thermal release is established to explore the distribution mechanism of temperature, stress, and deflection of the bimetal sheet. An experimental platform is established, and the active layer expansion coefficient is determined as the key parameter of bimetal sheet performance degradation through orthogonal tests. Secondly, the accelerated stress is temperature, and the accelerated life model is the Arrhenius model. The accelerated life test under 110℃, 130℃, and 150℃ is designed, and the specific bending K is used as the degradation parameter. With the increase in temperature stress, the K decreases by 7.01×10-6/℃ at 150℃ and 3.21×10-6/℃ at 130℃. The e overall decrease in the specific bending K at 110℃ is about 1.03×10-6/℃. The distribution of elements at the interface of the bimetal sheet is observed by SEM. Finally, the molecular dynamics model of the bimetal sheet is established. The diffusion behavior of atoms in the passive layer is more intense than in the active layer. The diffusion behavior of atoms at the interface is further explained by analyzing the mean orientation shift, diffusion activation energy, and diffusion factor of different atoms. The results show that the diffusion probability of all atoms was almost the same. Due to the low diffusion activity of the passive layer Ni atom, the diffusion is more intense. The performance degradation mechanism of the overload protection element of low-voltage DC circuit breakers is revealed from a microscopic point of view. The following conclusions can be drawn. (1) The active layer expansion coefficient is a key parameter affecting the degradation of bimetal sheets, so specific bending K can be used as a characteristic parameter characterizing the degradation of bimetal sheets. (2) The degradation rate of specific bending K is almost the same at the same temperature, and the decrease rate of specific bending K is greater with the increase of temperature. (3) The molecular dynamics analysis shows that the diffusion of atoms at the interface changes active and passive expansion coefficients, and the diffusion of atoms in the passive layer is intense. The degradation mechanism of the bimetal sheet is explained from the microscopic view.
Xing Yunqi,Wang Zihan,Yang Guangzheng等. Degradation Characteristics and Mechanism Analysis of Bimetal Sheet of Low Voltage DC Circuit Breaker[J]. Transactions of China Electrotechnical Society, 2024, 39(22): 7266-7277.
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