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[Objective] In the early operation stage of Jinan Metro Line 3, multiple sporadic high-speed circuit breaker closing failures are reported. To improve the reliability of train operation, it is necessary to optimize the high-speed circuit breaker control circuit in the traction system. [Method] According to the relevant closing command and the component status when a closure failure of the high-speed circuit breaker on Line 3 train occurs, and in accordance with the control logic principle of the high-speed breaker, the causes of the occasional closure failure are analyzed and the optimization measures are put forward. [Result & Conclusion] The causes of the occasional closure failure are that in the process of closure control of high-speed circuit breaker, the induced electromotive force generated at both ends of the high-speed circuit breaker coil makes the closing power insufficient, resulting in the failure closure of the breaker. The improvement measure is to connect freewheel diodes at both ends of the high-speed circuit coil to suppress the induced electromotive force generated by the above coil. With the above improvement measure, the closure failure of the high-speed circuit breaker caused by induced electromotive force never occurs again, and the reliability of train operation is effectively improved.

On May 22, 2021, an earthquake of M7.4 occurred in Maduo County, Qinghai Province, causing the collapse of the Yematan bridge and the Yematan No.2 bridge in Maduo County. According to the earthquake intensity announced by China Earthquake Administration, the earthquake intensity of the Yematan bridge is IX. However, the lack of strong seismic stations and the unrecorded time history of ground motion near the bridge is also hindering the research work on earthquake-induced failure mechanisms of the Yematan bridge. Therefore, this paper attempts to use the empirical Green's function method and refer to the concept of self-heterotopic skin transplantation in medicine to preliminarily evaluate the main characteristics of the ground motion intensity at the Yematan bridge, and try to give the possible range of peak ground acceleration (PGA) and the ground motion time history. The latest China seismic intensity table (GB/T17742—2020) and the design response spectra of the fifth generation seismic zoning map (GB18306—2015) are compared. The results show that: (1) the range of PGA (320~620 cm/s2) obtained in this paper matches well with the range of PGA (402~830 cm/s2) in China seismic intensity table (GB/T17742—2020); (2) The ground motion response spectrum synthesized matches well with the acceleration design response spectrum of extremely rare ground motions at the Yematan bridge in the fifth generation seismic zoning map (GB18306—2015), which indicates that the acceleration time history synthesized in this paper can cause the beam falling failure of the bridge. Our results show that the characteristics of ground motion intensity near the Yematan bridge are very possible and have a certain reference value. It can be used as the time history input of ground motion for the Yematan bridge and provide data support for the study of the collapse mechanism of bridge.

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