Soft-Landing Mechanism Design Driven by Electromagnetic Repulsion Force With Application to Bypass Switch

The bypass switch is a significant component of power electronic device protection. In case of a short circuit fault in the flexible dc transmission system, due to the rising rapidly fault current, the bypass switch must complete its closing operation quickly in 5 ms or even less. This puts forward strict requirements on the motion speed of the contacts. However, the high-speed closing leads to bounce which causes bypass failure. To address this problem, a high-speed soft-landing mechanism (SLM) based on electromagnetic repulsion force is proposed in this article. Compared with the traditional solenoid electromagnetic mechanism, the SLM can finish the closing motion in 3 ms, and the closing speed is 0.68 m/s, only about 1/4 of the traditional solenoid mechanism. Subsequently, the influence of the repulsion disk size and the buffer initiating time on the closing time and closing speed is further investigated. To achieve better dynamic characteristics, the inner radius of the repulsion disk should be smaller, and the outer radius should be greater than that of the coil. The optimal thickness of the repulsion disk and the buffer initiating time can be obtained through simulation analysis. The SLM solves the contradiction between the short closing time and the low closing speed of the bypass switch. It improves the reliability of power electronic device protection in the flexible dc transmission system, which is conducive to the system’s safe operation.