When the power relay disconnects a large current load, if the arc generated between the contacts cannot be extinguished in time, it will cause contact ablation, welding or even failure. The design of the arc extinguishing structure is the key to improving the breaking capacity. Its core lies in accelerating the cooling, elongation or segmentation of the arc through physical means, thereby shortening the arc burning time.
Arc extinguishing grids usually use copper-plated thin steel sheets, whose magnetic conductivity can enhance the pulling force of the magnetic field on the arc, and the copper plating improves arc resistance. For example, the thickness of the grid is controlled at 0.2-0.5mm, which can not only ensure mechanical strength, but also avoid the decrease of heat dissipation efficiency due to excessive thickness. In addition, the arc extinguishing cover material must have high temperature resistance, such as arc-resistant clay or asbestos cement, whose thermal conductivity can reach 0.8-1.2 W/(m·K), to ensure that the arc heat is quickly transferred to the outside.
The magnetic blow-out arc extinguishing device generates a magnetic field by connecting a magnetic blow-out coil in series in the contact circuit using the arc current itself. When the current direction is counterclockwise, according to the left-hand rule, the arc is subjected to the vertical upward Lorentz force, stretched and blown into the arc extinguishing hood. Experiments show that for every 10mT increase in magnetic field intensity, the arc movement speed can be increased by 15%-20%, significantly shortening the arc burning time.
Grid arc extinguishing divides the arc into multiple short arcs in series. When the voltage between each grid is less than 150V, the arc is difficult to reignite. Longitudinal seam arc extinguishing accelerates arc cooling through a narrow seam structure. The seam width is usually designed to be 2-4mm to maximize the contact area between the arc and the seam wall. For example, a double-break bridge contact with a longitudinal seam design can shorten the arc burning time to less than 1/3 of a single-break structure.
The inner wall of the arc extinguishing hood adopts a corrugated structure to increase the contact area between the arc and the cooling medium. When the arc enters the arc extinguishing chamber, the high-temperature gas rises due to the decrease in density, forming natural convection. At the same time, high melting point alloys such as tungsten and molybdenum are added to the contact material to improve the thermal radiation efficiency, so that the arc temperature can be reduced from 10000℃ to below 3000℃ within 1ms.
The electromagnetic-thermal coupling effect of the arc is analyzed by finite element simulation (FEM). For example, a three-dimensional model is established in ANSYS Maxwell to simulate the arc current density distribution and magnetic field intensity changes. The results show that when the number of turns of the magnetic blow coil increases by 20%, the arc energy density decreases by 35%, but the coil heating and power loss need to be balanced.
Arc simulation based on COMSOL Multiphysics can predict the performance of different arc extinguishing structures. For example, when the simulated grid spacing is adjusted from 2mm to 3mm, the arc voltage recovery time is extended from 8μs to 12μs, which verifies the influence of structural parameters on the breaking capacity. In the experiment, the arc morphology was captured by a high-speed camera (frame rate>10000fps), and the error compared with the simulation results was less than 5%.
With the development of semiconductor technology, vacuum arc chambers (VCB) are gradually used in large power relays, with insulation strength of up to 10⁷ V/m and breaking capacity of more than 100kA. In addition, solid-state relays (SSRs) achieve contactless switching through power electronic devices, and the response time is shortened to the μs level, but the conduction loss and cost issues need to be solved.
The arc extinguishing structure design of power relays requires comprehensive materials, magnetic fields, structures and cooling mechanisms, and is optimized through simulation and experiments. In the future, with the breakthrough of vacuum and solid-state technology, arc extinguishing devices will develop in the direction of miniaturization and intelligence, providing more reliable current interruption solutions for power electronic systems.
