In a vacuum interrupter, effectively controlling the high-current arc is crucial to the performance of the switchgear. The magnetic field design between contacts offers two main paths: longitudinal magnetic field (AMF) and transverse magnetic field (TMF). This is not a matter of superiority or inferiority, but rather a rational choice based on the application scenario.
Longitudinal Magnetic Field (AMF) – Allowing the Arc to "Diffuse"
When the magnetic field direction is parallel to the current direction, the arc plasma tends to be evenly distributed under the influence of the Lorentz force, avoiding local contraction. This "diffuse" arc significantly reduces the energy density on the contact surface, thereby reducing ablation and significantly improving the high-current breaking capacity. Therefore, AMF contacts dominate in high-voltage (e.g., above 72.5kV) and high-capacity (40kA and above) vacuum circuit breakers. Many mainstream international high-voltage products adopt this technology to ensure reliable breaking.
Transverse Magnetic Field (TMF) – Making the Arc "Rotate"
When the magnetic field direction is perpendicular to the current direction, the arc is driven by magnetic blowing force, rotating at high speed along the contact plate surface. This dynamic motion disperses the arc heat over a larger area, preventing overheating at the fixed point. TMF has a simple structure, small contact height, and low circuit resistance, which is beneficial for miniaturizing the arc-extinguishing chamber and reducing manufacturing costs. TMF designs are common in medium-voltage (12~24kV) and medium short-circuit current (31.5kA and below) switchgear, especially suitable for space-constrained or frequently operated applications.
How to Choose?
The decision mainly depends on the rated voltage, breaking current, and operating life requirements. High-voltage, high-capacity AMF is preferred to ensure breaking margin; medium- and low-voltage, economical TMF is preferred to optimize size and cost. In recent years, composite magnetic field technology (combining AMF and TMF) has become a research hotspot, attempting to combine the advantages of both. Regardless of the chosen approach, the ultimate goal is to provide the safest and most economical arc control strategy for specific operating conditions-the answer to this "choice question" is always found in the application requirements.
Shaanxi West Power Tongzhong Electrical Co., Ltd.
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