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A vacuum interrupter utilizes a high vacuum environment to extinguish the arc that forms between a pair of contacts. As the contacts begin to separate, the current initially flows through a progressively smaller area, leading to a sharp increase in resistance between the contacts. This increased resistance causes a rapid rise in temperature at the contact surface, eventually resulting in the evaporation of electrode metal. Simultaneously, the electric field across the small contact gap becomes extremely intense. The breakdown of this gap initiates a vacuum arc.
During each half-cycle of the alternating current, the current is naturally forced to pass through zero due to the high arc resistance. As the gap between the fixed and moving contacts continues to widen, the conductive plasma generated by the arc is displaced from the gap and loses its conductive properties. Consequently, the current is effectively interrupted.
To enhance the performance and longevity of the vacuum interrupter, the contacts are often designed with specific geometries that promote better arc control and distribution. Two prominent designs are Axial Magnetic Field (AMF) and Radial Magnetic Field (RMF) contacts. Both types feature spiral or radial slots cut into their faces, which serve to generate magnetic forces that move the arc spot across the surface of the contacts.
AMF contacts have spiral slots that create a magnetic field parallel to the axis of the contacts. This magnetic field exerts a force on the arc, causing it to rotate and spread over the contact surface. By distributing the arc evenly, the magnetic forces help maintain a low arc voltage and minimize localized contact erosion. This even distribution ensures that no single point on the contact surface bears the brunt of the arc's energy, thereby extending the life of the contacts.
RMF contacts, on the other hand, have radial slots that create a magnetic field perpendicular to the axis of the contacts. Similar to AMF contacts, the radial magnetic field moves the arc spot across the contact surface, ensuring that the arc does not remain stationary. This movement helps to distribute the arc's energy more evenly, reducing the risk of localized overheating and contact wear. The even distribution of the arc also contributes to maintaining a low arc voltage, which is crucial for efficient current interruption.
The use of AMF and RMF contacts offers several advantages:
-Even Distribution of Arc Energy: By moving the arc spot across the contact surface, these designs ensure that the arc energy is distributed evenly, reducing localized wear and tear.
- Low Arc Voltage: The even distribution of the arc helps maintain a low arc voltage, which is essential for efficient current interruption.
- Reduced Contact Erosion: By preventing the arc from remaining in one place, the designs significantly reduce contact erosion, thereby extending the operational life of the vacuum interrupter.
- Enhanced Reliability: The improved arc control and reduced contact wear contribute to the overall reliability and performance of the vacuum interrupter.
The vacuum interrupter's ability to extinguish arcs and interrupt current is enhanced by the use of high-vacuum conditions and specially designed contacts. The AMF and RMF contact designs play a crucial role in controlling the arc, ensuring even energy distribution, and reducing contact erosion, thereby improving the efficiency, reliability, and longevity of the device.
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