Rotary Contact Interruption: Why Can Electron Temperature Drop by 40%? - Blog

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The difficulty of extinguishing an arc in a vacuum circuit breaker depends, to a large extent, on the electron temperature of the arc. Experiments have revealed a noteworthy phenomenon: when contacts open while rotating at an angle of 2.4°, the electron temperature drops from 2.5×10⁴ K-the level observed during a standard linear (non-rotating) opening-to 1.5×10⁴ K, a reduction of exactly 40%. This figure is no coincidence; it stems from the way centrifugal force alters the arc's morphology.

Centrifugal force shifts the arc from a "concentrated" to a "dispersed" state.

During a linear opening, the arc plasma remains concentrated at the center of the arc column. The high electron density keeps the temperature elevated. Once the contacts begin to rotate, centrifugal force comes into play, preventing the arc roots from remaining stationary. Instead, they are forced to migrate rapidly across the contact surfaces. Deprived of the conditions necessary for concentration, the arc is compelled to spread outward. While the total energy input remains constant, it is distributed over a larger volume; consequently, the electron density per unit volume decreases, leading to an inevitable drop in temperature.

Continuous movement of the arc roots prevents heat accumulation.

Another reason for high electron temperatures is the prolonged heating of a single point by the arc roots. In a linear opening mode, the arc roots remain fixed, causing heat to accumulate layer by layer. Rotation, however, forces the arc roots to constantly shift positions. This ensures a more uniform distribution of energy across the contact surfaces and the gap space, disrupting any localized overheating before it can fully develop. As heat is prevented from concentrating in one spot, the electron temperature falls.

Ultimately, this 40% reduction is achieved by trading space for temperature-rotation dilutes the arc's energy, thereby reducing the difficulty of arc extinction.

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