What are the arc extinguishing methods of vacuum interrupter?

The arc extinguishing method of the vacuum interrupter can be summarized as follows: when the current of the metal vapor arc generated in the high vacuum medium passes through zero, its plasma products can diffuse and condense extremely quickly, thereby quickly restoring the dielectric strength and realizing arc extinguishing.

Three Stages of the Arc Extinguishing Process

1. Arc Generation: Metal Vapor Arc
When the contacts of a vacuum interrupter separate under load current:

The contact point decreases dramatically, the resistance increases dramatically, and the contact area rapidly melts and vaporizes.

The vaporized metal material is ionized by the strong electric field in the vacuum, forming a highly ionized metal vapor plasma—this is the vacuum arc.

Unlike the gas arcs in oil circuit breakers or SF6 circuit breakers, the plasma in a vacuum arc is primarily composed of vapor from the contact material (such as copper or chromium), rather than ambient gas molecules.

 

2. Arc Maintenance and Form
The vacuum arc is sustained by the metal vapor evaporated from the contacts.

Under high power frequency current, the vacuum arc shrinks and rotates due to its own magnetic field, preventing it from stably burning at a single point on the contact surface, thereby preventing local overheating and severe erosion of the contacts.

 

3. Arc Extinction: The Key Step (Rapid Recovery of Dielectric Strength)
This is the most delicate part. The success of arc extinguishing does not depend on how the arc is "blown out," but rather on whether the contact gap can rebuild its insulation capacity faster than the system recovery voltage after the current passes through zero.

a. Current Zero Crossing

AC naturally passes through zero once every half cycle (10ms). At the moment the current passes through zero, the arc power approaches zero, and the arc is temporarily extinguished.

b. Rapid Plasma Diffusion and Condensation (Core Mechanism)

After the current passes through zero, the metal vapor plasma that sustains the arc loses its energy source.

Because the arc extinguishing chamber is in a high vacuum (typically better than 10^-4 Pa), gas molecules are extremely sparse, and the probability of interparticle collisions is extremely low. As a result, metal ions, electrons, and neutral atoms fly freely into the surrounding space at extremely high speeds (up to the speed of sound).

The vast majority of these particles quickly collide with and condense on the cold shield (especially the main shield) and contact surfaces. This process occurs within microseconds.

c. Rapid Recovery of Dielectric Strength

With the rapid removal of plasma particles, the contact gap quickly recovers from its good conductor state to its original high-vacuum insulation state.

This recovery rate is extremely rapid, far exceeding the rise in the system recovery voltage.

Therefore, when the system voltage is reapplied across the contacts, the gap is already able to withstand this voltage without breaking down again, and the arc is successfully extinguished.

 

The condition for successful arc extinguishing is that the dielectric recovery strength curve remains consistently above the system recovery voltage curve.

Vacuum interrupters, with their extremely fast dielectric strength recovery rate, ensure this condition is met under all circumstances, resulting in reliable arc extinguishing.

 

Summary of Features

Compared to other arc extinguishing methods, vacuum arc extinguishing has the following advantages:

Passive arc extinguishing: No additional arc-extinguishing medium (such as oil, compressed air, or SF6 gas) is required to "blow" the arc, relying solely on the inherent properties of the vacuum environment.

Extremely Fast: The plasma diffusion and condensation process is completed within microseconds, resulting in a very short full-break time.

Low Energy: The arc energy is low, causing minimal contact erosion, resulting in a long electrical life.

Safe and Environmentally Friendly: Arc products are sealed internally, preventing external emission and emitting no polluting gases.

 

In summary, vacuum interrupters utilize a variety of arc extinguishing methods, each with its own unique advantages and applicable scenarios. Combining magnetic field control, metal vapor, vacuum circuit breaker, liquid, and compressed air, these methods can quickly and reliably extinguish arcs, ensuring the safe and stable operation of power systems. The continuous innovation and application of these arc extinguishing methods provide critical support for the development and safety of the power industry.

If you want to learn more about ,please feel free contact us at:pannie@hdswitchgear.com.