In this article we will learn about the vacuum circuit breaker , its working and application. we also read about the how to arc quench a circuit breaker.
Vacuum circuit breaker
When two current carrying contacts are separated in a vacuum medium, the arc is drawn between them. The intensely hot spot is created at the instant of contact separation from which metal overshoot off, constituting plasma. The amount of vapors in the plasma is proportional to the rate of vapor emission from the electrodes, hence to the arc current is tends to zero and amount of plasma tends to zero. Soon after natural current zero, the remaining metal vapor condenses and the dielectric strength builds up rapidly and preshrinking of arc is prevented. So this principle is used in vacuum circuit breaker.
Arc extinction in vacuum interrupters
The arc interruption process in vacuum interrupters is different from that in other types of circuit breakers. The vacuum as such as a dielectric medium and arc cannot persist in ideal vacuum. However, the vacuum as such is an dielectric medium and arc cannot persist in ideal from the contacts giving rise to plasma. Thus, as the contacts separate, the contact spare is filled with vapor of positive ions liberated by the contact material. The vapor density are depends on the current in the arc
Advantage of vacuum circuit breaker
1. VCB is self-contained does not need filling have oil or gas. They do not need auxiliary air system; oil handling system etc. does not need of periodic refilling.
2. No emission of gases or other pollution, pollution free.
3. Modest maintenance of the breaker, no maintenance of interrupters. Hence economical over long period.
4. Breaker forms a unit which can be installed at any required orientation. Its unit is compact and self-contained.
5. Non explosive
6. Its Silent operation
7. Large number of operations on load or short circuit. Suitable for repeated operating duty. Long life
8. Suitable for capacitor switching, cable switching, industrial load switching.
9. Constant dielectric.
There are no gas decomposition products in vacuum and the hermetically sealed vacuum interrupter keeps out all environmental effects.
10. Constant contact resistance
In vacuum the contacts cannot oxidize a react which ensures that their very small resistance is maintained throughout their life.
11. High total current switched.
Since contact piece erosion is small, rated normal current can be interrupted up to 30,000 times and rated short-circuit breaking current on average a hundred times.
Disadvantage of vacuum circuit breaker
• The vacuum interrupter is more expensive than the interrupting devices in other types of circuit breakers and its cost is affected by production volume. It is uneconomical to manufacture vacuum interrupters in small quantities.
• Rated voltage of single interrupter is limited to about 20KV . above 36KV two interrupters are required to be connected in series.
• Vacuum interrupters require high technology for production.
• In the event of loss of vacuum due to transit damage or failure, the entire interrupter is rendered useless. It cannot be repaired at site
• For interruption of low magnetizing currents in certain range, additional surge suppressors are required in parallel with each phase of a
if you want to know more about vaccum circuit breaker you must sea this video.