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How Vacuum Circuit Breaker Works And its Operation and advantages

Updated on December 28, 2012

Vacuum circuit breaker

Vacuum circuit breaker
Vacuum circuit breaker | Source

Introduction of Vacuum Circuit Breaker

First of all I will discuss about introduction. Now you are in this page that means you have searched only for details about "how vacuum circuit breaker works". So, I am going to discuss only about vacuum circuit breaker. In this article I have included some images and diagram made by myself. So it will easy for you to understand. Siemens also makes vacuum circuit breaker. I am not including construction of vacuum circuit breaker.

In Vacuum Circuit Breaker "VACUUM" is used as a arc quenching medium. Now the question is what is vacuum. vacuum is simply pressure below atmospheric pressure. (760mm of Hg) (1mm of Hg=1 torr). In vacuum circuit breaker high vacuum of the order of 10-5 to 10-7 torr is used. In such a very low pressure the free path of electrons is very large of order of few meters and therefore when the electrodes are separated by few mm an electron crosses gap without any collision. Because of this reason vacuum has high die-electric strength.

vacuum circuit breaker operation

vacuum circuit breaker operation
vacuum circuit breaker operation


Develop glass-to-metal seal technology

- Fernico, an iron- nickel-cobalt alloy, was developed.

Method of Gas Removal

- the electrodes gave off a large amount of gas during arcing, thus destroying the vacuum.

Contact Materials

- pure tungsten, both sintered and single crystal, or pure molybdenum

Effect on Contacts of Vacuum Circuit Breaker

Here when contacts separate contact pressure reduces. Therefore real contact surface reduces and the temperature of contacts increases to melting temperature. This produces metal vapours which initiates and support vacuum arc, maintaining until the next current zero. So, to prevent this spiral geometry is used in contacts. that keeps arc column by the radial magnetic field produced in order to involve a wider surface then that of a fixed contracted arc.Thus overheating and corosion of the contacts are prevented

Rotating arc between two electrodes of vacuum CB

In below these figures the rotating arc in very short time period is shown. first Arc starts to diffuse by Axial Magnetic Field. then Arc spreads and interruption is completing. Here there are two images at different time period. so you can see the differences.

vacuum circuit breaker operation arc quenching process
vacuum circuit breaker operation arc quenching process
vacuum circuit breaker operation arc quenching process time peroid
vacuum circuit breaker operation arc quenching process time peroid

Advantages of Vacuum Circuit Breaker

  1. Very simple in construction
  2. very little maintenance
  3. Very long life time of contacts so, longer circuit breaker life
  4. Less moving part in mechanism
  5. Compact size and reliable
  6. Less force needed to separate the contacts
  7. Vacuum has very high dielectric strength (1000 times more)
  8. No explosion
  9. Small size so, less power required
  10. Low arc energy comparing other type of CBs
  11. Arcing time is short.
  12. Arcing voltage is very low.
  13. Very fast in operation and suitable for repeated operations 20,000
  14. Capable for interrupting capacitive currents and small inductive currents without producing excessive TRV
  15. Environment friendly. (as there is no gas)

Read My Circuit Breaker Articles

How to Test of Circuit Breaker?: Circuit Breaker Testing Procedure and Tests and Sequence Switch

In this article i have described Why circuit breaker tests are necessary to operate. I have also included Testing procedure and types of circuit breaker tests. I hope this will help you to get some circuit breaker knowledge.


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