Vacuum Circuit breaker working principle and advantages of VCB

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Vacuum Circuit Breaker (VCB): Working Principle, Operation, and Maintenance Guide

A Vacuum Circuit Breaker (VCB) is one of the most reliable and widely used switchgear technologies for medium-voltage applications. It extinguishes arc inside a vacuum, where no medium (oil, gas, or air) is required, making it safer and more eco-friendly compared to conventional circuit breakers.



Working Principle of VCB

The main function of any circuit breaker is to quench the arc that forms when contacts open under load. In a VCB:

  • The arc quenching medium is vacuum, with pressure maintained around 10⁻⁶ bar.

  • When contacts separate, a metal vapor arc is formed at the last contact point.

  • At current zero, the arc is extinguished as the vapor condenses back on the contacts.

  • The high dielectric strength of vacuum (8× air, 4× SF₆) prevents re-ignition.

This ensures fast arc extinction and minimizes contact erosion.

Construction of Vacuum Interrupter

A typical vacuum interrupter consists of:

  • Steel arc chamber in the center

  • Symmetrical ceramic insulators around it

  • CuCr (Copper-Chromium) contacts, which ensure high performance and minimal erosion

The compact design requires low drive energy and minimal maintenance compared to oil or SF₆ circuit breakers.

Operation of Vacuum Circuit Breaker

  • For currents ≤ 10 kA, the arc is diffused across the contact surface.

  • For currents > 10 kA, the arc becomes constricted due to magnetic fields. To avoid overheating, specially designed spiral/radial contacts are used, forcing the arc to move continuously.

  • This ensures uniform wear and longer life of the breaker.

Advantages of VCB

  1. Long service life compared to oil or SF₆ breakers

  2. No fire hazard unlike oil circuit breakers

  3. Eco-friendly and safe (no greenhouse gases like SF₆)

  4. Compact and user-friendly construction

  5. Easy replacement of vacuum interrupters



Maintenance of Vacuum Circuit Breakers

Preliminary Checks Before Maintenance

  • Ensure power supply is disconnected

  • Discharge fixed and moving contacts using an earthing rod

  • Visually inspect breaker for external damage

Recommended Maintenance Activities

  • Cleaning & lubrication of moving parts

  • Calibration of protection relays

  • Vacuum integrity check (using vacuum test kit / high-pot test)

  • Testing closing and opening mechanisms

  • Checking motorized spring charging mechanism

  • Verifying trip and interlock functions

  • Inspecting control wiring, fuses, and instrument transformers

  • Insulation resistance test using 5 kV megger

Frequency of Maintenance

  • Every 2 years or

  • Every 2000 operations, whichever is earlier

Conclusion

Vacuum Circuit Breakers are highly reliable, eco-friendly, and require minimal maintenance, making them the preferred choice for medium-voltage switchgear. With proper inspection and servicing, VCBs can provide decades of safe and efficient operation.

⚡ Pro Tip for Engineers: Always follow OEM manuals for breaker-specific checks, and ensure maintenance logs are properly recorded for compliance and reliability tracking.


Comments

  1. AnonymousMay 9, 2022 at 5:41 AM

    Your post is very nice. Vacuum Circuit Breakers (VCB) is must be carefully operation because Its supply high voltage.

    ReplyDelete
  2. globeinternationalwebJuly 12, 2022 at 12:49 AM

    Thank You For Sharing Great Information. for more details something like visit vaccum circuit breaker types get more informations.

    ReplyDelete

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