MCQ on Vacuum Circuit Breaker – A Complete MCQ Series

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Test your knowledge with MCQ on Vacuum Circuit Breaker (VCB). Practice objective questions on VCB operation, construction, arc extinction, applications, and protection systems.

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Vacuum Circuit Breaker (10 Questions)

Question 1
The outstanding feature of a vacuum circuit breaker is:
A. It is cheap
B. It is compact
C. It is clean
D. It is light weight
Question 2
The dielectric strength of a vacuum in a VCB is primarily due to:
A. High pressure inside the interruptor chamber.
B. The presence of SF6 gas.
C. The mean free path of electrons being longer than the contact gap.
D. The use of special cooling mechanisms.
Question 3
The material commonly used for the contacts in a Vacuum Circuit Breaker is:
A. Copper-Bismuth
B. Silver-Tungsten
C. Copper-Beryllium
D. Copper-Chromium
Question 4
In comparison to SF6 circuit breakers, a major advantage of Vacuum Circuit Breakers is:
A. Higher short-circuit breaking capacity.
B. Noiseless operation.
C. Better performance for EHV applications above 245 kV.
D. No generation of hazardous gases during arcing.
Question 5
The phenomenon of "current chopping" in a VCB primarily causes:
A. Excessive contact erosion.
B. High-frequency current oscillations.
C. Overvoltages across the equipment.
D. A delay in arc extinction.
Question 6
The primary function of the metallic bellows in a VCB is to:
A. Provide insulation.
B. Absorb the shock during closing.
C. Allow the movement of the moving contact while maintaining the vacuum seal.
D. Act as a shield to protect the enclosure.
Question 7
Vacuum Circuit Breakers are most suitable for which voltage level?
A. Low Voltage (up to 1 kV)
B. Medium Voltage (3.3 kV to 36 kV)
C. High Voltage (66 kV to 132 kV)
D. Extra High Voltage (above 220 kV)
Question 8
The main purpose of the shield (or vapor condenser) placed between the contacts and the envelope in a VCB is to:
A. Increase the dielectric strength.
B. Protect the ceramic envelope from metal vapors during arcing.
C. Provide a path for heat dissipation.
D. All of the above.
Question 9
Which of the following statements is FALSE regarding Vacuum Circuit Breakers?
A. They require less maintenance compared to oil circuit breakers.
B. They have a high arc voltage.
C. They are fire hazards.
D. They are capable of interrupting high-frequency currents.
Question 10
For interrupting capacitive currents (e.g., switching of unloaded transmission lines), a potential problem with VCBs is:
A. Thermal breakdown
B. Virtual Current Chopping
C. Dielectric breakdown
D. Prestriking of contacts

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