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Examoogle • User • info@examoogle.com • EE-2024-8821
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Which circuit breaker is generally used in railway traction?
SF6
Air break
Vacuum
Minimum oil
Air break
Quick Summary: Air break circuit breakers are traditionally used in railway traction systems because they are robust, easily maintainable, and cost-effective for the specific voltage and current levels encountered in electrified locomotive operations. These breakers utilize atmospheric air at normal pressure to extinguish the arc created during contact separation.
Air break circuit breakers are traditionally used in railway traction systems because they are robust, easily maintainable, and cost-effective for the specific voltage and current levels encountered in electrified locomotive operations. These breakers utilize atmospheric air at normal pressure to extinguish the arc created during contact separation.
Rarc=Aρl — Resistance of the arc depends on arc length l and resistivity ρ.
Varc=Vstatic+Ink⋅l — The arc voltage increases with arc length l and inversely with current I.
When the contacts of an air break circuit breaker separate, an arc is formed between them. The arc is elongated and forced into an arc chute using magnetic blow-out coils, where it is cooled and de-ionized by the surrounding air. This rapid cooling and lengthening of the arc path increases the arc resistance until the arc is extinguished at the next natural current zero.
Air break circuit breakers are widely used in DC traction systems.
The magnetic blow-out principle is essential for effective arc interruption in air.
Arc chutes consist of refractory material to withstand high temperatures during arcing.
They are preferred due to their simple construction and lack of high-pressure gas handling requirements.
Low initial cost
Simple maintenance
No risk of oil fire or toxic gas leaks
Robust mechanical operation
Limited capacity for very high voltage levels
Bulky design for high power ratings
Potential for slower arc interruption compared to vacuum/SF6 at high speeds
Railway locomotives and traction substations
Industrial low-voltage and medium-voltage distribution
Short-circuit protection in DC electrified lines
Modern high-speed locomotives sometimes shift to vacuum or SF6 for high voltage ac traction, but air-break remains the standard for traditional DC traction.
Option A (SF6) is used in high-voltage switchgear substations (132kV+). Option C (Vacuum) is used in distribution networks up to 33kV. Option D (Minimum oil) is largely obsolete due to fire hazards.
B is correct — Air break circuit breakers are the standard choice for railway traction due to their simplicity and reliability in DC electrified systems.
Always remember that in electrical traction, the DC supply environment makes arc extinction more challenging than in AC, which is why robust mechanical arc control like air-break is favored.