Introduction to Air brake circuit breaker
“Air break circuit breakers safely interrupt electrical currents by using air as the extinguishing medium, eliminating fire hazards associated with oil, and employing advanced principles for efficient arc extinguishing in circuits up to 12,000 volts.”
Air break circuit breakers are designed to interrupt electrical currents without the associated risks found in oil-based systems. The decision to locate the air disruption for arc extinguishing was motivated by the production of hydrogen gas due to the decomposition of oil in oil-based systems. Although hydrogen is more effective in arc interruption, air has distinct advantages over oil as a quenching medium:
1. Elimination of fire risks: Air brake circuit breakers eliminate the risk of fire and maintenance issues associated with the use of oil.
2. Absence of mechanical stresses: Unlike mechanical stresses caused by gas pressure and oil movement, air brake circuit breakers do not create such stresses.
3. No regular oil replacement costs: Eliminates the need for periodic oil replacement resulting from oil deterioration following continuous braking operation.
To compensate for the relatively low arc quenching properties of air, various arc control principles are employed along with operating the air at elevated pressures. These circuit breakers find common use in both DC and AC circuits up to 12,000 volts, usually installed indoors on vertical panels or draw-out switchgear.
1. Plain Break Type Air Break Circuit Breaker:
• The simplest form with two horn-shaped contacts.
• The air initially hits the horns at the shortest distance.
• The arc becomes taller and cooler as air is pushed upward by convection currents.
• Limited to about 500 volts and low-power circuits due to slow process and potential arc propagation.
2. Magnetic Blow Out Type Air Break Circuit Breaker:
• Uses the magnetic field generated by the blow-out coils to extinguish the arc.
• Blow-out coils assist in magnetically blowing the arc into the arc chute.
• In an arc chute the arc is lengthened, cooled and extinguished.
• Increases breaking capacity for circuits up to 11 KV.
3. Arc-Shoot Air Break Circuit Breaker:
• Uses main and arcing contacts for low and medium voltage circuits.
• Main contacts conduct current in the closed position, while arcing contacts protect the main contacts from damage caused by arcing.
• The arc chute efficiently confines, controls and cools the arc for extinction.
• It has high breaking capacity and is suitable for heavy works.
Operation:
• During a fault, the main contacts are the first to move, allowing current to transfer to the arcing contacts.
• The arc is drawn between the arcing contacts and forced upward by electromagnetic forces and thermal action.
• The arc is divided, lengthened, and cooled through various mechanisms for efficient extinction.
Application:
• Suitable for controlling power station auxiliary and industrial plants.
• It is recommended where risk of fire or explosion due to the absence of oil is a concern.
• Employed for DC circuit breakers up to 15 KV.
While air break circuit breakers offer advantages in safety and maintenance, their efficiency may be reduced at low currents. As operating voltage and breaking capacity increase, the breaker becomes heavier, more complex, and may not be suitable for modern power systems.
BRIEF SUMMARY
Air Brake Circuit Breakers:
Designed to safely interrupt electrical currents, avoiding the risks associated with oil-based systems.
Air is chosen over oil to eliminate fire and maintenance issues.
Advantages:
1. No Fire Risk:
• Eliminates the risk of fires linked to oil.
2. No Mechanical Stresses:
• Avoids stresses caused by gas pressure and oil movement.
3. No Regular Oil Replacement:
• Eliminates the need for regular oil changes.
Properties and Applications:
• Utilizes various principles to compensate for lower arc-quenching abilities.
• Commonly used in both DC and AC circuits up to 12,000 volts.
Types:
1. Plain Break:
• Simple design with two horn-shaped contacts, suitable for low-power circuits.
2. Magnetic Blow Out:
• Utilizes magnetic fields to extinguish arcs, suitable for higher-capacity circuits.
3. Arc-Shoot:
• Efficient for heavy-duty use, incorporating main and arcing contacts.
Operation:
• During a fault, main contacts transfer current to arcing contacts.
• Electromagnetic forces and thermal action work together to extinguish the arc.
Application:
• Suitable for power stations, industries, and areas where fire risk is a concern.
• Used for DC circuit breakers up to 15 KV.
Considerations:
• Efficiency may decrease at low currents.
• Becomes heavier and more complex with higher voltage, potentially not ideal for modern power systems.