Air air circuit breaker, also known as air switch or automatic air switch, is an automatic switching device that uses air as arc extinguishing medium and insulation medium. Its core value can be summed up in one sentence: it helps you connect and disconnect circuits under normal circumstances, and automatically jumps to shut off power and protect lines and equipment in the event of a malfunction.
I. How does it work? -Three lines of defense
air circuit breaker has a sophisticated "detection + action" system that uses different tripping units to respond to different failures:
First line of defense: Overload Protection (Temperature Tripping) When a circuit is overloaded for a long period of time, the current is high, but not to the extent of a short circuit. The bimetallic strip inside the circuit breakers slowly buckle under the heat. When it bends to a certain extent, it pushes the tripping mechanism, causing the switch to flip. Since heating takes time, this protection has a delay and does not malfunction due to short current fluctuations.
Second line of defense: short circuit protection (Electromagnetic Tripping) During a short circuit, electricity can surge dozens or even hundreds of times its normal value in an instant. At this point, the electromagnetic tripping unit (coil) generates a strong magnetic field that immediately attracts the armature and pulls the tripping device, cutting off the circuit in milliseconds. This is the fastest and most powerful first line of defence against cable burning and equipment damage.
Third line of defence: Undervoltage protection (undervoltage trip unit)
When the power supply voltage drops to 70%–35% of the rated voltage, the undervoltage trip unit automatically trips, cutting off the power supply. The circuit breaker can only be re-energized if the voltage is restored to above 85%. This prevents equipment from malfunctioning and damaging due to low voltage.
How is the arc go out?
When a circuit breaker interrupts a large current, an arc of electricity with temperatures in tens of thousands of degrees Celsius is created when the contact is separated. Air circuit breakers has an arc killing grid (a set of metal plates) inside, where the arc is rapidly elongated, split and cooled, eventually ending in an arc killing. Some high-performance models also have arc blowers, which use electromagnetic force to blow the arc rapidly into the arc extinguishing grille, making arc extinguishing more efficient.
ii. What is its purpose? Normal on/Off Functions: manual or electric off and on circuit.
Short circuit protection: Gigabit short circuit current interruptions to prevent fire and equipment damage.
Overload Protection: Bimetallic thermal trip to prevent prolonged-term overheating of wiring.
Undervoltage Protection: Protect electrical equipment from Automatic tripping when voltage is too low.
Infrequent Motor Starting: can be used as a full voltage motor start.
Remote control: equipped with a shunt trip unit or an electric operating mechanism, can automatically open and close circuits remotely.
III. The "Two Identities" of Air Circuit Breakers Air have completely different meanings in different areas and must be distinguished:
Label 1: Commonly known as an "air switch" (low voltage, domestic/commercial)
This is what your home's distribution box, technically known as a mini-circuit breaker (MCB), also known as an air circuit breaker.
Rated Voltage: 220 volts /380 volts
Rated: 0.5A to 63A
Uses: Lighting and socket circuit protection in homes, offices and shops
Features: Small size, cheap, only a few yuan to a few dozen yuan each.
Mark II: High-Voltage Compressed Air Circuit Breaker (ACB for power system)
This is a the true "air circuit breaker," utilizing compressed air (0.4 to 6 MPa) as an arc extinguishing and insulation medium, and even compressed air as a power source.
Rated: 110kV and above
Rated current: hundreds to thousands of amperes
Uses: Large power plant outlets, substation, high voltage transmission line
Features: Very high short-circuit capacity, extremely fast operation speed, no fire hazard (unlike oil circuit breakers), but requires a complete compressed air system, complex structure. It has Currently been largely replaced by SF6 circuit breakers in systems of 110kV and above.
IV. INTRODUCTION How does it compare to other circuit breakers? Compared with vacuum circuit breakers, air circuit breakers are large in size and have weak arc extinguishing performance, but they are cheap and easy to maintain. Vacuum circuit breakers, once the king of low to medium pressure at 35kV and below, have been replaced by SF6.
Compared to SF6 circuit breakers: The biggest advantage of air circuit breakers is that they do not pose a fire hazard because they do not use oil or natural gas and the arc extinguishing medium is air. However, SF6 is far more insulating and arc extinguishing than air, so in the 110kV to 500kV high voltage field, SF6 completely replaces air circuit breakers.
Compared to oil circuit breakers: oil is used to extinguish the arc, and there is a fire and explosion risk. Air circuit breakers have no such problems and provide an order of magnitude above safety. However, due to its simple structure and low cost, oil circuit breakers is still used in 35kV outdoor systems.
V. WHERE TO USE? Home/Commercial Scenarios: Low voltage air circuit breakers (mini-circuit breakers) for your home's distribution box, lighting circuit protection for shopping malls and office buildings, motor protection for small factories.
Industrial Power Distribution Scenarios: Molded case circuit breakers (MCCB) is used in building and mining enterprises distribution cabinets. Their rated current ranges from tens of thousands of amperes to thousands of amperes and is suitable for high-frequency interruptions.
Power System Scenarios: Compressed air circuit breakers have been widely used in large power plant vents and substations of 110kV and above. They have now largely been replaced by SF6 circuit breakers, but are still used in exceptional circumstances (such as largecurrent applications that require rapid interruptions).
Abstract: air circuit breaker is an automatic switch that uses air to extinguish arc. A small switch for a your home's distribution box is one, as is a large switch for a high voltage substation. Its core value is to connect and disconnect circuits properly and "take a hit" if something goes wrong. Additionally, it can be reset and reused after the fault is extinguished, unlike a fuse that burns when it needs to be replaced. It is the basic and indispensable protection device in power system, which is equivalent to the combination of knife switch, fuse, thermal relay and under-voltage relay.
