ACBs

Air circuit breakers (ACBs) are protective devices used in electrical power systems to interrupt fault currents and protect equipment. They are designed for medium-voltage applications and are typically installed in indoor or outdoor switchgear within substations and industrial facilities. ACBs handle high interrupting capacities and can be rated for voltages from roughly 1 kV up to around 40 kV, with fault-current ratings spanning several kiloamperes.

Construction and operation

An ACB consists of insulated housings that enclose main and arcing contacts, an arc-quenching chamber, and a mechanism to open and close the contacts. When a fault occurs, the main contacts separate and an electric arc forms between the contacts. The arc is guided into an arc chamber or arc chute where it is cooled and divided into smaller arc streams to extinguish it, allowing the circuit to break safely. Many ACBs use stored-energy springs to achieve rapid opening, often triggered by a protective relay or timer. Protection and control is typically provided by electromechanical or electronic trip units, which monitor current, voltage, and time characteristics and initiate tripping according to preset curves or logic.

Applications and context

ACBs are commonly used in air-insulated switchgear and other MV switchgear configurations, serving as the primary fault-interrupting devices in distribution networks and industrial plants. They are generally robust and straightforward but tend to be larger and less compact than alternative technologies such as vacuum circuit breakers or gas-insulated switchgear. In modern installations, ACBs may be supplemented or replaced by these newer technologies where higher reliability, tighter protection, or reduced footprint is required.