An air circuit breaker (ACB) is a device that is used to isolate faulty a circuit from a healthy system when any abnormal fault exists in the Electrical system.
Air circuit breaker provide protection against overcurrent, under voltage, earth fault, short circuit. The above diagram shows the air circuit breaker (ACB).
The purpose of an air circuit breaker is to break the circuit and isolate a faulty part from the system in abnormal conditions.
and stop the current flow in an overload situation without causing damage to the electrical circuit or the circuit breaker.
Air circuit breakers (ACBs) are breakers where the interruption of the breaking contacts happens in the air and air acts as an arc quenching medium.
Air circuit breakers (ACB) are used in commercial and large industrial electrical systems.
ACB circuit breakers are available in different ratings as per the application requirement.
ACB has current ratings as high as 6300 amps, and current interrupting ratings up to 150,000 amps.
Air Circuit Breaker Construction
Air circuit breaker consist mainly two contacts
- Main contact
- Arcing contact
Throughout normal operation of ACB main contact remains closed.
The Main Contact has very low resistance and the arcing contact is very hard, and heat resistant.
Arc runners are provided at one end of arcing contact to carry the arc during contact separation.
These arc runners open on the arc splitter /arc chute provided on the upper side of the arcing contact.
Air Circuit Breaker Working
During normal operation of the breaker, the main contact remains closed.
Whenever a fault occurs in the system, a tripping command is received by the breaker and the breaker opens its contact to isolate the faulty part.
During the separation of contact, the main contact separates first and the current shifts to the arcing contact after that arcing contact gets separated.
Arc strike between arcing contact during the separation of contact.
When arcing contact separates arc is shifted upward by electromagnetic action.
Arc travels upward through arc runners and is finally split by an arc chute or arc splitter and the arc gets extinguished.
Air circuit breakers use a closing device, known as a “stored energy mechanism,” for fast, positive closing action.
Energy is stored by compressing springs that are attached to the breaking contact assembly of a circuit breaker.
Once these springs are compressed, the latch may be operated to release the springs, and spring pressure will close the air circuit breaker contact.
Circuit breaker closing springs may be compressed manually or by means of a small electric motor.
This type of circuit breaker can be classified as either a manually- or electrically-operated circuit breaker.
When a large air circuit breaker is closed, the operating mechanism is latched.
As the circuit breaker is closed, a set of tripping springs is compressed, and the circuit breaker may then be tripped by means of a trip latch.
The tripping and closing mechanism may be operated either manually or remotely by means of a solenoid trip coil and the closing coil.
Electrically-operated circuit breakers are used when circuits are to be operated frequently or when remote closing and tripping are required.
When the electrically operated circuit breaker is tripped, the spring is recharged by the spring charging motor so that the breaker is ready for the next closing operation.
The manually-operated circuit breaker closing springs are normally compressed by a hand crank just before the operation of the ACB.
Application of ACB
- Air circuit breakers are mainly used in low-voltage applications.
- ACBs are also used to start and protect induction motors
- for the distribution of power in PCC.