The full form of ACB in electrical is Air Circuit Breaker. An air circuit breaker is a device used in low-voltage electrical systems, typically 415 volts, to control power flow and provide overcurrent and short circuit protection.
Air circuit breakers use relays and releases to protect loads from different kinds of faults. When a fault occurs, these devices trip the circuit breaker to prevent damage. Releases are sensing devices that are installed inside the breaker, while relays are installed outside of it. Releases are internal features of ACB, while relays are external.
After knowing about the full form of ACB and its application in electrical circuits, let’s learn more about ACBs.
Working Principle
The working principle of an ACB (Air Circuit Breaker) is similar to circuit breakers such as SF6 circuit breakers and vacuum circuit breakers, which are used in HT supply. In HT circuit breakers, an extra arc quenching medium such as oil, SF6, or vacuum is required due to the high voltage. On the other hand, in LT (Low Tension) systems, no additional quenching medium is necessary as the arc is extinguished in normal ambient air. Nevertheless, some special arrangements are made in the breaker to extinguish the arc.
Arcing horns increase the contact area and spread arc heat between fixed and moving contacts.
- Arcing horns – Arcing horns increase the contact area and spread arc heat between fixed and moving contacts.
- Arc Chutes – Arc chutes are installed above the contacts. These chutes split the heat generated by the electric arc inside the chamber, which causes the arc to cool down, lengthen, and split. This results in the voltage of the arc becoming much higher than the voltage of the system when the ACB is closed. Eventually, the arc is quenched automatically.
Important Terms Related to ACB
- Fixed type ACB – This breaker is fixed with the cradle and the cradle is attached to the panel, making it impossible to remove the breaker.
- MDO ACB –MDO stands for Manually Operated Draw Out type of breaker. The breaker is operated manually, and it can be racked in and out with the help of a handle.
- EDO ACB –EDO stands for Electrically Operated Draw Out (type of breaker). This breaker can be operated both electrically and manually; it can be easily racked in and out with the help of a handle.
- Releases –These relays are fitted inside the breaker for various types of protection. There are different types of releases.
- Shunt release – This release is used to trip a breaker remotely. When the shunt release is energized, it sends a command to trip the breaker, and the breaker mechanism disconnects the contacts.
- Under Voltage release – It trips when the voltage drops below 80% of the supply voltage to protect equipment from low voltage. You can set the under-voltage release setting as per the system requirement.
- Electromagnetic or Electronic Release – There are two types of ACBs available in the market based on their release mechanism: electromagnetic and electronic. In electromagnetic releases, trip settings are fixed in percentage steps for fault protection. However, electronic releases allow for customizable trip settings. Additionally, electronic releases have a faster response time compared to electromagnetic releases.
- Poles – Circuit breakers come in different configurations, such as 4P, TP, and TPN. Here are the details:
- 4p ACB – When an ACB operates, all three phases (R, Y, B) and one neutral will operate in the 4P configuration.
- TP ACB – It is a 3-pole ACB. When the TP breaker is activated, only the R, Y, and B phases are involved in the breaker’s operation. The neutral is connected through a link and is not part of the ACB.
- TPN ACB – TPN stands for Triple Pole with Neutral. In this configuration, the R, Y, and B phases and the neutral are part of an ACB (Air Circuit Breaker). When the ACB operates, only the R, Y, and B phases operate, and the neutral does not. However, the neutral remains connected.
