A circuit breaker is an important electrical device that can operate automatically to protect an electric circuit from the damage of excess current or low or faulty current. The basic function of the circuit breaker is to disrupt current flow after a faulty current is detected. When there is an overload or short circuit that occurs when a hot wire touches a neutral wire, ground wire or another hot wire, the circuit breaker trips and breaks the current to prevent the wires from overheating, preventing the potential for electrical fires.
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow after a fault is detected. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.
Circuit breakers are made in varying sizes, from small devices that protect low-current circuits or individual household appliance, up to large switchgear designed to protect high voltage circuits feeding an entire city. The generic function of a circuit breaker, or fuse, as an automatic means of removing power from a faulty system is often abbreviated as OCPD (Over Current Protection Device).
All circuit breaker systems have common features in their operation, but details vary substantially depending on the voltage class, current rating and type of the circuit breaker.
The circuit breaker must first detect a fault condition. In small mains and low voltage circuit breakers, this is usually done within the device itself. Typically, the heating or magnetic effects of electric current are employed. Circuit breakers for large currents or high voltages are usually arranged with protective relay pilot devices to sense a fault condition and to operate the opening mechanism. These typically require a separate power source, such as a battery, although some high-voltage circuit breakers are self-contained with current transformers, protective relays, and an internal control power source.
Once a fault is detected, the circuit breaker contacts must open to interrupt the circuit; this is commonly done using mechanically stored energy contained within the breaker, such as a spring or compressed air to separate the contacts. Circuit breakers may also use the higher current caused by the fault to separate the contacts, such as thermal expansion or a magnetic field. Small circuit breakers typically have a manual control lever to switch off the load or reset a tripped breaker, while larger units use solenoids to trip the mechanism, and electric motors to restore energy to the springs.
The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting (opening) the circuit. Contacts are made of copper or copper alloys, silver alloys and other highly conductive materials. Service life of the contacts is limited by the erosion of contact material due to arcing while interrupting the current. Miniature and molded-case circuit breakers are usually discarded when the contacts have worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts.
When a high current or voltage is interrupted, an arc is generated. The length of the arc is generally proportional to the voltage while the intensity (or heat) is proportional to the current. This arc must be contained, cooled and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas, or oil as the medium the arc forms in. Different techniques are used to extinguish the arc including:
- Lengthening or deflecting the arc
- Intensive cooling (in jet chambers)
- Division into partial arcs
- Zero point quenching (contacts open at the zero current time crossing of the AC waveform, effectively breaking no load current at the time of opening. The zero-crossing occurs at twice the line frequency; i.e., 100 times per second for 50 Hz and 120 times per second for 60 Hz AC.)
- Connecting capacitors in parallel with contacts in DC circuits.
Finally, once the fault condition has been cleared, the contacts must again be closed to restore power to the interrupted circuit.
The circuit breaker is ergonomically designed to reset manually or automatically to resume normal operation. Circuit breakers are available in the market in various sizes, from small devices to protect low current or individual household appliances and large switchgear to protect high-voltage circuits feeding an entire city.
Standard circuit breakers are either single- or double-pole
• These are a common type of circuit breakers used more often
• They are designed to protect one energized wire.
• It can supply up to 120V to a circuit.
• It can handle up to 15- to 30-amps.
• Single-pole breaker is available in three types: Full size of 1-inch wide, half size of 1/2-inch wide, and twin/tandem of 1-inch wide with two switches and controls two circuits.
• Double-pole breakers can occupy two slots on a breaker panel and protect two energized wires.
• Double-pole breakers consist of two single-pole breakers with one handle and a shared trip mechanism.
• Double-pole breakers can supply 120V/240V or 240V to a circuit.
• Double-pole breakers range in capacity from 15- to 200-amps.
• Used for large appliances such as dryers and water heaters.
What Are The Main Parts Of A Circuit Breaker?
The main parts of a circuit breaker are a frame, an operating mechanism, interrupting
structure, trip unit, and terminal connections.
1.Frame — The frame consists of the components and also provides insulation to contain the arc.
2.Operating Mechanism — shuts and opens the contacts in the circuit breaker
3.Interrupting Structure — This specific part includes all the current-carrying parts except the trip unit and arcing probe.
4.Trip Unit — This is designed to sense abnormal or faulty current flow and helps the operating mechanism to open the contacts. The circuit trip units are usually of the thermal-magnetic type.
5.Terminal Connections — Terminal connections establish a suitable connection from the breaker to the conductor.
How Does A Circuit Breaker Work?
The circuit breaker mainly comes with fixed and moving contacts. These contacts touch each other to allow the flow of current under normal conditions when the circuit is closed. When the circuit breaker is closed, the electrodes carrying the current called, engage with each other under the pressure of a spring. Under normal conditions, the circuit breaker arms either open or close for switching or maintenance of the system. A certain amount of pressure is required to trigger and open the circuit breaker. In an event of fault current, the trip coil of the circuit breaker gets activated and the moving contacts move apart from each other with an operating mechanism and result in opening the circuit.
Advantages of a circuit breaker:
• Circuit-breakers come as a great replacement for mechanically operating fuses.
. Circuit breakers are sensitive and respond quicker than fuses
• Circuit-breakers are highly reliable and are more functional.
• A circuit-breaker can be installed once and is easy to reset and lasts for a longer duration
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Article Source: https://www.123articleonline.com/articles/1196285/what-is-a-circuit-breaker-and-how-does-it-help
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