Circuit Breakers

Circuit Breakers



The circuit breaker is a popular and most important electrical device to ensure safety in the modern world. The circuit breaker is used to cut the power supply when an electrical wire has too much current flowing through it. Without these simple devices, household electricity would not be possible because of the chances for fire and short circuit resulting from simple wiring problems and equipment failures.

The device serves in the course of normal system operation to energize or de-energize loads. In case of conditions where excessive current develops, a circuit breaker opens for protecting equipment and surroundings from possible damage due to excess flow of current.

This automatically-operated electrical switch, unlike a fuse, can be reset (either manually or automatically) for resuming normal operation. These devices are made in varying sizes, right from small devices for protecting an individual household appliance up to large switchgear designed for protecting high voltage circuits feeding an entire city.

Circuit breakerCircuit breaker

Types of Circuit Breakers
There are different technologies being used for manufacturing different circuit breakers and it is difficult to categorize them into distinct categories. Different circuit breakers are used in domestic, commercial and light industrial applications at low voltage (less than 1000 V). These include:

* MCB (Miniature Circuit Breaker): The rated current of the device is not more than 100 A. These have thermal or thermal-magnetic operation... more

* MCCB (Moulded Case Circuit Breaker): The rated current of the device is up to 1000 A. These have thermal or thermal-magnetic operation.

Circuit Breaker Variants

* Magnetic Circuit Breakers: These are a type of circuit breakers that make use of a magnetic actuator to trip the circuit. These circuit breakers allow the current to flow through the electrical device and then pass through an electromagnetic actuator. When the current flow reaches a preset or pre-determined level, the magnetic field in the electromagnet is strong enough to trip the breaker and allow the contacts to open. A magnetic breaker needs to be manually set.

* Hydraulic Circuit Breakers: These are a popular type of circuit breakers designed for those applications requiring higher amperage and voltage handling capability.

* Thermal Circuit Breakers: A simple thermal circuit breaker allows the current to flow from a battery terminal, through the bi-metal strip and then to the other terminal. The bi-metal strip is made of two different types of metals, having different coefficients of expansion. This results in one metal expanding more than the other, in case of same rise of temperature. In this circuit breaker, when one metallic strips expands more than the other, and thus disconnects the contacts.
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* Auto Reset Circuit Breakers: These circuit breakers re set automatically in case of a faulty load or circuit. These circuit breakers are widely used in case of leakage, short - circuit, surge or overload etc. Auto reset circuit breakers do not require manual assistance for re setting and cut off power supply in case of power trip. This power is than again restored after auto resetting.

High Voltage Circuit Breakers
There are electric power systems requiring the breaking of higher currents at higher voltages. It is such systems that high-voltage AC circuit breakers are used.

* Vacuum Circuit Breaker: The rated current of the device is up to 3000 A. These specialty circuit breakers interrupt the current by creating and extinguishing the arc in a vacuum container. These devices can only be practically used for voltages up to about 35,000 V, which corresponds to the medium-voltage range of power systems. These circuit breakers have longer life expectancies between overhaul than do air circuit breakers.
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* Air Circuit Breaker: The rated current of the device is up to 10,000 A. Some of them are electronically controlled, while others are microprocessor controlled. These circuit breakers are used for main power distribution in large industrial plants.