Blog A Guide to Circuit Breakers

A Guide to Circuit Breakers


During normal operation of a power system, such as a transmission line, distributor, generating plant, or other, it is often necessary to switch the various circuits on or off in both normal and abnormal conditions. In older power systems, this function was carried out by a series of fuses within the circuit. However, this method of control brought multiple disadvantages. For one, when a fuse blows out, it can take a great deal of time to replace it and restore the system. Second, fuses are not capable of interrupting heavy fault currents that result from faults on modern, high-voltage, large capacity circuits. Because of this, fuses’ uses are limited to low-voltage and small capacity circuits where only intermittent operation is expected.


As power systems have advanced, so too has the need for equipment that can operate at high voltages and carry large currents. As fuses have shown not to be capable of this, the need for a more dependable means of control became apparent. This is where the circuit breaker comes in. Generally speaking, circuit breakers can do three things: make or break a circuit manually or by remote control in normal conditions, break a circuit automatically under fault conditions, and make a circuit either manually or remotely under fault conditions. These characteristics have made it a very useful piece of equipment for switching as well as protection of components within the power system.


A circuit breaker essentially consists of fixed and moving contacts known as electrodes. Under normal conditions, the electrodes remain closed and do not open automatically unless the system fails. That said, they can be opened manually or by remote at any point. When a failure occurs in any part of the system, the circuit breaker’s trip coils become energized and the contacts are pulled apart from each other, thereby opening the circuit. When a circuit breaker’s contacts are separated under fault conditions, the result is an arc that allows the current to continue until the discharge ends. The arc causes a delay in the current interruption process and also generates a lot of heat that could damage the circuit breaker and the system at large. As such, arcs are the main problem faced by circuit breakers and must be extinguished as quickly as possible to prevent the resulting heat from reaching a dangerous level.


There are many different types and classifications of circuit breakers, but the distinguishing factor is most often the medium used for arc extinguishing. The four most common types of circuit breakers are oil circuit breakers, air-blast circuit breakers, sulphur hexafluoride circuit breakers, and vacuum circuit breakers. Oil circuit breakers utilize an insulating oil, such as transformer oil, to extinguish an arc. In air-blast circuit breakers, this is done by a high-pressure blast of air. In sulphur hexafluoride circuit breakers, sulphur hexafluoride, a type of gas, is used. Finally, vacuum circuit breakers use vacuum pressure to extinguish the arc.


Circuit breakers can also be classified based on their voltage levels (low, medium, and high voltage circuit breakers), their working principle (hydraulic, pneumatic, and spring-actuated circuit breakers), and whether they are used indoors or outdoors. Whatever type of circuit breaker you are in need of, ASAP Distribution can help.


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April 15, 2020
December 20, 2017

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