DC breakers are used to safeguard electrical devices that run on direct current. But are wondering about the working of a DC Circuit breaker? The following article by AGM Electrical Supplies is helpful to understanding the working of a circuit breaker from the scratch.  

• The Voltage

The voltage driving the circuit breaker determines what devices it can safely handle and when there is an issue with power flow within the circuit.

DC breakers can manage a single, unidirectional flow of constant current. Unlike alternating current, which consists of periodic cycles with various amplitudes, DC breakers handle an uninterrupted, one-directional stream.

A DC breaker must be able to maintain a voltage that will interrupt current flow in order to protect itself and its users. However, this can prove challenging since the breaker needs to stay above a certain level of voltage for extended periods of time.

• The Contacts

Circuit breakers feature contacts designed to withstand current flow and arcing while interrupting faults. This ensures the operation of the device while maintaining its desired ratings.

Commonly, main contacts are made of copper or silver alloys due to their excellent conductivity and superior corrosion resistance.

Arcing between main contacts can damage the contact material and eventually result in the failure of a circuit breaker. To prevent arcing between main contacts and another set of contacts, usually an insulating barrier is placed between them.

DC breakers are much stronger than AC ones when faced with an arc, since electrons in an AC system do not flow with momentum like they do when connected to DC. This is because AC changes direction and magnitude 50 or 60 times per second, while DC remains steady.

• The Switching Mechanism

When current levels reach unsafe heights, a circuit breaker switches off the power. This safeguards equipment such as appliances from being damaged due to excessive current.

Contrary to a fuse, which only works once, a DC circuit breaker can be used repeatedly to cut off power. They may be operated manually with a switch or remotely by relay.

In either case, the breaker works by drawing upon stored potential energy. This could be in the form of a deforming metal spring, compressed air or hydraulic pressure.

The circuit breaker's operating mechanism consists of two sets of contacts, the primary and auxiliary (or trip) contact poles. When a command signal is received, the primary contact poles move accordingly, while the auxiliary (or trip) contact poles close or open depending on whether the main contact poles have been closed or opened.

Primary contact poles are housed in vacuum chambers to prevent air arcing across them when they separate. Likewise, auxiliary contacts also operate under vacuum conditions.

• The Arc

A DC circuit breaker is used to protect power lines, electrical systems and equipment. These can range in size from small devices that shield individual appliances to large switchgear that shields high voltage circuits.

Industrial control panels often use relays. Usually, these are employed for low-voltage applications.

However, in certain instances the arc generated can be too much for these devices to handle. In such cases, an arc suppressor may help prevent the arc from transferring onto contacts.

This device is mounted on a movable contact arm next to the fixed contact, facing away from the arc chute so that it won't transfer into the fixed contact during opening of the circuit breaker.

Furthermore, an arc suppressor can be mounted on the operating mechanism for pivoting a movable contact arm. In this way, it will not move with the contact arm during pivoting operations.

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