What is a Vacuum Circuit Breaker : Working & Its Applications

A vacuum circuit breaker (VCB) is a type of circuit breaker that uses vacuum interrupters to extinguish electrical arcs when interrupting a current flow. It is designed to provide reliable and efficient interruption of fault currents in high voltage electrical systems. VCBs are widely used in medium and high voltage applications where fast and reliable interruption of electrical circuits is essential.

Working Principle:

The operation of a vacuum circuit breaker involves the use of vacuum interrupters that are housed in a sealed vacuum bottle. The vacuum interrupter consists of stationary and movable contacts within the vacuum-sealed chamber. When the circuit breaker is closed, the contacts are in a closed position, allowing current to flow through.

When the breaker needs to interrupt the circuit, such as during a fault condition or for maintenance purposes, the contacts are pulled apart by the operating mechanism. As the contacts move away from each other, the current flowing between them encounters the vacuum in the interrupter chamber.

The vacuum acts as an insulating medium, and as the contacts separate, an arc is initiated due to the ionization of the particles in the gap. However, the vacuum's high dielectric strength quickly extinguishes the arc by preventing the sustained flow of current. The arc interruption happens within a fraction of a second, ensuring rapid and efficient interruption of the circuit.

Working Steps:

Closing Operation: The contacts are brought into contact, allowing the current to flow through.

Opening Operation: When the breaker needs to trip, the operating mechanism initiates the separation of contacts, creating an arc.

Arc Extinction: The vacuum interrupter's high dielectric strength causes rapid arc extinction, interrupting the current flow.

Applications:

Power Distribution Systems: Vacuum circuit breakers are used in high voltage power distribution systems, substations, and power plants for protecting electrical equipment and networks from short circuits and overloads.

Railways: They are employed in railway systems to protect overhead lines and electric traction systems.

Industrial Applications: VCBs find use in various industrial applications where reliable interruption of high voltage circuits is critical for safety and equipment protection.

Switching Capacitors and Transformers: They are utilized in switching operations for capacitors and transformers in power systems.

VCBs offer several advantages, including high reliability, fast operation, minimal maintenance requirements, and the absence of environmentally harmful gases, making them a preferred choice in many high voltage applications compared to other types of circuit breakers.