A circuit breaker stands as a vital electrical component, acting as a swift-switching apparatus capable of rapidly opening and closing an electrical circuit within a fraction of a moment. This action occurs both during standard operational scenarios and in reaction to glitches or anomalies. Typically, circuit breakers are employed to safely disconnect the load circuit from its power source, ensuring the secure and controlled distribution of electrical power when irregularities arise.
Circuit breakers represent a varied category of automated gear and are classified based on the medium utilized to quell electrical arcs. In high-power settings, three primary types of circuit breakers frequently find application: ACB (Air Circuit Breaker), VCB (Vacuum Circuit Breaker), and SF6 Circuit Breaker (Sulfur Hexafluoride Circuit Breaker).
In this piece, we will delve into the fundamental distinctions between ACB (Air Circuit Breaker) and VCB (Vacuum Circuit Breaker) in a simple manner.
Introduction to VCB
A Vacuum Circuit Breaker, commonly referred to as a VCB, is a circuit breaker fashioned to extinguish electrical arcs within a vacuum environment. This technology is especially well-suited for medium-voltage applications.
When dealing with higher voltages, vacuum technology has been developed, although it may not always be economically efficient. The interruption and establishment of current-carrying connections and arc quenching occur within a vacuum chamber, encapsulated by a vacuum interrupter, a specialized circuit breaker component.
The vacuum interrupter features a central steel arc chamber symmetrically positioned within ceramic insulators. Maintaining a vacuum pressure of approximately 10^-6 bar, the vacuum interrupter’s material composition for current-carrying contacts is crucial. Notably, Cr/Cr is an ideal material for vacuum circuit breaker connections.
Pros of Vacuum Circuit Breaker
- Exceptional insulating strength within a vacuum, making it highly effective at arc quenching.
- Eliminates gas emissions into the environment.
- Requires minimal maintenance.
- Silent operation.
- No fire hazard.
- Enhanced safety for operational personnel, minimizing the risk of explosions.
- Extended service life for VCB.
Cons of Vacuum Circuit Breaker
- Limited cost-effectiveness for small-scale production.
- Prohibitive costs for consumers at higher voltages, particularly when multiple circuit breakers above 38 kV need to be coupled in series.
Introduction to ACB
An Air Circuit Breaker, commonly known as an ACB, is an electrical device primarily designed for short-circuit protection and overcurrent protection in electrical circuits operating within the range of 800 to 10,000 amps. These devices are commonly found in distribution panels, and ACBs rely on air as their arc-extinguishing medium.
There are numerous types of high-performing and durable ACBs available on the market, which are easy to install and maintain. In the modern era, ACBs have effectively replaced oil circuit breakers. Various industrial facilities and electrical equipment, such as generators, capacitors, and transformers, rely on ACBs for protection.
Pros of ACB
- Ideal for regulating industrial facilities and power plant auxiliaries.
- Safeguards electrical machinery and equipment.
- Suitable for power-sharing schemes, including voltages up to 15 kV.
- ACB exhibits high arc resistance through extending, cooling, and splitting, thanks to its air brake technology.
- Applicable in both AC and DC circuits up to 12 kV.
Cons of Air Circuit Breaker
- Less efficient de-ionizing and arc-extinguishing capabilities within the chute.
- Inefficient at low currents, with vulnerability to electromagnetic fields.
Key Differences Between ACB & VCB
- ACBs are best suited for low voltage applications below 690 volts, often referred to as LT applications (Low Tension). VCBs are employed in medium voltage applications with voltages below 33 kV.
- ACB uses open air as the arc quenching medium, while VCB relies on a vacuum (negative pressure) environment, maintaining vacuum pressures between 10^-2 and 10^-6 torr.
- ACBs are typically rated from 630 Amps to 6,300 Amps for LT applications, whereas VCBs are rated from 630 Amps to 4,000 Amps.
- The short circuit breaking capability is determined by the arc quenching medium. ACB, with its air-filled environment, readily ionizes, while VCB offers superior short circuit breaking capabilities due to the absence of free electrons within the vacuum.
- ACBs are typically used for LT MCC, distribution transformer secondary feeder circuits, and LT PCC applications. VCBs, on the other hand, are employed for starting higher HP motors.
