What are the 4 types of circuit breakers?

I. Introduction Module

The critical question for any electrical system begins with: What are the four primary types of circuit breakers? Based on their distinct arc-extinguishing media, the most prevalent classifications in circuitry are the Vacuum Circuit Breaker (VCB), the Sulfur Hexafluoride Circuit Breaker ( $SF_{6}$ CB), the Air Circuit Breaker ( $ACB$ / $ABCB$ ), and the Oil Circuit Breaker ( $OCB$ ). These devices are far more than just sophisticated switches; they represent the foundation of safety and control within modern electrical infrastructure.

A circuit breaker is a cornerstone of the power system, serving the dual function of control and protection. In any power grid, the selection of the correct breaker type is a complex engineering trade-off that balances system reliability, equipment economy, maintenance difficulty, and environmental compliance. Understanding the physics, characteristics, and application limits of these four mainstream technologies is non-negotiable for ensuring safe and efficient electrical operations.

II. Core Content: Principles, Characteristics, and Applications of the Four Main Breaker Types

Circuit breakers are primarily categorized by the "arc-quenching medium" they employ. The choice of this medium fundamentally dictates the breaker's insulating performance, its interrupting capacity, its physical size, and its long-term maintenance needs.

2.1 Vacuum Circuit Breaker ( $VCB$ )

2.1.1 Arc Interruption Principle: Rapid Isolation in High Vacuum

The central component of a $VCB$ is the vacuum interrupter bottle. This sealed vessel maintains an extremely high vacuum, typically $\leq 1 0^{- 4} Pa$ creating an environment where electrical discharge is highly unstable. When the contacts separate to interrupt the current, an arc forms, but the charged particles (ions and electrons) within this arc rapidly diffuse and recombine onto the contact surface shields and the interrupter walls.

Crucially, the vacuum dielectric strength recovers with incredible speed, often in mere microseconds. This rapid restoration happens right at the moment the AC naturally crosses zero, effectively preventing the arc from reigniting. Modern VCBs often utilize advanced axial magnetic field technology to keep the arc spread out and mobile in the vacuum, further optimizing the overall arc-extinguishing efficiency.

2.1.2 Key Advantages and Application Scenarios

The exceptional characteristics of VCBs have established them as the dominant choice in medium-voltage systems, ranging from $3.3 kV$ up to $38 kV$ . They are valued for their high reliability and "maintenance-free" operation, as the contacts are fully sealed from external environmental factors like humidity and pollution, leading to superior mechanical and electrical endurance.

Furthermore, VCBs are highly desirable from an environmental and safety perspective, utilizing a non-toxic, non-flammable arc-extinguishing medium that poses virtually zero risk of fire, explosion, or harmful gas byproducts. Their fast operating speed and short arcing duration minimize fault impact, which is essential for grid stability.

What are the 4 types of circuit breakers?

Tip: The zero-maintenance nature of VCBs makes them ideal for urban power distribution networks, industrial facilities, and rail traction power substations, where operational environments are demanding and frequent downtime for maintenance is highly undesirable.

2.2 Sulfur Hexafluoride Circuit Breaker ( $SF_{6}$ CB)

2.2.1 Arc Interruption Principle: The "Gaseous Magic" of Efficient Insulation

The $SF_{6}$ CB relies on sulfur hexafluoride gas ( $SF_{6}$ ) as both its primary arc-quenching and insulating medium. $SF_{6}$ is an odorless, non-toxic, non-flammable, and chemically stable gas, yet its insulating and arc-extinguishing properties far surpass those of air or oil.

Specifically, the insulating strength of $SF_{6}$ gas is two to three times that of air at the same pressure. Its remarkable arc-quenching capability stems from its extremely high electron affinity, allowing it to rapidly capture free electrons from the arc channel to form stable negative ions. This process dramatically reduces the conductive particle density within the arc path, leading to rapid extinction at the current zero-crossing.

$SF_{6}$ CBs generally employ either puffer-type or self-blast-type interrupting mechanisms. The self-blast method is more energy-efficient, utilizing the thermal energy of the arc itself to rapidly expand the surrounding $SF_{6}$ gas, creating a high-pressure flow that forces the arc to dissipate.

2.2.2 Key Advantages and Application Scenarios

The $SF_{6}$ CB is the undisputed technology of choice for high-voltage and ultra-high-voltage transmission systems, handling levels from $72.5 kV$ up to $800 kV$ and beyond. This dominance is due to two critical engineering factors.

First, its unparalleled arc-quenching strength provides an extremely high interrupting capacity, allowing it to reliably clear the massive fault currents encountered in extra-high-voltage systems. Second, the superior insulating properties facilitate the miniaturization of high-voltage equipment, enabling the creation of Gas Insulated Switchgear (GIS $GIS$ ), which significantly reduces the required footprint of substations. $SF_{6}$ CBs also exhibit excellent reclosing performance; the rapid recovery of dielectric strength makes them perfect for quick auto-reclosing operations, which is essential for boosting power grid reliability following transient faults.

Note: Despite its technical superiority, $SF_{6}$ is a potent greenhouse gas, with a Global Warming Potential ( $GWP$ ) approximately $23, 500$ times that of $CO_{2}$ . Strict control of leakage and mandatory lifecycle-end recovery are major environmental compliance challenges facing the power industry today.

2.3 Air Circuit Breaker ( $ACB$ / $ABCB$ )

Air circuit breakers are essentially divided into two distinct categories, serving entirely different voltage applications and relying on fundamentally different principles.

2.3.1 Low-Voltage: Air Circuit Breaker ( $ACB$ )

ACBs primarily function as main protective switches in low-voltage distribution systems, typically operating from $400 V$ to $1000 V$ . These breakers use ambient air as the arc-extinguishing medium, critically assisted by specialized arc chute structures. When the contacts open, the resulting arc is rapidly elongated by electromagnetic and thermal forces, driving it into the metallic plate structure of the arc chute.

The chute’s design fragments the arc into numerous smaller, series-connected segments, which are rapidly cooled and extinguished. ACBs are structurally straightforward, offering excellent mechanical and electrical life, and typically integrate sophisticated trip protection features for overloads, short circuits, and under-voltage conditions.

What are the 4 types of circuit breakers?

2.3.2 High-Voltage: Air Blast Circuit Breaker ( $ABCB$ )

ABCBs were historically prevalent in high-voltage applications. They rely on a complex air compression system to generate a high-pressure air blast, typically $2 MPa$ to $3 MPa$ , which is forcefully directed at the arc. The powerful air stream rapidly removes hot, conductive particles from the arc channel, quickly restoring the dielectric strength of the contact gap.

While ABCBs achieved extremely fast interruption speeds, they required a massive, noisy, and high-maintenance air compressor station. Due to these operational drawbacks and high maintenance requirements, ABCBs have been largely superseded by VCBs and $SF_{6}$ CBs in modern grids.

2.4 Oil Circuit Breaker ( $OCB$ )

2.4.1 Arc Interruption Principle: Utilizing the Energy of Vaporization

OCBs use mineral insulating oil as their arc-extinguishing medium. When the contacts separate in the oil, the extreme heat of the arc instantaneously vaporizes and decomposes the surrounding oil. This process generates massive quantities of high-pressure gas, predominantly hydrogen (H_2).

The resulting dramatic volume expansion and rapid gas movement create powerful oil and gas flows that forcibly cool and physically sweep the arc away until it is fully extinguished. OCBs are categorized as bulk oil (BOCB) or minimum oil ( $MOCB$ ) based on the amount of oil used, but the core arc-quenching principle remains the same.

2.4.2 Key Limitations and Current Status

Despite their historical importance in medium- and high-voltage applications, OCBs are being systematically phased out due to inherent design flaws. The insulating oil is flammable, and the hydrogen gas generated during arcing is highly explosive, posing a significant fire and explosion risk. Furthermore, repeated interruption of large fault currents contaminates the oil with carbon deposits, demanding frequent and complex maintenance, including oil testing and replacement.

The disposal of waste insulating oil also presents considerable environmental and cost challenges. Consequently, OCBs are now considered an obsolete technology in most new construction projects.

To gain a more visual and systematic understanding of the technological evolution of circuit breakers from oil to vacuum and $SF_{6}$ , and to review the different classification criteria, please refer to the following video resource:

III. Professional Comparison and Technical Selection (The Core Metrics Module)

For the electrical engineer, selecting the appropriate circuit breaker is not a matter of media preference but a critical decision based on quantified electrical performance and operational economics. This section provides the engineering-grade parameters necessary for informed choice.

3.1 Core Metrics Comparison Table

Characteristic	Vacuum CB ( $VCB$ )	$SF_{6}$ CB ( $SF_{6}$ CB)	Air CB ( $ACB$ )	Oil CB ( $OCB$ )
Quenching Medium	High Vacuum	Sulfur Hexafluoride ( $SF_{6}$ )	Air (Ambient/Compressed)	Insulating Oil
Typical Voltage	Medium Voltage ( $3.3 kV - 38 kV$ )	High/EHV ( $> 72.5 kV$ )	Low Voltage ( $0.4 kV /1 kV$ )	MV (Obsolete)
Total Interrupting Time	Extremely Fast: 1–3 Cycles ( $20-60 ms$ )	Fast: 2–3 Cycles ( $40-60 ms$ )	Moderate: 3–5 Cycles	Slower: 4–6 Cycles
Interrupting Capacity	Moderate ( $\leq 50 kA$ )	Extremely High ( $\geq 63 kA$ and above)	Large ( $\leq 100 kA$ Low Voltage)	Moderate
Reclosing Performance	Excellent, fast dielectric recovery	Excellent, suitable for rapid reclosing	Poor (needs recharge)/Fair	Poor (requires degassing/oil circulation)
Electrical Life	Extremely High (Tens of thousands)	High	High (Low Voltage $ACB$ )	Moderate
Environmental Impact	Best	Poor (Potent Greenhouse Gas)	Good	Poor (Waste oil disposal)

3.2 Selection Criteria and Limitation Analysis: The Key to Engineering Decisions

In real-world engineering projects, circuit breaker selection is a multi-objective optimization challenge. The interrupting capacity is the paramount consideration; the device must reliably clear the maximum prospective short-circuit current at its installation point, which is why $SF_{6}$ dominates ultra-high-voltage systems where $VCB$ capacity is insufficient.

Operating speed is equally vital; a faster interruption significantly reduces the destructive thermal and electrodynamic stresses on nearby equipment like busbars and transformers. Modern systems commonly demand that breakers complete the full fault interruption sequence within three cycles, or $60 ms$ . Finally, in low-voltage systems, selective coordination is critical; the trip characteristics (instantaneous, short-time, long-time delay) of the breaker must perfectly coordinate with upstream and downstream devices to ensure that only the faulty section is isolated, minimizing system disruption.

Tip: When selecting high-voltage breakers, always scrutinize their ability to withstand the Transient Recovery Voltage ( $TRV$ ). $TRV$ is the high-frequency voltage that appears across the breaker contacts immediately after current interruption; this characteristic is a crucial differentiator between quality products and directly determines the breaker's reliability when clearing reactive or capacitive currents.

IV. Beyond Tradition: The Future Frontiers of Circuit Breaker Technology (Differentiation Module)

While the four conventional classifications provide the historical and current framework, next-generation technologies are fundamentally breaking these boundaries. This section explores the unique value proposition of emerging trends, highlighting the industry's direction toward radical improvements in performance and functionality.

4.1 Trend One: Intelligence and Internet of Things ( $IoT$ ) Integration

4.1.1 The Core Philosophy: Shifting from "Passive" to "Proactive"

Traditional circuit breakers function as passive protection devices, only acting reactively when a fault has already occurred. In contrast, Smart Circuit Breakers (SCBs) integrate sensors, microprocessors, and communication modules directly into the traditional breaker structure, enabling proactive prevention and remote asset management. This integration allows for real-time monitoring and diagnosis, continuously collecting vital parameters such as current, voltage, temperature, power factor, and harmonic content.

Crucially, the real-time monitoring of contact and cable joint temperature allows operators to detect hidden "hot spots" early, a capability mechanical breakers entirely lack. This data-driven approach facilitates Predictive Maintenance ( $PdM$ ); by analyzing operational data (e.g., number of operations, contact wear, accumulated arcing energy), $AI$ algorithms can forecast equipment failure, transforming routine maintenance into highly efficient on-demand maintenance.

What are the 4 types of circuit breakers?

4.1.2 Enhancing $EEAT$ Engineering Value

Smart breakers allow maintenance personnel to "see" the internal health of the equipment, providing an unprecedented level of Experience and insight into operational performance. This capability helps avoid unnecessary planned outages for maintenance, thereby enhancing overall system reliability and embodying true engineering value.

4.2 Trend Two: The Solid-State Circuit Breaker ( $SSCB$ ) Revolution

4.2.1 Technical Principle: Bypassing Mechanical Contacts

The Solid-State Circuit Breaker ( $SSCB$ ) represents a fundamentally disruptive technology in the power industry. It eliminates mechanical contacts and arc-extinguishing media, relying instead on high-performance power electronic semiconductor devices, such as Silicon Carbide ( $SiC$ MOSFETs) or Insulated Gate Bipolar Transistors (IGBTs), to achieve current interruption.

The most compelling feature of the $SSCB$ is its sub-microsecond ( $μ s$ ) interruption speed, making it $100$ to $1000$ times faster than conventional mechanical breakers. This unparalleled speed allows the device to interrupt a short-circuit current before it reaches its destructive peak (known as current-limiting interruption), offering vastly superior protection for downstream components. Its operational benefits include zero arcing, no mechanical wear, virtually infinite lifespan, and silent operation.

4.2.2 Core Application Fields

The $SSCB$ is the ideal solution for future Direct Current (DC $DC$ ) systems, where mechanical breakers face extreme difficulty in clearing $DC$ arcs, which lack the natural zero-crossing of AC. They are essential for ensuring reliability in microgrids and energy storage systems, as well as in critical facilities like data centers and Electric Vehicle (EV $EV$ ) fast-charging stations that demand extremely high power quality and sub-cycle fault isolation.

What are the 4 types of circuit breakers?

4.3 Trend Three: The Search for Eco-Friendly Media

In response to the significant environmental concerns surrounding $SF_{6}$ , the industry is actively promoting and developing eco-friendly alternatives.

"Clean Air" Solutions: Utilizing treated, dry air or mixtures of nitrogen and oxygen, combined with innovative structural designs, is now enabling the replacement of $SF_{6}$ in many medium-voltage applications, and even some $145 kV$ systems.
Fluoroketone Mixtures: Newer gaseous dielectric mixtures with significantly lower $GWP$ values than $SF_{6}$ are being explored for high-voltage applications. These alternatives aim to maintain the superior insulating and arc-quenching performance while drastically reducing environmental impact.

V. Engineering Application Case Studies ( $EEAT$ : The Experience Module)

By analyzing specific scenarios, we can validate the professional selection logic for each circuit breaker type, underscoring the importance of practical Experience ( $E$ ).

5.1 Case Study 1: The Medium-Voltage Revolution in Urban Distribution ( $VCB$ Replacing $OCB$ )

Scenario: $10 kV$ ring main units and package substations in densely populated urban areas.

Selection Logic: Urban environments place a premium on compactness and maintenance-free operation. The $VCB$ technology, being oil-free, $SF_{6}$ -leak-free, small in size, and having an extremely high lifespan, significantly reduces the operational and maintenance burden in these critical, space-constrained locations. The $VCB$ has completely and irreversibly replaced the bulky, fire-prone $OCB$ in nearly $100%$ of new urban $10 kV$ indoor switchgear installations.

5.2 Case Study 2: The Last Line of Defense in Extra-High-Voltage Transmission ( $SF_{6}$ CB's Irreplaceability)

Scenario: Substation equipment and long-distance transmission lines at $500 kV$ voltage levels and higher.

Selection Logic: Interrupting massive fault currents at extra-high voltages presents an extreme test of a breaker's dielectric strength and interrupting capacity. The $SF_{6}$ CB’s unmatched performance is the only mature technology capable of reliably clearing faults at $800 kV$ and above. Furthermore, high-voltage line faults, such as those caused by lightning strikes, are often transient; the $SF_{6}$ CB's rapid reclosing capability is essential for quickly restoring power and maintaining grid stability.

5.3 Case Study 3: $DC$ Microgrids and the Solid-State Breaker

Scenario: Industrial park $DC$ distribution networks, large-scale solar farms, or shipboard power systems.

Selection Logic: The primary challenge in $DC$ systems is the difficulty mechanical breakers face in extinguishing a $DC$ arc. The $SSCB$ provides the solution by utilizing its semiconductor cutoff capability to achieve arc-free interruption in microseconds. This ultra-fast protection limits the fault energy accumulation to a minimum, making the $SSCB$ critical for the reliability and safety of future $DC$ systems.

What are the 4 types of circuit breakers?

VI. Conclusion Module

This comprehensive analysis confirms that circuit breaker technology remains central to the secure operation of any electrical system. The four traditional types have established clear roles based on their physical limits.

The $VCB$ , with its environmental benefits and low maintenance, dominates the medium-voltage segment. The $SF_{6}$ CB retains its absolute necessity in the high-voltage and ultra-high-voltage transmission domains due to its unmatched performance. Meanwhile, older technologies like $OCB$ and $ABCB$ are being systematically retired due to safety and maintenance liabilities.

Looking forward, the industry is unequivocally moving toward "greener, faster, and smarter" solutions. Smart circuit breakers are transforming grid maintenance from a reactive to a predictive discipline, drastically improving uptime and efficiency. The Solid-State Circuit Breaker ( $SSCB$ ) represents the ultimate advancement in speed and reliability, and it is the key enabling technology for managing the complexities of future $DC$ systems and distributed energy resources. For the modern electrical engineer, mastering the traditional four types is foundational, but understanding and embracing the $SSCB$ and intelligent technologies is essential for navigating the future grid.

Appendix: $FAQ$ from an Engineer's Perspective

These frequently asked questions provide real-world insights often encountered in electrical engineering practice.

$∙$ $FAQ 1$ : At what point does the vacuum drop low enough to require replacement?

This is a critical maintenance question because a drop in vacuum severely compromises both interrupting capacity and insulation strength. Since direct measurement is impractical, engineers rely on indirect methods like the AC Withstand Voltage Test or the Magnetron Discharge Method. For a $10 kV$ $VCB$ , if the power frequency withstand voltage test value falls below the manufacturer's threshold (e.g., $42 kV$ ), or if testing shows signs of persistent reignition, the vacuum interrupter must be replaced immediately.

$∙$ $FAQ 2$ Why must the "moisture content" in $SF_{6}$ CBs be strictly controlled?

Moisture (water content) is the primary enemy of $SF_{6}$ gas, degrading both its safety and insulating properties. In the presence of water, the heat generated by arcing causes $SF_{6}$ to chemically decompose, generating corrosive byproducts like hydrofluoric acid ( $HF$ ). These corrosive substances can damage internal components and insulation, potentially leading to catastrophic flashovers or internal explosions. Therefore, industry standards mandate stringent limits, often requiring a pressure dew point below $- 3 0^{\circ} °C$ or $- 4 0^{\circ} °C$ .

$∙$ $FAQ 3$ : Why are the breaking capacities for low-voltage ACBs often listed as two values, $I_{cu}$ and $I_{cs}$ ?

Low-voltage breakers are rated with two standard values to reflect their reliability under different fault conditions. The Rated Ultimate Short-Circuit Breaking Capacity ( $I_{cu}$ ) is the maximum fault current the breaker can safely clear, but it is not expected to be functional afterward. Conversely, the Rated Service Short-Circuit Breaking Capacity ( $I_{cs}$ ) is the current that he breaker can safely clear and remain fully operational and fit for continued use. Engineers should always design the system such that the maximum prospective short-circuit current is less than $I_{cs}$ to ensure optimal system resilience.

$∙$ $FAQ 4$ : What are the main technical hurdles for SSCBs, and can they completely replace mechanical breakers?

The two primary hurdles for SSCBs are conduction losses and cost. Even advanced $SiC$ devices generate significantly higher heat losses than zero-resistance mechanical contacts when conducting high current, requiring complex cooling systems (like water cooling). Furthermore, the manufacturing cost of high-power $SiC$ components far exceeds that of traditional mechanical structures. Consequently, SSCBs cannot fully replace mechanical breakers yet; their use is concentrated in $DC$ systems or specific applications where microsecond speed is essential.

$∙$ $FAQ 5$ : How should an engineer select the correct trip curve (B, C, or D) for a based on load?

This is fundamental to distribution design; the trip curve dictates the breaker's tolerance for momentary inrush current. $∙$

B-Type: Instantaneous trip at $3 In$ to $5 In$ (3 to 5 times rated current). Best suited for purely resistive loads, such as lighting circuits or long cable runs, where the impedance is high. $∙$

C-Type: Instantaneous trip at $5 In$ to $10 In$ . The most common type, ideal for general inductive loads like standard motors, transformers, or fluorescent lighting, where a moderate starting current is expected. $∙$

D-Type: Instantaneous trip at $10 In$ to $20 In$ . Reserved for loads with extremely high inrush currents, such as large motors, $X$ -ray equipment, or power supply primary circuits. The $D$ -type prevents nuisance tripping during the high initial power-up surge.