Oil Circuit Breakers: Construction, Operation, and Benefits

Introduction to Oil Circuit Breakers

Oil circuit breakers are vital for protecting and ensuring power systems. These devices use oil as a dielectric medium. It extinguishes arcs that occur when interrupting fault currents. Oil circuit breakers are better than other types. Their design and operation give them an edge.

When electrical systems face overloads, Oil Circuit Breakers spring into action. These devices, dating back to the early 1900s, use oil to snuff out dangerous arcs. The same oil also serves as an insulator, providing a dual-purpose solution. In high-voltage networks, OCBs protect equipment and ensure safety. They are vital in substations and industrial uses. They can handle high currents and voltages. Their reliable performance is vital for electrical networks’ safety and efficiency. Despite newer technologies, OCBs are still widely used. They are effective and durable.

What is an oil circuit breaker?

Oil circuit breakers employ oil for dual purposes: insulation and arc suppression. This specialized circuit breaker uses oil to safely stop electrical currents. It protects power systems. The breaker’s contacts are in an oil-filled chamber. When a fault occurs, the separation of these contacts causes an arc. The surrounding oil absorbs the heat from the arc and helps to extinguish it. This ensures that the circuit is safely interrupted.

Types of Oil Circuit Breakers

Oil circuit breakers have two main types based on oil usage:

• Bulk Oil Circuit Breaker (BOCB): High-voltage, oil-filled breakers use a lot of oil to snuff out arcs. Their design caters to demanding electrical environments. They cool and quench arcs.
• Low Oil Circuit Breaker (LOCB): These breakers use less oil. Compact by design, these units excel in medium-voltage scenarios. Their small size and light weight are vital where every inch and ounce counts.

Construction of Oil Circuit Breakers

Core Components

An oil circuit breaker has a simple but strong design. It works reliably even in extreme conditions. The main components include:

• Current-Carrying Contacts: Transformer oil bathes the vital contacts within a sturdy metal tank. These components, shielded from the elements, control the circuit’s rhythm. Circuit breakers pulse life through the system, managing the flow of energy. They do this by connecting and disconnecting in a delicate dance.
• Transformer Oil: The oil has two purposes. It insulates between the live parts and the earth. It also helps to extinguish arcs.
• Air Cushion: The air at the top of the oil tank cushions and controls the displaced oil when gas forms around the arc. It also absorbs the mechanical shock caused by the movement of the oil.
• Breaker Tank: The tank is made of sturdy metal. It is securely bolted to withstand vibrations and stresses during high-current interruptions.
• Gas Outlet: A gas outlet is in the tank cover. It lets out gases from arc extinction.

Working Principle of Oil Circuit Breakers

Arc Formation and Extinction

During normal operation, the oil circuit breaker’s contacts stay closed. This allows current to flow through the circuit. When a fault is detected, the contacts begin to separate, creating an arc between them. The intense heat generated by the arc vaporizes the surrounding oil, converting it into gas. This gas forms a bubble around the arc, and its explosive expansion displaces the oil, aiding in arc extinction.

The arc goes out when the distance between the contacts reaches a critical value. This depends on factors like the arc current and recovery voltage. The oil quenches the arc and insulates the contacts, stopping current flow.

Reliability and Cost-Effectiveness

Oil circuit breakers are reliable and affordable. They are a top choice for power systems. No special devices for arc control are needed. The oil itself provides efficient arc quenching. This simplicity in design contributes to their widespread use in various electrical systems.

Advantages and Disadvantages of Oil Circuit Breakers

Advantages

• High Dielectric Strength: The oil insulates the contacts after the arc goes out. This ensures safe operation.
• Compact Design: Oil allows a smaller gap between the conductors and earth components. This leads to a more compact design.
• Effective Cooling: The hydrogen gas formed during arc extinction diffuses quickly. Its superior cooling properties enhance the breaker’s performance.

Disadvantages

• Flammable oil in these breakers creates a significant fire risk, particularly during malfunctions. This design flaw is dangerous. It needs urgent attention to ensure safety. Oil and air can form explosive, explosive mixtures. This is dangerous under certain conditions.
• Carbonization of Oil: Arcing can decompose oil and form carbon particles. These reduce the oil’s dielectric strength and necessitate regular maintenance.

Maintenance of Oil Circuit Breakers

Importance of Regular Maintenance

Oil circuit breakers thrive on diligent upkeep. Regular care ensures these vital components endure, performing reliably for years to come. Neglect shortens their lifespan. Attentive care keeps them efficient. After interrupting a short-circuit current, the contacts may burn. The dielectric oil may also carbonize. This degradation can reduce the breaker’s capacity to interrupt faults effectively.

Maintenance Procedures

Regular maintenance includes checking and replacing the contacts and the dielectric oil. Test the oil for dielectric strength. Replace any contaminated oil to keep the breaker working. The contacts should be inspected for wear and replaced if necessary.

Conclusion

Oil circuit breakers are vital in electrical systems. This is true for high and medium voltage applications. Their ability to extinguish arcs and their low cost makes them a preferred choice in many cases. They are reliable, too. However, regular maintenance is essential. It ensures their operation and reduces risks from oil-based systems.

Understanding oil circuit breakers and their maintenance is key. It helps us appreciate their role in keeping power systems safe and reliable.

FAQs

What is the use of an oil circuit breaker?

• Interrupting Fault Currents: When a fault occurs, the circuit breaker opens its contacts. This creates an arc. The oil around the contacts helps extinguish the arc. This stops the current flow and protects the system.
• Providing insulation: The oil in the breaker acts as a dielectric. It insulates the contacts from the surrounding parts and prevents unwanted current paths.
• Cooling: The oil absorbs the heat from the arc. This prevents the breaker components from overheating. It also helps dissipate the energy released during arc extinction.
• Ensuring Reliable Operation: Oil circuit breakers are for high- and medium-voltage use. They must interrupt fault currents to keep the network safe.

What is the principle of arc extinction in an oil circuit breaker?

• Arc Formation
  Electrical faults trigger the oil circuit breaker’s swift response, severing the connection. This causes an electrical arc to form between its contacts. This arc generates intense heat, which can reach extremely high temperatures.
• Oil Vaporization
  The arc’s heat vaporizes the oil, creating a hydrogen gas bubble. This gas cools well and diffuses quickly. Both are crucial for extinguishing the arc.
• Arc Quenching
  The gas bubble around the arc is rapidly expanding. It displaces the oil and reduces the medium’s density around the arc. The hydrogen gas, with its high thermal conductivity, cools the arc by absorbing heat. As the arc cools, its energy diminishes. The arc voltage rises until it reaches a critical value. At that point, the arc cannot sustain itself.
• Interruption of Current
  As the contacts separate, the arc lengthens. The gas and oil cool. Eventually, the arc goes out. The gap between the contacts is too great for it to sustain itself. This interrupts the current flow.
  Reestablishment of Insulation
  After the arc goes out, the oil insulates the contacts. It prevents any current from flowing until the breaker is reset or re-closed.

What is the difference between air circuit breaker and oil circuit breaker?