Oil Circuit Breaker

Introduction to Oil Circuit Breaker

Oil circuit breakers are one of the oldest types of circuit breakers, using insulating oil to extinguish the arc and interrupt electrical currents. Here’s a simplified description of how they work and their key features.

Oil circuit breakers use insulating oil to separate the contacts within the breaker. When a fault occurs and the contacts open, an arc forms under the oil, producing hydrogen gas and other by-products. The pressure and flow of gases play an important role in disrupting the circuit current.

Oil circuit breakers are a type of circuit breaker that uses insulating oil for improved performance. In the event of a fault, the breaker contacts open within the oil, initiating an arc. The heat generated by the arc converts the oil into high-pressure gaseous hydrogen, effectively extinguishing the arc. The desalination process involves the high thermal conductivity of hydrogen and the turbulence generated in the oil, which pushes it between the contacts to eliminate the byproducts that are generated.

“Oil circuit breaker is an electrical device that uses insulating oil to extinguish the arc during a fault, providing reliability, simplicity and cost-effectiveness with little to no routine maintenance required for continued functionality.”

There are two primary categories of oil circuit breakers:

1. Bulk Oil Circuit Breakers: These contain substantial quantities of oil and can accommodate various voltages and interrupting ratings. They are further classified into dead tank type (with the tank at ground potential) and live tank type (with the tank insulated from the ground).

2. Low oil circuit breakers: These use minimum amount of oil and are sometimes known as minimum oil circuit breakers. Although they offer benefits such as less oil and space requirements, they face challenges such as increased carbonization and rapid degradation of dielectric strength.

Advantages of oil as arc quenching medium:

Efficient absorption of arc energy during oil decomposition.
Rapid cooling due to high diffusion rate of hydrogen.
The high dielectric strength of the oil provides insulation after arc extinction.
Effective cooling surface provided by oil.

Disadvantages of oil as arc quenching medium:

The flammable nature of oil creates a fire hazard.
Danger of forming explosive mixture with air.
Decomposition of oil leads to pollution, which requires periodic maintenance and replacement.

Types of Oil Circuit Breaker:

1. Plain break oil circuit breakers: These are straightforward in construction, with no special arc control devices, resulting in relatively long and inconsistent arcing times.

2. Arc Control Oil Circuit Breaker:

• Self Blast: Arc control is achieved by using the pressure generated by the arc.
• Externally generated pressure: The pressure for arc control is mechanically generated, providing more consistent performance.

3. Low oil or minimum oil circuit breakers: These use a minimum amount of oil, reducing the risk of fire and maintenance problems. However, they face challenges such as increased carbonization and degradation in dielectric strength.

Maintenance of Oil Circuit Breakers:

Regular maintenance is necessary after many times the streams are interrupted. Tasks include checking and potentially replacing contacts and oil, inspecting insulation for damage, ensuring proper functioning of mechanisms, and checking indicator devices and lamps. Regular inspection every 3 to 6 months is recommended.

In short, oil circuit breakers offer reliability, simplicity and cost-effectiveness with variations in design to balance advantages and disadvantages for different applications. Regular maintenance is important to ensure proper functionality over time.


Oil circuit breakers use insulating oil to enhance performance by extinguishing the arc by means of high-pressure hydrogen.

The two primary categories include bulk oil circuit breakers (dead tank and live tank) and low oil circuit breakers (minimal oil, space saving, but with increased challenges).

Benefits include efficient arc energy absorption, rapid hydrogen-induced cooling, high dielectric strength, and an effective cooling surface.

Drawbacks include flammable oil, risk of explosive mixtures, pollution from oil decomposition, requiring periodic maintenance.

The different types of oil circuit breakers include plain break (resulting in extended and inconsistent arcing times), arc control (self-exploding or using externally generated pressure), and low oil (resulting in less fire risk but carbonization and dielectric strength.

Regular maintenance is important: checking/replacing contacts and oil, inspecting insulation, ensuring the functioning of mechanisms, and checking indicators every 3 to 6 months.

Oil circuit breakers provide reliability, simplicity and cost-effectiveness with a variety of designs balancing advantages and disadvantages for specific applications. Frequent maintenance ensures proper functionality over a long period of time.