Short Answer:

Circuit breakers are important safety devices used in power transmission systems to protect electrical equipment from faults like short circuits and overloads. They automatically disconnect the faulty part of the system to prevent damage and allow smooth operation of the rest of the network. Unlike fuses, circuit breakers can be reset and used again after clearing the fault.

There are different types of circuit breakers used in power transmission based on the method they use to extinguish the arc. Common types include air circuit breakers, oil circuit breakers, SF₆ (sulphur hexafluoride) circuit breakers, and vacuum circuit breakers. Each type is used for different voltage levels and applications depending on reliability, speed, and maintenance requirements.

Detailed Explanation:

Types of circuit breakers used in power transmission

In power transmission systems, circuit breakers play a very critical role. These systems operate at high voltages and carry large amounts of power. A small fault can cause serious damage if not cleared immediately. Circuit breakers are devices that sense the fault and open the circuit to stop the current flow. Once the fault is cleared, they can be closed again to restore power.

The main purpose of a circuit breaker is to interrupt high current safely and quickly during faults. When a fault occurs, such as a short circuit or equipment failure, the current suddenly increases. This causes an electrical arc when the breaker contacts open. The circuit breaker must quickly extinguish this arc to stop the current and protect the equipment.

To do this, different types of circuit breakers use different methods and mediums to cool and break the arc. These breakers are chosen based on the voltage level, cost, speed of operation, and how much maintenance is needed.

Air Circuit Breaker (ACB)

Used for low to medium voltage applications (usually below 15 kV).
Uses compressed air to extinguish the arc formed when contacts separate.
Commonly used in indoor switchgear and industrial systems.
Easy to maintain and safe, but not suitable for very high voltage transmission.

Oil Circuit Breaker (OCB)

Used for medium voltage levels (up to 132 kV).
Uses insulating oil as an arc-quenching medium.
When arc is formed, the oil breaks down into gases which cool and extinguish the arc.
Types include bulk oil circuit breakers and minimum oil circuit breakers.
Needs regular maintenance due to oil degradation and possibility of fire.

SF₆ Circuit Breaker

Used in high-voltage transmission systems (up to 800 kV).
Uses sulphur hexafluoride (SF₆) gas which is very effective at absorbing arc energy.
Offers excellent insulation and arc-extinguishing properties.
Very compact and reliable.
Requires careful handling and maintenance due to SF₆ being a greenhouse gas.

Vacuum Circuit Breaker (VCB)

Commonly used for medium voltage applications (up to 66 kV).
Uses vacuum as the arc-extinguishing medium.
Arc is quickly extinguished because there is no air or gas in the vacuum.
Long life, requires very little maintenance.
Used in switchgear panels for industries and substations.

Air Blast Circuit Breaker

Mainly used in high-voltage outdoor systems.
Uses a high-pressure air blast to blow out the arc.
Fast and suitable for frequent operation.
Less common now due to high maintenance and noise.

Selection of Circuit Breakers in Transmission Systems

In power transmission networks, the choice of circuit breaker depends on:

Voltage level of the system (medium or high voltage).
Speed of interruption required to maintain system stability.
Environmental concerns, such as gas emissions.
Installation type, like outdoor or indoor substations.
Cost and maintenance factors.

For example:

For 400 kV and 220 kV transmission lines, SF₆ breakers are commonly used.
For 66 kV and 33 kV systems, both vacuum and SF₆ breakers are used depending on location and preference.
Oil breakers were common earlier but are now being replaced due to high maintenance needs.

Advantages of Using Circuit Breakers in Transmission

Provides fast isolation of faults.
Minimizes damage to equipment.
Helps maintain power supply to unaffected areas.
Reduces downtime and improves system reliability.
Can be reset or operated remotely in modern smart systems.

Conclusion

Different types of circuit breakers are used in power transmission systems based on voltage level, reliability, and type of application. Air, oil, vacuum, and SF₆ breakers each have their own working method and benefits. Among them, SF₆ and vacuum breakers are most widely used today due to their high efficiency and low maintenance. Circuit breakers ensure that any fault in a transmission line is quickly and safely cleared, which keeps the power grid stable and reduces damage to expensive equipment.