Electrical Substation Equipment: Circuit Breaker and Its Functions

A circuit breaker is an electrical switching device that automatically interrupts the flow of electric current in a circuit when it detects an overcurrent or a fault condition. It is designed to protect electrical circuits and connected devices from damage due to excessive current or short circuits.

The primary purpose of a circuit breaker is to prevent electrical fires and equipment damage that could occur if an excessive current flows through a circuit for an extended period. By interrupting the current flow, the circuit breaker stops the current from reaching dangerous levels and thereby protects the circuit and connected appliances or devices.

Circuit breakers are commonly used in residential, commercial, and industrial electrical systems, as well as in power distribution networks. They are essential safety devices that play a crucial role in maintaining electrical system integrity and safeguarding against potential hazards. When a circuit breaker trips, it needs to be manually reset or replaced before the circuit can be restored to its normal operation. This manual intervention allows users to identify and address the underlying issue that caused the circuit overload or fault condition before the circuit is re-energized.

Functions of Circuit Breaker in Electrical Substations

Circuit breakers play a crucial role in electrical substations, which are key components of power systems. Their primary function is to protect the substation equipment, transmission lines, and other electrical devices from overloads, short circuits, and other electrical faults. Here are the main functions of circuit breakers in electrical substations:

1. Overcurrent Protection: Circuit breakers monitor the current flowing through the electrical components and interrupt the circuit when an excessive current is detected. This protection prevents damage to the equipment and helps maintain the stability of the power system.
2. Short Circuit Protection: In the event of a short circuit (a low-resistance path between two conductors), the circuit breaker quickly interrupts the current flow to prevent catastrophic damage to the substation equipment and surrounding infrastructure.
3. Isolation of Faults: When a fault occurs in a specific section of the power system, the circuit breaker isolates that section by opening its contacts. This helps in locating and repairing the fault without affecting the rest of the system's operation.
4. Switching Operations: Circuit breakers facilitate the safe switching and operation of electrical devices and equipment in the substation, allowing for maintenance, repairs, and reconfiguration of the power system.
5. Load Shedding: In emergency situations when the power demand exceeds the supply capacity, circuit breakers can be used to shed or disconnect non-critical loads, helping to maintain the stability of the power system.
6. Transformer Protection: Circuit breakers are essential for protecting transformers in the substation. They quickly disconnect a faulty transformer from the system, preventing further damage to the transformer and the rest of the substation.
7. Protection Coordination: Circuit breakers are coordinated with other protective devices in the substation and the wider power system. Proper coordination ensures that the circuit breaker closest to the fault operates first, minimizing the impact on the rest of the system.
8. Remote Control and Automation: Modern circuit breakers in advanced substations often come with remote control and automation capabilities, allowing operators to control and monitor them remotely. This enhances the overall efficiency and reliability of the power system.
9. Load Switching: In some cases, circuit breakers can be used as load switches to disconnect or connect specific parts of the network during maintenance or repair activities.
10. Ground Fault Protection: Circuit breakers may have additional features for detecting and protecting against ground faults, where current flows to the earth due to insulation failure or accidental contact.

In summary, circuit breakers in electrical substations are essential devices for maintaining the reliability and safety of the power system. Their ability to quickly interrupt faulty circuits and protect valuable equipment helps prevent power outages, electrical fires, and damage to infrastructure.

Types of Circuit Breakers Used in Electrical Substations

In electrical substations, various types of circuit breakers are used to protect and control the power system. Each type of circuit breaker has its specific applications and advantages. Here are some of the most commonly used types of circuit breakers in electrical substations:

Air Circuit Breaker (ACB)

• Operates in an air medium and is suitable for low-voltage applications.
• Used for protection against overload, short circuits, and earth faults.
• Typically used in LV distribution panels and motor control centers.

Oil Circuit Breaker (OCB)

• Utilizes oil as the arc quenching medium.
• Suitable for medium voltage applications.
• Mostly outdated due to environmental concerns and replaced by more modern types.

Vacuum Circuit Breaker (VCB)

• Uses a vacuum as the arc quenching medium.
• Suitable for medium and high voltage applications.
• Offers fast and reliable arc extinction.
• Commonly used in indoor substations and switchgear.

SF6 Circuit Breaker

• Uses sulfur hexafluoride (SF6) gas as the arc quenching medium.
• Suitable for high voltage applications.
• Provides excellent arc extinction properties.
• Widely used in outdoor substations and high-voltage transmission systems.

Gas-insulated Circuit Breaker (GCB)

• Utilizes a combination of SF6 gas and solid insulating materials.
• Suitable for high voltage and extra-high voltage applications.
• Offers a compact design and high reliability.
• Commonly used in gas-insulated substations (GIS).

Hybrid Circuit Breaker

• Combines the features of different circuit breaker technologies.
• Designed to optimize performance and cost-effectiveness.
• May include combinations like vacuum and SF6 technologies.

Solid-State Circuit Breaker

• Utilizes semiconductor devices for circuit interruption.
• Offers fast switching and high reliability.
• Suitable for low and medium voltage applications.
• Still an emerging technology, not widely used in all substations.

It's important to note that advancements in technology may lead to the development of new circuit breaker types or modifications to existing ones. The choice of circuit breaker type depends on factors such as the voltage level, load capacity, substation design, and environmental considerations.

How to Choose a Correct Circuit Breaker?

Choosing the right circuit breaker is essential for ensuring the safety and protection of electrical circuits in your home or workplace. Here are some steps to help you make an informed decision:

Determine the application: Identify the specific purpose of the circuit breaker. Will it be used for residential, commercial, or industrial applications? Different environments and electrical loads require different types of circuit breakers.

Understand the circuit specifications: Know the voltage rating and current rating of the circuit you want to protect. The current rating is crucial as it must match the circuit's load to ensure proper protection.

Select the right type: There are several types of circuit breakers available, such as:

a. Miniature Circuit Breakers (MCBs): Typically used in residential applications and low-current circuits.

b. Molded Case Circuit Breakers (MCCBs): Suitable for higher current ratings and found in commercial and industrial settings.

c. Residual Current Devices (RCDs): Designed to protect against electrical shocks by monitoring imbalances in current.

d. Residual Current Circuit Breakers (RCCBs): Combining the features of MCBs and RCDs, providing both overload and leakage protection.

e. Air Circuit Breakers (ACBs) and Vacuum Circuit Breakers (VCBs): Utilized in high-current applications like power distribution and heavy machinery.

Determine the breaking capacity: The breaking capacity refers to the maximum current the circuit breaker can interrupt without sustaining damage. Ensure the breaker's breaking capacity is higher than the potential fault current in the circuit.

Consider additional features: Some circuit breakers come with additional features like built-in surge protection, adjustable trip settings, and compatibility with smart systems. Choose the features that align with your needs and budget.

Comply with safety standards: Ensure the circuit breaker meets the relevant safety standards for your region, such as UL (United States), IEC (International Electrotechnical Commission), or other local regulations.

Seek professional advice: If you are uncertain about which circuit breaker to choose, consult with a qualified electrician or electrical engineer. They can assess your specific requirements and provide appropriate recommendations.

Quality and reliability: Opt for reputable brands and manufacturers known for producing high-quality and reliable circuit breakers. Electrical safety is not an area to compromise on quality.

Future expansion: Consider potential future expansions or upgrades in your electrical system and select a circuit breaker with some headroom to accommodate these changes.

Remember that electrical work should always be performed by trained professionals to ensure safety and compliance with local codes and regulations.

Substation-related major equipment is discussed in another episode.