Types and Related Knowledge of High Voltage Circuit Breakers

I. Definition of High-Voltage Circuit Breakers

A high-voltage circuit breaker is a core power equipment whose core function is to reliably connect, carry and interrupt the operating current during the normal operation of the power system; when a fault such as short circuit or overload occurs in the system, it can quickly carry the fault current and interrupt it, thereby protecting the safety and stable operation of power equipment and the system.

As a key protection equipment in the power system, high-voltage circuit breakers must meet the following core requirements:

- High operational reliability and efficient action response, capable of accurately coping with various working conditions;

- Good overload and high-voltage tolerance to adapt to extreme electrical stress during switching processes;

- Excellent electrical conductivity in the closed state to reduce power loss;

- Excellent insulation performance in the open state to prevent mis-conduction of the circuit;

- Fast switching capability, able to complete the state transition from open to closed in a short time.

II. Types of High-Voltage Circuit Breakers

The core classification basis of high-voltage circuit breakers is their arc extinguishing mechanism, that is, the extinguishing method of the arc generated when the moving contact is separated from the fixed contact. Based on this, they can be roughly divided into the following categories: Air Blast Circuit Breakers, Vacuum Circuit Breakers, SF₆ Circuit Breakers, Minimum Oil Circuit Breakers, and Bulk Oil Circuit Breakers.

The following is a detailed introduction to various types of high-voltage circuit breakers commonly used in substation scenarios:

1. Air Circuit Breaker (ACB)

An Air Circuit Breaker (ACB) is a power switching device that uses compressed air as the arc extinguishing medium and insulation medium to realize circuit overload protection. Its core function is to quickly cut off the fault current to avoid equipment damage when an overload or fault is detected in the circuit.

When a fault occurs, compressed air is sprayed at high speed through a dedicated nozzle to enhance the arc extinguishing effect; when the circuit overload causes the moving and fixed contacts to separate and generate an arc, the air blast mechanism uses compressed air to quickly disperse the arc in the cavity, and at the same time pushes the two contacts to swing alternately in the sealed cavity to ensure sufficient air diffusion, thereby completely extinguishing the arc.

Air circuit breakers are suitable for high-voltage working conditions. Before the emergence of new technologies such as oil circuit breakers, SF₆ circuit breakers and vacuum circuit breakers, they were widely used in 15kV voltage level systems in the United States. At present, although their application range has been reduced, in countries such as Italy and France, air circuit breakers are still preferred in circuits with voltage levels below 15kV. The core advantage of its air jet arc extinguishing lies in its dual role: it can not only extinguish the arc efficiently, but also disperse the ionized particles between the contacts, improve the dielectric strength of the medium, and finally cut off the current.

2. Vacuum Circuit Breaker (VCB)

With the continuous iteration and upgrading of vacuum arc extinguishing technology, the product performance of vacuum circuit breakers has been continuously optimized, and related manufacturing enterprises have gradually developed and grown. High-voltage vacuum circuit breakers are mainly applicable to the medium voltage range of 3kV to 38kV. Their core feature is that the arc extinguishing process is completed in a sealed vacuum cavity, which is also called a vacuum interrupter. The opening and closing of contacts and the interruption of arcs are all carried out in the cavity. At present, this technology has not been applied to ultra-high voltage scenarios.

The structure of the vacuum circuit breaker is composed of ceramic insulators symmetrically arranged around the steel cavity. Its arc extinguishing principle is to use the characteristics of the current zero crossing to extinguish the arc, and at the same time, the contacts form sufficient dielectric strength inside the system to prevent arc reignition. Compared with other types of circuit breakers, the vacuum circuit breakers used in substations have more advantages in dielectric strength.

After years of technological iteration, the performance of vacuum circuit breakers has been greatly improved. Its reliability is 4 times that of air circuit breakers and SF₆ circuit breakers, making it one of the most reliable technologies among high-voltage circuit breakers, which is very suitable for various application scenarios of medium-voltage systems. Compared with other types of circuit breakers, vacuum circuit breakers require minimal maintenance and have many advantages: easy disassembly, assembly and replacement, environmental protection, no harmful gases like SF₆ circuit breakers, simple operation, and no fire hazards like oil circuit breakers.

3. SF₆ Circuit Breaker

SF₆ circuit breakers use pressurized sulfur hexafluoride (SF₆) gas as the arc extinguishing and insulation medium, mainly used in medium and high voltage scenarios. SF₆ gas is widely used in high-voltage circuit breakers due to its excellent arc extinguishing and insulation performance. Compared with other gas media, it has higher insulation strength and stronger gas recombination ability after arc extinguishing.

SF₆ gas has extremely strong electronegativity and is easy to absorb free electrons to form negative ions. The mobility of negative ions is much lower than that of free electrons, so the circuit needs higher dielectric strength to conduct electricity; at the same time, SF₆ gas has high convective heat transfer efficiency and high viscosity, which further improves the reliability of arc extinguishing. SF₆ circuit breakers in substations are widely used in the voltage level of 33kV to 800kV, and some products can be adapted to ultra-high voltage scenarios above 800kV.

Its working principle is similar to that of air blast circuit breakers. SF₆ gas is compressed and stored in a high-pressure gas storage tank; when the circuit is overloaded, high-pressure SF₆ gas is quickly released through the arc area, flowing from the high-pressure gas storage tank to the low-pressure gas storage tank. After the arc is extinguished, the gas is sent back to the high-pressure gas storage tank for recycling through a pump.

It should be noted that SF₆ gas is a toxic gas that is harmful to human health and the natural environment, and it is also a strong greenhouse gas. Therefore, in the use of SF₆ circuit breakers, perfect sealing, recovery and other measures are taken to ensure that the gas does not leak into the external environment.

4. Oil Circuit Breaker

Oil circuit breakers use mineral oil as the arc extinguishing and insulation medium, and are one of the earliest applied circuit breaker technologies. Its structural feature is that both moving and fixed contacts are immersed in mineral oil. When the circuit is overloaded, the current-carrying contacts separate, generating an arc in the oil; the high temperature generated by the arc vaporizes and decomposes the mineral oil to produce hydrogen. Hydrogen forms bubbles around the arc, and the compressed hydrogen in the bubbles can effectively prevent arc reignition and insulation breakdown, thereby realizing arc extinguishing.

The insulation performance of mineral oil is better than that of air, so the insulation effect of oil circuit breakers is more advantageous. However, due to the flammable characteristics of oil, the fire risk is relatively high. According to the difference in oil volume and structure, oil circuit breakers are mainly divided into the following two types:

- Bulk Oil Circuit Breaker (BOCB): Oil is not only used for arc extinguishing, but also as an insulation medium between moving contacts, fixed contacts and other components of the oil tank. It has a large oil volume and a wide insulation range.

- Minimum Oil Circuit Breaker: Only oil is used as the arc extinguishing medium, and the oil volume is small, which is only filled in the live area inside the circuit breaker; the moving and fixed contacts use ceramics and air as insulation media. The research and development of this type of circuit breaker is intended to reduce the amount of oil used and reduce the fire risk.

III. Application Scenarios of High-Voltage Circuit Breakers

Different types of high-voltage circuit breakers have different application scenarios due to their performance differences, which are specifically as follows:

1. Air Circuit Breaker

- Used to protect low-voltage transformers and ensure the safe operation of transformers;

- Adapt to railway power systems to meet the protection needs of railway power supply;

- Applied in industrial plants with high explosion and fire risks to improve the safety of circuit operation;

- Used in power distribution systems to realize the safe distribution of electrical energy;

- Suitable for the maintenance of indoor medium-voltage switchgear to ensure the stable operation of switchgear.

2. Oil Circuit Breaker

- Applied in switch station equipment as a core protection component;

- Used for the protection of distribution lines in small and medium-sized substations to cut off fault current.

3. Vacuum Circuit Breaker

- Low maintenance cost, widely used in transmission lines in rural areas;

- Adapt to generators and substations to ensure the safety of power generation and substation systems;

- Due to the small maintenance workload, it has become the most commonly used circuit breaker type in the construction industry;

- Applied in the nuclear industry to meet the high-reliability power supply needs of nuclear facilities;

- Widely used in data centers to ensure the stability of power supply in data centers;

- Long service life, suitable for power systems of public infrastructure such as railways, highways, subways and airports.

4. SF₆ Circuit Breaker

- Mainly used in high-voltage transmission lines to ensure the stable transmission of high-voltage electrical energy;

- Used for the protection of high-voltage transmission systems to quickly cut off fault current and avoid system collapse.

IV. Working Principle of High-Voltage Circuit Breakers

High-voltage circuit breakers adopt an electric control operation mode. Its core working principle is: when a fault occurs in the power system, the arc generated between the moving and fixed contacts is cut off through the action of the magnetic blowout coil; when the circuit is overloaded, the moving and fixed contacts are separated from each other, and the arc moves horizontally and disperses between the contacts to avoid concentrated arc damage to the circuit.

The magnetic blowout coil provides a magnetic field for the arc, making the arc extend upward to the arc chute. The arc chute divides the arc into several small arc segments, further accelerating arc extinguishing, and finally completing the circuit breaking operation to ensure the safety of the power system.

V. Conclusion

This paper elaborates on the definition, core requirements, classification, structure and principle of various products of high-voltage circuit breakers, and clarifies the application scenarios and overall working principle of different types of high-voltage circuit breakers, aiming to help relevant practitioners fully understand high-voltage circuit breakers and provide reference for type selection in practical applications.

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