Types of electrical breakers 2
Types of electrical breakers 2
In the world of electricity and electrical distribution systems, circuit breakers form a vital part of the protection and control infrastructure. These key devices are crucial to ensuring the safety of electrical circuits and equipment, and protect us from over-currents and short-circuits that can lead to serious accidents. The concept of “electrical circuit breaker” includes A variety of devices, each performing a specific function within an electrical system.
This article includes a closer examination of the different types of circuit breakers, as they vary according to different purposes and applications. We will explore the main and detail breakers, as well as fuses and circuit breakers, focusing on the role of each type and how to choose the right type to optimally meet your electrical distribution needs.
This analysis will provide a comprehensive overview of circuit breakers and their importance in maintaining the safety of electrical systems, whether in homes or industries, and how they can contribute to improving the efficiency of electricity distribution and ensuring effective protection for individuals and property.
Role and functions of circuit breakers:
The role of a circuit breaker requires performing vital tasks to ensure safety and protection in electrical systems. Here’s a refresher:
- Opening the circuit safely: Opening the circuit safely is the primary goal of circuit breakers, as the circuit breaker ensures that the power is cut off quickly and effectively.
- Withstand moments of fault current:The circuit breaker must be able to temporarily withstand fault current, allowing other circuit breakers to intervene and solve the problem without causing damage.
- BREAKING A CIRCUIT SAFELY: A circuit breaker breaks a circuit using stored mechanical energy, whether a spring or compressed air, to effectively separate contacts and prevent current from flowing.
- Quickly extinguishing the arc:The circuit breaker must be able to quickly extinguish the arc generated between the contacts, in order to avoid overheating and damage resulting from continued arcing.
- Withstand voltage after disconnection: It requires the circuit breaker to be able to withstand voltage after disconnection, as it prevents side effects on contacts or electrical equipment.
- Re-triggering prevention: Re-triggering prevention is an essential part of a circuit breaker’s functions to achieve effective protection of electrical systems and equipment.
In short, a circuit breaker plays a vital role in maintaining the integrity of electrical circuits and ensuring their safe and efficient operation.
Oil thrust circuit breaker:
In this type of oil circuit breaker, the pressure necessary to extinguish the arc is developed by a piston connected to the moving contact. The piston is driven by external mechanical means rather than by the influence of arc current, making the pressure independent of the fault current. This type of breaker uses less oil than a regular oil circuit breaker and can extinguish the arc independently of the arc current and voltage.
Electrical circuit breakers without oil:
There are different types of arc cooling media that can be used instead of oil in high voltage circuit breakers. Among these types:
- Air breakers:
- Air is used as a medium to cool the arc and extinguish the electric arc.
- Air is induced by the arc current, and it plays a role in cooling and stabilizing the arc.
- SF6 circuit breakers:
- Sulfur difluoride (SF6) gas is used as a medium to cool the arc and extinguish the arc.
- It is characterized by its high insulating properties and its ability to handle high electrical voltage.
- CO2 circuit breaker:
- Carbon dioxide gas is used as a medium to cool the arc and extinguish the electric arc.
- It decomposes oxygen to produce carbon gas, which is useful in extinguishing the arc.
- Circuit breaker:
- It uses advanced media such as solid polymers to cool the arc and extinguish the arc.
- Offers an oil-free and effective solution for handling high voltage.
These media vary in their specific properties and uses, and the type of media is selected according to the application requirements and ambient conditions.
Air Circuit Breaker (ACB):
Air circuit breaker or ACB is a type of oil-free high voltage circuit breaker that uses air as the arc extinguishing medium. It is used for short-circuit and over-current protection in the range from 15 kV up to 800 to 10 kA. ACB is preferred over oil circuit breakers due to the lack of flammable oil and to reduce the risk of fire.
The goal of circuit breakers is to safely extinguish the arc and prevent re-arc. ACB uses air as the medium to extinguish the arc, and air can be used in various ways to extinguish the arc using arc quenching, arc length increase, arc splitting, air blasting, etc.
In an ACB, there are two pairs of contacts, the main contacts (made of copper) and the arc contacts (made of carbon). Under normal circumstances, the main contacts are used for the normal supply of current. Under fault current, the main contacts open while the arc contacts remain closed.
Once the main contacts are open, current flows through the arc contacts. At this point, there is no arcing and the main contacts are secure. An arc is generated once the arc contact is opened. The arc sweeps upward, cooling it and increasing the arc length. Thus the arc is extinguished at zero current.
Types of ACB:
- Ordinary air circuit breaker:
- Also known as a crossover circuit breaker.
- Used for low voltage applications.
- It has a chamber surrounding the main contacts, called the arc chute.
- It is used to extinguish the arc made of refractory material.
- Chute arc breakers:
- It contains a metal separation within the arc duct.
- Metal separation breaks the arc into smaller arcs, which increases the effort required to maintain the arc.
- Magnetic blowing circuit breakers:
- It has a magnetic device to move the contacts.
- Features magnetic blast technology to extinguish arc.
- Air breakers:
- It has two types of contacts: main and arc.
- Air is used as a medium to extinguish the arc.
- The current is shunted through the bent contacts after the main contacts are opened.
Magnetic air circuit breakers:
Magnetic air circuit breakers use a blast coil that generates a magnetic field. This field diverts the arc into the arc stream to lengthen and cool it. The arc is quenched inside the breaker, where the magnetic field does not directly quench the arc but only deflects it, and it is subsequently quenched by air. This provides arc control to increase its voltage.
Pneumatic magnetic circuit breakers are used up to 11 kV.
Air breakers:
Air blast circuit breaker (ABCB) uses a blast of compressed air to interrupt an arc. Air is stored and compressed in a tank, and is released at high speed through a nozzle to extinguish the arc. It has high voltage capacity up to 450KV and is used for 220KV lines in switchyards.
Air blast circuit breakers are divided into four types:
- Axial air circuit breaker:
- Air flows axially in the same direction as the arc.
- The air lengthens the arc and cools it.
- The arc is extinguished inside the breaker.
- Axial blast with sliding contact ACB:
- It is considered an ACB modifier.
- It has a horizontal moving connection with a spring and a piston.
- The arc is cooled in the same way as in an axial ACB.
- Radial blast air circuit breaker:
- The contacts are hollow and allow free space for airflow to cool the arc.
- Air flows radially into the contact points to cool the arc.
- Air crossed circuit breakers:
- The air blast is directed at a right angle to the arc.
- It is used to twist and lengthen the arc to extinguish the arc.
- The air tank is installed vertically for the movement of the contacts.
Advantages of ACB:
- There are no fire hazards, they are fast and require less maintenance.
- Small size and high reliability.
- Suitable for operation at high frequencies.
- Used in switch yards and allows fast disconnection speed.
Disadvantages of ACB:
- Air compressor maintenance required.
- The air compressor needs a lot of space.
- Air duct leaks can occur.
- There is a chance of high bounce rate and stream interruption.
- Air emits noise and has lower extinguishing properties compared to other insulating gases.
Sulfur hexafluoride (SF6) circuit breaker
Sulfur hexafluoride, also known as SF6, is a non-flammable insulating gas with an extremely high electrical potential. It is characterized by its great ability to absorb electrons.
When an electric arc occurs between the contacts, the medium is ionized by the action of free electrons. SF6 absorbs these electrons and forms negative ions with a heavier weight than the free electrons, which reduces the movement of charges and enhances the dielectric strength of the medium, leading to arc quenching. SF6’s insulation and arc cooling properties are approximately 100 times better than air.
SF6 is an expensive gas and is classified as a greenhouse gas. Although SF6 itself is not toxic, branch gases resulting from its use can be toxic and negatively impact the environment. Hence the design of the closed circuit system for this type of breakers, where SF6 gas is reused after each operation, and the system pressure is monitored periodically to ensure its dielectric strength.
There are three main types of circuit breakers using SF6:
- Non-aerosol type SF6 circuit breaker:Compressed SF6 gas is stored in the gas chamber, and arc cooling takes place inside the breaker unit. This unit includes moving and fixed contacts, and relies on hollow cylinders to ensure simultaneous movement of these contacts.
- SF6 single-pressure circuit breakers:This type contains a spray cylinder that moves axially to open and close the circuit, and this technology is considered simpler than the previous type.
- SF6 double-pressure circuit breakers:The gas is compressed and stored in a chamber that opens to suppress the arc when the contacts are opened. This type has been outdone due to the complexity of the gas system.
Advantages of SF6 circuit breaker:
- High arc quenching capacity.
- Short period of time for circuit curvature.
- Dielectric strength is many times higher than air.
- Compact design and low installation cost.
- It does not form carbon particles, which improves the dielectric strength.
- Silent and non-flammable.
Disadvantages of SF6 circuit breaker:
- SF6 greenhouse gas emissions and byproducts may be toxic.
- Requires constant monitoring for SF6 leakage.
- High cost.
- It requires special transportation and storage of gas.
- SF6 may cause breathing difficulties.
- Requires maintenance with additional equipment.
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