Blog

Types of circuit breaker are classified into various terms. One of the most common methods of classifying the circuit breakers is arc extinction method.

Arc extinction method divides the circuit breaker into four types. These are:

• Air break circuit breaker
• Air Blast Circuit Breaker
• Sulphur hexafluoride circuit breaker
• Vacuum circuit breaker

Lets discuss in detail;

Air Circuit Breaker

In air circuit breaker arc moves in the static air and the arc extinction takes place with the static air.

Air circuit breakers are usually used for low voltage systems.

The air break circuit breakers are also of three types which are plain air break circuit breaker, arc chute circuit breaker and magnetic blow out type circuit breaker.

In the plain air circuit breaker the contacts are made in the shape of horns. In arc chute circuit breaker low voltage circuits are used for the arc extinction and in magnetic below-out type circuit breaker magnetic field is used as arc interrupter medium.

Air circuit breaker is one of the most common used CB in domestic and industrial loads. The miniature circuit breaker (MCB) in your home electricity box is an Air CB.

To safeguard an electrical system or device from overcurrent and electrical short circuit different devices are in use.

 

The air breakers are rated for low voltages. Due to high performance, durability, easy installation, and maintenance the air breakers are very common to use.

Construction

Circuit breakers (CBs) have some main components such as:

• Frame its made of some kind of plastic
• Operating mechanism which include springs and other mechanical parts that helps in closing and opening fast.
• Contacts, moving and static contacts are the parts that connect electricity from one circuit to another, they should be able to carry making and breaking currents of the circuit breaker.
• Arc Extinguisher, also refereed to as arcing chamber, the arc should have somthing to stop it during closing and opening.
• CT to sense current
• Trip units

Of course the air circuit breaker has some other accessories like buttons, indicators, toggle switches and nameplate.

How Does Air CB work?

The air CB consists of two pairs of contacts. Contacts 1, usually called the main pair carries the current at normal load.

Contact 2, also called the second pair is the arcing contact. Contact 1 is made of copper metal and contact 2 is made of carbon.

When the circuit breaker opens, the main pair i.e. contact1 opens first while the arcing contacts are still connected with each other.

When current flows through a low resistive path through the arcing contact. It heats up and the contacts detach from each other.

During this process arcing initiates. Due to electromagnetic and thermal effects, the arcs move upward and fit in the chute. Where in chute the arc becomes colder and extinguishes at zero current.

Types of Air CB

There are three types of Air CB. These types are common in use for low voltages. Each type is discussed below.

• Plain Break Type: In this type of breakers, the main points of contacts are made in the shape of two horns. During the operation, the arc extends from one tip to another. These types are most commonly in use.
• Magnetic Blowout Type: In this type of circuit breaker, the arcing is providing with help of a magnetic field. These are normally used for rated voltage up to 11KV.
• Air Chute Air CB: In this type of circuit breaker, the main contact is made up of copper. It conducts current in closed positions. The contacts are silver plated and have low contact resistance. The arcing contacts are made of copper alloy and they resist heating up.

Applications of Air Breaker

• Air CBs are used in power generation station auxiliaries and other industrial plants. It safeguards electrical equipment from overcurrent and short circuit.
• It can be used in both AC and DC circuits.
• Air CBs offers high resistance power by expanding, splitting & cooling the arc during contacts movement, closing or opening.
• Sometimes this type of breaker is used in the electricity sharing system.

Air circuit breaker vs MCCB

Selecting electrical installation protective devices is critical to minimize difficulties caused by abnormal service circumstances. Both ACB and MCCB are used to ensure the safety of electrical systems.

Both serve the same goal in theory. Although there may be some similarities between these two devices, there are also some differences between them. Let us have a look.

Air CB	MCCB
ACB is an abbreviation for Air Circuit Breaker.	MCB stands for Molded Case Circuit Breaker.
ACBs are often utilized on the circuit’s upstream end.Because of its less frequent operation, the ACB is not suitable for use at the load end.	MCCBs are used on the load side of the circuit to break the circuit in the event of a failure or any fault that might harmful to the circuit.Because of its compatibility with regularly functioning with accuracy, the MCCB circuit cab be employed at the load end.
The ACBs for a circuit are chosen based on two parameters: the operating voltage and the fault voltage. ACB parameters perform worse than MCCBs.	MCCBs are thought to be more accurate than ACBs due to the usage of different technologies in MCCBs. The advancement of technology has made circuit breakers more accurate and precise.
The air circuit breaker has a lesser breaking efficiency than the MCCB.	The MCCB outperforms the ACB in some areas, including breaking capability.
The ACB has a higher rating than the MCCBs. Because of its high current rating, an ACB is employed in a circuit with a higher circuit current.There is a 6300 A rating for general ACBs at the present time.	MCCBs can have ratings higher or lower than this rating, depending on their features.There is approximately 3200 Amps of rated current for the MCCB.
The tripping thresholds in the ACBs can be adjusted, although it’s a bit complicated.	The MCCB’s tripping thresholds are easily adjustable. This characteristic makes the MCCB preferable to alternative circuit breakers in certain circuits.
The ACB also has two modes of operation. The magnetic mode is one possibility, while the thermal magnetic mode is another.	The MCCBs use thermal magnetic functioning. Previous MCCBs only had one operation, which was typically magnetic.
The ACB’s trips unit might be the same as that of MCCBs.	The units that have been tripped might be either magnetic or electrical. Thermal magnetic units can also be used as trip units.
ACBs are rarely utilized in circuit breakers.	MCCBs are more prevalent breakers than ACBs.

Air Blast Circuit Breaker

The air blast circuit breaker uses the blast of air to interrupt the arc. In this type of circuit breaker the air is stored and compressed in a tank and released through the nozzle which produces the high velocity jet. The jet of air is used for the arc extinction to break the circuit.

These circuit breakers are used for both indoor and outdoor services. They are used for voltages up to 15 KV. Their rupturing capacity is 2500 MVA.

Types

1. Axial Blast Circuit Breaker: The air moves longitudinally in the direction of the arc for arc extinction.
2. Cross Blast Air Circuit Breaker: The air flows at the right angle of the arc.

Vacuum Circuit Breaker

It is a type of the circuit breaker in which the arc quenching takes place inside the vacuum medium.

The operation of opening and closing the circuit and arc interruption takes place inside the vacuum chamber. This vacuum chamber is called the arc interrupter. The interrupter contains a steel arc chamber in the center of ceramic insulator placed symmetrically.

This is used commonly for most standard voltage circuits. Vacuum technology is developed for the higher voltage but not the commercially practicable.

The pressure inside the vacuum chamber is maintained at 10 – 6 bar. Its performance mainly depends upon the conducting materials used for the contacts for the flow of current. Most commonly used materials for the contacts are Cu/Cr.

My other related Topics: What are MCB Types And Applications.

Why vacuum is used in circuit breakers?

Because vacuum gives high insulating strength due to superior arc quenching properties, that’s why it’s used in circuit breakers. The dielectric strength of the vacuum is far better than any type of medium.

A steel arc chamber is housed within the middle of symmetrically positioned ceramic insulators in this interrupter. The vacuum pressure within a vacuum interrupter can be maintained at 10- 6 bar.

The performance of a vacuum circuit breaker is mostly determined by the material chosen for current-carrying contacts, such as Cu/Cr.

 Vacuum Circuit Breaker Working Principle

When the circuit breaker contacts open inside the vacuum chamber, the generation of the arc takes place among contacts.

This arc is generated through metal vapor ionization between the contacts. But the arc can be quenched easily because these vapors can be condensed quickly on the CB contacts. In this way the strength of dielectric can easily be recovered.

The most significant feature of vacuum circuit breaker is that after generating the arc inside the vacuum chamber, it can be quenched quickly.

Contact Materials

The contact materials used for the vacuum circuit breaker should have the following properties.

• It should have a high density to diminish the arc erosion.
• It should have low resistance and high electrical conductivity to pass the current without overheating.
• It should have high thermal conductivity. It is necessary to dissipate all the heat quickly produced during arcing.
• It should have high thermionic function fir the early arc destruction.
• It should have low welding tendency, less current chopping level and high arc resist capability.

Construction of Vacuum Circuit Breaker

As mentioned earlier it consists of a steel arc chamber placed in the center of the symmetrically arranged insulators. The pressure inside the chamber is maintained below 10-4 bar.

The materials used in the vacuum circuit breaker plays an important role specially the current carrying materials.

In the common circuit breakers the alloys of copper and bismuth or copper and chrome are used to make the contacts.

The vacuum circuit breaker consists of one moving contact, one fixed contact and a vacuum interrupter which is the main part of VCB.

The control mechanism is connected with the contacts with the help of stainless steel. An insulating housing supports the arc shield and cover these shields in this way prevent them from condensing on insulating enclosure.

The probability of leaking is highly reduced by sealing the vacuum chamber permanently. For this purpose a glass vessel or ceramic vessel is used as outer body. It also provides the outer insulation to the chamber.

Working of Vacuum Circuit Breaker

When any abnormal condition occurs the contacts are separated and the arc struck between contacts. The production of the arc is mentioned earlier that it is produced by production of vapors.

The process of arc interruption is slightly different in vacuum interrupters as compared to the other circuit breakers. The vapors formed due to the separation of contacts are filled between the contacts.

The density of the vapors depends upon the current in the arc. When the amount of current is decreased, the rate of production of vapors is also decreased.

When the current becomes zero the medium regain dielectric strength when the vapor density is decreased with current.

When the amount of current which causes the interruption is very small, it is divided in the several parallel paths of the arc. They repel each other and spread over the contact surface. This condition is called the diffused arc. This type of arc can be interrupted easily.

When the current to be interrupted has the high values, it makes the arc concentrated in a small region. At this position rapid vaporization occurs at the contact surface.

If the arc remains in diffuse state only then the interruption of arc may be possible. If diffused state is removed quickly the arc will be quenched again.

The strength of dielectric rapidly builds up after the interruption of the final arc. Sometimes due to abnormal formation of vapors and abnormal emission of electrons in the contact material causes the current chopping in vacuum circuit breakers.

How to check vacuum in a vacuum circuit breaker?

By providing a voltage across the open contacts of the vacuum interrupters, VI’s that is greater than the breakdown voltage of such contacts in air, the presence of the vacuum can be checked in the vacuum circuit breaker. This technique has a solid track record of 50 years and has gained universal approval.

Other ways of detecting the existence of a vacuum are being presented today. These techniques are further classified into three kinds based on the pressure range in which they operate. Each class has a distinct edge over the others.

High vacuum pressure gauges in vacuum pressure monitors might warn of an impending breakdown. Low vacuum pressure gauge monitors detect dielectric failure caused by vacuum loss as it occurs. Monitors with barometer gauges show the VI’s end of life. Only these three systems can be utilized to monitor the vacuum pressure continually.

The continuous vacuum monitor based on low-pressure vacuum gauges is regarded as the best engineering alternative since it does not influence the VI’s design.

Advantages

• Long life time.
• More safe than air blast CB or oil CB
• Fast operation and quickly fault removing.
• Environmental friendly, as no gas
• Low or no maintenance.
• Lowest fire hazard or no fire hazard at all.

Disadvantages

The VCB has almost the best technical performance, and the disadvantages are regarding its economic side.

This is because producing it in small quantities is not economic. Besides the higher the voltage rating the more expensive the VCB

Applications

Vacuum circuit breakers are almost the most reliable current interruption technology in case of using it in medium voltage switchgear. As mentioned above it is almost maintenance free.

SF6 Circuit Breaker

Sulfur Hexafluoride SF6 Circuit Breaker is a type of circuit breaker in which high-pressure sulfur hexa-fluoride (SF6) gas is used for extinguishing the Arc. Just like air, vacuum or oil sulfur hexa-fluoride is pure dielectric.

Due to its physical and chemical properties, SF6 CB is used in many places with rating voltage up to 800Kv. Another circuit breaker (those containing, air or oil) function on high voltages was a little bit slower.

Sf6 circuit breaker maximum rating is 420kV, and it has been used satisfactorily in many countries since 1983 in different environments.

Working Principle

Why do we use SF6 gas in a circuit breaker? SF6 gas has a break down voltage much higher than air and oil. Its used also in electrical transformers as isolation medium.

The use of SF6 gas in circuit breaker and transformer increases the break down voltage and helps very well in arc extinguishing.

Due to its physical and chemical properties, SF6 gas is used in this circuit breaker to reduce the arc. In case of the breaker is closed in normal operation there is no arc, in case of fault or even in case of opening the breaker, current passes between the moving and fixed contacts, causing an arc.

Using SF6 gas, the circuit breaker is able to extinguish the arc faster. The current stops passing between the fixed and moving parts of the CB, and the arc is completely extinguished.

After the contact separation, the extinguishing force was slower than normal. While the function of SF6 Circuit Breaker was up to the mark even in high voltages, SF6 circuit breaker is mainly used in medium voltage switchgear.

Where is SF6 circuit breaker used?

Sulfur hexafluoride circuit breakers also can be utilized as self-contained apparatus in outdoor air-insulated substations or as part of gas-insulated switchgear, allowing for compact high-voltage installations.

They are commonly used at the outlet of high-power generators (30 MVA to 1800 MVA) to safeguard them in a dependable, quick, and cost-effective manner.

Such circuit breakers have a large breaking capacity (50 kA to 275 kA) and a high carrying current rating (4 kA to 40 kA). When triggered by a protective relay,SF6 circuit breakers halt electric currents, protecting electrical power stations and distribution networks.

Why is SF6 a Good Insulator?

Due to its inertness as well as its ability to block the internal discharge of the device, it’s employed as an electrical insulator gaseous in high-voltage generators and switch gears.

The SF6 gas, when kept at room temperature, is odorless, colourless, and non-toxic. Despite its thermal stability and chemical inertness, it is a very durable gas. 

Furthermore, due to its high electrical insulating properties, non-flammability, non-toxicity, low maintenance, and competitive cost, SF6 is used for high voltage.

SF6 has been the go-to dielectric insulating material for high-voltage electrical systems installed in enclosed spaces for many decades.

How do you check for SF6 gas leaks?

In order to detect SF6 leaks, there are three main methods that can be used:

1. SF6 Camera
2. Handheld Gas Detectors (Sniffers)
3. Bubble Mix (Snoop)

SF6 Camera

Using an SF6 camera to detect leaks is perhaps the most effective way. A camera like the FLIR GF306 has the ability to detect extremely minor leaks (up to 0.5lb SF6 annually).

The advantage of employing a camera is that there is no guesswork involved; simply point it at the region where you feel there is a leak and let the camera record the observations. In just a few decades, this technology has come a long way.

Handheld Gas Detectors (Sniffers)

Because of the low cost and excellent accuracy of sniffers these days, this sort of leak detection is the most popular.

These are quite simple to use: switch them on, aim the nozzle, and move it about. They may also enter regions where a standard camera cannot, such as a cabinet or between metal fittings.

Bubble Mix (Snoop)

A home soap detergent and some water, similar to locating a leak in a tyre, can be used to locate an SF6 leak.

All you need is a spray bottle and a 20:1 water-to-soap combination. To locate a leak, spray the solution over flanges, tubing, or porous castings. If you find more bubbles forming when the mixture settles, you’ve discovered your leak.

Types

SF6 Circuit Breakers are mainly divided into three types. This division is done on the dielectric medium inside the circuit breaker. We will discuss each type of the Sf6 breaker in detail.

• Non-puffer type circuit breaker: This type of circuit breaker contains an Interrupter part, this part is used for the arc quenching process. While talking about the construction it consists of a fixed contact and moving contact. These contacts are like hollow cylinders. The fixed part has arc horns connected which limit switching components contact during flash-over. The moving part consists of a rectangular gas outlet. The gas goes through these holes after the arc extinction.
• Single- puffer type circuit breaker: In this type of Circuit Breaker movable cylinder which is also called a puffer cylinder is placed. While a fixed piston connects the puffer cylinder. The SF6 gas is filled between the fixed piston & movable cylinder. When the circuit breaker operates gas passes through both nozzles.
• Double-puffer type circuit breaker: In this type of circuit breaker, two pressure pistons are used as shown. The nozzles are placed current-carrying contacts. The placement of the nozzle is done in such a manner made up when gas flow increases, it passes through the nozzle.

Advantages

1. As all the breakers are completely sealed & enclosed therefore no risk of fire or explosion.
2. Also, SF6 is non-inflammable gas. It reduces the risk of fire.
3. Quick operation and arcing time are very short.
4. Uninterrupted and noiseless operation.
5. Working in all type of weather conditions
6. Less maintenance cost.
7. It can be operated up to 800 kV.

Disadvantages

1. The first disadvantage is in the term of cost.
2. For each operation, multiple types of equipment are needed.
3. There exists the danger of gas leakage all time. While the gas is colorless and odorless.
4. Internal parts need periodic cleaning.

Oil Circuit Breaker

The circuit breaker which uses oil for an arc extinction is called oil circuit breaker. It is further classified into two types. These are bulk oil type and the minimum oil type circuit breaker.

• Bulk Oil Circuit Breaker: This type of oil circuit breaker uses the transformers oil as the arc extinction medium. The oil is also used to make the insulation between the two conducting parts of the circuit breaker. The range of oil circuit breaker lies from 25 MVA to 5000 MVA at voltages of 2.5 KV to 230 KV respectively.
• Minimum Oil Circuit Breaker: In this type of circuit breaker the oil is used by the blast action. The oil is not used to insulate the live parts of the earth, but it is used to interrupt the arc formation in the circuit breaker.
• Oil Impulse Circuit Breaker: This is another type of minimum oil circuit breaker. It uses oil in the form of oil jets. The oil jet is formed as a result of piston pump for the arc extinction. The oil is present at the position between the gaps created by the contacts of circuit breaker.

 DC circuit breaker

The circuit breakers which are used for breaking the circuits of high voltage direct currents are called HVDC circuit breaker.

Their voltage breaking range is 33KV approximately and 2KA for the current. They use air or oil for the arc extinction process.

AC circuit breakers can’t be used in a DC circuit, This is because AC current is easier in arc extinction as the current goes to zero 50 or 60 times per second. While DC arc is hard extinction.

DC breakers are well designed to deal with this non zero value arc.

Read our article: Never use AC fuse in DC circuit.

Other Classifications of Circuit breaker

Some other classifications of circuit breakers are,

1. Single pole circuit breaker.
2. Double pole circuit breaker.
3. Three poles breaker.
4. GFCI breaker.
5. AFCI breaker

Single Pole Circuit Breaker Type

This type of breakers has only one pole i.e can monitor and protect single wire circuit from short circuit and overload.

They are most used in residential electrical wiring.

Double Poles Circuit Breaker

This type has two poles and can protect a two wires electrical circuit.

It trips if one or both wires get shorted or overloaded.

Three Poles Circuit Breaker

In case of protecting small three phase loads, like small sized three phase induction motors, or any other three phase loads, We use this circuit breaker type.

GFCI breakers

This circuit breaker type (ground fault circuit interrupter) is a great choice to protect in places where water is near electricity, like bathroom and kitchen.

For more information about GFCI circuit breaker read My detailed Article: GFCI Circuit Breaker Working Principle, Testing and Tripping

AFCI breaker

This type of breakers provide protection from arc fault. The regular breaker doesn’t protect from arc faults.

I have written detailed articles about, Bad circuit breakers, signs and causes, and what causes a circuit breaker tripping.