Circuit breaker Overview:
Circuit breaker is very useful equipment for switching and protection of various parts of power system. Circuit breaker operates automatically by measuring heat or current flowing through the circuit if the current exceeds a pre-set limit, the circuit breaker will ‘trip’ and sever the electricity supply as quickly as possible it will disconnect the electricity load. When the fault in the system is removed it will be simply switched on they do not require replacing and can simply be reset. A few days back I posted an article about “electric motor tripping”, which explains the practical use of a circuit breaker with common issues solved.
Operation of Circuit breaker:
Circuit breaker consists of two contacts one fixed and other is moving contact. The moving contact is connected with fixed contact. When faulty current produce the moving contact trap energized moving contact separate from fix contact the area will be reduced due which its current density will be increased and heat will be generated due to which radiation will be produce. The medium oil or air which is present between them their ions will be ionized which will create conducting path due to which arc will be developed. This arc is dangerous for circuit if it is in huge amount. To remove this arc we use circuit breaker.
Now let us consider the above diagram in which current transformer is connected with circuit breaker. The current transformer converts high current in low current. For example we have 100A of current in the line of primary coil of current transformer while the relay operate on 5A current then the current transformer will convert 100A current to 5A current through secondary coil the relay will get 5A. When the faulty current occur the current in the primary coil of current transformer will be increased due to which current in secondary coil of current transformer will also be increased. The relay will sense that faulty current occur the relay coil will make mmf this coil work like a magnet it will pull the relay contacts and the joints will be close. The trip coil will be energized and it will start working like a magnet. The rod in the circuit breaker is connected. As the trip coil start working like a magnet it will pull the rod and the line will be break.
Need for Circuit Breaker
Circuit breaker is a very important part of any electrical system. It is used in series with proper grounding, they can safeguard against electrocution when the current exceed certain limit or if there is short circuit in the electric system it will be automatically disconnect the load. When abnormal current flow or short circuiting occur for example if both live and ground wire combine or overloading occur by increasing load like driving ac, refrigerator, iron, fans at same time the Circuit breaker will protect appliances by breaking the circuit. Circuit breakers protect electrical circuits from abrupt current changes or large current surges.
Purpose of Circuit Breakers
Electricity has made over life comfortable but it the same time it is very dangerous if high electric voltage shock someone it can cause has death. So to prevent ourselves from this tragedy we use circuit breaker. Circuit breakers are devices that automatically stop current from flowing if it reaches a certain level .Circuit breakers have an advantage over fuses. In fuses when the current exceeds the wire in the fuse will break and it disconnect electric supply now to make it work again we will use another wire in the fuse while in the circuit breaker we can connect electric supply easily by simply switching on the circuit breaker.
Circuit breakers have to be simple, because they are a major safety measure in the electrical grid and common households. The overloading or short circuiting can cause fire in the wiring system to prevent ourselves from this problem we use circuit breaker.
Usually, these problems involve momentary power surges, but sometimes there may be system problems that will need to be diagnosed. Mostly in our home we have separate circuit breaker for every room and one main circuit breaker it occur very rear that main circuit breaker to “trip,” as we have separate breaker for every section it is individual circuit breakers that trip long before there is a need for the main breaker to shut off.
Basic Design of Circuit Breakers
Circuit breaker designs vary with the passage of time because companies are trying to produce best circuit breaker that will operate in mini seconds. A circuit breaker must be wired in series because in series connection when the wire breaks it will disconnect the entire load. We will connect the circuit breaker with one or two of the wires that run throughout a house’s electrical system. There is a place for each wire to go in the circuit breaker enclosure as well as to exit the enclosure. In between, inside the circuit breaker enclosure, there needs to be a section of conductor that completes the circuit and is held in place by some force, usually a spring.
The purpose of the circuit breaker is to push the conductor out of contact with the wires leading in and out of the breaker, thereby stopping the flow of electricity. A latching mechanism ensures that the circuit remains broken until an operator (you, for example) comes to reset it and once again pushes the conductor in contact with the rest of the circuit.
In order to push or pull the conductor away and out of contact with the rest of the wiring, the circuit breaker uses one of various types of mechanisms, which are discussed in the following section.
Function of Circuit Breaker
A circuit breaker is an automatic circuit protection system that we used in our homes factories etc. Breakers are installed in an electrical panel (breaker box) from where all power of the home or industry can be controlled and each circuit is attached to a singular breaker for example we used separate breaker for each room in our home so that we can easily connect and disconnects it load when needed. The breaker will monitor the circuit and shut off the circuit when the event of a complication such as an overload, short circuit occurs. This is process is called a “tripping a breaker” or “breaker trip” and it commonly happens when highly power rating appliances or equipment are placed in circuit.
Think about a home outlet with a space heater, air condition, iron, washing machine, water pump, a television, and a vacuum all plugged into it. This would almost certainly cause a breaker trip, which will shut off access and operation of that circuit because the circuit is overloaded and it will not working until the problem is fixed and the breaker is reset and placed back into position.
Difference between fuse and circuit breakers:
Fuses and breakers serve the same purpose overall, though breakers in many cases have overtaken fuses in use the operating time of fuse in 0.1sec means if short circuit or overloading occur the fuse will break the circuit in 0.1sec while in the circuit breaker the operating time is 0.01sec it will disconnect the circuit in 0.01sec which is very fast than fuse. Fuse is not reusable because it consist of wire when it melts we cannot used it again. While the circuit breaker can be reused again.
How to use Circuit breaker:
If we want to perform some major work on the system or installing new electric appliance we can shut off power to the entire house with the help of circuit breaker. To shut off the power we will follow some instructions:
- Shut off each individual circuit breaker in the panel, one at a time.
- Then flip the lever on the main circuit breaker to the OFF position.
- When it comes time to turn the power back on, begin by resetting the main breaker to the ON position, the turn on each individual circuit breaker, and one at a time.
Resetting a Circuit Breaker
There are various reasons due to which the circuit breaker might trip. Lightning strikes as the light contain high voltage, power surges, or an overload to the electrical panel can all cause the main breaker to trip. The main breaker provides extra safety if an individual circuit breaker fails to trip the main circuit breaker will trip. To reset the circuit breaker we will follow the following procedures:
- First, we will turn off all the individual circuit breakers that controlling various portion in home or industry. We will turn on the individual circuit breaker one by one because It is safer after resetting the main breaker.
- When we reset the main breaker to the ON position with the help of lever. Stand off to side when resetting any breaker. Use safety glasses and turn your head while resetting any breaker. By doing this, you will protect yourself from any possible electrical flash or sparks. The chances of this happening are remote, but such episodes have been known to occur.
- Turn on each individual circuit one at a time by resetting its lever to the ON position. So that entire load not comes on the main circuit breaker.
Usually, the main breaker trips due to a temporary issue and resetting it will solve the problem. But if the main breaker trips again, or trips repeatedly, you are well advised to call in a professional. The problem may involve a short circuit in the main panel because the main circuit breaker bears all the power so their damage can cause a series problem.
Working of Circuit breaker:
Electric circuit breaker shut off the circuit to protect home and family against fire and electrical injury, if this limit is reached; the act of the breaker tripping opens the circuit and prevents the flow of current when excess current or overloading occur. The circuit breaker will work when following conditions occur:
- A short circuit, such as a wiring issue such as mixing of live wire with ground wire or fault an appliance those results in excess current being pulled.
- An overloaded circuit, when the loads of appliances are increased by using air conditioner microwave oven iron etc.
- A ground fault, which typically occurs in high moisture when the circuit absorb moisture such as the kitchen and bathroom , and the reason GFCIs are required by current electrical code for your protection.
Circuit breakers installation:
Circuit breakers are found in our home in circuit breaker box. The circuit breaker box contains all circuit breakers of home for example we use separate breaker for each room in home.
Types of circuit breaker:
There are various types of circuit breaker we will discuss them one by one:
According to Voltage level:
According to Voltage level there are three types of circuit breakers:
- Low voltage circuit breaker
- Medium voltage circuit breaker
- High voltage circuit breaker
Low-Voltage Circuit Breakers
Low voltage circuit breaker types are commonly in commercial, domestic and industrial application and include.
Miniature Circuit Breakers (MCB): Miniature Circuit Breakers do not handle currents higher than 100 amps. Trip characteristics normally not adjustable. It is suitable for many home and business applications. They operate on thermal or thermal-magnetic properties.
- Molded Case Circuit Breakers (MCCB): These circuit breakers can handle currents up to 2,500 amps, making them a more robust choice for higher-power residential and industrial purposes. With higher amp ratings, their trip load can typically be adjusted.
Difference between MCB and MCCB circuit breakers
MCCBs can handle more voltage than MCB also its trip characteristics can be adjustable while in MCB trip characteristics are not adjustable.
Low-voltage circuit breakers are mounted in multi tiers in low voltage switch gears. Low voltage circuit breakers can be easily disassembled for repairs without a user having to take the switchgear apart. Some assemblies of circuit breakers are automatic that can be controlled remotely the user can open and close the circuit breaker through remote control. Direct current applications also used these circuit breakers. Because direct current’s internal electrical arc does not stop and start as with alternating current, a different type of breaker must be used within the unit.
Medium-Voltage Circuit Breakers
These circuit breakers handle voltages between 1KV to 72KV may be assembled into metal enclosed switch gear line and are installed for both indoor and outdoor use. Current transformers detect the current moving through the circuits and trip circuits using an electrically controlled switch. Protective relays monitor the current for dangerous abnormalities.
Air-break interrupters: These breakers are usually controlled electronically, though some are computerized with a microprocessor. In air break interrupters we can manually set the trip level it is highly configurable. Main stations distribute power through Air circuit breakers in industrial plants. This breaker uses air as an interrupting and insulating medium. The breaker is further divided into two categories:
- Low voltage circuit breaker is used for lower voltage whose value lies below 1000 V
- High voltage circuit breaker is used for high voltages whose value is 1000 V and above. It is further classified into oil less circuit breakers and the oil circuit breaker
- Vacuum-break interrupters: Vacuum-break interrupters use the fact that electricity cannot arc in a vacuum where there are no particles to ionize. They contain the arc in so-called “bottles.” These breakers have a longer life expectancy than air-break interrupters.
- Single pole circuit breaker – This breaker is connected with two wires in which one wire is live wire and other is neutral wire it on operate at 120 V having current 15-20A. When there is a fault in the circuit, it will interrupt only the live wire. Single pole breakers are mostly appropriate for non-heating and low amperage.
- Double pole circuit breaker-This type of circuit breaker is used for 220 V having current rating 20 to 60 amperes. There are two live wires and both the poles need to be interrupted.
- GFCI circuit breaker:
GFCI circuit breaker work on ground fault current it break the circuit when it detects the slightest variance between phase and neutral wires. If the difference exceeds a small threshold (typically 4-6 milliamps), then the breaker trips to protect the wiring and personnel that may have inadvertently become exposed to a ground fault hazard.
- Arc Fault circuit interrupter (AFCI)-The AFCI breaker will work when large amount of arc is produced in the circuit. This breaker prevents us from fire. Under the normal arcing condition, this breaker will not break the circuit and will be operated normally.
High-Voltage Circuit Breakers
Electric power transmission network is controlled and controlled by high voltage circuit breakers. The definition of high voltage varies but in power transmission work is usually to be 72.5KV or higher. High voltage breakers are usually always solenoid operated with current sensing relays operated throughout current transformers.
These breakers use a number of different forms to break the arc: bulk oil, minimal oil, air blast, vacuum, sulfur hexafluoride and carbon dioxide. It should be mentioned, though, that oil and carbon dioxide are being ruled out in favor of sulfur hexafluoride, which is a more environmentally friendly option.
There are four types in this category:
- Air circuit breaker
- Oil circuit breaker
- SF6 circuit breaker
- Vaccum circuit breaker
Air circuit breaker:
Air circuit breaker is type of circuit breaker that provide over current and short circuit protection for electric circuits over 800Amps to 10K A. These are usually used in low voltage application below 450. Air break the circuit breaker the arc is initiated and extinguish in substantially static air in which the arc moves.
Oil Circuit breakers:
Oil circuit breakers are such type of circuit breakers which used oil as a dielectric or insulating medium for arc extinction.
Sulphur hexafluoride SF6 breakers:
A circuit breaker in which sulphur hexaflouride under pressure gas is used to extinguish the arc. SF6 gas has an excellent dielectric, chemical and other physical arc quenching, property due to which it is used in the circuit breaker which has proved its superiority over other arc quenching medium such as air or oil. These circuit breakers are low-maintenance, low-noise and do not release hot gases.
Vaccum circuit breakers:
A vaccum circuit breaker is type of circuit breaker which work in the voltage range from 11KV to 33KV .The operation of switching n vaccum circuit breakers are very fast. It is mostly used in industries it takes 1 to 2 second to trip
Magnetic Circuit Breakers
Magnetic circuit breakers are those that use a solenoid which become electromagnet when the current pass through it. It’s magnetic field depend upon on the current passing through it. it undergoes a magnetic force that is angled perpendicularly through its center. This force increases with the amount of current.
When the current exceeds the preset value of the breaker due to a high current condition from a short circuit, overloading or another source, the magnetic field strength in the solenoid causes the breaker to trip open, breaking the flow of current.
Thermal Circuit Breakers
Thermal circuit breakers are the type of circuit breaker which consists of bimetallic strip. It work on the heat phenomena when the excess current pass through the circuit it produce heat and the bimetallic strip eventually reaches a point of deformation that causes the breaker to trip to the open state, once again interrupting the flow of current in that circuit. Thermal circuit breaker is reset when the bimetallic strip cools. Thermal circuit breakers are temperature sensitive. In colder operating conditions, the trip point moves higher, whereas, in warmer conditions, there may be a downward shift in the current level at which the device trips.
Thermal-Magnetic Circuit Breakers
This type of breaker used both magnet and heat to detect overcurrent. This circuit breaker is the most common type found in distribution boards, which are the panels of breakers controlling different circuits within a house or building. A magnetic circuit breaker uses a solenoid to catch fast-acting overcurrent, allowing it to react to short-circuit.
One of the benefits of having a thermal trip unit in the circuit breaker is that it allows for quick but non-harmful overloads. These are commonly produced by the bursts of current required to start up engines, electrical saws and the like. These spikes of current are not so large as to cause damage.
Magnetic-Hydraulic Circuit Breakers
This type of circuit breaker operates on solenoid as its core operating part. The solenoid responds to current in the same way when the current will flow through it will act as electromagnet and is held in place by a spring that will not compress until a threshold limit is reached.
However, this time, the movement of the solenoid is dampened by a viscous hydraulic fluid. When the circuit reaches its overload point, the solenoid begins to move against the spring. Its movement is slowed by the hydraulic fluid so that if the overcurrent turns out to have bene a momentary spike in current — such as that caused by a motor starting up — it will stop its movement and return to the starting position without having tripped the circuit.
This system is a convenient one because it allows short-lived spikes in operating current without having to flip the circuit breaker. If a short circuit occurs, it will move the solenoid enough to trip the circuit, overpowering the time delay feature.
Brands of Circuit breaker:
There are many manufacturers out there who make safe, reliable and affordable circuit breakers for residential and business use. Here are some of the most popular companies that are manufacturing circuit breakers:
- General Electric – GE
- ABB – BBC – Gould – ITE
- Siemens – Allis Chalmers
- PACS Industries
- Federal PacificSquare D
Other Circuit breakers:
There are some other types of the circuit breakers used for the protection against earth faults which are too small to trip an over-current device.
Earth Faults circuit breakers
- Residual Current Device (RCD).
- Residual Current Circuit Breaker.
- Earth Leakage Circuit Breaker (ELCB).
The Residual current device RCD is also known as the Residual Current Circuit breaker RCCB. This circuit breaker is used to detect current imbalance. The RCD or RCCB does not provide over-current protection. These circuit breakers are also called as the ground fault circuit interrupters GFCI.
Residual current circuit breaker with overcurrent protection (RCBO). The RCBO combines the functions of a MCB and RCD in one single package. These are also called the GFCI breakers.
The earth leakage circuit breaker ELCB does not detect the imbalance but it detects the current in the earth wire directly. The ELCBs are no longer used in all new installation as they cannot detect any dangerous condition where the current is returning to earth by another route. ELCBs are still used in UAE on the most frequent basis.