The air circuit breaker is a switching mechanical device that extinguishes the arc with compressed air, and turns off, conducts, turns on currents when the circuit is installed. It is used to prevent short circuits and overloads in electrical installations, as well as in the control of electrical circuits. Some units are equipped with an additional protection function against critical voltage drops and other situations.
Description
There are certain requirements for devices of this kind, including ensuring safe continuous use and reliable protection against overloads and short circuits in the network. The quality of the device has a special role, since the operation of air circuit breakers can occur in various temperature and humidity conditions, in the presence ofvibration loads and frequent switching. Electric receivers are under electrodynamic and thermal influence from switches, thanks to this, technological losses are minimized and the service life is increased.
Automatic air circuit breakers control and protect the network at the same time. They are classified into several types according to the response time, which is allotted for opening contacts from the moment of the signal:
- selective;
- standard;
- high-speed (have a current-limiting function).
Oil devices
Such products are made in the form of a tank of rectangular, oval or round shape. Oil air circuit breakers were invented at the end of the last century and acted as a circuit breaker in circuits characterized by high voltage. Insulators with fixed contacts are passed through their cover, fixed at both ends. Using an insulating rod, the drive unit is connected to a moving contact, which, in turn, is located between two single-pole fixed contacts. They are completely covered with transformer oil, which fills the tank up to a certain level. The air cushion occupies the space between the cover and the oil surface.
Mount
The design of the device is in a dielectric case. Air circuit breakers used for low voltage are fixed in place with a DIN rail. To screw elementswiring is connected, and using the lever, the device is turned off and on. The case is held on the rail by a special latch - so the device can be quickly removed by first moving it away. The fixed and moving contacts are essential for the circuit switching process. The moving element uses a spring to allow the contacts to be released. This action can be performed by a magnetic or thermal splitter.
Heat Splitter
The bimetallic plate that makes up the thermal splitter is heated by the flowing voltage. The splitting mechanism occurs after the plate is bent, caused by the passage of a current with a voltage above the set value. The properties of the current directly affect the response period, which can be within an hour. The element responds to the voltage set during production. The HBV air circuit breaker can be used immediately after the plate reaches normal temperature, which is not typical for a float fuse.
Magnetic Splitter
The action mechanism of the magnetic device is driven by a movable core. The splitter of this type is a solenoid, through the winding of which the current passes through the switch, when the nominal value is exceeded, the core begins to retract. The magnetic type has the property of instantaneous response, which the thermal one cannot boast of, but the reaction occurs only if the set threshold is significantly exceeded. Several varieties are used, which have varying degrees of sensitivity.
In the process of splitting, there is a possibility of an electric arc. To prevent this, an arcing grid is placed next to the contacts, and the elements themselves are made in a special form.
Views
Air circuit breaker may have different characteristics and features, which are divided into certain types:
- with and without current limiting capability;
- the pole of the device depends on the number of poles available;
- with zero, independent or maximum voltage splitter;
- without contacts and with existing free contacts for secondary networks;
- properties of the current splitter period delay may be different: for example, devices may have a delay that has an inverse dependence on voltage, independent of voltage, or it may be absent; a variant that combines all properties is also possible;
- air circuit breakers, the device of which has a universal, combined (lower terminals with rear connection, and upper terminals with front) and front connection;
- Spring actuated, motor or manual.
Arc quenching
The design can have from one to four poles, while in any case there are auxiliary contacts, a splitter, a splitting device, an electric arc extinguishing systemand the main contact system. It can be single-stage (in the case of using ceramic-metal elements), two-stage (arcing and main contacts) and three-stage (in addition to arcing and main contacts, intermediate contacts are added).
The arc extinguishing system can be made with special arc chutes in chambers or have chambers with small gaps. For high voltage operation, combined types are used, combining two options for extinguishing the arc.
Features
Any VVB air circuit breaker has a set short-circuit voltage limit, if there is a current higher than the existing parameter, there is a possibility of welding or burning of the contacts, and as a result, the device will break. It can be carried out in a retractable or stationary version, and have a motor or manual drive. The drive can have pneumatic, remote, electromagnetic and other actions and is designed to turn off and turn on the device.
A relay with a direct mechanism of action acts as a splitter. In this case, thermobimetallic or electromagnetic parts provide a shutdown if the primary network is characterized by the absence of current, as well as during overload and short circuit. The splitting design includes trip springs, rocker arms, latches and levers. In addition to opening the circuit breaker, it is used to prevent the possibility of closing on a short circuit.
Excerpt
The shutdown process can be characterized by the presence of a delayor its absence. The type of switch, in particular the speed of its response, depends on the time interval during which the existing value is exceeded and the contacts diverge. Thus, high-speed, selective and standard switches have become widespread. The last two options do not have the ability to current limit. In selective devices, network protection is carried out using installed switches with different response speeds: the consumer has the minimum value, this parameter gradually increases towards the power source.
Switch and fuse
Overloads in the network can lead to fire or at least damage to the installed electrical equipment. To prevent such situations, an air circuit breaker for STP 100 and a fuse are used, the mechanism of which is to interrupt the current, but each of them has its own characteristics. The main part of the fuse is a metal element that melts when heated excessively. The air circuit breaker uses a special mechanism that is triggered by a critical voltage, and it is enough to actuate the device after reacting, while the fuses often have to be replaced with new ones, but their main advantage is the fast response speed.
It is also worth noting that depending on the operating conditions, each of the options is more preferable. Fuses are implemented in allstores of related products and are notable for their low cost. Fast overvoltage response provides reliable protection for highly sensitive devices.
Besides being resettable, the 110kV air circuit breaker has many other positives. For example, you can immediately identify the reacting device and quickly bring it to work.
Negative sides
The main disadvantage is the costly installation and subsequent repair of air circuit breakers. They are also characterized by a slower response speed for exceeding the rated current, because of this there is a possibility of damage to electronic devices. In addition, they are sensitive to mechanical stress and vibration.
Because the air circuit breaker and the fuse have different functions, they cannot be interchanged. In order to decide which device you need, you should contact the professionals, they will help you choose the best option for the existing electrical network.
Additional protection
In order to prevent damage to devices caused by power surges, network surge protection is used. There are two options for mounting such devices: on a special rail in an electrical cabinet when used for a group of energy consumers or locally at a specific device.
Such devices make it possible to filter emergency power surges in the external network and block high-power flows. In spite ofthe fact that the voltage peaks do not reach the energy consumers, the current flow remains at the same level. The latest electronic circuits ensure long run times and fast response times. Network protection due to electronic processors reacts to exceeding parameters in thousandths of a second.
Efficiency
Today, various types of air circuit breakers have become more perfect and functional, this has been achieved by making the following additions:
- Generator sets use a forced cooling circuit.
- Quality materials and meticulous construction ensure great reliability and a long service life before the need for repair.
- Switching surges have acquired a limitation, the presence of which plays a special role for high voltage devices.
- Modular series layout provides the ability to create from identical modules of several series, characterized by a wide voltage range, to test and realize devices that are easy to manufacture, install and operate.
- Use control schemes with fast response and minimal time variation. Their main task is to ensure the operation of devices for a significant excess of voltage and disconnection during a half-cycle. Also, due to them, devices with synchronous switching on and off function.
- Elements for extinguishing the arcplaced in compressed air. This achieves high throughput characteristics for rated voltage, reliable insulation of gaps between contacts, fast response and switching properties. Most often, the air pressure is in the range of 6-8 MPa.
