The air circuit breaker is a switching mechanical device that provides arc extinction using compressed air, and disconnecting, conducting, and turning on currents when the circuit condition is established. It is used to prevent short circuits and overloads in electrical installations, as well as in the management of electrical circuits. Some units are equipped with an additional protection function against critical voltage drops and other situations.
Description
Certain requirements are imposed on devices of this type, including ensuring safe continuous use and reliable protection against overloads and short circuits in the network. The performance 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 of vibration loads and frequent switching. Power consumers are under the electrodynamic and thermal effects of the circuit breakers, due to this, technological losses are minimized and the service life is increased.
Automatic air circuit breakers simultaneously control and protect the network. They are classified into several types according to the response time, which is allocated to opening the 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 rectangular, oval or round tank. Oil air circuit breakers were invented at the end of the last century and acted as circuit breakers in circuits characterized by high voltage. Through their cover insulators with fixed contacts are passed, fixed at both ends. Using an insulating rod, the drive unit is connected to a movable contact, which, in turn, is located between two unipolar fixed contacts. They are completely coated with transformer oil, which fills the tank 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 housing. The circuit breakers used for low voltage are fixed at the installation site using a DIN rail. Wiring is connected to the screw elements, and using the lever, the device is turned off and on. The housing is supported on the rail by means of a special latch - so the device can be quickly removed by first pushing it away. Fixed and movable contacts are necessary for the circuit switching process. A spring is used in the movable member to enable contact separation. This action can be performed by a magnetic or thermal splitter.
Thermal splitter
The bimetallic plate, which the thermal type splitter consists of, is heated by flowing voltage. The splitting mechanism occurs after the plate is bent, caused by the passage of current with a voltage above the set value. The current properties directly affect the response period, which can be within an hour. The element is triggered by the voltage set during production. The VNV air circuit breaker can be used immediately after the plate reaches normal temperature, which is not typical for a float fuse.
Magnetic splitter
The mechanism of action of the magnetic device is driven by a movable core. A splitter of this type is a solenoid, through the winding of which a current passes through the switch, when the nominal value is exceeded, the core begins to retract. The magnetic form has the property of instantaneous response, which cannot boast of a thermal, but the reaction occurs only if the threshold is significantly exceeded. Several varieties are used that have varying degrees of sensitivity.
In the process of splitting, the probability of the appearance of an electric arc. To prevent this, an arcing lattice is placed next to the contacts, and the elements themselves are made in a special form.
Kinds
An air circuit breaker can have various characteristics and features, according to which it is divided into certain types:
- with the possibility of current limitation and without it;
- the pole of the device depends on the number of poles available;
- with zero, independent or maximum voltage splitter;
- without contacts and with available free contacts for secondary networks;
- the exposure properties of the period of the current splitter can be different: for example, devices may have an exposure having an inverse dependence on voltage, independent of voltage, or it may be absent; a variant that combines all the properties is also possible;
- air circuit breakers, the device of which has a universal, combined (lower clamps with rear connection, and upper with front) and front connection;
- with spring drive, motor or manual.
Extinguishing
The design can have from one to four poles, while in any case there are auxiliary contacts, a splitter, a splitting device, an arc extinction system and the main contact system. It can be one-stage (in the case of ceramic-metal elements), two-stage (arcing and main contacts) and three-stage (in addition to arcing and main, intermediate contacts are added).
The system for extinguishing the arc can be performed with special arcing gratings in the chambers or have cameras with small gaps. For operation at high voltage, combined types are used that combine two options for extinguishing the arc.
Features
Any VVB air circuit breaker has a set limit value for short circuit voltage, if there is a current above the existing parameter, there is a chance of welding or burning of the contacts, and as a result, breakdown of the device. It can be carried out in a retractable or stationary version, and have a motor or manual drive. The drive may have pneumatic, remote, electromagnetic and other actions and is intended to turn the device off and on.
A relay with a direct mechanism of action acts as a splitter. Thermobimetal or electromagnetic parts in this case provide shutdown if the primary network is characterized by a lack of current, as well as during overload and short circuit. The splitting design includes breaking springs, rocker arms, latches and levers. In addition to tripping a circuit breaker, it is used to prevent the possibility of closing a circuit.
Excerpt
The shutdown process may be characterized by the presence of exposure or 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. So, high-speed, selective and standard switches have gained distribution. The last two options do not have the possibility of current limitation. In selective devices, network protection is carried out using installed circuit breakers with different response speeds: the consumer has a minimum value, gradually this parameter increases to the power source.
Circuit breaker and fuse
Overloads in the network can lead to a fire or at least to damage to the installed electrical equipment. To prevent such situations, an air switch for the STP 100 and a fuse are used, the mechanism of action 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, melted by excessive heating. The air circuit breaker uses a special mechanism that responds to critical voltages, and it is enough to activate the device after reacting, while 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 sold in all related products stores and are not expensive. Rapid response to overvoltage provides reliable protection for devices with high sensitivity.
In addition to the possibility of reset, the 110 kV air circuit breaker has many other positive aspects. For example, you can immediately identify the reacted device and quickly bring it to work.
Negative sides
The main disadvantage is the costly installation and subsequent repair of air circuit breakers. They also have a lower response speed for exceeding the rated current, because of this there is a likelihood of damage to electronic devices. In addition, they are sensitive to mechanical stress and vibration.
Given that the air circuit breaker and fuse are designed for various functions, they cannot replace each other. In order to determine which device is necessary, it is worth contacting professionals, they will help you choose the best option for your existing electrical network.
Additional protection
To prevent damage to devices caused by power surges, network protection against voltage peaks is used. There are two possible mounting options for such devices: on a special rail in an electrical cabinet when used for a group of power consumers or locally at a specific device.
Such devices allow filtering emergency power surges in the external network and block high-power flows. Despite the fact that voltage peaks do not reach energy consumers, the current flow remains at the same level. The latest electronic circuits provide a long period of operation and a fast response speed. Network protection through electronic processors responds to excess parameters in thousandths of a second.
