Air circuit breaker: principle of operation and advantages

The air circuit breaker is a switching mechanical device providing arc quenching with the help of compressed air, and switching off, conducting, switching 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 function to protect against a critical drop in voltage and other situations.

Description

To devices of this kind there are certain requirements, among them the provision of safe long-term 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 different temperature and humidity conditions, with vibration 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 extended.

Automatic air switches simultaneously control the network and protect it. They are classified into several types according to the response time, which is allocated to the opening of the contacts from the moment of the signal:

• Selective;
• Standard;
• Speedy (have a current-limiting function).

Oil devices

Such products are made in the form of a container of rectangular, oval or round shape. Oil air switches were invented at the end of the last century and acted as a switch in circuits characterized by high voltage. Insulators with fixed contacts, fixed at both ends, are passed through their cover. With the help of an insulating rod, the drive device is connected to a movable contact, which in turn is located between two unipolar fixed contacts. They are completely covered with transformer oil, which fills the tank to a certain level. The air cushion occupies the space between the lid and the oil surface.

Mounting

The design of the device is in a dielectric casing. Automatic air circuit breakers, Used for a small voltage, are fixed to the installation site using a DIN rail. The wiring elements are connected to the wiring, and by means of the lever, the device is switched off and turned on. The case is held on the rail by means of a special latch - so the device can be removed quickly, before pushing it aside. The stationary and movable contacts are necessary for the circuit switching process. The movable element uses a spring to enable the contacts to be disengaged. This action can be performed by a magnetic or thermal splitter.

Thermal splitter

The bimetallic plate, from which the thermal-type splitter consists, is heated by the flowing voltage. The splitting mechanism occurs after the plate is bent due to the passage of a current with a voltage higher than 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 air vent switch can be used immediately after the plate reaches normal temperature, which is not typical for the float fuse.

Magnetic splitter

The mechanism of action 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 be drawn in. The magnetic form has the property of instantaneous triggering, which can not boast of thermal, but the reaction occurs only in the case of a significant excess of the threshold set. Several varieties are used, which have a different degree of sensitivity.

In the process of splitting, a probability arises of the appearance of an electric arc. To prevent this, an arc interrupter is placed next to the contacts, and the elements themselves are executed in a special form.

Kinds

The air circuit breaker can have different characteristics and features, which are divided into certain types:

• With the possibility of current limitation and without it;
• The polarity of the device depends on the number of poles available;
• With a zero, independent or maximum voltage splitter;
• Without contacts and with available free contacts for secondary networks;
• The properties of the period of the current splitter may be different: thus, the devices may have an exposure having an inverse voltage dependence independent of the voltage, or it may be absent; Also an option is possible that combines all the properties;
• Air circuit breakers, the device of which is universal, combined (bottom clips with rear connection, and upper ones with front) and front connection;
• With a spring drive, motor or manual.

Arc suppression

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 suppression system and a basic contact system. It can be single-step (in the case of using metal-ceramic elements), two-stage (arcing and main contacts) and three-stage (in addition to arc and main, intermediate contacts are added).

The system for damping the arc can be performed with special arc interrupters in the chambers or have chambers with small gaps. For operation at high voltage, combined views are used, combining two options for arc extinction.

Features

Any air circuit breaker BBB has a set short-circuit voltage limit value, if there is a current above the available parameter, there is a probability of welding or burning of contacts, and as a consequence, breakdown of the device. It can be performed in a retractable or stationary version, and have a motor or manual drive. The actuator may have a pneumatic, remote, electromagnetic and other action and is designed to turn the device off and on.

As a splitter is a relay with a direct mechanism of action. Thermobiometallic or electromagnetic parts in this case provide a shutdown if the primary network is characterized by a lack of current, as well as during overload and short circuit. The splitting design includes disconnecting springs, rocker arms, latches and levers. In addition to disconnecting the circuit breaker, it is used to prevent the possibility of switching on the short circuit.

Excerpt

The shutdown process can be characterized by the presence of an exposure or its absence. The type of the switch, in particular the speed of its response, depends on the time interval during which the existing value and the divergence of the contacts occur. Thus, the distribution of high-speed, selective and standard switches has been acquired. The last two options have no possibility of current limitation. In selective devices, the protection of networks is performed by means of installed switches having different speed of operation: the minimum value is assigned to the consumer, gradually this parameter increases to the power source.

Switch and fuse

Overloads in the network can lead to a fire or at least to damage the installed electrical equipment. To prevent such situations, an air circuit breaker is used for the STP 100 and a fuse, the mechanism of which is to interrupt the current, but each has its own characteristics. The main part of the fuse is represented by a metal element, melted under excessive heating. The air circuit breaker uses a special mechanism that responds to the critical voltage, and it is enough to activate the device after the reaction, 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 sold in all stores of related products and are of low cost. Rapid response to voltage surges provides reliable protection for devices that are highly sensitive.

In addition to the possibility of a 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 costly installation and subsequent repair of air circuit breakers. They also have a lower response speed to exceed the rated current, because of this, there is a possibility of damage to electronic devices. In addition, they are distinguished by their sensitivity to mechanical influences and vibrations.

Given that the air circuit breaker and fuse are designed for different functions, they can not replace each other. In order to determine what device is necessary, it is worth to turn to professionals, they will help to choose the best option for the existing electrical network.

Additional protection

To prevent damage to devices caused by voltage surges, network protection against voltage peaks is used. There are two possible 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 certain device.

Such devices allow the filtering of emergency power surges in the external network and blocking high-power flows. Despite the fact that energy peaks do not reach the 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. The protection of the network due to electronic processors responds to the exceeding of parameters in thousandths of a second.

Efficiency

Today, various types of air circuit breakers have become more sophisticated and functional, this has been achieved by introducing the following additions:

• The generator circuit uses a forced cooling circuit.
• Qualitative materials and careful execution of structural elements ensured greater reliability and a long period of use before the need for repair.
• Switching overvoltages have acquired a limitation, the presence of which plays a special role for high voltage devices.
• The modular layout of the series provides the ability to create from identical modules of several series, characterized by a wide voltage range, to test and implement devices that differ in simple manufacture, installation and subsequent operation.
• Use of control schemes with rapid response and minimal time variation. Their main task is to ensure the operation of the devices for a significant excess of voltage and shutdown during the half-cycle. Also, due to them, devices with synchronous switching on and off function.
• Elements to extinguish the arc are placed in compressed air. This achieves high throughput characteristics at rated voltage, reliability of isolation of gaps between contacts, rapid response and switching properties. Most often, the air pressure is in the range of 6-8 MPa.