The principle of operation of the circuit breaker: types and purpose of the device, the functionality of the machines

In the article you will learn about the device and the principle of operation of the circuit breaker. Today, such protection against short circuits and overloads can be found in every home and in production. The so-called plugs, which, in fact, are made in the same way as the circuit breakers, have gone into oblivion. And even the principle of operation is similar for them, but it’s not very convenient to use it - you can’t put such a jam on the din rail.

And what can we say about fusible inserts - fuses, in which a short wire burns out during a short circuit. Such can be found only in transformer substations. And then they use fusible inserts that are filled with sand. In low-current circuits, so to speak, exclusively circuit breakers are used. Types and device will be considered in the article. And start with a description of the operation of the machines that are used most often in everyday life.

Normal operation

So, let's look at the device and the principle of operation of the circuit breaker. He has several modes of operation, each will be considered separately. In normal mode, a current that is less than or equal to the rated current flows through the circuit breaker. In this case, the supply voltage is supplied to the upper terminal, which is connected to the fixed contact. From the last, the current goes to the movable contact, then through a flexible copper conductor to the solenoid. Further, the current from the solenoid enters the release (thermal relay) and then to the terminal located below. It is she who connects with consumers of electricity.

Emergency operating modes

The principle of operation of an AC circuit breaker is such that in an emergency (overload or short circuit), the protected circuit is switched off. The free trip mechanism starts to work, it is driven by a special release (usually electromagnetic or thermal are used in structures). Let's look at the features of both types of releases.

Thermal is a bimetal plate that consists of two layers of alloys that have different coefficients of thermal expansion. When the current passes through the plate, it heats up and it bends in the direction on which the metal with the lowest coefficient is located. When the value of the current exceeds the permissible values, the bend becomes such that it is sufficient to actuate the entire trip mechanism. This opens the circuit.

Electromagnetic releases consist of a solenoid with a core (movable), which is held by a spring. When the maximum current is exceeded, a field begins to be induced in the coil. Under its action, the core begins to retract into the solenoid, while the spring is compressed. At the same moment, the release starts to trip. In normal mode, the coil also induces field guidance, but it has a small force, it is not enough to compress the spring.

Overload mode

Overload mode is when the current consumed by the load connected to the machine becomes higher than the rated value of the device. In this case, the current that passes through the release causes heating of the plate from bimetal, which leads to an increase in its bend. This causes the trip mechanism to trip. At this moment, the machine turns off and the circuit opens.

Thermal protection does not work instantly, since it takes some time to heat the plate. And it varies depending on how much the rated current is exceeded. The time interval can vary from a couple of seconds to an hour. The delay will allow you to get rid of a power outage with a short and random increase in current. Often, such excesses can be observed when starting the electric motor.

Tripping current

The minimum current value at which the thermal release is required to operate is regulated by a special screw at the factory. The value is about one and a half times higher than the nominal value that is indicated on the switch case. As you can see, the principle of operation of the circuit breaker release is not very complicated. But the current strength at which the thermal protection is triggered is also greatly affected by the temperature of the environment.

If the room is hot, then heating and bending of the bimetallic plate will begin to occur at a low current value. And if it is cold in the room, then the thermal release will start to work at a higher current. Therefore, the same circuit breaker with a bimetallic plate will operate differently in winter and summer. This does not apply to machines with electromagnetic trip units.

Overload in electrical circuits

It is worth noting that the principle of operation of a DC circuit breaker is approximately the same as a similar device operating on alternating current. The bottom line is that when the permissible load is exceeded, the plate heats up and the circuit is disconnected. What could be causing the overload? The most common reason is the connection of a large number of consumers who have more power than the calculated one.

If you simultaneously connect several consumers to the machine - an electric kettle, a refrigerator, an iron, a washing machine, an air conditioner, an electric stove - it is quite possible that the trip will work. Even if you use a circuit breaker with a rated current of 16 A, it may trip. It all depends on how much power consumers have.

If a frequent shutdown occurs, then you need to decide which electrical appliances you can refuse for a while. Should I turn on the electric stove and the washing machine at the same time? Knowing the purpose and design of circuit breakers, you can, of course, install a device with a large value of the rated current. But here we should expect a catch from the wiring of the house and input - will they withstand a large load?

Short circuit mode

And now let's look at one of the "main" operating modes - with a short circuit. You know the general structure and principle of operation of the circuit breaker in overload mode. But a special case is a short circuit mode. The machine works a little differently. The current increases to infinity, the insulation of the wiring can melt. To prevent this from happening, you need to instantly open the circuit.

It is against short-circuit that the electromagnetic release helps to protect. Earlier we talked about what elements this circuit breaker assembly consists of. When the current increases several times, then the magnetic flux begins to increase in the winding. Under its action, the core is retracted, the spring is compressed. In this case, the trigger is pressed, which is located in the release mechanism. And the power is interrupted, as the power contacts instantly open.

An electromagnetic release is a device that can protect against short-circuit and fire of electrical wiring. Protection works literally in hundredths of a second, therefore, the wiring does not have time to warm up to a dangerous temperature.

Opening the power contacts

It should be noted that a very large current flows through the power contacts. And when they open, an arc forms, it has a very high temperature - about 3000 degrees. To protect contacts and other components from damage, one small element is introduced into the structure - the arcing chamber. This is a lattice of several metal plates isolated from each other.

In the place where the contacts open, an arc appears. And one of its edges begins to move along with that contact, which disengages. And the second edge of the arc, as it were, slides along a fixed contact, after which it passes to a conductor connected to it. This conductor connects to the arcing chamber. Then the arc begins to crush on the plates, gradually weakens, and then completely goes out.

If you look closely at the VK-45 circuit breaker (the principle of its operation is discussed in our material), you can see that there are small holes below, it is through them that the gases that appear during combustion leave. If the machine has shut down due to the operation of the electromagnetic release, then you cannot turn it on until you eliminate the cause of the short circuit. As for the thermal release, you can restart the machine after the bimetallic plate has cooled.

How do air circuit breakers work?

Above, we examined devices that are used in everyday life and in production. But it is worth considering the principle of operation of automatic air circuit breakers - this is a completely different category of devices. They are classified by the type of air movement:

1. Transverse.
2. Longitudinal.

Air vending machines can have a large number of contact breaks, it all depends on what voltage they are designed for. To facilitate arc extinction, a resistance is connected to the contacts as a shunt.

An arcing chamber is a set of partitions that break the arc into small components. That is why the arc cannot flare up and it goes out quickly enough. High-voltage circuit breakers operating with compressed air are distinguished by the fact that they either have a separator or not. If the design has a separator, then the power contacts are connected to the pistons. The result is a single mechanism. The separator is connected in series with the contacts of the arc damper.

The arrester separator and contacts are the first pole of the machine. When a shutdown signal is applied, the mechanical pneumatic valve is triggered. He opens the pneumatic drive, and the air begins to act on the contacts of the arc damper. The contacts open, and the arc is extinguished with compressed air. After this, the disconnector also disconnects. It is worth noting that it is necessary to clearly adjust the air supply so that its amount is enough to extinguish the arc.

Automation classification

All high-voltage air circuit breakers can be divided into several groups:

1. Networked - operate at voltages above 6 kV, can be used in AC circuits to turn off and on consumers in normal modes (non-emergency). And also to disconnect the load when a short circuit occurs.
2. Generator sets - operate in electric networks with a voltage of 6-24 kV for connecting generator sets. Can withstand significant inrush currents. There is a mode of operation during short circuit.
3. For use in electrothermal installations - they have a voltage range of 6-220 kV. They work both in regular and emergency modes.
4. Special purpose machines - such devices are available only on order, there are no serial samples. They are made taking into account all the features of operation.

Classification by type and location of the air injection mechanism:

1. Support type constructions.
2. Outboard.
3. Built in complete switchgears.
4. Roll-out type.

Pros and cons of air vending machines

Among the advantages are the following:

1. They have been using such devices for a long time, so there is plenty of experience in their operation and repair.
2. More modern appliances (e.g. SF6) are not repairable.

But there are also disadvantages, for example:

1. You must have additional pneumatic equipment or a compressor.
2. When disconnected (especially during an emergency) it makes a lot of noise.
3. To install, you need a large space - the device has rather large dimensions.
4. Do not install in dusty and humid rooms. Therefore, additional measures have to be taken to reduce dust and humidity.

Differential automatic machine - what is it?

And finally, we will deal with the principle of the differential circuit breaker. This is a protection device that, in the event of an accident, disconnects both zero and phase immediately. The instrument functions include:

1. Tracking the short circuit current, as well as disconnecting the circuit when it appears.
2. Circuit disconnection when exceeding the permissible load.
3. Are there leakage currents? In the event that someone touches the exposed wires, current leakage occurs. The differential machine is turned off.

In fact, this device combines two devices - a simple circuit breaker and an RCD. The main plus is that your safety and wiring are always protected (of course, if everything is done according to the rules). You can also highlight another plus - there is no need to install an RCD. In addition, the instrument takes up little space in the shield. And to connect the device to the mains is not difficult.

But there are also disadvantages. In particular, on some models there are no flags, so it is difficult to immediately determine the cause of the operation. The second drawback is that if one half of the device fails, you will have to change the entire device completely. It is impossible to repair it. And the main drawback is the cost. It is significantly higher than that of an RCD and a conventional machine. Therefore, before setting up differential switches, decide if you need it. It is possible that it will be easier to put an RCD and a regular machine.