The principle of operation of the circuit breaker. Electric machines. Types and work. Characteristics. Differential machine - what is it

Installation of circuit breakers

Automatic circuit breakers in electrical circuits are devices that automatically turn off the power supply by opening contacts. The contacts open in the event of a short circuit, excess current load in excess of the calculated one, and in the event of abnormal leakage currents in the network. Circuit breakers also serve as a switch for manually opening the network.
In turn, automatic protection devices are divided into the following groups:

• modular fuses (single use);

• electromechanical devices ( reusable), reacting to currents above the operating current and to heating of the wires due to the excess of the rated load currents, which replaced the fuses.

• relatively recent devices protective shutdown(RCD) that respond to the appearance of a leakage current, which should not be in a normal network. They are used to protect people who are at risk of electric shock, as well as to protect against the risk of fire in case of violation of the insulation of wires and contacts;

Recently, combined devices have also appeared that combine a circuit breaker and an RCD, the so-called differential automata.

In this article we will consider circuit breakers, features of their device, selection and installation.

The device of automatic protection

• 1. A modern circuit breaker consists of one (one phase) to four (three phases with a neutral wire) pairs of spring-loaded contacts enclosed in a plastic case. Contacts in the closed state are held by a latch. To close the contacts, a lever is brought out to the outside. By pressing the lever, overcoming the resistance of the opening spring, we close the contacts, and they are fixed in the closed state by a latch.

• 2. To open the contacts, simply move the latch and the opening spring attached to the break contact(s) will open the circuit. The electric arc that occurs when the contacts open is extinguished by a special extinguishing device. The latch is pushed back to open, firstly, by a solenoid connected in series in the circuit at a certain

the value of the current flowing through it, and, secondly, a bimetallic plate, also connected in series, bending when heated and shifting the latch to open. You can also open the contacts manually by pressing the button, which is mechanically connected to the latch. Contacts (terminals) for connecting to wires are located above and below. The device is fastened by snapping onto the so-called DIN - rail (DIN - Deutsche Industri Normen - German industry standards) DIN - rail is equipped with power input shields, these shields are also equipped with electricity meters. The machine is mounted on a DIN rail by simple snapping, and to remove it, you need to move a special fixation frame with a screwdriver.

Automatic circuit breaker protects the power grid and devices connected after it.
In the event of a short circuit, the current flowing through the solenoid increases many times, the solenoid retracts the core connected to the latch and the circuit opens. If the current load increases (before the solenoid is triggered) and this causes excess heating of the wires, the bimetallic plate is triggered. Moreover, if the response time of the solenoid is about 0.2 seconds, then the response time of the bimetallic plate is about 4 seconds.

Rated current and instantaneous tripping current of the machine. Circuit breaker selection

The main characteristic when choosing a machine is the rated current, which is indicated on the marking of the machines. To understand its meaning, you need to know that any electrical network consists of so-called groups, each group forms an independent "loop", all loops are connected to the input wires in parallel, that is, independently. This is done, firstly, to increase the reliability of the electrical network and reduce the possibility of overloads, and secondly, with the help of groups, all current loads are equalized and reduced to some standard values, which allows you to save on wires - for each group, its own wire section is selected.
As a rule, one group consists of lighting devices, the other - sockets, the third - energy-consuming electric stoves, washing machines etc. For each group, when designing a power supply network, the rated current is determined, based on which the cross section of the wires is calculated. It should be noted that the rated current of a group of consumers is calculated not by simply summing up the powers of consumers, but taking into account the probability of simultaneous inclusion of several consumers in the network. For this, the so-called probability coefficient is introduced, calculated by a special method.

Based on the calculated rated currents of each consumer group, the required wire cross-section is calculated, and circuit breakers are selected (each group has its own circuit breaker). The automata are selected in such a way that, according to the known rated current of the group, the automaton with the nearest higher value of the rated current is selected. For example, with a rated current of a group of 15A, we select an automaton with a rated current value of 16A.

It must be understood that the circuit breaker does not operate when the rated current is slightly exceeded, but when the current in the network is several times higher than the rated current. This current is called the instantaneous trip current (as opposed to the bimetallic plate operation current) of the circuit breaker. This is the second parameter to consider when choosing a machine. By the magnitude of the instantaneous trip current, or rather by its relation to the rated current, the automata are divided into three groups, denoted with Latin letters AT; WITH; and D. (In the European Union, class A machines are also produced.) What do these letters mean?

Class B circuit breakers are designed for instantaneous tripping at currents above 3 and up to 5 rated currents.
Class C, respectively, above 5 and up to 10 rated currents.
Class D - above 10 and up to 20 rated currents.

What are these classes for?

The fact is that there is such a thing as the starting load current, which for some consumers can exceed the rated operating current several times. For example, any electric motors at the moment of start-up (while the motor rotor is stationary) operate practically in short circuit mode, that is, they load the network only with active resistance copper windings, which is small. And only when the motor rotor is gaining momentum, reactance appears, reducing the current. The starting currents of electric motors are 4-5 times higher than the nominal (working currents). (True, the duration of the flow of starting currents is small, the bimetallic plate of the circuit breaker will not have time to work).

If we use class B automata to protect motors, we will get a false operation of the automaton at the starting current every time the engine is started. And we may not be able to start the engine at all. That is why class D circuit breakers must be used to protect engines.

Class B - for the protection of lighting networks, heating appliances, where starting currents are minimal or absent. Accordingly, class C is for devices with average starting currents.

Naturally, to select a circuit breaker, you need to take into account the voltage, type of current, working environment, etc., but all this does not need special comments.

Installation and installation of circuit breakers

We note right away that the installation and installation of circuit breakers must be carried out by qualified personnel who have received appropriate training and have permission to carry out such work. This is a safety requirement set out in the PUE.

Installation and installation of machines are made on the basis of a circuit diagram, which must be attached in a conspicuous place inside the power supply input panel. circuit diagram specific installation is developed on the basis of typical schemes. As a rule, the following equipment is located in the input shield:

1. A switch is installed at the entrance - a knife switch, a batch switch or a general circuit breaker (circuit breakers are installed in modern shields). This is done in order to be able to electric installation work inside the shield by simply disconnecting the entire shield from the power supply.
2. Next, an electric meter is connected, which is sealed to protect against all kinds of "craftsmen" to "save" electricity.
3. After the meter, the supply wires branch into groups, and at the input of each group, its own circuit breaker is placed, and after it, an RCD (residual current device). RCDs are selected so that their rated current exceeds the rated current of the circuit breaker. Further, the wires go out of the shield to the groups of consumers, to each group with its own separate cable.

Circuit breakers and RCDs are mounted on a DIN rail. The installation itself is not difficult, you just need to note that to facilitate installation, there are ready-made jumper strips or jumpers - this is for supplying, for example, to all machines phase voltage, the input wire is connected to the first machine, and to the rest - using jumpers. Also, common clamping strips are installed in the shield for zero wires and for ground wires. All this greatly simplifies installation.

Circuit breakers are devices that are designed for the protective shutdown of circuits of constant and alternating current in cases of short circuit, current overload, voltage drop or its disappearance. Unlike fuses, circuit breakers have a more accurate tripping current, can be reused, and also with a three-phase design, when a fuse is triggered, one of the phases (one or two) can remain energized, which is also emergency mode work (especially when supplying three-phase electric motors).

Circuit breakers are classified according to their functions, such as:

• Automatic machines of the minimum and maximum current;
• Undervoltage circuit breakers;
• reverse power;

We will consider the principle of operation circuit breaker on the example of a maximum current machine. Its diagram is shown below:

Where: 1 - electromagnet, 2 - armature, 3, 7 - springs, 4 - axis along which the armature moves, 5 - latch, 6 - lever, 8 - power contact.

When the rated current flows, the system operates normally. As soon as the current exceeds the allowable value of the setting, the electromagnet 1 connected in series in the circuit will overcome the force of the retaining spring 3 and retract the armature 2, and turning through the axis 4, the latch 5 will release the lever 6. Then the disconnecting spring 7 will open the power contacts 8. Such an automaton is turned on manually.

At present, automatic machines have been created that have a trip time from 0.02 - 0.007 s for trip currents of 3000 - 5000 A.

Designs of circuit breakers

There are quite a few various designs circuit breakers of both alternating circuits and circuits direct current. Recently, small-sized automatic machines have become very widespread, which are designed to protect against short circuits and current overloads of household and industrial networks in installations for currents up to 50 A and voltages up to 380 V.

chief protective agent in such switches are bimetallic or electromagnetic elements that operate with a certain time delay when heated. Automatic machines in which an electromagnet is present have a rather high speed, and this factor is very important in case of short circuits.

Below is a plug machine for a current of 6 A and a voltage not exceeding 250 V:

Where: 1 - electromagnet, 2 - bimetallic plate, 3, 4 - on and off buttons, respectively, 5 - release.

A bimetallic plate, like an electromagnet, is connected in series to the circuit. If more than the rated current flows through the circuit breaker, the plate starts to heat up. With a prolonged flow of excess current, plate 2 is deformed due to heating, and acts on the release mechanism 5. If a short circuit occurs in the circuit, electromagnet 1 instantly draws in the core and this also acts on the release, which opens the circuit. Also, this type of machine is turned off manually by pressing button 4, and the inclusion is only manual by pressing button 3. The release mechanism is made in the form of a breaking lever or latch. principled circuit diagram machine is shown below:

Where: 1 - electromagnet, 2 - bimetallic plate.

The principle of operation of three-phase circuit breakers is practically no different from single-phase ones. Three-phase circuit breakers are supplied with special arc chutes or coils, depending on the power of the devices.

Below is a video detailing the operation of the circuit breaker:

For an electrician, switching equipment is one of the main devices that you have to work with. Circuit breakers carry both switching and protective roles. Not a single modern electrical panel is complete without automatic machines. In this article, we will look at how the circuit breaker is designed and works.

Definition

A circuit breaker is a switching device designed to protect cables from critical currents. This is necessary in order to avoid damage to the conductive cores of wires and cables in the event of phase-to-phase faults and ground faults.

Important: The main task of the circuit breaker is to protect cable line from the consequences of the flow of short circuit currents.

The main characteristics of circuit breakers are:

Rated current (1, 2, 3, 4, 5, 6, 8, 10, 13, 16, 20, 25, 32, 35, 40, 50, 63, 80, 100, 125, 160, 250, 400, 630 , 1000, 1600, 2500, 4000, 6300);

Switching voltage;

Time current characteristic.

The machines are most widely used in household and industrial power networks with a voltage of 220/380 volts. Voltages are given for domestic electrical networks. Abroad, they may differ. High voltage lines use relay circuits and current transformers. reflects after what period of time and at what value of current relative to the nominal value the opening of its contacts will occur. An example of it is shown in the figure below:

Principle of operation

The circuit breaker (AB) is a switching device that contains two types of protection:

Electromagnetic release.

Thermal release.

Each of them performs the same job - opening power contacts, but with different conditions. Let's consider them in more detail.

When currents flow through the machine below the nominal value, its contacts will be closed indefinitely. But with a slight excess of current, the thermal release, represented by a bimetallic plate, will open them.

The greater the current flowing through the contacts of the circuit breaker, the faster the heating of the bimetallic plate will occur - this is described during the current characteristic and is indicated by the speed of the machine (a letter near the rated current in the marking). Depending on how overloaded the machine is with the current, the time of its shutdown depends, it can be tens of minutes, or it can be units of seconds.

The electromagnetic release is activated when rapid growth current. The magnitude of the current of its operation is orders of magnitude higher than the rated current.

This raises the question: "So why does the machine need two protections, if you can simply design it so that it turns off immediately when the rated current is exceeded?"

There are two answers to this question:

1. The presence of two protections increases the reliability of the system as a whole.

2. When connecting devices to the circuit breaker, the current of which changes during start-up and operation, so that there is no false positives. For example, for electric motors, the starting current can be ten times higher than the rated current, and also during their operation, short-term overloads on the shaft can occur (for example, lathe). Then, during a protracted start, the machine will also knock out.

Device

The circuit breaker consists of:

Cases (in the figure - 6).

Terminals for connecting conductive wires (in the figure - 2).

Power contacts (in the figure - 3, 4).

Arc chute (in the figure - 8).

Levers connected to buttons or checkboxes to turn it on and off (closing and opening contacts) (in the figure - 1 and what it is connected to).

Thermal disconnector (in the figure - 5).

Electromagnetic disconnector (in the figure - 7).

The number 9 indicates the latch for mounting on a DIN rail.

To the terminals (usually top, in practice it does not have special significance) is connected to the power supply, the load is connected to the terminals on the opposite side. The current passes through the power contacts, the coil of the electromagnetic disconnector, the thermal disconnector.

Electromagnetic protection is made in the form of a coil of copper wire, it is wound on a frame, inside of which there is a movable core. The coil contains from several units to a couple of tens of turns, depending on its rated current. In this case, the lower the rated current, the more turns and the smaller the cross section of the coil wire.

When current flows through the coil, a magnetic field is formed around it, which affects the movable core inside. As a result, he extends and pushes the lever, as a result of which the power contacts open. If you look at the figure, then the lever is below the coil, and when its core is lowered, the mechanism is activated.

Thermal protection is needed for prolonged overcurrent. It is a bimetallic plate that bends to one side when heated. When a critical state is reached, she pushes the lever, and the contacts are disconnected. The arc chute is needed to extinguish the arc that occurs due to the opening of the circuit under load.

The process of arc formation depends on the nature of the load and its magnitude. In this case, when switching off an inductive load (electric motor), stronger arcs occur than when switching a resistive load. The gases formed as a result of its combustion are discharged through a special channel. This significantly increases the service life of power contacts.

The arc chute consists of a set of metal plates and dielectric covers. Conclusion Previously, circuit breakers were repaired, and it was possible to assemble one normally functioning one from several. It was possible to adjust and replace the power contacts and its other components.

Currently, the machines are enclosed in a non-separable cast or assembled with rivets case. Their repair is impractical, complicated and will take a lot of time. Therefore, the machines are simply replaced with new ones.

From the very beginning of the emergence of electricity, engineers began to think about the safety of electrical networks and devices from current overloads. As a result, many different devices, which are distinguished by reliable and high-quality protection. One of the latest developments has become electric machines.

This device is called automatic due to the fact that it is equipped with the function of turning off the power in automatic mode, in the event of short circuits, overloads. Conventional fuses after operation must be replaced with new ones, and the machines can be turned on again after the causes of the accident have been eliminated.

Such a protective device is necessary in any electrical network scheme. The circuit breaker will protect the building or premises from various emergencies:

• Fires.
• Electric shocks to a person.
• Electrical faults.

Types and design features

Need to know information about existing types circuit breakers in order to select the right device at the time of purchase. There is a classification of electric machines according to several parameters.

Breaking capacity

This property determines the short circuit current at which the machine will open the circuit, thereby turning off the network and the devices that were connected to the network. According to this property, automata are divided into:

• Automatic machines for 4500 amperes are used to prevent malfunctions in the power lines of old residential buildings.
• At 6000 amperes, they are used to prevent accidents during short circuits in the network of houses in new buildings.
• At 10,000 amps, used in industry for protection electrical installations. A current of this magnitude can be formed in the immediate vicinity of the substation.

The operation of the circuit breaker occurs during short circuits, accompanied by the occurrence of a certain amount of current.

The machine protects the wiring from damage to the insulation by high current.

Number of poles

This property tells us about most wires that can be connected to the machine to provide protection. In the event of an accident, the voltage at these poles is turned off.

Features of machines with one pole

Such electric machines are the simplest in design, and serve to protect individual sections of the network. Two wires can be connected to such a circuit breaker: an input and an output.

The task of such devices is to protect electrical wiring from overloads and short circuits of wires. The neutral wire is connected to the neutral bus, bypassing the machine. Grounding is connected separately.

Electric machines with one pole are not introductory, since when it is turned off, the phase breaks, and neutral wire still connected to power. It does not provide 100% protection.

Properties of automata with two poles

In cases where an accident requires a complete disconnection from the electrical network, use circuit breakers with two poles. They are used as input. In emergency cases, or in case of a short circuit, the entire electrical wiring turns off at the same time. This makes it possible to carry out repair and maintenance work, as well as work on connecting equipment, since complete safety is guaranteed.

Two-pole electric machines are used when it is necessary to have a separate switch for a device powered by a 220 volt network.

An automatic machine with two poles is connected to the device using four wires. Of these, two come from the power supply, and the other two come out of it.

Three-pole electric machines

In an electrical network with three phases, 3-pole machines are used. Grounding is left unprotected, and the phase conductors are connected to the poles.

A three-pole machine serves as an input device for any three-phase load consumers. Most often, this version of the machine is used in industrial environment for powering electric motors.

6 conductors can be connected to the machine, three of which are the phases of the electrical network, and the remaining three are coming from the machine, and provided with protection.

Using a four-pole machine

To provide protection three-phase network with a four-wire system of conductors (for example, an electric motor connected according to the "star" scheme), a 4-pole circuit breaker is used. He plays the role input device four-wire network.

It is possible to connect eight conductors to the device. On the one hand - three phases and zero, on the other hand - the output of three phases with zero.

Time-current characteristic

When devices that consume electricity and electrical network operate normally, normal current flows. This phenomenon also applies to the electric machine. But, in the event of an increase in current strength for various reasons above the nominal value, the automatic release trips, and the circuit breaks.

The parameter of this operation is called the time-current characteristic of the electric machine. It is the dependence of the time of operation of the machine and the ratio between the real strength of the current passing through the machine and the nominal value of the current.

The importance of this feature lies in the fact that smallest number false positives on the one hand, and current protection is carried out, on the other hand.

In the energy industry, there are situations when a short-term increase in current is not associated with an accident, and the protection should not work. It also happens with electric machines.

Time-current characteristics determine how long the protection will operate, and what current strength parameters will occur.

Electric machines marked "B"

Circuit breakers with a property marked with the letter "B" are capable of tripping in 5 to 20 s. In this case, the current value is up to 5 nominal current values. Such models of machines are used to protect home appliances, as well as all electrical wiring of apartments and houses.

Properties of machines marked "C"

Electric machines with this marking can turn off in a time interval of 1 - 10 s, at 10 times the current load. Such models are used in many areas, most popular for houses, apartments and other premises.

The meaning of the marking "D" on the machine

With this class, automata are used in industry and are made in the form of 3-pole and 4-pole versions. They are used to protect powerful electric motors and various three-phase devices. Their operation time is up to 10 seconds, while the operation current can exceed the nominal value by 14 times. This makes it possible to use it with the necessary effect to protect various circuits.

Electric motors with significant power are most often connected through electric machines with characteristic "D".

Rated current

There are 12 versions of automatic machines, which differ in the characteristics of the rated operating current, from 1 to 63 amperes. This parameter determines the speed at which the machine switches off when the current limit is reached.

The machine for this property is selected taking into account the cross-section of the conductors of the wires, the allowable current.

The principle of operation of electric machines

normal mode

At normal work the control lever of the machine is cocked, the current flows through the power wire at the top terminal. Next, the current goes to the fixed contact, through it to the moving contact and through the flexible wire to the solenoid coil. After it, the current goes through the wire to the bimetallic release plate. From it, the current passes to the lower terminal and further to the load.

Overload mode

This mode occurs when the rated current of the machine is exceeded. The bimetallic plate is heated by a large current, bends and opens the circuit. The action of the plate requires time, which depends on the value of the passing current.

The circuit breaker is an analog device. There are certain difficulties in setting it up. The tripping current of the release is adjusted at the factory with a special adjusting screw. After the plate has cooled down, the machine can function again. The temperature of the bimetal strip depends on the environment.

The release does not act immediately, allowing the current to return to its nominal value. If the current does not decrease, the release trips. Overload can occur due to powerful devices on the line, or connecting several devices at once.

Short circuit mode

In this mode, the current increases very quickly. The magnetic field in the solenoid coil moves the core, which activates the release, and disconnects the contacts of the power supply, thereby removing the emergency load of the circuit and protecting the network from possible fire and destruction.

The electromagnetic release operates instantly, which is different from the thermal release. When the contacts of the working circuit are opened, an electric arc appears, the magnitude of which depends on the current in the circuit. It causes destruction of contacts. To prevent this negative effect, an arc chute is made, which consists of parallel plates. In it, the arc fades and disappears. The resulting gases are discharged into a special hole.

Despite the variety of types of circuit breakers (automatic machines), many operate on similar principles and are built on the basis of a standard set of functional elements. In connection with the widespread use of modular-type automata (especially in household and low-voltage electrical networks), it is reasonable to study the operation of a circuit breaker using their example. An inexpensive single-pole automatic machine of the DEK brand of the VA-101-1 C3 type will act as a test sample.

The modular-type automatic machine externally is a device standardized in dimensions in a plastic case, having two or more input terminals (depending on the number of poles) for connecting power on one side (usually, from above) and connecting the load on the other (from below). On the front panel of the machine there is a control lever, with the help of which the machine (load) is switched on and off manually. On the sides of the case there are technological holes for installation additional devices, for example, contacts of the status of the machine, shunt trip and some others. From above, the machine has openings for access to the adjusting screw of the thermal release and the exit of the combustion products of the arc discharge. Mounting (fastening) of a modular machine in an electrical cabinet is carried out on the so-called DIN rail - a metal or plastic profile of a certain shape.

Mounting the machine on a DIN rail and removing it.

Windows for connecting additional devices to the machine.

DEC machine. View from above.
1 - opening for the exit of arc combustion products; 2 - hole with adjusting screw of the thermal release.

AT electrical circuit the machine is connected in series - to break the power supply circuit of the load (consumers). The operating principle of the circuit breaker is to control the force electric current through the machine and, if necessary, breaking the circuit (disconnecting the load) at a particular speed (delay), starting from the moment of exceeding the current and depending on the “severity” (multiplicity) of this excess.

Scheme of connecting a single-pole machine to the power supply circuit of an incandescent lamp.

The body of the modular machine, in most cases, is non-separable. To open it, for the purpose of studying, you will need to remove (drill and remove) all the rivets and divide the body into two parts. The housing elements are made of flame retardant plastic with sufficient (calculated) electrical insulating capacity. With inside half-shells have grooves and guides for installing the functional elements of the machine.

The process of opening the machine.

DEK circuit breaker inside.

The machine is completely disassembled.

The device of the circuit breaker with the signatures of its functional elements.

Arming and release mechanism - mechanical system of springs and levers, which performs two main functions: keeping the contacts in a closed state during normal operation, and, in the event of emergency, by the commands of the releases or the operator ( manual shutdown) quickly move the moving contact away from the fixed one.

The machine is on, the mechanism is cocked.

Electromagnetic release is an electromagnet with a movable core (anchor) that works like a pusher. When the current through the winding reaches a certain value, the armature presses on the trigger lever, which causes it to operate and disconnect the load. The number of turns of the coil and the section of the winding wire of the electromagnet are designed so as to operate only at relatively large excesses of the rated current of the machine (for example, during a short circuit), and also to withstand such excesses repeatedly.

The lower terminal, the coil of the electromagnetic release and the bimetal plate are connected by welding.

Anchor of the electromagnetic release in assembled (left) and disassembled (right) form.

When the anchor moves down in the direction of the red arrow, the trigger disengages (red circle).

When the armature moves down, it drags the moving contact with it, which helps the release mechanism to separate the contacts.

Thermal release- , bending in a certain direction when heated as a result of the passage of current through a special high-resistance conductor wound over it (bimetallic plate indirect heating). At a certain bending angle of the plate, its tip presses on the lever of the list mechanism - the machine turns off. Unlike an electromagnetic release, a thermal release is slower and cannot operate in a fraction of a second, however, it is more accurate and can be fine-tuned.

When the tip of the bimetallic plate is bent in the direction of the red arrow, the trigger mechanism disengages (red circle).

arc chute, which is available in the device of the circuit breaker, provides a quick extinguishing of the arc discharge, which can be formed when the contacts are opened. It is a set of metal plates located at a short distance from each other. Getting on the plates, the arc is divided, lured inside the arc chute and goes out. Arc combustion products and excess pressure are discharged outside through a special channel in the body of the machine.

The circuit breaker is designed and operates on the principle of constant monitoring of the strength of the electric current, it uses two detector-releases at once: electromagnetic and thermal. The first has high speed reaction, which is necessary for protection against rapidly growing overcurrents, the second - with accuracy and a certain delay in operation, which makes it possible to exclude false load shutdowns in case of short-term and small excess of current.