Rated current of the thermal release of the circuit breaker. The operating principle of a circuit breaker. Automatic with thermal and electromagnetic release. Electromagnetic release AV Types of circuit breaker releases

How does a circuit breaker work?

Normal operating mode of the machine at rated or low current. The operating current passes through the upper terminal of the machine, through the pendant contact, through the coil of the electromagnetic release, then through the thermal mechanism of the release and the lower terminal of the machine. When the current exceeds the nominal value, electromagnetic or thermal protection is triggered.

Varieties circuit breakers

In order to protect against overcurrent, the machine uses a thermal release as overload protection - this is a bimetallic narrow strip of plate assembled from two types of alloys that have different coefficients of thermal expansion.

The composite bimetallic plate is heated by the flowing current and bends towards the metal with a slight expansion. When the current is greater than the rated value, then over time the plate bends so much that this bending is enough for the thermal protection to respond. The time at which the release reacts depends on the degree of excess relative to rated current.

With a significant increase in current rating, thermal protection will turn off the circuit breaker faster than with a small excess of the rating. The second type of circuit breaker protection is triggered by a short circuit in the load - this is an electromagnetic release. It consists of copper coil with a metal core. Relative to the magnitude of the passing current, the electromagnetic field of the coil also increases, which magnetizes the steel core.

Demonstration of machine mechanisms

The magnetized core is attracted, overcoming the force of the spring holding it, pushes the mechanism electromagnetic protection and breaks contacts. The rated current and the current slightly higher are not enough to magnetize the core to trigger the release mechanism. A current short circuit creates magnetization of the core sufficient to turn off the machine in hundredths of a second or even less.

Protection of the machine under different overloads

Mechanism thermal release will not work with a small and short-lived current above the rated current. If the current duration is greater than the rated one, the thermal release will operate. The time it takes to turn off the machine by thermal protection can reach up to an hour.

Circuit breaker mechanisms

The time delay allows you not to turn off the circuit breakers in case of significant starting currents of the engine and short-term surges of current. The time-current characteristic of thermal releases also depends on the ambient temperature. At elevated temperatures, thermal protection will work faster than in the cold.

You can cause an overload by turning on several household appliances - a kettle, washing machine, air conditioning, electric stove. When overloaded, the machine turns off, but it is impossible to turn it on immediately; you need to wait for the bimetallic plate to cool down.

Operation of the machine during a short circuit

Large short circuit currents can melt electrical wiring or burn insulation. To save electrical wiring, use electromagnetic release. In case of short circuits, the mechanics of the electromagnetic release are triggered instantly, protecting the electrical wiring, and it does not have time to heat up.

However, when the contacts open, an electric arc with enormous temperature appears. An arc-extinguishing chamber is designed to protect against burnt contacts and destruction of the housing. Structurally, the chamber consists of an element with a set of thin copper plates with a small gap.

Electromagnetic and thermal protection of circuit breaker

An electric arc touching a set of plates through a copper wire connected to a contact breaks into pieces, cools down and disappears. When a short circuit occurs, gases are formed that escape through the holes in the chamber. To turn the machine back on, you need to eliminate the cause of the short circuit, or the machine will turn off again.

The culprit of the short circuit can be determined by sequential shutdown household electrical appliances. But if after turning off all the devices the short circuit does not disappear, then there is a high probability that it originated in the electrical wiring. A short circuit condition can be caused by electric lighting devices, which also need to be turned off.

The circuit breaker is electrical device, the main purpose of which is to switch its operating state when a certain situation arises. Electrical machines combine two devices, this regular switch and a magnetic (or thermal) release, the task of which is to timely break the electrical circuit if the threshold current value is exceeded. Circuit breakers, like all electrical devices, also have different varieties, which divides them into certain types. Let's take a look at the main classifications of circuit breakers.

1" Classification of machines by number of poles:

A) single-pole circuit breakers

b) single-pole circuit breakers with neutral

c) two-pole circuit breakers

d) three-pole machines

e) three-pole circuit breakers with neutral

e) four-pole machines

2" Classification of automatic machines according to the type of releases.

The design of various types of circuit breakers usually includes 2 main types of releases (breakers) - electromagnetic and thermal. Magnetic ones are used for electrical protection from short circuits, and thermal circuit breakers are designed mainly to protect electrical circuits for a certain overload current.

3" Classification of automatic machines according to tripping current: B, C, D, (A, K, Z)

GOST R 50345-99, according to instantaneous tripping current, automatic machines are divided into the following types:

A) type “B” - over 3 In to 5 In inclusive (In is the rated current)

b) type “C” - over 5 In up to 10 In inclusive

B) type “D” - over 10 In to 20 In inclusive

Machine manufacturers in Europe have a slightly different classification. For example, they have additional type"A" (over 2 In to 3 In). Some manufacturers of circuit breakers also have additional switching curves (ABB has circuit breakers with K and Z curves).

4" Classification of machines according to the type of current in the circuit: constant, variable, both.

Rated electric currents for the main circuits of the release are selected from: 6.3; 10; 16; 20; 25; 32; 40; 63; 100; 160; 250; 400; 630; 1000; 1600; 2500; 4000; 6300 A. Automatic machines are also additionally produced with rated currents of the main electrical circuits of the automatic machines: 1500; 3000; 3200 A.

5" Classification according to the presence of current limitation:

a) current-limiting

b) non-current limiting

6" Classification of automatic machines by types of releases:

A) with overcurrent release

b) with independent release

c) with minimum or zero voltage release

7" Classification of machines according to time delay characteristics:

A) without time delay

b) with a time delay independent of current

c) with a time delay inversely dependent on the current

d) with a combination of the specified characteristics

8" Classification according to the presence of free contacts: with and without contacts.

9" Classification of machines according to the method of connecting external wires:

A) with rear connection

b) with front connection

c) with combined connection

d) with universal connection (both front and rear).

10" Classification by type of drive: with manual, motor and spring.

P.S. Everything has its own varieties. After all, if there was only one thing in its only copy, it would be, at a minimum, simply boring and too limited! The good thing about the variety is that you can choose exactly what best suits your needs.

Any circuit breaker has an important component of the device: a release, which serves to open or close the switching device. Essentially, the release opens the contacts of the circuit breaker when overcurrents occur and the voltage decreases. GOST R 50030.1 (5) defines the concept of a release as “A device mechanically connected to a contact switching device, which releases the holding devices and thereby allows opening or closing switching device" Standard IEC 61992‑1 (6) complements this definition of a circuit breaker release - the release may consist of mechanical, electronic or electromagnetic components; applies to any device with mechanical action, which are used for tripping operation when certain conditions are met in the input circuit; a machine may have several releases.

Types of releases

The following types of releases are most often found in household circuit breakers: thermal, electronic and electromagnetic. They quickly recognize a critical situation (the appearance of overcurrents, overloads and voltage surges) and open the circuit breaker contacts, preventing damage to electrical equipment and protecting the wiring. In addition to these types, there are also zero-voltage, minimum-voltage, independent, semiconductor, and mechanical releases.

Overcurrents - an increase in current in the electrical network exceeding the rated current of the machine. These are overload and short circuit currents.

Overload current - overcurrent in a functional network.

Short circuit current is an overcurrent resulting from the short circuit of two network components with extremely low resistance between these elements.

Thermal release

The thermal release opens the contacts of the circuit breaker when the rated current is slightly exceeded and is characterized by an increased response time. In case of short-term excesses of the current load, it does not operate; this is convenient in networks where short-term excesses of the rated current of the machine are frequent.

The thermal release is a bimetallic strip, one end of which is located next to the release trigger. If the current increases, the plate begins to bend and approach the trigger mechanism, touches the bar, and it, in turn, opens the contacts of the circuit breaker. The operating principle is based on the physical properties of metal, which expands when heated, which is why such a release is called thermal.

The advantages of a thermal release include the absence of surfaces rubbing against each other, resistance to vibration, and low cost due to its simple design. But you also need to pay attention to the disadvantages - the operation of a thermal release is highly dependent on the ambient temperature, they should be placed in places with a stable temperature, away from heat sources, otherwise numerous false alarms are possible.

Electronic release

The electronic release includes measuring devices (current sensors), a control unit and an actuating electromagnet. Electronic releases are designed to issue a command to automatically turn off the machine with a given program when an overcurrent or short circuit occurs in the electrical circuit. When the current through the circuit breaker is exceeded, the electronic release unit begins counting the response time in accordance with the time-current characteristic. If during the actuation time the current decreases to a value below the threshold, then automatic operation will not occur.

The advantages of electronic releases include: a wide range of settings, strict adherence of the device to a given program, and the presence of indicators. The main disadvantage is quite high price, as well as the sensitivity of the release to the effects of electromagnetic radiation.

Electromagnetic release

Electromagnetic release(cut-off) operates instantly, preventing the slightest possibility of damage to the components of the electrical circuit. This is a solenoid with a movable core that acts on the tripping mechanism. As current flows through the solenoid winding, if the current load is exceeded, the core is retracted under the influence of the electromagnetic field.

The electromagnetic release is triggered when the short circuit current is exceeded. It has sufficient strength, is resistant to vibration, but creates a magnetic field.

Circuit breaker release current

The current of the circuit breaker release has a specific value (nominal), meaning the amount of current at which the circuit breaker will open the circuit. The current in the thermal release is always equal to or less than the rated current of the circuit breaker. Whenever the current load on the release is exceeded, the machine will shut down. In this case, the time after which the contacts open depends on the time of flow of the excess load current. The tripping time of the thermal release can be calculated using the time-current characteristics.

The current of the electromagnetic release switches off the circuit breaker instantly when the rated current of the circuit breaker is exceeded, most often this happens during a short circuit. Before a short circuit, the current in the network increases very quickly, which is taken into account by the electromagnetic release device, resulting in a very rapid impact on the release mechanism. The response speed in this case is a fraction of a second.

They can be equipped with the following releases built into them:

Electromagnetic or electronic overcurrent release of instantaneous or delayed action with a time delay practically independent of the current;

Electrothermal or electronic inertial overcurrent release with a current-dependent time delay;

Leakage current release;

Minimum voltage actuator;

Reverse current or reverse power release;

Independent release (remote switch off).

The first two types are installed in all three poles, the rest - one per switch. The set currents, as well as the time delays of the current releases, can be adjustable. One or more types of current releases and, in addition to them, an undervoltage release can be used in one circuit breaker. independent release and switching electromagnet.

According to the response time, electromagnetic and similar electronic releases have four varieties:

Releases that ensure the operation of the circuit breaker in a time much less than 0.01 s, and the switching off of the short-circuit current before it reaches its impact value. Such AVs are called current-limiting.

Releases that provide disconnection of the short-circuit current during the first passage of the current through the zero value tc = 0.01 s.

Unregulated releases, the response time of which exceeds 0.01 s;

Releases with an adjustable time delay (0.1-0.7 s), which make it possible to achieve slow operation relative to other circuit breakers in the same network, are called selective.

Leakage current releases are used to quickly disconnect sections of the network in which, due to insulation failure or people touching the conductors, a leakage current to the ground has occurred. In this case, the release setting current is selected in the range from 10 to 30 mA, and the voltage dependence time is selected in the range from 10 to 100 ms. This protection is now considered more effective in protecting people from electric shock.

Minimum voltage releases are used to disconnect power sources when they stop supplying the network (early ATS)_, as well as to disconnect electrical receivers, the self-starting of which when the voltage is automatically restored is undesirable. The release voltage is selected in the range from 0.8 to 0.9 Un, the response time is in accordance with the requirements of automatic network power restoration systems.

Independent releases are used for local remote and automatic shutdown AB when external protective devices are triggered.

Reverse current or reverse power releases are used to protect generators operating at electrical system from loss of synchro.

17. Overcurrent directional protection (principle of operation, circuit diagram, calculation of time delays).

Directional current protection of MTNZ line

T 1 > t → 2 > t 3

I p = I` short I p = I` short

U p = U in U p = U in

φ p = 180 - φ a φ p = φ a t 4 > t ← 3 > t 2

I p = I`` short I p = I` short

U p = U in U p = U in

φ p = φ a φ p = 180 - φ a

Switches Q1 - Q3 have directional overcurrent protection. It differs from conventional MTZ in that an additional body is introduced that determines the direction of the short-circuit power - a power direction relay, which reacts to the phase of the short-circuit current relative to the voltage on the substation buses at the installation site of the protection kit, then the “-” power sign and the power direction relay blocks the set protection. If the direction of the short circuit power is from the busbars to the line, then this is the “+” sign of the short circuit power and the power direction relay, closing its contacts, allows the MTNZ set to operate.

As a result of the action of directional protection, sets 2 and 3 do not need to be coordinated, because they are decoupled using the directional action of a relay. This page violates copyright

In order for all equipment in your home or workplace to be protected from electrical surges, you need to install special circuit breakers. They will be able to detect a surge and quickly react to it by disconnecting the entire system from the electricity supply. A person cannot do this on his own, but a certain type of machine can do it in a few seconds.

Types of machines

Device sensitivity

Before you get acquainted with the types of machines, you need to find out with what sensitivity the devices are suitable for home use, and which ones will be inappropriate. This indicator will indicate how quickly the device will respond to a power surge. It has several markings:

Classification of machines

There are different types of machines in relation to the type of current, rated voltage or current indicator and other technical characteristics. Therefore, you need to specifically understand each point separately.

Current type

In relation to this characteristic, machines are divided into:

For operation on AC power;
For operation in a DC network;
Universal models.

Everything is clear here and no additional explanation is needed.

Based on rated current

The value of this characteristic will determine in the network what maximum value the circuit breaker can operate with. There are devices that can operate from 1 A to 100 A and more. The minimum value with which machines can be found on sale is 0.5 A.

Rated voltage indicator

This characteristic indicates what voltage this type of circuit breaker can operate with. Some can operate on a network with a voltage of 220 or 380 Volts - these are the most common options for household use. But there are machines that will cope well with higher rates.

By ability to limit the flow of electricity

According to this characteristic, the following are distinguished:

Other characteristics

The number of poles can be from one to four. Accordingly, they are called single-pole, double-pole, and so on.

Automatic machines by number of poles

By structure they are distinguished:

Based on the discharge speed, high-speed, normal and selective devices are produced. They can have a time delay function that can be inversely dependent on the current or independent of it. The time delay may not be set.

Automatic machines also have a drive, which can be manual, connected to a motor or a spring. Switches differ in the presence of free contacts and in the method of connecting conductors.

An important characteristic will be protection from environmental influences. Here we can highlight:

IP protection;
From mechanical impact;
Current conductivity of the material.

All characteristics can be combined in various combinations. It all depends on the model and manufacturer.

Switch types

The machine inside contains a release, which, using a lever, latch, spring or rocker, can instantly disconnect the network from the supply of electricity. Types of circuit breakers are distinguished by the type of release. There are:

Circuit breakers are much more cost effective than fuses. This is because after cooling, the machine can already be turned on, and it will work as it should if the cause of the overload is eliminated. The fuse needs to be replaced. It may not be available and replacing it may take a long time.

Hello friends. The topic of the post is the types and types of circuit breakers (automatic circuit breakers, AB). I also want the results of the crossword puzzle tournament.

Types of machines:

Can be divided into AC, DC and universal switches operating at any current.

Design - there are air, modular, in cast case.

Rated current indicator. The minimum operating current of a modular machine is 0.5 Amperes, for example. Soon I will write about how to choose the right rated current for a circuit breaker, subscribe to the blog news so as not to miss it.

Voltage rating is another difference. In most cases, AVs operate in networks with a voltage of 220 or 380 Volts.

There are current-limiting and non-current-limiting.

All switch models are classified by the number of poles. They are divided into single-pole, double-pole, three-pole and four-pole circuit breakers.

Types of releases - maximum current release, independent release, minimum or zero voltage release.

Speed of operation of circuit breakers. There are high-speed, normal and selective automatic machines. They are available with or without a time delay, independent or inversely dependent on the current response time delay. Characteristics can be combined.

They differ in the degree of protection from the environment - IP, mechanical influences, conductivity of the material. By type of drive - manual, motor, spring.

By the presence of free contacts and the method of connecting conductors.

Types of machines:

What does type AB mean?

Automatic circuit breakers contain two types of circuit breakers - thermal and magnetic.

Magnetic quick-release switch is designed for short-circuit protection. The tripping of the circuit breaker can occur in a time from 0.005 to several seconds.

The thermal breaker is much slower, designed to protect against overload. It works using a bimetallic plate that heats up when the circuit is overloaded. Response time ranges from a few seconds to minutes.

The combined response characteristic depends on the type of connected load.

There are several types of AV shutdown. They are also called types of time-current shutdown characteristics.

A, B, C, D, K, Z.

A– used for breaking circuits with long electrical wiring, serves as good protection for semiconductor devices. They operate at 2-3 rated currents.

B– for a general purpose lighting network. They operate at 3-5 rated currents.

C– lighting circuits, electrical installations with moderate starting currents. These can be motors, transformers. The overload capacity of the magnetic circuit breaker is higher than that of type B switches. They operate at 5-10 rated currents.

D– used in circuits with active-inductive loads. For electric motors with high starting currents, for example. At 10-20 rated currents.

K– inductive loads.

Z– for electronic devices.

It is better to look at the data on the operation of switches of types K, Z in the tables specifically for each manufacturer.

That seems to be all, if there is anything to add, leave a comment.

Modern electrical network impossible to imagine without necessary funds protection, in particular the circuit breaker. Unlike outdated fuses, it is designed for reusable protection of networks and electrical equipment. At the same time, the circuit breaker protects against short circuit currents, excessive overloads, and some models even against unacceptable voltage drops. And at the center of this entire structure, the most significant element is the circuit breaker release. Reliability and response speed depend on it, so it’s worth comparing all existing this moment varieties.

Comparison

So, one of the first can be called a thermal release. Due to its design, the thermal release operates with a time delay. The greater the current excess, the faster the thermal release operates. So the response time can vary from a few seconds to an hour. That is why the sensitivity of the machine where the thermal release is installed is always determined by the time-current characteristic and corresponds to class B, C or D.

The next type is classified as instantaneous releases. We are talking about such a concept as an electromagnetic release. It operates in a fraction of a second, which compares favorably with thermal releases. However, the electromagnetic release also has its own peculiarity - operation occurs when the rated current is significantly higher than the rated current. Based on this, the electromagnetic release also has a certain sensitivity and belongs to one of the classes - A, B, C or D.

Perhaps the most effective is the electronic circuit breaker release. The fast response speed and high sensitivity make the electronic trip unit ideal for protection against overloads and short-circuit currents. For this reason, this instantaneous release is used for higher currents.

It is the electronic trip unit that is often mounted on both air circuit breakers and molded case circuit breakers. Air circuit breakers have an open design (usually in metal case) and are designed for current up to several thousand amperes. As already mentioned, the electronic release due to its instantaneous response speed is ideal for power networks. As for molded case circuit breakers, they are distinguished by their compact dimensions and closed design in a housing made of thermosetting plastic. They are convenient to mount on a DIN rail, but closed body implies increased requirements for the reliability of the release. This again is an electronic release, where there are no moving mechanical elements.

Principle of operation

Regardless of the type of release, the principle of its operation is based on opening the circuit in case of exceeding the current characteristics. Any release is an integral part of the circuit breaker, built into it or mechanically connected to it. The circuit breaker release, under the influence of short circuit currents or when the load is exceeded, initiates the release of the holding device in the circuit breaker housing. As a result, the electrical circuit opens.

Design

The design largely depends on the type of release. Thus, the basis of a thermal release is a bimetallic plate - a metal strip of two strips having different coefficients of thermal expansion. When currents exceeding the permissible value pass through it, the bimetallic plate is deformed, thereby triggering the release mechanism.

The design of an electromagnetic release is a solenoid (cylindrical winding) with a movable core. The current passes through the solenoid winding and if the current characteristics are exceeded, the core is retracted, affecting the opening mechanism.

But the electronic release of the circuit breaker is not based on mechanical action and is of a slightly different design. It consists of a controller and current sensors. The controller compares the values of the current sensors with the established characteristics, and if the specified current parameters are exceeded, it gives a signal to shut down. Thus, the electronic release has more flexible settings, allowing you to configure the parameters of the circuit breaker to meet the specific requirements of power network protection.

The main purpose of circuit breakers is to use them as protective devices from short circuit currents and overload currents. Modular circuit breakers of the BA series are in predominant demand. In this article we will look at the design of the BA47-29 series circuit breaker from iek.

The design of circuit breakers and the principles of their operation are similar; the differences lie, and this is important, in the material of the components and the quality of assembly. Serious manufacturers use only high-quality electrical materials (copper, bronze, silver), but there are also products with components made from materials with “lightweight” characteristics.

The easiest way to distinguish an original from a fake is price and weight: the original cannot be cheap and light if there are copper components. The weight of branded machines is determined by the model and cannot be lighter than 100 - 150 g.

Structurally, the modular circuit breaker is made in a rectangular housing, consisting of two halves fastened together. On front side of the machine, its technical characteristics are indicated and a handle for manual control is located.

How does a circuit breaker work - the main working parts of the machine?

If you disassemble the housing (for which you need to drill out the rivet halves connecting it), you can see the circuit breaker device and gain access to all its components. Let's consider the most important of them, which ensure the normal functioning of the device.

1.Top terminal for connection;

2.Fixed power contact;

3.Movable power contact;

4. Arcing chamber;

10.Bottom terminal for connection;

11. Hole for the exit of gases (which are formed when the arc burns).

Electromagnetic release

The functional purpose of the electromagnetic release is to provide a practically automatic switch when a short circuit occurs in the protected circuit. In this situation, currents arise in electrical circuits, the magnitude of which is thousands of times greater than the nominal value of this parameter.

The type of characteristic is indicated in the rated current parameter on the machine body, for example, C16. For the given characteristics, the response time ranges from hundredths to thousandths of a second.

Electrically, the solenoid coil is connected in series to a chain consisting of power contacts and a thermal release.

Maximum operating current

Maximum operating current. The choice of machines based on the maximum operating current is that the rated current of the machine (rated current of the release) is greater than or equal to the maximum operating (calculated) current that can pass for a long time through the protected section of the circuit, taking into account possible overloads:

To find out the maximum operating current for a section of the network (for example, for an apartment), you need to find the total power. To do this, we sum up the power of all devices that will be connected through this machine (refrigerator, TV, stove, etc.). The amount of current from the received power can be found in two ways: by comparison or by formula.

For a 220 V network with a load of 1 kW, the current is 5 A. In a network with a voltage of 380 V, the current value for 1 kW of power is 3 A. Using this comparison option, you can find the current through a known power. For example, the total power in the apartment turned out to be 4.6 kW, the current being approximately 23 A. For more exact location current, you can use the well-known formula:

For household electrical appliances.

Breaking capacity

Breaking capacity. The choice of a circuit breaker based on the rated shutdown current comes down to ensuring that the current that the machine is capable of shutting off is greater than the short circuit current at the point where the device is installed: The rated shutdown current is the highest short-circuit current. which the machine is capable of turning off at rated voltage.

When choosing automatic machines for industrial use, they are additionally checked for:

Electrodynamic resistance:

Thermal resistance:

Circuit breakers are produced with the following rated current scale: 4, 6, 10, 16, 25, 32, 40, 63, 100 and 160 A.

In residential sectors (houses, apartments), as a rule, two-pole circuit breakers with a rating of 16 or 25 A and a shutdown current of 3 kA are installed.

What are time and current characteristics of circuit breakers

At normal operation electrical network and all appliances, electric current flows through the circuit breaker. However, if the current strength for some reason exceeds the rated values, the circuit opens due to the operation of the circuit breaker releases.

The tripping characteristic of the circuit breaker is very important characteristic, which describes how much the operation time of the machine depends on the ratio of the current flowing through the machine to the rated current of the machine.

This characteristic is complex in that its expression requires the use of graphs. Machines with the same rating will be switched off differently at different current levels depending on the type of the machine’s curve (as the current characteristic is sometimes called), making it possible to use machines with different characteristics For different types loads.

Thus, on the one hand, the protective current function is carried out, and on the other hand, a minimum amount of false positives- this is the importance of this characteristic.

In energy industries, there are situations when a short-term increase in current is not associated with the occurrence of an emergency mode and the protection should not respond to such changes. The same applies to automatic machines.

When you turn on a motor, for example, a country pump or a vacuum cleaner, a fairly large surge of current occurs in the line, which is several times higher than normal.

According to the operating logic, the machine, of course, should turn off. For example, the motor consumes 12 A in starting mode, and 5 in operating mode. The machine is set at 10 A, and at 12 it will turn it off. What to do in this case? If, for example, you set it to 16 A, then it is not clear whether it will turn off or not if the motor jams or the cable shorts out.

This problem could be solved if it was set to a lower current, but then it would be triggered by any movement. This is why such a concept for a machine was invented as its “time-current characteristic”.

What are the current characteristics of circuit breakers and how they differ from each other?

As is known, the main organs for triggering a circuit breaker are thermal and electromagnetic releases.

The thermal release is a bimetal plate that bends when heated by a flowing current. Thus, the release mechanism is activated, and in the event of a prolonged overload, it is triggered with an inverse time delay. The heating of the bimetallic strip and the tripping time of the release directly depend on the overload level.

The electromagnetic release is a solenoid with a core, the magnetic field of the solenoid at a certain current draws in the core, which activates the release mechanism - instantaneous operation occurs during a short circuit, due to which the affected section of the network will not wait for the thermal release (bimetallic plate) to warm up in the circuit breaker.

The dependence of the response time of the circuit breaker on the strength of the current flowing through the circuit breaker is precisely determined by the current characteristic of the circuit breaker.

Probably everyone has noticed the image of the Latin letters B, C, D on the bodies of modular machines. So, they characterize the multiple of the setting of the electromagnetic release to the nominal value of the machine, indicating its time and current characteristics.

These letters indicate the instantaneous operation current of the electromagnetic release of the machine. Simply put, the response characteristic of a circuit breaker shows the sensitivity of the circuit breaker - the lowest current at which the circuit breaker will turn off instantly.

Slot machines have several characteristics, the most common of which are:

B - from 3 to 5 ×In;

C - from 5 to 10 ×In;

D - from 10 to 20 ×In.

What do the numbers above mean?

Let me give you a small example. Let's say there are two machines of the same power (equal in rated current), but the response characteristics (Latin letters on the machine) are different: machines B16 and C16.

The operating range of the electromagnetic release for B16 is 16*(3...5)=48...80A. For C16, the instantaneous response current range is 16*(5...10)=80...160A.

At a current of 100 A, the B16 circuit breaker will turn off almost instantly, while the C16 will not turn off immediately, but after a few seconds from thermal protection (after its bimetallic plate heats up).

In residential buildings and apartments, where the loads are purely active (without large starting currents), and any powerful motors are turned on infrequently, the most sensitive and preferable for use are machines with characteristic B. Today, characteristic C is very common, which can also be used for residential and administrative buildings.

As for characteristic D, it is just suitable for powering any electric motors, large engines and other devices where there may be large starting currents when they are turned on. Also, due to the reduced sensitivity during short circuit, machines with characteristic D can be recommended for use as input ones to increase the chances of selectivity with lower group ABs during short circuit.

What does a circuit breaker protect?

Before choosing a machine, it is worth understanding how it works and what it protects. Many people believe that the machine protects household appliances. However, this is absolutely not true. The machine does not care about the devices that you connect to the network - it protects the electrical wiring from overload.

Indeed, when the cable is overloaded or a short circuit occurs, the current increases, which leads to overheating of the cable and even fire of the wiring.

The current increases especially strongly during a short circuit. The magnitude of the current can increase to several thousand amperes. Of course, no cable can last long under such a load. Moreover, the cable has a cross-section of 2.5 square meters. mm, which is often used for laying electrical wiring in private households and apartments. It will simply light up like a sparkler. An open fire indoors can cause a fire.

Therefore, the correct calculation of the circuit breaker plays a very important role. A similar situation occurs during overloads - the circuit breaker protects the electrical wiring.

When the load exceeds the permissible value, the current increases sharply, which leads to heating of the wire and melting of the insulation. In turn, this can lead to a short circuit. And the consequences of such a situation are predictable - open fire and fire!

What currents are used to calculate machines?

The function of a circuit breaker is to protect the electrical wiring connected downstream of it. The main parameter by which automatic machines are calculated is the rated current. But the rated current of what, the load or the wire?

Based on the requirements of PUE 3.1.4, the setting currents of circuit breakers that serve to protect individual sections of the network are selected as less as possible than the calculated currents of these sections or according to the rated current of the receiver.

The calculation of the machine based on power (based on the rated current of the electrical receiver) is carried out if the wires along the entire length in all sections of the electrical wiring are designed for such a load. That is permissible current electrical wiring is greater than the machine's rating.

For example, in an area where a wire with a cross-section of 1 square meter is used. mm, the load value is 10 kW. We select the machine according to the rated load current - set the machine to 40 A. What will happen in this case? The wire will begin to heat up and melt, since it is designed for a rated current of 10-12 amperes, and a current of 40 amperes passes through it. The machine will turn off only when a short circuit occurs. As a result, wiring may fail and even cause a fire.

Therefore, the determining value for choosing the rated current of the machine is the cross-section of the current-carrying wire. The load size is taken into account only after selecting the wire cross-section. The rated current indicated on the machine must be less than the maximum current allowed for a wire of a given cross-section.

Thus, the choice of machine is made based on the minimum cross-section of the wire used in the wiring.

For example, the permissible current for a copper wire with a cross-section of 1.5 kW. mm, is 19 amperes. This means that for this wire we select the closest value of the rated current of the machine to the smaller side, which is 16 amperes. If you choose a machine with a value of 25 amperes, the wiring will heat up, since the wire of this cross-section is not designed for such a current. In order to correctly calculate the circuit breaker, it is necessary, first of all, to take into account the cross-section of the wire.

It's no secret that circuit breakers are not just switches that pass operating current and provide two states of the electrical circuit: closed and open. A circuit breaker is an electrical device that, in real time, “monitors” the level of current flowing in the protected circuit and turns it off when the current exceeds a certain value.

The most common combination in circuit breakers is the combination of a thermal and an electromagnetic release. It is these two types of releases that provide the main protection of circuits from overcurrents.

Thermal release designed to disconnect overload currents in the electrical circuit. The thermal release is structurally composed of two layers of metals with different linear expansion coefficients. This allows the plate to bend when heated and affect the free release mechanism, ultimately turning off the device. Such a release is also called a thermobimetallic release after the name of the main element - the bimetallic plate.

However, this type of release has significant drawback- its properties depend on the ambient temperature. That is, if the temperature is too low, even if the circuit is overloaded, the thermal release of the circuit breaker may not turn off the line. The opposite situation is also possible: in very hot weather, the circuit breaker may falsely disconnect the protected line due to heating of the bimetallic plate environment. In addition, the thermal release consumes electrical energy.

Electromagnetic release consists of a coil and a movable steel core held by a spring. When the specified current value is exceeded, according to the law of electromagnetic induction, an electromagnetic field is induced in the coil, under the influence of which the core is drawn into the coil, overcoming the resistance of the spring, and triggers the release mechanism. In normal operation, an electromagnetic field is also induced in the coil, but its strength is not enough to overcome the resistance of the spring and retract the core.

The design of the electromagnetic release mechanism is shown using the example of AP50B

This type of release does not consume as much electrical energy as a thermal release.

Currently, electronic releases based on microcontrollers are widely used. With their help, you can fine-tune the following protection parameters:

operating protection current level
overload protection time
response time in the overload zone with and without the thermal memory function
selective cut-off current
selective current cut-off time

The implemented function of self-testing the operation of the free release mechanism using the TEST button allows the consumer to check the device.

Adjusting the electrical circuit settings on front panel The device allows personnel to easily understand how the outgoing line protection is configured.

Using rotary switches on the front panel, the operating current level of the circuit is set. Adjustment operating current settings of the IR release set in multiples: 0.4; 0.45; 0.5; 0.56; 0.63; 0.7; 0.8; 0.9; 0.95; 1.0 to the rated current of the circuit breaker.

There are two modes of operation of the semiconductor release when the electrical circuit is overloaded:

with “thermal memory”;
without "thermal memory"

“Thermal memory” is an emulation of the operation of a thermal release (bimetallic plate): the microprocessor release programmatically sets the time it would take for the bimetallic plate to cool down. This function allows the equipment and the protected circuit to cool down more time and, accordingly, their service life is not reduced.

One of the advantages is the setting of the current level and operation time of the circuit breaker during a short circuit, which provides the necessary selectivity of protection. This is necessary so that the input circuit breaker turns off later than the devices closest to the accident. It is important to note that, unlike a thermal release, the time settings in a microprocessor release do not change when the ambient temperature changes.

Adjusting the selective current cut-off current setting selected as a multiple of the operating current I R: 1.5; 2; 3; 4; 5; 6; 7; 8; 9; 10.

Adjusting the selective current cut-off time setting selectable in seconds: 0 (no time delay); 0.1; 0.15; 0.2; 0.25; 0.3; 0.35; 0.4.

Electromagnetic compatibility of microprocessor releases of OptiMat D circuit breakers allows the use of these devices in general industrial electrical installations. In turn, the electromagnetic fields created by the elements of the microprocessor release do not have a negative impact on the surrounding equipment.

Let's consider the choice of settings using the example of the microprocessor release MR1-D250 of the OptiMat D circuit breaker. There is an AIR250S2 asynchronous motor with parameters P = 75 kW; cosφ=0.9; Ip/Inom=7.5; for which you need to select the settings of the protective device (the circuit breaker protects directly the line with this electric motor). Let us accept the following conditions: starting the electric motor is easy and the starting time is 2 s.

We select a setpoint for our engine of 4 seconds with a thermal memory function:

In our case, the rated current of the electric motor is 126.6 A. Accordingly, we set the switch for adjusting the rated current of the switch to a value of 0.56, so that the closest value is 140 A.

To prevent the circuit breaker from tripping falsely due to starting currents, the multiplicity of which for the selected motor is 7.5, we will take the selective current cut-off setting equal to 8.

Since this switch will be installed directly to protect the electric motor, to ensure selectivity in the operation of the switches, we accept instantaneous selective current cutoff (without time delay).

It should also be noted that if the short circuit current exceeds 3000 A, the switch will operate instantly, that is, without a time delay.

Thus, we have looked at an example of choosing the settings of a microprocessor release that provide protection asynchronous motor. This example selecting the settings of the microprocessor release is not technical manual. In the final form, the microprocessor circuit breaker settings panel will look like this:

Electromagnetic compatibility, meeting the requirements of GOST R 50030.2-2010, and the possibility of integration into an automation system makes circuit breakers more reliable, convenient and profitable solutions by many indicators.

The main purpose of circuit breakers is to use them as protective devices against short circuit currents and overload currents. Modular circuit breakers of the BA series are in predominant demand. In this article we will look at BA47-29 series from iek.

Thanks to their compact design (uniform module widths), ease of installation (mounting on a DIN rail using special latches) and maintenance, they are widely used in domestic and industrial environments.

Most often, automatic machines are used in networks with relatively small operating and short-circuit currents. The machine body is made of dielectric material, which allows you to install it in publicly accessible places.

Circuit breaker design and the principles of their operation are similar, the differences lie, and this is important, in the material of the components and the quality of the assembly. Serious manufacturers use only high-quality electrical materials (copper, bronze, silver), but there are also products with components made from materials with “lightweight” characteristics.

Structurally, the modular circuit breaker is made in a rectangular housing, consisting of two halves fastened together. On the front side of the machine its specifications and a handle for manual control is located.

How a circuit breaker works - the main working parts of the circuit breaker

If you disassemble the body (for which you need to drill out the rivet halves connecting it), you can see and gain access to all its components. Let's consider the most important of them, which ensure the normal functioning of the device.

1. Upper terminal for connection;
2. Fixed power contact;
3. Movable power contact;
4. Arc chamber;
5. Flexible conductor;
6. Electromagnetic release (coil with core);
7. Handle for control;
8. Thermal release (bimetallic plate);
9. Screw for adjusting the thermal release;
10. Bottom terminal for connection;
11. Hole for the exit of gases (which are formed when the arc burns).

Electromagnetic release

The functional purpose of the electromagnetic release is to ensure almost instantaneous operation of the circuit breaker when a short circuit occurs in the protected circuit. In this situation in electrical circuits currents arise whose magnitude is thousands of times greater than the nominal value of this parameter.

The operation time of the machine is determined by its time-current characteristics (the dependence of the operation time of the machine on the current value), which are designated by the indices A, B or C (the most common).

The design of the electromagnetic release is a solenoid with a spring-loaded core, which is connected to a movable power contact.

Electrically, the solenoid coil is connected in series to a chain consisting of power contacts and a thermal release. When the machine is turned on and the rated value of the current, current flows through the solenoid coil, however, the magnitude of the magnetic flux is small to retract the core. The power contacts are closed and this ensures the normal functioning of the protected installation.

During a short circuit, a sharp increase in current in the solenoid leads to a proportional increase in magnetic flux, which can overcome the action of the spring and move the core and the moving contact associated with it. The movement of the core causes the power contacts to open and the protected line to de-energize.

Thermal release

The thermal release performs the function of protection when the permissible current value is exceeded slightly, but lasts for a relatively long period of time.

The thermal release is a delayed release; it does not respond to short-term current surges. The response time of this type of protection is also regulated by the time-current characteristics.

The inertia of the thermal release makes it possible to implement the function of protecting the network from overload. Structurally, the thermal release consists of a bimetallic plate mounted in a cantilever in the housing, the free end of which interacts with the release mechanism through a lever.

Electrically, the bimetallic strip is connected in series with the coil of the electromagnetic release. When the machine is turned on, current flows in the series circuit, heating the bimetallic plate. This causes its free end to move in close proximity to the release mechanism lever.

When the current values specified in the time-current characteristics are reached and after a certain time, the plate bends when heated and comes into contact with the lever. The latter, through a release mechanism, opens the power contacts - the network is protected from overload.

The thermal release current is adjusted using screw 9 during the assembly process. Since most machines are modular and their mechanisms are sealed in the housing, it is not possible for a simple electrician to make such adjustments.

Power contacts and arc chute

Opening of power contacts when current flows through them leads to the occurrence of an electric arc. Arc power is usually proportional to the current in the circuit being switched. The more powerful the arc, the more it destroys the power contacts and damages the plastic parts of the housing.

IN circuit breaker device The arc suppression chamber limits the action of the electric arc in a local volume. It is located in the power contact area and is made of copper-coated parallel plates.

In the chamber, the arc breaks up into small parts, hits the plates, cools down and ceases to exist. The gases released when the arc burns are removed through holes in the bottom of the chamber and the body of the machine.

Circuit breaker device and the design of the arc chute determine the connection of power to the upper fixed power contacts.

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Basic information

Circuit breaker releases

A release is a part of the circuit breaker that acts directly on the mechanism for its shutdown at critical parameters of the protected circuit (current, voltage).

Releases are relays or relay elements built into switches.

body using its elements or adapted to its design.

Releases are made on the basis of conventional electromagnetic relays (current, voltage)

nia). However, in Lately Releases based on static electronic relays are increasingly being used. The electronic part of these relays controls one or another physical quantity, but in their output circuit doesn't matter the electromagnetic relay is turned on, the armature of which

This affects the release mechanism.

Any circuit breaker must have electromagnetic dis-

overcurrent feeder, instantly short-circuit disconnect switch -

research (Fig. 4.14 and 4.15).

In some types of switches, in addition to electromagnetic, electric

thermal, disconnect switch with time delay in the zone of overload currents.

Such a release is called combined (Fig. 4.16). It should be noted that circuit breakers with one electrothermal release are not available.

A device that has only an electrothermal release is called an electrothermal relay (see below “Electrothermal relays”).

Additionally, the switches can be equipped with releases:

minimal(minimum or zero voltage) – for automatic shutdown of the switch when the voltage drops below the permissible level or disappears (Fig. 4.17 and 4.18);

independent– for remote shutdown of the circuit breaker by applying to

voltage to the release coil (Fig. 4.19 and 4.20).

Let us consider in turn the structure and principle of operation of each mentioned system.

chainer.

The electromagnetic release is designed to disconnect the current switch -

mi short circuit, It is often called the maximum release. According to the device

according to its operating principle, it is an overcurrent relay.

Rice. 4.14. Schematic diagram of the maximum release:

1 – power handle; 2 – holding lever; 3 – shut-off lever; 4 – adjusting spring; 5 – disconnecting spring; 6 – coil; 7 – anchor; 8 – moving contact; 9 – fixed contact

In the initial state, the switch is on, the circuit current is less than the set current. At

In this case, the holding lever 2 is engaged with the trip lever 3. Moves

The fixed 8 and fixed 9 contacts are closed, and current flows through them and the current coil 6.

During a short circuit, the current in the coil increases and armature 7, overcoming the

the counteraction of the adjusting spring 4 moves downwards. The anchor acts on the trip lever 3 and disengages it from the holding lever 2.

The moving contact 8, under the action of the trip spring 5, rotates to

counterclockwise direction and opens with the stationary 9.

Switch 1 operating handle is installed in intermediate position

information by which it is easy to determine that the circuit breaker has turned off automatically.

Rice. 4.15. Kinematic diagram of the maximum release:

1 – tire, 2 – core; 3 – anchor, 4 – disconnecting roller; 5 – disconnecting rod

wife; 6 – shut-off lever; 7 – arm of the disconnecting roller; 8 – adjusting

nut

In Fig. 4.12 shows one of the designs of the maximum tripping

It uses a current-carrying busbar as an overcurrent relay coil.

on 1, on which the core 2 is placed. On the armature 3 of the relay, the disconnecting lever 6 is mounted, on -

engaged in engagement with the shutdown roller 4. The shutdown spring 5 retracts

The shut-off lever 6 is down.

In the event of a short circuit, armature 3 is attracted to core 2. Disconnecting rod

Bar 6, overcoming the resistance of the adjusting spring 5, rotates clockwise

arrow around the axis Oi hits the protruding shoulder 7 of the shutdown roller 4. The roller rotates in a counterclockwise direction around the axis O, which causes

causes the switch contacts to open.

The value of the actuation current (set current) is adjusted using nut 8. The more spring 5 is stretched using this nut, the greater the set current, and vice versa

mouth. An arrow-pointer is connected to the spring, sliding along the scale, graduated

no in fractions of the rated current, for example, 0.7; 1.0; 1.5; 1.7; 2.0.

Circuit breakers are devices that are designed to protective shutdown DC and AC circuits in cases of short circuit, current overload, voltage drop or disappearance. Unlike fuses, automatic switches have a more accurate shutdown current, can be used repeatedly, and also in a three-phase design, when a fuse trips, one of the phases (one or two) may remain energized, which is also an emergency mode of operation (especially when powered three-phase electric motors).

Circuit breakers are classified according to the functions they perform, such as:

Minimum and maximum current machines;
Minimum voltage circuit breakers;
Reverse power;

We will look at the principle of operation of a circuit breaker using the example of an overcurrent circuit breaker. 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 permissible setting value, the electromagnet 1 connected in series with the circuit will overcome the force of the restraining spring 3 and retract the armature 2, and turning through the axis 4, the latch 5 will release the lever 6. Then the tripping spring 7 will open the power contacts 8. Such a machine is turned on manually.

Currently, automatic machines have been created that have a shutdown time of 0.02 - 0.007 s for shutdown currents of 3000 - 5000 A.

Circuit breaker designs

There are quite a lot various designs automatic switches of both AC and DC circuits. Recently, small-sized automatic machines have become very widespread, which are intended for protection against short circuits and current overloads household and industrial networks in installations for currents up to 50 A and voltage up to 380 V.

Main protective agent in such switches are bimetallic or electromagnetic elements, triggered with a certain time delay when heated. Automatic machines that contain an electromagnet have a fairly high operating speed, and this factor is very important in case of short circuits.

Below is a cork machine with 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.

The bimetallic plate, like the electromagnet, is connected in series to the circuit. If more than rated current flows through the circuit breaker, the plate begins to heat up. When an excess current flows for a long time, plate 2 is deformed due to heating, and affects the release mechanism 5. If a short circuit occurs in the circuit, electromagnet 1 will instantly retract the core and thereby also influence the release, which will open the circuit. Also, this type of machine is turned off manually by pressing button 4, and turned on only manually by pressing button 3. The release mechanism is made in the form of a breaking lever or latch. The circuit diagram of the machine is shown below:

Where: 1 – electromagnet, 2 – bimetallic plate.

The operating principle of three-phase circuit breakers is practically no different from single-phase ones. Three-phase switches are equipped with special arc-extinguishing chambers or coils, depending on the power of the devices.

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