Independent release. Types of circuit breaker releases Electromagnetic circuit breaker release

Thermal release- provides protection only against overcurrent.

Electromagnetic release- provides protection only against short circuits.

Thermal-magnetic (magnetic-thermal, combined) release- consists of two types of releases - thermal and electromagnetic. Provides protection against both overcurrent and short circuits.

Thermal-magnetic (magnetic-thermal, combined) release, with protection against leakage currents- in addition to protection against overloads and short circuits, it protects people and electrical installations from ground faults.

Electronic release (the electronic unit protection - Overcurrent Release) - (depending on the version) provides the maximum number of types of protection.

Release device

Thermal release

The thermal release is a bimetallic plate that, when heated, bends and acts on the free release mechanism. A bimetallic plate is made by mechanically joining two metal strips. Two materials with different coefficients of thermal expansion are selected and connected to each other by soldering, riveting or welding.

Advantages:

no moving parts;
undemanding to pollution;
simplicity of design;
low price.

Flaws:

high own energy consumption;
sensitive to changes in ambient temperature;
when heated from third-party sources, they can cause false alarms.

Electromagnetic release

The electromagnetic release is an instantaneous device. It is a solenoid, the core of which acts on the free release mechanism. When a supercurrent flows through the solenoid winding, a magnetic field is created that moves the core, overcoming the resistance of the return spring.

The EM release can be configured (at the manufacturer's factory or by the consumer) to operate at short-circuit currents ranging from 2 to 20 In. The setting error varies approximately ±20% of the set current value for molded case switches.
For power circuit breakers, the short-circuit trip setting (the current value at which tripping is initiated) can be indicated either in amperes or as a multiple of the rated current.
There are settings: 3.5In; 7In, 10In; 12In and others.

Advantages:

simplicity of design;

Flaws:

creates a magnetic field.

Thermomagnetic release

The thermal release is a bimetallic plate consisting of two layers of alloys with different coefficients of thermal expansion. When an electric current passes, the plate heats up and bends towards the layer with a lower coefficient of thermal expansion. When the specified current value is exceeded, the bending of the plate reaches a value sufficient to activate the release mechanism, and the circuit opens, cutting off the protected load.

The electromagnetic release consists of a solenoid with 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 solenoid coil, overcoming the resistance of the spring, and triggers the release mechanism. In normal operation, a magnetic field is also induced in the coil, but its strength is not enough to overcome the resistance of the spring and retract the core.

How does the machine work in overload mode?

An overload mode occurs when the current in the circuit connected to the circuit breaker exceeds the rated value for which the circuit breaker is designed. In this case, the increased current passing through the thermal release causes an increase in the temperature of the bimetallic plate and, accordingly, an increase in its bending until the release mechanism is activated. The machine turns off and opens the circuit.

The thermal protection does not operate instantly, since it will take some time for the bimetallic strip to warm up. This time can vary depending on the magnitude of the excess current from a few seconds to an hour.

This delay allows you to avoid power outages during random and short-term increases in current in the circuit (for example, when turning on electric motors that have high starting currents).

The minimum current value at which the thermal release must operate is set using an adjusting screw at the manufacturer. Typically this value is 1.13-1.45 times higher than the denomination indicated on the machine’s labeling.

The magnitude of the current at which the thermal protection will operate is also affected by the ambient temperature. In a hot room, the bimetallic strip will warm up and bend until it triggers at a lower current. And in rooms with low temperatures the current at which the thermal release will operate may be higher than permissible.

The reason for network overload is the connection to it of consumers whose total power exceeds the calculated power of the protected network. Simultaneous activation of various types of powerful household appliances (air conditioner, electric stove, washing machine, dishwasher, iron, electric kettle, etc.) may well lead to an operation thermal release.

In this case, decide which consumers can be disabled. And don’t rush to turn on the machine again. You still won't be able to cock it into the operating position until it cools down and the bimetallic release plate returns to its original state. Now you know how a circuit breaker works during overloads

How does a machine work in short circuit mode?

In the event of a short circuit, the operating principle of the circuit breaker is different. During a short circuit, the current in the circuit increases sharply and many times to values that can melt the wiring, or rather the insulation of the electrical wiring. In order to prevent such a development of events, it is necessary to immediately break the chain. This is exactly how an electromagnetic release works.

The electromagnetic release is a solenoid coil containing a steel core held in a fixed position by a spring.

A multiple increase in the current in the solenoid winding, which occurs during a short circuit in the circuit, leads to a proportional increase in the magnetic flux, under the influence of which the core is drawn into the solenoid coil, overcoming the resistance of the spring, and presses the release bar of the release mechanism. The power contacts of the machine open, interrupting the power supply to the emergency section of the circuit.

Thus, the operation of the electromagnetic release protects the electrical wiring, the closed electrical appliance and the machine itself from fire and destruction. Its response time is about 0.02 seconds, and the electrical wiring does not have time to warm up to dangerous temperatures.

At the moment the power contacts of the machine open, when a large current passes through them, an electric arc appears between them, the temperature of which can reach 3000 degrees.

To protect the contacts and other parts of the machine from the destructive effects of this arc, an arc-extinguishing chamber is provided in the design of the machine. The arcing chamber is a grid from a set metal plates, which are isolated from each other.

An arc occurs at the point where the contact opens, and then one of its ends moves along with the movable contact, and the second slides first along the fixed contact, and then along the conductor connected to it, leading to back wall arc extinguishing chamber.

There it divides (splits) on the plates of the arc-extinguishing chamber, weakens and goes out. At the bottom of the machine there are special openings for the removal of gases formed during arc combustion.

If the machine turns off when the electromagnetic release is triggered, you will not be able to use electricity until you find and eliminate the cause of the short circuit. Most likely the cause is a malfunction of one of the consumers.

Disconnect all consumers and try to turn on the machine. If you succeed and the machine does not kick out, it means that one of the consumers is indeed to blame and you just have to find out which one. If the machine breaks down again even with the consumers disconnected, then everything is much more complicated, and we are dealing with a breakdown of the wiring insulation. We'll have to look for where this happened.

This is the principle of operation of a circuit breaker in various emergency situations.

If tripping your circuit breaker has become a constant problem for you, do not try to solve it by installing a circuit breaker with a higher rated current.

The machines are installed taking into account the cross-section of your wiring, and, therefore, higher current It's simply not allowed on your network. A solution to the problem can only be found after a complete inspection of your home’s electrical system by professionals.

Criteria for selecting circuit breakers

The main indicators that are referred to when choosing machines are:

Number of poles;

Rated voltage;

Maximum operating current;

Breaking capacity (short circuit current).

Number of poles

The number of machine poles is determined from the number of network phases. For installation in a single-phase network, single-pole or double-pole are used. For a three-phase network, three- and four-pole ones are used (networks with a TN-S neutral grounding system). In the domestic sectors, one- or two-pole circuit breakers are usually used.

Rated voltage

The rated voltage of the machine is the voltage for which the machine itself is designed. Regardless of the installation location, the voltage of the machine must be equal to or greater than the network:

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

During normal operation of the electrical network and all devices, 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 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, the permissible current of the electrical wiring is greater than the rating of the machine.

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 permissible 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.

Definition and types of releases, their advantages and disadvantages; examples of circuit breakers with thermal, electromagnetic, semiconductor and electronic tripping devices; processes occurring at supercurrents

Definition of release

Releases divide by two conditional groups:

main releases for circuit protection;
auxiliary releases for increased functionality.

Main release (first group), in relation to a circuit breaker, it is a device capable of recognizing a critical situation (the appearance of an overcurrent) and preventing its development in advance (causing divergence of the main contacts).

Auxiliary releases - additional devices(they are not included with the basic versions of the machines, but are supplied only with custom-made special versions):

independent release(remote shutdown of the circuit breaker based on a signal from the auxiliary circuit);
minimum voltage release (turns off the circuit breaker when the voltage drops below the permissible level);
zero voltage release (causes contacts to trip when there is a significant voltage drop).

Definitions of terms

Under overcurrent understand the current strength exceeding the rated (operating) current. This definition includes short circuit current and overload current.

Overload current- overcurrent operating in a functional network (prolonged exposure to overloads can cause damage to the circuit).
Short circuit current (SC)- overcurrent, which is caused by the short circuit of two elements with a very low total resistance between them, while in normal operation these elements are endowed with different potentials (a short circuit can be caused by incorrect connection or damage). For example, mechanical stress or aging of the insulation causes contact of current-carrying wires and a short circuit.
A high short-circuit current value is recognized from the formula:
I = U / R (current is equal to the ratio of voltage to resistance).
Therefore, as soon as R→ to 0, then I→ to infinity.

The main contacts in the circuit breaker carry the rated current during normal operation. The free release mechanism of the switching device has sensitive elements (for example, a rotary trip bar). The action of the release on these elements contributes to instantaneous automatic operation, that is, the release of the contact system.

Overcurrent release (MRT)- a release that causes the main contacts to open, with or without a certain period of time, as soon as effective value current exceeds the specified threshold.
Inverse time MRT is an overcurrent release that initiates tripping of the contacts after a specified time has elapsed, which is inversely dependent on the current strength.
MRI direct action- maximum current release, which initiates operation directly from the current overcurrent.

Definitions of maximum current release, short-circuit current and overload are taken (paraphrased without loss of meaning) from the GOST 50345 standard.

Types of releases, used in circuit breakers

In circuit breakers install one or a combination of the following releases:

provide basic overcurrent protection, factory settings do not change during operation:
- thermal release or overload release;
- electromagnetic or short-circuit release;

one of the ones proposed below replaces the first two; during operation, adjustment is allowed (holding time at overcurrent to ensure selectivity, which current is considered an overload, which is a short circuit):
- semiconductor release;
- electronic release;

additional tripping devices to expand functionality:
- independent release;
- undervoltage release;
- zero voltage release.

It should be taken into account that cheap devices are electromagnetic and thermal releases. Automatic switches equipped with a semiconductor or electronic release (they functionally replace a combination of a thermal and electromagnetic release) cost from $1200 and above, so they are used as input devices for rated currents from 630 A (there are rare exceptions of lower amperage).

Briefly in the video describes the design of the circuit breaker, in particular about thermal and electromagnetic releases:

Thermal release

The thermal release is a bimetallic plate, which bends when heated and affects the free release mechanism.
A bimetallic plate is made by mechanically joining two metal strips. Two materials with different coefficients of thermal expansion are selected and connected to each other by soldering, riveting or welding.
Let's say bottom material in a bimetallic plate, when heated, it elongates less than the upper metal, then the bending will occur downward.

The thermal release protects against overload currents and is configured for certain operating modes.

For example, for a product of the BA 51-35 series, the overload releases are calibrated at a temperature of +30 °C to:

conditional non-trip current 1.05·In (time 1 hour for In ≤ 63 A and 2 hours for In ≥ 80 A);
conditional tripping current 1.3 In for alternating current and 1.35·In for direct current.

The designation 1.05·In means a multiple of the rated current. For example, with a rated current In = 100 A, the conditional non-trip current is 105 A.
The time-current characteristics (graphs are always available in factory catalogs) clearly show the dependence of the response time of thermal and electromagnetic releases on the value of the flowing overcurrent.

Advantages:

no rubbing surfaces;
have good vibration resistance;
easily tolerate pollution;
simplicity of design → low price.

Flaws:

constantly consume electrical energy;
sensitive to changes in ambient temperature;
when heated from third-party sources, they can cause false alarms.

Electromagnetic release

An electromagnetic (abbreviated as EM) release is an instantaneous device. It is a solenoid, the core of which acts on the free release mechanism. When a supercurrent flows through the solenoid winding, a magnetic field is generated that moves the core, overcoming the resistance of the return spring.

The EM release is configured to operate at short-circuit currents ranging from 2 to 20·In. The setting error varies within ±20% of the set value.

For power circuit breakers The short-circuit setpoint (the current value at which tripping is initiated) can be indicated either in amperes or as a multiple of the rated current. There are settings:

3.5·In;
7·In;
10·In;
12·In;
and others.

For example, with the rated current of the machine In = 200 A, with a setting of 7 In, tripping will occur when the overcurrent reaches a value of 7 200 = 1400 A.

B (3-5);
C (5-10);
D (10-50).

The limit values of the rated current In at which the contacts will diverge are indicated in parentheses.

Advantages:

simplicity of design;

Flaws:

creates a magnetic field;
triggers instantly, without delay.

Time delay means ensuring selectivity. Selectivity or selectivity is achieved when the input circuit breaker recognizes a short circuit and passes it for a specified time. This time is sufficient for the downstream protective device to trip. In this case, not the entire object is disabled, but only the damaged branch.

Devices with a time delay or selective - application category B (all machines with an electronic or semiconductor release).
Instantaneous or non-selective devices - application category A (virtually all circuit breakers with an electromagnetic tripping device).

Thermomagnetic or combined release

A series connection of a thermal and electromagnetic release is often used. Depending on the manufacturer, this linking of two devices is called combined or thermomagnetic release. The phrase “thermomagnetic release” is often used in foreign catalogs and literature.

Phenomena caused by overcurrents

When a short circuit current occurs, the following phenomena occur:

electrodynamic forces;
a magnetic field;
thermal stress (overheating).

In case of overload, the determining factor remains overheating of the conductive parts.

Electrodynamic forces

Electrodynamic forces act on a conductor with a current flowing through it, which is in a magnetic field with induction B.
When the rated current flows, the electrodynamic forces are insignificant, but when a short-circuit current appears, these forces can lead not only to deformation and breakage of individual parts of the switching device, but also to the destruction of the machine itself.
Special calculations are made for electrodynamic resistance, which are especially relevant when there is a tendency to decrease overall characteristics(the distances between the conductive parts of the poles are reduced).

A magnetic field

The magnetic field is one of the factors generating electrodynamic forces.
Magnetic fields negatively affect the operation of electrical equipment, especially measuring instruments and computers.

Thermal stress (overheating)

When any current with strength I flows through a conductor, its core heats up, which can lead to fires or damage to the insulation.
When overcurrents occur, overheating is of current importance if the short circuit is not blocked, allowing it to reach maximum values.

How to choose the right circuit breaker?

A circuit breaker (in the language of electricians, “automatic”) is the basis of protection in low-voltage (up to 1000 Volt) power electrical circuits. This is a combined electrical device that combines the functions of a switch and a protective device. Almost the entire distribution and protection system for household electrical wiring is built on automatic devices. I would like to immediately note that the main use of the machine is to protect that section of electrical wiring that is located between the outlet of the machine and the consumer. If there is another machine further along the line, then our machine must defend the area between these two machines. If an overload or short circuit occurs in any section of the circuit, only one circuit breaker should operate, protecting that particular section of the circuit.

How to choose a machine?

Let's take classic example. We are making repairs in an apartment (or in a private house), changing the electrical wiring and want to protect it from overloads and short circuits. A common practice these days is to divide the wiring into several branches and protect each of them with a separate machine. In apartments, lighting and sockets are often separated into separate lines. In addition, a separate line can be allocated for an electric stove, another for kitchen sockets and utility room sockets, which usually include the most powerful electrical appliances in the apartment: an electric kettle, a microwave oven, etc. It should be noted that standard electrical outlets used in our homes are usually designed for a maximum current of 10 or 16A, and are often the weakest link in the electrical wiring. Therefore, the rating of the circuit breaker protecting the line with such sockets cannot be higher than 16A, no matter how thick the wire is.

About the material and thickness of the wire - this is a separate topic, here I will just say briefly: copper and only copper, for apartments and private houses we take a cross-section of 1.5 sq. mm for lighting, 2.5 sq. mm for standard sockets. Accordingly, the ratings of circuit breakers for lighting lines are 10A, for lines feeding sockets, 16A (provided that the sockets are also 16-amp). This raises a number of questions. It turns out that each socket can withstand 16 Amps alone, but the total current of the entire group of sockets should also not exceed the same 16 Amps.

Some people don’t like this situation, and they install machines with a higher current - 25A and even higher. For some reasons, this should not be done, even if the cross-section of the wire allows such a current to pass long time. Let's imagine a situation where some powerful power tool is plugged into one of the sockets, which consumes current up to 25-30A. It is clear that with such a current, unpleasant processes can occur in the outlet, including fire, but a 25-amp circuit breaker will not feel this overload. Well, or he will feel it, but only when everything is already burning with a blue flame. Someone may argue that there is no standard power tool with such a current consumption, but the tool can be non-standard and faulty. Or it may happen that several powerful electrical appliances are connected to the outlet through an extension cord at the same time, with the same result.

Therefore, if it is assumed that the total current of equipment simultaneously plugged into sockets will be more than 16A, then the right decision will divide the sockets into several groups and power each group through a separate machine. It must be borne in mind that both 16 and 10 amp outlets are available for sale. I will not say that they are of poor quality, they are simply designed for a maximum load current of 10 A. For such sockets, it is permissible to lay wiring with a cross-section of 1.5 mm 2, but the machine in this case must also be 10-amp. Regarding extension cords. Very often you can find cheap options, the cross-section of the cord of such an extension cord is 1 mm 2, sometimes even smaller. Extension cords themselves usually do not have any protection. Therefore, use such extension cords with extreme caution, understanding that the machine does not protect them.

Marking of circuit breakers

We can see some mysterious inscriptions on the body of the machine gun. The main ones are indicated by numbers below:

Explanation:

Rated current of the machine
Triggering characteristics
Maximum breaking current
Trip class.

In addition to the above inscriptions, the case usually contains the manufacturer’s logo and the type of machine, as well as a brief schematic designation, showing where the fixed contact is located (when positioned vertically, it is usually placed on top) and how the releases are located relative to the contacts. The clamping contact screws can be closed with curtains (see the machine on the far left), this is convenient for sealing. The case is usually made of polystyrene - in my opinion, not the most suitable material for a device that can get quite hot.

Rated current of the machine

The time has come to figure out what the rated current of the machine actually means and what the protection operation current will be. A common mistake is that people often think that the rated current is the tripping current. In fact, a working circuit breaker will never trip at its rated current. Moreover, it will not work even at 10% overload. If there is a large overload, the machine will turn off, but this does not mean that it will turn off quickly. A conventional modular circuit breaker has 2 releases: a slow thermal one and a fast-reacting electromagnetic one. The thermal release basically contains a bimetallic plate, which is heated by the current passing through it. When heated, the plate bends and, at a certain position, acts on the latch and the switch turns off. The electromagnetic release is a coil with a retractable core, which, at high current, also acts on the latch that turns off the circuit breaker. If the purpose of a thermal release is to turn off the circuit breaker during overloads, then the task of an electromagnetic release is to quickly turn off during short circuits, when the current value is several times higher than the rated value.

Range of rated currents

I had to install circuit breakers with a rating of 0.2A. In general, I have come across modular machines of the following denominations: 0.2, 0.3, 0.5, 0.8, 1, 1.6, 2, 2.5 3, 4, 5, 6, 6.3, 8, 10, 13, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125 Amp. That is, I cannot say that the ratings correspond to any single standard series, such as E6, E12 for resistors or capacitors. They sculpt whatever they want. With machines above 100A the situation is approximately the same. The maximum rating of a machine designed to operate in 0.4 kV networks that I have seen is 6300A. This corresponds to a transformer with a capacity of 4 MVA, but we don’t make more powerful transformers for this voltage, this is the limit.

Triggering characteristics

The sensitivity of electromagnetic releases is regulated by a parameter called the response characteristic. This important parameter, and it’s worth dwelling on it a little. The characteristic, sometimes called a group, is denoted by one Latin letter; on the body of the machine it is written right before its nominal value, for example, the inscription C16 means that the rated current of the machine is 16A, characteristic C (the most common, by the way). Less popular are machines with characteristics B and D; current protection of household networks is mainly based on these three groups. But there are machines with other characteristics.

According to Wikipedia, circuit breakers are divided into following types(classes) for instantaneous tripping current:

type B: over 3 I n up to 5 I n inclusive (where I n- rated current)
type C: over 5· I n to 10· I n inclusive
type D: over 10 I n up to 20 I n inclusive
type L: over 8· I n
type Z: over 4 I n
type K: over 12· I n

At the same time, Wikipedia refers to GOST R 50345-2010. I specifically re-read this entire standard, but it never mentions any types L, Z, K. And for some reason I don’t see such machines on sale. For European manufacturers, the classification may be slightly different. In particular, there is additional type A(over 2· I n until 3· I n). Some manufacturers have additional shutdown curves. For example, at ABB there are circuit breakers with curves K(8 - 14 I n) and Z (2 - 4· I n), complying with IEC 60947-2 standard. In general, we will keep in mind that, in addition to B, C and D, there are other curves, but in this article we will consider only these. Although the curves themselves are the same - they generally show the dependence of the response time of the thermal release on the current. The only difference is the point to which the curve reaches, after which it abruptly ends to a value close to zero. And here are the graphs themselves:

These are average graphs; in fact, some variation in the response time of thermal protection is allowed. What should we keep in mind when choosing a shutdown characteristic? Here the starting currents of the equipment that we are going to turn on through this machine come to the fore. It is important for us that the starting current in sum with other currents in this circuit does not exceed the operating current of the electromagnetic release (cut-off current). It’s easier when we know exactly what will be connected to our machine, but when the machine protects a group of sockets, then we can only guess what and when it will be turned on. Of course, we can take it with a reserve - install group D machines. But it is far from a fact that the short circuit current in our circuit somewhere on a distant outlet will be sufficient to trigger the cutoff. Of course, after ten seconds the thermal release will heat up and turn off the circuit, but this will be a serious test for the wiring, and a fire may occur at the point of the circuit. Therefore, we need to look for a compromise. As practice has shown, to protect sockets in residential premises, offices - where the use of powerful power tools is not expected, industrial equipment, - it is best to install machines of group B. For the kitchen and utility unit, for garages and workshops, machines with characteristic C are usually installed - where there are sufficiently powerful transformers, electric motors, there are also starting currents. Group D machines should be installed where there is equipment with difficult starting conditions - conveyors, elevators, lifts, machine tools, etc.

Look at the following picture, very similar in meaning to the previous one; here you can see the spread of thermal protection parameters of circuit breakers:

Notice the two numbers at the top of the graph. These are very important numbers. 1.13 is the multiplicity below which no serviceable machine will ever work. 1.45 is the multiplicity at which any working machine is guaranteed to work. What do they actually mean? Let's look at an example. Let's take a 10A machine. If we pass a current of 11.3A or less through it, it will never turn off. If we increase the current to 12, 13 or 14 A, our machine may turn off after some time, or it may not turn off at all. And only when the current exceeds 14.5A can we guarantee that the machine will turn off. How fast depends on the specific instance. For example, with a current of 15A, the response time can range from 40 seconds to 5 minutes. Therefore, when someone complains that his 16-amp circuit breaker does not work at 20 amperes, he does it in vain - the circuit breaker is absolutely not obliged to work at such a multiplicity. Moreover, these graphs and figures are normalized for an ambient temperature of 30°C; at lower temperatures the graph shifts to the right, at higher temperatures - to the left.

Current limiting class

Let's move on. An electromagnetic release, although called instantaneous, also has a certain response time, which reflects such a parameter as the limitation class. It is indicated by one number and for many models this number can be found on the device body. Basically, machines with current limiting class 3 are now produced - this means that from the time the current reaches the response value until the circuit is completely broken, no more than 1/3 of the half-cycle will pass. With our standard frequency of 50 Hertz, this turns out to be about 3.3 milliseconds. Class 2 corresponds to a value of 1/2 (about 5 ms), there are probably others, but I am not aware of their existence. According to some sources, the absence of marking of this parameter is equivalent to class 1. I would call this parameter not a current limiting class, but a cutoff speed. It would seem that the faster, the better. In fact, sometimes it makes sense to install a machine with a slower response - this applies to group machines, so that during a short circuit on some outgoing line they do not trip together with the machine of this line, i.e. so that there is selectivity. Although there is no guarantee that a machine with a lower class will work slower than a machine with big class. Therefore, I would not build selectivity based on this parameter, and there are no official recommendations about this.

Maximum breaking current

A very important parameter is the maximum shutdown current. This parameter largely reflects the quality of the power part of the machine. Usually in the retail network we are offered machines with a shutdown current of up to 4.5 or 6 kA. Sometimes you come across cheap models with a breaking capacity of 3 kA. And although in living conditions The short-circuit current rarely reaches such values; nevertheless, I do not recommend using circuit breakers with a breaking capacity of less than 4.5 kA. Because if the breaking capacity is small, then we should expect smaller area contacts, worse arc chutes, etc.

Where to buy machines?

It is usually not a problem to buy a circuit breaker with characteristic C - they are presented in sufficient assortment in construction and hardware stores and markets. Machines with characteristics B and D are also found in these places, but quite rarely. They can be ordered from companies or small specialized stores. Or you can buy it in the ABC-electro online store. This store has almost all machines of all denominations and characteristics. It’s nice that there are not only the usual ratings of 6, 10, 16, 25, but also 8, 13, 20 Amperes, which are often not enough to ensure good selectivity.

Dependence of response on ambient temperature

Another point that is often forgotten is the dependence of the thermal protection of the machine on the ambient temperature. And it is very significant. When the machine and the protected line are in the same room, it’s usually okay: as the temperature drops, the sensitivity of the machine decreases, but the load capacity of the wire increases, and the balance is more or less maintained. Problems can arise when the wire is warm and the machine is cold. Therefore, if such a situation occurs, then an appropriate amendment must be made. Examples of such dependencies are shown in the graph below. More accurate information on a specific model should be found in the manufacturer's data sheet.

Number of poles of the machine. Series and parallel connection of poles and circuit breakers

The machine can have from 1 to 4 poles. Each pole has its own thermal and electromagnetic release. When one of them is triggered, all poles are switched off simultaneously. It is also possible to turn on only all poles together with one common handle. There is another type of slot machine - the so-called 1p+n. This machine synchronously switches 2 wires: phase and neutral, but it has only one release - only on the phase contact. When the release is triggered, both contacts open. Despite the fact that 2 wires pass through such a machine, it is not considered two-pole.

Can poles be connected in parallel or in series? Can. But you need to have good reasons for this. For example, when disconnecting an inductive load or simply in cases of overload or short circuit - that is, when a large current has to be broken, an electric arc occurs. To break it, there are arc-extinguishing chambers, but still this does not pass without a trace - the contacts may burn, soot may appear. If we connect the poles in series, the arc will be divided between them, it will be extinguished faster, and there will be less wear on the contacts. The disadvantages of this method include increased losses - after all, there is some kind of voltage drop on the contacts, and the higher the current, the more power is lost on them (usually several watts at currents of 10-100A, usually the manufacturer includes this information in the passport) . Parallel connection of poles is usually used when there is no machine of the required rating, but there is a machine of a lower rating, but with “extra” poles. In this case, usually, to calculate the total rated current, it is recommended to multiply the rated current of one pole by 1.6 for 2 parallel poles, for 3 parallel poles by 2.2, for 4 parallel poles by 2.8. Perhaps in some emergency cases this is a way out, but at the first opportunity you need to replace such a surrogate with a machine of the required denomination.

The situation is even more complicated when connecting machines in parallel and in series. Of course, you can come up with a situation and somehow even justify the parallel connection of two or more machines, but I would not recommend even considering this option. How the currents will be distributed, what will happen after one of the machines is turned off - all this is doubtful and difficult to predict. It makes more sense to turn on the machines sequentially. For example, this can be considered as increasing the reliability of protection: if one of the machines malfunctions, the other will cover it. But usually they don’t do this, and a group machine is considered as insurance. In addition, the circuit breaker itself consumes a certain amount of electricity, so an additional circuit breaker also means additional losses.

Circuit breaker power dissipation

As an example, I will give the passport values of this parameter for VA 47-63 automatic machines (the values are given for new automatic machines at current values equal to the rated one):

Rated current In, A	Power dissipation, W
Rated current In, A	1-pole	2-pole	3-pole	4-pole
1	1,2	2,4	3,6	4,8
2	1,3	2,6	3,9	5,2
3	1,3	2,6	3,9	5,2
4	1,4	2,8	4,2	5,6
5	1,6	3,2	4,8	6,4
6	1,8	3,6	5,5	7,2
8	1,8	3,6	5,5	7,33
10	1,9	3,9	5,9	7,9
13	2,5	5,3	7,8	10,3
16	2,7	5,6	8,1	11,4
20	3,0	6,4	9,4	13,6
25	3,2	6,6	9,8	13,4
32	3,4	7,5	11,2	13,8
35	3,8	7,6	11,4	15,3
40	3,7	8,1	12,1	15,5
50	4,5	9,9	14,9	20,5
63	5,2	11,5	17,2	21,4

As you can see, the circuit breaker also wants to eat. Therefore, you should not get carried away and stick machine guns wherever possible. Where do the losses occur? The main part falls on the thermal release. But there is no need to overdramatize the situation. These losses are proportional to the current flowing. Therefore, if, for example, the load is 2 times less than the rated load, then the losses will be correspondingly half as much, and if there is no load, there will be no losses. If they are presented as a percentage, then the values will be on the order of 0.05-0.5%, with the smallest percentage for the most powerful machines. In the contacts themselves, while the machine is new, losses are insignificant. But during operation, the contacts will burn out, the contact resistance will increase, and with it the losses will increase. Therefore, with an old machine, losses may be noticeably greater. By the way, measuring losses is quite simple - you need to measure the voltage drop across the machine and the current passing through it. At home, I do this using this very inexpensive device that combines a multimeter and a clamp meter:

Yes - cheap Chinese consumer goods, but quite suitable for household purposes.

Selecting a machine based on load power (current)

Although the main purpose of the machine is to protect electrical wiring, under certain conditions it is advisable to calculate the machine based on the load current. This is possible in cases where the line extending from the machine is intended to power one specific electrical appliance. In household networks, this could be an electric stove or air conditioner, some kind of machine, electric boiler, etc. As a rule, we know the rated current of an electrical appliance, or we can calculate it by knowing the load power. Since the wiring is selected with a certain margin, in this case the rating of the machine is usually less than what we would get by calculating the permissible current of the wire. Therefore, in case of any short circuits inside the electrical device or its overload, our protection will work, protecting it from further destruction.

Selecting a machine for an electric drive (electric motor, solenoid valve, etc.)

If the load in the circuit is an electric motor, then you need to remember that the starting current of the motor is several times higher than the rated current, so in this case you need to use machines with characteristic C, and in some cases (non-household) even D. We select the rating of the machine according to the rated current of the motor . It can be read on the plate or measured with the aforementioned pliers. You need to measure the current with a loaded engine, don’t forget. It is clear that the machine cannot exactly match the motor current; choose the closest value. Some manufacturers claim machines with special characteristics, especially for electric motors. Although, upon closer examination, these characteristics are usually somewhere between C and D. Of course, such an automatic machine will not protect the engine properly and, if, for example, the shaft jams, the following will happen: the cutoff will not work, because the current will not be higher than the starting current, and the thermal protection may not be in time - overheating of the windings in the motor occurs very quickly. Therefore, the electric motor requires additional protection in the form of a special high-speed thermal (or electronic) relay. The same rules should be followed when choosing a machine for an electromagnetic drive (various valves, curtains, etc.).

Circuit breaker manufacturers

Large machines are a separate topic; here we consider manufacturers exclusively in the context of modular products. In the post-Soviet space, brands such as ABB, Legrand, Shneider Electric have proven themselves well. Usually the products of these companies will be recommended to you when you ask for something more reliable. From Russian manufacturers Quite decent devices are made by KEAZ, Kontaktor, DEKraft. IEK received the most unflattering reviews - probably rightly so, although they are perhaps the most popular on sale due to their low price.

A fuse is an electrical device that protects the electrical network from emergency situations associated with current parameters (current, voltage) going beyond the specified limits. The simplest fuse is a fuse link.

This is a device connected in series to the protected circuit. As soon as the current in the circuit exceeds a predetermined one, the wire melts, the contact opens, and the protected section of the circuit thus remains undamaged. The disadvantage of this method of protection is that the protective device is disposable. Burnt out - needs to be replaced.

Circuit breaker device

A similar problem is solved using so-called automatic switches (AB). Unlike disposable fuses, automatic machines are quite complex devices; when choosing them, several parameters should be taken into account.

They are also connected in series in the circuit. When the current increases, the circuit breaker breaks the circuit. Circuit breakers are produced in a wide variety of design and with various parameters. The most common machines today are those for mounting on a DIN rail (Fig. 1).

AP-50 assault rifles (Fig. 3-5) and many others are widely known from Soviet times. The machines are produced with the number of poles (lines for connection) from one to four. At the same time, two- and four-pole circuit breakers can include not only protected, but also unprotected contact groups, which are usually used to break the neutral.

Composition and structure of AB

Most circuit breakers include:

manual control mechanism (used to manually turn the machine on and off);
switching device (set of moving and fixed contacts);
arc extinguishing devices (grid of steel plates);
releases.

Arc extinguishing devices provide extinguishing and blowing of the arc, which is formed when the contacts through which the overcurrent passes are opened (Fig. 2)

A release is a device (part of a machine or an additional device) mechanically connected to the AB mechanism and ensuring the opening of its contacts.

The circuit breaker usually contains two releases.

The first release - reacts to long-term, but small network overload (thermal release). Usually this device is based on a bimetallic plate, which, under the influence of a current passing through it, gradually heats up and changes its configuration. Eventually she presses down on the retaining mechanism, which releases and opens the spring-loaded contact.

The second release is the so-called “electromagnetic” one. It provides a quick response of the AV to a short circuit. Structurally, this release is a solenoid, inside the coil of which there is a spring-loaded core with a pin that rests on a movable power contact.

The winding is connected in series. During a short circuit, the current in it increases sharply, due to which the magnetic flux increases. In this case, the resistance of the spring is overcome, and the core opens the contact.

AB parameters

The first parameter is the rated voltage. Automatic machines are produced for direct current only and for alternating and direct current. DC circuit breakers for general use are quite rare. In household and industrial networks, AVs are mainly used for alternating and direct current. Most often, AVs with a rated voltage of 400V, 50Hz are used.

The second parameter is the rated current (In). This is the operating current that the machine passes through itself in a long-term mode. The usual range of ratings (in amperes) is 6-10-16-20-25-32-40-50-63.

The third parameter is the breaking capacity, the ultimate switching capacity (UCC). This is the maximum short circuit current at which the machine can open the circuit without being destroyed. The usual series of PKS passport values (in kiloamperes) is 4.5-6-10. At a voltage of 220 V, this corresponds to a network resistance (R=U/I) of 0.049 Ohm, 0.037 Ohm, 0.022 Ohm.

As a rule, the resistance of household electrical wires can reach 0.5 Ohm; a short circuit current of 10 kA is possible only in the immediate vicinity of an electrical substation. Therefore, the most common PKS are 4.5 or 6 kA. Circuit breakers with PKS 10 kA are used mainly in industrial networks.

The fourth parameter characterizing the AB is the setting current (setting) of the thermal release. This parameter for various machines ranges from 1.13 to 1.45 of the rated current. We noted that when the rated current passes, long-term operation of the circuit with AV is guaranteed.

The setting of the thermal release is greater than the nominal value; it is the actual current reaching the set value that will cause the machine to turn off. It should be noted that automatic machines of the Soviet period provide for manual adjustment of the thermal protection setting (Fig. 5). Access to the adjusting screw is not possible in machines installed on a DIN rail.

The fifth parameter of the circuit breaker is the setting current of the electromagnetic release. This parameter determines the multiple of excess of the rated current at which the AV will operate almost instantly, reacting to a short circuit.

An important characteristic of the machine is the dependence of the response time on the current (Fig. 6). This dependence consists of two zones. The first is the area of responsibility of thermal protection. Its peculiarity is a gradual decrease in the time it takes for the current to pass before tripping. This is understandable - the higher the current, the faster the bimetallic plate heats up and the contact opens.

If the current is very high (short circuit), the electromagnetic release is triggered almost instantly (within 5–20 ms). This is the second zone on our chart.

According to the setting of the electromagnetic release, all automatic machines are divided into several types:

A Primarily for protection electronic circuits and long chains;
B For conventional lighting circuits;
C For circuits with moderate starting currents (motors and transformers of household appliances);
D For circuits with large inductive loads, for industrial electric motors;
K For inductive loads;
Z For electronic devices.

The most common are B, C and D.

Characteristic B - used for general purpose networks, especially where it is necessary to ensure selectivity of protection. The electromagnetic release is configured to operate at a current ratio of 3 to 5 relative to the nominal value.

When connecting purely active loads (incandescent light bulbs, heaters...), the starting currents are almost equal to the operating currents. However, when connecting electric motors (even refrigerators and vacuum cleaners), the starting currents can be significant and cause false operation of the machine with the characteristic in question.

The most common are machines with characteristic C. They are quite sensitive, and at the same time do not give false alarms when starting motors of household appliances. Such a switch operates at 5-10 times the nominal value. Such machines are considered universal and are used everywhere, including industrial facilities.

Characteristic D is the setting of the electromagnetic release for 10 - 14 current ratings. Typically such values are needed when using asynchronous motors. As a rule, circuit breakers with characteristic D are used in a three- or four-pole design to protect industrial networks.

When using circuit breakers together, you need to have an understanding of the concept of selective protection. The construction of selective protection ensures that circuit breakers located closer to the accident site are triggered, while more powerful circuit breakers located closer to the voltage source should not operate. To achieve this, more sensitive and fast-acting machines are installed closer to consumers.

Good day, dear friends!

Today I will continue to talk about circuit breakers in the light of measuring the resistance of the phase-zero loop.

In the last article devoted to measuring the resistance of the phase-zero loop, I mentioned the time-current characteristics of circuit breakers. Today I will give as an example the following characteristics for an assault rifle of the VA47-29 type:

Each circuit breaker has its own characteristic. Usually it is given in the passport for the machine in the form shown in the figure. Those. there is some variation in the parameters. As you can see, this spread is quite large.

For characteristic “B”, the cut-off current (current of the electromagnetic release) can be in the range from 3In to 5In;

For characteristic “C” - from 5In to 10In;

For characteristic “D” - from 10In to 14In.

This means that the short circuit current measured or calculated by us for a specific line may either satisfy the parameters of the circuit breaker (be sufficient to turn it off) or not.

The real characteristic of the dependence of the response time of a circuit breaker on the current flowing through it for each specific machine can only be obtained by checking the parameters of this machine.

But many laboratories do not have the equipment to test circuit breakers. and accordingly, they do not have this type of work. They do it simply. To check the compliance of the circuit breaker with the line parameters (possible short circuit current), use upper value cut-off current, i.e. for characteristic “C” it is 10In. This approach is quite justified, because the machine will probably turn off at a current greater than the possible tripping current of the release, but in some cases it is not reliable enough. Because if the measured short circuit current is less than 10In, then, of course, if the line wires are in good condition, it is necessary to replace the circuit breaker with a suitable one. Although, when checking the circuit breaker, it may become clear. that its operation current is, for example, 7In and in this case, even with the short-circuit current we measured, the machine should reliably turn off, i.e. There was no need to replace the machine.

Let's return to the time-current characteristic. Let's say we checked the machine and, based on the measured parameters, obtained its individual characteristics (displayed by the green line in the figure).

What does it give us?

According to the PUE clause 1.7.79, the automatic power shutdown time in the TN system should not exceed 0.4 s at a phase voltage of 220V, but in circuits supplying distribution, group, floor and other switchboards and panels, the shutdown time should not exceed 5 s.

Thus, we have two points on the characteristic 0.4s and 5s. Depending on the installation location of the circuit breaker, we determine which point we need and find the tripping (shutdown) current of the circuit breaker at this point.

From the characteristics we received (green line) we can see that the machine will turn off in 0.4 s at seven times the rated current, and in 5 s at a current of 4.5 In.

Once again I will answer a frequently asked question: Why measure the resistance of the phase-zero loop?

Knowing the resistance of the phase-zero loop of a circuit (line), you can find the short circuit current that can develop in this line. And knowing this current, you can answer the question: will the circuit breaker installed in this line work and in what time?

That's all for today. If you have any questions, please ask.

To protect household electrical circuits, modular circuit breakers are usually used. Compactness, ease of installation and replacement, if necessary, explains their wide distribution.

Externally, such a machine is a body made of heat-resistant plastic. On the front surface there is an on/off handle, on the back there is a latch for mounting on a DIN rail, and on the top and bottom there are screw terminals. In this article we will look at.

How does a circuit breaker work?

In normal operation mode, a current flows through the machine that is less than or equal to the rated value. The supply voltage from the external network is supplied to the upper terminal connected to the fixed contact. From the fixed contact, current flows to the movable contact closed with it, and from it, through a flexible copper conductor, to the solenoid coil. After the solenoid, the current is supplied to the thermal release and after it to the lower terminal, with the load network connected to it.

In emergency modes, the circuit breaker disconnects the protected circuit by triggering a free tripping mechanism driven by a thermal or electromagnetic release. The reason for this operation is an overload or a short circuit.

Thermal release is a bimetallic plate consisting of two layers of alloys with different coefficients of thermal expansion. When an electric current passes, the plate heats up and bends towards the layer with a lower coefficient of thermal expansion. When the specified current value is exceeded, the bending of the plate reaches a value sufficient to activate the release mechanism, and the circuit opens, cutting off the protected load.

Electromagnetic release consists of a solenoid with 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 solenoid coil, overcoming the resistance of the spring, and triggers the release mechanism. In normal operation, a magnetic field is also induced in the coil, but its strength is not enough to overcome the resistance of the spring and retract the core.

How does the machine work in overload mode?

This delay allows you to avoid power outages during random and short-term increases in current in the circuit (for example, when turning on electric motors that have high starting currents).

The magnitude of the current at which the thermal protection will operate is also affected by the ambient temperature. In a hot room, the bimetallic strip will warm up and bend until it triggers at a lower current. And in rooms with low temperatures, the current at which the thermal release will operate may be higher than permissible.

How does a machine work in short circuit mode?

In case of a short circuit it is different. During a short circuit, the current in the circuit increases sharply and many times to values that can melt the wiring, or rather the insulation of the electrical wiring. In order to prevent such a development of events, it is necessary to immediately break the chain. This is exactly how an electromagnetic release works.

The electromagnetic release is a solenoid coil containing a steel core held in a fixed position by a spring.

At the moment the power contacts of the machine open, when a large current passes through them, an electric arc appears between them, the temperature of which can reach 3000 degrees.

To protect the contacts and other parts of the machine from the destructive effects of this arc, an arc-extinguishing chamber is provided in the design of the machine. The arc chamber is a grid of a set of metal plates that are insulated from each other.

The arc occurs at the point where the contact opens, and then one end of it moves along with the movable contact, and the second slides first along the fixed contact, and then along the conductor connected to it, leading to the rear wall of the arc chamber.

This is how it is in various emergency situations.

If tripping your circuit breaker has become a constant problem for you, do not try to solve it by installing a circuit breaker with a higher rated current.

The machines are installed taking into account the cross-section of your wiring, and, therefore, more current in your network is simply not allowed. A solution to the problem can only be found after a complete inspection of your home’s electrical system by professionals.

Similar materials on the site:

The independent release is an addition to the protective device for the electrical network. It is mechanically connected to the circuit breaker. An independent release performs the function of breaking the circuit when factors are detected that can lead to damage to the line and the devices included in it. These include an increase in current strength above the limit that the cable can withstand, a breakdown of electric current to the ground or the body of a device connected to the circuit, as well as a short circuit. This material will help you understand what circuit breaker releases are, what types of this device there are and what the operating principle of each of them is. In addition, we will tell you how to check the functionality of these elements.

Automatic safety switch with independent release

The independent release, as mentioned, is an additional element of the circuit protection device. It allows you to turn off the AV at a distance when voltage is applied to its coil. To return it to its original state, press the button on the device that says “Return”.

Circuit breaker releases of this type can be used in single-phase and three-phase networks.

The independent release is most often used in electrical circuits and automatic switchboards of large objects. Energy supply control in these cases, as a rule, is carried out from the operator’s console.

An example of an independent release triggering in the video:

What causes an independent type tripping element to trip?

An independent release can trip for various reasons. We list the most common of them:

Excessive decrease or, on the contrary, increase in tension.
Changing the specified parameters or the state of the electric current.
Malfunction of circuit breakers, malfunction for an unknown reason.

In addition to independent tripping devices, there are similar elements included in circuit breakers. Built-in circuit breaker releases are divided into thermal and electromagnetic. These devices also help protect the line from excessive loads and short circuits. Let's look at them in more detail.

Thermal release of circuit breaker

The main element of this device is a bimetallic plate. In its manufacture, two metals with different coefficients of thermal expansion are used.

Being pressed together, they expand to varying degrees when heated, which leads to curvature of the plate. If the current is not normalized for a long time, then upon reaching a certain temperature the plate touches the AB contacts, interrupting the circuit and de-energizing the wiring.

The main reason for excessive heating of the bimetallic plate, due to which the thermal release is triggered, is too high a load on a certain section of the line protected by the circuit breaker.

For example, the cross-section of the AB output cable going into the room is 1 square meter. mm. It can be calculated that it is capable of withstanding the connection of devices with a total power of up to 3.5 kW, while the strength of the current passing in the line should not exceed 16A. Thus, you can easily connect a TV and several lighting fixtures to this group.

If the owner of the house decides to include additional power in the sockets of this room washing machine, electric fireplace and vacuum cleaner, then the total power will be much higher than what the cable can withstand. As a result, the strength of the current passing through the line will increase, and the conductor will begin to heat up.

Overheating the cable can cause the insulating layer to melt and catch fire.

To prevent this from happening, a thermal release is activated. Its bimetallic plate heats up along with the metal of the wire, and after some time, bending, turns off the power to the group. When it has cooled down, the protective device can be turned on again manually, after first unplugging the power cords of the devices that caused the overload. If this is not done, after a while the machine will turn off again.

Example of using a release in fire protection on video:

It is important that the AB rating matches the cable cross-section. If it is less than required, then operation will occur even under normal load, and if it is more, then the thermal release will not respond to a dangerous excess of current, and as a result the wiring will burn out.

In order to protect electric motors from prolonged overloads and phase failure, these units can also be equipped with thermal relays tripping. They are several bimetallic plates, each of which is responsible for a separate phase of the power unit.

Automatic network protection switch with electromagnetic release

Having figured out how a machine with a thermal release works, let's move on to the next question. The protective device, the operation of which we have just analyzed, does not operate immediately (it takes at least a second), so it is not able to effectively protect the circuit from short circuit overcurrents. To solve this problem, an electromagnetic release is additionally installed in the AV.

Circuit breaker releases electromagnetic type include an inductor (solenoid) as well as a core. When the circuit is operating normally, the flow of electrons passing through the solenoid creates a weak magnetic field that is unable to influence the function of the network. When a short circuit occurs, the current instantly increases tens of times, and the magnetic field power increases in proportion to it. Under its influence, the ferromagnetic core instantly moves to the side, affecting the shutdown mechanism.

Since the process of strengthening the magnetic field during a short circuit occurs in a fraction of a second, the electromagnetic release under its influence is triggered instantly, turning off the power to the network. This allows you to avoid serious consequences associated with short-circuit overcurrents.

Checking the functionality of releases

Quite often, amateur electricians are interested in whether it is possible to independently check the serviceability of circuit breaker releases. It should be said that such testing cannot be carried out on your own, and if it is carried out by a novice installer, then the work should be supervised by an experienced specialist. Here are step-by-step instructions for performing this procedure:

First of all, the surface of the box should be inspected visually to ensure the integrity of the body part.
Then you need to click the switch lever several times. It should be easy to install in either the on or off position.
After this, the device is loaded. This is the name for checking the quality of equipment operation under adverse conditions. This stage requires the presence of specialized equipment, and a qualified electrician must be present when performing it. During testing, the time that passes from the moment the current begins to increase until the release is turned off is recorded.

Finally, a similar test is performed on the device from which the housing has been removed.
During testing for the operation of a thermal release, the time required to turn off the device under the influence of an electric current of increased strength is recorded.

Checking the serviceability of protective devices in accordance with the requirements of the PUE is carried out only in special clothing. As mentioned above, this procedure should be supervised by an experienced specialist.

The video shows the process of installing an independent release in a circuit breaker:

Conclusion

In this article, we dealt with the topic of tripping devices, talked about what they are and how independent releases, as well as those built into the circuit breaker, work. Now you know what principle they work on Various types of this equipment, and what function each of them performs.

Circuit breakers are devices whose task is to protect an electrical line from exposure to powerful current that can cause overheating of the cable with further melting of the insulating layer and fire. An increase in current strength can be caused by too much load, which occurs when the total power of the devices exceeds the value that the cable can withstand in its cross-section - in this case, the machine does not turn off immediately, but after the wire heats up to a certain level. During a short circuit, the current increases many times over within a fraction of a second, and the device immediately reacts to it, instantly stopping the supply of electricity to the circuit. In this material we will tell you what types of circuit breakers are and their characteristics.

Automatic safety switches: classification and differences

In addition to residual current devices, which are not used individually, there are 3 types of network circuit breakers. They work with loads different sizes and differ from each other in their design. These include:

Modular AB. These devices are installed in household networks in which negligible currents flow. Typically have 1 or 2 poles and a width that is a multiple of 1.75 cm.

Molded switches. They are designed to operate in industrial networks with currents up to 1 kA. They are made in a cast case, which is why they got their name.
Air electric machines. These devices can have 3 or 4 poles and can handle currents up to 6.3 kA. Used in electrical circuits with high power installations.

There is another type of circuit breaker for protecting the electrical network - differential. We do not consider them separately, since such devices are ordinary circuit breakers that include an RCD.

Types of releases

Releases are the main operating components of the automatic circuit breaker. Their task is to break the circuit when the permissible current value is exceeded, thereby stopping the supply of electricity to it. There are two main types of these devices, differing from each other in the principle of tripping:

Electromagnetic.
Thermal.

Electromagnetic type releases ensure almost instantaneous operation of the circuit breaker and de-energization of a section of the circuit when a short circuit overcurrent occurs in it.

They are a coil (solenoid) with a core that is drawn inward under the influence of a large current and causes the tripping element to operate.

The main part of the thermal release is a bimetallic plate. When a current exceeding the rated value of the protective device passes through the circuit breaker, the plate begins to heat up and, bending to the side, touches the disconnecting element, which trips and de-energizes the circuit. The time it takes for the thermal release to operate depends on the magnitude of the overload current passing through the plate.

Some modern devices are equipped as an addition with minimum (zero) releases. They perform the function of turning off the AV when the voltage drops below the limit value corresponding to the technical data of the device. There are also remote releases, with the help of which you can not only turn off, but also turn on the AV, without even going to the distribution board.

The presence of these options significantly increases the cost of the device.

Number of poles

As already mentioned, the circuit breaker has poles - from one to four.

Selecting a device for a circuit based on their number is not at all difficult; you just need to know where different types of AVs are used:

Single-pole circuits are installed to protect lines that include sockets and lighting. They are mounted on phase wire, without capturing null.
The two-terminal network must be included in the circuit to which household appliances with sufficiently high power are connected (boilers, washing machines, electric stoves).
Three-terminal networks are installed in semi-industrial networks, to which devices such as borehole pumps or auto repair shop equipment.
Four-pole AVs allow you to protect electrical wiring with four cables from short circuits and overloads.

The use of machines of different polarities is shown in the following video:

Characteristics of circuit breakers

There is another classification of machines - according to their characteristics. This indicator indicates the degree of sensitivity of the protective device to exceeding the rated current. The corresponding marking will show how quickly the device will react in the event of an increase in current. Some types of AVs work instantly, while others will take some time.

There is the following marking of devices according to their sensitivity:

A. Switches of this type are the most sensitive and react instantly to increased load. They are practically not installed in household networks, using them to protect circuits that include high-precision equipment.
B. These machines operate when the current increases with a slight delay. They are usually included in lines with expensive household appliances (LCD TVs, computers and others).
C. Such devices are the most common in household networks. They are turned off not immediately after increasing the current strength, but after some time, which makes it possible to normalize it with a slight difference.
D. The sensitivity of these devices to increasing current is the lowest of all types listed. They are most often installed in shields at the line approach to the building. They provide security for apartment automatic machines, and if for some reason they do not work, they turn off the general network.

Features of the selection of machines

Some people think that the most reliable circuit breaker is the one that can handle the most current, and therefore can provide the most protection to the circuit. Based on this logic, you can connect a machine to any network air type, and all problems will be solved. However, this is not at all true.

To protect circuits with different parameters, it is necessary to install devices with the appropriate capabilities.

Errors in the selection of AB are fraught with unpleasant consequences. If you connect a high-power protective device to a regular household circuit, it will not de-energize the circuit, even when the current significantly exceeds what the cable can withstand. The insulating layer will heat up and then begin to melt, but no shutdown will occur. The fact is that the current strength destructive to the cable will not exceed the AB rating, and the device will “consider” that there was no emergency. Only when the melted insulation causes a short circuit will the machine turn off, but by then a fire may already have started.

We present a table that shows the ratings of machines for various electrical networks.

If the device is designed for less power than what the line can withstand and which the connected devices have, the circuit will not be able to operate normally. When you turn on the equipment, the AV will constantly knock out, and ultimately, under the influence of high currents, it will fail due to “stuck” contacts.

Visually about the types of circuit breakers in the video:

Conclusion

The circuit breaker, the characteristics and types of which we reviewed in this article, is very important device, which protects the electrical line from damage by powerful currents. The operation of networks not protected by automatic circuit breakers is prohibited by the Electrical Installation Rules. The most important thing is to choose the right type of AV that is suitable for a specific network.

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Definition of release

Releases divide by two conditional groups:

circuit protection releases;

Under overcurrent

Overload current
Short circuit current (SC)

Therefore, as soon as R→ to 0, then I→ to infinity.

Thermal release

The thermal release is a bimetallic plate, which bends when heated and affects the free release mechanism.
A bimetallic plate is made by mechanically joining two metal strips. Two materials with different coefficients of thermal expansion are selected and connected to each other by soldering, riveting or welding.
Suppose the lower material in a bimetallic plate, when heated, elongates less than the upper metal, then the bending will occur downward.

The thermal release protects against overload currents and is configured for certain operating modes.

For example, for a product of the BA 51-35 series, the overload release is calibrated at a temperature of +30ºС to:

conditional non-trip current 1.05·In (time 1 hour for In ≤ 63A and 2 hours for In ≥ 80A);
conditional tripping current is 1.3·In for alternating current and 1.35·In for direct current.

The designation 1.05·In means a multiple of the rated current. For example, with a rated current In = 100A, the conditional non-trip current is 105A.
The time-current characteristics (graphs are always available in factory catalogs) clearly show the dependence of the response time of thermal and electromagnetic releases on the value of the flowing overcurrent.

Advantages:

no rubbing surfaces;
have good vibration resistance;
easily tolerate pollution;
simplicity of design → low price.

Flaws:

constantly consume electrical energy;
sensitive to changes in ambient temperature;
when heated from third-party sources, they can cause false alarms.

It consists in principle of the same parts as the semiconductor release: an actuating electromagnet, measuring devices and a release control unit.

The operating current and holding time are set in steps, guaranteeing protection during single-phase circuit and with starting currents.
Example: products of the BA 88-43 series with an electronic release manufactured by the IEK company.

Advantages:

a varied selection of settings needed by the user;
high accuracy of execution of a given program;
performance indicators and reasons for operation;
logic selectivity with upstream and downstream switches.

Minuses:

high price;
fragile control unit;
exposure to electromagnetic fields.

Shunt release

Using an independent release(NR) carry out remote control specific circuit breaker. Voltage from the control circuit is applied to the independent release coil, a magnetic field is created, the core moves, and affects the free release mechanism.
The independent release can be designed for alternating or direct current (the manufacturer indicates the voltage range).
HP allows operating voltage fluctuations in the range from 0.7 to 1.2 from Un. Its operating mode is short-term.
After the independent release has tripped, you need to go to the switchboard and manually reset the circuit breaker, and then turn it on.
An alternative to HP can be electromagnetic drive– it allows you to remotely both turn off and turn on the circuit breaker.

Most frequent use – remote shutdown of the switching device that controls ventilation system, in case of fire. When a fire is detected, the ventilation is turned off so that air (oxygen) is not forced into the building.

Electrodynamic forces

Electrodynamic forces act on a conductor with a current flowing through it, which is in a magnetic field with induction B.
When the rated current flows, the electrodynamic forces are insignificant, but when a short-circuit current appears, these forces can lead not only to deformation and breakage of individual parts of the switching device, but also to the destruction of the machine itself.
Special calculations are made for electrodynamic resistance, which are especially relevant when there is a tendency to reduce overall characteristics (the distances between conductive parts are reduced).

A magnetic field

The magnetic field is one of the factors generating electrodynamic forces.
Magnetic fields negatively affect the operation of electrical equipment, especially measuring instruments and computers.

Thermal stress (overheating)

Rated current

The rated current (denoted In) of a circuit breaker is the current at which the device is designed for continuous operation and does not activate protective operation. If the current specified in the marking is exceeded, the machine interrupts the supply to the network after a certain time.

A small disclaimer:

rated current of a circuit breaker - the current for which the current-carrying elements are designed;
rated current of a thermal release - the current to which the release devices are adjusted (it does not cause operation).

In what follows, by rated current we mean the rated current of the thermal release.
The rated current is one of the defining characteristics of a circuit breaker, since overcurrents are calculated relative to this value, at which the releases cause the contacts to open. For the right choice circuit breaker, you need to know the rated current of the network.

The rated current of the network is calculated from the power consumption. It is known which device consumes how much power. The total power is obtained and, as a first approximation, the following relation is used:
P = U · I, where P is the power consumption in watts, U is the network voltage in volts, I is the network current in amperes.

But this formula is true for a DC network; for an AC network, everything is much more complicated.
Apparent power (S) is a vector sum active power(P) and reactive power (Q):
S 2 = P 2 + Q 2 .
In its turn:

active power P = I · U · Cosϕ;
reactive power Q = I · U · Sinϕ.

Where ϕ is the angle with which the current lags behind or advances the voltage. To measure the reactive power factor (Cosϕ), phase meters are used.

Instantaneous tripping current ( protective characteristic B, C or D)

A circuit breaker is characterized by a current that causes instantaneous tripping of the main contact group. This occurs when there is a short circuit that latches and trips the electromagnetic release.

For modular and power circuit breakers, the instantaneous protection characteristic is indicated differently:

modular machines are assigned a protective characteristic: B, C, D;
For power switches, the current value is set in amperes or a multiple of the rated current.

High-speed machines

Achieving a shutdown time of 0.002-0.008 s requires special measures and other principles of operation of the drive electromagnets. In known designs, the following methods are used to obtain performance:

1) according to the principle of flow displacement (performance 0.003-0.005 s). The machine is turned off not by turning off the coils of the holding electromagnet, but by displacing the flow from the core-armature section. In this case, the demagnetizing flow is created by a forced short-circuit current.

2) mechanical latches (locks) t o up to 0.002 s. Switching on is also carried out by a short-term operating electromagnet, and holding in the on position is carried out by a mechanical (electromechanical) latch. The latch is released by a tripping electromagnet operating in a forced mode created by the short-circuit current.

3) systems with an impact electromagnet - an electromagnet working with high force creates " impact force", exceeding the force of the holding electromagnet and "tears off" the armature, i.e. turns off the switch.

4) a switch with an explosive release - shutdown time 0.001 s - has not become widespread due to its complexity.

5) vacuum switches providing arc extinction t0=0.003-0.007s. Examples of some switches are shown below.

a) Switch BVP-5. Built on the principle of magnetic field displacement. It is designed to protect the power circuit of DC electric locomotives. U nom =4000 V, U max=4000 V, I nom=1850 A, own shutdown time 0.003 s.

b) DC vacuum switch type VPTV-15-5/400 on

U nom=15 kV, I nom =400 A, I off =5 kA.

c) VAB series automatic machine - 28 the most versatile I nom =1.5-6 kA, U=825-3300 V.

HIGH VOLTAGE SWITCH

High voltage circuit breaker- a switching device designed for operational switching and emergency switching in power systems, for performing operations on and off of individual circuits or electrical equipment under manual or automatic control.

A high-voltage circuit breaker consists of: a contact system with an arc extinguishing device, current-carrying parts, a housing, an insulating structure and a driving mechanism (for example, an electromagnetic drive, a manual drive).

Options

In accordance with GOST R 52565-2006, switches are characterized by the following parameters:

rated voltage Unom (voltage of the network in which the switch operates);
rated current Inom (current through the switched-on switch, at which it can operate for a long time);
rated interruption current Iо.nom - the highest short-circuit current (rms value) that the switch is capable of disconnecting at a voltage equal to the highest operating voltage under given conditions of recovery voltage and a given cycle of operations;
permissible relative content of aperiodic current in the shutdown current;
If the circuit breakers are designed for automatic reclosing (AR), then the following cycles must be provided:

Cycle 1: O-tbp-VO-180 s-VO; Cycle 2: O-180 s-VO−180 s-VO, where O is the shutdown operation, VO is the operation of switching on and immediate shutdown, 180 is the time period in seconds, tbp is the minimum dead-time pause guaranteed for switches during automatic reclosure (time from extinguishing arc until current appears upon subsequent switching on) For circuit breakers with autorecloser it should be within 0.3-1.2 s, for circuit breakers with autorecloser (high-speed) 0.3 s.

stability under through short-circuit currents, which is characterized by thermal stability currents It and maximum through current
rated switching current - short-circuit current that a switch with a corresponding drive is capable of switching on without welding contacts and other damage at Unom and a given cycle.
own shutdown time - the time interval from the moment the shutdown command is given until the moment the arc-extinguishing contacts begin to diverge.
parameters of recovery voltage at rated shutdown current - speed of recovery voltage, normalized curve, coefficient of excess amplitude and recovery voltage.

Automatic releases. Operating principle. Design and types of releases.

Definition of release

Releases divide by two conditional groups:

circuit protection releases;
releases performing auxiliary functions.

Trip release (first group), in relation to a circuit breaker, it is a device capable of recognizing a critical situation (the appearance of an overcurrent) and preventing its development in advance (causing divergence of the main contacts).

To the second group of releases Additional devices can be distinguished (they are not included with the basic versions of the machines, but are supplied only with custom versions):

independent release (remote shutdown of the circuit breaker based on a signal from the auxiliary circuit);
minimum voltage release (turns off the circuit breaker when the voltage drops below the permissible level);
zero voltage release (causes contacts to trip when there is a significant voltage drop).

Definitions of terms found below

Under overcurrent refers to the current strength exceeding the rated (operating) current. This definition includes short circuit current and overload current.

Overload current– overcurrent operating in a functional network (prolonged exposure to overloads can cause damage to the circuit).
Short circuit current (SC)– overcurrent, which is caused by the short circuit of two elements with a very low total resistance between them, while in normal operation these elements are endowed with different potentials (a short circuit can be caused by incorrect connection or damage). For example, mechanical stress or aging of the insulation causes contact of current-carrying wires and a short circuit.
A high short-circuit current value is recognized from the formula:
I = U / R (current is equal to the ratio of voltage to resistance).
Therefore, as soon as R→ to 0, then I→ to infinity.

Overcurrent release (MRT)– a release that causes the main contacts to open, with or without a certain period of time, as soon as the effective current value exceeds a specified threshold.
Inverse time MRT is an overcurrent release that initiates tripping of the contacts after a specified time has elapsed, which is inversely dependent on the current strength.
Direct action MRI is a maximum current release that initiates operation directly from the current overcurrent.

Definitions of maximum current release, short-circuit current and overload are taken (paraphrased without loss of meaning) from the GOST R 50345 standard.

cyberpedia.su

Types of switches

All machines are divided according to the type of release. They are divided into 6 types:

thermal;
electronic;
electromagnetic;
independent;
combined;
semiconductor.

They very quickly recognize emergency situations, such as:

the occurrence of overcurrents - an increase in the current strength in the electrical network that exceeds the rated current of the circuit breaker;
voltage overload – short circuit in the circuit;
voltage fluctuations.

At these moments, the contacts in the automatic releases open, which prevents serious consequences in the form of damage to wiring and electrical equipment, which very often leads to fires.

Thermal switch

It consists of a bimetallic plate, one of the ends of which is located next to the release device of the automatic release. The plate is heated by the current passing through it, hence the name. When the current begins to increase, it bends and touches the trigger bar, which opens the contacts in the “machine”.

The mechanism operates even with slight excesses of the rated current and an increased response time. If the load increase is short-term, the switch does not trip, so it is convenient to install it in networks with frequent but short-term overloads.

Advantages of a thermal release:

absence of contacting and rubbing surfaces;
vibration stability;
budget price;
simple design.

The disadvantages include the fact that its operation largely depends on the temperature regime. It is better to place such machines away from heat sources, otherwise there is a risk of numerous false alarms.

Electronic switch

Its components include:

measuring devices (current sensors);
Control block;
electromagnetic coil (transformer).

At each pole of the electronic circuit breaker there is a transformer that measures the current passing through it. The electronic module that controls the trip processes this information, comparing the obtained result with the specified one. In the event that the resulting indicator is greater than the programmed one, the “machine” will open.

There are three trigger zones:

Long delay. Here, the electronic release serves as a thermal release, protecting the circuits from overloads.
Short delay. Provides protection against minor short circuits that usually occur at the end of the protected circuit.
The working area “instantly” provides protection against high-intensity short circuits.

Pros - a large selection of settings, maximum accuracy of the device to a given plan, the presence of indicators. Cons: sensitivity to electromagnetic fields, high price.

Electromagnetic

This is a solenoid (a coil of wound wire), inside of which there is a core with a spring that acts on the release mechanism. This is an instant action device. As the supercurrent flows through the winding, a magnetic field is generated. It moves the core and, exceeding the force of the spring, acts on the mechanism, turning off the “automatic machine”.

Pros: resistance to vibration and shock, simple design. Cons – forms a magnetic field, triggers instantly.

This is an additional device to automatic releases. With its help, you can turn off both single-phase and three-phase circuit breakers located at a certain distance. To activate the independent release, voltage must be applied to the coil. To return the machine to its original position, you must manually press the “return” button.

Important! The phase conductor must be connected from one phase from under the lower terminals of the switch. If it is connected incorrectly, independent switch will fail.

Basically, independent automatic machines are used in automation panels in highly ramified power supply devices of many large facilities, where control is transferred to the operator’s console.

Combination switch

It has both thermal and electromagnetic elements and protects the generator from overloads and short circuits. To operate the combined automatic release, the current of the thermal circuit breaker is indicated and selected: the electromagnet is designed for 7–10 times the current, which corresponds to the operation of heating networks.

The electromagnetic elements in the combination switch provide instantaneous protection against short circuits, and the thermal elements protect against overloads with a time delay. The combined machine is switched off when any of the elements is triggered. During short-term overcurrents, none of the types of protection are triggered.

Semiconductor switch

It consists of alternating current transformers, magnetic amplifiers for direct current, a control unit and an electromagnet that functions as an independent automatic release. The control unit helps set the selected contact release program.

Its settings include:

regulation of the rated current in the device;
setting the time;
triggered when a short circuit occurs;
protective switches against overcurrent and single-phase short circuit.

Pros - a large selection of regulation for different power supply schemes, ensuring selectivity to series-connected circuit breakers with fewer amperes.

Cons: high cost, fragile control components.

Installation

Many home-grown electricians believe that installing a machine is not difficult. This is fair, but it must be followed certain rules. Circuit breaker releases, as well as plug fuses, must be connected to the network so that when the plug of the circuit breaker is turned out, its screw sleeve is without voltage. Connection of the supply conductor at one-way feeding with a machine should be carried out to fixed contacts.

Installation of an electric single-phase two-pole circuit breaker in an apartment consists of several stages:

securing the switched-off device to the electrical panel;
connecting wires without voltage to the meter;
connecting voltage wires to the machine from above;
turning on the machine.

Fastening

We install a DIN rail in the electrical panel. We cut it to the required size and fasten it with self-tapping screws to the electrical panel. Snap it in automatic release network onto the DIN rail using a special lock, which is located on the back of the machine. Make sure that the device is in shutdown mode.

Connection to the electricity meter

We take a piece of wire, the length of which corresponds to the distance from the meter to the machine. We connect one end to the electric meter, the other to the terminals of the release, observing the polarity. We connect the supply phase to the first contact, and the neutral supply wire to the third. Wire cross-section – 2.5 mm.

Connecting voltage wires

From the central electrical distribution panel, the supply wires are connected to the apartment panel. We connect them to the terminals of the machine, which must be in the “off” position, observing the polarity. The wire cross-section is calculated depending on the energy consumed.

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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. The reliability and speed of operation depends on it, so it is worth comparing all the currently existing 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.

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