The main purpose of circuit breakers is to use them as protective devices against short circuit currents and overload currents. Modular circuit breakers of the BA series are in predominant demand. In this article we will look at BA47-29 series from iek.
Thanks to their compact design (uniform module widths), ease of installation (mounting on a DIN rail using special latches) and maintenance, they are widely used in domestic and industrial environments.
Most often, automatic machines are used in networks with relatively small operating and short-circuit currents. The body of the machine is made of dielectric material, which allows it to be installed in publicly accessible places.
Circuit breaker design and the principles of their operation are similar, the differences lie, and this is important, in the material of the components and the quality of assembly. Serious manufacturers use only high-quality electrical materials (copper, bronze, silver), but there are also products with components made from materials with “lightweight” characteristics.
The easiest way to distinguish an original from a fake is price and weight: the original cannot be cheap and light if there are copper components. The weight of branded machines is determined by the model and cannot be lighter than 100 - 150 g.
Structurally, the modular circuit breaker is made in a rectangular housing, consisting of two halves fastened together. On the front side of the machine its technical characteristics are indicated and there is a handle for manual control.
How a circuit breaker works - the main working parts of the circuit breaker
If you disassemble the body (for which you need to drill out the rivet halves connecting it), you can see and gain access to all its components. Let's consider the most important of them, which ensure the normal functioning of the device.
- 1. Upper terminal for connection;
- 2. Fixed power contact;
- 3. Movable power contact;
- 4. Arc chamber;
- 5. Flexible conductor;
- 6. Electromagnetic release (coil with core);
- 7. Handle for control;
- 8. Thermal release (bimetallic plate);
- 9. Screw for adjusting the thermal release;
- 10. Bottom terminal for connection;
- 11. Hole for the exit of gases (which are formed when the arc burns).
Electromagnetic release
The functional purpose of the electromagnetic release is to ensure almost instantaneous operation of the circuit breaker when a short circuit occurs in the protected circuit. In this situation, currents arise in electrical circuits, the magnitude of which is thousands of times greater than the nominal value of this parameter.
The operation time of the machine is determined by its time-current characteristics (the dependence of the operation time of the machine on the current value), which are designated by the indices A, B or C (the most common).
The type of characteristic is indicated in the rated current parameter on the machine body, for example, C16. For the given characteristics, the response time ranges from hundredths to thousandths of a second.
The design of the electromagnetic release is a solenoid with a spring-loaded core, which is connected to a movable power contact.
Electrically, the solenoid coil is connected in series to a chain consisting of power contacts and a thermal release. When the machine is turned on and the rated value of the current, current flows through the solenoid coil, however, the magnitude of the magnetic flux is small to retract the core. The power contacts are closed and this ensures the normal functioning of the protected installation.
During a short circuit, a sharp increase in current in the solenoid leads to a proportional increase in magnetic flux, which can overcome the action of the spring and move the core and the moving contact associated with it. The movement of the core causes the power contacts to open and the protected line to de-energize.
Thermal release
The thermal release performs the function of protection when the permissible current value is exceeded slightly, but lasts for a relatively long period of time.
The thermal release is a delayed release; it does not respond to short-term current surges. The response time of this type of protection is also regulated by the time-current characteristics.
The inertia of the thermal release makes it possible to implement the function of protecting the network from overload. Structurally, the thermal release consists of a bimetallic plate mounted in a cantilever in the housing, the free end of which interacts with the release mechanism through a lever.
Electrically, the bimetallic strip is connected in series with the coil of the electromagnetic release. When the machine is turned on, current flows in the series circuit, heating the bimetallic plate. This causes its free end to move into close proximity to the release mechanism lever.
When the current values specified in the time-current characteristics are reached and after a certain time, the plate bends when heated and comes into contact with the lever. The latter, through a release mechanism, opens the power contacts - the network is protected from overload.
The thermal release current is adjusted using screw 9 during the assembly process. Since most machines are modular and their mechanisms are sealed in the housing, it is not possible for a simple electrician to make such adjustments.
Power contacts and arc chute
Opening of power contacts when current flows through them leads to the occurrence of an electric arc. Arc power is usually proportional to the current in the circuit being switched. The more powerful the arc, the more it destroys the power contacts and damages the plastic parts of the housing.
IN circuit breaker device The arc suppression chamber limits the action of the electric arc in a local volume. It is located in the power contact area and is made of copper-coated parallel plates.
In the chamber, the arc breaks up into small parts, hits the plates, cools down and ceases to exist. The gases released when the arc burns are removed through holes in the bottom of the chamber and the body of the machine.
Circuit breaker device and the design of the arc chute determine the connection of power to the upper fixed power contacts.
Automatic switches are designed for installation in power distribution panels. Their main purpose is to compensate for voltage drops, as well as to disconnect a certain section of the electrical network. Automatic machines, or VA for short, are designed for installation at the beginning of an electrical circuit, at the entrance of a building, apartment, house.
Currently, there is a fairly wide variety of circuit breakers on the market, which are designed not only to cut off high-rated currents during voltage surges, but also from overloading a section of the electrical circuit, as well as from reduced network loads. According to their type, all automatic switches are divided into:
- selective;
- regulatory;
- fast-acting.
The standard cut-off time for selective and standard automatic machines is within 0.02-0.1 seconds. But for high-speed ones it is an order of magnitude higher, and reaches a value of 0.05 seconds.
All machines have fastening elements that allow them to be mounted in electrical boxes, panels, etc., which are equipped with a special fastening strip at the rear.
Installing circuit breakers in a box is not difficult. To do this, you need to press the back of it against the mounting plate of the box and press it a little until you hear a characteristic click. If you need to remove the machine, you will need to pull the tab located on top of the machine.
Operating principle of circuit breaker
The automatic mechanism is located inside a plastic case. In addition, there are also safety devices or releases , of which there can be two – electromagnetic and thermal. They are designed to cut off the electrical circuit.
The thermal release is a bimetallic plate, which, in the event of the passage of high currents, is straightened, breaking the electrical circuit. This is a fairly slow breaker.
The electromagnetic release is a special coil that is designed for currents of a certain threshold value. If this value exceeds the norm, the coil breaks the electrical circuit. Thanks to this property, the machine with an electromagnetic release has a significantly short cut-off time.
Machine sensitivity level
Modern machines have the ability to turn off the voltage in two ways. The first one is fast. Thanks to the electromagnetic release, the machine is triggered when the voltage exceeds 140% (this is the threshold value for standard machines). If the overvoltage does not reach a predetermined level, then over time, due to overheating, the thermal release will operate.
Depending on the thermal characteristics of the release itself, the voltage, as well as the ambient temperature, the cutoff process can last several hours.
Circuit breaker polarity
All modern machines are also divided depending on the poles. This means that the machine can have several electrical lines, which will be independent of one another, but united by one disconnecting mechanism. Currently, machines can have 1,2,3,4 poles.
Circuit breaker threshold current
Circuit breakers They are also divided according to a certain threshold sensitivity. This allows you to cut off the voltage of the corresponding current strength from the network. Machines with a nominal value are manufactured and configured at the manufacturer. The value of this indicator is written on the machine itself.
In private construction and everyday life, circuit breakers with the following current values are used: 3A, 6A, 10A, 16A, 25A, 32A, 40A, 63A, 100A, 160A. In addition, there are circuit breakers with increased performance - these are 1000A, 2600A, which are not used in private construction. This value shows us the total power of the electrical circuit consumers that will be under the control of a given machine. In addition to the total power of the devices, it is also necessary to take into account the electrical wiring of the electrical circuit, sockets, switches, etc.
Types of modern circuit breakers
Currently, all machines are divided by manufacturers into several types, designated by certain letters:
A– designed for operation in circuits containing semiconductor devices, as well as of a fairly large length;
IN– placed in the circuit of general purpose lighting systems;
WITH– installed in circuits of lighting systems, as well as in electrical installations with moderate starting currents. Such installations include motors and transformers.
D– installed in an active-inductive load circuit. In addition, these machines can also be installed on electric motors with high starting currents.
TO– circuit breakers designed for installation in networks with inductive loads.
Z– provide protection for electronic devices.
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. Automatic switches are produced in a wide variety of designs and with different 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 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 protecting electronic circuits and long-distance circuits;
- 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 automatic 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.
This article continues a series of publications on electrical protection devices- circuit breakers, RCDs, automatic devices, in which we will analyze in detail the purpose, design and principle of their operation, as well as consider their main characteristics and analyze in detail the calculation and selection of electrical protection devices. This series of articles will be completed by a step-by-step algorithm, in which the full algorithm for calculating and selecting circuit breakers and RCDs will be briefly, schematically and in a logical sequence discussed.
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Well, in this article we will figure out what a circuit breaker is, what it is intended for, how it works and how it works.
Circuit breaker(or usually just “machine”) is a contact switching device that is designed to turn on and off (i.e., for switching) an electrical circuit, protecting cables, wires and consumers (electrical appliances) from overload currents and short circuit currents.
Those. The circuit breaker performs three main functions:
1) circuit switching (allows you to turn on and off a specific section of the electrical circuit);
2) provides protection against overload currents, turning off the protected circuit when a current exceeding the permissible flows in it (for example, when connecting a powerful device or devices to the line);
3) disconnects the protected circuit from the supply network when large short-circuit currents occur in it.
Thus, automata simultaneously perform the functions protection and functions management.
According to design, three main types of circuit breakers are produced:
— air circuit breakers (used in industry in circuits with high currents of thousands of amperes);
— molded case circuit breakers (designed for a wide range of operating currents from 16 to 1000 Amperes);
— modular circuit breakers , the most familiar to us, to which we are accustomed. They are widely used in everyday life, in our houses and apartments.
They are called modular because their width is standardized and, depending on the number of poles, is a multiple of 17.5 mm; this issue will be discussed in more detail in a separate article.
You and I, on the pages of the site, will consider modular circuit breakers and residual current devices.
Design and principle of operation of a circuit breaker.
The thermal release does not operate immediately, but after some time, allowing the overload current to return to its normal value. If during this time the current does not decrease, the thermal release is activated, protecting the consumer circuit from overheating, insulation melting and possible wiring fire.
Overload can be caused by connecting powerful devices to the line that exceed the rated power of the protected circuit. For example, when a very powerful heater or electric stove with oven is connected to the line (with a power exceeding the design power of the line), or several powerful consumers at the same time (electric stove, air conditioner, washing machine, boiler, electric kettle, etc.), or a large number at the same time included devices.
In case of short circuit the current in the circuit instantly increases, the magnetic field induced in the coil according to the law of electromagnetic induction moves the solenoid core, which activates the release mechanism and opens the power contacts of the circuit breaker (i.e., moving and fixed contacts). The line opens, allowing you to remove power from the emergency circuit and protect the machine itself, the electrical wiring and the closed electrical appliance from fire and destruction.
An electromagnetic release operates almost instantly (about 0.02 s), unlike a thermal one, but at significantly higher current values (from 3 or more rated current values), so the electrical wiring does not have time to heat up to the melting temperature of the insulation.
When the contacts of a circuit open and an electric current passes through it, an electric arc occurs, and the greater the current in the circuit, the more powerful the arc. An electric arc causes erosion and destruction of contacts. To protect the contacts of the circuit breaker from its destructive effect, the arc that occurs at the moment the contacts open is directed towards arc chute (consisting of parallel plates), where it crushes, damps, cools and disappears. When an arc burns, gases are formed; they are vented out of the machine body through a special hole.
The machine is not recommended to be used as a regular circuit breaker, especially if it is turned off when a powerful load is connected (i.e., with high currents in the circuit), since this will accelerate the destruction and erosion of the contacts.
So let's recap:
— the circuit breaker allows you to switch the circuit (by moving the control lever up, the machine is connected to the circuit; by moving the lever down, the machine disconnects the supply line from the load circuit);
— has a built-in thermal release that protects the load line from overload currents, it is inertial and trips after a while;
— has a built-in electromagnetic release that protects the load line from high short-circuit currents and operates almost instantly;
— contains an arc-extinguishing chamber that protects power contacts from the destructive effects of an electromagnetic arc.
We have analyzed the design, purpose and principle of operation.
In the next article we will look at the main characteristics of a circuit breaker that you need to know when choosing one.
Look Design and principle of operation of the circuit breaker in video format:
Useful articles
Circuit breakers are devices whose task is to protect an electrical line from damage under the influence of large currents. This can be either short-circuit overcurrents or simply a powerful flow of electrons passing through the cable for quite a long time and causing it to overheat with further melting of the insulation. The circuit breaker in this case prevents negative consequences by cutting off the current supply to the circuit. In the future, when the situation returns to normal, the device can be turned on again manually.
Circuit breaker functions
Protective devices are designed to perform the following main tasks:
- Electrical circuit switching (possibility of disconnecting the protected area in the event of power problems).
- De-energizing the entrusted circuit when short-circuit currents occur in it.
- Protection of the line from overloads when an excessive current passes through the device (this happens when the total power of the devices exceeds the maximum permissible).
In short, AVs simultaneously perform protective and control functions.
Main types of switches
There are three main types of AVs, differing from each other in design and designed to work with loads of different sizes:
- Modular. It got its name because of its standard width, a multiple of 1.75 cm. It is designed for small currents and is installed in household power supply networks, for a house or apartment. As a rule, this is a single-pole or two-pole circuit breaker.
- Cast. So called because of the cast body. Can withstand up to 1000 Amps and is used primarily in industrial networks.
- Airborne. Designed to work with currents up to 6300 Amperes. Most often this is a three-pole machine, but now devices of this type are also produced with four poles.
A single-phase protective circuit breaker is a circuit breaker that is most common in household networks. It comes in 1- and 2-pole types. In the first case, only the phase conductor is connected to the device, and in the second case, the neutral conductor is also connected.
In addition to the listed types, there are also residual current devices, designated by the abbreviation RCD, and differential circuit breakers.
The former cannot be considered full-fledged AVs; their task is not to protect the circuit and the devices included in it, but to prevent electric shock when a person touches an open area. A differential circuit breaker is an AV and an RCD combined in one device.
How are circuit breakers arranged?
Let us consider in detail the device of the circuit breaker. The body of the machine is made of dielectric material. It consists of two parts, which are connected to each other with rivets. If it is necessary to disassemble the housing part, the rivets are drilled out, and access to the internal elements of the circuit breaker is opened. These include:
- Screw terminals.
- Flexible conductors.
- Control handle.
- Movable and fixed contact.
- An electromagnetic release, which is a solenoid with a core.
- Thermal release, which includes a bimetallic plate and an adjusting screw.
- Gas outlet.
On the rear side, the automatic protective fuse is equipped with a special lock, with which it is mounted on a DIN rail.
The latter is a metal rail 3.5 cm wide on which modular devices, as well as some types of electric meters, are mounted. To attach the machine to the rail, the body of the protective device should be placed behind its upper part, and then snap the latch by pressing on the lower part of the device. You can remove the circuit breaker from the DIN rail by lifting the latch from below.
The modular switch lock may be very tight. To attach such a device to a DIN rail, you need to first pick up the latch from below and place the protective device in place of the fastener, then release the fixing element.
You can make it simpler - when snapping the latch, press firmly on its lower part with a screwdriver.
It is clear why a circuit breaker is needed in the video:
Operating principle of circuit breaker
Now let's figure out how the network circuit breaker works. It is connected by lifting the control handle upwards. To disconnect the AV from the network, the lever is lowered down.
When the electrical protective circuit breaker operates in normal mode, the electric current when the control handle is raised up is supplied to the device through the power cable connected to the upper terminal. The flow of electrons goes to the fixed contact, and from it to the moving one.
Then, through a flexible conductor, the current flows to the solenoid of the electromagnetic release. From it, electricity goes through a second flexible conductor to a bimetallic plate included in the thermal release. Having passed along the plate, the flow of electrons through the lower terminal goes into the connected network.
Features of the thermal release
When the current in the circuit in which the circuit breaker is installed exceeds the device rating, an overload occurs. A flow of high-power electrons, passing through a bimetallic plate, has a thermal effect on it, making it softer and causing it to bend towards the disconnecting element. When the latter comes into contact with the plate, the machine is triggered and the current supply to the circuit is stopped. Thus, thermal protection helps prevent excessive heating of the conductor, which can lead to melting of the insulating layer and failure of the wiring.
Heating the bimetallic plate to such an extent that it bends and triggers the AB occurs over a certain period of time. It depends on how much the current exceeds the rating of the machine, and can take a few seconds or an hour.
The thermal release is triggered if the current in the circuit exceeds the nominal value of the machine by at least 13%. After the bimetallic strip has cooled and the current current has normalized, the protective device can be turned on again.
There is another parameter that can affect the operation of the AV under the influence of a thermal release - this is the ambient temperature.
If the air in the room where the device is installed is at a high temperature, the plate will heat up to the tripping limit faster than usual and can trip even with a slight increase in current. Conversely, if the house is cold, the plate will heat up more slowly, and the time before the circuit turns off will increase.
The operation of the thermal release, as mentioned, requires a certain time, during which the circuit current can return to normal. Then the overload will disappear and the device will not shut down. If the magnitude of the electric current does not decrease, the machine de-energizes the circuit, preventing the melting of the insulating layer and preventing the cable from catching fire.
The cause of overload is most often the inclusion in the circuit of devices whose total power exceeds the calculated power for a particular line.
Nuances of electromagnetic protection
An electromagnetic release is designed to protect the network from short circuits and differs in operating principle from a thermal release. Under the influence of short-circuit supercurrents, a powerful magnetic field arises in the solenoid. It moves the coil core to the side, which opens the power contacts of the protective device, acting on the release mechanism. The power supply to the line is stopped, thereby eliminating the risk of fire in the wiring, as well as destruction of the closed installation and circuit breaker.
Since in the event of a short circuit in the circuit there is an instantaneous increase in current to a value that can lead to serious consequences in a short time, the operation of the circuit breaker under the influence of an electromagnetic release occurs in hundredths of a second. True, in this case the current must exceed the nominal value of the AB by 3 or more times.
Video about circuit breakers:
When the contacts of a circuit through which electric current flows open, an electric arc appears between them, the power of which is directly proportional to the magnitude of the mains current. It has a destructive effect on the contacts, therefore, to protect them, the device includes an arc-extinguishing chamber, which is a set of plates installed parallel to each other.
Upon contact with the plates, the arc fragments, as a result of which its temperature decreases and attenuation occurs. Gases generated when an arc occurs are removed from the body of the protective device through a special hole.
Conclusion
In this article we talked about what circuit breakers are, what these devices are like and on what principle they work. Finally, we will say that circuit breakers are not intended for installation in a network as ordinary switches. Such use will quickly lead to destruction of the contacts of the device.