Automatic switches. Types, characteristics, calculation of the circuit breaker
An electrical network is a system that includes inputs, wires, current consumers, and switching equipment. Installation of circuit breakers provides protection of the network as a whole and individual consumers in emergency situations when the current parameters are outside the normal range (short circuit, voltage surges, changes in the direction of the current, etc.). In addition, they allow, if necessary, to perform infrequent switching of consumers remotely or in manual mode (6-30 on / off cycles per day).
Maintenance of electrical equipment
Evolution and basic structure of circuit breakers
The history of electrical equipment began long before the appearance of the first commercial power grids. Thus, the principle of operation of a circuit breaker was discovered back in 1836 by the American scientist C. G. Page, but the modern design was patented only in 1924 by the Swiss company Brown, Boveri & Cie. Since then, each machine has included the following elements:
- contact block;
- arc neutralization (extinguishing) chamber;
- release of the following types: thermal, electromagnetic, electronic, microprocessor;
- control mechanism: manual, spring or with a drive;
- free release mechanism.
A lot of electrical equipment is currently being produced, which is illustrated by characteristics of circuit breakers, which provide reliable switching and protection of power grids and consumers of any complexity and power in any operating conditions. The number of models of these devices from different manufacturers is incalculable.
In the catalogs of "Skat Technology" are presented the products of the leading companies Siemens, Andeli, Schneider, whose products rightfully occupy the leading positions in the electrical engineering market. Here you can see circuit breakers in the photo, as well as familiarize yourself with their main characteristics and installation methods. If you are not a professional in electrical engineering, we recommend using the help of our specialists, which can be obtained, including online.
For those who are interested in how the circuit breaker works, we will give a short explanation. Each device has settings for certain parameters of current and conductor heating. These settings are provided by the sensitivity of the current release solenoid and by a screw-regulated thermal relay (calibration). If, during the operation of the network, the parameters go beyond the established limits, the circuit is broken and the consumers are de-energized.
Classification of circuit breakers
For the classification of electrical devices, there are regulatory documents that set out the technical and operational requirements for them. Classes of circuit breakers domestic and foreign production are determined in accordance with the following documents:
- GOST 9098-78;
- GOST 14255-69;
- GOST R 50345-2010;
- GOST R 50030.2-99;
- IEC 60898-95;
- EN 60947-2;
- EN 60898.
In accordance with domestic regulatory and technical documents, the classification of machines is carried out according to 12 parameters, which take into account dozens of operational characteristics of the devices. The quantitative and qualitative values of these parameters determine the purpose of the circuit breaker and the permissible conditions for its operation.
The main classification parameters of circuit breakers
The higher the level of the power grid architecture, the more difficult it is to select protection and control equipment for it, since a large number of different operating parameters have to be taken into account. To achieve the desired result, it is necessary to carry out engineering calculations of all parameters so that the selection of a circuit breaker and other electrical devices would ensure reliable and safe operation of the network. The list of the main characteristics of the machines is as follows:
- rated currents of the main circuit and releases - respectively 6.3-6300 (total 22 ratings) and 15-3200 amperes (total 12 ratings);
- design - air or ACB (800-6300 A), in a molded case or MCCB (10-2500 A), modular or MCB (0.5-125 A) automatic machines;
- the number of poles of the main circuit - from one to four;
- the presence or absence of current restrictions;
- release types: zero, minimum, independent, maximum;
- presence or absence of contacts for connecting secondary circuits;
- way of connecting inputs / outputs: front, rear, combined, universal;
- mounting method: stationary, withdrawable (on a DIN rail), on connectors;
- cutoff type: normal, selective, instant;
- type of drive: manual, spring, with a propeller (electromagnet, pneumatics, etc.);
- regular or protected execution.
The listed characteristics have their own designation or quantitative expression. For example, the trip curve of a circuit breaker is a graphical representation of the trip of the trip unit. It indicates at what value of overshoot of the rated current "In" the device is triggered. According to this parameter, foreign-made products are divided into 6 groups (types):
- A - 2-3 In;
- B - 3-5 In;
- C - 5-10 In;
- D - 10-20 In;
- Z - 2-4 In;
- K - 8-14 In.
The trip class of domestic circuit breakers is designated by the letters B, C and D, since our industry does not produce other types of products. In turn, according to the cut-off response speed, the automatic machines are divided into normal (0.02-1 sec.) And high-speed or instantaneous (less than 0.005 seconds). Selectivity of circuit breakers means the possibility of setting different cut-off times with a delay of 0.25-0.6 seconds for slave electrical devices.
Automatic devices of this type have main and additional working circuits, which allows you to turn off the emergency section of the power grid, controlled by the slave device, and keep the current supply to the remaining consumers. The time range of the speed and selection processes also reflect circuit breaker curves... The protection devices are triggered not only by the current, but also by the heating of the wires, which is provided by a thermal relay. Simply put, the electromagnetic release reacts to current consumption, and the thermal relay reacts to heating of the wiring.
The time-current characteristic of the circuit breaker depends on the setting of the latter. The magnitude of the heat load should not exceed the nominal value for wires of a certain section by more than 1.45 times. It is determined taking into account the method of wiring and the total load. Depending on the installed setting, the thermal relay can be triggered instantly or keep the network operational for a certain time, but not more than an hour.
The importance of timely triggering of protection equipment
From the above data, it is clear how important the trip time of the circuit breaker is. The minimum value of this indicator is required for powerful industrial equipment. Class D apparatus with instantaneous tripping is usually used here. For domestic needs, there are enough class C circuit breakers with normal tripping with a margin.
The exception is worn out networks and especially sensitive current consumers, where devices of classes A and B should be used, in which the minimum operation time of the circuit breaker in case of short circuit not only provides protection, but also prevents the wiring from burning. By the way, the state of the latter is often of decisive importance when choosing electrical equipment. If the cross-section of the wires does not correspond to the load on the network, the thermal characteristic of the tripping of the circuit breaker will interfere with its normal operation.
Reflection of characteristics of electrical equipment in its marking
For electrical products, it is characteristic to use the most important performance characteristics in product labeling. For lighting lamps, this is the power consumption and the luminous flux. Circuit breaker marking much more difficult, a minimum of information can be squeezed into the name of the product. This is usually the nominal operating voltage. Therefore, the marking symbols are applied to the machine body:
- the current limiting class is indicated by a number inside the square; the number of poles is indicated by the pictogram;
- the class or utilization category of the circuit breakers is displayed together with the rated current - eg "C16";
- the maximum permissible operating current value, at which the risk of damage to the machine is excluded, is indicated in a rectangular frame.
The listed information in the product labeling is enough for a specialist to decide how to choose / select a circuit breaker in full accordance with the parameters of the electrical network. However, when purchasing the device yourself, it is easy to make a mistake if you do not take into account the characteristics of the wiring and the magnitude of the loads. For example, the operating parameters of open and closed wiring, copper and aluminum wires differ significantly.
If you are wondering how to choose / select a circuit breaker for power, it should be borne in mind that a copper wire with a cross section of 4 mm, laid in an open way, can withstand a load of 9 kW. The same wire with closed wiring will withstand 5.9 kW. It is clear that the power of the current consumer should not exceed the wiring capability.
Likewise ratings of circuit breakers should be less than the corresponding network parameters. Otherwise, there is a risk of overloading the power grid up to the point of fire of the wiring, to which the machine simply will not react. In order to avoid such a situation, preliminary calculations are necessary, which will provide a balance between current consumers, wiring and protection and control means. For those who are interested in the question, how to choose a circuit breaker for home, we will give advice: choose the nominal value of the device according to the throughput of the wiring (cross-section and material of the wires, as well as the method of laying them).
Basic rules for connecting a circuit breaker
A competent design of the architecture of power grids makes it possible to increase their reliability by an order of magnitude. Currently, we use a lot of household appliances and equipment, including those with significant power. The old Soviet-style wiring was not designed for such loads, so consumers often face the question of how to calculate the current of the circuit breaker in order to ensure the safe operation of the home electrical network.
Based on the experience of its work, the company "Skat Technology" concluded that with a significant increase in the load on the network (for example, installing an electric stove), you should not use the old wiring. The correct choice of the circuit breaker for the load current will not help either, since the wiring for it is not designed. It is best to completely reconstruct or replace the network with distribution of current consumers by groups.
Electrical engineering is an exact applied science, so the production of electrical goods is carried out to certain standards. This is clearly seen in the example of what kind of circuit breakers are, the design of which is designed for specific operating conditions. The division of consumers into groups has long been practiced in industrial networks. At the household level, this approach looks like this:
- for lighting fixtures, the rating of the machine should not exceed 10 A;
- for conventional sockets - 16 A;
- for power outlets for electric stoves, boilers and other things, a circuit breaker is selected according to the power of consumers.
To implement this approach to the arrangement of networks, manufacturers offer a sufficient selection of machines with different numbers of poles, differential type and other units. For domestic purposes, use devices in molded cases, in which all live parts are protected, which excludes accidental electric shock. In order to install a universal circuit breaker, switchgears (cabinets, assemblies, etc.) are required.
The variety of electrical devices is also explained by the fact that their design provides for all kinds of installation conditions. In other words, a device with identical parameters can have several versions. That's why circuit breaker connection diagram is a mandatory supplement for every product. It indicates the number of poles, connection points of phases and neutral, methods of preparing wires for connection and other features of a particular model.
If a person has a minimal understanding of electrical engineering, he will not think long about how to connect a single-phase circuit breaker on the dashboard of his apartment. Just look at the diagram, which is not complicated. The only warning: if you are changing the machine, in no case put a switch with a higher power than the previous one. First, you need to make sure that the wiring is able to withstand the increased load.
Maintenance of electrical equipment
Electrical equipment, like any other device, needs care. Maintenance of circuit breakers is carried out according to a specific procedure with strict intervals. Users are often unaware of this need, but it is there. Electrical equipment is subject to wear and tear, contacts oxidation, insulation aging, wear of moving parts and other changes occur gradually. Therefore, the calculation of the circuit breaker in terms of power, performed 5 years ago, may not correspond to the real state of affairs.
Probably, many of you have had situations when a perfectly working network starts to fail. An obvious manifestation of this is the fact that, for no apparent reason, the circuit breaker often trips. The reason may be in the device itself, but most often this happens due to problems with wiring and hidden defects in the electrical circuits of household appliances and equipment.
To identify and prevent such situations, there is loading circuit breakers... It is carried out every three years using special equipment and is performed in order to check the compliance of the actual state of the machine with the requirements for safe operation of power grids. The method for testing circuit breakers provides for checking the state of insulation, the response time of the overcurrent and heating protection, the state of the contacts and other parameters.
Regular maintenance ensures that problems are identified early, prevents more serious consequences, and ensures that your networks are safe for the foreseeable future. The detected malfunctions of the circuit breakers are eliminated as far as possible, but most often in such cases a complete replacement of electrical devices is required, especially in the case of their small standard sizes.
Manufacturers of electrical products manufacture many spare parts for powerful industrial machines. For household or low-power equipment, only spare contact groups are usually produced. That's why replacement of circuit breakers- a typical activity in the repair of electrical networks. Regular maintenance of electrical equipment is a completely easy procedure, including for the money. Its main goal is prevention.
Among the technical characteristics of the machines, the guaranteed number of on / off cycles is also indicated. According to these indicators, the circuit breakers have a service life measured in decades, provided that the devices are correctly installed and maintained in a timely manner. They must fully comply with the parameters of the network. In addition, to extend their service life, you should not use faulty electrical appliances that provoke frequent network outages.
Professional services from the company "Skat Technology"
Our company specializes in works on engineering communications, including power grids. Our experts are ready to give recommendations on the selection of circuit breakers and design networks, including calculations of loads and their distribution, taking into account all the norms of safe operation. Experienced engineers will answer any practical questions, including how to connect a circuit breaker for different categories of current consumers, taking into account the installation conditions, the state of the wiring and other factors.
Our catalogs contain a wide selection of electrical products from leading manufacturers. Our assortment will allow you to easily carry out a complete complete set of works on the arrangement of power grids. If confuses you cost of circuit breakers with logos of famous brands, we remind you that quality products cannot be frankly cheap. In addition, the service life of such electrical equipment is an order of magnitude higher than that of products of dubious origin.
Those who are wondering which circuit breakers are better should decide what meaning you are putting into it. Is reliability and safety at the right cost the determining factor for us? We offer electrical products at the most fair prices, therefore we are convinced that our customers do not overpay. Dimensions of circuit breakers They are far from always equivalent to prices, therefore, if you want to get a normal result of arranging the power grid, use the services of Skat Technology professionals.
An electrical machine, or circuit breaker, is a mechanical switching device through which you can manually de-energize the entire electrical network or a specific section of it. This can be done in a house, apartment, country house, garage, etc. Moreover, such a device is equipped with the function of automatically turning off the electrical cable in the event of an emergency: for example, in the event of a short circuit or overload. The difference between such circuit breakers from conventional fuses is that after they have been triggered, they can be turned on again with a button.
Let's talk about how to choose machines: electric machines exist in a wide variety, which requires taking into account a number of factors at once when buying them.
Do you need such a machine? An affirmative answer must be given. A properly working circuit breaker will protect your premises from various unpleasant situations, including:
- fires;
- electric shock;
- damage to the wiring.
So, when choosing a machine, as we noted, several indicators should be taken into account at once. Let's consider them in order.
The main criteria for selection
Short-circuit current limit
This indicator must be taken into account immediately. It means that maximum current value at which the electric machine will work and open the circuit. The choice is not great here, as there are only three options:
- 4.5 kA;
- 6 kA;
- 10kA.
When choosing, one should be guided by the theoretical probability of a strong short-circuit current. If there is no such probability, then it will be enough to purchase a 4.5 kA automatic machine.
Machine current
Accounting for this indicator is the next step. We are talking about the required nominal value of the operating current of the electrical machine. To determine the operating current, you need to be guided by the power that is expected to be connected to the wiring, or by the value of the allowable current (the level that will be maintained in normal mode).
What do you need to know when determining the parameter in question? It is not recommended to use machines with an overestimated operating current. It's just that in this case, the machine will not turn off the power during overload, and this can cause thermal destruction of the wiring insulation.
This is perhaps the simplest indicator. To choose the number of poles for a circuit breaker, you need to proceed from how it will be used.
So, a single-pole circuit breaker is your choice if you need to protect the wiring that goes from the electrical panel to the sockets and lighting circuits.
A two-pole switch is used when you need to protect all wiring in an apartment or house with a single-phase power supply.
Three-phase wiring and load protection is provided by a three-pole circuit breaker, and four-pole ones are used to protect the four-wire power supply.
Machine characteristics
This is the last indicator that you need to pay attention to. The time-current characteristic of the circuit breaker is determined by the loads that are connected to the protected line. When choosing a characteristic, the following are taken into account: the operating current of the circuit, the rated current of the machine, the throughput of the cable, the operating current of the switch.
- In the event that it is necessary to connect small inrush currents to the power supply line, i.e. electrical devices characterized by a small difference between the operating current and the current that occurs when switched on, the tripping characteristic B should be preferred.
- Finally, there is one more characteristic - D. You should stop your choice on it if you intend to connect powerful devices with high starting points. What devices are we talking about? For example, about the electric motor.
The final stage of selection
These are the main indicators to consider when choosing a circuit breaker. Accordingly, if you know all the necessary data, then the choice will not be difficult. It only remains to take into account the very last criterion - the manufacturer of the machine. What does this affect?
- obviously at the cost. Indeed, there is a difference. So, well-known European brands offer their circuit breakers at a price that is twice the cost of domestic counterparts and three times more than the price of devices from the South-Eastern countries;
- also the presence or absence of a switch with clearly defined indicators in the warehouse depends on the choice of a specific manufacturer.
Another useful way to choose an electric machine is offered in the video below:
The main difference between these switching devices from all other similar devices is the complex combination of capabilities:
1. to maintain the rated load in the system for a long time due to the reliable transmission of powerful flows of electricity through its contacts;
2. to protect the operating equipment from accidental faults in the electrical circuit by quickly removing power from it.
Under normal operating conditions of the equipment, the operator can manually switch the loads with the circuit breakers, providing:
different power schemes;
changing the network configuration;
withdrawal of equipment from work.
Emergency situations in electrical systems occur instantly and spontaneously. A person is not able to quickly respond to their appearance and take measures to eliminate them. This function is assigned to automatic devices built into the circuit breaker.
In the power industry, the division of electrical systems by type of current is accepted:
constant;
alternating sinusoidal.
In addition, there is a classification of equipment according to the magnitude of the voltage for:
low voltage - less than a thousand volts;
high voltage - everything else.
For all types of these systems, their own circuit breakers are created, designed for repeated operation.
AC circuits
According to the power of the transmitted electricity, automatic switches in alternating current circuits are conventionally divided into:
1.modular;
2. in a molded case;
3. power air.
Modular designs
A specific design in the form of small standard modules with a width of multiples of 17.5 mm determines their name and design with the possibility of mounting on a Din-rail.
The internal structure of one of these circuit breakers is shown in the picture. Its body is completely made of durable dielectric material, excluding.
The supply and outgoing wires are connected to the upper and lower terminal clamp, respectively. For manual control of the state of the switch, a lever with two fixed positions is installed:
the upper one is designed to supply current through a closed power contact;
bottom - provides a break in the power supply circuit.
Each of these machines is designed for long-term operation at a certain value (In). If the load becomes larger, then the power contact breaks. For this, two types of protections are placed inside the case:
1. thermal release;
2.current cutoff.
The principle of their operation makes it possible to explain the time-current characteristic, which expresses the dependence of the protection operation time on the load current or failure passing through it.
The graph shown in the picture is for one specific circuit breaker, when the cut-off operating zone is selected at 5 ÷ 10 times the rated current.
At the initial overload, a thermal release is made, which, with an increased current, gradually heats up, bends and acts on the disconnecting mechanism not immediately, but with a certain time delay.
In this way, it allows small overloads associated with short-term connection of consumers to self-eliminate and eliminate unnecessary shutdowns. If the load provides critical heating of the wiring and insulation, then the power contact breaks.
When an emergency current arises in the protected circuit, capable of burning equipment with its energy, then an electromagnetic coil comes into operation. With an impulse, due to the surge of the load that has arisen, it throws the core onto the disconnecting mechanism in order to instantly stop the out-of-limit mode.
The graph shows that the higher the short-circuit currents, the faster they are disconnected by the electromagnetic release.
The household automatic steam fuse works according to the same principles.
When large currents are broken, an electric arc is created, the energy of which can burn out the contacts. To eliminate its effect, an arc-extinguishing chamber is used in circuit breakers, which divides the arc discharge into small flows and extinguishes them due to cooling.
Multiplicity of cutoffs of modular structures
Electromagnetic releases are tuned and matched to work with certain loads because they create different transients when they start. For example, during the switching on of various luminaires, the short-term inrush current due to the changing resistance of the filament can approach three krats of the nominal value.
Therefore, for the socket group of apartments and lighting circuits, it is customary to choose automatic switches with a time-current characteristic of the "B" type. It is 3 ÷ 5 In.
Asynchronous motors, when spinning a rotor with a drive, cause higher overload currents. For them, select machines with the characteristic "C", or - 5 ÷ 10 In. Due to the created margin in time and current, they allow the engine to spin up and it is guaranteed to enter the operating mode without unnecessary shutdowns.
In industrial production, on machine tools and mechanisms, there are loaded drives connected to motors, which create more increased overloads. For such purposes, automatic switches of characteristic "D" with a rating of 10 ÷ 20 In are used. They have proven themselves well when working in circuits with active-inductive loads.
In addition, the machines have three more types of standard time-current characteristics that are used for special purposes:
1. "A" - for long wiring with an active load or protection of semiconductor devices with a value of 2 ÷ 3 In;
2. "K" - for pronounced inductive loads;
3. "Z" - for electronic devices.
In the technical documentation from different manufacturers, the cutoff rate for the last two types may differ slightly.
This class of devices is capable of switching higher currents than modular designs. Their load can reach values up to 3.2 kiloamperes.
They are manufactured according to the same principles as modular structures, but, taking into account the increased requirements for the transmission of the increased load, they are trying to give them relatively small dimensions and high technical quality.
These machines are designed for safe operation in industrial facilities. By the value of the rated current, they are conventionally divided into three groups with the ability to switch loads up to 250, 1000 and 3200 amperes.
Constructive design of their case: three- or four-pole models.
Power air switches
They work in industrial installations and handle very heavy currents up to 6.3 kiloamperes.
These are the most complex devices for switching devices of low-voltage equipment. They are used for the operation and protection of electrical systems as input and output devices for high power distribution plants and for connecting generators, transformers, capacitors or powerful electric motors.
A schematic representation of their internal structure is shown in the picture.
Here, a double break of the power contact is already used and arc extinguishing chambers are installed with gratings on each side of the disconnection.
The operation algorithm involves the closing coil, the closing spring, the motor-drive of the spring charging and the automation elements. To monitor the flowing loads, a current transformer with a protective and measuring winding is integrated.
Circuit breakers for high-voltage equipment are very complex technical devices and are made strictly individually for each voltage class. They are usually used.
Requirements are imposed on them:
high reliability;
security;
performance;
ease of use;
relative noiselessness during operation;
optimal cost.
Loads that break during a fault trip are accompanied by a very strong arc. Various methods are used to extinguish it, including breaking the circuit in a special environment.
This switch includes:
contact system;
arc extinguishing device;
live parts;
insulated housing;
drive mechanism.
One of these switching devices is shown in the photograph.
For high-quality operation of the circuit in such structures, in addition to the operating voltage, take into account:
the rated value of the load current for its reliable transmission in the on state;
maximum short-circuit current at rms value that the tripping mechanism can withstand;
the permissible component of the aperiodic current at the moment of circuit rupture;
automatic reclosing capabilities and two AR cycles.
According to the methods of extinguishing the arc during tripping, the switches are classified into:
oil;
vacuum;
air;
SF6 gas;
autogas;
electromagnetic;
auto-pneumatic.
For reliable and convenient operation, they are equipped with a drive mechanism that can use one or several types of energies or their combinations:
cocked spring;
lifted load;
compressed air pressure;
electromagnetic pulse from the solenoid.
Depending on the conditions of use, they can be created with the ability to operate under voltage from one to 750 kilovolts inclusive. Naturally, they have a different design. dimensions, automatic and remote control capabilities, protection settings for safe operation.
The auxiliary systems of such circuit breakers can have a very complex branched structure and be located on additional panels in special technical buildings.
DC circuits
A huge number of circuit breakers with different capabilities also operate in these networks.
Electrical equipment up to 1000 volts
Modern modular devices with the ability to mount on a Din-rail are massively introduced here.
They successfully complement the classes of old automatic machines such as, AE and other similar ones, which were fixed on the walls of the panels with screw connections.
DC modular designs have the same structure and principle of operation as their alternating voltage counterparts. They can be performed by one or several units and are selected according to the load.
Electrical equipment above 1000 volts
High-voltage circuit breakers for direct current are used in electrolysis plants, metallurgical industrial facilities, railway and urban electrified transport, and energy enterprises.
The main technical requirements for the operation of such devices correspond to their alternating current counterparts.
Hybrid breaker
Scientists from the Swedish-Swiss company ABB managed to develop a high-voltage DC circuit breaker that combines two power structures in its device:
1. SF6 gas;
2. vacuum.
It was named hybrid (HVDC) and uses the technology of sequential arc quenching in two environments at once: sulfur hexafluoride and vacuum. For this, the following device is assembled.
Voltage is applied to the upper busbar of the hybrid vacuum circuit breaker, and voltage is removed from the lower busbar of the SF6 circuit breaker.
The power parts of both switching devices are connected in series and controlled by their individual drives. In order for them to work simultaneously, a synchronized coordinate operations control device was created, which transmits commands to the control mechanism with independent power supply via a fiber-optic channel.
Due to the use of high-precision technologies, the designers managed to achieve the coordination of actions of the actuators of both drives, which fits into a time interval of less than one microsecond.
The circuit breaker is controlled from a relay protection unit built into the power line through a repeater.
The hybrid circuit breaker has made it possible to significantly increase the efficiency of composite SF6 and vacuum structures through the use of their combined characteristics. At the same time, it was possible to realize the advantages over other analogues:
1.the ability to reliably disconnect short-circuit currents at high voltage;
2. the possibility of a small effort to carry out the switching of the power elements, which made it possible to significantly reduce the dimensions and. accordingly, the cost of equipment;
3. the availability of implementation of various standards for the creation of structures operating as part of a separate circuit breaker or compact devices at one substation;
4. the ability to eliminate the effects of rapidly increasing recovery stress;
5. Possibility of forming a basic module for working with voltages up to 145 kilovolts and above.
A distinctive feature of the design is the ability to break an electrical circuit in 5 milliseconds, which is almost impossible to perform with power devices of other designs.
The hybrid circuit breaker device was ranked among the top ten developments of the year according to the MIT (Massachusetts Institute of Technology) Technology Review.
Other manufacturers of electrical equipment are engaged in similar research. They also achieved certain results. But ABB is ahead of them in this matter. Its management believes that the transmission of AC power is causing its great losses. They can be significantly reduced by using high voltage direct voltage circuits.
Surely many of us wondered why circuit breakers so quickly replaced outdated fuses from electrical circuits? The activity of their implementation is justified by a number of very convincing arguments, including the opportunity to buy this type of protection, ideally matching the time-current data of specific types of electrical equipment.
Doubt which machine you need and don't know how to choose the right one? We will help you find the right solution - the article discusses the classification of these devices. As well as important characteristics that you should pay close attention to when choosing a circuit breaker.
To make it easier for you to deal with the machines, the article material is supplemented with visual photos and useful video recommendations from specialists.
The automatic machine almost instantly turns off the line entrusted to it, which excludes damage to the wiring and equipment powered from the network. After a shutdown has been completed, the branch can be restarted immediately without replacing the safety device.
If you have knowledge or experience in performing electrical work, please share it with our readers. Leave your comments about the choice of a circuit breaker and the nuances of its installation in the comments below.
Circuit breakers They are not at all like the usual ones that are installed in every room to turn on and off the light (Fig. 1). Their task is somewhat different. Circuit breakers are installed in distribution boards and serve to protect the circuit from voltage surges and non-periodic power outages in certain sections of the power grid.
Rice. 1.
Automatic machines, as they are more often called, are installed at the entrance to a house or apartment and are located in special boxes, metal or plastic (Fig. 2).
Rice. 2. Switchboard with automatic devices
There are many types of circuit breakers. Some of them only serve as circuit breakers and overload protection. Such are, for example, the old automatic switches type AE in a black carbolite casing (Fig. 3).
Rice. 3. AE series circuit breaker
In most of the old shields in the entrances of residential buildings, there are just such. However, they are quite reliable and are still in operation.
Modern variations allow additional functions, such as protection against underload currents.
According to the response time to an unacceptable voltage, the machines are divided into 3 types: selective, normal and high-speed. The response time of a normal machine ranges from 0.02 to 0.1 s. In selective circuit breakers, this time is the same. High-speed circuit breakers work more quickly - they have this value is only 0.005 s.
All circuit breakers are enclosed in a plastic shatterproof case with a special fastening (strip or rail) on the back plane. It is very easy to install the machine on such a mount - just insert it on the rail until it clicks. It can be removed with a screwdriver by slightly pulling on the special tab on top of the circuit breaker. This greatly facilitates the task of installing the machine in a cabinet (Fig. 4).
Rice. 4.
Inside the body is the "stuffing" of the machine, its main safety devices, of which there can be 2 (Fig. 5).
Rice. 5. Internal
We are talking about electromagnetic and thermal releases - a kind of automatic circuit breaker mechanisms. The bimetallic plate, when heated by an unacceptably high current passing through it, straightens and opens the contacts - this is a thermal release. In terms of response time, it is the slowest.
The electromagnetic release operates according to the "dead hand" rule. The coil located in the center of the machine is continuously maintained in place by a stable voltage. As soon as it jumps out of the nominal limits, the coil literally jumps out of its place, breaking the circuit. This is the fastest way to break the chain.
All circuit breakers have contacts for connecting incoming and outgoing wires (fig. 6).
Rice. 6. The wires are connected to the contacts of the circuit breaker using screw clamps.
The machines are distinguished by the degree of sensitivity to tripping tripping. In the standard most common models, circuit breakers with a threshold value of about 140% of the nominal are most often used. When the voltage rises one and a half times, the electromagnetic (fast) release is triggered. If the rated voltage is slightly exceeded, the thermal release operates. In this case, the shutdown process can take hours, which greatly depends on the ambient temperature. However, the machine will react to voltage changes in any case.
Circuit breakers are distinguished by the number of poles. What does it mean? One machine can have several independent electrical lines, which are interconnected by a common shutdown mechanism (Fig. 7 and 8). The machines are one-, two-, three- and four-pole (this applies to domestic use).
Rice. 7.in a plastic box off
Rice. 8.: All lines are triggered at the same time when disconnected, they are connected together with one jumper lever
The circuit breaker has differences in other indicators. They differ in the threshold current strength that they pass through themselves. In order for the machine to work and in an emergency to turn off the power grid, it must be set to a certain sensitivity threshold. This setting is made by the manufacturer, therefore, the numerical value of this threshold is immediately written on the machine. For domestic needs, machines are used with indicators of 6.3, 10, 16, 25, 32, 40, 63, 100 and 160 A (Fig. 9). There are machines with values of both 1000 and 2600 A, but they are not used in everyday life. These figures mean the total power of all consumers of electric current that will be connected to the circuit "protected" by the machine.
The sensitivity of the machine it is necessary to calculate not only by the total power of the prospective energy consumers, but also by the wiring and wiring products - sockets and switches.
Table 1 shows the typology of machines.
Table 1. Types of machines
| Type of | Appointment |
| A | For breaking circuits with long wiring lengths and protecting semiconductor devices |
| B | For general purpose lighting networks |
| C | For lighting circuits and electrical installations with moderate starting currents (motors and transformers) |
| D | For circuits with resistive-inductive loads, as well as protection of electric motors with high starting currents |
| K | For inductive loads |
| Z | For electronic devices |
Table 2. Two-core copper cable laid in a duct
| Section, mm2 | Cable current / 1.45, A | Automatic machine, A | Excess current strength,% | |
| 1,5 | 19 | 13,1 | 13 | - |
| 2,5 | 27 | 18,62 | 16 | - |
| 4 | 38 | 26,2 | 25 | - |
| 6 | 50 | 34,48 | 32 | - |
| 10 | 70 | 48,27 | 40(50) | 3,5 |
| 16 | 90 | 62,06 | 50(63) | 1,5 |
Table 3. Two-core copper wire laid in a box
| Section, mm2 | Maximum continuous current of the cable, A | Cable current / 1.45, A | Automatic machine, A | Excess current strength,% |
| 1 | 15 | 10,34 | 10 | - |
| 1,5 | 18 | 12,41 | 10(13) | 4,7 |
| 2 | 23 | 15,86 | 13(16) | 0,87 |
| 2,5 | 25 | 17,24 | 16 | - |
| 4 | 32 | 22,06 | 20 | - |
| 6 | 40 | 27,58 | 25 | - |
| 10 | 48 | 33,1 | 32 | - |
| 16 | 55 | 37,93 | 32(40) | 5,4 |
The maximum continuous current of the cable is taken for a core temperature of +65 and an air temperature of +25 ° C. The number of simultaneously laid conductors - up to 4. Range of automatic machines: 0.5 A, 1 A, 2 A, 3 A, 4 A, 6 A, 10 A, 13 A, 16 A, 20 A, 25 A, 32 A, 40 A, 50 A and 63 A. 3 are also suitable for a 3-core cable. In this case, the third core must be a protective earth or neutral conductor.
Rice. 9. A row of single-pole machines for 16 A. For example, for a separate area in an apartment, for example, a kitchen, we have one machine for 6.3 A (sometimes this happens - the electricians joked). Using the well-known formula Watt = Volt x Ampere, we calculate how many devices (and which ones) can be powered from our network. It turns out that this value is 1386 W, since the default voltage is 220 V. It means that even a powerful kettle cannot be turned on in such a kitchen, not to mention a refrigerator or an electric stove - the machine will work instantly and will not allow an inadmissible, in his opinion, current to pass through controlled territory. In this case, it is necessary to urgently change the circuit breaker for 25 or even 32 A.
