Single pole DC circuit breaker. Short circuit breakers in a solar power plant

  • 0.4kV
  • switch
  • fuse

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4-13. DC NETWORK PROTECTORS FOR RATED VOLTAGE UP TO 24 V

To protect circuits from overcurrents fed by low-power DC sources with voltage up to 24 V, single-pole circuit breakers are used (Fig. 4-40) with a rated direct current from 2 to 50 A. They are produced in the same size and have a time delay inversely dependent on the current at all currents greater than the boundary current, which is between the rated current and 120-130% of the rated current.

Rice. 4-40. Automatic circuit breaker for DC networks 50 A, 24 V.

At a current equal to 200% of the rated current, the time delay for different versions is in the range of 25 - 80 seconds when heated from a cold state and at least 5 seconds after heating with a rated current. The breaking capacity is 10.00 A for the rated current of the releases up to 10 A and 1,500 A for versions for higher rated currents. Guaranteed service life of 10,000 inclusions.

A characteristic feature of the design is the absence of a free trip, which in some cases is advisable, since it makes it possible to keep the machine in a closed state, despite the presence of overcurrent.

When the handle is in the “on” position, the movable contact 1 is always pressed against the fixed contact 2 by means of the pin 8, which is acted upon by the spring 9. In this case, the block 3 compresses the spring 4. It is held due to the fact that its tooth 5 jumped over the tooth 6 of the thermobimetallic plate 7. When overloaded, the thermobimetallic plate bends, teeth 5 and 6 disengage, and if the handle is not held in the on position, then a switch-off occurs, since under the influence of spring 4 the handle goes into the off position and the pin 8 located inside it opens the contact.

4-14. SEMI-QUICK AUTOMATIC AB-45-1/6000

Automatic machine AB-45-1/6000 for voltage 750 V, current 6 000 A direct current - single-pole, with electromagnetic drive, opening release and maximum instantaneous release with adjustable setting 6 000-12 000 A. It has been designed to protect high power DC installations, mainly metallurgical ones. The principal kinematic diagram of the automaton is approximately the same as that of universal automata; however, its own operating time has been reduced, for which purpose an overcurrent release with an inductive shunt has been used (fig. 4-41).

Rice. 4-41. Maximum release with inductive shunt for AB-45-1/6000 circuit breaker for 6,000 I, 750 V DC.

Part of the magnetic flux created by the current passing through the window 1 of the magnetic circuit passes through the shunt 2 and keeps the armature 3 from turning on. At high current growth rates, the flow through the holding shunt slowly increases due to the influence of the copper sleeve 4, which leads to an accelerated attraction of the release armature.

During the test (L. 4-9), despite the huge rate of current rise (25-10 + 6 a / sec), the own response time was 10 - 15 ms, the current was not limited by the machine and reached 200 kA, the machine was destroyed by electrodynamic forces Under similar conditions, the VAB-2 automaton limited the current to 42 kA.The breaking capacity of the AB-45-1 / 6000 was tested up to 90 kA at a voltage of 500 V. The automaton turned off such a current with its own time of 20-35 ms and a total time of about 40 ms. Forward

DC circuit breakers are used to disconnect the circuit under load. At traction substations, switches are used to turn off 600 V supply lines during overloads and short circuit currents and to turn off the reverse current of rectifier units during reverse ignition or breakdown of valves (i.e., internal short circuits during parallel operation of units).

The electric arc is extinguished by automatic switches in the air on the arcing horns. Arc elongation can be done by magnetic blowing or in chambers with narrow slots.

In all cases of disconnection of the circuit and the formation of an electric arc, a natural upward movement of the arc occurs along with the movement of the air heated by it, i.e., thermal blast.

Mainly used high speed circuit breakers.

Rice. 1. Oscillograms of current and voltage when the short-circuit current is turned off: a - by a non-quick-acting switch, b - by a quick-acting circuit breaker

The total time T for breaking the short circuit current or overload by the circuit breaker consists of three main parts (Fig. 1):

T \u003d t o + t 1 + t 2

where t0 is the rise time of the current in the disconnected circuit to the value of the set current, i.e., to the value at which the tripping device of the circuit breaker operates; t1 is the circuit breaker opening time, i.e., the time from the moment the set current is reached to the moment the circuit breaker contacts begin to diverge; t2 - arc burning time.

The rise time of the current in the circuit t0 depends on the parameters of the circuit and the setting of the circuit breaker.

The intrinsic opening time t1 depends on the type of circuit breaker: for slow-acting circuit breakers, the intrinsic opening time is in the range of 0.1-0.2 sec, for high-speed circuit breakers it is 0.0015-0.005 sec.

The arc burning time t2 depends on the magnitude of the interrupted current and the characteristics of the arc extinguishing devices of the circuit breaker.

The total shutdown time of a non-quick-acting switch is in the range of 0.15-0.3 sec, of a fast-acting one - 0.01-0.03 sec.

Thanks to its short tripping time, the high-speed circuit breaker limits the maximum value of the short-circuit current in the protected circuit.

At traction substations, high-speed automatic DC switches are used: VAB-2, AB-2/4, VAT-43, VAB-20, VAB-20M, VAB-28, VAB-36 and others.

Switch VAB-2 is polarized, i.e., responsive to current in only one direction - forward or reverse, depending on the setting of the switch.

On fig. 2 shows the electromagnetic mechanism of a DC switch.


Rice. Fig. 2. The electromagnetic mechanism of the VAB-2 circuit breaker: a - a section of the circuit breaker, b - the limits of the limiting wear of the contacts of the VAB-2 circuit breaker, (A - the minimum thickness of the fixed contact is 6 mm, B - the minimum thickness of the movable contact is 16 mm); 1 - holding coil, 2 - magnetic circuit, 3 - switching coil, 4 - magnetic armature, 5 - upper steel bar, 6 - anchor, 7 - main yoke coil, 8 - calibration coil, 9 - U-shaped magnetic circuit, 10 - current carrying output, 11 - adjusting screw, 12 - shunt plate, 13 - flexible connection, 14 - stop, 15 - armature lever, 16 - armature lever axis, 17 - fixed contact, 18 - movable contact, 19 - contact lever, 20 - axis contact lever, 21 - axle with roller, 22 - stop lever, 23 - opening springs, 24 - rod, 25 - adjusting screws, 26 - bracket, 27 - holding coil core

The armature lever 15 (Fig. 2, a) rotates around the axis 16, passed through the upper steel beam 5. In the lower part of the lever 15, consisting of two silumin cheeks, a steel anchor 6 is clamped, and in the upper part there is a spacer sleeve with an axis 20, around which the contact lever 19, made of a set of duralumin plates, rotates.

A movable contact 18 is fixed in the upper part of the contact lever, and a copper shoe with a flexible connection 13 is fixed at the bottom, with the help of which the movable contact is connected to the main current coil 7 and through it to the output 10. Stops 14 are attached to the lower part of the contact lever on both sides, and on the right side there is a steel axle with a roller 21, to which two trip springs 23 are attached on one side. On the other side, the trip springs are fixed with the help of adjusting screws 25 in a bracket 26, fixedly mounted on a steel beam 5.

In the off position, the lever system (armature lever and contact lever) is rotated by disconnecting springs 23 around axis 16 until the armature 6 stops against the left rod of the U-shaped magnetic circuit.

The making 3 and holding 1 coils of the circuit breaker are powered by their own direct current needs.

To turn on the circuit breaker, you must first close the circuit of the holding coil 1, then the circuit of the closing coil 3. The direction of the current in both coils must be such that the magnetic fluxes created by them are added to the right core of the core of the magnetic circuit 9, which serves as the core of the closing coil; then the armature 6 will be attracted to the core of the switching coil, i.e., it will be in the “On” position. In this case, the axis 20, together with the contact lever 19, will turn to the left, the opening springs 23 will stretch and will tend to rotate the contact lever 19 around the axis 20.

When the switch is turned off, the magnetic armature 4 lies on the end of the core of the closing coil and, when the switch is turned on, remains attracted to the end of the core by the total magnetic flux of the closing and holding coils. The magnetic armature 4 is connected by means of a rod 24 to the locking lever 22, which prevents the contact lever from turning until the movable contact stops against the fixed one. Therefore, a gap remains between the main contacts, which can be adjusted by changing the length of the rod 24 and should be equal to 1.5-4 mm.

If the voltage is removed from the switching coil, then the electromagnetic forces holding the armature 4 in the attracted position will decrease and the springs 23, using the locking lever 22 and the rod 24, will tear the armature from the end of the core of the switching coil and turn the contact lever until the main contacts close. Therefore, the main contacts will close only after the closing coil circuit has been opened.

Thus, the principle of free tripping is implemented for VAB-2 circuit breakers. The gap between the magnetic armature 4 (otherwise called the armature of free tripping) and the end of the core of the closing coil in the on position of the switch must be within 1.5-4 mm.

The control circuit provides for the supply of a short-term current pulse to the closing coil, the duration of which is only sufficient to have time to transfer the armature to the “On” position. The closing coil circuit is then automatically opened.

The presence of a free trip can be checked in the following way. A piece of paper is placed between the main contacts and the contactor is closed. The switch is turned on, but while the contactor contact is closed, the main contacts should not close and the paper can be freely removed from the gap between the contacts. As soon as the contactor contact is open, the magnetic armature will be torn off from the end of the core of the closing coil and the main contacts will close. In this case, the paper will be sandwiched between the contacts and it will not be possible to remove it.

When the switch is turned on, a characteristic double blow is heard: the first - from the collision of the armature and the core of the switching coil, the second - from the collision of the closed main contacts.

The polarization of the circuit breaker consists in choosing the direction of the current in the holding coil, depending on the direction of the current in the main current coil.

In order for the switch to turn off the circuit when the direction of the current in it changes, the direction of the current in the holding coil is chosen so that the magnetic fluxes created by the holding coil and the main current coil coincide in direction in the core of the closing coil. Therefore, with current flowing in the forward direction, the main circuit current will assist in keeping the breaker in the closed position.

In emergency mode, when the direction of the main current is reversed, the direction of the magnetic flux created by the main current coil in the core of the switching coil will change, i.e. the magnetic flux of the main current coil will be directed against the magnetic flux of the holding coil and at a certain value of the main current, the core of the switching coil will demagnetize and trip springs will trip the breaker. The speed is determined to a greater extent by the fact that while the magnetic flux decreases in the core of the switching coil, the magnetic flux increases in the core of the main current coil.

In order for the circuit breaker to open the circuit when the current increases above the setting current in the forward direction, the direction of the current in the holding coil is chosen so that the magnetic flux of the holding coil in the core of the closing coil is directed against the magnetic flux of the main current coil when the forward current flows through it. In this case, with an increase in the main current, the demagnetization of the core of the closing coil increases, and at a certain value of the main current, equal to or greater than the setting current, the circuit breaker turns off.

The setting current in both cases is controlled by changing the value of the holding coil current and changing the gap δ1.

The current value of the holding coil is controlled by changing the value of the additional resistance, connected in series with the coil.

Changing the gap δ1 changes the resistance to the magnetic flux of the main current coil. With a decrease in the gap δ1, the magnetic resistance decreases and, consequently, the value of the breaking current decreases. Changing the gap δ1 is carried out using the adjusting screw 11.

The gap δ2 between the stops 14 and the cheeks of the armature lever 15 in the on position of the switch characterizes the quality of the closure of the main contacts and should be within 2-5 mm. The plant produces switches with a gap δ2 equal to 4-5 mm. The gap value δ2 determines the angle of rotation of the contact lever 19 around the axis 20.

The absence of a gap δ2 (stops 14 are in contact with the cheeks of the armature lever 15) indicates poor contact or no contact between the main contacts. A gap δ2 less than 2 or more than 5 mm indicates that the main contacts are in contact only at the lower or upper edge. The gap δ2 can be small due to the high wear of the contacts, which in this case are replaced.

If the dimensions of the contacts are sufficient, then the regulation of the gap δ2 is carried out by moving the entire switching mechanism along the frame of the switch. To move the mechanism, two bolts are released, with which the mechanism is attached to the frame.

The distance between the main contacts in the open position should be 18-22 mm. The pressing of the main contacts for switches with a rated current up to 2000 A inclusive must be within 20-26 kg, and for switches with a rated current of 3000 A - within 26-30 kg.

On fig. 2, b shows the movable system of the circuit breaker with the designation of the boundary of the limiting wear of the contacts. The moving contact is considered worn when dimension B is less than 16 mm, and the fixed contact is considered worn when dimension A is less than 6 mm.

On fig. 3 shows a detailed control scheme for the VAB-2 circuit breaker. The circuit provides for the supply of a short-term pulse to the switching coil and does not allow multiple repeated switching on when the power button is pressed for a long time, i.e., it protects against "voicing". The holding coil is energized all the time.

To turn on the switch, press the "On" button, thereby closing the circuit of the coils of the contactor K and the blocking RB. In this case, only the contactor is activated, which closes the circuit of the closing coil VK.

As soon as the armature takes the “On” position, the closing auxiliary contacts of the BA of the circuit breaker will close, and the breaking contacts will open. One of the auxiliary contacts shunts the coil of the contactor K, which will break the circuit of the closing coil. In this case, the entire mains voltage will be applied to the coil of the blocking relay RB, which, having actuated, by its contacts once again shunts the contactor coil.

To re-close the circuit breaker, open the power button and close it again.

The discharge resistance CP, connected in parallel with the holding coil DC, serves to reduce the overvoltage when the coil circuit is opened. The adjustable resistance of the LED makes it possible to change the current of the holding coil.

The rated current of the holding coil at a voltage of 110 V is 0.5 A, and the rated current of the closing coil at the same voltage and parallel connection of both sections is 80 A.

Rice. 3. Electric circuit for controlling the switch VAB-2: Off. - opening button, DK - holding coil, SD - additional resistance, CP - discharge resistance, BA - auxiliary contacts of the switch, LK, LZ - red and green signal lamps, Incl. - power button, K - contactor and its contact, RB - blocking relay and its contact, VK - closing coil, AP - automatic switch

Voltage fluctuations of operational circuits from - 20% to + 10% of the rated voltage are permissible.

The total time of switching off the circuit by the VAB-2 switch is 0.02-0.04 sec.

Extinguishing the arc when the circuit breaker breaks under load occurs in the arc chute using magnetic blast.

The magnetic blow coil is usually connected in series with the main fixed contact of the switch and is a coil of the main current-carrying bus, inside of which there is a core made of steel tape. To concentrate the magnetic field in the zone of arc formation on the contacts, the core of the magnetic blowing coil of the switches has pole pieces.

The arc extinguishing chamber (Fig. 4) is a flat box made of asbestos cement, inside of which two longitudinal partitions 4 are made. A horn 1 is installed in the chamber, inside which the axis of rotation of the chamber passes. This horn is electrically connected to a moving contact. The other horn 7 is fixed on a fixed contact. To ensure a quick transition of the arc from the movable contact to the horn 1, the distance of the horn from the contact should be no more than 2-3 mm.

The electric arc that occurred when switching off between contacts 2 and 6 under the influence of a strong magnetic field of the magnetic blast coil 5 is quickly blown onto horns 1 and 7, lengthens, is cooled by the oncoming air flow and the chamber walls in narrow slots between the partitions and quickly goes out. It is recommended to insert ceramic tiles into the walls of the chamber in the arc extinguishing zone.

The arc extinguishing chambers of circuit breakers for voltages of 1500 V and above (Fig. 5) differ from the chambers for voltages of 600 V in large overall dimensions and the presence of holes in the outer walls for the release of gases and an additional magnetic blast device.

Rice. 4. Arc extinguishing chamber of the VAB-2 circuit breaker for a voltage of 600 V: 1 and 7 - horns, 2 - moving contact, 3 - outer walls, 4 - longitudinal partitions, 5 - magnetic blowing coil, 6 - fixed contact


Rice. Fig. 5. Arc extinguishing chamber of the VAB-2 circuit breaker for a voltage of 1500 V: a - chamber arrangement, b - arc extinguishing circuit with additional magnetic blowing; 1 - movable contact, 2 - fixed contact, 3 - magnetic blowing coil, 4 and 8 - horns, 5 and 6 - auxiliary horns, 7 - auxiliary magnetic blowing coil, I, II, III, IV - arc position during extinguishing

The additional magnetic blowing device consists of two auxiliary horns 5 and 6, between which the coil 7 is connected. As the arc lengthens, it begins to close through the auxiliary horns and the coil, which, due to the current flowing through it, creates additional magnetic blowing. All chambers have metal pole strips on the outside.

For fast and stable extinguishing of the arc, the divergence of the contacts must be at least 4-5 mm.

The body of the switch is made of non-magnetic material - silumin - and is connected to a moving contact, so during operation it is under full operating voltage.

Switch automatic high-speed DC VAT-42

Operation of DC circuit breakers

In operation, it is necessary to monitor the condition of the main contacts. The voltage drop between them at rated load should be within 30 mV.

The contacts are cleaned from oxide with a wire brush (brushing brush). When sagging appears, they are removed with a file, however, the contacts should not be filed to restore their original flat shape, as this leads to their rapid wear.

It is necessary to periodically clean the walls of the arc extinguishing chamber from copper and coal deposits.

During the revision of the DC circuit breaker, the insulation of the holding and switching coils is checked in relation to the body, as well as the insulation resistance of the walls of the arc extinguishing chamber. The insulation of the arc chamber is tested by applying voltage between the main moving and fixed contacts with the chamber closed.

Before putting the switch into operation after repair or long-term storage, its chamber must be dried for 10-12 hours at a temperature of 100-110 ° C.

After drying, the chamber is mounted on the switch and the insulation resistance is measured between two points of the chamber opposite the moving and fixed contacts when they are open. This resistance must be at least 20 mΩ.

Switch settings are calibrated in the laboratory with current received from a low-voltage generator with a rated voltage of 6-12 V.

At the substation, the switches are calibrated with the load current or with the help of a load rheostat at a rated voltage of 600 V. A method for calibrating DC circuit breakers can be recommended using a calibration coil of 300 turns of PEL wire with a diameter of 0.6 mm, mounted on the core of the main current coil. By passing a direct current through the coil, the current setting is set by the number of ampere turns at the moment the switch is turned off. Switches of the first version, produced earlier, differ from switches of the second version by the presence of an oil damper.

Content:

In all electrical networks, a large number of devices are used, the main function of which is to protect lines and equipment from current overloads and short circuits. Among them, the circuit breaker is widely used, which performs not only protection, but also circuit switching. Thus, circuit breakers provide switching on and off of specific sections, protect them from current overloads by disconnecting protected circuits in case of emergency.

Types of electric machines

Circuit breakers are widely used in power supply systems, providing reliable protection for electrical circuits and networks, household appliances and electrical equipment. Their main task is to de-energize the circuit at the right time by turning off the supply of electric current. The circuit breaker trips during short circuits, as well as when the wires are heated due to overloads in the network.

Circuit breakers can operate in DC and AC circuits, and universal designs are able to work in the presence of any electric current in the network. In accordance with the design, they are divided into three types, which serve as the basis for other types of circuit breakers:

  • Air machines. They are used in industrial production, where currents in circuits can reach several thousand amperes.
  • Die-cast automata. They have a wide operating range from 16 to 1000 A.
  • Modular machines. They are widely used in apartments and private houses. Their name is associated with the standard width, which is a multiplicity of 17.5 mm, depending on the number of poles. That is, several switches can be used in one block at once.

All circuit breakers are divided according to the rated current and voltage, since most protective devices are installed in 220 or 380V networks.

Circuit breakers can be current-limiting or non-current-limiting. In the first case, the circuit breaker is a switch in which the opening time is set to an extremely small value, during which the short-circuit currents do not have time to reach a maximum.

Automata are classified according to the number of poles and can be one-, two-, three- and four-pole. They are equipped with overvoltage, shunt, undervoltage or zero voltage releases. Of great importance is the speed of response, when the devices can be normal, fast and selective. Some devices allow a combination of specifications. Some models are equipped with free contacts, and conductors are connected to them in different ways.

There is a division into different types according to the design of the release or circuit breaker installed in the machine. These elements play an important role and are separated as magnetic and thermal. In the first case, the circuit breaker is fast-acting and provides protection in case of short circuits. The response time is from 0.005 to 3-4 seconds. The operation of the thermal release is much slower, so it is mainly used for overload protection. The basis of the element is a bimetallic plate, which heats up with increasing loads. The response period is in the range from 3-4 seconds to several minutes.

In addition, the machines are divided by type of shutdown or by. Each type is A, B, C, D, K, Z. For example, type A is used when opening circuits that have a significant length of wiring, it protects semiconductor devices well. The operating limit is 2-3 rated currents. Type B is used in general purpose lighting systems and has a response threshold of 3-5 rated currents. More detailed information about each type of machine can be taken from the table.

Types of releases of circuit breakers

All releases used in circuit breakers can be divided into two groups. The first group includes devices that protect electrical circuits and are able to recognize the onset of a critical situation when overcurrents appear. As a result of operation, the further development of the accident is stopped due to the divergence of the main working contacts.

The second group of releases is represented by additional devices that are not included in the basic equipment of the machines. Under the order can be installed:

  • Shunt releases capable of remotely tripping the circuit breakers when a signal is received from the auxiliary circuit.
  • Undervoltage release. Performs a shutdown of the machine in the event of a voltage drop below acceptable limits.
  • Zero voltage release. Its contacts open when a significant voltage drop occurs.

Thermal release

A sample of a thermal release, shown in the figure, is made in the form of a bimetallic plate. In the process of heating, it bends, changes shape and affects the release mechanism. For the manufacture of the plate, two metal strips are mechanically interconnected. The material of each tape has a different coefficient of thermal expansion. The connection is made by soldering, welding or riveting. The bending of the plate is formed due to different changes in length during heating. Thermal releases provide protection against overload currents and can be configured for a given operating mode.

The main advantage of the thermal release is its high resistance to vibrations, the absence of rubbing parts and the ability to work in a dirty state. They are characterized by simple design and low cost. As disadvantages, it should be noted the constant consumption of electricity, sensitivity to temperature changes, the possibility of false alarms when heated by extraneous sources.

Electromagnetic releases with instantaneous action have received the same wide application. Structurally, they are made in the form of a solenoid with a core acting on the tripping mechanism. When an overcurrent flows through the solenoid winding, this creates a magnetic field that moves the core and simultaneously overcomes the resistance of the return spring.

The setting of the electromagnetic release is made for operation in case of a short circuit, the value of which is 2-20 ln. In turn, the value ln = 200 A. The error of settings can be 20% in one direction or another from the specified value. Therefore, the operation settings for power machines are indicated in amperes or in multiples of the rated current. Modular circuit breakers have protective characteristics, denoted B (3-5), C (5-10) and D (10-50), where the digital values ​​\u200b\u200bcorrespond to the limiting rated current ln, at which the contacts diverge.

Electromagnetic release

The main advantages of electromagnetic releases are resistance to vibrations, shocks and other mechanical influences, as well as simplicity of design, which facilitates the repair and maintenance of the device. The disadvantages include instant response, without time delays, as well as the creation of a magnetic field during operation.

The time delay is of great importance, since it ensures selectivity. In the presence of selectivity or selectivity, the presence of a short circuit is recognized by the introductory machine, but it is skipped for a certain set time. During this time period, the downstream protective device should have time to operate, which does not turn off the entire object, but only the damaged area.

Quite often, thermal and electromagnetic releases are used together, by connecting both elements in series. Such a bundle is called a combined or thermomagnetic release.

Semiconductor release

More complex devices include semiconductor releases. Each of them includes a control unit, instrument transformers for alternating current or magnetic amplifiers for direct current, as well as an executive electromagnet that performs the function of an independent release. With the help of the control unit, a user-defined program is set, under the guidance of which the main contacts will be disconnected.

During the setup process, the following steps are performed:

  • The rated current of the machine is regulated
  • The time delay in the zones of overloads and short circuits is adjusted.
  • Short-circuit operation threshold is determined.
  • Setting of safety switches for operation from single-phase switching.
  • Setting of the switch that disables the time delay when the selectivity mode changes to instantaneous mode in the event of a short circuit.

Electronic release

The design of the electronic release resembles the device of a similar semiconductor device. It also consists of an electromagnet, measuring devices and a control unit. The value of the operating current and the exposure time are set in steps, providing guaranteed operation in case of short circuit and starting currents.

The advantages of these devices are the variety of settings and the ability to choose, the operation of the installed program with high accuracy, the presence of health indicators and the reasons for operation, the logical selective connection with the switches located above and below the machine.

The disadvantages include the high price, the fragility of the control unit and sensitivity to the influence of electromagnetic fields.

Modular DC circuit breakers, or more simply automata, are used in electrical networks and electrical installations, telecommunication cabinets, automation panels. Why are they called modular? The thing is that they are available in standard compact housings and are single-pole modules, which can consist of single-pole, two-pole or three-pole devices. According to the existing standard, the width of one such pole is 17.5 mm.

The DC circuit breaker differs from the usual one in that it breaks the circuit in the event of a short circuit or overload automatically. The design of the device includes several main elements:

  • housing made of heat-resistant plastic;
  • automatic releases that provide automatic circuit breaking in the aforementioned situations;
  • mechanical switch mechanism;
  • a handle located on the front side, which actuates the switch, that is, it allows you to connect and open contacts;
  • terminals for connecting the machine to the mains.

    Modern circuit breakers contain two releases (protective devices):

  • Thermal - react to the ambient temperature. A break in the network with such a release does not occur immediately, since it takes some time for it to heat up in the event of a network overload. Due to this, the machine does not work at small time peaks that the wiring can withstand;
  • Electromagnetic - is triggered by an increase in the magnetic field that occurs in emergency situations. Since this release is independent of the ambient temperature, it trips instantly. It is installed in case of short circuits, since the thermal release plate in such a situation can melt even before it has time to open the contacts.

    From the foregoing, it follows that DC switches are capable of solving the following tasks:

  • allow to de-energize the network, that is, they can be used as ordinary switches;
  • perform a protective function, preventing the consequences of short circuits and overload. Therefore, they often say not just “machine”, but a DC circuit breaker.

    Note that the DC automaton differs from the AC analogue primarily in that it has polarity. This must be taken into account when connecting it.

    Main advantages

    Circuit breakers are widely used due to a number of advantages:

  • compactness, as a result of which they are placed in any electrical panel for DC networks;
  • simplicity of design, which ensures durability and reliability;
  • low price;
  • the possibility of compiling automata from separate modules with any necessary number of poles.
    In addition, automatic circuit breakers for operation with direct current are available in a wide variety of current ratings from 6 to 125 A, which allows you to choose them for any equipment and any electrical network.

    Important Features

    Circuit breakers for DC operation have the following main characteristics:

  • Rated current - shows the maximum current that the circuit breaker can withstand constantly. In the event of an increase in current strength above this value, protection is triggered and the network opens;
  • The time-current characteristic (shutdown characteristic) is the smallest value of the current strength at which the instantaneous operation of the protection occurs, that is, the operation of the electromagnetic release. It is measured not in amperes, but as a ratio with the rated current, that is, how many times the time-current characteristic is greater than the rated value. For this characteristic, the letter designation "B" or "C" is used;
  • Maximum breaking capacity - the maximum current strength, during the passage of which the operation of the protection becomes impossible due to the fact that the contacts are simply welded.

    As we said above, a letter designation is used for the time-current characteristic:

  • B - exceeds the rated current by 3-5 times;
  • C - exceeds the rated current by 5-10 times.

    Thus, to ensure the protection of the network, when choosing a circuit breaker, it is necessary to select its characteristics in accordance with the characteristics of the equipment and cables.
    Why you should buy from our store

    In the ATLANT SNAB store you can choose a DC circuit breaker with any characteristics you are interested in. But, this is not the only reason why you should buy a switch from us:

  • In our online store, high-quality DC machines are presented only from trusted manufacturers;
  • We offer electrical equipment on the most favorable terms;
  • Your order will be delivered on time in Moscow or to any region of Russia;
  • We have qualified specialists who can advise you and help you choose the best circuit breakers for your purposes for DC networks.

    To buy DC switches right now, make a purchase on the website or simply call our contact number. Turning to us at least once, you will surely become our regular customer!

  • Many people know from a school physics course that current can be variable and constant. If we can still say something with certainty about the use of alternating current (all household electrical receivers are powered by alternating current), then we know practically nothing about direct current. But since there are direct current networks, then there are consumers, and, accordingly, protection for such networks is also needed. Where are direct current consumers found and what is the difference between protection devices for this kind of current, we will consider in this article.

    No one type of electric current is "better" than the other - each is suitable for solving certain problems: alternating current is ideal for generating, transmitting and distributing electricity over long distances, while direct current finds its application in special industrial facilities, installations solar energy, data centers, electrical substations, etc.

    Distribution cabinet of direct operating current of an electrical substation

    Understanding the differences between AC and DC provides a clear understanding of the challenges faced by DC circuit breakers. Alternating current of industrial frequency (50 Hz) changes its direction in the electrical circuit 50 times per second and “passes” through the zero value the same number of times. This "passage" of the current value through zero contributes to the rapid extinction of the electric arc. In DC circuits, the value of the voltage is constant - just like the direction of the current is constant in time. This fact significantly complicates the extinguishing of the DC arc, and therefore requires special design solutions.

    Combined graphs of normal and transient modes when disconnected: a) alternating current; b) direct current

    One such solution is the use of a permanent magnet (3). The movement of the arc in a magnetic field is one of the methods of extinguishing in devices up to 1 kV and is used in modular automatic switches. An electric arc, which is essentially a conductor, is affected by a magnetic field, and it is drawn into the arc chute, where it finally fades.

    1 - moving contact
    2 - fixed contact
    3 - silver-containing contact soldering
    4 - magnet
    5 - arc chute
    6 - bracket

    Polarity must be observed

    Another and, perhaps, the key difference between AC and DC circuit breakers is the presence of polarity in the latter.

    Wiring diagrams for single-pole and double-pole DC circuit breaker

    If you are protecting a single-phase alternating current network with a two-pole circuit breaker (with two protected poles), then it does not matter which of the poles you connect the phase or neutral conductor. When connecting circuit breakers to the DC network, the correct polarity must be observed. When connecting a single-pole DC switch, the supply voltage is supplied to terminal "1", and when connecting a two-pole DC switch, to terminals "1" and "4".

    Why is it so important? See video. The author of the video conducts several tests with a 10-amp switch:

    1. Turning on the switch in the network with respect to the polarity - nothing happens.
    2. The switch is installed in the network with reverse polarity; network parameters U = 376 V, I = 7.5 A. As a result: strong smoke emission with subsequent ignition of the switch.
    3. The switch is installed with respect to polarity, and the current in the circuit is 40 A, which is 4 times its rating. Thermal protection, as it should be, opened the protected circuit after a few seconds.
    4. The last and most severe test was carried out with the same 4-fold overcurrent and reverse polarity. The result was not long in coming - instant ignition.

    Thus, DC circuit breakers are protection devices used for alternative energy facilities, automation and control systems for industrial processes, etc. Special versions of the protective characteristics Z, L, K allow you to protect high-tech equipment of industrial enterprises.