Anton Tsugunov
Reading time: 4 minutes
The differential circuit breaker is one of the most common devices found in almost every electrical panel. It is designed to protect the electrical network from short-circuit currents, overloads, as well as from the occurrence of leakage currents in the grounding wires. These currents arise due to damage to the insulation of consumers or connecting wires. In other words, a residual current circuit breaker combines the functions of an RCD and a circuit breaker.
Features of the design of the difavtomat
Since the difavtomat is designed to perform several different functions, its design includes relatively isolated elements, the principle of operation and the purpose of which are somewhat different. All components of the device are assembled in a compact dielectric housing with fasteners for mounting on a DIN rail in the electrical panel.
The working part of the differential machine includes:
- Shunt tripping mechanism.
- Electromagnetic release. This device consists of an inductor equipped with a movable metal core. The core is connected to a spring-loaded return mechanism, which ensures reliable closure of the switch contacts in normal operation of the electrical circuit. The electromagnetic release is triggered if a short-circuit current flows in the circuit.
- Thermal release. This device opens the electrical circuit when a current flows through it slightly exceeding the nominal value.
- Reset rail.
The protective part of the device includes the differential protection module, which is triggered in cases where there is current in the grounding wires of the electrical installation. If this current exceeds a certain value, the device gives a command to open the main contacts, and also signals the reasons for the operation of the protection of the differential machine.
The constituent parts of the design of the protection module are:
- Differential transformer.
- Electronic amplifier.
- Electromagnetic reset coil.
- Device for monitoring the health of the protective part of the difavtomat.
There is a special button on the front of the product body, which is designed to check the functionality of the protective part of the device. To provoke the control operation of the difavtomat, you just need to press the button, while the circuit closes, causing a leakage current, to which the protection reacts.
To ensure normal operation of the protective module, it is connected in series behind the working part of the difavtomat.
A leakage current in an apartment's power supply system can occur when the insulation of electrical appliances is damaged. If, in this case, a grounding conductor is used, then there is no voltage increased in relation to earth on the body of the electrical installation. The flow of current through the grounding conductor leads to its heating and a possible increase in resistance or even a break in the grounding wire. In the event that the electrical installation turns out to be ungrounded, there is a high probability of electric shock to a person.
A significant disadvantage of protective grounding is the inability to control the state of insulation integrity and the flow of differential currents. The principle of operation of the machine consists in the implementation of such control with the disconnection of the electrical circuit in case of exceeding the permissible leakage current values.
The operation of the protective part of the difavtomat is based on the principle of electromagnetic induction. A measuring transformer is used as a sensor that reacts to the difference in currents in the incoming and outgoing wires.
The design of this device includes two oppositely connected windings, each of which creates its own magnetic flux in the core. As long as these fluxes are equal to each other, the current in the secondary winding of the transformer is zero. If a magnetic flux appears in the core, then it provokes the appearance of a current in the secondary winding, which triggers a protective mechanism that opens the main contacts of the difavtomat.
Scope of application of difavtomats
The use of these devices is determined by their functionality. A correctly connected differential automaton allows:
- Achieve the required level of electrical safety in cases where the insulation of the electrical installation is damaged or the phase conductor is shorted to its body.
- Prevent overheating and ignition of damaged insulation points, through which leakage current can flow for a long time.
- Provide protection against electric shock to a person in case of unintentional contact with open live parts of the electrical installation.
- Reliably protect the power supply system from failure of its elements in the event of short circuits and overloads in them.
- If there is a need to reduce the weight and dimensions of switchgear, then the use of difavtomats will help to solve this problem. By combining a circuit breaker and an RCD in one case, you can significantly save space in the electrical panel.
Differential machine selection
A large number of manufacturers of electrical equipment, as well as a wide range of difavtomats on the market, significantly complicate the choice of these devices. In order to correctly choose a high-quality leakage current switch for a specific power supply system, you need to pay attention to its following characteristics:
- Number of poles. Each pole provides an independent current path and can be disconnected by a common disconnecting mechanism. Thus, for the protection of a single-phase network, two-pole differential automatic devices should be used, and for installation in a three-phase network, four-pole ones.
- Depending on the rated voltage, 220 and 400 V machines are distinguished.
- Since the difavtomat performs the functions of protection against short-circuit currents and overloads, then when choosing it, you should be guided by the same rules as for a circuit breaker. The most important parameters of these devices are the rated current, the value of which is determined based on the rated power of the connected load, as well as the type of time-current characteristic. This parameter shows the dependence of the current flowing through the circuit breaker on the trip time of the release. For installation in electrical networks for household use, it is recommended to use machines with a time-current characteristic of type C.
- Leakage current rating. Shows the maximum value of the difference in currents (to determine this parameter there is a special symbol Δ, printed on the device case), at which the difavtomat does not open the electrical circuit. Typically, for domestic electrical networks, the rated leakage current is 30 mA.
- There are differential current circuit breakers designed to operate in direct (A or DC) or alternating (AC) current networks.
- The reliability of the device. This parameter is highly dependent on the manufacturer. When choosing and purchasing a differential machine, you need to beware of counterfeits by purchasing electrical equipment in specialized stores that have all the necessary documents and permits.
It should be noted that in the event of a break in the neutral wire, the protection provided by the differential machine will not be able to function due to the lack of power supply. In most models of difavtomats, protection against damage to the neutral conductor is provided, which opens the circuit in the event of a voltage failure.
In the event of a break in the grounding conductor, a situation may arise in which the difavtomat does not react to the appearance on the body of the electrical installation of an increased potential relative to the ground. However, in this case, the device will work if a person touches such an electrical installation and thus creates a path for the leakage current.
Connection
The connection diagram of the differential machine is quite simple. It is advisable to consider it on the example of one of the most popular models of this device VD1 - 63.
To operate this difavtomat in a single-phase network, you need to use neutral and phase wires, which are connected to the corresponding terminals of the VD1 - 63 device. neutral and phase wire.
The connection of the VD1 - 63 difavtomat is carried out according to the diagram shown in the figure.
Such a device protects several groups of consumers from the occurrence of currents in the grounding circuit at once. If a leakage current occurs in one of the elements of the electrical network, then all consumers will be immediately disconnected by the VD1 - 63 automatic machine. The advantage of such a scheme is its simplicity, as well as a small number of elements that do not clutter up the space in the electrical panel. This scheme can be used in cases where it is necessary to protect a small number of consumers.
To eliminate the disadvantage associated with the indiscriminate protection provided by the VD1 - 63 difavtomat, the connection of similar devices to each consumer group is used. The range of rated currents for VD1 - 63 machines is wide enough and includes standard values from 16 to 100A. A branched connection scheme is more expensive and difficult to install, the connection of its elements requires much more space in the switchboard. However, the use of such protection significantly increases its reliability and selectivity.
A residual current device, further RCD, is designed to protect a person from electric shock, as well as from the occurrence of a fire that can occur when an electric current leaks, due to poor insulation or poor connection of electrical installations (EI).
The RCD must work, that is, open the contacts, thereby completely stop supplying voltage to the protected line, provided:
1 Human touching non-current-carrying parts of the power plant that are energized due to insulation breakdown.
2 Human touch to live parts of the EI that are energized.
3 Occurrence of (differential) leakage current to the EU frame or ground to prevent fire.
The principle of operation of the RCD. Scheme
Rice. 1
1
Differential current transformer
2
Starting element
3
Actuating mechanism
4
"Test" button to control the RCD serviceability
I 1 - I 2 direction of current relative to load
I D - leakage current
Ф 1 - Ф 2 magnetic fluxes
Purpose of blocks.
1
Differential current transformer(used in most RCDs) measures the balance of currents between its incoming conductors.
2 Starting element(consists, as a rule, of electromagnetic relays) serves to control (influence) the actuator.
3
Actuating mechanism designed for emergency shutdown of the electric circuit controlled by the RCD.
4
"Test" button to control the RCD serviceability by creating a simulation of the leakage current.
The principle of operation of the residual current device (RCD)
Basic electrical diagram
Rice. 2
1, 2 Primary windings
3 Secondary winding
With the serviceability of the monitored line, there is no specified leakage current, and the transformer is at rest (equilibrium), because the currents in the oppositely connected primary windings of the transformer are equal. Due to the fact that equal magnetic fluxes going towards each other are mutually subtracted (that is, they are equal to zero), then an electromagnetic field does not arise in the secondary coil, which means there is no voltage and there is no EMF that can act on the relay, on the basis of which the trigger is assembled (Fig. .1 ).
And as soon as a leak occurs on the protected (monitored) line equal to the RCD trip value (as a rule, from 10 to 30 mA), then the equality in the primary windings of the transformer will be violated. As a result, an electromagnetic field arises in the primary and secondary coils, which forms a voltage coupling. That is, in the secondary winding there is a relay actuation voltage (Fig. 2), of which the starting element (Fig. 1) consists of an impact, which on the actuator (Fig. 1) and disconnects the contact group, thus de-energizing the protected line.
Attention!
It should be remembered that the RCD requires a monthly check, which is carried out by pressing the "Test" button. In this case, the electrical circuit is closed, emitting an artificial leakage of current and the operation of the residual current device. Failure to operate will indicate a complete malfunction of the device.
According to modern requirements, all electrical installations must have or. In this case, the resulting specified leak will automatically disable the protection.
An example of this can be seen in the diagram in Fig. 3
Rice. 3
If we represent the differential protection in the form of a simple mechanical device as a balance (Fig. 4) with a response threshold of up to 10 mA. It immediately becomes clear that when a value of 10 mA is reached on one of the scales, they will go out of balance, and the contacts will open and the monitored (protected) line will be de-energized. Moreover, we note that the center of balance of the scales is precisely or, therefore, it is precisely them that must be used so that the person himself is not this center.
Attention!
You also need to understand that an RCD is an additional safety measure that only reacts to differential current (leakage current) and does not respond to short circuits and line overload. Therefore, as a rule, RCDs are installed together with circuit breakers that react to short-circuit (short circuit) and line overload by voltage, for which they are designed.
Visual electrical diagram for connecting an RCD
Rice. 5
RCD. Video explanation
Choosing an electromechanical RCD
I wish you a successful installation and remember about electrical safety.
DIFFERENTIAL SWITCHES, type VD1-63 (RCD). Manual
Passport
3421-033-18461115-2007 RE, PS
1 Purpose and scope
1.1 Automatic circuit breakers controlled by differential current, without built-in overcurrent protection, functionally independent of the voltage of the network for household and similar use, type VD1 -63 (RCD) of the IEK® trademark (hereinafter - VD) are intended for operation in single-phase or three-phase AC power networks. current with voltage up to 400 V and frequency 50 Hz
and their characteristics correspond to GOST R 51326.1 and technical specifications TU 3421-033-18461115-2002.
1.2 VD perform the function of detecting a differential current, comparing it with the value of the differential current of operation and disconnection of the protected circuit in the case when the differential current exceeds this value. VD provide:
- protection of people from electric shock in case of indirect contact with accessible conductive parts of electrical installations in case of insulation damage (HP with a rated breaking differential current of 10; 30 and 100 mA);
- protection against fires arising as a result of ignition of insulation of current-carrying parts of electrical appliances from differential (residual) current to the ground or due to prolonged flow of fault current in case of failure of overcurrent protection devices (HP with rated breaking differential current I D n = 300 mA);
- VDs with a rated residual current of no more than 30 mA can be used as additional protection in the event of failure of devices designed to protect against electric shock.
1.3 The main area of VD use is metering and distribution boards of residential and public buildings, temporary power supply devices for construction sites, garden houses, garages, retail facilities.
2 Main characteristics
2.1 The main characteristics of the VD are given in Table 1.
Table 1
| Description of characteristics | Meaning | ||
| Number of poles | 2 | 4 | |
| Rated operating voltage of alternating current Ue, V | 230 | 230, 400 | |
| Rated mains frequency, Hz | 50 | ||
| Voltage range of the operational control device operability, V | 115 to 265 | from 200 to 460 | |
| Rated current In, A | 16, 25, 32, 40, 50, 63, 80, 100 | ||
| Rated breaking differential current I D n, mA | 10, 30, 100, 300 | ||
| Rated non-breaking differential current I D n o, mA | 0.5 I D n | ||
| Rated short-circuit making and breaking capacity Inm, A | 1000 | ||
| Rated maximum differential making and breaking capacity I D m, A | 1000 | ||
| Rated conditional short-circuit current, not less, A | 3000 | ||
| Rated conditional differential short-circuit current I nc, not less, A | 3000 | ||
| Functional characteristics in the presence of a differential current with a DC component, type | AS | ||
| Electrical durability, on-off cycles (V-O), not less | 4000 | ||
| Mechanical durability of cycles B-0, not less | 10 000 | ||
| Maximum cross-section of the wire connected to the power terminals, mm 2 | 50 | ||
| Presence of precious metals, silver, g | 0.25 (per contact) | ||
| Climatic modification and placement category according to GOST 15150 | UHL14 | ||
| Protection degree according to GOST 14254 | IP20 | ||
| Service life, not less, years | 15 | ||
2.2 The values of the maximum HP shutdown time in the presence of a differential current are given in Table 2.
table 2
Attention! The HP does not have built-in overcurrent protection, therefore, in series with it, it is necessary to turn on a circuit breaker of the same or lower rating with the type of protective characteristics against overcurrents B and C.
2.3 Overall and mounting dimensions are shown in Figure 1.
2.4 Electrical schematic diagrams of VD are shown in Figures 2 and 3.
2.5 The use of VD in apartment and floor panels in electrical installations with TN-S, TN-C-S, TN-C grounding systems is regulated in GOST R 51628.
3 Completeness
Package Included:
- VD - 1 pc.;
- packing box - 1 pc .;
- operation manual and passport - 1 copy.
4 Installation and operation
4.1 Installation, connection and commissioning of HP should be carried out only by qualified electrical personnel.
4.2 VD is installed on a 35 mm wide mounting rail (DIN rail) in electrical switchboards with a degree of protection in accordance with GOST 14254 not less than IP30.
4.3 After installation and checking its correctness, supply the voltage of the electrical network to the electrical installation and turn on the VD by moving the control handle to the "I" - "ON" position, press the button
"TEST". Immediate operation of the HP (disconnection of the circuit protected by the device) means that the HP is working properly.
4.4 If after switching on the HP immediately or after a while it turns off, it is necessary to determine the type of malfunction in the electrical installation in the following order:
a) cock the HP with the control handle. If the VD is cocked,
This means that an earth leakage has occurred in the electrical installation, caused by an unstable or short-term insulation fault. Check the VD operability by pressing the "TEST" button;
b) if the VD is not cocked,
then this means that in the electrical installation there is a defect in the insulation of any electrical receiver, electrical wiring, installation conductors of the electrical panel or VD is faulty.
In this case, you must perform the following actions:
- turn off all electrical receivers and cock the VD. If the HP is charged, then this indicates the presence of an electrical receiver with damaged insulation. The malfunction is detected by serial connection of electrical receivers until the HP is triggered. The damaged electrical receiver must be disconnected. Check the VD operability by pressing the "TEST" button;
- if the HP continues to operate when the electrical receivers are disconnected, it is necessary to call a qualified electrician to determine the nature of the damage to the electrical installation or identify the HP malfunction.
The check is carried out by pressing the "TEST" button. Immediate activation of the HP and disconnection of the protected electrical installation mean that the HP is working properly.
Recent questions:
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Any leakage is undesirable. In the normal mode of operation of any electrical system, the current should flow only through electrical circuits relative to phases and zero (figuratively speaking). The resulting current relative to the ground will be this very leak. It can occur as a result of a breakdown to the case, which is initially grounded, when a person accidentally touches current-carrying parts (the leakage current will pass through this person's body), obsolescence of the electrical wiring, etc.
The best option for connecting an RCD (residual current device) will be as close as possible to the power input. Since the interval of the electrical network to the electric meter is subject to strict control of the electric power organizations, it is still more correct to install an RCD immediately after the meter. Thus, complete protection against all kinds of earth leakage throughout the entire circuit is ensured.
The disadvantage with such an RCD connection will be the de-energization of the entire electrified area that passes through this protection. In case of critical undesirability of such a phenomenon, you will have to install either several RCDs or install only for that section (for that circuit) that is most significant and important from the point of view of electrical safety (although electrical safety is necessary everywhere).
The figure shows RCD connection diagram, which is most often used in practice. On the right side there is a general diagram of the internal structure of this protection. And so, an RCD is a residual current device or, as it is also called, "differential protection". Its main task is to automatically cut off the power supply when an earth leakage current occurs.
Now for the RCD itself. The basic principle of the residual current device is to monitor the difference in current values between the neutral and phase conductors. With the nominal operation of any device and electrical equipment, this difference cannot be (that is, how much current passed through the phase wire, the same amount will pass through the zero wire). Let's say the electrical wiring runs in a damp room and there is damage to the insulation (cracks). Moisture penetrated through the crack on the current-carrying conductor, thereby creating a circuit between this wire and the ground. As a result, this very leakage current will be the difference to which the RCD should respond.
Further, this leakage current was taken from one of the coils of the internal transformer and transferred to a polarized relay. In it, the signal will amplify, and launched the RCD disconnection mechanism. Thus, until this very malfunction of the wiring is found and eliminated, the residual current device will be knocked out again at the next platoon.
Since any device tends to break sometimes, the RCD will be no exception. In this case, a test function (self-test) is provided. There is a test button on the front of the RCD. When it is pressed, this very leakage current is simulated, which leads to automatic operation and subsequent shutdown. If you suspect a fault in the differential protection device, or just for a routine recheck, do not be lazy and press the test button.
It is advisable to connect the residual current device following the inscriptions on the body of the RCD itself. As shown in the figure, the device has neutral contacts that are connected to zero and phase contacts, which are most often designated by the numbers 1 and 2 or L (although phase contacts are sometimes not indicated at all).
The figure shows an RCD connection diagram for a single-phase consumer, but of course there are RCDs and three-phase ones. The only difference is only in the number of contacts. The general essence of connection and operation remains the same. We fasten the neutral wire to the neutral, and, of course, three phases to the three phase contacts.
And the last thing that can be said about RCDs is that it is advisable to install them in those places where it is necessary to ensure high electrical safety. In the same places where an accidental shutdown can lead to undesirable consequences, differential protection, perhaps, is better not to install. Despite the main task of the RCD of ensuring electrical safety, in practice it often brings additional problems.
Leakage currents in worn-out electrical equipment are common (example: old lamps operating in non-buildings). RCDs are very sensitive to these things. As a result, you will be tortured by the constant operation of this protective device. You will either have to abandon the RCD, or replace all the old electrical equipment with wiring with a new one. What is cheaper and safer is up to you.
Analyzing the letters received, I concluded that many of you still do not see the difference between a differential machine and an RCD, so in this small article I decided to explain this issue to you in detail.
It will be about functional and external differences between a differential machine and an RCD... In order not to confuse you completely, I will immediately amend the name and designation of these devices:
- residual current device (RCD) - it is also a differential switch (VD)
- differential automatic or, in abbreviated form, difavtomat - it is also a differential current circuit breaker (RCBO)
As an example, consider products from IEK:
- RCD type VD1-63, 16 (A), 30 (mA)
- differential automatic machine type AVDT32, C16, 30 (mA)
The photographs show that they are very similar in appearance.
The main difference between a differential machine and an RCD
First of all, you need to know that these two devices have different functionality, which is their main difference.
1. Residual current device (RCD)- a switching device that protects and also controls the current state of the wiring, and if any damage occurs in it in the form of leaks, it turns it off. I wrote about this in my next articles (follow the links and read):
2. Difautomat or differential automaton Is a switching device that combines both a circuit breaker and an RCD in one case, i.e. the differential machine is able to protect the electrical network from, as well as from the occurrence of leaks associated with damage to electrical wiring, electrical appliances and when a person gets under voltage.
Conventionally, a difavtomat can be represented as an identity:
To put it simply, the difavtomat is the same RCD, only with the function of protection against short-circuit and overload currents.
Hope this is clear. Now let's figure out how these two devices can be distinguished from each other.
How to distinguish an RCD from a difavtomat?
1. Inscription of the device name
Currently, most manufacturers, in order not to mislead buyers (and more often the sellers themselves), began to write the name of the device on the front side or on the side of the cover, either it is an RCD (differential switch) or a difavtomat (differential current circuit breaker).
2. Marking
The second way to distinguish an RCD from a difavtomat is to pay attention to the marking.
If only the value of the rated current is indicated on the case, and there is no letter in front of the number, then this is a residual current device (RCD). In my example, at VD1-63, only the rated current of 16 (A) is indicated on the case, and the letter of the characteristic type is absent.
If the letter B, C or D is shown in front of the figure that indicates the value of the rated current, then this is a differential machine. For example, in a differential machine RCBO32, before the value of the rated current, there is the letter "C", which stands for.
3. Scheme
If the diagram shows only a differential transformer with a "Test" button, then this is an RCD.
If the diagram shows a differential transformer with the "Test" button and the windings of the electromagnetic and thermal releases, then this is a difavtomat.
4. Overall dimensions
Now this parameter is no longer relevant, but when the first difavtomats were produced, they were an order of magnitude wider than RCDs, because it was necessary to additionally place thermal and electromagnetic releases in the housing. At present, on the contrary, difavtomats began to be produced with smaller overall dimensions than RCDs.
As you can see, in my example, the VD1-63 RCD and the AVDT32 difavtomat have exactly the same dimensions. Therefore, this point should not be taken into account when the RCD is different from the difavtomat.
P.S. In this article, we have sorted out all differences between a differential machine and an RCD and learned to outwardly distinguish them from each other. Now we need to make a choice in one direction or another. Read about this in my next article: “What to choose? RCD or difavtomat ". I look forward to your questions and comments.
