Electricity in the modern world is an indispensable source of energy. It is used in every home. To ensure the operation of the power supply is safe, special devices are used. Their design and principle of operation may vary.
Differential current circuit breakers are designed for industrial and domestic power networks. They have special functions. Thanks to such a system, the operation of the power grid becomes simple and safe.
general characteristics
The differential current circuit breaker (AVDT) is an electromechanical type device. It is designed to protect the electrical circuit from current leakage, as well as from its overload. They also exclude the possibility of a short circuit.
Difavtomat combines the qualities of a circuit breaker and an RCD. If a person comes into contact with the wiring, AEDT will exclude electric shock. This function is similar to an RCD. If overload is observed in the network, the device, like the circuit breaker, will stop supplying electricity to the circuit.
However, difavtomat has a number of differences from similar aggregates. The design implies the presence in the small case of two of the above devices. The constituent elements of the presented variety of switches allow them to be used in a wide range of areas of human activity.
Design
The difference between the residual current circuit breaker and the RCD is determined primarily in the field of their design. The presented unit consists of two parts. They perform protective and control functions. The latter works in accordance with the principle of RCD. The working part that performs the control is a conventional voltage switch. It can be single, double or four pole.
If the working part of the unit determines the presence of an electric leak, its protective mechanism is activated. This allows you to protect household, industrial equipment, as well as a person from electric shock. A special module disables sequentially the working and then the control part of the device.
The difference between a difavtomat and an RCD is primarily in the ability of the presented device to protect not only a person, but also the equipment from network overvoltage.
Principle of operation
Characteristics of automatic differential current circuit breakers allow their use in various types of networks. So that the presented devices can monitor and recognize the current in the circuit, a small transformer is built into them. This element is triggered when the voltage at the input and output has a different value. With equal performance on the outgoing and incoming conductors, the unit operates in normal mode.
The transformer has a core. Inside it, the current forms directed magnetic fluxes. Depending on the direction in which they are moving, the voltage of the secondary winding is determined. If there is a leakage of electricity, a current indicator will be observed on this coil, which will not be zero. In this case, the magnetic switch is activated.
The machine constantly compares incoming and outgoing voltage. If for some reason the balance of the magnetic field is disturbed, the latch will work. Electricity shuts down.
Varieties
There are various classifications of AVDT. They can be single-phase and three-phase. Depending on the type of wiring, it is necessary to select the appropriate unit.
Automata are distinguished by the principle of their maximum permissible current in the network. There are AVDT 32, 25, 100, 40A. This indicator makes it clear what load the machine is designed for, the current rating in Amperes. And when it is exceeded, the machine will turn off the supply of electricity to the circuit. The rated current is indicated by the letter "C". In household networks, C16 or C25 units are most often used (wiring condition is taken into account).
In some cases, at the time of the start-up of some consumers, the current can increase several times. The unit must withstand such a jump. There are three types of devices that differ in varying degrees of resistance to inrush currents. Category B includes AEDT, designed for overload at the time of start by 3-5 times. Type C devices are designed for a starting load exceeding the working load by 5-10 times. Category D units are able to withstand a jump in electricity at startup 10-20 times.
Leakage current rating and RCD characteristics
Single, four- or bipolar automatic differential current switches have different characteristics of the built-in circuit breaker and RCD. The leakage current to which the automation responds is indicated by the delta symbol. A standing number shows the value of this indicator. Its units are milliamps (ma).
In lighting, domestic networks, most often used machines with a leakage rating of 10 to 30 mA. For group networks, devices with a presented indicator of at least 30 mA are required. Input AVDTs may have an RCD with a nominal value of 100 to 300 mA.
Built-in protective equipment can be of various classes. If the RCD of the unit is of the AC type, it reacts exclusively to an alternating current type. Class A devices are designed to control direct current in devices with electronic converters. Type A is most often used in household networks.
Ground wire protection
The differential current circuit breaker 25A, 10A, 16A and other varieties have different characteristics of the operation of the RCD. It needs power supply. It is brought in from the input of the differential protection block. In other words, for the protection against current leakage to work, the voltage in the network is required. In order, there must be both phase and neutral wires.
If a break occurs in the "phase", the leak is eliminated automatically. But if the work of the neutral conductor is disrupted, the RCD may not work due to the lack of power to the unit. To exclude the likelihood of a similar situation, some difavtomats have in their design a special block for the protection of an open circuit breaker. This is a voltage relay.
If the presented unit is not in the system, it is strongly recommended to install it additionally. When choosing equipment, it is necessary to check the presence of a voltage relay, which allows the RCD to operate even when the neutral conductor breaks.
Manufacturers
Experts recommend purchasing protective equipment only from trusted brands in specialized stores. The safety of users and consumers of the power grid depends on this.
Selective and non-selective devices are on sale. The first category includes equipment that disconnects only one circuit. The remaining consumers will operate as before. Such products include, for example, the IEK, Schneider Electric, Legrand, and ABB.
Non-selective devices disconnect all circuits connected to them. Such products are supplied to the market by the EKF, DPN N Vigi trademarks. Selective varieties are more popular.
Popular varieties
In household power networks, it is most often selective types of devices that are used. They have the letter “S” in their markings. One of the most popular in our country are models of ABB residual current circuit breakers. The cost of a single-pole device 16A is about 1800-1900 rubles.
The Legrand company presents to the market devices of a similar class from 2000 rubles. This is the average cost of good appliances.
The IEK difavtomat is somewhat cheaper. Equipment with similar characteristics will cost the buyer about 800-900 rubles. However, the quality of European brands is considered an order of magnitude higher.
It should be noted that in the network, difavtomats are extremely rarely duplicated by other similar protective devices. Therefore, the entire responsibility for the safe operation of the power grid lies with the AEDT. To eliminate the likelihood of an accident, damage to property, the choice of the presented device must be approached responsibly.
Features of choice
To ensure the normal functioning of the power supply network, it is necessary to select a difavtomat, which will fully comply with existing operating conditions. First you need to calculate the number of amperes of the device.
The power of all network consumers should be written out. They are added, and the result obtained is divided by an indicator of the network voltage. For example, if devices that consume 7 kW in total are connected to the line, the calculation will be as follows: 7,000 W: 220 V = 31.8 A.
Next, you should choose the machine closest to the obtained value. In the presented example, it will be AVDT 32 A. The indicator of the unit amperes should slightly exceed the result obtained in the calculations. This is necessary to ensure full protection.
Specifications
Differential current circuit breakers differ from RCD by marking features. It is applied to the body. When purchasing the device, the designations indicated by the manufacturer of the equipment should be considered. On the machine, the current strength, voltage, and also the maximum current closure indicator for disconnecting the network are indicated without fail. Also, all characteristics of the device are indicated in its passport and quality certificate.
The device indicates its type (selective or non-selective), the number of phases, as well as the size of the device (necessary to determine the type of installation). Marking of foreign and domestic devices may vary.
The device indicates the temperature range in which the equipment operates, type of RCD. Almost all the devices on sale are designed for use in a dry, heated room.
Also, the device may have a “test” button. When it is pressed, the operation of the machine is checked. An artificial leakage of electricity is created. Thus it turns out to evaluate the reliability of the system, the correct installation.
Connection
Residual current circuit breakers require proper mains connection. Having chosen a device that is suitable for the operating conditions, it is necessary to carefully study the manufacturer's instructions. Connection is made to the network that the machine should protect. Otherwise, his work will be wrong.
Installation of devices of today's popular brands is carried out according to the same scheme. Installation is performed above the wiring line. Most often, this process involves mounting the unit on a din rail.
Conductors must be connected in series. Cables of different circuits cannot be connected. Compliance with this requirement must be carefully monitored. Otherwise, the selective device will not fulfill the functions assigned to it in full. The metal terminals must be grounded.
After installation, a check must be performed. To do this, the “test” button is pressed, an artificial leak is created. If the unit works, then the installation was successful.
Having considered what the differential current circuit breakers are, as well as their features, you can correctly select and independently install the equipment presented on the network.