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 ground wires. These currents arise due to damage to the insulation of consumers or connecting wires. In other words, the residual current switch 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 separate elements, the principle of operation and the purpose of which are somewhat different. All component parts of the device are assembled in a compact dielectric housing, which has fasteners for mounting on a DIN rail in an electrical panel.
The working part of the differential machine includes:
- Independent release 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 closing of the circuit breaker contacts in normal operation of the electrical circuit. The electromagnetic release is activated in cases where 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 a differential protection module that operates in cases where there is current in the ground 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 components of the protection module design are:
- Differential transformer.
- Electronic amplifier.
- Electromagnetic reset coil.
- The device for monitoring the health of the protective part of the difavtomat.
There is a special button on the front of the product case, which is designed to check the operability of the protective part of the device. To provoke the control operation of the difavtomat, you just need to press the button, and the circuit closes, causing a leakage current, to which the protection responds.
To ensure the normal operation of the protective module, it is connected in series behind the working part of the difavtomat.
Operating principle
Leakage current in the power supply system of the apartment can occur if the insulation of electrical appliances is damaged. If a grounding conductor is used in this case, then there is no voltage increased in relation to the ground on the electrical installation case. The flow of current through the ground conductor leads to its heating and a possible increase in resistance or even a break in the ground wire. In the event that the electrical installation is ungrounded, there is a high probability of electric shock to a person.
A significant disadvantage of protective grounding is the inability to control the integrity of the insulation and the flow of differential currents. The principle of operation of the machine is to carry out such control with the disconnection of the electrical circuit in case the leakage current exceeds the permissible 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 back-to-back windings, each of which creates its own magnetic flux in the core. As long as these flows 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 difavtomatov
The use of these devices is determined by their functional purpose. A properly connected differential machine allows you to:
- To achieve the necessary level of electrical safety in cases where the insulation of the electrical installation is damaged or the phase wire is shorted to its housing.
- 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 current-carrying parts of the electrical installation.
- Reliably protect the power supply system from failure of its elements in the event of short circuits and overloads.
- If there is a need to reduce the weight and size indicators of switchgears, then the use of difavtomatov will help solve this problem. By combining the circuit breaker and RCD in one housing, you can significantly save space in the electrical panel.
Selection of a differential automaton
A large number of manufacturers of electrical equipment, as well as a wide range of difautomats on the market, make it difficult to choose these devices. In order to choose the right high-quality leakage current switch for a particular power supply system, it is necessary to pay attention to its following characteristics:
- Number of poles. Each pole provides an independent current path and can be disconnected by a common disconnect mechanism. Thus, to protect a single-phase network, two-pole differential automata should be used, and for installation in a three-phase network, four-pole ones.
- Depending on the rated voltage, automatic machines for 220 and 400 V are distinguished.
- Since the difavtomat performs the functions of protection against short-circuit currents and overloads, when choosing it, one 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 tripping time of the release. For installation in domestic electrical networks, it is recommended to use automatic machines with a time-current characteristic of type C.
- Rated leakage current. Shows the maximum value of the current difference (to determine this parameter there is a special symbol Δ printed on the body of the device), at which the difavtomat does not open the electrical circuit. As a rule, for household electrical networks, the nominal value of the leakage current is 30 mA.
- There are automatic differential current switches designed to operate in direct (A or DC) or alternating (AC) current networks.
- Device reliability. This parameter largely depends on the manufacturer. When choosing and purchasing a differential machine, you need to be wary of fakes 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 a lack of power.In most models of difavtomatov, protection against damage to the neutral conductor is provided, which opens the circuit when there is a voltage drop in it.
If the grounding conductor breaks, a situation may arise in which the difavtomat will not react to the appearance of an increased potential relative to the ground on the electrical installation case. However, in this case, the device will operate if a person touches such an electrical installation and thus creates a leakage current path.
Connection
The circuit for connecting a differential machine is quite simple. It is advisable to consider it using the example of one of the most popular models of this device VD1 - 63.
To operate this difavtomat in a single-phase network, you must use the neutral and phase wires, which are connected to the corresponding terminals of the device VD1 - 63. The input terminals of the differential current switch VD1 - 63 are located in the upper part of its case and are marked "N" and "1", corresponding neutral and phase wire.
The connection of the difavtomat VD1 - 63 is carried out according to the scheme shown in the figure.
Such a device protects several groups of consumers from the occurrence of currents in the ground circuit at once. If a leakage current occurs in one of the elements of the electrical network, then all consumers will be immediately turned off by the VD1 - 63 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 automatic machines VD1 - 63 is quite wide 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.
Flaws
Connecting a differential machine provides much more advantages than disadvantages. However, in addition to the rather high cost of these devices, their negative qualities include the impossibility of determining the location of the damage to the insulation of the electrical circuit, due to which the difavtomat worked.
Another negative point is the relative complexity of these devices, which, firstly, leads to a decrease in their reliability, and secondly, requires the replacement of the entire product in cases where any of its elements fails.
