To understand what difavtomats are for, first of all, you need to familiarize yourself with the purpose of protective devices used in existing electrical networks. These include such varieties as circuit breakers and residual current devices. In addition, universal devices replacing them are installed in the power circuits under the general name "differential automaton".
What is a differential automaton and how does it work
Difavtomat is a combined device, in the case of which two devices are combined at once - a circuit breaker and an RCD. The automatic machine, like all other products of this class, is triggered in case of overload and short circuit on the line. The RCD circuit works on the principle of comparing the current components flowing through its coil in the forward and reverse directions. If the equality of these values is violated, the difference signal is fed to the executive relay, which in a fraction of a second turns off the emergency section of the power circuit.
The combination of two functionally interconnected devices in one housing provides the following advantages:
- the ability to reliably protect power lines from overloads, short circuits and dangerous earth leakage currents;
- their use as protection devices against electric shock;
- saving space when mounting on a DIN rail (two slots instead of three);
- gain in price when compared with the separate use of modern models of automatic machines and RCDs.
The only drawback relating only to electronic modifications is the loss of performance when the zero bus is broken. In this case, the phase conductor remains energized, which, under certain conditions, can lead to electric shock to a person.
Difavatomats are installed like conventional devices right after the electric meter. Each of them ensures the safe operation of a separate supply line. In terms of their functionality, these devices completely replace the devices they replace, the principle of operation of difavtomats is the same.
Types of difavtomats
According to the number of simultaneously serviced phases, all electrical differential automatic machines are divided into single-phase and three-phase devices. The first of them are installed in 220 Volt networks by supplying phase and neutral wires to them.
According to the requirements of the PUE, the conductors supplied to the two-pole devices must be connected only to the upper terminals.
The phase and neutral conductors are connected to the lower contacts, which are taken directly to the consumer (to the load). The need to enter two buses into it at once is explained by the requirement for the operation of a differential current leakage protection device. Depending on the brand of instrument and series used, two or more locations are required for DIN rail mounting.
For installation in three-phase 380 Volt networks, 4-pole difavtomats are used. Three phase wires and a zero bus are connected to their upper terminals from the side of the electric meter. And from the lower terminals in the direction of the load, there are three working conductors and zero.
In accordance with the design features and the internal circuit of these devices, they are all subdivided into electromechanical and electronic samples.In the first models, the release of the differential current and decoupling is carried out in a combined way, and in the second samples the built-in electronics are "responsible" for this.
According to the possibilities of protecting the power supply line from dangerous potential, all known types of difavtomats are divided into devices that are connected to a grounding device and do without it.
Parameters of residual current circuit breakers
The versatility of differential automata, which allows you to combine the functions of two devices at once, is explained by their design and the capabilities embedded in them. The main parameters characterizing the differential circuit breaker include:
- type of electromagnetic release;
- rated current at which the device can operate for a long time;
- speed indicator and operating voltage;
- earth leakage current;
- breaking capacity and class of limitation on the current component.
It is usually installed only in special custom-made devices, which can be:
- independent type with the possibility of remote shutdown by a special signal;
- minimum voltage - triggered when it falls below the permissible level.
- devices of zero potential.
According to the current indicator, all known samples of difavtomats, like AB, are divided into a number of devices with strictly standardized values from the following series: 6, 10, 16, 25, 50 Amperes, etc.
In addition, a current indicator is used in their marking, denoted by the letters "B", "C" or "D". They are located in front of the rating code (amperage) and indicate the speed of this model.
Another group of technical characteristics includes the trip current of the RCD circuit (differential indicator), called "leakage". For most models of circuit breakers, these values fit into the typical range: 10, 30, 100, 300 and 500 milliamperes.
On the case of a typical device, leakage currents are indicated by a delta symbol with a corresponding number.
The next characteristic of protective difavtomats is the value of the operating voltage at which they are able to function in normal mode: 220 Volts - for single-phase circuits and 380 Volts - for their three-phase analogs. Its value is indicated under the designation of the rating or under the key of the device.
According to the leakage current and the selectivity index, the known types of residual current switches have the following designations:
- "A" - samples that react to AC (pulsating) current leakage.
- "AC" - models of electric devices, operated from leaks with a constant component.
- "B" is a combined option that combines both of these possibilities.
The characteristic "RCD type" is indicated by an alphabetic index or a symbolic drawing.
By analogy with AB, difavtomats are triggered by overloads in the wiring according to a selective principle that takes into account the time delay. This approach makes it possible to disconnect the network selectively according to the limiting current and provides good electrodynamic stability of the entire protective system. According to this most important indicator for human safety, the differences between differential current devices are taken into account by the following icons:
- the symbol "S" representing a delay of approximately 200-300 milliseconds;
- English letter "G" (temporary pause of 60-80 milliseconds).
The operating conditions of single-phase electrical machines are determined by their location in the switch cabinet on a DIN rail.According to the manufacturer's requirements, humidity and air temperature are subject to regulation, as well as dustiness in the room where the cabinet is located.
Electronic or electromechanical
To choose a suitable model, first of all, you need to decide what type of machine to choose: a traditional electromechanical or a more modern electronic one. Getting to know the features of each of these performances will help you make the right choice.
Electromechanical machines
These models are non-volatile, that is, they retain their functionality even in the absence of electricity. In contrast to them, electronic models can only work with a supply voltage consumed for their own needs.
In the first samples, the following electrical and mechanical components are "responsible" for shutting down and generating useful signals:
- electromagnetic circuit breakers;
- thermal releases;
- inductive coils emitting a differential current;
- electromagnetic relays and other modules.
All these elements have nothing to do with electronic circuits and work at the expense of their own energy reserves. For the operation of a difavtomat of this class, a leakage current or short circuit in the serviced line is sufficient.
Electronic variant
Electronic devices require additional power supply and are faster than their electromechanical counterparts. The electronic circuit, usually assembled on a microprocessor or on transistors, is “responsible” for the selection of differential currents and the generation of control signals in them.
This electronic circuit is called conditionally, since it still contains electrical components.
To isolate leakage currents in these devices, a differential transformer of an electromagnetic type is used, and a relay of the same class is used to disconnect the power circuit.
