The action algorithm of differential switches is based on providing reliable protection against possible leakage currents. For example, in cases of indirect contact with conductive elements or in moments of short-circuit of current-carrying parts to the housing. The choice of protective device should be taken responsibly. Do you agree?
We will tell you how to correctly select a differential circuit breaker, endowed with advanced protective functionality. The article presented by us describes in detail the types of devices that can prevent a lot of threatening situations. Valuable recommendations are given to future buyers.
The content of the article:
- Operation of the differential current device
Types of protective devices
- Standard devices
- Differential automatic monoblocks
- Surge protectors
- Mobile protective devices
- UZO marking (UDT) on the instrument case
- How to choose a differential current device?
- Conclusions and useful video on the topic
Operation of the differential current device
Considering the standard design of the RCD (UDT), it is necessary to highlight three main modules:
- Current transformer summing.
- The device locks the switching elements.
The current-carrying conductors of the current circuit are connected to the contacts of the summing transformer. Considering Ohm's law, according to which the sum of all currents gives zero, the magnetic effect of the current-carrying conductors of the transformer is mutually compensated.
The magnetic field, which causes the induction effect to cause the voltage of the secondary winding of the transformer, is not formed. This state corresponds to the normal conditions of current flow in the circuit.
UDT device: 1 - input circuit contacts; 2 - output circuit contacts; 3 - cocking button; 4 - make contacts; five - summing transformer; 6 - secondary winding; 7 - tracking device; 8 - button "test"; 9 - test conductor
However, the formation of even a small leakage current breaks this balance. The core area of the transformer is exposed to a residual magnetic field. As a result, the secondary winding produces a voltage.
The release is naturally triggered, converting an electrical quantity into a mechanical action. Next, the differential current blocking device is activated.
This protection technique is characterized as high-level, because the circuit is broken regardless of the mains voltage or the voltage of the auxiliary power source. It is this principle of action that guarantees 100% protection operation in any circumstances.
The design of each differential current switch is usually equipped with a test key. The so-called "control button" is specifically displayed on the front panel of the device so that users can check the operational readiness of the protective device.
The test button is used to test the performance of the device. The usual use of a button is after the device is first installed and put into operation, as well as as part of maintenance.
If the "Test" key is pressed, the device mechanism artificially generates a leakage current. In this case, a working device necessarily works. Usually, the "Test" button is used immediately after installing the machine into the circuit, when the electricity is first connected. In the subsequent test on schedule, about once a quarter.
Types of protective devices
The variety of automatic differential switches is impressive. Thanks to this diversity, the possibilities of organizing effective protection in projects of any purpose open up. Consider a few examples of the design of the RCD to evaluate all the existing benefits.
The main purpose of standard devices, for example, the F series, FH is the protection of service personnel. Direct / indirect contact with equipment items under voltage, the risk of electric shock - such situations are reduced to zero when using switches of the F, FH series.
The device is a series of protective disconnect devices known company ABB, manufactured by a series of F and FH. A product from the category of economical, but quite effective products.
The optimum choice for application in schemes of the household and commercial sphere. Instruments also provide fire protectionif there are risks of cable fires under the conditions of long-term leakage current.
This type of device is designed for implementation in AC networks with minimal levels of high harmonics and the absence of a constant voltage. Load current 16 - 63A, the stock of mechanical cyclicity - 20000.
Another example of standard selective devices is the DS series from ABB. They are designed for installation and operation in single-phase networks. WITH principle of selectivity read the article, which we highly recommend to read.
The purpose of the DS series automatic circuit breakers is to organize protective circuits against overloads and short circuits. The modules ensure the accurate operation of protective functions in case of accidental contact with current-carrying lines or pieces of equipment.
The device is a selective action - a product manufactured by ABB. Products like DS serial modules have shown long-term flawless performance in practice and are therefore in demand.
A distinctive feature of the DS series development is the presence of a visually detectable indication that indicates the presence of a leakage current. This is one of those structures of the protective device, thanks to which it is possible to prevent a fire, to signal a violation of electrical insulation. Permissible load 6 - 40A. Cyclicity - 20,000.
The “home” differential switch of the AD, BD series - a product of the German company “Schneider Electric”, was developed, first of all, for the introduction into the composition of household electrical networks.
The main purpose is to exclude damage to the physical body by electric current. Also this type of protective devices is quite effective and efficiently protects electrical equipment, cables, equipment.
A series of devices specially designed for use in home (residential) networks. This type of differential switch was designed by the German manufacturer Schneider Electric.
The sensitivity of the machine for direct (indirect) contact with parts of electrical equipment under voltage meets the standard (30 mA). Standard sensitivity (100 - 300 mA) is also provided in case of current leakage as a result of fires. A good solution for home equipment and office space.
Differential automatic monoblocks
Monoblock devices function in a complex manner, and this is their main difference from standard developments. Cover the whole range of protective functions that modern protection devices should possess. True standard devices also provide users with broad functionality.
A striking example of differential current circuit breakers operating in complex functionality are products of the same Schneider Electric company. In particular, the Multi series models are load switches of selective and instant action.
Another option is effective and reliable devices developed in the framework of projects called “Multi”. The devices have a wide range of properties that provide protective functions.
Automatic machines, depending on the model, are intended for installation as part of distribution networks of administrative (economic) buildings of industrial production.
These UDTs provide open circuit with leakage currents from 10 to 500 mA. A design feature is the ability to adjust for the exclusion of random triggers (lightning discharges, breakdown through a layer of dust, etc.).
Perhaps, a separate type of devices should be considered as design developments, like circuit breakers, the execution of which provides protection against surge overvoltages.
As a rule, this type of device is endowed with ultra-high speed, a sensitivity level of 10–30 mA in the event of a response after touching current-carrying surfaces. The same machines guarantee reliable protection of equipment against overcurrents.
Devices designed for use in circuits where there is a risk of pulsed overvoltages. Differ in some advanced functionality
The range of rated currents is usually 6 - 63A at voltages of 230 - 440 volts. Switching capacity reaches 4500A. Structurally produced under power through 2 or 4 poles.
From the same series, but somewhat modified, see switches with characteristic "A". A good example is the AD12M series, where the expansion of protective functionality is noted. Among the extras is a shutdown function in case the mains voltage rises above 265 volts for 0.3 seconds.
It should also be noted that devices endowed with the characteristic "A" have significant differences from the performance of differential automata with the characteristic "AC". The first option is able to respond to a constantly pulsating differential current and a sinusoidal current.
Mobile protective devices
Industry (foreign and domestic) produces another kind of automatic differential switches in a mobile type design. That is, we are talking about portable devices controlled by a differential current.
Such performance is typical for modern models of portable type. Mobile differential current protection devices are recommended for use in the residential sector.
Such mobile modules are made in the form of a miniature block that is simply inserted into a household outlet. Meanwhile, this type of device is intended for use indoors, in the group of especially dangerous (with increased danger).
These devices are often installed as additional modules to existing ones. residual current devices.
The same kind of devices - portable configuration, it is recommended to use in a domestic environment to protect children and the elderly. As is known, the resistance of the body of young and old organisms is somewhat different from the same size of the body of a man of middle age.
Therefore, portable RCDs are designed constructively as devices that have an increased triggering setpoint. This setting value typically does not exceed 10 mA for mobile devices.
Portable machines, for example, the UZO-DP series, are considered optimal protection for private urban and suburban real estate - cottages, country houses, garages, etc.
UZO marking (UDT) on the instrument case
It should be noted that the case characteristic (designations on the case) of modern devices shows almost complete information on electromechanical and temperature parameters devices.
All information about the performance, scope and even the best connection option is applied to the body of the protective device in the form of a clear, easily readable marking.
In fact, the user does not even need to refer to the accompanying documentation, since, knowing the notation, all the information can be obtained by reading the information from the front of the case.
Among the notation, it is recommended to study the graphic showing the characteristics of the automata relative to the conditions functioning: "A", "B", "AC", "F", which determines the sensitivity of the device to alternating and direct current different forms.
The abbreviated designation of devices often reflects their typical and serial belonging. For example, “AD12M” is a differential automaton, the serial number is 12, upgraded. Or this: "ВД63" - differential switch, 63 series.
True, there are models (as a rule, imported ones) that have a somewhat tangled abbreviation, say, FH200. Here: the symbol F is the device series, H is the version of the case, 200 is the serial number.
Or another example: a device denoted by the abbreviation DS. The first character is clear without the "translation" - differential. The second indicates that the device belongs to the category of selective devices.
The question of choosing between differential automat and RCD requires detailed study. We recommend that you familiarize yourself with the material, which examines their differences, the specifics of use, as well as advantages with disadvantages.
How to choose a differential current device?
Differential current devices are selected in the same way as, for example, with automatic switches.
Selection UDT. With the extensive information that is displayed on the front panel of the module, you can easily select devices directly at the place of purchase.
That is, the choice is made on the basis of traditional criteria for the selection of electrical equipment of this type:
- The purpose of the application.
- Matching load current.
- Sensitivity criterion to trigger.
- Hull execution.
For use in the conditions of the usual life, the choice usually falls on the single-phase devices characteristics "AC" or "A". For use on residential networks of residential buildings, it is better to take devices with a sensitivity of 10-30 mA (per touch) and 100 mA (fire protection and short circuit). Case execution - the most convenient under installation and in respect of operation.
It should be noted: the differential current device is always mounted in series with a circuit breaker. Therefore, the current characteristics of both devices must match or the rated current of UDT should be higher.
Conclusions and useful video on the topic
Even more interesting information about the device, types and principle of operation of diffutomats can be found in the following video:
Differential current protection devices are actually automatic switches, supplemented by a sensitive current leakage detection system.
It is mandatory to equip with such devices electrical networks, the execution of which is associated with the risk of contact between people and current-carrying parts of equipment. Schemes of modern execution by default involve the introduction of UDT.
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