A differential automaton is a monoblock, which consists of a circuit breaker and electronic circuit breaker. A differential allows the machine to implement comprehensive protection circuits against short circuit, overload currents and leakage currents (for damage to the insulation). Protective device (RCD) or, alternatively, differential protection devices (about them in detail in this article), are designed to protect people from electric shock, electrical faults or in contact with live parts of electrical installations, as well as to prevent fires and fires caused by leakage currents and earth fault. These functions are not inherent to conventional circuit-breakers, only reacts to an overload or short circuit. UST is useful for damaged wire insulation in electrical devices, careless use of electrical wiring or appliances. Short circuit, usually develop because of defects in insulation, earth fault, current leakage to earth (for instance when part of the current does not return to UST), etc. It monitors the leakage current and prevent a short circuit, disabling the electrical installation of power supply and thereby preventing invalid heating conductors, arcing and subsequent fire. Since the inception of leakage current auto shut off all phases of an emergency site electrical circuit is made of time, usually not exceeding a period of 0,03-0,3 seconds, depending on the leakage current. Thus, the RCD compares the current, gone to the apartment, with a current, which returned to the apartment. If these currents are different, RCD disconnects the voltage. The first such action on the UST-based differential transformer and the polarized relay, which took 0,01 A sensitivity and speed of 0.1 seconds was founded in France in 1937. And early in the second half of last century (1960-1970 gg.) Worldwide, and especially in Western Europe, Japan, the U.S. began its active introduction into wide practice. Currently, hundreds of millions of UST successfully protect life and property from electrical shock and fire. Today, UST is an indispensable element of any electrical industrial or social amenities. These devices fail to equip all mobile objects (commercial trucks, vans, catering), sheds and garages. Despite the fact that everyone in developed countries accounts for about two UST, dozens of manufacturers are developing new devices Electrical various modifications, constantly improving their technical parameters. Modern RCD-mounted distribution board are divided into two types - the AU and A. Since the AC type reacts to the leakage of the variables (sinusoidal) currents. However, in electrical circuits may leak not only AC but also DC (pulsed) current. RCD type A is specifically designed for such cases. Since the scheme for measuring the difference between the currents in the RCD type A is more complex, these devices in 1,1-1,5 times more expensive. Such devices must necessarily be applied in some cases, for example, the operation of washing machines, dishwashers and other high-power electrical appliances. In addition to UST, installed on an approved panel, you can find electrical outlets with built-in RCD. These devices come in two forms: the first set in place an existing outlet, the second is connected to an existing outlet, and then have it turn the plug on the appliance. The advantages of these devices can be attributed to the absence of the need to replace the old building houses the wiring and the shortcomings - the high cost (sockets with built-in RCD will cost about 3 times more expensive than the RCD installed at the switchboard). The third type of devices with built-in RCD is "RCD-fork." UST action based on the work of a differential current transformer. Total magnetic flux in the core is proportional to the difference of currents in conductors that are the transformer primary current. Under the influence of EMF in the circuit of the secondary winding current flows which is proportional to the difference between the primary currents. This current and activates the trigger. In normal operation, the resultant magnetic flux is zero, the current in the secondary winding of differential transformer is also zero. When you touch a person to open the conductive parts or to the body of an electric receiver, which took place insulation breakdown, according to the phase conductors through the RCD than the load current flows an additional current - the current leakage. For CT it is a differential (difference). If this current exceeds the threshold element of the starter, the latter works and acts on the actuator. For monitoring proper operation (efficiency), RCD provides circuit test ("Test" button), works by artificially creating a differential current switch-off. Protective devices such as RCDs are installed in the switch cabinet apartments, a cottage (can use existing cabinets). There are several options for mounting. Installing a UST with a leakage current of 30 mA for the whole apartment or cottage. The advantages of such solutions include low cost devices, as well as the fact that UST will not take up much space. The disadvantage of this solution is that in this case, it is difficult to determine which of these lines leak, and the fact that the triggering device, all areas remain without electricity. Installation of two UST is one of 30 mA at the Female line and another RCD (10 mA) per line (for example, the line feeding the washing machine, Jacuzzi, and "warm" floors). Compared to the previous, it is more reliable and convenient option, since if there any problems with the wiring or electrical appliances will be switched off only the corresponding line, not the whole apartment or house. Disadvantages of this system - higher costs and the need to have much more free space. More than one RCD, usually can be identified in individual intra plate specially designed for this purpose. In a conventional shield on the landing for this is usually not enough space. When using this option (in the absence of a differential machine) next to the circuit breaker that protects the entire house, installed UST. In this case it is better not to apply the usual, and the so-called selective RCD trip time which is from 0,3-0,5. Longer response time would allow to react to the evolving leak and shut down the first line of devices that protect individual appliances, or line (apartments). Only if they do not work, it will disable the entire scheme of power entirely. During installation UST should pay special attention to a number of characteristic errors. The most common of which is connected to the RCD load in the circuit which has a connection to the zero conductor working with exposed conductive parts or electrical connection to the protective earth conductor. Also, the following error: connect loads to the neutral conductor to the RCD, a connection to the load neutral conductor of another UST jumper between the neutral conductor of various UST. Calculation, installation and commissioning of electrical circuits using the RCD should be dealt with only by qualified professionals. Only in this case, you can get a guarantee that the protection work on time. It should also be noted that the RCD is inexpedient to establish if there is an old worn-out wiring in the room, as in this case the property of RCD to detect leakage current can cause some problems. For example, if the old wiring Electrical device can operate in an unpredictable way. Therefore, in this case, we recommend installation in places with high-risk outlets with built-in RCD. In many countries the use of RCD in electrical installations regulated by norms and standards. For example, in the Russian Federation - GOST R 50571.3-94 adopted, GOST 50807-95, etc. According to GOST 50669-94 UST is set to fail in the electric power supply of mobile buildings made of metal or a metal frame for street trading and consumer services. In recent years, the administration of large cities, in accordance with state standards and recommendations Glavgosenergonadzora decided to equip these devices stock of residential and public buildings.
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