Line surge arresters
Surge arresters on the line are one of the elements of the lightning protection system. They ensure the protection of low-voltage lines against the effects of atmospheric and switching overvoltages. They are most often used to protect important network elements (such as a transformer or generator). This device can also be found under the names: lightning arrester, surge protector, varistor (or varistor). These elements are important for the safe and efficient use of the network, as overvoltages can occur, for example, when an unloaded overhead line is switched on or off, or as a result of a lightning strike on an overhead line, as well as following power grid failures (overvoltage is any increase in voltage exceeding the maximum voltage that is intended for the device or electrical installation). These types of events can damage insulation and other network components. In the assortment, in the LIMITERS category, you can find such products as: surge arresters, magnetic card, arrester insert, earthed socket, surge arrester (single-pole, four-pole), surge arrester with replaceable modules, combined replaceable module, lightning barrier, protective varistor. Types of surge arresters Protectors - in terms of how they work - are divided into three types: - cut-off - after exceeding a certain voltage value, the internal resistance drops sharply and there is a quick transition from the non-conducting to the conducting state; Cut-off limiters have a simple structure and are very reliable in operation, but they are strongly affected by environmental factors and phenomena related to the so-called follow current; - limiting (they are usually made of metal oxides and enclosed in a plastic, weather-resistant housing) - there is no phenomenon of the so-called follow current and there is no delay in ignition of the arrester in the event of a fault. The downside of this type of solutions is the lower ability to discharge lightning current than in the case of a cut-off arrester; - combined (combination of the other two solutions). A proper understanding of the classification and properties of individual types of surge arresters allows for the proper and effective selection of devices protecting power installations. Limiters should be selected primarily depending on the types of expected hazards. Failure to adjust the strength of the device to possible threats often results in damage to it and the protected installation. Taking into account the specificity of the electrical installation and possible hazards, the following types of surge arresters can be distinguished: Type 1 surge arresters (formerly class B) provide protection for the electrical installation (and the receivers connected to it) in the event of a direct lightning strike to the power line or the building's lightning protection system. These surge arresters are also designed to discharge the lightning current to the grounding system, resulting from a direct lightning strike in the supply network. This type of limiter is most often installed at the beginning of the installation, which is powered from the overhead network or cable line. This place can be a cable joint or a main switchboard. Hybrid type "1+2" surge arresters (former class B+C) provide protection against atmospheric overvoltages caused by lightning strikes in objects located in the vicinity of overhead lines or directly in the low-voltage line, at a great distance from the place of installation of the surge arresters. They also provide protection against switching overvoltages. They are installed in front of the meter, thus protecting the measuring system. Type 2 arresters (former class C) protect the electrical installation against the effects of overvoltages resulting from indirect lightning discharges or switching processes in the electrical network (such as switching on electrical devices such as motors, transformers or welding machines). These limiters also reduce overvoltages resulting from the activation of the installation's protections. Type 3 arresters (former class D) protect sensitive receivers against overvoltages, reduced by the previous protection level. They are used to protect computer devices and audiovisual equipment. These devices are also used in the case of a large (several dozen meters) distance between the sensitive device and the last degree of protection. Type 1 surge arresters are characterized by a much higher resistance to current surges than Type 2 arresters. The lowest surge resistance is characterized by Type 3 arresters, but these, in turn, are used only for final protection and ensuring an appropriately low voltage level of protection. How to choose surge arresters Type 1+2 arresters are most often used as the only means of protection to protect small objects, such as containers and free-standing apparatus cabinets. In such cases, one properly selected and installed device can provide a sufficient level of protection for the entire installation. However, it should always be remembered that the use of a Type 1+2 arrester in the main switchgear, in extensive facilities with many sub-switchboards (local/storey), does not ensure the same level of protection in the entire installation. In this situation, it is recommended to use a second stage (Type 2 SPD) to protect the extensive installation against induced overvoltages. Surge arresters should be selected in such a way as to reduce overvoltages to a value considered safe (in the event of an uncontrolled increase in voltage in the cables, the connected devices may be damaged or even destroyed). It is important that the voltage parameters of the arrester do not exceed the insulation strength of the electrical installation and end devices. Use of surge arresters Type 1 (class B) arresters, used in main switchboards, limit the direct effects of atmospheric discharges. On the other hand, Type 2 arresters (class C) installed in sub-switchgears are responsible for limiting overvoltages arising in the event of indirect discharges or switching operations that may be present in the network. Type 2 arresters are the second level of protection after type 1 arresters. Type 3 (class D) surge arresters are installed in the circuits and terminal equipment to prevent overvoltages from entering the circuits of terminal equipment. In residential buildings that do not have an external lightning protection system or other factors that increase the risk of direct lightning discharges, only Type 2 surge arresters are most often used. They are able to guarantee protection for devices classified in overvoltage categories IV to I. also devices with sensitive electronics. On the other hand, in the case of buildings that are equipped with an external lightning protection system, Type 1+2 surge arresters are installed. The place of installation of this type of apparatus is the main switchboard behind the meter. In this way, the excessive amount of energy, e.g. as a result of direct lightning discharges, is limited to the appropriate level, and devices with sensitive electronic components gain protection. REMEMBER: From the designer's point of view, the selection of the appropriate arrester is determined by the PN-EN 62305 standard (especially the second part concerning risk assessment). On its basis, it is necessary to assess the strength and class of the device that should be used.
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