Protection against retension
- Customer pickup,
- In detail
All who use electronics need protection against emissions. Really, the distortions which are present at the power supply network influence quality of any activity connected with the equipment. Therefore it is recommended to use an integrated approach to a solution.
It is not enough to establish only a suppressor of emissions and the device of improvement of quality of food in a point of input of the electric power in the building as transition processes can be created after this point. Really 65% of all transition processes are created by the equipment installed in the building, for example, by such mechanisms as the elevator or the device of air conditioning.
Telecommunication and broadcasting
Networks for a voice transfer and data, and also television and broadcasting carry out transfer without distortions only in the presence of high-quality food.
Plants and factories for ensuring the maximum productivity of control units with technological processes at the minimum idle time require food without hindrances.
Computer equipment and networks
Offices, shops, large supermarkets and other establishments require "pure" food for maintenance of operability of the computer equipment and integrity of data.
Telecommunication switching stations and centers of cellular communication
Reliable food is especially important for ensuring the round-the-clock reliable network functioning.
The food which is giving in to exact management is especially important in critical zones, such as operating rooms and intensive care units.
(limiters of retension)
Recently there was very actual a question of negative influence on electric equipment of the short-term retension arising in electropower lines 220/380 V. Istochnikami of this retension, lightning discharges and industrial (switching) hindrances usually are. The distortions which are present at the power supply network influence quality of any activity connected with the electronic equipment. Statistically, over 38% of failure of the electronic equipment happen for the reasons of emissions in power supply networks. The statistics shows that cases of damage of low-current electronic equipment because of emissions of tension double each 3-4 years. Influence of retension can lead not only to damage of the fed equipment and failures in its work, but also to failure of elements of the electrofeeding installations (EPU): rectifiers, switchboards and other electroadjusting equipment. Foreign and domestic experience shows that without use of special protection devices (overstrain limiters) reliable operation of EPU is impossible. The cost of carrying out minimum necessary measures for protection in tens and hundreds of times is less, than possible damage from damage and violation of normal work of object.
As element base for the protection devices capable to maintain great values of pulse currents and tension, use spark rated sportsmen and oxide-zinc varistors now. The main techniques and rules of their application are developed and described in various international and European standards still in the late eighties, the beginning of the 90th years. The domestic regulatory base lags behind in this area and, unfortunately, is presented or outdated documents which comprise the requirements which are not corresponding to modern conditions, or the separate departmental documents which are not connected with each other and not considering questions of protection in full. The real analysis of a problem shows that the comprehensive and integrated approach is necessary for its decision.
Modern classification of the EPU protection devices is based according to the zone concept of lightning protection developed by MEK which basic provisions are formulated in two main standards: IEC-61024-1 (1990-02): "Lightning protection of building constructions. Part 1. General principles"
IEC-61312-1 (1995-05): "Protection against electromagnetic impulses at a lightning stroke. Part 1. General principles".
The main classes of protection devices and technique of their tests are given in the standard:
IEC-61643-1 (1998-02): "Devices of protection against retension for low-voltage systems of distribution of the electric power. Part 1. Requirements to operational characteristics and test methods".
There are also various national standards which in general duplicate requirements of the MEK standards.
According to the documents given above, devices of protection against retension, depending on an installation site and ability to pass through itself various pulse currents, are divided into the following main classes: I, II, III (according to the IEC-61643-1 (1998-02) or B, C, D standard (according to the E DIN VDE 0675-6 (1989-11) and A1:1996-03/A2:1196-10 standard). The main requirements to limiters of an overstrain of different classes are provided in table 1.
|Device class||Purpose of the device|
|I (In)||Are intended for protection against direct strokes of a lightning to the building,
antenna and mast construction, high voltage line.
Are established on input to the building (in an introduction board).
|II (C)||Are intended for protection of a current-distributing network against switching hindrances as the second step of protection at a lightning stroke. Are established in switchboards.|
|III (D)||Protection against differential retension (between a phase and a neutral), filtrations of high-frequency hindrances are intended for protection of consumers against residual throws of tension. Are established directly near the consumer. Can have the most various design (in the form of sockets, network forks, separate modules for installation on a DIN lath, etc.