Дугогасительная камера - Arc-suppression chamber
Электрод 2 - Electrode 2
Электрод 1 - Electrode 1
А - A
Б - B
Газовыделяющая пластмасса - Gas-releasing plastics
An SDP should remain operating in case of maximum currents. This task is typical for the most critical facilities where high reliability of operation of the electronic equipment in storm is required.
We should consider that the space in the mounting cabinet is limited. There is always some lack of space in the cabinet. Specialists try to locate all SDP elements in the enclosure that can be installed on a typical mounting rack. The working space in the SDP is thus dramatically limited. Both zinc oxide washer and glass enclosure of the arrester have limited dimensions. Both can be mechanically destroyed in case of high fraction of the lightning current flowing through the SDP. Operating experience and laboratory tests have shown that we can hardly count on the current flowing through the SDP and being much more than 10 kA. Is this current sufficient for the most applied problems related to critical facilities?
The situation is the most difficult when the lightning current goes to the ground along the minimum amount of conductors, usually two (a single-phase two-wire line). The Russian regulatory documents for lightning protection and the IEC 62305 standard set the estimated lightning current depending on the protection level. Even for the weakest levels III and IV, its magnitude is taken as 100 kA (50 kA per each wire). It is clear that SDPs with the allowable current equal to about 10 kA are not suitable in this case. It is also not suitable for a three-phase 4-wire circuit, where the lightning current 100 kA is divided in the wires by 25 kA. Often SDP manufacturers do fakes by forcing the lightning current distribution in the way most suitable for them. In many situations, the varistor-based SDP cannot cope with the strong lightning. Allowable current flowing through it can be increased.
As noted, there are two weak elements. Both varistor and gas-filled arrester give in to great currents. Thus, both elements should be removed. The varistor was used to avoid short circuits. However, the problem will not be a specialist's concern any more, if we provide the SDP with an arc-suppression chamber. They have been successfully used for a long time, e.g. in air high-voltage breakers.
Read more details in the article by Prof. E. M. Bazelyan "SDPs Unvarnished".
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