Explosion-proof electrical equipment is generally designed after the product has reached the basic technical requirements, and then adds some explosion-proof measures to meet the explosion-proof requirements. But there are also some explosion-proof electrical equipment, such as intrinsically safe electrical equipment is required to consider the basic technical requirements of the product, while considering the explosion-proof technical requirements, the two need to take into account each other, when the basic technical requirements and explosion-proof technical requirements conflict, must be explosion-proof technical requirements performance-based. Let's take a look at the basic methods for electrical equipment to meet the requirements of explosion-proof technology.
1 Limit explosion with shell
The basic idea of explosionproof is to adopt the idea of structural explosion-proof and use the explosionproof shell to obtain safety characteristics. The performance of the flameproof enclosure includes two parts: explosion resistance and explosion isolation.
(1) Explosion resistance: Explosion resistance refers to the strength of the shell. When the most serious explosive mixture explosion occurs in the shell, or when the organic insulation in the shell is decomposed due to high temperature, and a flammable high-pressure gas is generated, the pressure does not cause deformation and damage to the shell, and its high temperature does not cause damage to the shell.
(2) Flameproof: Flameproof refers to the joint surface of each component of the shell, which must meet certain requirements, so that the flame or scorching metal particles that spew out when the shell explodes will not cause the explosion of the explosive mixture outside the shell.
2 Control the electrical ignition source
(1) Reduce sparks, arcs and high temperatures.
For electrical equipment that does not produce spark arcs and dangerous high temperatures during normal operation, some additional measures can be taken to improve the safety and reliability of the equipment, such as the use of high-quality insulation materials, reducing the temperature rise, increasing the electrical clearance, creepage distance, improving the quality of the wire connection, etc., thereby greatly reducing the possibility of sparks, arcs and dangerous high temperature phenomena, so that it can be used in dangerous places.
(2) Limit spark energy.
By rationally selecting electrical parameters, the system in a normal or faulty state, the generated electric spark becomes quite small and cannot ignite the surrounding explosive mixture.
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3 Isolate the ignition source with a medium
The principle is to place the conductive parts of the electrical equipment in a safe medium, so that the ignition source is isolated from the explosive mixture outside to achieve the purpose of explosion protection.
(1) Isolate the ignition source with a gas medium
When the medium used is a gas (generally fresh air or inert gas), the gas inside the equipment should have a certain positive pressure relative to the outside atmosphere, thereby preventing the outside atmosphere from entering.
(2) Isolate the ignition source with a liquid medium
The medium used is liquid (usually transformer oil) as the isolation medium.
(3) Isolate the ignition source with a solid medium
The medium used is a granular solid (usually quartz sand) as the isolation medium, or the medium used is a cured filler (usually epoxy resin), which pours the ignition source inside the filler and isolates it from the explosive mixture outside.
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4 Isolate the external ignition source with a housing
(1) The shell is sealed by melting, extrusion or gluing to prevent external flammable gases from entering the shell, and is isolated from the ignition source to achieve the purpose of explosion-proof.
(2) The shell with good sealing performance is used to limit the entry of flammable gases or vapors, so that the time for the flammable gas or vapor concentration accumulated inside the shell to reach the lower limit value is longer than the possible existence of flammable gases or vapors in the external environment.
(3) The use of sealing performance to meet the specified requirements of the shell so that the flammable dust can not or difficult to enter the shell
Internally, and isolated from the ignition source, to achieve the purpose of explosion protection.
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