Explosive mixture produces explosive conditions

Explosion refers to the material from a state, through physical or chemical changes, suddenly into another state and release a huge amount of energy, resulting in light and heat or mechanical work.

Here only the explosion of explosive mixtures is mentioned, that is, the explosion of all combustible gases, vapors, and explosive mixtures of dust and air. Such an explosion would require a combination of three conditions:

First, there must be an explosive or combustible substance; Second, there must be combustion-supporting substances, mainly oxygen in the air; Third, there are also ignition sources (such as sparks, arcs, and hazardous temperatures) that provide the amount of energy necessary to ignite the mixture.

Only these three conditions exist at the same time, there is the possibility of explosion, any of them do not have, will not produce combustion and explosion. Therefore, to take appropriate measures, so that the three conditions are not at the same time can achieve the purpose of preventing explosion.

Because explosive mixtures are commonly found in the production, processing, storage and transportation of coal, petroleum, chemical, textile, grain processing and other industries, such as explosions are extremely harmful. Therefore, people have adopted a variety of explosion-proof technology methods to prevent the formation of explosive dangerous environment and explosion

Basic explosion-proof type

(1) Flameproof type "d"

The explosion-proof type is to seal all the parts of the equipment that may ignite explosive gas mixture in a shell, and the shell can withstand any joint surface or structural gap through the shell, and the flammable mixture that penetrates into the shell inside the internal explosion without damage. It will not cause the ignition of an explosive environment formed by one or more gases or vapors outside (see GB 38362 standard).

Parts that may generate sparks, arcing, and dangerous temperatures are placed in the flameproof housing, which separates the space inside the device from the surrounding environment. There is a gap in the flameproof shell, due to the breathing action of electrical equipment and gas penetration, so that the inside may be in the explosive gas mixture, when it explodes, the shell can withstand the explosion pressure without damage, and the shell structure gap can cool the flame, reduce the flame propagation speed or terminate the acceleration chain. The flame or dangerous flame product can not cross the flameproof gap to ignite the external explosive environment, so as to achieve the purpose of flameproof.

Flameproof type "d" is divided into class I and Class IIA, IIB and IIC according to the type of explosive gas environment it allows to use.

The explosion-proof type equipment is suitable for places in 1 and 2 zones.

(2) Increased safety type "e"

Increased safety explosion-proof type is a type of explosion-proof type that takes some additional measures to improve the safety of electrical equipment that does not produce arc and spark under normal operating conditions and prevents the possibility of dangerous temperatures, arcs and sparks that may occur in its internal and external components. It does not include devices that produce sparks or arcs under normal operation (see GB 38363 standard).

On electrical equipment structures that do not produce sparks, arcs and dangerous temperatures during normal operation, reduce the possibility of ignition failure by taking measures to reduce or control the operating temperature, ensure the reliability of electrical connections, increase the insulation effect and improve the protection level of the enclosure to reduce the possibility of contamination caused by dirt and moisture entry, etc. Improve the safety and reliability of equipment under normal operation and specified failure conditions (e.g., motor rotor lock).

This type of equipment is mainly used in zone 2 dangerous places, and some types can be used in zone 1, such as increased safety low-voltage asynchronous motors with appropriate protection devices, junction boxes, etc.

(3) Intrinsically safe "i"

The intrinsically safe explosion-proof type is an intrinsically safe circuit in which all circuits inside the equipment are generated by any electrical spark or any thermal effect that cannot ignite the specified explosive gas environment under the standard specified conditions (including normal operation and specified fault conditions).

"i Alpha" class electrical equipment 〖HT〗 is an intrinsically safe electrical equipment that cannot cause ignition under normal operation and the application of one fault and any combination of two fault conditions;

Class "ib" electrical equipment (HT) is an intrinsically safe type of electrical equipment that cannot cause ignition under normal operation and the application of a fault condition (see GB 38 364).

Intrinsically safe starts from limiting the energy in the circuit, reduces the potential spark energy to below the specified gas mixture energy by reliable control circuit parameters, and limits the surface heating temperature of the wire and components to below the ignition temperature of the specified gas mixture.

This type of explosion protection can only be applied to weak current equipment, which is suitable for zones 0, 1, 2 (Exia) or zones 1, 2 (Exib).

(4) Positive pressure "p"

An explosion-proof type of electrical equipment. It is an electrical equipment that achieves safety by keeping the pressure of the protective gas inside the equipment housing higher than the pressure of the surrounding explosive environment (see GB 3836-5).

The protection type of positive pressure equipment can be used in different ways. One approach is to protect the static positive pressure inside the system, while the other is to maintain a continuous flow of air or inert gases to limit the entry of combustible mixtures into the inside of the housing. Both methods need to flush the housing with protective gas before setting up to start, to remove the combustible gas that enters the housing when the equipment is not under positive pressure, and to prevent the formation of combustible mixture in the housing. The point of these methods is to monitor the system and perform periodic ventilation to ensure the reliability of the system.

This type of equipment can be used in zone 1 or Zone 2 hazardous places according to the protection method.

(5) Oil-immersed "o"

Oil-immersed explosion-proof type is the whole equipment or equipment components immersed in oil (protective fluid), so that it can not point above the fuel level or outside the shell of the explosive gas environment (see GB 38366 standard).

This is an old explosion-proof technique used primarily in switchgear. The resulting arc and spark are immersed in oil.

This type of equipment is suitable for hazardous areas in Zone 1 or Zone 2.

(6) Sand filling type "q

The sand-filled explosion-proof type is a type of electrical equipment protection that fills the shell with sand or other powder materials with specified characteristics, so that under specified conditions of use, the arc or high temperature generated in the shell cannot ignite the surrounding explosive gas environment (see GB 38367 standard).

This type of explosion protection imbeds and fully buries the conductive components that ignite the explosive gas environment into the sand-filled material, thus preventing the spread of sparks, arcing and dangerous temperatures so that they cannot ignite the external explosive gas environment.

Typically it is used for components within Ex "e" or Ex "n" devices and for heavy-duty traction battery packs.

This type of equipment is suitable for hazardous areas in Zone 1 or Zone 2.

(7) "n" type explosion-proof electrical equipment

This type of electrical equipment, during normal operation, cannot ignite the surrounding explosive gas environment and is unlikely to cause a failure that causes ignition (see GB 38368 standard).

When the "n" type electrical equipment is in normal operation, it means that the equipment is electrically and mechanically in accordance with the design specifications and is used within the scope specified by the manufacturer, and it is impossible to produce sparks, arcs and dangerous temperatures.

This type of electrical equipment is only applicable to zone 2 dangerous places.

(8) Casting type "m"

The cast type explosion protection type is the pouring agent (compound) of the electrical part that may produce sparks, arcing or dangerous temperature parts that cause explosive mixtures to explode, so that it cannot ignite the surrounding explosive mixtures (see GB 3836-9).

The use of pouring sealing measures can prevent short circuit of electrical components, solidify electrical insulation, avoid the spark on the circuit and the generation of ignition sources such as arc and dangerous temperature, prevent the intrusion of explosive mixtures, and control the surface temperature under normal and fault conditions.

This type of equipment is suitable for dangerous places in Zone 1 and 2.

(9) Airtight "h"

This type of explosion-proof equipment adopts airtight housing. That is, the explosive gas mixture in the environment cannot enter the inside of the equipment housing. The airtight shell is sealed by melting, squeezing or gluing, and the shell is mostly non-removable to ensure air tightness