1. Explosive mixture explosive conditions Explosion refers to the light and heat or mechanical work produced by a substance from a state, through physical or chemical changes, suddenly to another state and emits huge amounts of energy. Only the explosion of explosive mixtures is mentioned here, that is, the explosion of all combustible gases, vapours and explosive mixtures of dust and air. This kind of explosion needs to have three conditions at the same time: first, there must be explosive substances or flammable substances; second, there must be combustion-supporting substances, mainly oxygen in the air; third, there must be ignition Sources (such as sparks, arcs, hazardous temperatures, etc.) that provide the energy necessary to ignite the mixture. Only when these three conditions exist simultaneously can the possibility of explosion occur. If any one of the conditions is not available, there will be no burning or explosion. Therefore, appropriate measures should be taken to prevent the explosion from being achieved when the three conditions are different. Because explosive mixtures are common in the production, processing, storage and transportation of coal, petroleum, chemical, textile, grain processing and other industries, such as the explosion is extremely harmful. Therefore, people have adopted a variety of explosion-proof technical methods to prevent the formation of explosive atmospheres and their explosion. 
2. Basic explosion-proof type
(1) Flameproof "d"
Explosion-proof type is a device that encloses a component that may ignite an explosive gas mixture in an outer casing. The outer casing can withstand any joint surface or structural gap through the outer casing, and the flammable mixture penetrating into the outer casing explodes inside without being damaged. It does not cause ignition of an explosive atmosphere formed by one or more gases or vapors (see GB 3836î€ 2 standard). 
Components that may generate sparks, arcs, and hazardous temperatures are placed in an explosion-proof enclosure that separates the interior of the equipment from the surrounding environment. There is a gap in the flameproof enclosure. Due to the respiration of the electrical equipment and the gas permeation, there may be an explosive gas mixture inside. When it explodes, the outer casing can withstand the explosion pressure generated without damage, and the outer structure gap can cool the flame and reduce The flame spreads or terminates the acceleration chain, so that the flame or dangerous flame products cannot ignite the external explosive environment through the explosion-proof gap, thereby achieving the purpose of explosion-proof. 
The explosion-proof type "d" is classified into Class I and Class IIA, IIB, and IIC according to the type of environment in which it is allowed to use an explosive gas. 
The explosion-proof type equipment is suitable for the 1st and 2nd districts. 
(2) Increased safety type "e"
The increased safety type is an additional measure to prevent the occurrence of dangerous temperatures, arcs and sparks in the internal and external components of electrical equipment that does not generate arcs or sparks under normal operating conditions. Explosion-proof type. It does not include equipment that produces sparks or arcs under normal operating conditions (see GB 3836î€3). 
In the electrical equipment structure that does not generate sparks, arcs and dangerous temperatures during normal operation, measures to reduce or control the operating temperature, ensure the reliability of electrical connections, increase the insulation effect and improve the degree of protection of the enclosure to reduce pollution due to dirt The possibility and the entry of moisture, etc., reduce the possibility of causing ignition failure, and improve the safety and reliability of the normal operation of the equipment and the specified faults (for example, the rotor of the motor is blocked). 〖JP〗
This type of equipment is mainly used in hazardous areas in Zone 2, and some types can be used in Zone 1, such as increased safety low voltage asynchronous motors with suitable protective devices, junction boxes, and the like. 
(3) Intrinsically safe "i"
Intrinsically safe explosion-proof type is the intrinsic safety of all the circuits inside the equipment that are caused by any spark or any thermal effect generated under standard conditions (including normal operation and specified fault conditions) that cannot ignite the specified explosive atmosphere. Circuit. 〖HTH〗 “iɑ†grade electrical equipment 〖HT〗 is an intrinsically safe electrical equipment that can not cause ignition under normal fault conditions and two fault conditions of application of a fault and any combination; [HTH] “ib†grade electrical equipment HT is an intrinsically safe electrical device that does not cause ignition under normal conditions of operation and application of a fault condition (see GB 38 36î€4 standard). 
The intrinsically safe type starts with limiting the energy in the circuit, and reduces the potential spark energy below the energy of the specified gas mixture by reliable control circuit parameters. The heating temperature of the wire and the component surface is limited to the ignition temperature of the specified gas mixture. under. 
This type of explosion protection can only be applied to weak electrical equipment. This type of equipment is suitable for Zones 0, 1, 2 (Ex iɑ) or Zones 1 and 2 (Ex ib). 
(4) Positive pressure type "p"
An explosion-proof version of electrical equipment. It is a safe electrical device by keeping the pressure of the protective gas inside the equipment casing higher than the pressure of the surrounding explosive environment (see GB 3836î€5 standard).
Different methods can be used for positive pressure equipment protection. One method is to protect the static positive pressure inside the system, and the other is to maintain a continuous flow of air or inert gas to limit the entry of the flammable mixture into the interior of the enclosure. Both methods require the casing to be flushed with a protective gas prior to start-up of the equipment, taking away flammable gases entering the enclosure during non-positive pressure inside the equipment to prevent the formation of a flammable mixture within the enclosure. The point of these methods is to monitor the system and perform regular ventilation to ensure system reliability.
This type of equipment can be used in Zone 1 or Zone 2 hazardous locations according to the protection method. 
(5) Oil immersion type "o"
The oil-immersed explosion-proof type is to immerse the entire equipment or parts of the equipment in the oil (protective liquid) so that it cannot point above the fuel surface or the explosive gas environment outside the outer casing (see GB 3836î€6 standard).
This is an old explosion-proof technical method mainly used for switchgear. The formed arc and spark are immersed under the oil. 
This type of equipment is suitable for use in Zone 1 or Zone 2 hazardous locations. 
(6) Sand filling type "q"
The sand-filled explosion-proof type is a kind of powder material filled with sand or other specified characteristics in the outer casing, so that the arc or high temperature generated in the shell can not ignite the surrounding explosive gas environment under the specified conditions of use (see GB 3836î€7 standard). 
The explosion-proof version secures the electrically conductive components that ignite the explosive atmosphere and is completely embedded in the sand-filled material, thereby preventing the spread of sparks, arcs, and dangerous temperatures from igniting the external explosive atmosphere. Typically it is used for components in Ex "e" or Ex "n" devices and heavy-duty traction battery packs. 
This type of equipment is suitable for use in Zone 1 or Zone 2 hazardous locations. 
(7) “n†type explosion-proof electrical equipment This type of electrical equipment cannot ignite the surrounding explosive gas environment during normal operation, and it is unlikely to cause ignition failure (see GB 3836î€8 standard). 
“n†type electrical equipment is in normal operation, meaning that the equipment is electrically and mechanically compliant with the design specifications and is used within the limits specified by the manufacturer. It is not possible to generate sparks, arcs and dangerous temperatures. 
This type of electrical equipment is only suitable for hazardous areas in Zone 2. 
(8) Pouring type "m"
The encapsulated explosion-proof type is an electrical component that causes a spark, arc or dangerous temperature portion that may cause an explosion of an explosive mixture to be encapsulated in a potting compound (composite) so that it does not ignite the surrounding explosive mixture (see GB 3836î€9). standard). 
The encapsulation measures prevent electrical components from short-circuiting, solidify electrical insulation, avoid sparks on the circuit, and generate ignition sources such as arcs and hazardous temperatures, prevent the intrusion of explosive mixtures, and control the surface temperature under normal and fault conditions. #p#Page title#e#
This type of equipment is suitable for hazardous areas in Zones 1 and 2. 
(9) Airtight type "h"
This type of explosion-proof equipment is airtight. That is, the explosive gas mixture in the environment cannot enter the inside of the equipment casing. The hermetic enclosure is sealed by means of melting, extrusion or gluing. Most of the casing is non-removable to ensure permanent airtightness (see GB 3836î€11). 
The explosion-proof measures belong to the category of “n†type explosion-proof measures, and GB 3836î€11 has been replaced by GB 3836î€8-2003. 
(10) Special type explosion-proof electrical equipment "s"
Refers to the explosion-proof type that is not included in the national standard. This type can be temporarily formulated by the competent department and verified by the designated explosion-proof inspection unit for electrical equipment capable of explosion-proof performance. 
This type of equipment is developed according to actual use and can be applied to the corresponding hazardous places. 
(11) Combustible dust environment Electrical equipment Dust explosion-proof electrical equipment is used to limit the maximum surface temperature of the enclosure and to use a “dust-tight†or “dust-proof†enclosure to limit the ingress of dust to prevent ignition of flammable dust (see GB 12476î€1) standard).
This type of equipment installs live parts in a housing with certain protective capabilities, which limits the entry of dust and isolates the ignition source from dust to prevent explosions. The equipment is divided into Type A equipment or Type B equipment according to the difference in the dustproof structure of the equipment. The equipment is divided into 20, 21, and 22 levels according to the dustproof level of the equipment casing, such as DIP A20, DIP A21, DIP B20, and DIP B21.
This type of equipment is suitable for use in dust hazardous locations in Zones 20, 21 or 22, depending on the grade. 
It may be easy to see in normal practice that many explosion-proof electrical products use a variety of explosion protection methods in one product. For example, lighting fixtures may use increased safety protection (housing and terminal boxes), explosion-proof protection (switches), and encapsulated protection (ballasts). This allows manufacturers to adopt the most suitable composite explosion protection method. It is important to note that the order of the explosion-proof methods listed on the product nameplate will often tell the user the structure of the product. For example, if a product is identified as Ex de, it is most likely an explosion-proof type with an increased safety component. . Another product, labeled Ex ed, is most likely not a flameproof enclosure (such as stainless steel or reinforced polyester) with a flameproof switch or component mounted. Both products may be suitable for Zone 1, but they use different explosion protection measures for the same purpose. Users can choose the type of explosion-proof type that provides the best balance between cost, performance and safety, based on their actual needs and information.
Push Button Switches
The Push Button Switches, also known as the control button (referred to as the button), is a low-voltage electrical appliance that is manually and generally can be automatically reset. The Push Button Starter Switch is usually used to issue a start or stop command in the circuit to control the turning on and off of electrical coil currents such as electromagnetic starters, connectors, and relays.
The On Off Push Button Switches refers to a switch that pushes the transmission mechanism with a button to make the movable contact and the static contact open or close and realize circuit switching. It is a master control device with a simple structure and a wide range of applications. In the electrical automatic control circuit, used to manually send control signals to control connectors, relays, electromagnetic starters, etc.
This Pushbutton Switches is a kind of electric device that is used to switch on and off the small current circuit when the action is released. Generally used in AC and DC voltage below 440V, the current is less than 5A in the control circuit, generally do not directly manipulate the main circuit can also be used in the interconnection circuit. In actual use, in order to prevent desperation, different marks are usually made on the buttons or painted with different colors, and the colors are red, yellow, blue, white, black, green, and the like.
The Momentary Push Button Switch could be divided into metal push button switches and LED Light Switches and ordinary snap button type, mushroom head type, self-locking type, self-resetting type, rotary handle type, with indicator light type, lighted symbol type and key type, etc., with single button and double Buttons. Generally, it adopts a water-storage structure, which consists of a button cap, a return spring, a static contact, a moving contact and a casing. It is usually made into a composite type, and has a pair of normally closed contacts and normally open contacts, and some products can pass. The series connection of multiple elements increases the number of contact pairs. There is also a self-contained button that automatically holds the closed position when pressed, and can be turned on only after the power is turned off.
When the Metal Switches is not pressed, the movable contact is connected with the upper stationary contact. The pair of contacts is called a normally closed contact. At this point, the movable contact is disconnected from the following static contact. The pair of contacts is called a normally open contact: the button is pressed, the normally closed contact is open, the normally open contact is closed, and the button is released. Restore the original working state under the action of the return spring
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