1 Explosion-proof lighting fixtures are widely used in industrial enterprises where there is a mixture of flammable gases or explosive gases (or dust). These products are available in many varieties and specifications, but can be roughly divided into lighting, sign, signal, and portable; from light sources, they can be divided into incandescent, mercury, nano, halogen, and xenon lamps. And fluorescent lamps; from the structure is more numerous, generally hanging, hanging, wall-mounted, ceiling-mounted, portable, cantilever and so on. From the perspective of installation, explosion-proof luminaires can be realized from 30°9. In terms of power, it can range from tens of watts to hundreds of watts. The installation height starts from the ground to a few meters high. It can be said that explosion-proof lamps are the most productive and used products of all explosion-proof electrical products. The structure and shape of these products vary widely, but from the point of view of explosion-proof performance, it is basically explosion-proof type, and the shell material is mostly cast aluminum alloy, which can basically satisfy the users in the places below IIC. The need for lighting and display functions. Proper use of explosion-proof luminaires with advanced and reasonable structure, safe and reliable performance is an indispensable safety technical guarantee for the production of inflammable and explosive hazardous areas. In the process of explosion-proof testing, after the structural inspection of the explosion-proof luminaire products produced by some domestic manufacturers, the author believes that there are some problems in the structure of the explosion-proof luminaire products produced in China. The following is a brief introduction to the design requirements for non-mineral explosion-proof lamps.
2 Explosion-proof lamps commonly used explosion-proof type of explosion-proof principle
2.1 Flameproof enclosure "d" - an enclosure of electrical equipment capable of withstanding the explosive pressure of an internal explosive gas mixture and preventing internal explosions from propagating to explosive mixtures around the enclosure. Create a rugged enclosure for electrical equipment with a gap of less than the maximum experimental safety clearance for the corresponding flammable gas. If the flammable gas enters the enclosure and is ignited by the spark to produce an explosion, the explosive flame is confined within the outer casing and does not ignite the explosive mixture in the external environment of the outer casing, thereby ensuring environmental safety.
The flameproof enclosure must meet two basic conditions: 1 The enclosure has sufficient mechanical strength to withstand internal explosion pressure without damage and without permanent deformation affecting explosion-proof performance. 2 All seams and voids on the wall of the enclosure that communicate with the outside are less than the corresponding maximum experimental safety clearance.
Main explosion-proof measures: 1 flameproof shell material requirements; 2 gap length and width of the flameproof joint surface and surface finish requirements; 3 fasteners and tightening thread hole requirements; 4 transparent parts requirements; 5 adhesives and sealants Requirements; 6 grounding; 7 cable and conduit introduction devices; 8 interlocking or warning signs, etc.
National explosion-proof standard GB 3836.2-2000 "Electrical equipment for explosive gas atmospheres Part 2: Explosion-proof electrical equipment "d"" clearly stipulates the structure, experiments and signs of explosion-proof electrical equipment.
The mark of the flameproof enclosure is “dâ€. For example, the explosion-proof mark of an explosion-proof motor is Ex d IIB T4. Among them, Ex means explosion-proof, d stands for flameproof type, IIB stands for factory equipment class IIB, T4 stands for equipment Temperature group T4, that is, the surface temperature of the equipment does not exceed 135 °C.
2.2 Increased safety type “e†– measures are taken to improve the safety of equipment that does not generate sparks, arcs or may ignite explosive mixtures under normal operating conditions to avoid normal and approved overload conditions (including motor stalls) Condition) Electrical equipment in which these phenomena occur.
The safety-enhanced electrical equipment does not have an explosion-proof enclosure and protection medium. It adopts comprehensive safety measures: 1 limiting the type of equipment; 2 electrical clearance and creepage distance are relatively large; 3 good insulation materials; 4 specifying conductor connection ; 5 to reduce the temperature rise; 6 to improve the degree of protection of the enclosure; 7 with appropriate protective devices.
National explosion-proof standard: GB3836.3-2000 "Electrical equipment for explosive gas atmospheres Part 3: Increased safety type "e"" clearly stipulates the structure, experiment and signs of increased safety electrical equipment.
3 explosion-proof lighting selection requirements
The selection of explosion-proof luminaires should be based on the type and area of ​​the explosion hazard location and the level and group of explosive mixtures present in the site. The following conditions should be met when selecting explosion-proof luminaires: (1) Select the appropriate type of electrical explosion protection to meet the hazardous area classified by the hazardous location; divide the hazardous location into different areas according to the frequency and duration of the explosion environment. The gas field is divided into three areas: Zone 0, Zone 1, Zone 2. Zone 0: A site where explosive mixtures in an explosive atmosphere occur as gases, vapors or mists or for long periods of time. Zone 1: A location in an explosive atmosphere that may be an explosive mixture of gas, steam or mist in normal operation. Zone 1 is a typical application site for explosion-proof electrical equipment. Zone 2: In normal operation, explosive mixtures in the form of gases, vapors or mists are unlikely to occur in explosive atmospheres, and if they occur, they are only occasional and short-lived. The dust site is divided into three areas: Zone 20, Zone 21 and Zone 22. Zone 20: Combustible dust continuously or frequently occurs during normal operation, in an amount sufficient to form a flammable dust-like air mixture and a location and container interior that may form an uncontrollable and extremely thick dust layer. Zone 21: During normal operation, there may be a place where the amount of dust is sufficient to form a flammable dust and air mixture but not zoned into Zone 20. This area includes locations where flammable concentrations of flammable dust are present in the air mixture where there is direct or adjacent dusting, where dust is present and under normal operating conditions. Zone 22: Under abnormal conditions, flammable dust clouds occasionally appear and are only present for a short period of time, or where occasional accumulation of flammable dust or the presence of a dust layer and a flammable dust-air mixture but not zoned into Zone 21. If it is not guaranteed to exclude flammable dust accumulation or dust layer, it should be divided into 21 zones.
(2) The level and temperature group of explosion-proof electrical equipment should be selected according to the types of flammable and explosive gases or dusts that may exist in a hazardous environment;
(3) is to consider the impact of other environmental conditions on explosion-proof performance (for example: chemical corrosion, salt spray, high temperature and high humidity, sand and rain, or vibration); 1 class II electrical equipment, the highest surface temperature group temperature group highest surface Temperature, °CT1 450 T2 300 T3 200 T4 135 T5 100 (4) is the speciality to ensure the installation and maintenance; (5) is to choose the product with the explosion-proof certificate and the corresponding national certification.
According to the above requirements, the type of explosion-proof lamps selected for explosion-proof lamps should be determined according to the regional level and scope of the explosive gas environment. For example, explosion-proof lamps must be used in Zone 1; fixed lamps in Zone 2 can be explosion-proof and increased in safety. Mobile luminaires must be explosion-proof. The level or group of selected explosion-proof luminaires should not be lower than the level and group of explosive mixtures in an explosive atmosphere. At the same time, the impact of the environment on explosion-proof lamps should be considered, and the requirements of various environments such as ambient temperature, air humidity, corrosion or polluting substances should be met. The degree of protection and corrosion resistance of the luminaire should be selected according to different environmental requirements. Especially in the presence of corrosive gases in explosive atmospheres, it is important to choose a luminaire with appropriate corrosion protection. The explosion-proof structure selection of lamps for common explosive gas environments is as shown.
4 explosion-proof lighting design requirements
4.1 Explosion protection luminaire protection requirements
1 The luminaire must have transparent parts. The requirements for the transparent parts are: a. It can withstand the test of GB3836.1 thermal shock test and impact test; b. It is not allowed to make threaded structure.
The luminaire should be set to open the interlock of the transparent part after disconnecting the power supply, or replace it with a warning sign with the words “open the cover after the power is turned offâ€. I "Threaded explosion-proof lamp holder" requirements. Between the entrance cavity of the luminaire and the light source cavity, it must be separated by a reflector or other insulation measures. The connector that is fully connected to the lamp holder must be marked with a symbol "0". The metal protection mesh and the outer casing of the luminaire must be securely fixed. The mesh area and the mesh size must meet the requirements.
2 The requirements for Class II portable luminaires are: a. Each component shall be made of a material that is sufficiently resistant to chemical, mechanical, and battery dielectric corrosion. b. The outer casing and the protective net shall be made of a metal material that does not cause a dangerous spark due to impact and fall, or may be covered with a safety material. c. The distance between the transparent piece and the bulb, when the lamp power is less than 3W, it shall not be less than 3mm. When the power is not less than 3W, it shall not be less than 5mm.d. The distance between the transparent part and the protection net shall not be less than 5mm. The mesh area shall not exceed 2000mm2.e The pull-in cable of the luminaire's lead-in cable that applies a 15 kg force under clamping conditions must not be pulled out. f. The luminaire can withstand the drop test specified in the relevant provisions of GB3836.1.
4.2 The electrical structure of the explosion-proof lamp cavity must meet the requirements of two aspects:
1 In normal or abnormal work, it will not cause unsafe factors for people and the surrounding environment. 2 Provide excellent electrical parameters, ensure the photoelectric parameters of the light source, facilitate the start of the light source, do not affect the life of the light source, and let the light source achieve maximum efficiency.
The electrical structure of the explosion-proof lamp cavity mainly includes the following contents: (1) Electrical components The electrical components should meet the requirements of relevant national standards, can withstand the working temperature of the lamp cavity for a long time, provide electrical parameters matching the light source, and can be combined with explosion-proof lamps. The requirements for a specific type of explosion protection are consistent.
(2) The design of the wiring compartment wiring cavity size must meet the specific explosion-proof performance requirements, and should also be convenient for wiring, leaving room for the bending radius of the wire to ensure that the electrical clearance and creepage distance after correct wiring meet the relevant standards, the inner wall of the wiring cavity Arc-proof paint shall be applied to the inner wall of the metal casing which may cause sparks during normal work.
(3) Connector and terminal block 1 The connecting piece and the insulating sleeve and the terminal block should have sufficient mechanical strength to prevent damage when the wiring is installed. The wiring should be firm and reliable, anti-loose, and should not be loosened due to vibration, heat, thermal expansion and contraction of the conductor and the insulation. 2 The power connector should be designed so that after the stranded wire is wired, if the cable head is removed from the terminal, it will not touch the surrounding metal parts. 3 The terminal should take measures to prevent loosening to prevent the wire at the root of the terminal from being broken. It is not permissible to directly press the connecting wire with the screw head, which is easy to damage the terminal. 4 Insulating sleeves should be made of materials with less hygroscopicity. For explosion-proof lamps with a voltage higher than 127V, phenolic plastic products shall not be used.
(4) Grounding 1 Connect the accessible metal parts to the grounding terminal permanently and reliably, in case these metal parts may become charged parts during the insulation problem, causing electric shock and sparking. 2 Internal and external grounding shall be provided in the wiring cavity and the outer casing of the explosion-proof luminaire. The grounding terminal shall be provided with the grounding symbol “â€. Portable and portable luminaires are not provided with external grounding. The protection against electric shock is Class II and Class III luminaires without grounding terminals. 3 The diameter of the inner grounding screw should be the same as that of the connecting bolt. The outer grounding screw should be no smaller than M6-M8. The grounding screw should be made of stainless steel or stainless steel surface, and the contact surface is bare metal surface. The screws are tightened after tightening. 4 The ground connection should be low resistance. The grounding resistance must not exceed 0.5 Ω from any metal parts accessible to the ground terminal. 5 The grounding wire shall be a yellow-green two-color insulating conductor.
The grounding connection should be at least securely connected to one wire, see the cross-sectional area of ​​the wire.
The working temperature of the relevant components measured during operation is 25 °C, the insulation of the components in which the live parts are fixed, the test temperature is at least 125 °C, and the test temperature of the insulation of other components is at least 75 °C.
3 resistant to burning and anti-open flames. The insulating material of the fixed live parts shall be able to withstand the needle flame test, and the test flame shall be applied to the sample for 10 s.
After removing the test flame, the self-sustaining combustion time should not exceed 30 s.
4 resistant to scratches. The classification of the insulating material by the comparative tracking index (CTI) is listed, and the tracking index is measured according to the provisions of GB/T4207. Inorganic insulating materials, such as glass and ceramic materials, have no leak marks, so there is no need to determine their CTI and are classified as Class I by convention. Shown is the classification of the tracking index of common insulation materials compared to the tracking.
5 end
In short, in the selection of explosion-proof lamps, it must be clear in which hazardous area the luminaire is to be used, and then select the appropriate explosion-proof type, the level or group of selected explosion-proof lamps and the level of explosive mixture that should not be lower than the explosion-hazardous environment. And group. When designing the lamp housing, it should first distinguish its role in the flameproof enclosure, whether it is only for fastening, or both fastening and explosion-proof. The content discussed in this article is for reference only. We must also carry out the selection and design of explosion-proof lamps in accordance with the relevant national standards.
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