Problems in the design and manufacture of explosion-proof electrical appliances and explosion-proof lamps

Detailed introduction:

First, the overall design ideas of explosion-proof electrical products

1. Brief description

Class II non-mineral explosion-proof electrical equipment is used in petroleum, offshore petroleum, petrochemical, chemical industry and pharmaceutical industries (referred to as petrochemical industry). The flammable and explosive gases in the workplace of hazardous chemicals in these industries/ There are many kinds of steam, and the process equipments in production, storage and transportation are complex and changeable. There are many kinds of release sources, and it is difficult to analyze and judge the explosion risk factors. Therefore, the selection, installation and maintenance of explosion-proof electrical equipment are much more complicated than mine explosion-proof electrical equipment.

Explosion-proof electrical equipment is selected: one must meet the dangerous area classified by the dangerous place to select the corresponding type of electrical explosion-proof; the second is to select the level and temperature group of the explosion-proof electrical equipment according to the type of flammable and explosive gas/dust that may exist in the hazardous environment. The third 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); Fourth, to ensure the speciality of installation and maintenance; Certificate of conformity and products certified by the state.

2. Environmental requirements for explosion-proof electrical equipment applications

A. Explosive hazardous environment/workplace with flammable and explosive gas/vapor.

B. Explosive hazardous environment/workplace with flammable dust.

C. Environment/workplace where flammable and explosive gas/steam and flammable dust are present at the same time. Such places are more common in solid-state chemical products workshops and their transportation, packaging, weighing and coating process equipment. With the development of modernization, this situation will become more popular. Therefore, the selection of explosion-proof electrical equipment in such places has increasingly attracted the attention of design departments and petrochemical enterprises.

D. In the above three cases, there are also environmental/workplaces where corrosive media and other special conditions (high temperature, high humidity, low temperature, sand dust, vibration) are affected.

3. Selection of explosion-proof electrical equipment

According to the degree of explosion hazard, gas/vapor hazard sites are divided into: Zone 0, Zone 1 and Zone 2, and their division depends mainly on the release level of the release source (explosion hazard source). Of course, the structure of the building in the site, The ability of ventilation facilities and the natural factors of the site will have an impact on their division, and even have a great impact.

In the modern petrochemical project, the area of ​​the 2nd district accounts for more than 60%, and the area of ​​the 1st district accounts for about 20% to 30%; the old chemical enterprises generally account for 50% of the 1st and 2nd districts. Zone 0 sites are generally restricted to petroleum or chemical plants or to smaller areas of the discharge. For the 1st and 2nd districts, the company is generally willing to select the explosion-proof electrical equipment used in Zone 1 in order to improve the safety. If the application environment/location is outdoors or there are 2 areas with slight corrosion, dust and rain, it is often preferred to use explosion-proof electrical equipment with strong protection capability, for example: increased safety explosion-proof composite type "de", increased safety type "e ", "n" type, etc. In addition, in the temperature group, it is willing to choose a group that is higher than the ignition temperature of the applied environment gas.

For Zone 0 locations, explosion-proof electrical equipment can only be intrinsically safe with the “ia” rating. However, the International Electrotechnical Commission IEC60079-26 "Electrical Equipment for Explosive Gas Atmospheres Part 26: Structures, Tests and Marks for Class II Zone 0 Electrical Equipment" specifically specifies the electrical equipment used in Zone O, and the structural types in the regulations have been Not just the type of ia explosion protection.

At present, PCEC has begun to use IEC60079-26 for inspection and certification of special electrical equipment used in the environment of Zone 0. Fill the gaps in China's standards to meet the needs of the petrochemical industry.

In explosive places, chemical corrosion, salt spray and other special factors are often present. The impact of these factors will not only damage the electrical and mechanical properties of the equipment, but also destroy the explosion-proof safety performance of the equipment and shorten the explosion-proof of the equipment. The safety life makes the explosion-proof safety of the equipment uncertain. Therefore, when using explosion-proof electrical equipment in such places, it must be confirmed that it has the ability to resist these factors.

●Combustible dust refers to both flammable dust and conductive dust.

●Combustible dust refers to dust that may burn or smolder after mixing with air and form an explosive mixture with air at normal temperature.

● Conductive dust refers to dust, fibers or flying objects with a resistivity equal to or less than 1 × 103 Ω·m.

● Conductive dust is a dangerous dust. If it enters the insulation of the conductive parts in the outer casing of the electrical equipment, it will cause short circuit and malfunction of the circuit. Therefore, the conductive dust is likely to cause an ignition source inside the electrical equipment.

● The classification of flammable dust hazardous areas is similar to that of gas hazardous areas, and is divided into: 20, 21 and 22 areas.

● The pure dust hazardous area is not very large in stone chemical enterprises, mainly in coal chemical industry and granulation process. More common is the place where gas and dust coexist.

●Combustible dust hazardous environment Electrical equipment explosion-proof type is mainly used to protect the structure and limit the surface temperature protection structure (GB12476.1-2000), other explosion-proof types, such as the type of limiting ignition energy, there is no standard in China, However, the International Electrotechnical Commission has a special standard for this type (IEC61241-11:2005).

● For the above-mentioned equipment selection of dangerous places where gas and dust exist at the same time, it is necessary to select explosion-proof electrical equipment with double explosion of gas and dust. The explosion-proof grade should meet the characteristics of explosive gas and also meet the characteristics of flammable dust. This double-explosive-proof electrical product was only mass-produced by some domestic manufacturers in 2005. This year, the number of electrical equipment will increase significantly. It is expected that in the next three years, it will basically meet the types of electrical equipment used in such places. demand.

4. Quality awareness of explosion-proof electrical equipment

● Explosion accidents in the production of petroleum and chemical industries mainly include: leakage or explosion of reaction devices caused by high pressure and high temperature; mechanical impact, friction or static igniting explosion; electrical spark or high temperature ignition. Among them, sparks or high-temperature ignition accidents of electrical equipment account for a large proportion, and it is also the first equipment controlled and managed by countries all over the world, because the ignition of electrical equipment is not only due to its accident state or misoperation.

● Due to the decision of petroleum and chemical production process and facilities and environment, explosion-proof electrical equipment (except power generation, drag and analysis, and material parameter instruments) is basically auxiliary equipment. Therefore, some enterprises pay less attention to it and blindly pursue it. The profit indicator reduces the cost of purchasing auxiliary equipment, while ignoring the safety of people's lives and property, the quality of purchased equipment is poor, the explosion-proof performance is unstable, and even inferior products.

High quality explosion-proof electrical products are an important guarantee of safety

● High-quality explosion-proof electrical products are embodied in its electrical performance and explosion-proof structure design. Explosion-proof parameters and environmental indicators must meet the requirements of the application site, and can still have explosion-proof performance after installation, long-term use, maintenance and overhaul.

● To manufacture explosion-proof electrical products, it is necessary to strictly implement the relevant requirements of national standards and special requirements of the application environment.

● At present, explosion-proof electrical appliances and lighting products used in factories in China are generally subject to low safety margins due to many factors such as market competition and poor safety awareness.

● The so-called safety margin is: the product must not only meet the requirements of the corresponding standards, but also ensure that the explosion-proof performance cannot be invalid after installation, use and maintenance.

● A considerable part of the product is only to save raw materials, reduce costs, meet the basic requirements of the test sample to meet the standard, obtain the explosion-proof certificate, and ignore the user's explosion-proof performance failure during use.

Proper installation and maintenance to ensure explosion-proof safety

● Due to the structure and process characteristics of explosion-proof electrical, the guarantee of explosion-proof quality is greatly different from other industrial equipment.

As long as the quality of the general industrial equipment meets the requirements, the quality of the product can be guaranteed after installation and use.

Explosion-proof electrical equipment must not only ensure the safety and quality of explosion-proof in the manufacturing process, but also ensure that the installation, use and maintenance are proper, in order to truly achieve the purpose of explosion-proof. In this way, the quality of the explosion-proof electrical equipment manufacturing and the correct selection, installation and maintenance are guaranteed to be 50% important in their practical application. If the selection, installation and maintenance of explosion-proof electrical equipment are improper, the unsafe factors concealed are more dangerous than non-explosion-proof electrical equipment, which is easy to cause the user's paralysis.

Therefore, when manufacturing and designing, manufacturing companies must take into account the failures that users may have during use.

Establish the correct product design concept

● National standards are the basic guidelines for the development and design of Zui.

The development and design of a product is not only to meet the requirements of national standards and related standards, but also to take into account the failures that users may have during installation, use, maintenance and repair as far as possible from the safety interests of users. Improve product safety margins.

● The vitality and advancement of a product is mainly reflected in its superior performance and reliable work, followed by its practicality and appearance. The guarantee of explosion-proof safety performance is the basic moral concept of enterprise design and manufacture, and the design of explosion-proof safety must be realized around the former.

However, the guarantee of explosion-proof performance cannot fully meet the needs of the former, and sometimes it is impossible to achieve, and it is possible to abandon the development design.

● In development and design, it cannot be based on cost reduction, and product quality and safety margin should be considered.

Improve the level of explosion-proof electrical technology and correctly understand the standard

● To develop a design product, you should first fully understand the standard, not only the main terms of the standard, but also the details and annotations in the standard. When examining and inspecting, the inspection agency strictly enforces the standards and cannot arbitrarily waive certain clauses and test items in the standard.

Rational use of raw materials and electrical components and accessories

● To ensure the explosion-proof performance of the product under different environmental and operating conditions, the reasonable selection of raw materials is a very important factor. Especially non-metallic materials and adhesive and potting materials. For example: the flammability and flame ablation resistance of non-metallic d-type components; the illumination resistance of the e-shell (where the lampshade of the lamp (indicator) needs to be resistant to the light of its own light source), heat and cold resistance.

● Reasonable selection of electrical components and materials is also an important condition for ensuring explosion-proof performance. For example: the influence of heat and intensity caused by the short-circuit current of the e-type ammeter on the explosion-proof performance; the rational application of the e-type light source; the ballast heating of the e-tube type fluorescent lamp, the influence of the asymmetrical power and the special requirements of the lamp holder; Impact resistance of the lampshade; resistance to pull-out of the introduction device.

Reasonable structure and scientific process to ensure product reliability and stability

● Reasonable structural design can reduce the process links and achieve the standards.

E.g:

1) Consider the possible pressure overlap when the multi-cavity electrical connection between the d-type fluorescent lamp and the internal electrical components are arranged.

2) When the d-type electrical appliances and the transparent parts of the luminaire are combined with the metal parts, the IIA and IIB shall be made of metal-coated flame-resistant elastic gasket or metal gasket, or directly matched; IIC shall be glued. The fluorescent glass tube must be glued to the housing.

3) Large-diameter cable introduction device, reasonable use of anti-extraction device.

4) The wall thickness of the d-type outer casing and the reasonable use of the lacing, however, the use of the lacing does not completely equal the reduction of the wall thickness. In addition, care should be taken to avoid sudden changes in the design curve of the interior of the housing.

5) The d-type integrated luminaire should reasonably consider the reasonable layout of the starting components and reduce the influence of the temperature inside the light source cavity.

6) For appliances or lamps with d-type self-contained power supply (batteries or other energy storage components), short-circuiting of the battery should be considered, resulting in temperature rise and self-explosion.

7) Pay attention to the discharge of the energy storage component in the d-type housing and the delayed opening of the cooling element.

8) The internal live parts of the e-shell shall be protected.

9) Sealing rings for protection should take measures to prevent falling off.

10) e-type plastic foot fluorescent lamps should pay attention to the connection requirements between the lamp foot and the lamp holder.

11) The e-type lamp should consider the ballast heating caused by the aging of the lamp tube and the uneven pulse overheating during the limit life of the tube type fluorescent lamp, causing the lamp holder to burn out.

12) Reasonable selection of internal wiring terminals of e-type junction box and reasonable determination of the number of terminals.

13) Pay attention to the special requirements of the internal battery of the e-type product.

14) Non-metallic outer casing surface to avoid ignition of electrostatic charge generation, one of the following methods can be used:

A limits the surface resistance value;

B limits the surface area;

CSet the static warning sign.

15) Press-contact luminaire (wiring cavity thread structure) for IIC

The level should be increased again or the isolation seal should be used; the IIB level should consider whether the net volume of the chamber is less than 2 liters, otherwise it is the same as before.

In manufacturing, the process is the basis for ensuring product quality.

For the production of explosion-proof electrical products, after the design structure is reasonable, the production of the products depends on the process, equipment, personnel and quality assurance system.

The process is the basis of the production process.

E.g:

(1) d-type IIC electrical appliances or lamps thread explosion-proof and lamp pressure plate thread structure should pay attention to the precision of the matching and the quality of thread processing.

(2) Special consideration should be given to the welding method and process of steel plate welding products and the strength and thickness of steel plates. These products are rarely blown up during the strength test, but it is difficult to pass the internal ignition without the explosion test after the overpressure test.

(3) Pay attention to the preparation process and precision requirements of non-metallic material samples to prevent the dispersion and deformation of the sample properties.

(4) The internal electrical components or terminals of the d-type housing should be prevented from causing artificial multi-cavity during assembly, resulting in pressure superposition.

(5) The d-type outer casing, whether it is a sand mold casting outer casing or a pressure casting outer casing, is subjected to aging treatment to eliminate the casting stress and fully ensure the strength and parameter indexes of the outer casing.

(6) When formulating the gluing or potting process, consider their adhesion and strength to prevent the encased or glued parts, cables from being pulled off or pulled out by explosive strength.

(7) Explosion-proof products should be considered when assembling the torque of the bolts on the explosion-proof surface. At the same time, it is necessary to clearly indicate the torque requirements of the fastening bolts during installation and maintenance.