Discussion on safety measures in electrical design

2022-09-23
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Discussion on safety measures in the electrical design of explosion-proof workshop in chemical enterprises

in the production process of chemical enterprises, due to the use of a large number of volatile organic substances, some areas in the factory become explosion hazardous areas. The electrical design of the plant must treat explosion-proof safety as the primary factor of the design scheme with caution

therefore, it is necessary to study and consider various factors affecting safety, and fully consider various hazards that may occur in the process of production and maintenance, so as to improve the molecular weight and dispersion design level of explosion-proof plant in chemical enterprises and reduce the probability of explosion hazards due to electrical reasons

1 three basic conditions of explosion

1.1 release source

the location or location where substances that can form explosive mixtures can be released is called the release source. Closed containers and channels themselves are not regarded as release sources, but as release sources in case of accidents or spillage of explosive and combustible substances during normal operation. The release source shall be classified according to the frequency and duration of the release of flammable substances. For materials with explosion hazards, the most important thing is to strive to ensure that no spillage occurs

sometimes this release is inevitable, such as automatic metering or automatic analyzer. During normal operation, a small amount of combustible and flammable substances will also be released. Electrical equipment should be able to work normally in this state for a long time, and corresponding measures must be considered in the design so that it does not produce explosive mixtures

1.2 ignition source

cigarette butts, impact sparks, open flames, heat of chemical reaction, hot object surfaces, etc. can play the role of ignition and become ignition sources. The electric arc generated in the opening and closing process of electrical control equipment, such as light switches, magnetic starters, and the heat accumulation on the commissioning and running in surface of the electrical equipment table and the production line are all possible ignition sources. The most important thing in electrical design is to prevent ignition caused by electrical equipment

1.3 explosive concentration

explosive gases, vapors, dust, etc. must be mixed with air in a certain proportion to form explosive mixtures. This proportion is called explosive concentration. When the mixture concentration exceeds the upper limit of explosion concentration or is lower than the lower limit of explosion concentration, it cannot be ignited. In the dangerous areas of upper and lower limits, special attention should be paid to the lower limit, because the mixture below the lower limit may reach the lower limit of explosion concentration and be ignited at any time after accumulation. Therefore, all places where combustible substances may leak from the factory buildings of chemical enterprises cannot be ignored. The practice of release source and point has proved that the combustion source and explosion concentration constitute the three basic conditions of explosion, and the explosion cannot be achieved without any of them. Therefore, the explosion-proof measures in electrical design should be considered from these three aspects

2 several basic measures to improve electrical explosion-proof safety

2.1 do a good job in the selection of electrical equipment so that it does not become a source of ignition

in order to prevent the leakage of electric arcs and sparks and reduce the surface temperature of electrical equipment, the explosion-proof workshops of chemical enterprises often choose oil filled, explosion-proof, flameless, gas filled, positive pressure, increased safety electrical equipment. For example, transformers with nitrogen filling on the oil surface, transformers with non combustible liquid askarel as the cooling medium, sulfur hexafluoride switchgear using gas insulating gas, etc. Although the cost of these devices is high, they can effectively prevent the leakage of electric sparks

in recent years, the explosion-proof electrical appliance manufacturing industry has developed a non sparking explosion-proof electrical equipment, which does not produce sparks, arcs and dangerous temperatures in normal operation. The basic guarantee measures are to adopt new insulating materials, improve the insulation grade, prevent heat accumulation, and improve the safety of the equipment from the design and manufacturing level. For example, the allowable temperature rise of motor insulation winding resistance is 10 ℃ lower than that of other motors, and the absolute withstand voltage test voltage is 10% - 30% higher than that of other motors. Therefore, the non sparking equipment has the advantages of light weight, simple structure, convenient maintenance and so on. Due to the slow development of China's insulating material industry, the price of non sparking type has not decreased significantly compared with explosion-proof type, so it has not been widely used in engineering design, and many designs are still used to using explosion-proof equipment. In many complete chemical plants imported from China, non sparking electrical equipment has been widely used in technologically advanced countries such as Japan and the former West Germany. It is necessary for us to speed up our understanding of this kind of equipment and apply it to the electrical design of explosion-proof workshops in chemical enterprises as soon as possible

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