Protection types and explosion protection principles of explosion-proof certification

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This post was last edited by Zhongnuo Service Window 08 on 2021-9-6 09:40. I. The explosion-proof principles used in various types of explosion-proof electrical equipment at present 1. Gap explosion-proof principle (d): A housing is capable of withstanding the explosive pressure of explosive gas mixtures inside it, and it has one or several gaps in its metal surfaces that prevent the explosion from spreading to the explosive gas mixture surrounding the housing, thereby meeting the explosion-proof requirements. 2. Principle of explosion protection for energies below the ignition energy (ia/ib/ic): This principle effectively reduces the voltage, current, and values of energy-storing components in an electrical circuit. As a result, both the electrical sparks and thermal effects generated under normal operating conditions or specified fault conditions remain below the minimum ignition energy required to ignite the explosive gas mixture, thereby meeting explosion protection requirements. 3. Principle of explosion prevention by preventing ignition sources from coming into contact with explosive mixtures (p, o, q, m): Effective and reliable measures such as ventilation, filling with oil or sand, sealing, and airtightness are taken to isolate ignition sources from the surrounding explosive gas mixtures, thereby meeting explosion prevention requirements. 4. Enhancing electrical safety measures for electrical equipment under specific conditions – Explosion protection principles (e, n): For electrical equipment that does not generate electric sparks or thermal effects during normal operation, further improvements to electrical safety measures are needed to meet explosion protection requirements. II. Common types of explosion protection for environments with explosive gases
1. Flameproof electrical equipment (d)
Flameproof electrical equipment refers to electrical equipment equipped with a flameproof enclosure; its explosion protection marking is “d”. A flameproof enclosure is a type of explosion-proof enclosure that can withstand internal explosive pressures and prevent the spread of explosive flames to the surrounding environment. Due to respiration, explosive gas mixtures from the surroundings can enter the interior of electrical equipment enclosures. When the equipment generates electric sparks or dangerous high temperatures, these can ignite the explosive gas mixture inside the enclosure, resulting in tremendous explosive force and shock waves. On the one hand, the flameproof enclosure should be able to withstand internal explosion pressures without breaking ； On the other hand, the joint surfaces of the flame-proof enclosure should be able to prevent explosive flames from spreading outside the enclosure and igniting the surrounding explosive gas mixture. Therefore, flameproof enclosures must possess both explosion resistance and flameproof properties. 2. Increased safety electrical equipment (e) Increased safety electrical equipment refers to electrical equipment that does not generate arcs or sparks under normal conditions, to which additional measures are taken to enhance its safety level and prevent the generation of arcs, sparks, and dangerous high temperatures. Its explosion-proof mark is “e”. Increased safety electrical equipment adopts the following structural measures to enhance the safety of electrical devices: (1) Effective enclosure protection ； (2) Reliable connection of the circuit ； (3) Increase the electrical clearance and creepage distance ； (4) Limit the temperature rise of the equipment ； (5) Improve insulation performance. 3. Enclosed electrical equipment (m) (1) A type of explosion-proof design for electrical equipment. In this explosion-proof design, the sparks or overheated parts that could ignite explosive mixtures are enclosed within a composite, preventing them from igniting such mixtures under operating or installation conditions. The explosion protection mark is “ma/mb/mc”. (2) Composites are: thermosetting, thermoplastic, epoxy resins (cold-curing) or elastomeric substances, with or without fillers and/or additives; they are considered composites after curing. Composite materials should be capable, in terms of performance, of withstanding the operating temperatures as well as the temperatures generated during operation or in case of failure. (3) The potting process and requirements for the compound shall meet the standards. 4. Positively pressurized enclosure type electrical equipment (p) Positively pressurized enclosure type electrical equipment refers to electrical equipment that has a positively pressurized enclosure. The explosion protection mark is “p”. A positive-pressure enclosure refers to an enclosure that maintains the pressure of the protective gas inside at a level higher than that of the explosive gas environment surrounding it, thereby preventing external mixtures from entering. 5. “n”-type electrical equipment: “n”-type electrical equipment is designed for use in explosive gas environments in Zone 2; it was previously referred to as spark-free electrical equipment. Electrical equipment of this type shall not ignite the surrounding explosive gas environment under certain specified abnormal conditions during normal operation. Note 1: The requirements of this standard aim to ensure that failures that could cause ignition cannot occur. Note 2: An example of the specified abnormal condition is a light fixture with a faulty bulb. “N-type electrical equipment comes in the following explosion-proof types: Spark-free electrical equipment: nA; Spark-protection electrical equipment: nC; Restricted-breath enclosure: nR; Energy-restricted equipment: nL. 6. Sand-filled electrical equipment “q”: Sand-filled electrical equipment involves fixing the conductive components that could ignite explosive gases in appropriate positions and completely burying them in filling material to prevent ignition of the external explosive gas environment. This explosion-proof type cannot prevent explosive gases from entering the equipment and Ex components and being ignited by the circuit. However, due to the small gaps in the filler material, and the flame being extinguished as it passes through the pathways within the filler material, external explosions are prevented. The filler material is quartz or glass particles with a nominal value of 0.5–1 mm. The protective enclosures of electrical equipment shall be capable of withstanding specified external impacts and must have a protection rating of IP54 or higher. If the protection rating is higher than IP55, a breathing device should be added to the enclosure. Sand-filled electrical equipment is currently mainly used in electrical components that require good heat dissipation, such as ballasts for lighting fixtures. 7. Oil-immersed electrical equipment: The “o” oil-immersed explosion-proof type involves completely immersing the electrical equipment or its components in a protective liquid, thereby preventing the equipment from igniting any explosive gases present above the liquid surface or outside the enclosure. The protective fluid is a mineral oil compliant with IEC60296 or one that meets the following criteria: 1) A flash point of at least 300℃ ； 2) Flash point (closed cup) must be at least 200℃ ； 3) The dynamic viscosity of the protective solution measured at 25°C is at most 100 cSt ； 4) The minimum electrical breakdown strength is 27 kV. 5) The volume resistivity of the protective solution, measured at 25°C, is at least 1×1012 (25°C) Ω·m ； 6) The freezing point should be at most -30℃ ； 7) The protective fluid should not have an adverse effect on the properties of the materials it comes into contact with. The oil-immersed type structure is mainly used for cooling and fixing switches, controllers, etc. 8. Intrinsically safe electrical equipment (i) Intrinsically safe circuit: A circuit in which, under specified conditions (including normal operation and specified fault conditions), any electrical spark or heat effect generated cannot ignite the specified explosive gas environment. Intrinsically safe equipment: Electrical devices whose all internal circuits are intrinsically safe circuits. Associated equipment: Electrical equipment that is equipped with intrinsically safe circuits and non-intrinsically safe circuits, and whose design prevents the non-intrinsically safe circuits from having an adverse effect on the intrinsically safe circuits. It is generally a safety barrier, mainly used for instruments and equipment powered by the electrical grid.