I. Ambient temperature
Explosion-proof electrical equipment operating ambient temperature is -20 °C ~ 40 °C, because all explosion-proof electrical equipment technical parameters are specified within this temperature range, if you want to change the operating environment temperature, be sure to mark the product name brand, while adjusting The parameter or test is determined to ensure the reliability of explosion protection. If the ambient temperature is -40 °C, many materials will produce cold and brittle phenomenon, affecting the strength of the material at low temperatures, so the assessment of the indicators when the material is increased to -40 °C, has determined whether it can be used.
Second, the surface temperature
Explosion-proof electrical equipment, like normal electrical equipment, will cause temperature rises during normal operation and will be delivered to the equipment enclosure as the surface temperature of the equipment. The enclosure of the equipment will directly contact the explosive mixture in the environment if the surface temperature is higher than the explosive gas mixture. Auto-ignition temperature can cause an explosion. Therefore, for explosion-proof electrical appliances according to different groups, see 4-1.
Table 4-1 Group Table for Maximum Surface Temperature of Explosion Proof Electrical Equipment
Temperature Group T1T2T3T4T5T6
Allowable maximum surface temperature °C45030020013510085
The maximum temperature of class I explosion-proof electrical equipment is T1. If considering the downhole coal dust accumulation, the surface temperature limit is 150°C.
How the maximum surface temperature is measured can be calculated using the following formula:
Equipment surface temperature = measured surface maximum temperature - is the test environment temperature + the specified maximum operating environment temperature
Three. Resistance to moisture and slight corrosion
Because coal mines are wet and not ventilated, factory flammable gases are slightly corrosive. In order to ensure the safe and reliable operation of explosion-proof electrical equipment for a long period of time, explosion-proof electrical equipment must be tested for resistance to moisture and slight corrosion. The assessment test is conducted in accordance with the requirements of GB2423.4 Basic Environmental Test Procedures for Experiment Db: “Thermal Test Methodâ€. After the test, the insulation resistance and dielectric strength of the explosion-proof electrical equipment are tested. The explosion proof of the explosion-proof electrical equipment cannot be corroded. phenomenon.
4. Shell material requirements
Explosion-proof electrical equipment shell material requirements, can use cast steel, cast iron, cast aluminum, other non-ferrous metals, plastics and other materials can also be used. Because plastics have cold brittleness, easy accumulation of static electricity, shortcomings such as easy aging and light aluminum alloy friction pile foundation will generate a lot of heat, so the selection of these two materials are made as follows:
(1) The shell made of light-aluminum alloy in a plastic case shall have a shell that is to withstand the GB3831, 212.1th impact test. After the test, there shall be no deformation or damage that may affect the performance of the explosion-proof electrical device;
(2) The enclosure shall withstand the thermal stability test of Clause 24.2 of GB383.1 and shall not affect the explosion-proof performance after the test.
(3) The plastic housing needs to meet the requirements of BG1410 "Test methods for the resistance and volume resistivity of fixed electrical insulation materials"
Surface resistance measurement, measuring the surface resistance value shall not be greater than 1 * 10? To effectively prevent surface electrostatic accumulation.
(4) Plastic enclosures require non-flammable or flame-retardant materials.
(5) Light aluminum alloy material tensile strength needs to reach 120N/mm?, magnesium content needs to be less than 0.5% (weight ratio).
V. shell fastener requirements
(1) The degree of reliability of the main body and cover of the explosion-proof electrical apparatus with bolts and nuts shall directly affect the explosion-proof performance. Therefore, the following requirements must be met;
(2) Nuts and bolts for fastening shall not be made of plastic or aluminum alloy materials;
(3) When tightening with bolts and impermeable screw holes, a thread allowance greater than double the thickness of the lock washer is required for the impermeable screw hole.
(4) The thickness of the shell impervious screw hole and the shell wall and bottom should be greater than 3 mm.
Six. Wiring insulation requirements
Because the wiring insulators are subjected to a certain amount of torque when they are manufactured and assembled and wired by the user, if the insulators have low strength, they are easily broken and damaged, resulting in leakage and short circuit accidents and affecting the explosion-proof performance. Because the insulator needs to withstand the torsion test of GB3836.1 low 23, the connection and insulation after the test shall not be reversed or damaged.
Therefore, the insulator needs to be made of a less hygroscopic material. It is not allowed to use phenolic plastic as insulation for anti-riot electrical equipment with a voltage higher than 127V.
Seven. Junction box and wiring connector requirements
The external cables of the explosion-proof electrical equipment are allowed to connect with the electrical equipment first, but when the explosion-proof electrical equipment is operated, spark, arc or dangerous temperature will be generated, and when the rated power of the class I electrical equipment is greater than 250 watts, the rated power of the class II electrical equipment is greater than At 1000 watt hours, it is necessary to use limits and methods to connect with the equipment. Junction box can be made of explosion-proof type, increased safety type, oil-filled type, sand-filled type, and positive pressure type explosion-proof type. But any form must be easy to connect.
Usually the junction box can be made explosion-proof, increased safety, oil-filled, sand-filled, positive pressure explosion-proof type. There must be a radius space suitable for the bending of the wire. There should be no connections (connecting terminals) inside the terminal box to connect cables and wires. The interior of the terminal box must also be evenly painted with arc resistant paint to prevent arc leakage from the enclosure. The connectors inside the terminal box should have sufficient mechanical strength, and the structure must ensure reliable connection. It is not allowed to generate sparks and overheating under vibration and temperature changes. Clearances and creepage distances between the connectors and the housing must meet the requirements of Table 4-2 and Table 4-3, respectively.
General technical requirements for explosion-proof electrical equipment
Note: a, b, c, d are the grading of the insulation material resistance to leakage, which can be determined by the test.
Eight. Introduce device requirements
The introduction device is also called the line-in device, which is the input and output of the external power supply and control circuit to the explosion-proof electrical equipment, which belongs to the enclosure of the explosion-proof electrical equipment. Since the introduction device is in direct contact with the external explosive mixture, the wiring is often opened by the worker. Therefore, the structure needs to be safe and reliable, and the following structures are provided for design reference.
(1) Sealing ring introduction device
The sealing ring introduction device is to compress the rubber elastic sealing ring, so that the cable and the wire are passed through the sealing ring and sealed on the inner wall of the introduction device so as to isolate the inside of the introduction device from the surrounding explosive gas mixture. There is a pressure plate type for pressing the seal ring, as shown in Figure 4-1 and the compression nut type, as shown in Figure 4-2.
Because rubber seals tend to age and break seals, the following requirements must be met to ensure that the structure is safe and reliable.
1 The two fastening nuts on the pressure plate of the pressure plate type introduction device need spring washers to prevent the pressure plate from loosening and affect the sealing performance.
2 Compression nut is the introduction device. When the outer diameter of the cable is less than 20mm, it can not be installed to prevent the cable from pulling out and relaxing the device, but the mobile explosion-proof electric device still needs this setting.
3 The compression nut is the introduction device. In order to prevent the rubber seal from being damaged when the nut is pressed, a metal gasket must be added between the compression nut and the seal ring. It must be ensured that the metal gasket cannot be embedded into the groove and affect the compression nut. Screw in.
4 Where rubber cable is used, the nut must be made bell-shaped to avoid scratching the rubber cable.
5 rubber seals are the key parts of the introduction device. The dimensions and structure of the rubber seal are specified in Figure 4-3, and the elasticity of the rubber seal is specified between 45 and 55 degrees Shore hardness. It also needs to withstand the aging test of Article 29 of GB3836.1.
(2) Casting-cured packing seal introduction device
When the cable diameter is too large or infrequently dismantled, the explosion-proof electrical equipment adopts a cast-cured packing seal introduction device, as shown in Fig. 4-4. The cable of the introduction device needs to use a rubber or plastic sheath, and the filler needs to be inflammable or flame-retardant. It is required to be filled without heating, and it can be cured at room temperature.
(3) Metal seal ring type introduction device
When the introduction cable is a metal sheath, a metal seal ring type introduction device is adopted, and the metal seal ring is used to achieve the seal and isolation of the surrounding explosive mixture by the line contact of the metal seal ring, as shown in Figure 4-5.
Nine grounding requirements
The grounding of the enclosure of the explosion-proof electrical equipment not only prevents personal electric shock accidents, but more importantly, it prevents sparks from leaking and causes the ignition of explosive gas mixtures. Therefore, the ground clearance and how to do the following regulations:
(1) The metal shell of the explosion-proof electrical equipment needs to be provided with a metal grounding bolt, and the table must be directly marked with a symbol “┴â€. The ground bolt cannot be replaced with a foundation bolt or a fastening bolt.
(2) Explosion-proof electrical equipment inside the junction box need to have a grounding bolt, and the table directly symbol "â”´", can not replace the grounding bolt with a fastening bolt or other power neutral.
(3) The grounding bolt needs to be made of stainless steel.
X. Wiring requirements
Accidents in explosion-proof electrical equipment are a major part of the cause of poor wiring. Reliable wiring reduces sparks and overheating. Therefore, the following requirements are placed on the wiring.
(1) Press directly on the wire with a bolt, as shown in Figure 4-6. Because this method is easy to cause the wire to break and cause electric spark.
(2) Pressing the wire only with the compression nut is not allowed, as shown in Figure 4-7. The wire should be pressed with a bow or bowl washer, or a special connector should be used to connect the wire, as shown in Figure 4-8. Add spring washers or flat washers to prevent loosening.
(3) If aluminum cables are used, copper-aluminum transition joints are required to avoid electrolytic corrosion.
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