Explosion-proof electrical structure design features 1 design of the shell
Cases for portable, intrinsically safe instrumentation are sometimes plastic and sometimes metal. When the plastic shell is selected, in order to ensure that the plastic shell does not accumulate dangerous static electricity when it works normally, its surface resistance must not exceed 1*109Ω. Plastic housings should be subjected to impact tests and thermal stability tests.
Electrical equipment that generates sparks, arcs or dangerous temperatures during normal operation, Class I electrical equipment with power greater than 250W or current greater than 5A shall be connected to the main body of the equipment using a junction box. The junction box is specifically designed for the connection of cables or wires to electrical equipment. Parts. At present, explosion-proof type wiring is widely used for type I flameproof electrical equipment. The inner wall of the box junction box shall be painted with arc resistant paint. The explosion-proof joints on the junction box and the main body cavity shall be treated with anti-rust treatment, such as anti-rust oil.
In addition, for the explosion-proof electrical appliances, there must be a permanent Ex explosion-proof total mark and MA safety mark in the obvious place of its outer shell. In view of the phenomenon of violation of motor operation in underground coal mines in some localities, we have developed a QF40 type explosion-proof starter with a rated voltage of 380V and a rated current of 40A. The shell design is divided into a body cavity and wiring cavity. The shell is 3mm thick steel plate. Flameproof joint surface size and processing accuracy in line with GB3836.2 regulations. The external dimensions of the enclosure are 437mm*308mm and the enclosure protection class is IP54. There is a nameplate directly in front of the enclosure. The Ex logo is on the upper right corner of the nameplate. The explosion-proof logo dI (150°C). In addition, the nameplate, type, rated voltage, rated current, explosion-proof certification number, safety sign, Factory number, date of manufacture, etc.
2 circuit design
First of all, the design of the circuit of the explosion-proof electrical appliance should complete the electrical function of the electrical appliance, guarantee the correctness of the electrical principle. Second, the electrical clearances, creepage distances and insulation parameters of explosion-proof electrical appliances must meet the requirements of GB3836. For example, when developing the QF40 explosion-proof starter, the creepage distance of the terminal is designed to be no less than 16mm and the electrical clearance is not less than 10mm. The creepage distance between the electrical components and the assembly arrangement in the explosion-proof enclosure is not less than 16mm, and the electrical clearance is not less than 10mm. There is an internal grounding bolt in the explosion-proof wiring compartment. Explosion-proof electrical enclosures have external grounding bolts.
The maximum operating current and voltage of the intrinsically safe type steel string frequency meter under normal and fault conditions are not greater than the designed maximum allowable current: its creepage distance is 3mm, creepage distance under insulation coating is 1mm, The clearance is 3mm.
3 power supply design
Intrinsically safe type of explosion-proof electrical appliances The most common independent power supplies for portable electrical equipment are dry batteries and batteries. Both dry battery and battery power are resistive circuits, and the power safety parameters can be determined based on the minimum ignition current curve of the resistive circuit. According to the maximum voltage of the battery to find the corresponding minimum ignition current, and then divided by the safety factor value (2), that is, the battery design allows maximum safety current. The most severe discharge state of the battery is a direct short circuit of the battery. Therefore, explosion-proof electrical appliances should be based on the battery's maximum short-circuit current as a benchmark to measure the intrinsic safety performance of the power supply. If the maximum short-circuit current of the battery is greater than the design allowable value, the current limiting resistor must be added in series. In addition, the battery or battery is sealed together with the current limiting resistor to form an intrinsically safe component. Sealing materials are epoxy resin, silicone rubber, industrial paraffin and so on. For example, we have designed a specially designed intrinsic safety battery pack for the frequency measurement of steel strings, which is made up of four 5# rechargeable batteries connected in series. The current limiting resistor is made of Constantin wire and its power is 5.2W. The entire space of the battery box is filled with the epoxy resin glue, and the potting is firm.
There are many intrinsically safe electrical devices that are actually used in underground coal mines, and many are used to introduce rectified power supplies from the power grid. Because the input circuit is associated with the power grid, it is designed to be flameproof and intrinsically safe.
For the power supply of explosion-proof electrical appliances, when the upper power is cut off, the wiring is completed in the explosion-proof junction box to complete the electrical power supply connection work.
Cases for portable, intrinsically safe instrumentation are sometimes plastic and sometimes metal. When the plastic shell is selected, in order to ensure that the plastic shell does not accumulate dangerous static electricity when it works normally, its surface resistance must not exceed 1*109Ω. Plastic housings should be subjected to impact tests and thermal stability tests.
Electrical equipment that generates sparks, arcs or dangerous temperatures during normal operation, Class I electrical equipment with power greater than 250W or current greater than 5A shall be connected to the main body of the equipment using a junction box. The junction box is specifically designed for the connection of cables or wires to electrical equipment. Parts. At present, explosion-proof type wiring is widely used for type I flameproof electrical equipment. The inner wall of the box junction box shall be painted with arc resistant paint. The explosion-proof joints on the junction box and the main body cavity shall be treated with anti-rust treatment, such as anti-rust oil.
In addition, for the explosion-proof electrical appliances, there must be a permanent Ex explosion-proof total mark and MA safety mark in the obvious place of its outer shell. In view of the phenomenon of violation of motor operation in underground coal mines in some localities, we have developed a QF40 type explosion-proof starter with a rated voltage of 380V and a rated current of 40A. The shell design is divided into a body cavity and wiring cavity. The shell is 3mm thick steel plate. Flameproof joint surface size and processing accuracy in line with GB3836.2 regulations. The external dimensions of the enclosure are 437mm*308mm and the enclosure protection class is IP54. There is a nameplate directly in front of the enclosure. The Ex logo is on the upper right corner of the nameplate. The explosion-proof logo dI (150°C). In addition, the nameplate, type, rated voltage, rated current, explosion-proof certification number, safety sign, Factory number, date of manufacture, etc.
2 circuit design
First of all, the design of the circuit of the explosion-proof electrical appliance should complete the electrical function of the electrical appliance, guarantee the correctness of the electrical principle. Second, the electrical clearances, creepage distances and insulation parameters of explosion-proof electrical appliances must meet the requirements of GB3836. For example, when developing the QF40 explosion-proof starter, the creepage distance of the terminal is designed to be no less than 16mm and the electrical clearance is not less than 10mm. The creepage distance between the electrical components and the assembly arrangement in the explosion-proof enclosure is not less than 16mm, and the electrical clearance is not less than 10mm. There is an internal grounding bolt in the explosion-proof wiring compartment. Explosion-proof electrical enclosures have external grounding bolts.
The maximum operating current and voltage of the intrinsically safe type steel string frequency meter under normal and fault conditions are not greater than the designed maximum allowable current: its creepage distance is 3mm, creepage distance under insulation coating is 1mm, The clearance is 3mm.
3 power supply design
Intrinsically safe type of explosion-proof electrical appliances The most common independent power supplies for portable electrical equipment are dry batteries and batteries. Both dry battery and battery power are resistive circuits, and the power safety parameters can be determined based on the minimum ignition current curve of the resistive circuit. According to the maximum voltage of the battery to find the corresponding minimum ignition current, and then divided by the safety factor value (2), that is, the battery design allows maximum safety current. The most severe discharge state of the battery is a direct short circuit of the battery. Therefore, explosion-proof electrical appliances should be based on the battery's maximum short-circuit current as a benchmark to measure the intrinsic safety performance of the power supply. If the maximum short-circuit current of the battery is greater than the design allowable value, the current limiting resistor must be added in series. In addition, the battery or battery is sealed together with the current limiting resistor to form an intrinsically safe component. Sealing materials are epoxy resin, silicone rubber, industrial paraffin and so on. For example, we have designed a specially designed intrinsic safety battery pack for the frequency measurement of steel strings, which is made up of four 5# rechargeable batteries connected in series. The current limiting resistor is made of Constantin wire and its power is 5.2W. The entire space of the battery box is filled with the epoxy resin glue, and the potting is firm.
There are many intrinsically safe electrical devices that are actually used in underground coal mines, and many are used to introduce rectified power supplies from the power grid. Because the input circuit is associated with the power grid, it is designed to be flameproof and intrinsically safe.
For the power supply of explosion-proof electrical appliances, when the upper power is cut off, the wiring is completed in the explosion-proof junction box to complete the electrical power supply connection work.
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