Introduction to basic knowledge of explosion-proof motors
Release time:
2023-07-07 14:36
Source:
network
1. Explosion proof terminology
1.1 Explosion proof electrical equipment: Electrical equipment that, under specified conditions, will not cause ignition in the surrounding explosive environment.
1.2 Explosive mixture: A mixture of combustible gases, vapors, mist, dust, or fibers with air between the upper and lower limits of explosion.
1.3 Maximum surface temperature: The maximum temperature reached by any component or surface of electrical equipment that may ignite an explosive environment when operating under adverse operating conditions within the specified range.
1.4 Temperature group: The group of electrical equipment used in explosive environments divided by their highest surface temperature.
1.5 Ignition temperature: The minimum temperature at which a mixture of combustible substances formed from gas or vapor forms with air is ignited by a hot surface under specified conditions.
1.6 Flash point: The lowest temperature of a liquid that releases a certain amount of vapor under a certain standard condition to form an ignitable vapor air mixture.
1.7 Minimum ignition current: The minimum current that can ignite a mixture in a specified spark test device under specified conditions.
1.8 Upper explosive limit: the concentration of combustible gas, vapor or mist in the air, above which an explosive gas environment cannot be formed.
1.9 Lower explosion limit: the concentration of combustible gas, vapor or fog in the air, below which no explosive gas environment can be formed.
1.10 Explosion hazardous area: the area where explosive gas environment occurs in large quantities or is expected to occur in large quantities, so that special measures are required for the structure, installation and use of electrical equipment.
1.11 Extreme temperature: The maximum allowable temperature of electrical equipment or its components. It is determined by the following factors:
○ Hazardous temperature for ignition of explosive gas mixtures
○ Thermal stability of structural materials.
Note: When considering the extreme temperature, the lower temperature should be taken.
1.12TE time: The time required for the AC winding to reach the rated operating stable temperature at the highest ambient temperature, from the start of passing the starting current IA until it reaches the limit temperature.
1.13 Positive pressure electrical equipment: Electrical equipment with a positive pressure casing.
2. Explosion proof type, level, category, and temperature group
2.1 The main types of explosion-proof motors include: explosion-proof type (d), increased safety type (e), non-sparking type (w), positive pressure type (n), and dust explosion-proof type (A and B types).
2.2 Classification of explosion-proof motors for explosive gas environment:
I: Explosion proof motors for coal mines
II: Factory explosion-proof motors;
Explosion proof motors for explosive dust environments. According to its casing, it can be divided into two categories: dustproof casing and dustproof casing.
2.3 Class I explosion-proof motors are not classified into temperature groups, and their maximum allowable surface temperature is 150 ℃ (when dust may accumulate on the surface) or 450 ℃ (when measures are taken to prevent dust accumulation)
Class II explosion-proof motors are divided into six temperature groups based on their maximum allowable surface temperature, T1 to T6, as shown in the table below:
Group ignition temperature ℃ Equipment allowable maximum surface temperature ℃
TI450<t450
T2300<t ≤ 450300
T3200<t ≤ 300200
T4135<t ≤ 200135
T5100<t ≤ 135100
T685<t ≤ 10085
2. Level: Because Class I explosion-proof motors are used underground in coal mines, and the explosive gas in coal mines is mainly methane, Class I equipment is not classified. Class II electrical equipment is classified into Class A, B, and C according to its maximum test gap or minimum ignition current applicable to explosive gas mixtures. The following table shows:
Level Maximum Test * * Gap (MESG) (min) Minimum Ignition Current Ratio (MICR)
IIA ≥ 0.9>0.8
IIB0.5<MESG<0.90.45 ≤ MICR ≤ 0.8
IIC ≤ 0.5<0.45
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