It uses a flameproof enclosure to isolate the electrical parts that may produce sparks, arcs and dangerous temperatures from the surrounding explosive gas mixture. However, the housing is not sealed, and the surrounding explosive gas mixture can enter the motor through the gap between the joint surface of each part of the housing. When contact with spark, arc, dangerous high temperature and other ignition sources in the shell may explode, then the flameproof shell of the motor will not be damaged or deformed, but also the explosive flame or hot gas through the joint surface gap, can not ignite the explosive gas mixture around.
When a three-phase asynchronous explosion-proof motor is connected to three-phase ac, it must complete the above two processes simultaneously. The windings leading to the three-phase ALTERNATING current produce a rotating magnetic field, for example, the 4-pole windings produce four closed magnetic loops. The closed loop passes through the air gap, through the rotor core loss, and then back to the stator core closure. The rotating speed of the magnetic field is N1 = 60F /p (r/min), which also supports the synchronous speed of the explosion-proof motor. F: power frequency, Hz; P: polar logarithm. Under the action of rotating magnetic field, rotor guide bar due to cutting magnetic field lines, induced current, completion rate of the first process; The rotor guide bar of the current should receive the pull of the magnetic field in the magnetic field, completing the second process. The rotor of the explosion-proof motor rotates because of the pull of the guide bar, and the speed is N. If n=n1, there is no cutting magnetic field line between the guide bar and the rotating magnetic field due to the relative static, so there is no induced current, the guide bar can not get the tension of the magnetic field, and the rotor can not rotate.
That is, cutting magnetic field lines, generating an induced current and being pulled around by a rotating magnetic field. Without this "different" can not work, so it is called asynchronous motor. Increased safety type motor working principle: it is in normal operation condition won't produce arc, spark or dangerous high temperature structure of motor, then take some mechanical, electrical and thermal protection measures, to avoid further in the normal or recognized by the overload in the condition of arc, the risk of fire or high temperature, thus ensuring its explosion-proof safety. Working principle of sparkless motor: this motor refers to the motor that will not ignite the surrounding explosive mixture under normal operating conditions, and generally will not occur ignition failure. Compared with increased safety type motor, in addition to the insulation dielectric strength test voltage, winding temperature rise, tE (at ambient temperature reached highest rated running after the final temperature of ac winding, since started by starting current meter to temperature rise to the limit of time) and starting current than not like increased safety type has special provisions, and other aspects to add safety type motor design requirements. Working principle of positive pressure motor: equipped with a complete set of ventilation system, there is no structural dead Angle inside the motor that may affect ventilation; Housing and piping are made of non-combustible material and have sufficient mechanical strength; Maintain sufficient positive pressure in the shell and main pipe relative to the outside atmosphere;
The motor must be equipped with safety protection devices (such as time relays and flow monitors) to ensure adequate air change, as well as automatic protection or alarm devices for pressure underpressure in the housing; The quick door or cover on the housing shall have an interlocking device with the power supply. At present, there is no unified positive pressure motor series products in China. Dust explosion-proof motor refers to the working principle of the motor housing design and manufacture according to the prescribed conditions, can prevent the dust into the motor shell or cannot completely prevent dust to enter, but it into the quantity does not interfere with the safe operation of the motor, and internal dust accumulation is not easy to produce fire danger, when using, also won't cause around with explosive dust mixture explosion of the motor.