Basic knowledge of explosion-proof motors

Basic knowledge of explosion-proof motors

1. Model type of explosion-proof motor

Concept: The so-called explosion-proof motor refers to the motor that takes some explosion-proof measures to ensure that it can be used safely in explosion-hazardous places.

Explosion-proof motors can be divided into the following three types or their composite types according to their basic principles of meeting explosion-proof requirements:

1. Flameproof type, B type

A motor that does not cause an explosion of an external explosive mixture in the event of an explosion inside the motor. The motor casing has sufficient mechanical strength (high-grade cast iron, steel plate as the casing), so that it can withstand the explosion pressure and external force impact without damage; Structural parameters (gap and length) of the flameproof joint surface; requirements for junction boxes, wire inlet devices, etc.; control the temperature of the shell surface so that it cannot reach a dangerous temperature.

2. Increased safety type, type A

The sealing of the motor is better, and the protection level requirements of IP55 are adopted; the electromagnetic design should consider reducing the temperature rise; the time when the rotor reaches a dangerous temperature when it is locked, and is equipped with a self-control electrical device; improve the turn-to-turn, ground-to-ground and phase-to-phase tests of the winding insulation voltage; improve the reliability of conductor connection; control the minimum unilateral clearance of stator and rotor. In short, it prevents accidental sparks, arcs or dangerous temperatures from the structural and electrical aspects, thereby improving the safety of operation.

3. Positive pressure type, P type

An explosion-proof motor that injects positive pressure fresh air into the housing or fills it with inert gas (such as nitrogen) to prevent external explosive mixtures from entering the motor.

Scope of use: Flameproof and positive pressure types are suitable for all explosive hazardous places, and flameproof motors ( Type B ) are widely used in China. The manufacturing cost and price of the increased safety motor are lower than those of the flameproof type, and are only suitable for Zone 2 locations.

2. Classification of motors in explosive gas atmospheres

1. According to the classification of explosion sites

2. According to the type of explosive gas

3. Classified according to the natural temperature of the explosive gas

3. Explosion-proof signs of explosion-proof motors

1. Examples of explosion-proof marks for flameproof three-phase asynchronous motors:

ExDI   flameproof motor for coal mine

ExD IIBT4 factory IIBod T4 group such as: tetrafluoroethylene place

2. Examples of explosion-proof marks for increased safety three-phase asynchronous motors:

ExE IIT3   is applicable to places where the ignition temperature is T3 group flammable gas in the factory

4. Three certification requirements for explosion-proof motors

When the explosion-proof motor leaves the factory, the performance must meet the requirements of the technical conditions and standards, and it must also obtain the three certificates issued by the relevant departments of the state. The motor nameplate must indicate the three certificate numbers, namely:

1. Explosion-proof certificate

2. Explosion-proof motor production license number

3. Safety certification MA number.

There should be a red EX mark on the upper right corner of the motor nameplate and on the cover of the outlet box.