Explosion-proof electric motors: types and description

Explosion-proof electric motors are used in environments where there are flammable gas and steam-air mixtures. Often these are refineries, chemical and gas industries. The materials of manufacture of such devices are characterized by high strength and have a shell impermeable to explosions, due to which the resistance to damage from outside is guaranteed.

Device

Explosion-proof motors are completely hermetic installations. They are cooled by fans, which pump air from the outside onto the ribbed surface. Often the material of construction is cast iron and welded sheet steel.

The engines have bearings that are permanently lubricated. Periodicity of lubrication must be strictly observed. If the bearings in the engine are sealed, that is, do not require lubrication, it is necessary to monitor the operating temperature with special attention, since any deviation will affect the life of the parts.

Conventional explosion-proof electric motors have free, gross ends of elongated shape, equipped with keyways. On the shafts there is a central hole with a thread that pulls or, on the contrary, retracts the shaft.

The junction box is mounted on the top of the motor, from the side where the explosion-proof forced ventilation unit for the electric motor is located. Engines with a box have six additional terminals for connecting different sensors, heaters and other. Adapters and other connecting elements may also be provided.

Conventional engines of this type operate at a frequency of fifty Hertz, a temperature of up to forty degrees and a height of more than a thousand meters above sea level. Voltage in this case is from 380V to 415V.

Engines for gases

The engines for gases are fire-resistant and have a conventional terminal box or a safety device. They are suitable for various environments and can be operated at a higher temperature regime.

The motors are connected by cable inputs, which have special quality standards. They must be carried out in such a way that the protective properties are not changed.

Without terminal box

If the junction box has no explosion-proof design, the enclosure is closed with a plate. Such engines can be:

• With a plate, armored cable and cable gland (the armored cable comes out in the clamped form from the plate, free cables are used to power the motor, also coming out with the clutch);
• With a plate and a conduit (in this case the casing is closed by a locking clutch at the cable outlet, the conduit leaves from it);
• With a plate and loose cables (the casing is also closed by a locking clutch, from which free cables emerge from the engine).

Without fan

The design may provide for ventilation, coupled with the motor. The fan is at a distance of at least five millimeters from the stationary parts of the engine. During operation, it must be ensured that the temperature regime is maintained throughout the operation.

Ventilation in the engine may be absent. There are some limitations: depending on the operating mode, the electric motor is switched to half capacity or a shorter period of time at normal power.

With additional ventilation

Cooling can also be provided by an additional engine, resistant to fire. In this case, a temperature sensor is connected , which is able to disable the mechanism in case of a violation of the mode.

For additional ventilation, the device must have a separate certification displayed on the rear of the motor.

For low temperatures

Such explosion-proof electric motors are capable of operating at temperatures from minus twenty to minus fifty degrees. They should have built-in anticondensation resistors with a capacity of fifty to two hundred watts. To properly use the mechanisms, the electrician must be arranged in such a way that it can drive the engine to a temperature above minus twenty degrees. If there are heating resistors, then they should be able to work when the engine is off.

All hardware is made of stainless steel, and if they need to be replaced, the quality should be not lower than the original. Of the same material are made fan caps, and cooling fans are made of aluminum.

When using a protective grease for couplings, a tool is taken into account and used, which fully corresponds to the temperature regime during operation. The cables used for electric power supply must also be suitable for operation in the temperature operating mode. The same applies to all engine insulation materials.

For power supply from inverter

If the explosion-proof motors are powered by an inverter, the temperature is controlled by thermistors in the winding. Their clamps must be connected to the disconnect relay, so that when the non-operating temperatures are reached, the mechanism is disconnected from the power supply. Such a device can only be disengaged by a manual method.

Before starting three-phase asynchronous explosion-proof motors with inverter, check the nominal values for compliance with the real one. The frequency converter is selected in such a way that the motor is not on voltage peaks and does not exceed the nominal value 2.8, otherwise the windings will very quickly become unusable.

Single-phase

The explosion-proof asynchronous electric motor can be single-phase. For this, a starting capacitor is used, which is placed inside the terminal box. If it is separated from the engine, it must provide an explosion-proof casing. Its characteristics are indicated on the engine.

The capacitor must be permanently connected to the winding and be able to be discharged immediately when the power is turned off. It is advisable not to bring his condition to the need of replacement, as it can cause a change in the characteristics of the engine itself.

Repair of explosion-proof electric motors

All repair work must be carried out according to the criteria specified in the instructions and manuals for the devices. It is desirable that they be conducted by the manufacturer. If the repair is done by a third-party organization, then the premises must be properly equipped, and the specialists must have all the technical knowledge of engine protection.

If the work is carried out with the components of explosion protection, then it is impossible to change the quality characteristics, for example, the dimensions of the connections, the ventilation type and the like. If any spare part is changed, then the original one must be installed in return.

The operations performed can be of different complexity.

• Repair repairs the defective parts for return to the usable form, according to the technical documents.
• Inspection involves testing the operability of the device, if, for example, he lain for a while in the warehouse without turning on.
• Maintenance is a planned inspection and replacement of necessary parts to keep the engine running.
• Improvement involves the replacement or addition of any part that does not contradict the prescribed standards.
• Modification involves changing material, uniform or functional characteristics.

Only the manufacturer of explosion-proof electric motors is entitled to make structural changes. After carrying out of repair work on the engine establish the tablet according to standards, indicating the name of the organization, the serial number of the company and the date of repair.