Explosion-proof electric motors are used in environments where there are flammable gas and vapor-air mixtures. Often these are enterprises of the oil refining, chemical and gas industries. The manufacturing materials of such devices are highly durable and have a shell that is impervious to explosions, thereby guaranteeing resistance to damage from the outside.
Device
Explosion-proof motors are completely sealed units. They are cooled by fans, which pump air from the outside onto a ribbed surface. Often the material for the construction is cast iron and welded sheet steel.
Engines have bearings equipped with permanent lubrication. The lubrication intervals must be strictly observed. If the bearings in the engine are tight, that is, not requiring lubrication, it is necessary to carefully monitor the operating temperature, since any deviation will affect the life of the parts.
Conventional explosion-proof electric motors have elongated free shaft ends equipped with keyways. On the shafts there is a central hole with a thread that pulls or, conversely, retracts the shaft.
The junction box is installed on the top of the motor, on 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 various sensors, heaters and more. Adapters and other connecting elements may also be provided.
Conventional engines of this type operate at a frequency of fifty hertz, temperatures up to forty degrees and an altitude of more than a thousand meters above sea level. The voltage in this case is from 380V to 415V.
Gas engines
Gas engines are fire resistant and have a conventional terminal box or safety device. They are suitable for various environments and can be operated at higher temperatures.
Motors are connected by cable inputs, which have special quality standards. They must be designed so that the protective properties are not changed.
Without terminal box
If the explosion-proof electric motor does not have a junction box, the housing is closed with a plate. Such engines may be:
- with a stove, an armored cable and a cable gland (the armored cable comes out of the plate when the coupling is clamped, free cables are also used to power the motor, also coming out of the coupling);
- with a stove and conduit (in this case, the casing is closed by a lock sleeve at the cable outlet, the conduit departs from it);
- with a plate and free cables (the casing is also closed by a lock sleeve, from where free cables exit the engine).
No fan
The design may include ventilation coupled to the motor. The fan is located at least five millimeters from the stationary parts of the engine. During operation, you need to be sure that the temperature regime is observed throughout the work.
Engine ventilation may not be available. There are some limitations: depending on the operating mode, the electric motor is switched to half power or a shorter period of time is operating at normal power.
With additional ventilation
Cooling can be provided by an additional engine that is resistant to fire. In this case, a temperature sensor is connected , which is able to disable the mechanism in case of violation of the mode.
For additional ventilation to the device, there must be a separate certification displayed on the back 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 anti-condensation resistors with a capacity of from fifty to two hundred watts. To use the mechanisms correctly, an electrician must be arranged in such a way that it can bring the engine to a temperature above minus twenty degrees. If heating resistors are available, they should be able to operate with the engine turned off.
All hardware is made of stainless steel, and if they need to be replaced, then the quality should not be lower than the original. Fan covers are made of the same material, and cooling fans are made of aluminum.
When using protective grease for couplings, such a tool is taken into account and used that fully corresponds to the temperature regime during operation. The cables used for electrical power should also be suitable for operation in temperature conditions. The same applies to all engine insulation materials.
For power supply from inverter
If explosion-proof motors are powered by an inverter, the temperature is controlled by thermistors in the winding. Their clamps must be connected to the trip relay, so that when the temperature is not specified by the operating conditions, the mechanism is disconnected from the power supply. Such a device can only be tripped manually.
Before starting three-phase asynchronous explosion-proof electric motors with an inverter, check the ratings for compliance with real ones. The frequency converter is selected so that the motor is not at the peak voltage and does not exceed the nominal value of 2.8, otherwise the windings will become unusable very quickly.
Single phase
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, then it is necessary to 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 immediately discharge when the power is turned off. It is advisable not to bring its condition to the need for replacement, since it can cause a change in the characteristics of the engine itself.
Explosion-proof electric motor repair
All repairs must be carried out according to the criteria specified in the instructions and manuals for the devices. It is advisable that they be carried out by the manufacturer. If the repair will be done by a third-party organization, then the premises should be equipped accordingly, and specialists should have the entire set of technical knowledge about engine protection.
If the work is carried out with explosion protection components, then it is impossible to change the qualitative characteristics, for example, the dimensions of the joints, ventilation type and the like. If any spare part changes, then the original one must be installed instead.
The operations may be of varying complexity.
- Repair restores defective parts to return to serviceable condition, according to technical documents.
- Inspection involves checking the operability of the device, if, for example, it lay for some time in the warehouse without switching on.
- Maintenance is a planned inspection and replacement of necessary spare parts to keep the engine in working condition.
- Improvement involves the replacement or addition of any part that does not contradict the prescribed standards.
- Modification includes a change in material, uniform or functional characteristics.
Structural changes are only entitled to be made by the manufacturer of explosion-proof electric motors. After carrying out repair work, a plate is installed on the engine that meets the standards, indicating the name of the organization, the serial number of the company and the date of repair.