Motor flameproof

Cage induction motor, flameproof enclosure, with terminal box in increased safety ... 

Figure 6.96 Double-rotor cage induction motor, flameproof, shaft and stator housing water cooled.

Special provisions are laid down in lEC 60079-0 and lEC 60079-1 for motors required for such locations in view of fluctuating degrees of humidity and temperature. Such locations are defined with a surface temperature limit of 150°C where coal dust can form a layer, or 450°C where it is not expected to form a layer. Otherwise, other details are generally the same as for flameproof motors type Ex d , according to lEC 60079-1. For variations in length of paths, gaps, widths, creepage and clearance distances, the reader should consult these Standards. 

Selection of fans and ducting for local extract must be more rigorous than for other systems. The fan must be capable of withstanding abrasion or corrosion from the contaminants, and if they are flammable must have a flameproof or out-of-air stream motor. The ducting also must be able to withstand abrasion or corrosion and must be fully sealed to prevent escape of contaminants within the building. For specialist applications such as fume cupboard extract, ducting and fans are often of plastic construction. 

The rule described above forms a basis for the secondary type of explosion protection, which results in the avoidance of ignition sources, e.g. by using either a flameproof enclosure of a commutator motor or the pressurized enclosure of a gas analyser, or by limiting the electrical values in intrinsically safe circuits. 

Type(s) of protection (abbreviations only, see Table 5.1). The dominant/main type of protection, followed by auxiliary types of protection, e.g. a flameproof motor with an e -type terminal box de, or a pressurized motor with an e -type terminal box and flameproof standstill heaters ped... 

In consequence, e motors, generators, transformers and reactors designed for the common rated supply voltages 500, 690 V and 1000 V are not suitable for very low power ratings. Smaller conductor diameters ask for another type of protection, e.g. flameproof enclosure - d -, encapsulation - m or powder filling - q -, the last mentioned restricted to transformers and reactors. 

Type of protection (stator-rotor part of the motor and exciter set in e , diode wheel in a flameproof enclosure) EEx ed IIAT3 Rated voltage 6kV Rated current 356 A Rated speed (20 poles, 50 cps) 300 min-1. 

Compared with rotating machines in increased safety - e there are no additional requirements for the windings or for the gap between stator core and rotor. The interior of flameproof motors and generators is identical... 

Figure 6.85 Longitudinal section drawings of flameproof cage induction motors, indicating the flameproof joints ...

In the second case, the bearings are exposed to the environmental atmosphere, i.e. they are no longer a part of the flameproof enclosure. They shall comply with the temperature limitations according to the temperature class. So, this solution is adequate for Group I application and for Group II, classes T1-T3, sometimes even for class T4. Table 6.31 indicates a somewhat higher weight of flameproof motors in comparison with e - or non-explosion... 

Figure 6.87 Longitudinal section drawing of a cage induction motor with identical frame number (132) to that shown in Fig. 6.86 flameproof motor. Type of protection EEx de IIC T4 (terminal box in e ).

A special problem for flameproof motors is adequate cooling. Obviously, internal cooling by ventilation is not possible. So, flameproof motors are... 

Figure 6.89 Longitudinal section drawing of a flameproof cage induction motor, with an annular-shaped air-to-air heat exchanger.

Figure 6.92 Total view of a water-cooled flameproof cage induction motor for coal mines.

Following the philosophy of explosion protection, the piping for cooling water shall be considered as empty and, as a part of the environment, filled with the gas-air mixture according to the grouping of the motor. (This is the practice when type testing such a motor for flameproofness.)... 

Figure 6.95 Flameproof cage induction motor, with integrated piggyback frequency convertor.

Submersible centrifugal pumps are powered by a cage induction motor due to its maintenance-free design. An example of a flameproof drive unit is... 

Figure 6.97 Flameproof brake motor, totally enclosed, non-ventilated. Motor and brake housing flameproof, terminal compartments according to increased safety. Motor ...

Figure 6.99 Submersible centrifugal pump with flameproof cage induction motor. Motor ...

Frequency convertors for motor drives with variable speed have shown reliability and cost reduction for some time. An example for application in coal mines is shown in Fig. 6.104. A frequency convertor with impressed current in the DC link is installed in two separated flameproof enclosures ... 

Rated voltage 1000 V Max. motor rated power 511 kW Cooling water cooled Dimensions Height x width x depth 1000 x 2860 x 800 mm3 Added volume of flameproof compartments 1.5 m3 Weight (total) 3700 kg Type of protection EEx de I. (b) Frequency convertor according to Fig. 6.104(a), doors of flameproof compartments opened. 

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