Motors enclosures

Except for areas with fire or explosion hazards (hazardous areas), motor enclosures are designed to provide protection to the internal working parts. The development or improved insiilating materials and finishes has affec ted the required degree of protection and consequently the design and classification of enclosures. Examples of several types of enclosures are shown in Fig. 29-4. 

FIG. 29-4 Examples of open dripproof, totallv enclosed fan-cooled, and weadier-protected motor enclosures, (Pliolo cowiesij of R/ linnco Eloclnc Coinynmj, Clovolmuf Ohio.)... 

Fire or explosion hazards require special motor enclosures. Hazards include combustible gases and vapors such as gasoline dust such as coal, flour, or metals that can explode when suspended in air and fibers such as textile lint. The land of motor enclosure used depends on the type of hazard, the type and size of motor, and the probability of a hazardous condition occurring. Some available enclosures are explosionproof motors, which can withstand an internal explosion force-ventilated motors cooled with air from a safe location and totallv enclosed motors cooled bv air-to-water heat exchangers and pressurized with safe air, instrument air, or inert gas,... 

Figure 1.18(c) Large SPDP squirrel cage motor (enclosure IP 12) (Cooling system ICOA1)... 

Today s standard motor enclosure for indoor applications is the open, drip-proof enclosure for induction and high-speed synchronous motors. For large motors, open, drip-proof construction is available up to about 20,000 hp and is used for squirrel-cage, synchronous, and wound-rotor motors. 

The selection of the motor enclosure type involves not only economics but also assessment of two factors area hazard classification and other area operation conditions. 

The compressor or blower installation in a typical refinery or chemical process unit is not out-of-doors completely. Some form of shelter often is provided, ranging from only a roof to a completely closed building. When process equipment such as a centrifugal gas compressor, which is not hazardous in normal operation, is present in the shelter, the hazard classification depends on the extent to that which the shelter restricts ventilation. The extent of the shelter provided determines the area classification and the type of motor enclosure that should be applied. 

Motor enclosure types for compressor service under shelters are applied as follows ... 

Figure 8 18. Compressor driven by an electric motor through a speed increasing gear. The motor enclosure is a WP2. (Courtesy ofA-C Compressor Corporation)...

This chapter gives primary attention to the commonly used general-purpose alternating current motors, although others are noted to acquaint the engineer with the variety of motors, motor enclosures, and mechanical drive turbines available and sometimes used in the chemical and petrochemical industries. Because direct-current motors are not frequently used in the process industries (other than in heavy-duty processes), they are not examined further in this chapter. 

After an area classification has been established, then anelectrical equipment, instruments, and wiring must adhere to that classification. Therefore, some motor enclosure types would not be electrically acceptable for specific area classifications. 

Table 14-9 summarizes tJie more common motor enclosures by types and environment. 

Tables 14-lOA and 14-1 OB identify motor enclosures associated with applications.

Energy Efficient (EE) Motor Designs, 628 NEMA Design Classifications, 630 Classification According to Size, 630 Hazard Classifications Fire and Explosion, 631 Electrical Classification for Safety in Plant Layout, 647 Motor Enclosures, 649 ... 

Motor enclosures for outdoor use are NEMA weather-protected Type II, totally enclosed, fan-cooled, or drip-proof with weather protection. Motors of the latter type are widely used. Not only are they less expensive than the other types, but they also have a service factor of 1,15. The above enclosure types are all suitable for the Class I, Group D, Division 2 classifications usually encountered. 

Gas boosters may be fitted with motor enclosures or designed to operate at lower rotating speeds. Alternatively, they may be housed in an acoustic enclosure within the boiler house. The booster and drive unit can be supplied with anti-vibration mountings to isolate it from the floor or steelwork and flexible bellows fitted to the gas inlet and outlet connections. 

Clearly the cost increments beyond the basic drip-proof motor enclosures are severe, and may need to be balanced in large sizes against the cost of isolating the equipment in pressurized buildings away from the hazardous locations. 

Motor enclosure Open drip proof Totally enclosed. . Explosion proof ... 

Motor enclosure (circle one) drip proof, TEFC, explosion proof, other... 

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