Fan-cooled motors

Inlet pipe-circulation The coolant flows to the machine through inlet pipes from a source other than the surrounding medium and then freely discharges to the surrounding medium (as in the use of separately driven blowers) 1 Self-circulation Movement of the coolant is normally through a fan mounted on the rotor shaft, like a normal fan cooled motor (Figures I.l8(a)-(d) and 1.19(a) and (b)... 

For in-house correlations, the cost of electric motors should be correlated vs. horsepower with voltage, speed, and type of construction as correction factors or parameters. Correction factors for explosion proof or open drip-proof housings could he developed if most of the data is for TEFC (totally enclosed fan cooled) motors. Similarly, correction factors could be developed for 1,200 rpm and 3,600i pm with l.SOOrpm as the base. 

Totally enclosed fan-cooled motors are used where moisture or dirt is prevalent (protects the motor). 

Probably the most commonly found machine is the totally-enclosed, fan-cooled motor (TEFC). The motor winding is totally enclosed in the motor housing which is usually ribbed on the outside. A fan is mounted on the shaft external to the housing and 20 is protected by a shield. This fan blows air over the casing... 

Totally enclosed fan-cooled motors are cheaper than totally enclosed machines of the same output and are, to a certain extent, self-cleaning as the air-flow over the body shell from the external fan prevents the build-up of the dust. 

In addition to fan speed, the operating temperature of the motor is determined by how effectively the heat generated in the motor can be conducted to surfaces that are in contact with the cooling medium (generally air) and the ability to transfer this heat via convection to the cooling medium. In a conventional totally enclosed fan-cooled motor the heat must be transferred from the laminated steel... 

Totally enclosed motors offer the greatest protection against moisture, corrosive vapors, dust, and dirt. Totally enclosed fan-cooled (TEFC) motors are the obvious choice rather than weather-protected below 186.5 kW (250 hp). Their internal and external ventilating air are kept separate external air never gets inside except for the small amount that enters by breathing. 

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.)... 

The choice for severe applications below 250 hp is the totally enclosed fan-cooled (TEFC) motor (see Figure 7-1). TEFC motors separate the internal and external ventilating air. Breathing is the only way external air ever gets inside. At some size above 250 HP, manufacturers presently switch from a rib-cooled to an exchanger-cooled motor for totally... 

TEFC - Totally Enclosed Fan Cooled where the shaft extends from both ends with a cooling fan attached to one with a shroud that directs air over strategically located cooling fins. This motor is m.ore commonly used when the motor is outside the air stream as when driving a gear box with a drive shaft or on blow-through towers. 

Standard Open or Totally-Enclosed Fan-Cooled (TEFC) generators and motors are acceptable in Division 2 areas if they do not contain brushes or other arcing contacts or high-temperature devices. Three-phase TEFC motors are acceptable in Division 2 locations, but singlephase motors usually contain arcing devices and are not acceptable... 

Type and specifications on fan driver, gear types, pow er voltage, phase, cycles. Motors should at least meet specifications equivalent to totally enclosed, fan cooled, or if in explosive hazardous area, TEFC Class I, Group D (except this not acceptable in hydrogen or acetylene atmosphere). Due to moisture conditions around this equipment, it should be protected against moisture penetration and corrosion. 

Figure 14-2A. Alternating current (AC) induction motor cross-sectional view of 220/440V, 3-phase, 60-cycle, totally enclosed fan-cooled standard motor. (Used by permission Reliance Electric Co., Div. Rockwell Automation.)...

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. 

Where evaporative condensers and water cooling towers have only one fan (or fan drive motor), coarse control can he effected hy on-off switching. The time lag will then depend on the mass of water in the circuit, and the sensing element needs to have a wide differential to prevent frequent motor starts. Towers should have thermostatic control of the fan to prevent water freezing on the packing in winter. 

Air-conditioning, having the air cooling coil with drip tray under, expansion valve, fan and motor, air filters, inlet and outlet grilles. They may also include dampers and duct connections for return and fresh air, heaters, humidifiers and various controls. 

IEEE 841, Standard for petroleum and chemical industry— Severe duty totally enclosed fan-cooled (TEFC) squirrel cage induction motors — Up to and including 370 kW (500 hp). )... 

Motors shall be squirrel cage induction type with (totally enclosed, fan-cooled) (encapsulated) (splashproof) enclosure and roller-type bearings with NEMA Class A insulation. Motors shall be (single... 

Caution needs to be taken with local pressure variations of the environmental atmosphere. A well-known example is the outlet side of an external cooling fan of a surface-cooled motor or generator (see Fig. 6.15). At this point, the environmental potentially explosive atmosphere shows an increased pressure, which shall be overcompensated by an adequate internal overpressure. The p-standards ask for a minimum overpressure of 50 Pa (=0.5mbar) for Group I p-apparatus or Group II p-apparatus in zone 1. 

Table 6.22 Comparison of a non-explosion protected motor with (E)Ex eh design (rated synchronous speed 1500 min-1, frame number 132,50cps, totally enclosed/fan cooled) (by courtesy of Loher GmbH, Ruhstorf/Germany)...

Take-off Detailed quantity count of work components cubic yards, tons, feet, etc. TEFC Totally enclosed fan cooled. Term applied to electric motor. 

Electric motors select synchronous for low speed usual application for either synchronous or induction 500 to 2100 rpm 150 to 500 kW. Usually use total enclosed Fan cooled (TEFC) enclosure, efficiency 84 to 95%. 

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