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4.3 MOTOR WITH EXTERNAL FAN COOLING
Most totally enclosed fan-cooled (TEFC) and open ventilated 3-phase AC induction
motors will overheat if used beyond a limited speed range at full torque. Therefore, it
is necessary to reduce motor load as speed is decreased.
Note: Some fan-cooled motors can be used over a wider speed range. Consult the
motor manufacturer for details.
WARNING! Some motors have low speed characteristics which cause
overheating and winding failure under light load or no load conditions. If the motor is
operated in this manner for an extended period of time, it is recommended that the
unloaded motor current be checked from 1 – 5 Hz (30 – 150 RPM) to ensure motor
current does not exceed the nameplate rating. Do not use motor if the motor
current exceeds the nameplate rating.
It is recommended that the drive be used with Inverter Duty or TENV
motors.
Inverter duty and most totally enclosed non-ventilated (TENV) motors can provide full
rated torque over an extended speed range without overheating. See Figure 3.
FIGURE 3
MAXIMUM ALLOWED MOTOR TORQUE vs. SPEED
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