4 IMPORTANT APPLICATION INFORMATION
4.1 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 condi-
tions. If the motor is oper-
ated in this manner for an
extended period of time, it
is recommended that the
unloaded motor current be
checked from
2 – 15 Hz (60 – 450 RPM)
to ensure motor current
does not exceed the
nameplate rating. If the
motor current exceeds the
nameplate rating, the
Boost value may have to
be decreased (see
Function No. 3.11). 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 8.
If external fan cooling is provided, open ventilated motors can also achieve an extended speed
range at full rated torque. A box fan or blower with a minimum of 100 CFM per HP is recommend-
ed. Mount the fan or blower so the motor is surrounded by the airflow. See Figure 9.
4.2 ELECTRONIC MOTOR OVERLOAD PROTECTION – The drive contains Modified I
2
t Overload
Protection.* Part of this function consists of a Current Limit (CL) circuit, which limits the drive cur-
rent to a preset level of 160% of the Motor Nameplate Rated Current setting. The factory setting
for motor nameplate current is the drive rated current, which must be set to the actual
motor nameplate current (see Important Application Information (Item 2), on page 4). See
Table 3, on page 10. Also see Function No. 0.01, on page 32.
Standard I
2
t is undesirable because it causes nuisance tripping. It allows a very high motor current
to develop and will turn the drive off after a short period of time. KB’s RMS Current Limit Circuit
avoids this nuisance tripping while providing maximum motor protection.
16
FIGURE 8 – MAXIMUM ALLOWED MOTOR TORQUE VS. SPEED
FIGURE 9 – OPEN VENTILATED MOTOR WITH EXTERNAL FAN COOLING
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