18
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 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 2 – 15 Hz (60 – 450 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 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 recommended. 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
current to a factory preset
level of 160% of the rated
drive current. The CL
Trimpot is used to
recalibrate the drive
current from 60% thru 200%. The Power Start™ circuit provides an overshoot function that allows
most motors to develop more than 200% of starting torque and breakdown torque.
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.
If the motor is overloaded to 120% of full load (75% of the CL setting), the I
2
t Timer starts. If the
motor continues to be overloaded at the 120% level, the timer will shut down the drive after 30
minutes. If the motor is overloaded to 160% of full load, the drive will trip in 6 seconds.
*UL approved as an overload protector for motors.
and TENV Motors
Inverter Duty
Maximum A
llow
ed
Mot
or T
orque
(%)
TEFC and Open Ventilated
Motors
Fan Cooled
100
60
70
80
50
30
40
10
0
20
90
Motor Speed (%)
40
0
20
60
80
100
Figure 8 – Maximum Allowed Motor Torque vs. Speed
Open Ventilated Motor
Fan or Blower
(100 CFM Min.
per HP)
Airflow
Figure 9 – Open Ventilated Motor with External Fan Cooling
Summary of Contents for KBAC Series
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