KB Electronics KBAC-48 - Manual (Page 13)

13
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 to-
tally enclosed non-ventilated
(TENV) motors can provide
full rated torque over an ex-
tended speed range without
overheating. See Figure 5.
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 recom-
mended. Mount the fan or
blower so the motor is sur-
rounded by the airflow. See
Figure 6.
4.2 Electronic Motor Overload
Protection – The drive con-
tains 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 5 – Maximum Allowed Motor Torque vs. Speed
Open Ventilated Motor
Fan or Blower
(100 CFM Min.
per HP)
Airflow
Figure 6 – Open Ventilated Motor with External Fan Cooling