Manual

12
4 IMPORTANT APPLICATION INFORMATION
4.1 MOTOR WITH EXTERNAL FAN COOLING – Most totally enclosed fan-cooled (TEFC) and open ven-
tilated 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 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 recommended. Mount the fan or
blower so the motor is surrounded
by the airflow. See Figure 6.
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.
FIGURE 5 – MAXIMUM ALLOWED MOTOR TORQUE VS. SPEED
FIGURE 6 – OPEN VENTILATED MOTOR WITH EXTERNAL FAN COOLING
Motors
and TENV
Inverter Duty
Maximum Allowed
Motor Torque (%)
TEFC and Open Ventilated
Motors
Fan Cooled
10060708050304010020 90
Motor Speed (%)
40
0
20
60
80
100
Open Ventilated Motor
Fan or Blower
(100 CFM Min.
per HP)
Airflow