Lenze SCF frequency inverter - Manual (Page 45)

Lenze 13466146 EDBSF01 v24 EN
45
Commissioning 4
P25 CURRENT LIMIT
This sets the maximum allowable output current of the drive. The maximum setting is either 180%
or 150%, depending on whether LINE VOLTAGE SELECTION (Parameter 01) is set to HIGH or LOW.
The drive will enter current limit when the load demands more current than the CURRENT LIMIT
setting. When this happens, the drive will reduce the output frequency in an attempt to reduce the
output current. When the overload condition passes, the drive will accelerate the motor back up to
the speed setpoint.
P26 MOTOR OVERLOAD
The SCF Series is UL approved for solid state motor overload protection, and therefore does not require
a separate thermal overload relay for single motor applications.
The drive contains an adjustable thermal overload circuit that protects the motor from excessive
overcurrent. This circuit allows the drive to deliver up to 150% current for one minute. If the overload
circuit “times out”, the drive will trip into an OVERLOAD fault (displayed as "PF").
MOTOR OVERLOAD should be set to the ratio (in percent) of the motor current rating to the drive
current rating in order to properly protect the motor. See the example below.
Example: A 3 HP, 480 Vac drive with a 4.8 Amp rating is operating a 2 HP motor with a current rating
of 3.4 Amps. Dividing the motor current rating by the drive current rating yields 71% (3.4 / 4.8 = 0.71
= 71%), so this parameter should be set to 71%.
P27 BASE FREQUENCY
The BASE FREQUENCY determines the V/Hz ratio by setting the output frequency at which the drive
will output full voltage to the motor. In most cases, the BASE FREQUENCY should be set to match
the motor’s rated frequency.
Example: A 460 Vac, 60 Hz motor requires a V/Hz ratio of 7.67 (460 V / 60 Hz = 7.67 V/Hz) to produce
full torque. Setting the BASE FREQUENCY to 60 Hz causes the drive to output full voltage (460 Vac)
at 60 Hz, which yields the required 7.67 V/Hz. Output voltage is proportional to output frequency,
so the 7.67 V/Hz ratio is maintained from 0 - 60 Hz, allowing the motor to produce full torque from
2 Hz (below 2 Hz there is less torque due to slip) up to 60 Hz.
NOTE
If this parameter is changed while the drive is running, the new value will not take effect
until the drive is stopped.
P28 FIXED BOOST
FIXED BOOST increases starting torque by increasing the output voltage when operating below half
of the base frequency, which increases the V/Hz ratio (see diagram below). For better out-of-the-box
performance, SCF Series drives are shipped with a setting that is different from the factory default,
as seen in the table below. If a factory reset is performed, FIXED BOOST will default to 1.0 %.