Lenze TCF Series - Manual (Page 49)

NOTE
If either the Minimum Frequency or Maximum Frequency parameter is
changed while the drive is running, the new value will not take effect until the
drive is stopped .
P24 MAXIMUM FREQUENCY
This sets the maximum output frequency of the drive for all speed reference sources and
is used with MINIMUM FREQUENCY (Parameter 23) to define the operating range of the
drive .
P25
CURRENT LIMIT
This sets the maximum allowable output current of the drive . The maximum setting is either
200% or 167%, 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 TCF 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 over current . 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 . Refer to the example herein .
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
BASE FREQUENCY is active only in V/Hz mode (Parameter 80) and 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 .
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