VLT
®
FCD Series
switch frequency can be based on the load, the am-
bient temperature, the supply voltage and the cable
length.
The function ensures that the frequency converter
automatically adjusts the switch frequency between
f
sw,min
and f
sw, max
(parameter 411), see drawing be-
low.
■
Derating for air pressure
Below 1000 m derating is not necessary.
Above 1000 m the ambient temperature (T
AMB
) or
max. output current (I
MAX
) must be derated in accor-
dance with the diagram below:
1. Derating of output current versus altitude at T
AMB
= max. 40
C.
2. Derating of max. T
AMB
versus altitude at 100%
output current.
■
Derating for running at low speed
When a motor is connected to a frequency con-
verter, it is necessary to ensure adequate cooling of
the motor. At low rpm values, the motor fan is not
able to supply an adequate volume of cooling air.
This problem occurs when the load torque is con-
stant (e.g. with a conveyor belt) across the full
regulating range. The reduced amount of ventilation
determines the permissible torque in continuous op-
eration. If the motor is to run continuously at an rpm
lower than half the rated value, extra cooling air must
be supplied to the motor. Instead of providing extra
cooling, it is possible to reduce the motor load ratio.
This can be done by selecting a larger motor. How-
ever, the design of the frequency converter puts
limits on the size of motors that can be connected to
the frequency converter.
■
Motor cable lengths
The frequency converter has been tested using a 10
m unscreened/unarmoured cable and a 10 m
screened/armoured cable and has been designed to
work using a motor cable with a rated cross-section.
■
Vibration and shock
The frequency converter has been tested according
to a procedure based on the following standards:
IEC 68-2-6: Vibration (sinusoidal) - 1970.
IEC 68-2-34: Random vibration broad-band -
general requirements.
IEC 68-2-35: Random vibration broad-band -
high reproducibility .
IEC 68-2-36: Random vibration broad-band -
medium reproducibility.
■
Air humidity
The frequency converter has been designed to meet
the IEC 68-2-3 standard, EN 50178 item 9.4.2.2/
DIN 40040 class E at 40
C.
■
UL Standard
This device is UL-approved.
■
Efficiency
To reduce energy consumption it is very important to
optimize the efficiency of a system. The efficiency of
each single element in the system should be as high
as possible.
MG.04.A1.02 - VLT is a registered Danfoss trade mark
120
