cabinet fitting with fresh-air circulation in the cabinet is recommended, thereby ensuring that
aggressive gases are kept away from the frequency converter.
NB!
Fitting of frequency converters in aggressive environments increases the risk of
stoppages, in addition to considerably reducing the service life of the unit.
Before the frequency converter is installed, it must be checked whether there are liquids, particles
or gases in the air. This can be done by looking at existing installations in the same environment.
Typical indicators of harmful airborne liquids are water or oil on metal parts or corrosion of metal
parts. Too many dust particles are typically observed on top of installation cabinets and on existing
electrical installations. Indicators that there are aggressive gases in the air are copper rails and
cable ends that are black on existing electrical installations.
1.12.2 Derating for Ambient Temperature
The ambient temperature measured over 24 hours should be at least 5° C lower than the max.
ambient temperature.
If the frequency converter is operated above 45° C, the continuous output current should be
decreased.
1.12.3 Derating for Low Air Pressure
Above 1000 m the ambient temperature or max. output current must be derated.
For altitudes above 2000 m, please contact Danfoss regarding PELV.
1.12.4 Derating for Running at Low Speeds
When a motor is connected to at frequency converter, it is necessary to check that the cooling of
the motor is adequate.
A problem may occur at low speeds in constant torque applications. Running continuously at low
speeds – below half the nominal motor speed – may require additional air cooling. Alternatively,
choose a larger motor (one size up).
1.12.5 Derating for Long Motor Cables
The frequency converter has been tested using a 75 m unscreened/unarmoured cable and a 25
m screened/armoured cable and has been designed to work using a motor cable with a rated
cross-section. If a cable with a larger cross-section is required, it is recommended to reduce the
output current by 5% for each step the cable cross-section is increased. (Increased cable cross-
section leads to increased capacitance to earth, and thus to an increased earth leakage current).
1.12.6 Derating for High Switch Frequency
The frequency converter will automatically derate the rated output current I
VLT,N,
when the switch-
ing frequency exceeds 4.5 kHz.
In both cases, the reduction is carried out linearly, down to 60% of I
VLT,N
.
VLT 2800 Quick Guide 1 Quick Guide
MG.28.M1.02 - VLT
®
is a registered Danfoss trademark
33
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