Danfoss FC 300 Design Manual page 89

FC 300 Design Guide
4.7.3. Derating for Low Air Pressure
The cooling capability of air is decreased at a lower air pressure.
At an altitude lower than 3,280 ft [1,000 m], no derating is necessary; but at an altitude higher
than 3,280 ft [1,000 m], the ambient temperature (T
derated in accordance with the diagram shown.
4.33: Derating of output current versus altitude at T
please contact Danfoss Drives regarding PELV.
An alternative is to lower the ambient temperature at high altitudes and thereby ensure 100%
output current at high altitudes. As an example of how to read the graph, the situation at 6,600
ft [2 km] is elaborated. At a temperature of 113° F [45° C] (T
output current is available. At a temperature of 107° F [41.7° C], 100% of the rated output current
is available.
4.7.4. Derating for Running at Low Speed
When a motor is connected to an adjustable frequency drive, it is necessary to make sure that
the cooling of the motor is adequate.
A problem may occur at low RPM values in constant torque applications. The motor fan may not
be able to supply the required volume of air for cooling, which limits the torque that can be sup-
ported. Therefore, if the motor is to be run continuously at an RPM value lower than half of the
rated value, the motor must be supplied with additional air-cooling (or a motor designed for this
type of operation may be used).
An alternative is to reduce the load level of the motor by choosing a larger motor. However, the
design of the adjustable frequency drive limits the motor size.
MG.33.B9.22 - VLT ® is a registered Danfoss trademark.
) or max. output current (I
AMB
. At altitudes higher than 6,600 feet [2 km],
AMB, MAX
- 3.3 K), 91% of the rated
AMB, MAX
4. FC 300 Selection
) should be
out
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