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4.9 Special Conditions
4.9.1 Purpose of Derating
Derating must be taken into account when using the adjustable frequency drive at low air pressure (high elevations), at low speeds, with long motor
cables, cables with a large cross-section or at high ambient temperature. The required action is described in this section.
4.9.2 Derating for Ambient Temperature and IGBT Switching Frequency
The average temperature (T
AMB, AVG
) measured over 24 hours must be at least 9°F [5°C] lower than the maximum allowed ambient temperature
(T
AMB,MAX
).
If the adjustable frequency drive is operated at high ambient temperatures, the continuous output current should be decreased.
The derating depends on the switching pattern, which can be set to 60
º
AVM or SFAVM in par. 14-00
Switching Pattern
.
Frame size A
60
º
AVM - Pulse Width Modulation
Figure 4.2: Derating of I
out
for different T
AMB, MAX
for frame
size A, using 60
º
AVM
SFAVM - Stator Frequency Asyncron Vector Modulation
Figure 4.3: Derating of I
out
for different T
AMB, MAX
for frame
size A, using SFAVM
When using only 33 ft [10 m] motor cable or less in frame size A, less derating is necessary. This is due to the fact that the length of the motor cable
has a relatively high impact on the recommended derating.
Figure 4.4: Derating of I
out
for different T
AMB, MAX
for frame
size A, using 60
º
AVM and maximum 33 ft [10 m] motor
cable
Figure 4.5: Derating of I
out
for different T
AMB, MAX
for frame
size A, using SFAVM and maximum 33 ft [10 m] motor cable
FC 300 Design Guide
4 AutomationDrive FC 300 Selection
MG.33.BC.22 - VLT
®
is a registered Danfoss trademark
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