4.10 Special Conditions
4.10.1 Purpose of Derating
Derating must be taken into account when using the frequency converter at low air pressure (heights), 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.
4.10.2 Derating for Ambient Temperature and IGBT Switching Frequency
The average temperature (T
AMB, AVG
) measured over 24 hours must be at least 5 °C lower than the maximum allowed ambient temperature (T
AMB,MAX
).
If the frequency converter 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 60º AVM or SFAVM in par. F-37 Adv. Switching Pattern.
Unit Sizes 1x
60º AVM - Pulse Width Modulation
Illustration 4.2: Derating of I
out
for different T
AMB, MAX
for Unit Size
1x, using 60º AVM
SFAVM - Stator Frequency Asyncron Vector Modulation
Illustration 4.3: Derating of I
out
for different T
AMB, MAX
for Unit Size
1x, using SFAVM
When using only 10 m motor cable or less in Unit Size 1x, 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.
Illustration 4.4: Derating of I
out
for different T
AMB, MAX
for Unit Size
1x, using 60º AVM and maximum 10 m motor cable
Illustration 4.5: Derating of I
out
for different T
AMB, MAX
for Unit Size
1x, using SFAVM and maximum 10 m motor cable
AF-650 GP Design Guide
81
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