3.6. Special Conditions
3.6.1. Purpose of derating
Derating must be taken into account when us-
ing the frequency converter at low air pres-
sure (heights), at low speeds, with long motor
cables, cables with a large cross section or at
high ambient temperature. The required ac-
tion is described in this section.
3.6.2. Derating for Ambient Temperature
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 cur-
rent should be decreased.
The derating depends on the switching pattern, which can be set to 60 PWM or SFAVM in pa-
rameter 14-00.
A enclosures
60 PWM - Pulse Width Modulation
Illustration 3.1: Derating of I
out
for different T
AMB,
MAX
for enclosure A, using 60 PWM
SFAVM - Stator Frequency Asyncron
Vector Modulation
Illustration 3.2: Derating of I
out
for different T
AMB,
MAX
for enclosure A, using SFAVM
In enclosure A, the length of the motor cable has a relatively high impact on the recommended
derating. Therefore, the recommended derating for an application with max. 10 m motor cable is
also shown.
Illustration 3.3: Derating of I
out
for different T
AMB,
MAX
for enclosure A, using 60 PWM and maximum
10 m motor cable
Illustration 3.4: Derating of I
out
for different T
AMB,
MAX
for enclosure A, using SFAVM and maximum
10 m motor cable
VLT
®
HVAC Drive Design Guide
3. VLT HVAC Selection
MG.11.B2.02 - VLT
®
is a registered Danfoss trademark
63
3
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