Special Conditions; Purpose Of Derating - Danfoss VLT Series Design Manual

®
VLT HVAC Drive Design Guide

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
3.6.2. Derating for Ambient Temperature
The average temperature (T
the maximum allowed ambient temperature (T
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
for enclosure A, using 60 PWM
MAX
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
for enclosure A, using 60 PWM and maximum
MAX
10 m motor cable
) measured over 24 hours must be at least 5 °C lower than
AMB, AVG
for different T
out AMB,
for different T
out AMB,
®
MG.11.B2.02 - VLT is a registered Danfoss trademark
cables, cables with a large cross section or at
high ambient temperature. The required ac-
tion is described in this section.
).
AMB,MAX
SFAVM - Stator Frequency Asyncron
Vector Modulation
Illustration 3.2: Derating of I
for enclosure A, using SFAVM
MAX
Illustration 3.4: Derating of I
for enclosure A, using SFAVM and maximum
MAX
10 m motor cable
3. VLT HVAC Selection
for different T
out AMB,
for different T
out AMB,
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3