Danfoss VLT HVAC, Инструкция по эксплуатации, Страница: 149 / 156

8.2. Special Conditions
8.2.1. 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.
8.2.2. Derating for Ambient Temperature
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 PWM or SFAVM in pa-
rameter 14-00.
A enclosures
60 PWM (Pulse Width Modulation)
Illustration 8.1: Derating of I
out
for different T
AMB,
MAX
for enclosure A, using 60 PWM
SFAVM - Stator Frequency Asyncron
Vector Modulation
Illustration 8.2: 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. 32 ft. [10 m] motor
cable is also shown.
Illustration 8.3: Derating of I
out
for different T
AMB,
MAX
for enclosure A, using 60 PWM and a maximum
of 32 ft. [10 m] motor cable
Illustration 8.4: Derating of I
out
for different T
AMB,
MAX
for enclosure A, using SFAVM and a maximum
of 32 ft. [10 m] motor cable
VLT ® HVAC Drive Instruction Manual 8. Specifications
MG.11.A4.22 - VLT
®
is a registered Danfoss trademark
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