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VLT
®
HVAC Drive Instruction Manual
9.2 Special Conditions
9.2.1 Purpose of Derating
Derating must be taken into account when using the adjustable frequency drive 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.
9.2.2 Derating for Ambient Temperature
90% adjustable frequency drive output current can be maintained up to max. 122°F [50°C] ambient temperature.
With a typical full load current of EFF 2 motors, full output shaft power can be maintained up to 122°F [50°C].
For more specific data and/or derating information for other motors or conditions, please contact Danfoss.
9.2.3 Automatic Adaptations to Ensure Performance
The adjustable frequency drive constantly checks for critical levels of internal temperature, load current, high voltage on the intermediate circuit and low
motor speeds. As a response to a critical level, the adjustable frequency drive can adjust the switching frequency and / or change the switching pattern
in order to ensure the performance of the adjustable frequency drive. The capability to automatically reduce the output current extends the acceptable
operating conditions even further.
9.2.4 Derating for Low Air Pressure
The cooling capability of air is decreased at a lower air pressure.
At an altitude lower than 3,280 ft [1,000 m], no derating is necessary, but above 3,280 ft [1,000 m], the ambient temperature (T
current (I
) should be derated in accordance with the diagram shown.
out
Figure 9.1: Derating of output current versus altitude at T
contact Danfoss regarding PELV.
An alternative is to lower the ambient temperature at high altitudes and thereby ensure 100% output current at high altitudes. As an example of how to
read the graph, the situation at 6,600 ft [2 km] is elaborated. At a temperature of 113°F [45°C] (T
available. At a temperature of 107°F [41.7°C], 100% of the rated output current is available.
for frame sizes A, B and C. At altitudes above 6,600 feet [2 km], please
AMB, MAX
MG.11.AB.22 - VLT
®
is a registered Danfoss trademark
) or max. output
AMB
- 3.3 K), 91% of the rated output current is
AMB, MAX
9 Specifications
9
9-11
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