Special Conditions; Derating For Ambient Temperature; Derating For Low Air Pressure; Derating For Running At Low Speeds - Danfoss VLT Micro Drive FC 51 Series Quick Manual

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1.9 Special Conditions

1.9.1 Derating for Ambient Temperature

The ambient temperature measured over 24 hours should
be at least 9°F [5°C] lower than the max. ambient
temperature.
If the adjustable frequency drive is operated at a high
ambient temperature, the continuous output current
should be decreased.
The adjustable frequency drive has been designed for
operation at max 122°F [50°C] ambient temperature with
one motor size smaller than nominal. Continuous
operation at full load at 122°F [50°C] ambient temperature
will reduce the lifetime of the adjustable frequency drive.

1.9.2 Derating for Low Air Pressure

The cooling capability of air is decreased at low air
pressure.
For altitudes above 6,600 ft [2,000 m], contact Danfoss.
Below 3,300 ft [1,000 m] altitude, no de-rating is necessary,
but above 3,300 ft [1,000 m], the ambient temperature or
the maximum output current should be decreased.
Decrease the output by 1% per 330 ft [100 m] altitude
above 3,300 ft [1,000 m] or reduce the max. ambient
temperature by 1° per 660 ft [200 m].

1.9.3 Derating for Running at Low Speeds

When a motor is connected to at adjustable frequency
drive, check that the cooling of the motor is adequate.
A problem may occur at low speeds in constant torque
applications. Running continuously at low speeds – below
half the nominal motor speed – may require additional air
cooling. Alternatively, select a larger motor (one size up).
MG02B922 Danfoss A/S © Rev. 2014-02-27 All rights reserved. 21