Derating For Ambient Temperature; Derating For Low Air Pressure; Derating For Running At Low Speed - Danfoss VLT AutomationDrive FC 300 Design Manual

FC 300 Design Guide
Special Conditions
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Derating for Ambient Temperature

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The ambient temperature (T
(T ) measured over 24 hours must be at least 5 ºC lower.
AMB,AVG
If the frequency converter is operated at temperatures above 50 ºC, the continuous output
current should be decreased according to following diagram:

Derating for Low Air Pressure

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In case of lower air pressure the cooling
capability of air is decreased.
Below 1000 m altitude no derating is necessary.
Above 1000 m the ambient temperature (T
max. output current (I
in accordance with the shown diagram:
Derating of output current versus altitude
1.
at T = max. 50°C
AMB
2. Derating of max. T
at 100% output current.

Derating for Running at Low Speed

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When a motor is connected to a frequency converter, it is necessary to check that
the cooling of the motor is adequate.
At low RPM values, the motor fan is not able to supply the required volume of air for cooling. This problem
occurs when the load torque is constant (e.g. a conveyor belt) across the regulating range. The reduced
ventilation available determines the size of the torque that can be permitted under a continuous load.
If the motor is to run continuously at an RPM value lower than half the rated value, the motor must be
supplied with additional air for cooling (or use a motor designed for this type of operation).
Instead of such extra cooling, the load level of the motor can be reduced e.g. by choosing a bigger
motor. However, the design of the frequency converter sets a limit to the motor size.
How to Select Your VLT
) is the maximum temperature allowed. The average
AMB,MAX
) or
AMB
) should be derated
VLT,MAX
versus altitude
AMB
MG.33.B4.02 - VLT is a registered Danfoss trademark
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