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

FC 300 Design Guide
Special Conditions
"

Derating for Ambient Temperature

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The ambient temperature (T
measured over 24 hours must be at least 9 ºF (5 ºC) lower.
If the adjustable frequency drive is operated at temperatures above 122 ºF (50 ºC), a
derating of the continuous output current is necessary.

Derating for Air Pressure

"
Below 3000 ft (1000 m) altitude, no
derating is necessary.
Above 3000 ft (1000 m), the ambient temperature
(T ) or max. output current (I
AMB
derated in accordance with the shown diagram:
1. Derating of output current versus altitude
at T = max. 122 °F (50°C)
AMB
Derating of max. T
2.
at 100% output current.

Derating for Running at Low Speed

"
When a motor is connected to an adjustable frequency drive, 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).
62
How to Select Your VLT
) is the maximum temperature allowed. The average (T
AMB,MAX
) must be
VLT,MAX
versus altitude
AMB
MG.33.B3.22 - VLT is a registered Danfoss trademark
)
AMB,AVG