Design Guide | VLT® AutomationDrive FC 360
Manual derating
When the following conditions are present, Danfoss recommends selecting a drive 1 power size higher (for example H132 instead of
H110):
l Low-speed – continuous operation at low RPM in constant torque applications.
l Low air pressure – operating at altitudes above 1000 m (3281 ft).
l High ambient temperature.
l High switching frequency.
l Long motor cables.
l Cables with a large cross-section.
Automatic derating
If the following operating conditions are found, the drive automatically changes switching frequency or switching pattern (PWM to
SFAVM) to reduce excessive heat within the enclosure:
l High temperature on the control card or heat sink.
l High motor load or low motor speed.
6.6.2 Derating for Low-Speed Operation
When a motor is connected to a drive, it is necessary to check that the cooling of the motor is adequate. The level of cooling required
depends on the following:
l Load on the motor.
l Operating speed.
l Duration of operating time.
Constant torque applications
A problem can occur at low RPM values in constant torque applications. In a constant torque application, a motor can overheat at low
speeds because less cooling air is being provided by the fan within the motor.
If the motor is run continuously at an RPM value lower than half of the rated value, the motor must be supplied with extra air cooling. If
extra air cooling cannot be provided, a motor designed for low RPM/constant torque applications can be used instead.
Variable (quadratic) torque applications
Extra cooling or derating of the motor is not required in variable torque applications where the torque is proportional to the square of
the speed, and the power is proportional to the cube of the speed. Centrifugal pumps and fans are common variable torque applications.
6.6.3 Derating for Altitude
The cooling capability of air is decreased at lower air pressure. No derating is necessary at or below 1000 m (3281 ft). Above 1000 m (3281
ft), the ambient temperature (T
AMB
) or maximum output current (I
MAX
) should be derated. Refer to Figure 19 which shows that at 41.7 °C
(107 °F), 100% of the rated output current is available. At 45 °C (113 °F) (T
AMB, MAX-3K
), 91% of the rated output current is available.
Danfoss A/S © 2024.01 AJ435824192086en-000101 / 130R1295 | 47
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