Derating For Low Air Pressure; Derating For Running At Low Speed; Derating For Installing Long Motor Cables - Danfoss vlt FC 102 Operating Instructions Manual

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VLT HVAC Drive Operating Instructions

8.2.4. Derating for Low Air Pressure

The cooling capability of air is decreased at lower air pressure.
At altitudes higher than 2 km, please contact Danfoss regarding PELV.
Below 1000 m altitude no derating is necessary but above 1000 m the ambient temperature (T
accordance with the shown diagram.
Illustration 8.1: Derating of output current versus altitude at T
PELV.
An alternative is to lower the ambient temperature at high altitudes and thereby ensure 100% output current at high altitudes.

8.2.5. Derating for Running at Low Speed

When a motor is connected to a frequency converter, it is necessary to check that the cooling of the motor is adequate.
A problem may occur at low RPM values in constant torque applications. The motor fan may not be able to supply the required volume of air for cooling
and this limits the torque that can be supported. Therefore, if the motor is to be run continuously at an RPM value lower than half of the rated value, the
motor must be supplied with additional air-cooling (or a motor designed for this type of operation may be used).
An alternative is to reduce the load level of the motor by choosing a larger motor. However, the design of the frequency converter puts a limit to the
motor size.
8.2.6. Derating for Installing Long Motor Cables or Cables with Larger Cross-Section
The maximum cable length for this frequency converter is 300 m unscreened and 150 m screened cable.
The frequency converter has been designed to work using a motor cable with a rated cross-section. If a cable with a larger cross-section is used, reduce
the output current by 5% for every step the cross-section is increased.
(Increased cable cross-section leads to increased capacity to earth, and thus an increased earth leakage current).
AMB, MAX
MG.11.A6.02 - VLT ® is a registered Danfoss trademark
) or max. output current (I
AMB
. By altitudes above 2 km, please contact Danfoss regarding
8. Specifications
) should be derated in
out
8
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