Derating For Low Air Pressure; Derating For Running At Low Speed - Danfoss VLT Micro Drive FC 51 Design Manual

®
VLT Micro Drive Selection
Iout [%]
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4 4
40 %
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10 %
0
0 2
Illustration 4.40
Iout [%]
110 %
100 %
90 %
80 %
70 %
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50 %
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Illustration 4.41
Iout [%]
110 %
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Illustration 4.42
42
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VLT
M3 400 V
50 ℃
4 6 8 10 12 14
M4 400 V
4 6 8 10 12 14
M5 400 V
4 6 8 10 12 14
MG02K202 - VLT
®
Micro Drive FC 51 Design Guide

4.2.3 Derating for Low Air Pressure

The cooling capability of air is decreased at low air
pressure.
For altitudes above 2000 m, contact Danfoss regarding
PELV.
Below 1000 m altitude no de-rating is necessary but above
40 ℃
1000 m the ambient temperature or the maximum output
current should be decreased.
45 ℃
Decrease the output by 1% per 100 m altitude above 1000
16 fsw [kHz]
m or reduce the max. ambient temperature by 1 degree
per 200 m.
4.2.4 Automatic Adaptations to Ensure
Performance
The frequency converter constantly checks for critical levels
of internal temperature, load current, high voltage on the
intermediate circuit and low motor speeds. As a response
to a critical level, the frequency converter can adjust the
switching frequency and/or change the switching pattern
in order to ensure the performance of the frequency
converter. The capability automatically to reduce the
output current extends the acceptable operating
40 ℃
conditions even further.
45 ℃
50 ℃
16 fsw [kHz]

4.2.5 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. The level of heating depends on the load on the
motor, as well as the operating speed and time.
Constant torque applications (CT mode)
A problem may occur at low RPM values in constant
torque applications. In a constant torque application a
motor may over-heat at low speeds due to less cooling air
from the motor integral fan.
40 ℃
Therefore, if the motor is to be run continuously at an RPM
45 ℃
value lower than half of the rated value, the motor must
50 ℃
be supplied with additional air-cooling (or a motor
16 fsw [kHz]
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.
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is a registered Danfoss trademark