Derating For Low Air Pressure; Automatic Adaptations To Ensure Performance; Derating For Running At Low Speed - Danfoss VLT Micro Drive FC 51 Design Manual

Selection
M3 400 V
Iout [%]
110 %
100 %
90 %
80 %
70 %
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50 %
40 %
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20 %
10 %
0
0 2 4 6 8
Illustration 4.37 M3 400 V
M4 400 V
Iout [%]
110 %
100 %
90 %
80 %
70 %
60 %
50 %
40 %
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0
0 2 4 6 8
Illustration 4.38 M4 200 V
M5 400 V
Iout [%]
110 %
100 %
90 %
80 %
70 %
60 %
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40 %
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0
0 2 4 6 8
Illustration 4.39 M4 400 V
MG02K402
Design Guide
40 ℃
45 ℃
50 ℃
10 12 14 16 fsw [kHz]
40 ℃
45 ℃
50 ℃
10 12 14 16 fsw [kHz]
40 ℃
45 ℃
50 ℃
10 12 14 16 fsw [kHz]
Danfoss A/S © 01/2016 All rights reserved.

4.2.3 Derating for Low Air Pressure

The cooling capability of air is decreased at low air
pressure.
CAUTION
INSTALLATION AT HIGH ALTITUDE
For altitudes above 2000 m (6560 ft), contact Danfoss
regarding PELV.
Below 1000 m (3280 ft) altitude, no derating is necessary,
but above 1000 m (3280 ft), decrease the ambient
temperature or the maximum output current.
Decrease the output by 1% per 100 m (328 ft) altitude
above 1000 m (3280 ft), or reduce the maximum ambient
temperature by 1 °C per 200 m (656 ft).
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 DC link.
•
Low motor speeds.
As a response to a critical level, the frequency converter
can adjust the switching frequency and/or change the
switching pattern to ensure the performance of the
frequency converter. The capability for automatic output
current reduction extends the acceptable operating
conditions even further.

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 overheat at low speeds due to less cooling air
from the motor integral fan.
Therefore, if the motor runs continuously at an RPM value
lower than half of the rated value, supply the motor with
extra air-cooling (or use a motor designed for this type of
operation).
An alternative is to reduce the load level of the motor by
using a larger motor. However, the design of the frequency
converter puts a limit to the motor size.
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