Derating For Low Air Pressure; Automatic Adaptations To Ensure Performance; Derating For Running At Low Speed - Danfoss VLT FC51 Design Manual

Selection
Iout [%]
110 %
100 %
90 %
80 %
70 %
60 %
50 %
4 4
40 %
30 %
20 %
10 %
0
0 2
Illustration 4.39 M3 400 V
Iout [%]
110 %
100 %
90 %
80 %
70 %
60 %
50 %
40 %
30 %
20 %
10 %
0
0 2
Illustration 4.40 M4 200 V
Iout [%]
110 %
100 %
90 %
80 %
70 %
60 %
50 %
40 %
30 %
20 %
10 %
0
0 2
Illustration 4.41 M4 400 V
38
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
®
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 2,000 m, contact Danfoss regarding
PELV.
Below 1,000 m altitude no de-rating is necessary, but
40 ℃
above 1.000 m the ambient temperature or the maximum
output current should be decreased.
45 ℃
Decrease the output by 1% per 100 m altitude above 1,000
16 fsw [kHz]
m or reduce the max. ambient temperature by 1 ° C 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
to ensure the performance of the frequency converter. The
capability for automatic output current reduction extends
the acceptable operating conditions even further.
40 ℃
45 ℃
50 ℃

4.2.5 Derating for Running at Low Speed

16 fsw [kHz]
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.
Therefore, if the motor is to be run continuously at an RPM
40 ℃
value lower than half of the rated value, the motor must
45 ℃
be supplied with additional air-cooling (or a motor
50 ℃
designed for this type of operation may be used).
16 fsw [kHz]
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.
MG02K302 - Rev. 2013-12-03