Schaffner Group
User and Installation Manual
Output filter FN5420 and RWK5420
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2.4.2 Motor frequency derating
All sine wave filter FN5420 series and dv/dt reactor RWK5420 series can operate at rated current for a
motor frequency up to 60Hz. They can also operate in case of increased motor speed with motor
frequency up to 200Hz by applying a derating on the maximum current allowed in the filter or reactor.
For motor frequency of 100Hz the maximum allowed current in the filter or reactor must be derated to
90% of its rated value (0.9 times the value from the datasheet or value calculated according to the
ambient temperature derating).
For motor frequency of 200Hz the maximum allowed current in the filter or reactor must be derated to
50% of its rated value (0.5 times the value from the datasheet or value calculated according to the
ambient temperature derating).
All intermediary values can be optain from the curve in Figure 5
Figure 5 Curve of the current derating according to the motor frequency
2.4.3 Calculation example of derating
Example 1: to select a 10A sine wave filter for a 400V 50Hz application that will be running in a cabinet
where the ambient temperature can reach up to 60°C. The 10.2A will obsiouly not fit as we need to ap-
ply a derating due to the ambient temperature higher than 45°C. We would select the size above,
13.2A to make the calculation.
𝐼𝐼
𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑
=
𝐼𝐼
𝑛𝑛𝑛𝑛𝑛𝑛
�
𝑇𝑇
𝑛𝑛𝑑𝑑𝑚𝑚
− 𝑇𝑇
𝑑𝑑𝑛𝑛𝑎𝑎
𝑇𝑇
𝑛𝑛𝑑𝑑𝑚𝑚
− 𝑇𝑇
𝑛𝑛𝑛𝑛𝑛𝑛
= 13.2
�
100
−
60
100
−
25 = 11
𝐴𝐴
20
30
40
50
60
70
80
90
100
110
20
40
60
80
100
120
140
160
180
200
220
M
ax. c
ur
re
nt
[%
]
Motor frequency [Hz]
