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4.8.1 du/dt Conditions
NOTE
380-690V
To avoid premature ageing of motors (without phase
insulation paper or other insulation reinforcement) not
designed for frequency converter operation, Danfoss
strongly recommend to fit a du/dt filter or a Sine-Wave
filter on the output of the frequency converter. For further
information about du/dt and Sine-Wave filters see the
Output Filters Design Guide - MG.90.NY.XX.
When a transistor in the inverter bridge switches, the
voltage across the motor increases by a du/dt ratio
depending on:
- the motor cable (type, cross-section, length
screened or unscreened)
- inductance
The natural induction causes an overshoot U
PEAK
in the
motor voltage before it stabilises itself at a level
depending on the voltage in the intermediate circuit. The
rise time and the peak voltage U
PEAK
affect the service life
of the motor. If the peak voltage is too high, especially
motors without phase coil insulation are affected. If the
motor cable is short (a few metres), the rise time and peak
voltage are lower.
If the motor cable is long (100m), the rise time and peak
voltage are higher.
Peak voltage on the motor terminals is caused by the
switching of the IGBTs. The FC 300 complies with the
demands of IEC 60034-25 regarding motors designed to be
controlled by frequency converters. The FC 300 also
complies with IEC 60034-17 regarding Norm motors
controlled by frequency converters
Measured values from lab tests:
FC 300, P5K5T2
Cable
length [m]
Mains
voltage
[V]
Rise time
[
μ
sec]
Upeak
[kV] du/dt
[kV/
μ
sec]
5 240 0.13 0.510 3.090
50 240 0.23 2.034
100 240 0.54 0.580 0.865
150 240 0.66 0.560 0.674
FC 300, P7K5T2
Cable
length [m]
Mains
voltage
[V]
Rise time
[
μ
sec]
Upeak
[kV]
du/dt [kV/
μ
sec]
36 240 0.264 0.624 1.890
136 240 0.536 0.596 0.889
150 240 0.568 0.568 0.800
FC 300, P11KT2
Cable
length [m]
Mains
voltage
[V]
Rise time
[
μ
sec]
Upeak
[kV]
du/dt
[kV/
μ
sec]
30 240 0.556 0.650 0.935
100 240 0.592 0.594 0.802
150 240 0.708 0.587 0.663
FC 300, P15KT2
Cable
length [m]
Mains
voltage
[V]
Rise time
[
μ
sec]
Upeak
[kV] du/dt
[kV/
μ
sec]
36 240 0.244 0.608 1.993
136 240 0.568 0.580 0.816
150 240 0.720 0.574 0.637
FC 300, P18KT2
Cable
length [m]
Mains
voltage
[V]
Rise time
[
μ
sec]
Upeak
[kV] du/dt
[kV/
μ
sec]
36 240 0.244 0.608 1.993
136 240 0.568 0.580 0.816
150 240 0.720 0.574 0.637
FC 300, P22KT2
Cable
length [m]
Mains
voltage
[V]
Rise time
[
μ
sec]
Upeak
[kV]
du/dt
[kV/
μ
sec]
15 240 0.194 0.626 2.581
50 240 0.252 0.574 1.822
150 240 0.488 0.538 0.882
FC 300, P30KT2
Cable
length [m]
Mains
voltage
[V]
Rise time
[
μ
sec]
Upeak
[kV] du/dt
[kV/
μ
sec]
30 240 0.300 0.598 1.594
100 240 0.536 0.566 0.844
150 240 0.776 0.546 0.562
FC 300, P37KT2
Cable
length [m]
Mains
voltage
[V]
Rise time
[
μ
sec]
Upeak
[kV]
du/dt
[kV/
μ
sec]
30 240 0.300 0.598 1.594
100 240 0.536 0.566 0.844
150 240 0.776 0.546 0.562
FC 300 Selection FC 300 Design Guide
MG.33.BD.02 - VLT
®
is a registered Danfoss trademark 91
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