Specifications
8.4 Peak Voltage on Motor
When a transistor in the inverter bridge switches, the
voltage across the motor increases by a du/dt ratio
depending on:
•
Motor cable
-
type
-
cross-section
-
length
-
screened/unscreened
•
Inductance
The natural induction causes an overshoot U
PEAK
in the
motor voltage before it stabilizes itself at a level
depending on the voltage in the intermediate circuit. The
rise time and the peak voltage U
PEAK
affects the service life
of the motor. If the peak voltage is too high, motors
without phase coil insulation are especially affected. If the
motor cable is short (a few metres), the rise time and peak
voltage are lower.
If the motor cable is long (100 m), the rise time and peak
voltage increase.
In motors without phase insulation paper or other
insulation reinforcement suitable for operation with
voltage supply (such as a frequency converter), fit a sine-
wave filter on the output of the frequency converter.
To obtain approximate values for cable lengths and
voltages not mentioned below, use the following
guidelines:
1. Rise time increases/decreases proportionally with
cable length.
2. U
PEAK
= DC link voltage x 1.9
(DC link voltage = Mains voltage x 1.35).
3.
dU
/
dt
=
0.8 ×
U
PEAK
Risetime
Data are measured according to IEC 60034-17.
Cable lengths are in metres.
Frequency ConverterN110 - N315, T4/380-500 V
Cable
length [m]
Mains
voltage [V]
Rise time
[
μ
sec]
Vpeak
[kV]
dU/dt
[kV/
μ
sec]
30 400 0.26 1.180 2.109
Table 8.10 N110-N315, T4/380-480 V
Frequency Converter, P400 - P1M0, T4
Cable
length [m]
Mains
voltage [V]
Rise time
[
μ
sec]
Vpeak
[kV]
dU/dt
[kV/
μ
sec]
30 500 0.71 1.165 1.389
30 400 0.61 0.942 1.233
30
500
1
0.80 0.906 0.904
30
400
1
0.82 0.760 0.743
1) With Danfoss dU/dt filter.
Table 8.11 P400-P1M0, T4/380-480 V
Frequency Converter, P110 - P400, T7
Cable
length [m]
Mains
voltage [V]
Rise time
[
μ
sec]
Vpeak
[kV]
dU/dt
[kV/
μ
sec]
30 690 0.38 1.513 3.304
30 575 0.23 1.313 2.750
30
690
1)
1.72 1.329 0.640
1) With Danfoss dU/dt filter.
Table 8.12 P110-P400, T7/525-690 V
General Specifications and ... VLT® HVAC Drive FC 102 Design Guide
MG16C102 - Rev. 2013-08-20 195
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