Danfoss VLT AQUA Drive Design Manual page 57

VLT ® AQUA Drive Design Guide
3.4. Peak voltage on motor
When a transistor in the inverter bridge switches, the voltage across the motor increases by a dV/
dt ratio depending on:
-
-
The natural induction causes an overshoot U
a level depending on the voltage in the intermediate circuit. The rise time and the peak voltage
U
PEAK
coil insulation are especially affected. If the motor cable is short (by a few yards), the rise time
and peak voltage are lower.
If the motor cable is long (328 ft. [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 an adjustable frequency drive), fit a sine-wave filter on the output
of the FC 300.
To obtain approximate values for cable lengths and voltages not mentioned below, use the fol-
lowing rules of thumb:
1.
2.
3.
Data are measured according to IEC 60034-17.
Cable lengths are in meters/feet.
FC 202, P11KT5
Cable
length [m]
10
150
10
150
the motor cable (type, cross-section, length, shielded or unshielded)
inductance
affect the service life of the motor. If the peak voltage is too high, motors without phase
Rise time increases/decreases proportionally with cable length.
U = DC link voltage x 1.9
PEAK
(DC link voltage = Line voltage x 1.35).
/
U
0.8 ×
PEAK
dU dt =
Risetime
AC line
voltage
400 V
400 V
480 V
480 V
MG.20.N2.22 - VLT ® is a registered Danfoss trademark.
in the motor voltage before it stabilizes itself at
PEAK
Rise time Vpeak
[μsec] [kV]
0.22 0.470
0.52 0.512
0.34 0.580
0.36 0.598
3. VLT AQUA Selection
dU/dt
[kV/μsec]
1.573
0.846
1.394
1.328
3
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