Peak Voltage On Motor - Danfoss VLT Series Design Manual

3. VLT HVAC Selection
3.4. Acoustic noise
The acoustic noise from the frequency converter comes from three sources:
1.
3
2.
3.
The typical values measured at a distance of 1 m from the unit:
A2
A3
A5
B1
B2
C1
C2

3.5. 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
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 (100 m), the rise time and peak voltage increases.
If very small motors are used without phase coil insulation, connect an LC filter to the frequency
converter.
62
DC intermediate circuit coils.
Integral fan.
RFI filter choke.
Encapsulation
the motor cable (type, cross-section, length screened or unscreened)
inductance
affect the service life of the motor. If the peak voltage is too high, especially motors without
MG.11.B2.02 - VLT
At reduced fan speed
(50%)
51
51
-
61
58
52
55
in the motor voltage before it stabilises itself at
PEAK
®
is a registered Danfoss trademark
®
VLT HVAC Drive Design Guide
Full fan speed
60
60
-
67
70
62
65