Danfoss VLT AQUA Design Manual page 53

®
VLT AQUA Drive Design Guide
The typical values measured at a distance of 1 m from the unit:
Enclosure
A2
A3
A5
B1
B2
B3
B4
C1
C2
C3
C4
D1+D3
D2+D4
E1/E2 *
E1/E2 **
* 315 kW, 380-480 VAC and 355 kW, 525-600 VAC only!
** Remaining E1+E2 power sizes.
*** For D and E sizes, reduced fan speed is at 87%, measured at 200 V.
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 motor cable (type, cross-section, length screened or unscreened)
- inductance
The natural induction causes an overshoot U
circuit. The rise time and the peak voltage U
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.
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 rules of thumb:
1. Rise time increases/decreases proportionally with cable length.
2. U = DC link voltage x 1.9
PEAK
(DC link voltage = Mains voltage x 1.35).
/
0.8 ×
3.
dU dt
=
Risetime
Data are measured according to IEC 60034-17.
Cable lengths are in metres/feet.
At reduced fan speed (50%)
in the motor voltage before it stabilises itself at a level depending on the voltage in the intermediate
PEAK
affect the service life of the motor. If the peak voltage is too high, especially motors without phase coil
PEAK
U PEAK
®
MG.20.N3.02 - VLT is a registered Danfoss trademark
[dBA] ***
51
51
54
61
58
-
-
52
55
-
-
74
73
73
82
3. VLT AQUA Selection
Full fan speed [dBA]
60
60
63
67
70
-
-
62
65
-
-
76
74
74
83
3
53