Acoustic Noise; Du/Dt Conditions - Danfoss VLT AutomationDrive FC 300 Design Manual

4. FC 300 Selection
η = η x η
SYSTEM VLT MOTOR

4.6.1. Acoustic Noise

The acoustic noise from the frequency converter comes from three sources:
1. DC intermediate circuit coils.
2. Integral fan.
3. RFI filter choke.
The typical values measured at a distance of 1 m from the unit:
4
Enclosure
A1
A2
A3
A5
B1
B2
C1
C2
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.

4.7.1. du/dt conditions

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
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 are higher.
In motors without phase insulation paper or other insulation reinforcement suitable for operation with voltage supply (such as a frequency converter),
fit a du/dt filter or a sine-wave filter on the output of the frequency converter.
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:
Cable length
5
50
150 1)
1) FC 302 only
70
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
1.5 kW, 400 V
du/dt
U [V]
peak
V/μs
690 1329
985 985
1045 947
MG.33.BA.02 - VLT
[dBA] ***
51
51
51
54
61
58
52
55
74
73
73
82
4.0 kW, 400 V
du/dt
U [V]
peak
V/μs
890 4156
180 2564
1190 1770
® is a registered Danfoss trademark
FC 300 Design Guide
Full fan speed [dBA]
60
60
60
63
67
70
62
65
76
74
74
83
7.5 kW, 400 V
du/dt
U [V]
peak
V/μs
739 8035
1040 4548
1030 2828