Danfoss VLT Series Design Manual page 67

VLT ® HVAC Drive Design Guide
3.3. Acoustic noise
The acoustic noise from the adjustable frequency drive comes from three sources:
1.
2.
3.
Typical values are measured at a distance of 3.28 ft. [1 m] from the unit:
A2
A3
A5
B1
B2
C1
C2
3.4. Peak voltage on motor
When a transistor in the inverter bridge switches, the voltage across the motor in-
creases by a du/dt ratio depending on:
-
-
DC intermediate circuit coils.
Integrated fan.
RFI filter choke.
Encapsulation
the motor cable (type, cross-section, length, shielded or unshielded)
inductance
MG.11.B4.22 - VLT ® is a registered Danfoss trademark.
At reduced fan speed
(50%) [dBA]
51
51
-
61
58
52
55
3. VLT HVAC Selection
Full fan speed [dBA]
60
60
54
67
70
62
65
3
67