3.3 Acoustic noise
The acoustic noise from the adjustable frequency drive comes from three sources:
1. DC intermediate circuit coils.
2. Integrated fan.
3. RFI filter choke.
Typical values are measured at a distance of 3.28 ft. [1 m] from the unit:
Enclosure At reduced fan speed (50%) [dBA] *** Full fan speed [dBA]
A2 51 60
A3 51 60
A5 54 63
B1 61 67
B2 58 70
B3 59.4 70.5
B4 53 62.8
C1 52 62
C2 55 65
C3 56.4 67.3
C4 --
D1+D3 74 76
D2+D4 73 74
E1/E2 * 73 74
E1/E2 ** 82 83
F1/F2/F3/F4 78 80
* 450 hp [315 kW], 380–480 V AC and 600/675 hp [450/500 kW], 525–690 V AC only!
** Remaining E1+E2 power sizes.
*** For D, E and F 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 du/dt ratio depending on:
- the motor cable (type, cross-section, length, shielded or unshielded)
- inductance
The natural induction causes an overshoot U
PEAK
in the motor voltage before it stabilizes itself at a level depending on the voltage in the intermediate
circuit. The rise time and the peak voltage U
PEAK
affect the service life of the motor. If the peak voltage is too high, motors without phase 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 the voltage supply (such as an adjustable frequency
drive), fit a sine-wave filter on the output of the adjustable frequency drive.
To obtain approximate values for cable lengths and voltages not mentioned below, use the following rules of thumb:
3 VLT AQUA Selection VLT
®
AQUA Drive Design Guide
3-20
MG.20.N5.22 - VLT
®
is a registered Danfoss trademark
3
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