130 MG.30.A7.02 - VLT
®
is a registered Danfoss trademark
du/dt and peak voltage on motor - Acoustic noise
When a transistor in the inverter is acti-
vated, the voltage applied to the motor will
rise by a du/dt ratio determined by
• the motor cable (type, cross-section,
length, screened/unscreened)
• Inductors
The self-inductance will cause an over-
shoot U
PEAK
in the motor voltage before it
stabilizes at a level determined by the volt-
age in the intermediate circuit.
Both the du/dt ratio and the peak voltage
U
PEAK
influence the lifetime of the motor. Too
high values will primarily affect motors with-
out phase coil insulation.
With short (few metres) motor cable, the
du/dt ratio will be very high but the peak
voltage very low. At long (100 metres)
motor cable du/dt will decrease and U
PEAK
will increase.
To ensure a reasonable lifetime of the
motor, the VLT
®
3000 Series has as
standard built-in motor coils which ensure a
du/dt and
peak voltage
on motor
low du/dt ratio value even with very short
motor cable.
Note:
When using very small motors without
phase coil insulation it is recommended to
mount a clamp filter or an LC-filter in
series after the VLT
®
.
Clamp filter, code no. 175H5147 (fits all
units in the VLT
®
types 3002 - 3052).
Typical values for the du/dt ratio and the
peak voltage U
PEAK
measured on the ter-
minals of the frequency converter between
two phases (30 m screened motor cable):
VLT
®
type 3002 - 3052:
• du/dt ∼ 200 - 300 V/µs
• U
PEAK
∼ 800 - 1100 V
VLT
®
type 3060 - 3250:
• du/dt ∼ 2000 - 2100 V/µs
• U
PEAK
∼ 900 - 950 V measured with
20 m unscreened motor cable
The acoustic noise from the frequency
converter is generated from 3 sources:
1. D.C. (DC link) and AC coils
(motor coils).
2. RFI filter (acoustic noise increases
with the length of the motor cable).
3. Built-in fan.
Acoustic noise
Below are the typical values measured at a
distance of 1 metre from the unit and at full
load:
All units with built-in RFI filter and 100 m
screened motor cable.
For VLT
®
3011-52 the values will decrease
by approx. 2 dBA for units without RFI filter.
Thermal
motor protection
The motor temperature is calculated on the
basis of the motor current, output fre-
quency and time. See also description of
parameter 315.
VLT
®
type 3002 3003 3004 3006 3008 3011 3016 3022 3032 3042 3052
IP 00 (dBA) 38 38 38 53 57 ------
IP 20/21 (dBA) 38 38 38 53 (60) 57 (55) 60 (59) 61 (63) 62 (64) 67 63 67
IP 54 (dBA) 38 59 57 57 (58) 57 (58) 63 (66) 63 (66) 67 (66) 67 66 72
( ): 200 V units
3060 3075 3100 3125 3150 3200 3250
VLT
®
type
CT VT CT VT CT VT CT VT CT VT CT VT CT VT
IP 21 (dBA) 63,5 68,8 68,8 72,5 67,6 68,2 68,2 68,9 68,9 70,0 71,3 73,8 73,9 74,4
IP 54 (dBA) 63,9 68,2 68,2 72,0 67,3 68,0 68,0 68,5 68,5 69,6 73,4 75,4 75,2 75,4
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