Du/Dt And Peak Voltage On Motor - Acoustic Noise; Thermal Motor Protection - Danfoss VLT 3000 Series Product Manual

du/dt and
peak voltage
on motor
Acoustic noise
Thermal
motor protection
130

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 in the motor voltage before it
PEAK
stabilizes at a level determined by the volt-
age in the intermediate circuit.
Both the du/dt ratio and the peak voltage
U influence the lifetime of the motor. Too
PEAK
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
will increase.
To ensure a reasonable lifetime of the
motor, the VLT ® 3000 Series has as
standard built-in motor coils which ensure a
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.
®
VLT type 3002 3003
IP 00 (dBA) 38 38
IP 20/21 (dBA) 38 38
IP 54 (dBA) 38 59
( ): 200 V units
3060
VLT ® type
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
All units with built-in RFI filter and 100 m
screened motor cable.
®
MG.30.A7.02 - VLT is a registered Danfoss trademark
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
Typical values for the du/dt ratio and the
peak voltage U
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
PEAK
VLT ® type 3060 - 3250:
• du/dt ∼ 2000 - 2100 V/µs
• U
PEAK
20 m unscreened motor cable
Below are the typical values measured at a
distance of 1 metre from the unit and at full
load:
3004 3006 3008 3011
38 53 57 -
38 53 (60) 57 (55) 60 (59) 61 (63) 62 (64)
57 57 (58) 57 (58) 63 (66) 63 (66) 67 (66)
3075 3100 3125
CT VT CT VT CT
For VLT
by approx. 2 dBA for units without RFI filter.
The motor temperature is calculated on the
basis of the motor current, output fre-
quency and time. See also description of
parameter 315.
.
®
® types 3002 - 3052).
measured on the ter-
PEAK
∼ 800 - 1100 V
∼ 900 - 950 V measured with
3016 3022 3032 3042
- - - -
67 63
67 66
3150 3200
VT CT VT CT VT
® 3011-52 the values will decrease
3052
-
67
72
3250
CT VT