Du/Dt Testing - Danfoss VLT AQUA Drive FC 202 Design Manual

Specifications

7.9 dU/dt Testing

To avoid damage to motors without phase insulation paper
or other insulation reinforcement designed for operation of
the adjustable frequency drive, installation of a dU/dt filter
or LC filter on the output of the adjustable frequency drive
is recommended.
When a transistor in the inverter bridge switches, the
voltage across the motor increases by a dU/dt ratio
depending on:
•
Motor inductance
•
Motor cable (type, cross-section, length, shielded,
or non-shielded)
The natural induction causes an overshoot voltage peak in
the motor voltage before it stabilizes. The level depends
7 7
on the voltage in the DC link.
Peak voltage on the motor terminals is caused by the
switching of the IGBTs. The rise time and the peak voltage
affects the service life of the motor. If the peak voltage is
too high, motors without phase coil insulation can be
adversely affected over time.
With short motor cables (several feet or meters), the rise
time and peak voltage are lower. The rise time and peak
voltage increase with cable length.
The adjustable frequency drive complies with IEC 60034-25
and IEC 60034-17 for motor design.
7.9.1 Peak Voltage on Motor
To obtain approximate values for cable lengths and
voltages not mentioned below, use the following "Rules of
Thumb":
1. Rise time increases/decreases proportionally with
cable length.
2. U
PEAK
(DC link voltage = AC line voltage x 1.35).
3.
dU/dt =
Data is measured according to IEC 60034-17.
Cable lengths are in meters.
182
VLT
= DC link voltage x 1.9
0 . 8 × U
PEAK
Rise time
Danfoss A/S © 09/2014 All rights reserved.
®
AQUA Drive FC 202
200–240 V (T2)
Cable
length [m]
36
50
100
150
Table 7.32 Adjustable Frequency Drive, P5K5, T2
Cable
length [m]
5
50
100
150
Table 7.33 Adjustable Frequency Drive, P7K5, T2
Cable
length [m]
36
136
150
Table 7.34 Adjustable Frequency Drive, P11K, T2
Cable
length [m]
30
100
150
Table 7.35 Adjustable Frequency Drive, P15K, T2
Cable
length [m]
36
136
150
Table 7.36 Adjustable Frequency Drive, P18K, T2
AC line
voltage Rise time U
PEAK
[V] [μsec] [kV]
240 0.226 0.616
240 0.262 0.626
240 0.650 0.614
240 0.745 0.612
AC line
Rise time U
voltage
PEAK
[V] [μsec] [kV]
230 0.13 0.510
230 0.23 0.590
230 0.54 0.580
230 0.66 0.560
Rise time U
PEAK
[μsec] [kV]
240 0.264 0.624
240 0.536 0.596
240 0.568 0.568
AC line
voltage Rise time U
PEAK
[V] [μsec] [kV]
240 0.556 0.650
240 0.592 0.594
240 0.708 0.575
AC line
Rise time
voltage U
PEAK
[V] [μsec] [kV]
240 0.244 0.608
240 0.568 0.580
240 0.720 0.574
dU/dt
[kV/μsec]
2.142
1.908
0.757
0.655
dU/dt
[kV/μsec]
3.090
2.034
0.865
0.674
dU/dt
[kV/μsec]
1.894
0.896
0.806
dU/dt
[kV/μsec]
0.935
0.807
0.669
dU/dt
[kV/μsec]
1.993
0.832
0.661
MG20N622