Du/Dt Testing - Danfoss VLT Refrigeration Drive FC 103 Design Manual

Specifications
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C
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Illustration 7.2 Top and Bottom Mounting Holes (See
chapter 7.9 Power Ratings, Weight, and Dimensions)
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Illustration 7.3 Top and Bottom Mounting Holes (B4, C3, and
C4)

7.10 dU/dt Testing

To avoid damage to motors without phase insulation paper
or other insulation reinforcement designed for operation of
the frequency converter, install a dU/dt filter or LC filter on
the output of the frequency converter.
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, screened,
or unscreened).
The natural induction causes an overshoot voltage peak in
the motor voltage before it stabilises. The level depends on
the voltage in the DC-link.
Switching of the IGBTs causes peak voltage on the motor
terminals. The rise time and the peak voltage affect the
MG16G202
Design Guide
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Danfoss A/S © 08/2015 All rights reserved.
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 (a few metres), the rise time, and
peak voltage are lower. The rise time and peak voltage
increase with cable length.
The frequency converter complies with IEC 60034-25 and
IEC 60034-17 for motor design.
To obtain approximate values for cable lengths and
voltages not mentioned in the following, use the following:
•
Rise time increases/decreases proportionally with
cable length.
•
U = DC-link voltage x 1.9
PEAK
(DC-link voltage = Mains voltage x 1.35).
•
0 . 8 × U
PEAK
dU/dt =
Risetime
Data is measured according to IEC 60034-17.
Cable lengths are in metres.
200–240 V (T2)
Mains
Cable voltage Rise time
length [m] [V] [μsec]
36 240 0.226
50 240 0.262
100 240 0.650
150 240 0.745
Table 7.18 Frequency Converter, P5K5, T2
Mains
Cable voltage Rise time
length [m] [V] [μsec]
5 230 0.13
50 230 0.23
100 230 0.54
150 230 0.66
Table 7.19 Frequency Converter, P7K5, T2
Mains
Cable voltage Rise time
length [m] [V] [μsec]
36 240 0.264
136 240 0.536
150 240 0.568
Table 7.20 Frequency Converter, P11K, T2
U dU/dt
PEAK
[kV] [kV/μsec]
0.616 2.142
0.626 1.908
0.614 0.757
0.612 0.655
U dU/dt
PEAK
[kV] [kV/μsec]
0.510 3.090
0.590 2.034
0.580 0.865
0.560 0.674
U dU/dt
PEAK
[kV] [kV/μsec]
0.624 1.894
0.596 0.896
0.568 0.806
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